Modelling and Simulation of Osmotic Dehydration of Onion

SHRI SHIVAJI EDUCATION SOCITY’S
COLLEGE OF ENGINEERING & TECHNOLOGY,
AKOLA.
Certificate
This is to certify that, following students of Final Year B.Tech.
Chemical have submitted a Project entitled.
“ Modelling and Simulation of Osmotic
Dehydration of Onion. ”
during the academic section 2005 – 2006 in a satisfactory manner in
the partial fulfillment of the requirement for the Degree of “ Bachelor
of Technology ” in Chemical Engineering Branch, under affiliation of
Sant Gagde Baba University, Amravati.
Submitted By
1. Mr. Mohit Ulhaque 2. Mr. Rilesh Mehata
Prof. S. K. Navhale Prof. V. C. Renge
( Guide ) ( H.O.D)
Department of chemical technology
2005 – 2006

ACKNOWLEDGEMENT
It is with great pleasure we express our sincere
gratitude to all those who rendered us help
selflessly carrying out educative project.
We have the privilege of working under Prof.
S. K. Navhale ( Guide ) to whom we are indebted
for his immenselly valuable guidance, suggestions
and encouragement for the project.
We express our sincere gratitude to all
Professors, advices and facilities imparted to us
by them and also for giving us a good insight into
this project.
Mr. Mohit Ul haque Mr. Rilesh Mehata
Final Year B. Tech. Chemical
College of Engg. & Tech. Akola.

ABSTRACT
India is largest producess of onion after China with production of
4.06 million tonnes. In the past few years the demand of
dehydrated onions has increased tremendously.
In this study we tried to present different aspects of onion
drying. A comparison based on various aspects of onion
dehydration like size, onion quality was studied satisfactorily. We
also tried to study the application of phenomena of Osmotic
Dehydration and its effect on the Drying process.
We also studied the kinetics of onion dehydration by using
models. The results were simulated successfully and gave
satisfactory results. We also assumed an empirical equation for
onion which was also tested with good results.

INDEX
Sr. No. Topic Page No.
1. Introduction
2. Literature Survey
2.1 Drying Principles
2.2 Market Scenerio
2.3 Raw Material
2.4 Osmotic Dehydration
3. Experimentation
3.1 Experimental set-up & Procedure
3.2 Analysis
3.3 Result & Discussions
3.3.1 General Study
3.3.2 Comparative Graphs
4. Cost Estimation
4.1 Experimental Cost
4.2 Scale-up Cost
5. Plant Layout
6. Mathematical Modelling & Simulation
6.1 General Principles
6.2 Drying Equations
6.3 Mathematical Modelling
6.4 Simulation & Testing
7. Conclusion
8. References
9. Appendix

1. INTRODUCTION
Onion (Allium cepa L.) is one of the major bulb crops of the
world and is most important commercial vegetable vis-a-vis spice
crops grown in India. A large quantity of onion is used as fresh;
however, some of the surplus quantities of onion available in the
market are processed by dehydration and are meant for export
and armed forces . The pungency in onion is due to volatile oil
known as alkyl-propyl-disulphide. Nutritionally, fresh onions
contain about 868 g/kg moisture, 116 g/kg carbohydrates, 12
g/kg proteins, 2-5 g/kg calcium, 0.5 g/kg phosphorus and traces
of iron, thiamine, riboflavin and ascorbic acid. A distinctive
characteristic of onion is due to presence of alliaceous odour
which accounts for its use as food, salad, spice, condiment and
medicine; because of which it has a paramount effect in
preventing heart diseases and other ailments. Despite the fact that
the world production of onion is steadily increasing due to
improved production technology and expansion of area under
cultivation; the postharvest losses due to sprouting, rotting,
rooting and physiological loss in weight accounts for 40-60% of
annual production in India.
Preservation of food by drying is one of the oldest methods
and is used on large scale. The heart of the onion processing
operation centers around the dehydration of the produce.
"Dehydration" of onion is one of the economical and feasible
methods of preservation of surplus produce for use in season of
short fall. This method has advantages like greater concentration
in dry form to save packaging cost; requires minimal labor,
processing equipment and distribution cost. Dehydrated onions
are becoming a product of considerable importance in
international agricultural trade. Out of the total dehydrated

vegetables export from the developing countries, dehydrated
onions have the largest share of 45 per cent6
. Dried and processed
vegetables constitute total export of processed product between
40-42 per cent both by volume and by value, prominent among
them was dehydrated onion flakes and powder.
India is the largest producer of onions in the world after China
with a total production of 4.06 million tones in 1995-96. It is
cultivated widely covering about 16% of the total area and its
production is 10% among vegetables. Generally, it is available
throughout the year and can be stored under ambient conditions
on Improvised racks under a thatched roof with a free flow of air.
But heavy losses can occur due to non-availability of sufficient
storage, transport and proper processing facilities at the
production point. The preservation of vegetables by dehydration
offers a unique challenge and it may be considered as an alternate
low cost preservation process. Dried & processed vegetables
constitute between 40-42% of total exports of processed products
both by volume and by value, prominent among them being
dehydrated onion flakes and powder. Onions can be dehydrated
and conveniently used by the consumer in the dry form. Large
quantities of onions are dehydrated for export and use by armed
forces.
Objective
The objectives of this study are as follows :-
1. Maharashtra region is the largest producer of onion in
India. The price of onion grown in these region varies from
50 ps/kg. to 15 Rs/kg. during each year. Thus this study
was undertaken so as to store onion in dehydrated forms
like flakes or powder during the low cost season utilizing it
for exports.

2. To study the effect of pretreatment processes like osmotic
dehydration & sulphianition on the manufacture of
dehydrated onion.
3. To compare the different processes of onion dehydration and
to verify the most economic and effective processes.
4. To propose a mathematical model for onion dehydration and
further simulating it, which can be useful for designing and
improving the performance of predrying and drying
procedures.

2. LITERATURE SURVEY
2.1 Drying Fundamentals
Drying refers to an operation in which moisture of a
substance is removed by thermal means (i.e. with the help of
thermal energy).
It is an operation in which the solvent (usually water) is
evaporated from the wet solid with the help of heat. In majority of
drying operations, the heat is provided by hot air or any other gas
in which the solvent evaporates.
During drying operation, mass and heat transfer occur
simultaneously. Heat is transferred from the bulk of the gas phase
(drying media) to the solid phase and mass is transferred from the
solid phase to the gas phase in the form of liquid and vapour
through various resistances. The material (liquid) that is
transferred is the solute and transfer takes place as the gas phase
is always unsaturated with respect to the solute material.
In case of drying, relatively small amounts of water or other
liquid is removed from a solid or semi-solid material whereas in
case of evaporation, relatively large amounts of water are removed
from solutions. Drying involves the removal of water at a
temperature below the boiling point while evaporation involves the
removal of water as a vapour at its boiling point. Drying involves
the circulation of hot air or other gas over the material for removal
of water while in evaporation use of steam heat is done for
removal of water (i.e. for evaporator). To obtain the products
almost in dried form is the purpose of drying operation whereas
concentration of solution is the main purpose of evaporation. In
drying operation, the emphasis is usually on the solid product and
in evaporation, the emphasis is on concentrated liquor.

As the removal of moisture by thermal means is more costly
than mechanical means (e.g. filtration), the liquid content of solids
must be reduced to the minimum possible level by latter means
before the material is fed to drying equipments.
Drying is frequently the last operation in the manufacturing
process and is usually carried after evaporation, filtration, or
crystallisation.
Drying operations are mostly encountered in food, chemical,
agricultural, pharmaceutical and textile industries.
General Definitions
1. Moisture content on wet basis :
It is expressed as the ratio of the weight of moisture to the weight
of wet feed material. If X is the kg moisture associated with one kg
of dry solids, then
Moisture content on wet basis : = X/(1 + X)
Percent moisture on wet basis is the moisture associated with feed
material expressed as the percentage of weight of feed material
(i.e. wet solids).
2. Moisture content on dry basis:
It is expressed as the ratio of the weight of moisture to the weight
of dry solids present in the wet feed material. If the feed material
contains X kg moisture and 1 kg of dry solids, then
Moisture content on dry basis = soliddrykg
moisturekg
= X/1 = X
Percentage moisture content on dry basis = 100 X
3. Equilibrium moisture content (X*):
The moisture content of substance that is in thermodynamic
equilibrium with its vapour (given partial pressure of vapour) in
gas phase under specified humidity and temperature of gas is
termed as equilibrium moisture content. It represents the limiting

moisture content to which a given material can be dried under
constant drying conditions.

4. Bound moisture content:
It is that moisture in the substance which exerts a vapour
pressure less than that of the pure liquid at the same
temperature.
5. Unbound moisture content:
It is the moisture held by a material in excess of equilibrium
moisture content corresponding to saturation in the surrounding
atmosphere. It is primarily held in the voids of solid.
It is the moisture in the substance which exerts an equilibrium
vapour pressure equal to that if pure liquid at the given
temperature.
6. Free moisture content:
It is the moisture contained by a substance in excess of
equilibrium moisture content (X-X*). At a given temperature and
humidity, it is the moisture content of material that can be
removed by drying.
7. Critical moisture content (Xc):
The moisture content of a material at which the constant
rate period ends and the falling rate period starts is called as
critical moisture content. It is a function of constant drying rate,
material properties and particle size.
8. Relative humidity (R.H.):
It is defined as the ratio of the partial pressure of water
vapour in an air water-vapour mixture to the vapour pressure of
pure water at the temperature of the mixture (at DB).
% R.H. = (pA/p°) x 100
9. Humidity (H):
It is the ratio of the mass of water vapour to the mass of dry
air present in the air-water vapour mixture under any given set of
conditions.

10. Dry bulb temperature (DB):
The temperature of vapour-gas mixture recorded by the
thermometer whose bulb is kept dry, is called as dry bulb
temperature.
11. Wet bulb temperature (WB):
The temperature recorded by the thermometer whose bulb
is kept wet by wrapping a wet cloth in the open air is called as wet
bulb temperature.
12. Saturation humidity :
It is the humidity of air when saturated with water vapour
and is denoted by symbol — Hs.
13. Percentage humidity (Ho):
It is the ratio of the actual absolute humidity of air (H) to the
humidity of saturated air
Percentage humidity, H0 = pA (P – p0
A)/p0
A (P - PA)
14. Dew point (DP):
When the air-water vapour mixture is cooled at constant
pressure, it becomes saturated and further cooling results in
condensation of water vapour. The temperature at which the
condensation will first occur is known as the dew point. For the
saturated air, the dew point, wet bulb and dry bulb temperatures
are identical.
15. Equilibrium:
The moisture of wet solids exerts definite vapour pressure
depending upon the temperature and the nature of solid and the
moisture content. Consider that the wet solids containing water
which exert the vapour pressure of p° are exposed to continuous
supply of fresh gas (usually air) with fixed partial pressure of
vapour (pA). If the p° is greater than pA, then the solids will lose
moisture (reverse is true for p° < pA) by evaporation till the vapour

pressure of moisture of the solids equals the partial pressure of
vapour in gas. The solid and the gas are then said to be in
equilibrium with each other and corresponding moisture content
is referred to as equilibrium moisture content. The equilibrium
data in case of drying operations are given as the relationship
between the moisture content of solid (expressed on dry basis) and
relative humidity of gas (usually air) in contact with the solid.
When the humidity of air is less as compared with the moisture
content of solid, then solid will lose moisture by evaporation and
dry to equilibrium and if the air is more humid than the solids,
then solids will gain moisture until the equilibrium is attained.
(fig. 2.1.a)
Fig. 2.1.a Equilibrium Moisture Curve
16. Rate of batch drying and drying test:
A knowledge of time required for drying a substance from
one particular level of moisture content (initial) to another level
(desired) under specified drying conditions is needed for
determining the size of a dryer and also for setting up of drying
schedules. In respect of time required to dry a substance using
one particular type of dryer one is also interested to estimate the
effect of different drying conditions upon the time. For the said
purposes in many cases we have to run a drying test of material in
question in a model dryer of the type that is desired. Conducting

the test and measuring the rates of batch drying is relatively
simple and thus provides information useful for batch as well as
continuous drying operation.
In drying test, for determining the rate of drying (needed for
further calculations) we have to keep a sample of a wet material
uniformly distributed over the tray (of uniform thickness)
suspended from a weighing balance in the cabinet. The bottom
and edges of the tray should be well insulated. Then we have to
blow the air over the surface of the wet material. The air should be
blown over the material at constant velocity and should of of
constant temperature and humidity. Then, all that we have to do
is to measure the weight of a sample as a function of time and
also the dry weight of a sample. The test can be performed on
samples of different thickness.
17. Constant rate period:
It is that part of the drying process during which the rate of
drying expressed as the moisture evaporated per unit time per
unit area of drying surface, remains constant.

18. Falling rate period :
It is that part of the drying process during which the rate of drying
varies with time am instantaneous drying rate expressed as the
amount of moisture evaporated per unit time, per unit area of
drying surface continuously decreases.
2.2 Osmotic Dehydration:
2.2.1. Principle and Applications
The osmotic process is a technique for the concentration of
solid foods, which consists in placing pieces of fruit or vegetables
in a hypertonic solution (sugars, sodium chloride, glycerol etc...),
giving rise to at least two major simultaneous counter-current
flows (Fig. 1)
1) an important water flow out of the food into the solution .
2) a simultaneous transfer of solute from the solution into the food
. A third phenomenon has been described concerning leakage of
natural solutes from the food into the solution (sugars, organic
acids, mineral salts...). Though quantitatively neglectable, it may
remains essential as far as the organoleptic or nutritional
(vitamin, mineral) qualities are concerned.
Therefore, as opposed to mere drying processes, Osmotic
Dehydration., achieves a twofold transformation of the food item,
by both a decreasing water load, and a solute incorporation, which
may result in a subsequent weight reduction.
Provided that further lowering of water activity by moderate
air dry ing, or inhibition of microbial growth by heat and / or
chemical treatment, is achieved alter the osmotic dipping, the
“osmotically” dehydrated product can be stored up to several
months or longer, at room temperature, depending upon the
packaging material and the storage conditions. Air-drying
following osmotic dipping is still commonly used, especially in

tropical countries, for the production of so called "Semi candied"
dried fruit.

2.2.2. Advantages of an Osmotic Stage
An actual revival of interest for the process has been
triggered off by an awareness of the advantages of Osmosis over
traditional drying processes.
A) Improved organoleptic qualities, thanks to minimized heat
damages to colour and flavour, less volatile component drive,
favorable effect of the incorporated solute upon the sugar to acid
ratio , and the texture, less discoloration by enzymic oxydative
browning thus limiting, in some cases, the use of sulphur dioxide.
B) Considerable, potential energy-savings in comparison to
conventional processes, though hardly ever evaluated. In fact,
mass transport coefficient in liquid phase are generally good.
Moreover, water is removed from the product without undergoing
a phase change. Therefore, osmotic dehydration may be much
quicker than air drying or freeze-drying. Recycling the syrup by
reconcentration, which constitutes the second stage of the
process, is not limiting, thanks to the present perfected
techniques for the concentration of liquids.
2.2.3. Technological Limitations
With regard to other drying processes, the osmotic
dehydration has not been studied very much, in terms of
engineering properties. Current technologies, somewhat empirical,
result in detrimental erratic performances of processed items, and
often excessive sugar entrance in the product, because of poor
control of the main variables, Water Loss (WL) and Sugar
Gain(SG).
Yet, WL and SG show different and sometimes opposing
reactions to the influence of the process parameters
(concentration and composition of the solution, temperature,
nature of the product and chemical or physical pre-treatments)

and this intrinsic property of the process makes it theoretically
possible to conceive, in particular, combinations which result in
substantial water removal with only marginal sugar pickup or,
more generally, to obtain different WL/SG ratios, depending on
the desired organoleptic qualities of the end-product, and on
further treatments to be involved. For instance, increasing the
solute concentration will favour both WL, and SG, but a higher
sugar concentration has a significant effect on WL, whereas SG
shows little variation, which is reflected by an increasing Weight
Reduction (WR) with the concentration of the solute. Increasing
the specific surface area of the product (size and shape) may be
favourable to both WL and SG, especially for short osmosis
periods, but an over-reduced surface area will favour SG to the
detriment of WL.
The first reason for the poor control of the main variables is
that a full understanding of mechanisms involved with
simultaneous interacting counter-current flows is still lacking.
This is aggraved by the complex structure of natural tissues, and
by the specific problem for liquid /solid contacting which is found
in the osmotic process.
2.2.4. Mass Transfer Considerations
There have been several studies on the diffusion of solutes
in food items and gels.
But most of the diffusional mass transfer studies concern
binary processes ( interpretation of Fick's law) or assume an
independance of the movement of each species in multicomponent
systems. The only literature lo date in food systems where
interaction between components has been taken into account.
In osmotic dehydration, most available models are based on
Fick's law of diffusion with simplifying assumtions and use the

particular solution for unsteady one-dimensional transfers for
instance between a plane sheet and a well-stirred solution, either
with a constant surface concentration or with a limited volume of
solution. The resulting apparent diffusivities are generally
correlated with the concentration and temperature of the solution.
The limits of such models are the following:
A) In all cases, simultaneous mass transfer are reduced to a single
transfer of water, or solute. So, the resulting diffusivities are in
fact a combination of the respective water and solute diffusivities,
and hence, cannot be used to predict the contribution of each
transfer in the process.
B) As a corollary, the probable interaction between the counter
-current flows, which is strongly suggested by the opposing
response of Water Loss and Sugar Gain rates to some of the
process parameters, cannot be taken into account.
C) No proof is given that resulting diffusivities do represent the
internal transfers (transfers inside the particle) and not the
internal and external phenomena together. And yet, external
conditions prove to be a key- factor for the transfer rates. This
suggests a frequent control of the process by external phenomena,
related to specific circumstances involved in the osmotic process.
D) Lastly, the possible specific action of natural cell membranes
cannot be taken into account. The mass transfer phenomena that
occuring plant tissue upon osmosis are likely to involve complex
mechanisms, most ol them controlled by the plant cells. This
greatly impairs the use of such models. This essential influence of
tissue structure will be discussed further on. (Fig. 2.2.a )

Fig. 2.2.a Schematic drawing of mass transfer in soaking
processes

2.3 Market Survey
Onion is one of the most important horticultural products of
India is World’s second largest exporters of onion with the market
share of 13.6 percent in 1992-93. Since 1980 India’s onion export
have been mainly confined to the neighboring South East Asian
countries and a few Middle East Nations. The UAE, Bangladesh,
Malaysia and Srilanka are the major importers of Indian Onion.
There is a considerable scope for increasing the exports of
dehydrated onions from India, the demand for which is growing at
the rate of 7% per annum in E.C.markets India should take
advantage of this by strengthening its processing facilities.
The Gujarat Government has been permitted to export
50,000 tones of onions by the Union Government. The terms and
conditions were similar to the case of Maharashtra Government
for the export of 75,000 tonnes.
India happen to be the second largest produce of onions in
the world amounting up to 4.08 million tones during the year
1995-96 .
Onion is one of the India’s major export commodity
The prices of onion ranged between Rs.135/- 100 Kg and
Rs.1502/- 100 Kg during 1994-95. India exported fresh onions of
4.27 lakh tonnes worth Rs.265.21 crores during 1996-97 and
0.09 lakh tonne worth Rs.19.18 crores of preserved onions and
0.04 lakh tonnes worth Rs.17.82 crores of dehydrated onions
flakes / power as onion.
Onion occupies approximately 7.41 percent area out of a
total area of 5.33 million hectares of land under vegetable
cultivation. Major states producing of onion are Haryana,

Maharastra, Karnataka, Punjab, Gujarat, Tamilnadu, Rajasthan,
Madhya Pradesh, Uttar Pradesh, Andhra Pradesh, Bihar.
2.3.1. International Scenario On Dehydrated Products
The international scenario has been studied on the basis of the
exhaustive data obtained through secondary research. The
analysis of the international trade has been derived from the
import and export data of the entire E.U. comprising of 15
member countries, U.S.A and Japan as these three regions
constitute most of the global trade in dried fruit and vegetable
products. While E.U and U.S.A have significant intra as well as
extra import/export trade in these products, Japan is basically a
net importer.
Amongst all these products the dehydrated green peas is the
largest traded commodity of which India itself is a net importer to
the extent of about 1.05 lac tonnes. India stands at a total
disadvantage in terms of the quality of the green peas, the cost of
the raw material and that of the energy requirements for
dehydration due to which it is not able to compete. As regards the
exports from India the dehydrated Onion flakes and powder has
been the only product worth a mention. The total import of
selected dehydrated fruits in three foremost regions as mentioned
above has been about 562,000 MT valued at US$ 738 million in
1999 which in last three years has reduced to 268,000 MT valued
at US$ 372 million in the year 2001. The India's share has been
about 0.25% on the average. As regards the dehydrated
vegetables, the import in these regions has been 2,289,000 MT
valued at US$ 836 million in 1999 which has reduced to 87,200
MT valued at US$ 449 million in the year 2001 and the Indian
share has been 0.68% on the average.

The E.U. has a negative trade balance in DHD/VFD fruit and
vegetable products to the extent of 535,761 MT (year 2001) as the
total import has been about 929,162 tonnes against the total
export of about 393,401 tonnes. The major exporting countries to
E.U have been Canada, Turkey, U.S.A and China. The largest
importing commodity in DHD products has been green peas (73%)
followed by grapes (10.61%), mixed and other vegetables (7.21%)
and prunes (2.59%). The import of tropical fruit and vegetables
has been very insignificant. The maximum export from E.U has
been that of dehydrated peas (77.93%) followed by mixed and
other vegetables (9.26%) and grapes (7.25%). Thus E.U has been
mostly a net importer of fruits and vegetables in the world.
The opportunities of Indian products in E.U market lie mainly
with Onion, Mushroom, some tropical vegetables and fruits etc.
because of the enormous availability of the quality raw materials.
It is interesting to note that dry tropical fruits have started
attracting a good consumer market in E.U though until now dried
banana has been the only popular product. Dried tropical fruit
such as mango, papaya, banana and pineapple are now becoming
more common items in health food stores and super markets
where they are sold pre-packed in attractive polybags and cartons.
The major customers of dried tropical fruits are the companies
who cater to breakfast cereal industry, health foods and
confectionery industry. The major departmental stores dealing in
dried tropical fruit products in E.U include J. Sainsbury, Holland
& Barrett and Marks & Spencer but none of these stores have
been sourcing these products from India. The estimated import
market size of dehydrated tropical fruits in Europe is estimated at
about 11,500 MT of which about 4,700 MT would be the demand

for banana. U.K amongst the E.U members would be the largest
buyer.
The market for dried tropical fruits in U.S.A is estimated at
about 5,000 MT of which about 3,500 MT would be of banana
chips. This is the major opportunity for Indian producers as the
quality of Indian tropical fruits is any time better except for
pineapple, the superior quality of which comes from Thailand and
Philippines. Amongst the vegetables dried tomato and carrots are
items of interest in E.U but it is almost impossible to compete
against East European countries supplying to E.U. For DHD
vegetables the largest consumption comes from the soup industry
but the requirements of product quality are too high.
As regards the freeze dried products, the process is applicable
only to high valued items such as mushrooms, herbs and ready-
to-use delicacies in the form of pre-prepared meals. The products
exported from India at present are freeze dried mushroom, herbs
and to some extent onion flakes. .
As regards Japan, it is the net importer of most of the
dehydrated products. The average import of dehydrated products
in Japan is of the order of 62,000 MT valued at US$ 133 million in
1998 which is estimated to have gone up to 68,000 tonnes valued
at US$ 145 million in the year 2001. The maximum commodity of
import is dried grapes followed by vegetables, onion, radish and
sweet corn. In the export to Japan India as such has no
contribution except for small quantities of banana.
As regards the trade of DHD/VFD products of U.S.A, the
country is the largest exporter of prunes, shelled peas, raisins and
some dried fruits. U.S.A has a trade surplus of 413,000 MT in
these products against the total export of 556,236 MT (based on
the figure of the year 2001). The major products of import have

been onion (38%), mixed vegetables (12%), grapes (9%) and other
dried fruits including tropicals (6.4%). The Indian share in the
import of dried products in U.S.A is rather insignificant. India has
the potential to meet the increasing demand for tropical fruit
products and with assured determination it can even succeed in
exporting to U.S.A the traditional DHD products like garlic and
mushrooms etc.
The import of dehydrated products in U.S.A has been almost
static between US$ 186 million and about US$ 225 million in last
four years but the exports from U.S.A almost nose-dived in these
four years from US$ 1078 million in 1998 to US$ 419 million in
2001. The major reasons could be:
i. Surplus stocks of the previous year's imports
ii. The fall in demand for these products in other countries vis-a-
vis their indigenous production.
iii. The restructuring of the overall future business plans of E.U
and
iv. The vagaries of weather which affected the production and
supply from U.S.A.
Nevertheless this is not going to affect the potential of Indian
exports to U.S.A particularly for the products in which India has
the advantage. India has certainly the potential to achieve a
breakthrough in the export of dehydrated products to E.U, Japan
and U.S.A if the following aspects are carefully considered:
i. The products have to be innovative based on the exclusive and
exotic fruit and vegetable products grown in the country.
ii. The quality of the products and their packaging has to conform
to the Codex standards laid under WTO agreement.

iii. The growing, handling and processing of raw materials have to
follow GMP with the incorporation of HACCP systems.
iv. The commitments on the delivery schedule have to be adhered
to without pretext.
v. The market promotion has to be professional in all respects.
vi. The Indian producers/exporters would be required to
participate in the international thematic fairs for food ingredients
where the products can be displayed for the interested global
buyers.
2.3.2. Status of Dehydration in India
The dehydration of vegetables was started in India on
industrial scale in early sixties when Hindustan Levers Ltd. set up
a plant at Ghaziabad in U.P. The dehydrated green peas produced
in this unit was sold under the brand name 'HIMA'. The project
however was not a success, mainly because the Indian consumers
who are oriented to traditional use of fresh vegetables did not
accept the product. The company had fixed a sale target of 1500
tpa but could never realise a total sale of more than 300 tpa. In
the meanwhile India imported about seven mechanical dryers
from Bulgaria under a bilateral agreement which were set up at
various places in the country but all these units faced lot of
problems on account of:
i. Technology obsolescence leading to inefficient operation of the
dryers
ii. Locational disadvantage of some units which led to the
difficulties in procurement of raw materials as well as the sale of
products and
iii. The changing scenario of the food processing industry in India
and

iv. Lack of consumer preference for dehydrated products.
However a lot many units were set up in the state of Gujarat
for dehydration of onion and garlic as the primary product for
export. Most of these units have been operating somewhat
successfully but on low returns due to the fact that their cost of
production is much higher than in the developed countries where
the process operations are less energy intensive and the raw
materials are far superior.
The Indian industry for dehydration of fruits and vegetables
can therefore survive in the present scenario only on the strength
of product quality and cost competitiveness, which can be possibly
achieved in the following ways:
i. Growing raw materials through contract farming.
ii. Introducing technology upgradation in the manufacturing
process.
iii Keeping close interaction with the market demand and
producing products in concurrence with the market requirements.
iv. Promoting the products in a professional manner etc.
v. Imparting training to the personnel responsible for raw material
procurement, plant operation and quality control.
The existing status of the industry is far from being
satisfactory as most of the units in small and medium scale have
already closed down as they could not sustain under the pressure
of poor availability and high cost of the quality raw materials, high
cost of production and higher rates of interest on long and short
term loans. The other negative factor that put odds against the
Indian industry has been their failure to meet the commitments
on delivery schedules, the pretext for what is usually not the
concern of the buyer. Some successful units like Unique

Dehydrates Ltd., Chhatariya Dehydrate Exports Ltd., Murtuza
Foods Ltd., all from Gujarat attribute their success to mainly
technical innovations that they have introduced in their plants to
reduce the energy costs and their strong marketing efforts backed
by the quality aspects of the products. The units successfully
catering to the domestic market which is predominantly
dependent on army supplies are:
i. Oceanic Foods Pvt. Ltd., Gujarat.
ii. Pan Foods Ltd., Haryana
iii. Markfed Canneries Ltd., Punjab
Their success in the domestic market can be attributed to
their sound financial resources to manage the flow of working
capital requirements even while the stock inventories pile up
sometimes due to the lack of market demand. The comparative
statement of the product sale of 13 units producing dehydrated
food products both in domestic as well as in export market is
projected in table 4.1 from which it can be construed that lower
cost of production and better quality are the two basic aspects
responsible for the market success.
The existing institutional demand for dehydrated products
in India is of the order of about 2800 TPA while the sale of these
products in the year 2001 was about 2358 MT. Thus another 450
MT can be conveniently absorbed by the Indian market.
The export of dehydrated vegetables from India is dominated
by just five main products which are onion flakes and powder,
tamarind powder, dehydrated vegetables, garlic powder/flakes and
some small quantity of fruits. The main product of export is
dehydrated onion flakes/powder which has been of the order of
about 7224 MT valued at Rs.32.95 crores approximately in the

year 2000-01. It has slightly came down from the previous year
because of the mounting competition from other countries.
Germany was the largest importer of dehydrated onion followed by
Netherlands. The dehydrated vegetables from India in the same
year was just 848 MT valued at Rs.6.16 crores. Export of dried
tamarind powder matched almost the volume of onions exported
in the year 2000-01, to UAE, Saudi Arabia and Egypt etc. Likewise
598 MT of DHD garlic powder and flakes were exported in the
same year valued at Rs.2.62 crores. The export volume of
dehydrated tropical fruits from India continue to be dismal low
which should be a matter of serious concern.
Most of the DHD banana chips and slices exported to
Europe and U.S.A originate from Philippines, though India is the
largest producer of the fruit. Similarly other tropical fruits like
mango, papaya, guava etc. are sourced mainly from Thailand. This
is an opportunity that India has not been able to encash. The
estimated export demand forecast for dehydrated fruit and
vegetable from India by the year 2007 is estimated at 19500 MT
and the domestic demand at 3375 MT respectively.
As regards, the VFD industry in India, only two companies
are in commercial production which include Flex Foods Ltd.,
Dehradun and Saraf Foods Ltd., Vadodara. The former is a 100%
EOU and exporting mainly the freeze dried mushroom and
culinary herbs. Their export of last couple of years is averaging
around Rs.14 crores p.a. and the company is a regular winner of
APEDA export performance awards. They have already
incorporated the expansion of the plant capacity which was partly
financed by a soft loan from NHB and a grant from APEDA.
Saraf Foods Ltd. have recently changed the product mix and
are now producing ready-to-use pre-prepared Indian food recipes

in VFD form. They are now reported to be doing well. The present
export of VFD products from India are of the order of 150 MT
which by 2007 is expected to touch 176 MT. The estimated
domestic demand shall be around 6.5 MT.
The Indian dehydration and freeze drying industry have to
go a long way in their development and transformation into one of
the world standards.
The international scenario with respect to the trade in major
products and the selected countries involved in import/export of
these products has been studied in depth and detail. Based on the
findings of the survey the action plan that needs to be undertaken
to develop this industry has been accordingly chalked-out and
described in the report. The summary of the report follows as
under:
2.3.3. Raw material Availability
The dehydrated products which are presently of importance
to India on the, basis of their acceptability in the dehydrated form
in the world markets are onion and garlic, even though
mushroom, dehydrated vegetable and tamarind powder also figure
amongst the major products being exported. The raw material
availability for the products proposed for processing into
dehydrated products and for export are briefly described as under:
i. Onion
India with a production of 4.9 million tonnes of onion is the
second largest producer of onion in the world after China,
contributing almost 10% of the world production. The major onion
producing states are Maharashtra, Karnataka, Andhra Pradesh
and Gujarat etc. The export variety of onion is mostly white in

colour though the rose onion from Karnataka has started getting
quite popular in the world markets.
India has the most suitable climate for production of onion
and can be the world leader in its global trade. The peak
availability lasts for about three months It's storage properties are
quite good which can ensure a regular availability for a period of 9
months.
It is of interest to note that the raw onion variety in India
particularly for the purpose of dehydration is normally not
suitable because of it's relatively lower dry matter content. The
problem therefore needs to be referred to the pioneer R&D
institutions like IARI etc. with a time bound research programme
to develop the variety of onion with higher solid content and other
desired characterstics.
ii. Potato
India is the fourth largest producer of potato in the world
with a production of 25.0 million tonnes contributing 8% of the
total world production. U.P with 42% followed by West Bengal
with 30% are the two leading potato producing states. A number
of varieties of potato with high solid and low sugar content have
been successfully developed. These can compete even with the
world famous qualities that are specially grown for dehydrated
products. The predominant variety of this kind is Kufri Chipsona I
& II.
iii. Tomato
India produces 7.4 million tonnes of tomato which is
equivalent to 8% of the total world production. The processing
varieties with low water content and with extended period of

maturity are now available to ensure the raw material availablility
for processing for most of the time around the year.
iv. Cabbage
With a production of 5.9 million tonnes India is the largest
producer of cabbage in the world contributing almost 12% of the
total world production. The quality of Indian cabbage is very good.
v. Cauliflower
The production of cauliflower in India is about 4.7 million
tonnes which is equivalent to 34% of the total world production.
The best qualities are available between the months of September
to January.
vi. Okra
With a production of 3.4 million tonnes, India is the largest
producer of okra in the world market. Though okra is a typical
tropical vegetable, it's demand with the asian ethnic population
abroad is on the rise. The peak season of its availability is April to
September.
vii. Brinjal (Egg Plant/Aubergine)
India produces 8.1 million tonnes of brinjals which is 38%
of the world production. In fact it is produced in different varieties
such as spherical, cylindrical and so on.
viii. Garlic
Most of the garlic in India is produced in drought-prone
areas due to which it's availability fluctuates from season to
season. When the crop is hit by the drought the prices go up
almost about 7 times. Otherwise the availability of garlic in the
country remains somewhat stable.

The size of the raw garlic available in India is much smaller
than the variety grown in China. Besides the dry matter content of
Indian garlic is much lower, which calls for addressing the
problem to the Indian R&D Institutions like IARI for developing
the variety similar to the one available in China so that Indian
producers of dehydrated garlic are able to reduce the production
cost and compete in the international market.
2.4.General Process of Dehydration
2.4.1.Predrying Treatments
Predrying treatments prepare the raw fruits and vegetables
for the dehydration process, and include raw product preparation
and color preservation. Most fruits and vegetables follow similar
raw product preparation steps, although the peeling and the
blanching steps may be specific to the type of fruit or vegetable
that is being prepared. The color preservation method differs for
fruits and vegetables, with most fruits using sulfur dioxide (SO2 )
gas and most vegetables using sulfite solutions.
2.4.1.1.Raw Product Preparation.
Raw product preparation prepares the raw fruit or vegetable
for the color preservation step. Preparation includes selection and
sorting, washing, peeling (some fruits and vegetables), cutting into
appropriate forms, and blanching for some fruits and vegetables.
The initial step involved in the common predrying treatments for
fruits and vegetables is selection and sorting for size, maturity,
and soundness. The raw product is then washed to remove dust,
dirt, insect matter, mold spores, plant parts, and other material
that might contaminate or affect the color, aroma, or flavor of the
fruit or vegetable. Peeling or removal of any undesirable parts
follows washing. Methods used for peeling fruits and vegetables
for dehydrating include hand peeling (not generally used due to

high labor cost), lye solution, dry caustic and mild abrasion,
steam pressure, high pressure washers, or flame peelers. For
fruits that are commonly dehydrated, only apples, pears, bananas,
and pineapples are usually peeled prior to dehydration. Vegetables
normally peeled include beets, carrots, parsnips, potatoes, onions,
and garlic.
Except for potatoes, onions, and garlic, the specific method
of peeling is not identified for individual fruits and vegetables.
Potatoes are commonly peeled using dry caustic and mild
abrasion. Onions and garlic are peeled by either high-pressure
washers or flame peelers. Prunes and grapes are dipped in an
alkali solution to remove the waxy surface coating which enhances
the drying process. Next, the product is cut into the appropriate
shape or form (i.e., halves, wedges, slices, cubes, nuggets, etc.),
although some items, such as cherries and corn, may by-pass this
operation. Some fruits and vegetables are blanched, which
inactivates the enzymes by heating. Fruits and vegetables are
blanched by immersion in hot water (95E to 100EC [203E to
212EF] for a few minutes or exposure to steam.
2.4.1.2 Color Preservation.
The final step in the predehydration treatment is color
preservation,
also known as sulfuring. The majority of fruits are treated with
SO2 for its antioxidant and preservative effects. The presence of
SO2 is very effective in retarding the browning of fruits, which
occurs when the enzymes are not inactivated by the sufficiently
high heat normally used in drying. Sun-dried fruits (e.g., apricots,
peaches, raisins, and pears) are usually exposed to the fumes of
burning elemental sulfur before being put out in the sun to dry. In
addition to preventing browning, SO2 treatment reduces the

destruction of carotene and ascorbic acid, which are the important
nutrients for fruits. Sulfuring dried fruits must be closely
controlled so that enough sulfur is present to maintain the
physical and nutritional properties of the product throughout its
expected shelf life, but not be so large that it adversely affects
flavor. Some fruits, such as apples, are treated with solutions of
sulfite (sodium sulfite and sodium bisulfite in approximately equal
proportions) before dehydration. Sulfite solutions are less suitable
for fruits than burning sulfur (SO2 gas), however, because the
solution penetrates the fruit poorly and can leach natural sugar,
flavor, and other components from the fruit.
Although dried fruits commonly use SO2 gas to prevent
browning, this treatment is not practical for vegetables. Instead,
most vegetables (potatoes, cabbage, and carrots) are treated with
sulfite solutions to retard enzymatic browning. In addition to color
preservation, the presence of a small amount of sulfite in
blanched, cut vegetables improves storage stability and makes it
possible to increase the drying temperature during dehydration,
thus decreasing drying time and increasing the drier capacity
without exceeding the tolerance for heat damage.
2-4 Sulfur (as SO2 or sulfite) is the most widely used
compound to prevent browning of fruits and vegetables, but it can
cause equipment corrosion, induce off-flavors, destroy some
important nutrients, such as vitamin B1 , and is not approved in
some countries. Therefore, several alternative methods of color
preservation have been investigated. These include lowering pH by
using citric or other organic acids, rapid dehydration to very low
water contents, use of other antioxidants (e.g., ascorbic acid,
tocopherols, cysteine, and glutathione), heat inactivation or
individual quick blanching, reduction of the water activity

(osmotic treatment), and the centrifugal fluidized bed (CFB)
process.
The most commonly used sulfur-alternative treatments for
fruits are osmotic treatment and the CFB process. In osmotic
treatment, fruit pieces, slices, and chunks are exposed to
concentrated sugar syrup (dry syrup) or to salt to remove the
water from the fruit by osmosis. The partially dehydrated fruit
piece is then further dried using conventional dehydration
techniques (most commonly in a vacuum shelf drier). Fruits that
have successfully used the osmotic treatment are apples, peaches,
bananas, mangos, and plantains. Advantages of osmotic
treatment are reduced exposure time to high temperature,
minimized heat damage to color and flavor, reduced loss of fresh
fruit flavor, and removal of some fruit acid by the osmosis process.
However, the removal of fruit acid and addition of sugar may be
disadvantages in certain products. In the CFB process, blanching
and an approximate 50 percent reduction in water can be
achieved in less than 6 minutes. This treatment can then be
followed by any conventional dehydration process. This process
eliminates the disadvantages associated with the addition of sugar
or salt to the product during osmotic treatment and been
successfully use in diced apples. Advantages of the CFB treatment
include simplicity of design and an intimate gas-to-particle
conduction that provides uniform
particle exposure without mechanical agitation. However, the CFB
process is limited to small (one-half inch or smaller) cubes.
2.4.2.Drying or Dehydration
Drying or dehydration is the removal of the majority of water
contained in the fruit or vegetable and is the primary stage in the
production of dehydrated fruits and vegetables. Several drying

methods are commercially available and the selection of the
optimal method is determined by quality requirements, raw
material characteristics, and economic factors. There are three
types of drying processes: sun and solar drying; atmospheric
dehydration including stationary or batch processes (kiln, tower,
and cabinet driers) and continuous processes (tunnel, continuous
belt, belt-trough, fluidized-bed, explosion puffing, foam-mat,
spray, drum, and microwave-heated driers); and subatmospheric
dehydration (vacuum shelf, vacuum belt, vacuum drum, and
freeze driers).
2.4.2.1 Sun and Solar Drying.
Sun drying (used almost exclusively for fruit) and solar
drying (used for fruit and vegetables) of foods use the power of the
sun to remove the moisture from the product. Sun drying of fruit
crops has remained largely unchanged from ancient times in
many parts of the world, including the United States. It is limited
to climates with hot sun and dry atmosphere, and to certain fruits
such as prunes, grapes, dates, figs, apricots, and pears. These
crops are processed in substantial quantities without much
technical aid by simply spreading the fruit on the ground, racks,
trays, or roofs and exposing them to the sun until dry.
Advantages of this process are its simplicity and its small capital
investment. Disadvantages include complete dependence on the
elements and moisture levels no lower than 15 to 20 percent
(corresponding to a limited shelf life). Solar drying utilizes black-
painted trays, solar troughs, and mirrors to increase solar energy
and accelerate drying. Indirect solar driers collect solar energy in
collectors that, in turn, heats the air as it blows over the collection
unit before being channeled into the dehydration chamber. In
commercial applications, solar energy is used alone or may be

supplemented by an auxiliary energy source, such as geothermal
energy.
2.4.2.2 Atmospheric Dehydration.
Atmospheric forced-air driers artificially dry fruits and
vegetables by passing heated air with controlled relative humidity
over the food to be dried, or by passing the food to be dried
through the heated air. Various devices are used to control air
circulation and recirculation. Stationary or batch processes
include kiln, tower (or stack), and cabinet driers. Kiln driers utilize
the natural draft from rising heated air to dry the product and are
the oldest and simplest type of dehydration equipment still in
commercial use. Tower or stack driers consist of a furnace room
containing a furnace, heating pipes, and cabinets in which trays
of fruits or vegetables are dried. In a typical design, each tower or
stack holds approximately 12 trays and a furnace room holds
about 6 stacks. Heated air from the furnace rises through the
trays holding the product. As the trays of food at the bottom are
dried, they are removed. All trays are then shifted downward and
freshly loaded trays are inverted at the top. Cabinet driers are
similar in operation to a tower drier, except that the heat for
drying is supplied by steam coils located between the trays. This
design provides some temperature control and uniformity, and
thus represents an improvement over the tower drier. However,
cabinet driers are suitable only for establishing the drying
characteristics of a new product or for high-valued raw materials,
such as bananas or mushrooms, due to small capacity and high
operating costs.
Continuous processes include tunnel, continuous belt, belt-
trough, fluidized-bed, explosion puffing, foam-mat, spray, drum,

and microwave-heated driers. Tunnel driers are the most flexible
and efficient dehydration system used commercially, and is widely
used in drying fruits and vegetables. The equipment is similar to a
cabinet drier, except that it allows a continuous operation along a
rectangular tunnel through
which tray-loaded trucks move. The tunnel is supplied with a
current of heated air that is introduced at one end. Fruits and
vegetables of almost any size and shape can (so long as they are
solids) be successfully dried in a truck-and-tray tunnel drier.
Continuous belt or conveyor driers are similar to tunnel driers,
except that the food is conveyed through a hot air system on a
continuous moving belt without the use of trays. This difference
eliminates the costly handling of the product on trays before and
after drying and allows continuous operation and automatic
feeding and collection of the dried material. Belt-trough driers
have a continuous stainless steel wire mesh belt that forms a
trough about 10 feet (ft) in length and 4 ft wide. The raw material
is fed onto one end of the trough and is dehydrated by forcing hot
air upward across the belt and the product. Fluidized-bed driers, a
modification of the belt-trough drier, uses heated airflow from
beneath the bed to lift the food particles and at the same time
convey them toward the outlet. However, if the air velocity
becomes too great, channeling will occur and most of the air will
escape
without performing its function; therefore, fluidized-bed driers are
limited to the preparation of food
powders. In explosion puffing, fruit pieces (e.g., blueberries) are
partially dehydrated in a conventional manner and then heated in
a closed vessel, known as a gun because of its quick-opening lid.
Pressure is built-up in the vessel to a specific level and the closure

is then released, causing the pieces to expand by sudden
volatilization of internal mositure. The fruit particles are then
dried to 4 to 5 percent moisture content by conventional drying
methods. Foam-mat drying involves drying liquid or pureed
materials as a thin layer of stabilized foam by heating air at
atmospheric pressure. The prepared foam is spread on perforated
trays and dried by hot air, followed by crushing into powder.
Spray driers involve the dispersion of liquid or slurry in a stream
of heated air, followed by collection of the dried particles after
their separation from the air. This process is widely used to
dehydrate fruit juices. In drum driers, a thin layer of product is
applied to the surface of a slowly revolving heated drum. In the
course of approximately 300E of a full revolution, the moisture is
flashed off, and the dried material is scraped off the drum by a
stationary or reciprocating blade. Drum driers are generally
heated from within by steam and are suitable for a wide range of
liquid, slurried, and pureed products. Microwave driers have been
tried experimentally
for the dehydration of fruits, but no commercial installations are
in place.
2.4.2.3 Subatmospheric Dehydration.
Subatmospheric (or vacuum) dehydration occurs at low air
pressures and includes vacuum shelf, vacuum drum, vacuum
belt, and freeze driers. The main purpose of vacuum drying is to
enable the removal of moisture at less than the boiling point
under ambient conditions.
Because of the high installation and operating costs of
vacuum driers, this process is used for drying raw material that
may deteriorate as a result of oxidation or may be modified
chemically as a result of exposure to air at elevated temperatures.

All vacuum-drying systems have the following essential
components: vacuum chamber, heat supply, vacuum-producing
unit, and a device to collect water vapor as it evaporates from the
food. All vacuum driers must also have an efficient means of heat
transfer to the product in order to provide the necessary latent
heat of evaporation and means for removal of vapor evolved from
the product during drying.
There are two categories of vacuum driers. In the first
category, moisture in the food is evaporated from the liquid to the
vapor stage and includes vacuum shelf, vacuum drum, and
vacuum belt driers.
Vacuum shelf driers and drum driers are batch-type driers and
are suitable for a wide range of fruits and vegetables (e.g., liquids,
powders, chunks, slices, wedges, etc.). Vacuum belt driers are
continuous-type driers suitable for food pieces, granules, and
discrete particles. It operates at a relatively high vacuum and has
a capital cost much higher than a batch-type unit of similar
operating capacity. In the second category of vacuum driers, the
moisture of the food is removed from the product by
sublimination, which is converting ice directly into water vapor.
The advantages of freeze drying are high flavor retention,
maximum retention of nutritional value, minimal damage to the
product texture and structure, little change in product shape and
color, and a finished product with an open structure that allows
fast and complete rehydration. Disadvantages include high capital
investment, high processing costs, and the need for special
packing to avoid oxidation and moisture gain in the finished
product.
2.4.3 Postdehydration Treatments.

Treatments of the dehydrated product vary according to the
type of fruit or vegetable and the intended use of the product.
These treatments may include sweating, screening, inspection,
instantization treatments, and packaging. Sweating involves
holding the dehydrated product in bins or boxes to equalize the
moisture content. Screening removes dehydrated pieces of
unwanted size, usually called "fines." The dried product is
inspected to remove foreign materials, discolored pieces, or other
imperfections such as skin, carpel, or stem particles.
Instantization treatments are used to improve the rehydration rate
of the low-moisture product and include compressing the product
after dehydration (flaking) and/or perforating the product after it
is partially dehydrated and then dehydrating the perforated
segments to the desired moisture level (used primarily for apples).
Packaging is common to most all dehydrated products and
has a great deal of influence on the shelf life of the dried product.
Packaging of dehydrated fruits and vegetables must protect the
product against moisture, light, air, dust, microflora, foreign odor,
insects, and rodents; provide strength and stability to maintain
original product size, shape, and appearance throughout storage,
handling, and marketing; and consist of materials that are
approved for contact with food. Cost is also an important factor in
packaging. Package types include cans, plastic bags, drums, bins,
and cartons, depending on the end-use of the product.

3. Experimentation
3.1 Experimental set up & Procedures
The experimental set up for onion dehydration consist of
number of steps as shown in the fig. It consist of Following steps :
3.1.1. Predrying Treatments :
3.1.1.1 Raw Product Preparation
Medium & large sized red & white onion were chosen for
this drying experiment. Peeling & trimming were done manually
by sharp steel knifes.
After cutting the onion samples were meshed with
aluminium meshers manually with 4 mm mesh size.
3.1.1.2 Sulphination & pH lowering.
A combined sulphination & citric acid treatment was given
by steeping the onion slices successively in 0.2 % potassium
metabi-sulphite ( KM5 ) & 0.2 % citric acid for 5 min.
3.1.1.3. Osmotic Dehydration
After sulphination the weights of samples were noted down.
Then they were dipped in 5 %, 10% & 15% brine solutions
respectively both red & white onion. The volume was brine
solution was taken as double the volume of samples. A
intermediate agitation was provided during this period.
After 1 hr. the samples were removed from brine & dried
with using filter papers. The respective weights of each sample
was noted down.
3.1.2 Drying
3.1.2.1 Atmospheric Drying :
Atmospheric forced air dries artificially dry vegetables by
blowing hot air. For our experiment a commercial tray drier was
used. About 3 samples each of red & white onion species were

selected for this step of 5%, 10% & 15 % of brine in osmotic
dehydration.
The onions were spread uniformly in the aluminium trays.
The trays were stocked in dryer at 700
C. The drying was started &
weights of samples were noted down after each ½ hr. intervals till
the samples attained a weight corresponding to a moisture
content of 5 – 6 %. The samples were collected carefully used for
further process.
3.1.2.2 Solar Drying :
Six samples with similar specifications of the samples used
in atmospheric drying were used. The initial was were noted. The
samples were spread uniformly on aluminium trays. The trays
were placed in sun. The loss in weights by samples were measured
at hourly intervals till the weights reach to moisture content of 5
– 6 %. The samples were properly collected & weighted finally.
3.1.3 Post Dehydration Steps :
These techniques were used for powder forms.
3.1.3.1 Grinding :
The product or samples collected from the trays were
grinded in a ball mill for ½ hr.
The grinded product was then collected for further steps.
3.1.3.2. Sieving :
The product was the sieved to remove fines & the oversize.
The powder on 30 mesh size was collected for packing.
3.1.3.3 Packing & Storage :
Onion powder was packed in 200 & 400 gauge low density
pollyethylene ( LDPE ) & 200 gauge high density polyethylene
( HDPE ) pouches of 8 X 6 cm & stored at room temperature ( 18 –
35 0
C) 50 – 60 % RH & low temperature ( 7 0
C, 85 % RH )
respectively.

Fig. 3.a Onion dehydration process

3.2 Analysis
3.2.1 Physical characteristics
Average weight, average volume, average bulb size [length and
diameter] as measured by a vernier caliper, nature of bulb neck as
observed visually, per cent yield of edible bulb after peeling and
trimming were determined. (Table 3.2.a)
3.2.2 Chemical analysis
Moisture content was determined by drying the sample in a
vacuum oven at 700
C to constant weight. Total soluble solids (TSS)
content of pressed juice was determined by a hand refractometer.
Acidity in terms of total titratable acids was estimated by titrating
a known weight of the sample with standard NaOH solution using
phenolphthalein as indicator and the results were expressed as
per cent malic acid. Ascorbic acid content was estimated by
titrating a known weight of the sample with 2, 6-
dichlorophenolido-phenol dye using 3% metaphosphoric acid as
stabilizing agent. Water insoluble matter was determined by
washing onion paste free from soluble matter with water on a
weighted filter paper and drying it along with the residue at 60 0
C
to constant weight. To estimate reducing sugars, a known weight
of the prepared sample was mixed with water for extraction of
sugar. Following clarification with lead acetate and deleading with
potassium oxalate, reducing sugars were estimated. Total sugars
were estimated by the same method in an aliquot of the clarified
extract following hydrolysis with hydrochloric acid and
neutralisation of the excess acid with sodium hydroxide. Browning
in dehydrated onion was measured in terms of optical density at
420 nm of an aliquot of 10% NaCl solution with which the
dehydrated product was drenched thoroughly. The residual
sulphur dioxide in dehydrated onion was determined.
3.2.3 Drying studies

The ratio of the dried weight of the product to the weight
before drying was recorded as drying ratio. The dried was recorded
as drying ratio. The dried product was rehydrated by dipping in
distilled water and the rehydration ratio was computed in terms of
the ratio of the weight of the rehydrated sample to that of the
dried product. Moisture content, browning, total sugars, reducing
sugars, ascorbic acid and residual sulphur dioxide were estimated
in the dried products.
3.2.4 Sensory evaluation
Sensory evaluation of the dried onion takes in terms of
colours, flavour, texture and overall acceptability was performed
by a panel of 8 judges on a 9-point hedonic scale varying from ‘like
extremely’ [rating 9] to ‘dislike extremely’ [rating 1].
Sr. No Properties Red Onion White Onion
1 Average weigth(gm) 78 74.2
2 Average volume(ml) 81 79.6
3 Average Length (cm) 4.26 4.06
4 Average Diameter (cm) 5.02 5.41
5 Shape Index (L/D) 0.849 0.75
6 Bulb neck Disposition Closed Open
7 Moisture Content 88.531 % 88.899%
8 Rehydration Ratio 1 : 4.62 1 : 4.54
9 Dehydration
ratio(5%moisture)
6.07 : 1 5.85 :1
Table 3.2.a Physical characteristics of onion

3.3 Result & Discussion
3.3.1 General Discussion
Batch A] Tray Drying Of White Onions
Sample 1 = Osmotic treated in 5% brine.
Initial solid content (Ss) Area of Drying. (A)
Sample 1 = Ss1 = 0.059462 kg. A1 = 0.0629 m2
Sample 2 = Ss2 = 0.053027 kg. A2 = 0.0565 m2
Sample 3 = Ss3 = 0.064297 kg. A3 = 0.0680m2
Initial moisture content (W.B.) = 88.53%
Sr
.
No
.
Time
(Sec)
Sample 1 Sample 2 Sample 3 Type of
drying
W1 X1 N1 W2 X2 N2 W3 X3 N3
1 0 518.4 88.53 - 462.3 88.53 - 560.6 88.53 -
Osmotic
2 ½ - - - - - - - - -
3 1 307.9 47.94 - 299.6 53.35 - 370.9 54.70 -
4 1 ½ 191.9 25.54 42.33 187 28.98 45.72 245.8 32.38 42.22
Forced
drying
5 2 141.8 15.88 18.27 138.7 18.53 19.61 184.5 21.44 20.67
6 2 ½ 107.3 9.22 12.58 99.5 10.05 15.91 140.6 13.61 14.81
7 3 85 4.95 8.13 79.8 5.79 7.99 108.2 7.831 10.93
8 3 ½ 70 2.03 5.56 68 3.24 4.79 83.8 3.48 8.23
9 4 66.2 1.33 1.33 64.5 2.48 1.42 79.4 2.69 1.48
10 4 ½ 64.4 0.95 0.72 62.6 2.07 0.77 77.6 2.37 0.61
15 5 63.8 0.84 0.22 61.6 1.85 0.41 76 2.08 0.54

Batch A
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6
Time(Hr)
MoistureContent(%)
X1(%)
X2(%)
X3(%)
From the above graph it is clearly seen that the moisture remove
in 5% concentration osmotic dehydration is maximum &
minimum in 15% concentration brine. The above figure represents
the drying of white onion in tray drying.

Batch B] Solar Drying Of White Onions
Sample 1 = Ss1 = 0.00286kg. A1 = 0.00312 m2
Sample 2 = Ss2 = 0.00286 kg. A2 = 0.00312 m2
Sample 3 = Ss3 = 0.00286 kg. A3 = 0.00312 m2
Sr.
No
.
Time
(Hr.)
drying
W1 X1 N1 W2 X2 N2 W3 X3 N3
1 0 25 88.53 - 25 88.53 - 25 88.53 -
Osmotic
2 1 14.84 47.94 - 16.19 53.33 - 16.92 56.24 -
3 2 9.05 24.76 21.24 10.67 31.24 20.25 11.71 35.40 19.10 Forced
drying
4 3 5.41 10.20 13.34 6.96 16.40 13.61 8.23 21.48 12.76
5 4 3.68 3.28 6.34 4.60 6.96 8.65 5.85 11.92 8.76
6 5 3.14 1.12 1.98 3.44 2.32 4.25 4.52 6.64 4.84
7 6 3.06 0.8 0.29 3.24 1.52 0.73 4.24 5.52 1.03

Batch B
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8
Time(Hr.)
MoistureContent(%)
X1(%)
X2(%)
X3(%)
From the above graph it is clearly seen that the moisture
remove in 5% concentration osmotic dehydration is maximum &
the drying of white onion in solar drying.

Batch C] Tray Drying Of Red Onions
Sample 1 = Ss1 = 0.00277 kg. A1 = 0.00503 m2
Sample 2 = Ss2 = 0.00277 kg. A2 = 0.00503 m2
Sample 3 = Ss3 = 0.00277 kg. A3 = 0.00503 m2
Sr.
No
.
Time
(Hr.)
drying
W1 X1 N1 W2 X2 N2 W3 X3 N3
1 0 25 88.89 - 25 88.89 - 25 88.89 -
Osmotic
2 ½ - - - - - - - - -
3 1 13.86 44.36 - 14.62 47.4 - 14.82 48.20 -
4 1 ½ 8.45 22.72 23.83 8.91 24.56 25.15 9.03 25.04 25.51
Forced
drying
5 2 5.05 9.12 14.97 5.33 10.24 9.87 5.50 10.92 15.55
6 2 ½ 3.44 2.68 7.09 3.63 3.44 7.48 3.78 4.08 7.53
7 3 2.93 0.6 2.29 3.09 1.28 2.38 3.25 1.92 2.38
8 3 ½ 2.86 0.36 0.264 3.02 1.0 0.31 3.18 1.64 0.31

Batch C
0
20
40
60
80
100
0 1 2 3 4
Time(Hr.)
MoistureContent(%)
X1(%)
X2(%)
X3(%)
the drying of red onion in tray drying.

Batch D] Solar Drying Of Red Onions
Sample 1 = Ss1 = 0.00277kg. A1 = 0.00503 m2
Sample 2 = Ss2 = 0.00277 kg. A2 = 0.00503 m2
Sample 3 = Ss3 = 0.00277 kg. A3 = 0.00503 m2
Sr.
No
.
Time
(Hr.)
drying
W1 X1 N1 W2 X2 N2 W3 X3 N3
1 0 25 88.89 - 25 88.89 - 25 88.89 -
Osmotic
2 1 13.86 44.36 - 14.62 47.4 - 14.82 48.2 -
3 2 8.86 24.36 11.01 9.35 26.32 11.61 9.48 26.84 11.76 Forced
drying
4 3 5.09 9.28 8.31 5.37 10.4 8.77 5.44 10.68 8.90
5 4 3.07 1.20 4.44 3.24 1.88 4.69 3.28 2.04 4.96
6 5 2.91 0.56 0.35 3.07 1.20 0.36 3.12 1.40 0.35
7 6 2.81 0.16 0.22 2.96 0.76 0.24 3.02 1.00 0.22

Batch D
0
20
40
60
80
100
0 2 4 6 8
Time(Hr.)
MoistureContent(%)
X1(%)
X2(%)
X3(%)
the drying of red onion in solar drying.

3.3.2 Comparative Graphs
Comparison A) Moisture removed versus concentration of brine.
Sr. No. Concentration of brine
(%)
Moisture removed
(%)
1 2 40.56
2 5 45.85
3 10 39.75
4 15 38.21
Comparison A
0
10
20
30
40
50
0 10 20
Brine Conc. (%)
MoistureRemoved(%)
Moisture
Removed(%)
removed in 5% concentration osmotic dehydration is maximum &
minimum in 15% concentration brine. From the above figure it is
clearly seen that the optimum brine concentration for osmotic
dehydration is 5%.

Comparison B) Comparison between osmotic dehydrated white
onion dried in tray & solar drier & without osmotic effect.
Sample 1 = 5% osmotic treated white onion (tray dried).
Sample 2 = 5% osmotic treated white onion (solar dried).
Sample 3 = white onion without osmotic treatment (tray dried).
Sr. No. Time
(Hr.)
Sample 1
% X1 (W.B.)
Sample 2
% X2 (W.B.)
Sample 3
% X3 (W.B.)
1 0 88.53 88.53 88.53
2 1 47.94 47.94 53.54
3 2 15.88 24.76 28.85
4 3 4.93 10.20 12.2
5 4 1.33 3.28 4.68
6 5 0.84 1.12 1.82
7 6 - 0.80 1.4

Comparison B
0
20
40
60
80
100
0 2 4 6 8
Time(Hr.)
MoistureContent(%)
% X1
% X2
% X3
From the above graph represents the drying of white onion
with and without osmotic dehydration in tray & solar drying. It is
seen that maximum moisture is removed in osmotic dehydrated
tray drying & less moisture is removed in without osmotic
treatment.

Comparison C) Comparison on basis of size of onion (white onion,
tray dried).
Sample 1 = 5% osmotic dehydrated meshed white onion.
Sample 2 = 5% osmotic dehydrated sliced white onion.
Sr. No. Time
(Hr.)
Sample 1
(moisture %)
Sample 2
(moisture %)
1 0 88.53 88.53
2 1 47.94 80.92
3 2 15.88 40.40
4 3 4.93 24.81
5 4 1.33 14.31
6 5 0.83 9.94
7 6 - 6.75
8 7 - 4.71

The above graph gives comparison of white onion
dehydration on the basis of size. As by general rule the drying in
smaller size in onion is more as compare to bigger sized one. From
above it is seen that the drying of meshed onion is with faster rate
then of the slice one.
Comparison C
0
20
40
60
80
100
0 2 4 6 8
Time(Hr.)
MoistureContent(%)
X1(%)
X2(%)

Comparison D) Comparison between RED & WHITE onions (tray
dried).
Sample 1 = 5% osmotic dehydrated meshed white onion.
Sample 2 = 5% osmotic dehydrated meshed red onion.
Sr. No. Time
(Hr.)
Sample 1
(moisture %)
Sample 2
(moisture %)
1 0 88.53 88.89
2 1 47.94 44.36
3 2 15.88 9.12
4 3 4.93 0.66
5 4 1.33 -
6 5 0.84 -

Comparison D
0
20
40
60
80
100
0 2 4 6
Time(Hr.)
MoistureContent(%)
X1
X2
From above figure shows comparison between white and
red onion. By the above figure we can consider the drying rate of
red onion is more than white onion because of its high moisture
contain and low quality.

4.COST ESTIMATION
4.1.Experimental cost
BASIS:- 24 Kgs of onion (5%osmotically dehydrated onion)
Sr.
No.
Operation Tray Drying Solar Drying
White
(Rs.)
Red
(Rs.)
White
(Rs.)
Red (Rs.)
1 Raw material 3x24=72 2.25x24
= 54
3x24=72 2.25x24
= 54
2 Man power
Peeling &
Meshing)
24 24 24 24
3 Chemical
required (salt &
KMS)
8 8 8 8
4 Power
consumption
(3.37 Kw x (Hr.)x
4Rs.)
27 29 - -
5 Utilities (Water) 2 2 2 2
6 2 2 2 2
7 Total 135 119 108 90
Yield / batch (5% M.C.) :-
Losses in (cutting + peeling) = 5%
= 0.05 x 24
= 1.2 kgs.
Wt. after peeling = 24 – 1.2 = 22.8 kgs.
Considering 5% moisture in products we get yield as :-
For red onion = 22.8 (1-0.8353)
= 3.755 kgs.

For white onion = 22.8 (1-0.8290)
= 3.899 kgs.
Cost/Kg.of the product:-
For White onion
Tray Drying , Cost Price=135/3.899= 34.628 Rs./Kg.
Solar Drying , Cost Price = 119/3.899= 30.521 Rs./Kg.
For Red onion
Tray Drying , Cost Price = 108/3.755 = 28.762 Rs./Kg.
Solar Drying , Cost Price = 90/3.755 = 23.968 Rs./Kg.

4.2.Scale-up cost consideration
Basis:
a. 1500 kgs. of onion .
b. Working hours - Three shifts each of 8 hours duration
c. Working days in a year - 300 days
d. Annual production capacity - 112.5 M.T. of dehydrated
vegetables and 37.5 M.T. of dehydrated onion .
e. Capacity utilisation - 100%
f. Annual output envisaged - 150 M.T.
Plant and Machinery
The equipment required for the unit are:
SL. Description Nos Amount (Rs.)
i Pre cooling facility at + 10 degrees
centigrade as raw material store
85000.00
ii Stacking trays for vegetables with
each tray holding 10 kilograms of
the vegetable
500 75000.00
iii Preparatory section comprising
washing tank,
slicers, cubers, dicers etc
220000.00
iv Blanching tank with thermostat
control solenoid
valves, circulation pump to keep
blanching solution in circulation
155000.00
v Stainless steel vibratory shaker to
remove excess water after
blanching
50000.00

vi Fluidized bed driers for
dehydrating vegetables at a
capacity of 1000 kgs. in a span of 8
to 10 hours, complete with heat
changers, blower fans and
accessories.
440000.00
vii Form fill and seal packing machine
with augur weighers and fillers
236000.00
viii How water boiler and accessories 165000.00
ix Pin mill with accessories at a
capacity of 50 kgs. per hour
500000.00
x Laboratory testing equipment
comprising Precision weighing
scales; Hot air oven; Ashing oven;
Soxhlet apparatus; PH meter;
Kjeldhal apparatus; Glassware;
Chemicals
75000.00
xi Total 2136000.00
Infrastructural Facilities
a. Land 15000 square feet
b. Shed 8000 square feet
c. Power 50 HP connected load
d. Water 500 kilo litres per month
e. Fuel Furnace oil for boiler
Total Capital Requirement
a. The total capital requirement is Rs. 96.38 lakhs.
b. Fixed capital is Rs. 66.36 lakhs as follows.

c. Working capital is Rs. 30.02 lakhs as follows.
d. Project cost comprising fixed capital and margin money for
working capital is Rs. 77.80 lakhs.
A. FIXED CAPITAL
Rs. in lakhs
a. Land and building 25.00
b. Plant and machinery 21.36
c. Delivery vehicle - LCV 4.00
d. Erection and commissioning 3.50
e. Cost of power connection and electrification 3.00
f. Moulds, fixtures and office equipment 2.50
g. Preoperative expenses 3.00
h. Contingencies 2.00
i. Know how fees 2.00
Total (A) 66.36
B. WORKING CAPITAL
Period (days) Rs. in lakhs
a. Raw material 30 5.76
b. Packing material 30 0.51
c. Finished goods 7 3.50
d. Debtors 30 15.00
e. Salaries and wages 30 1.64

f. Utilities 30 0.61
g. Contingencies 30 3.00
Total (B) 30.02
Total (A) + (B) 96.38
Working Capital to be Finances As:
Margin money Rs. 11.44 lakhs
Bank Finance Rs. 18.58 lakhs
Means of Finance
a. Promoters contribution Rs. 28.03 lakhs
b. Term loan Rs. 49.77 lakhs
c. Subsidy nil
d. Total Rs. 77.80 lakhs
Requirement of Raw and Packing Materials Per Month
sl Description Unit Qty Price (Rs.)
a. Onions kgs 40000 160000.00
b. Total raw material 54000 482000.00
c. Primary packing material
metallized polyester-poly film
kgs 50 12500.00
d. Secondary packing material
cartons and straps
nos 2500 30000.00
e. Total packing material 42500.00

Salaries and Wages of Employees Per Month
sl. Designation No Salary per
head
Total salary
i Factory Manager 1 8000.00 8000.00
ii Maintenance Engineer 1 6000.00 6000.00
iii Production Supervisor 3 4000.00 12000.00
iv Skilled labour 4 3000.00 12000.00
v Packing labour 3 3000.00 9000.00
vi Unskilled labour 15 2000.00 30000.00
vii Van driver 1 3000.00 3000.00
viii Administrative staff 1 3000.00 3000.00
ix Marketing Manager 1 8000.00 8000.00
x Sales officers 3 6000.00 18000.00
xi Marketing salesmen 6 5000.00 30000.00
xii Security staff 2 2000.00 4000.00
xiii Total 38 143000.00
xiv Perquisites @ 15% 21450.00
xv Total 164450.00
Operating Expenses
The annual operating expenses at full capacity utilisation are
estimated at Rs. lakhs as follows:
sl Description Total value (Rs.
lakhs)
i Raw materials 57.84

ii Packing materials 5.10
iii Utilities 7.32
iv Salaries and wages 19.73
v Contingencies 36.00
vi Depreciation on land and civil works
@ 10%
2.50
vii Depreciation on machinery @ 10% 2.15
viii Depreciation on moulds and fixtures
@ 10%
0.25
ix Depreciation on office equipment @
20%
0.20
x Depreciation on vehicle @ 10% 0.40
xi Interest on term loan @ 14% 6.98
xii Interest on short term borrowings @
14%
3.34
xiii Total production cost 141.81
Sales Realisation
sl Item Qty in
kgs.
Rate/kg
(Rs.)
Total Value (Rs.
lakhs)
ii Dehydrated onion 285000 60.00 171.00
iii Total 285000 171.00
Profitability

6. Mathematical Modelling & simulation
6.1 Modelling Fundamentals
6.1.1 Chemical Engineering Modelling
The use of models in chemical engineering is well established, but
the use of dynamic models, as opposed to the more traditional use
of steady-state models for chemical plant analysis, is much more
recent. This is reflected in the development of new powerful
commercial software packages for dynamic simulation, which has
arisen owing to the increasing pressure for design, process
integrity and operation studies for which a dynamic simulator is
an essential tool. Indeed it is possible to envisage dynamic
simulation becoming a mandatory condition in the safety
assessment of plant,, with consideration of such factors as start
up, shutdown abnormal operation, and relief situations. Dynamic
simulation can thus be an essential part of any hazard or
operability study, both in assessing the consequences of plant
failure and in the mitigation of possible effects. Dynamic
simulation is thus of equal importance in large scale continuous
process operations as in other inherently dynamic operations such
as batch, semi-batch and cyclic. Manufacturing processes.
Dynamic simulation also aids in a very positive sense in gaining a
better understanding of process performance and is a powerful
tool for plant optimisation, both ai the operational and at the
design stage. Furthermore steady-state operation is then seen in
its rightful place the end result a dynamic process for which rates
of change have become eventually zero.
The approach in this book is to concentrate on a simplified
approach to dynamic modelling and simulation. Large scale
commercial software packages for chemical engineering dynamic
simulation are now very powerful and contain highly sophisticated

mathematical procedures which can solve both for the initial
steady-stat: condition as well as for the following dynamic
changes. They also contain extensive standard model libraries and
the means of synthesising a complete process model by combining
standard library models. Other important aspects are the
provision for external data interfaces and built-in model
identification and optimisation routines, together with access to a
physical property data package. The complexity of the software,
however, is Basic Concepts
such that the packages are often non-user friendly and the
simplicity of .the basic modelling approach can be lost in the
detail of the solution procedures. The correct use of such design
software requires a basic understanding of the sub-model blocks
modeling. Our simplified approach to dynamic modelling and
simulation incorporates no large model library, no attached
database and no relevant physical property package. Nevertheless
quite realistic process phenomena can be demonstrated, using a
very simple approach. Often a simplified approach can also be
very useful in clarifying preliminary ideas before going to the large
scale commercial package, as we have found several times in fir
research. Again this follows our general philosophy of starting
simple and building in complications as the work and as a full
understanding of the process model progresses.
Kapur (1988) thus listed thirty-six characteristics or principles of
mathematical modelling. These are very much a matter of
common sense, but it is very important to have them restated, as
it is often very easy :o lore sight of the principles during the active
involvement of modelling. Thev can he summarised as follows:
1)The mathematical model can only he an approximation of
real-life. processes, which are often extremely complex and

often only partially understood. Thus models are themselves
neither good nor bad but, as pointed out by Kapur, will either
give a good fit or a bad fit to actual process behaviour.
Similarly, it is possible to develop several different models for
the same process, and these will all differ in some respect in
the nature of predictions. Indeed it is often desirable to try to
approach the solution of a given problem from as many
different directions as possible, in order to obtain an overall
improved description. The purpose of the model also needs lo
be very clearly defined,
I. Of course, whilst the aim of the modelling exercise is
always to obtain as realistic a description of (h^ process
phenomena as possible, additional realism often involves
adJ'tionat numerical complexity and vi!J demand
additional data, which may be difficult or impossible to
obtain. A marginal additional decree of realism can thus
become rapidly outv/eighed by the large amount of extra
time and efiort ncjr"ed.
?. Modelling is a process of continuous development, in which it is
generally advisable to slart off witii i!ic simplest conceptual
lepiesentafion of (he process and to build in more and more
complexities, as the model develops Starting off with the process
in its most complex form, often Icadn to confusion. A process of
continuous validation is necessary, in which the model theory,
data, equation formulation and model predictions must all be
examined repeatedly. In formulating any moUcl. it is therefore
important to include the potential for change. The final form of the
model will lie somewhere between the initial highly-simplified and
unrealistic model and a possible final overcomplicated and over-

ambitious model, but should provide a reasonable description of
the process :;nd must be capable of being used.
Often it is possible to consider the process or plant, as a system of
independent sub-sets or modules, which are then modelled
individually and combined to form a description of the complete
system. This technique is also used in the large scale commercial
simulation software, in which various library sub-routines or
modules for the differing plant elements, arc combined into a
composite simulation program.
3. Modelling i.% an art but also a very important learning process.
In addition to a mastery c! the relevant theory, considerable
insigh' ! '^ the actual functioning of the process is required. One of
the most important factors in modelling is to understand the basic
cause and effect sequence of individual processes. Often the model
itself, by generating unexpected behaviour, will assist in gaining
the additional process Insight, since ;hc basic cause for the
anomalous behaviour must be thought out and a plausible
explanation found. The modelling process will often also uggest
the need fur new data or for experimentation needed to elucidate
various aspects of process beha iour that arc no: well
undersiood.
4. Modclr must be both realis'i; and also robust. A model which
predicts effects which are quite contrary to common sense or to
normal experience is unlikely tv: be met with confidence. To
accord with this, some use of empirical adjustment factors in the
model may be needed, in order to represent combinations of
relatively unknown unknown factors.
The basic stages in the above modelling methodology are indicated
in Fig. I.I.

Compared to purely empirical methods of describing chemical
process phenomena, the modelling approach attempts to describe
performance, by the use of well-established thcc.y, which when
described !n mathematical termj. represents a working 'model for
the process. In carrying out a modelling exercise, the modeller is
forced to consider the nature of all the important parameters of
the process, their effect on the proce.- s and how each parameter
can be defined in quantitative terms, i.e., the modeller must
identify the important variables and their separate effects, which
in practice may have a very highly interactive effect on the overall
process. Thus the very act of modelling is one that forces a better
understanding of the process, since all the relevant theorv must
be critically assessed. Jn addition, the task of formulating theory
into terms of mathematical equations is also a very positive factor
that forces a clear formulation of basic concepts.
Once formulated, the model can be solved and the behaviour
predicted by the model compared wlih experimental data. Any
differences in performance may then bo used to further redefine or
refine rhe model until good agreement is obtained. Once the model
is established it can then be used, with reasonable confidence, to
predict "pjru>r
marice under differing process conditions, and used
for process design, optimisation end control. Input of-plant or
experimental data is, of course, required in order to establish or
validate the model, but the quantity of data required, as compared
to the empirical approach is considerably reduced.
A comparison of the modelling and empirical approaches are given
below.
Empirical Approach: Measure productivity for all combinations of
plant operating conditions, and make correlations.
- Advantage: Little thought is necessary.

- Disadvantage: Many experiments are required.
Modelling Approach: Establish a model and design experiments to
determine the model parameters. Compare the mode! behaviour
with the experimental measurements. Use the model for rational
design, control and optimisation.
- Advantages: Fewer experiments are required and greater
understanding is obtained.
- Disadvantage: Time is required for developing models.
1.1.2 General Aspects of the Modelling Approach
An essential stage in the development of any model, is the
formulation of the appropriate mass and energy balance equations
(Russell and Denn, 1972). To these must be added appropriate
kinetic equations for rates of chemical reaction, rates of heat and
mass transfer and equations representing system property
changes, phase equilibrium, and applied control. The combination
of these relationships provides a basis for the quantitative
description of the process and comprises the basic mathematical
model. The resulting model can range from a simple case of
relatively few equations to models of great complexity. The greater
the complexity of the model, however, the greater is then the
difficulty in identifying the increased number of parameter values.
One of the skills of modelling is thus to derive the simplest
possible model, capable of a realistic representation of the
process.
A basic use.of a process model is to analyse experimental data
and ro use this to characterise the process, by assigning
numerical values to the important process variable.?. The model
can then also be solved with appropriate numerical data values
and the model predictions compared with actual practical results.
This procedure is known as simulation and may be used to

confirm that the mode' and the appropriate parameter values are
"correct''. Simulations, however, can also be used in a predictive
manner to test probable behaviour under varying conditions,
leading to process optimisation and advanced control strategies.
The application of a combined modelling and simulation approach
leads to the following advantages:
1. Modelling improves understanding. In formulating a
mathematical model, the modeller is forced to consider the
complex cause-and-effect sequences of the process in detail,
together with all the complex inter-relationships ilrit may be
involved in the process. The comparison of a model prediction with
actual behaviour usually leads to an increased understanding of
the process, simply by having to consider the v/ays in which the
mods! might be in error.
2. Models help in experimental design. It is important that
experiments be designed in such a way mat the model can be
properly tested. Often the model itself will suggest the need for
data for certain parameters, which might otherwise be neglected.
Conversely, sensitivity tests on the model may indicate that
certain parameters may be negligible and her.ce can be neglected
in the model. ..
3. Models may be used predictively for design and control. Once
the model has been established, it should be capable of predicting
performanc- under differing process conditions, that may be
difficult to achieve experimentally Models can aiso be used for the
design of relatively sophisticated control , systems and can often
form an integral par! of the control algon'thm. Both mathematical
and know/edge based models can be used in designing and
optimising new processes.

4. Models may be used in training and education. Many
important aspects of reactor operation can be simulafed by the
use of simple models. These include process start-up and shut
down, feeding strategies, measurement dynamics, heat effects and
control. Such effects are easily uemonstrated by computer, as
shown in the accompanying simulation examples, but are often
difficult and expensive to demonstrate in practice
5. Models may be used for process optimisation. Optimisation
usually involves the influence of two or more variables, with one
often directly related to profits and the other related to costs.
1.1.3 General Modelling Procedure
One of the more important, features of modelling is the frequent
reed to . reassess both the basic theory (physical model), and
fhe mathematical equations, representing the physical model,
(mathematical model), in order to achieve agreement, between the
mode) prediction and actual plant performance (experimental
data).
.As shown in Fig. 1.2, the following stages in the modelling
procedure can be identified:
(i) The first involves tit" proper "Pliniu'on of the problem and hence
the gonls and objectives of the study. All the relevant theory must
be assessed in combination with any prac.icr.J experience, and
perhaps alternative physical models need to be developed and
examined.
(ii) The available theory must then be formulated in mathematical
terms. Most reac'or operations involve many different variables
(reactar.t ana product concentrations, temperature, rates cf
rcactan; consumption, product formation and heat production) ?
nd many vary as a function of time (batch, semi-batch operation).

For these reasons the -nathematical model w'.'A often consist of
many differentia' ecjirUions.
(Hi) Having developed a model, the equation., must then be solved.
Mathematical models of chemical engineering systems, are usually
quite complex and highly non-linear and are such thai an
analytical means of solution is not possible. Numerical methods of
solution must therefore be employed, wiih the method preferred in
this iexi being that of digital simulation. With this method, the
solution of even very complex models i accomplished with relative
ease. Digital simulation languages are designed specially for the
solution of sets of simultaneous differentia! equations, based on
the use of numerical integration. Many fas! and efficient numerical
integration routines are now available, such that many digi'a!
simulation languages are able to offer a choice of integration
routine. Sorting algorithms within the structur
e of the language
enable very simple programs to be written, having an almost cne-
to-one conespondencc.-with the way in which the basic
model'equations are originally formula'ed. Tne resulting
simulation programs ape therefore very easy to understand and
airo to write. A further major advantage is a convenient output of
results, in both tabulated and graphical form, obtained via very
simple program commands.
(iv) The validity of the computer prediction must be checked and
steps (i) to (iii) will often need to be revised at frequent intervals.
The validity of uie solution depends on the correct choice of theory
(piiysicnl and mathematical model), the ability to identify model
parameters correctly and accuracy in the numerical solution
method. In iiian> cases, the system will not be fully understood,
thus leaving large areas of uncertainty. The relevant theory may
also be very difficult to apply. In such cases, it is then often

necessary to make simplifying assumptions, which may
subsequently be eliminated or improved as a better understanding
is obtained. Care and judgement must be taken such that the
model does not become over complex and'that it is not defined in
terms of immeasurable parameters. Often a lack of agreement can
be caused by an incorrect choice of parameter values, which can
even lead to quite contrary trends being observed dui-'ng the
course of the simulation. It is evident that these parameters to
which the model response is very sensitive have to be chosen or
determined with greatest care.
It should be noted that often the model does not have to give an
exact fit to data as sometimes it iuuj be sufficient to s;
mply have a
qualitative agreement with the process.
1.1.4 Simulation Tools
Mar.y different digital simulation software packages are available
on the market. Fortunately many, but not 'til, conform tc the
standard strucfre of a Continuous System Simulation Language
(CSSL). The programming structures for aii CSSL languages are
very similar. In addition, all CSSL languages are adjuncts to other
high level languages such as FORTRAN, PASCAL or BASIC and tin
s provide the programmer with ail the facilities and all the power
of the host language.
()ther
interesting features of simulation tools concern user
interfacing, compu.mg power, portability to various computer
systems, optimisation and parameter estimation. Some tools allow
a graphical set-up of a mode! Some languages, for example ACSL
and ESL, a development by the ISIM-group as advertised in the
back of this book, run on PC's and larger machines, and include
more powerful numerical algorithms and supply many predefined

building blocks, which facilitate such tasks as the modelling of
control systems.
Mathematical software, such as MATLAB and MATHEMATICA
have great computing power and may be portable to almost any
available computer system. One useful application of modelling
and simulation is optimisation of a process. MATLAB and
SIMUSOLV include powerful algorithms for nonlinear
optimisation, which can also be applied for parameter estimation.
For this latter purpose SIMUSOLV is an excellent tool especially
for practical work owing to its flexibility in handling experimental
data (Heinzle and Saner, 1991). Some eharacteristics of the
differing simulation programs are given in Table 1.1. Optimisation
and parameter estimation are also discussed in greater detail in
Sees. 2.4.1 and 2.4.2. Recent surveys of the differing packages
now available include Matko et al. (1992) arid Wo/.ny and Lut?.
(1991).
1SIM and HSL, 1SIM International Simulation Ltd., Technology
House. Salford University Business Park. Lissadd Street, Salford
M6 6AP. UK; STELLA, High-performance Systems Inc.. 13
Dartmouth College Highway, Lyme, New Hampshire, 03768. USA;
MATLAB, The Math Works, Inc., 21 Eliot Street. South Nntick, MA
01760, USA; MATHEMATICA, Wolfiam Res. Inc., P.O. Box 6059,
Champaign. Illinois 61821, USA; ACSL, SIMUSOLV, Mitchcll &
Gautllier Associates, 73 Junction Square Dr., Concord, MA
01742-3096, USA: MODEL WORKS, A. Fischlin, Inst. Terrestr.
Ecology, ETH, Grabcnstr. 11, CH-8952 ScUieren, Switzerland;
SIMNON, Oepartment of Automatic Control, Lund Institute of
Technology, Sweden; SPEEDUP, Aspen Technology. Inc. Ten Canal
Park. Cambridge, Mass. 02141, USA.

The drying characteristics of wet solids are general
described by the drying rate curves. Such curve with moisture
contain verses time and drying rate verses moisture contain are
shown below. Generally, experimental evaluation of this curve is
done before performing design calculation.
Consider that the wet solids with initial moisture content
(Xi) are exposed to air of constant temperature and humidity. If we
then measure the moisture content with time (i.e. moisture
content of material is measured at various values of time), then
curve as shown in Fig. (a) is obtained from the collected data. The
curve relates the moisture content on dry basis with time. It is
clear from the curve that the moisture content of solids decreases
with time and after some time it remains constant at X , which is
the equilibrium moisture content.
From this curve, we can draw another type of curve which is
known as rate of drying curve. This curve is much more
descriptive of drying process. The rate of drying gives relationship
between rate of drying, expressed as, the moisture evaporated per
unit time per unit area of drying surface and moisture content on
dry basis. This curve can be constructed by measuring the slopes
of tangents drawn to the curve of X v/s θ at various values of
moisture content and then calculating rate as N = -Ss dX/dθ x
1/A, where Sg is the weight of dry solids and A is the area of
drying surface.
Fig. C shows the rate of drying curve. The section AB of the
curve represents the warming up period during which the
temperature of the solid is becoming equal to the temperature of
drying air. From B to C, the curve is straight line parallel to x-axis
representing the constant rate of drying, thus the section BC is
called constant rate period during which the layer of water on the

Modelling and Simulation of Osmotic Dehydration of Onion

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