1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
115
WASTE HEAT RECOVERY TO INCREASE BOILER EFFICIENCY USING
BAGASSE AS FUEL
Rajendra N. Todkar1
, P.E.Chaudhari2
, U.M.Shirsat3
1
post graduate student of Mechanical Engineering, MIT College of Engineering, Pune, India,
2
Dept. of Mechanical Engineering, MIT College of Engineering, Pune, India,
3
Nav shayadri College of Engineering, Pune, India,
ABSTRACT
Many industrial heating processes generate waste energy in textile industry; especially
exhaust gas from the boiler at the same time reducing global warming. Waste heat found in the
exhaust gas can be used to preheat the incoming gas. This is one of the basic methods for recovery of
waste heat. Therefore, this article will present a study the way to recovery heat waste from boiler
exhaust gas by mean of shell and tube heat exchanger. The present investigation has been carried out
in order to increase the efficiency of the boiler, used in the sugar mills. Methods for recovering the
heat of flue gases from boilers were using Water preheater, Air preheater. With the help of real
example of sugar factory.
Keywords: Bagasse; Boiler Efficiency; Exhausts Gas; Heat Exchanger; Heat Recovery.
1. INTRODUCTION
Growing cost of fuel and the need to fulfill the requirements of the Kyoto Protocol force the
majority of countries, even with temperate climate, to revise their attitude to district heating systems.
Heat is generated in boiler by combustion process of fuel. The strategy of how to recover this
heat depends in part on the temperature of the waste heat gases and the economics involved. Large
quantity of hot flue gases is generated from Boilers, Kilns, Ovens and Furnaces. If some of this waste
heat could be recovered, a considerable amount of primary fuel could be saved. The energy lost in
waste gases cannot be fully recovered. However, much of the heat could be recovered and loss
minimized [1].
Depending upon the type of process, waste heat can be rejected at virtually any temperature
from that of chilled cooling water to high temperature waste gases from an industrial furnace or kiln.
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
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ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 2, February (2014), pp. 115-121
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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Usually higher the temperature, higher the quality and more cost effective is the heat recovery. In
waste heat recovery must have some use for the recovered heat. It can be use would be preheating of
combustion air, space heating, or pre-heating boiler feed water or process water. In any heat recovery
situation it is essential to know the amount of heat recoverable and also how it can be used.
Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected
by reduction in the utility consumption & costs, and process cost. We have taken real example of one
boiler of sugar factory having flue gas temperature 200O
C , heat loss in dry gases is 16.96%. Heat
loss due to moisture formed by burning is 11.55% and due to moisture in fuel is 14.22%. Boiler
efficiency is 53.31%.So aim is to minimize heat losses through flue gas [2].
These systems have many benefits which could be direct or indirect of waste heat recovery.
Direct benefits: The recovery process will add to the efficiency of the process and thus decrease the
costs of fuel and energy consumption needed for that process. Indirect benefits: Reduction in
Pollution: Thermal and air pollution will dramatically decrease since less flue gases of high
temperature are emitted from the plant since most of the energy is recycled. Reduction in the
equipment sizes: As Fuel consumption reduces so the control and security equipment for handling
the fuel decreases. Also, filtering equipment for the gas is no longer needed in large sizes. Reduction
in auxiliary energy consumption: Reduction in equipment sizes means another reduction in the
energy fed to those systems like pumps, filters, fans, etc.
Nomenclature:
m’w mass flow rate of water (kg/s).
m the moisture fraction of the fuel.
a the ash fraction of the fuel.
Cpw specific heat of water (kJ/ kgO
C).
Tw1 initial temperature of water (O
C).
Tw2 final temperature of water (O
C).
m’f mass flow rate of flue gases (kg/s).
Cpf specific heat of flue gases (kJ/ kgO
C).
Tf1 initial temperature of flue gases (O
C).
Tf2 final temperature of flue gases (O
C).
m’a mass flow rate of combustion air (kg/s).
Cpa specific heat of air (kJ/kg K).
Ta1 initial temperature of combustion air (O
C).
Ta2 final temperature of combustion air (O
C).
η Efficiency of boiler (%).

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
117
Q quantity of steam generated (TPH).
q quantity of bagasse consumed (TPH).
hg enthalpy of steam (kJ/kgO
C)
hf enthalpy of feed water (kJ/kgO
C)
GCV gross calorific value of bagasse. (kJ/kg)
2. LITERATURE REVIEW
The paper [3] [4] explained about methods for recovering the heat of flue gases from boilers
using heat of vaporization are analyzed. High profitability of the developed thermal circuit involving
deep recovery of the heat of flue gases and its storage, as well as good prospects for using it, are
demonstrated by a real example in this paper. It conclude that Use of a comprehensive approach for
attacking the problem of deeply recovering the heat of boiler flue gases, including heat of
vaporization and involving consideration of all elements participating in the heat supply cycle, makes
it possible not only to solve this problem technically, but also to optimize the parameters of coolant.
J Barroso, H Amaveda, Antonio Lozano [5] carried out investigation in order to increase the
efficiency of the RETAL-type boiler, used in the Cuban sugar mills. A test method is used in the
evaluation process and further adjustment of the boilers operation was ASME and GOST. Pointing
the attention on the importance of the stoichiometric ratio and steam power on the overall efficiency.
They calculated gas temperature as well as the range of the optimal value for the excess air fraction.
Their influence on the efficiency was analyzed and the total costs determined.
Drying bagasse by using flue gas which comes from air preheater to chimney is an optimum solution
to enhance efficiency of boiler in sugar factory as bagasse has high calorific value but due to its
moisture about 50% not able to use its full heat is explain by Sankalp Shrivastav1, Ibrahim Hussain
[6]. The work suggest to place Cylindrical shell type dryer, in between the air preheater and
chimney, and flue gas pass from dryer’s one end and from another end bagasse by carriage, makes
dryer to act as a counter flow heat exchanger where flue gas gives its heat at 190°C to the bagasse at
45°C this reduce moisture of bagasse from 50% to 46%, increased CV of bagasse around 784 KJ/kg
which increases boiler efficiency from 79% to 81% in sugar industries.
3. METHODS TO INCREASE BOILER EFFICIENCY
a. Reduce Excess Air.
b. Preheat Combustion Air.
c. Blow down Heat Recovery.
d. Exhaust Heat Recovery.
e. Turbulators and Soot Blowers.
f. Replace Burners.
g. Condensate Return.
4. METHODS OF HEAT RECOVERY
The principal reason for attempting to recover waste heat is economic. All waste heat that is
successfully recovered directly substitutes for purchased energy and therefore reduces the
consumption of and the cost of that energy. A second potential benefit is realized when waste-heat

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
118
substitution results in smaller capacity requirements for energy conversion equipment. Therefore, the
use of waste-heat recovery can reduce the requirement for space heating energy. This permits a
reduction in the capacity of furnaces or boilers used for heating the plant. In every case of waste-heat
recovery, a gratuitous benefit is derived: That of reducing thermal pollution of the environment by an
amount exactly equal to the energy recovered, at no direct cost to the recover.
4.1. Preheat Combustion Air
Efficiency Improvement Up to 1 percentage point. If we have a large temperature difference
(20° to 40°) between your boiler intake air location and the ceiling of your boiler room and this hot
air is a result of boiler and stack losses, you can increase your boiler efficiency by either extending
the intake upwards or forcing the hot air down. Both options may require a fan and ductwork. If the
hot air is due to boiler wall losses, we may want to consider insulating the boiler.
4.2. Exhaust Heat Recovery
A device like the one shown below can be attached to the flue to recover a portion of the
exhausted heat. This heat can be used to preheat boiler make-up water. Take care not to extract so
much heat that the flue gases condense (causing corrosion).
4.3. Feed water preheater
A feed water heater is a power plant component used to pre-heat water delivered to a steam
generating boiler. Preheating the feed water reduces the irreversibility’s involved in steam generation
and therefore improves the thermodynamic efficiency of the system. This reduces plant operating
costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced
back into the steam cycle.
In a steam power plant (usually modeled as a modified Rankine cycle), feed water heaters
allow the feed water to be brought up to the saturation temperature very gradually. This minimizes
the inevitable irreversibility’s associated with heat transfer to the working fluid (water).
5. CALCULATIONS
Thermodynamic Analysis
1 st
Law 2 nd
Law
Input/output Input/output
Energy balance
Exergy balance
HHV LHV
Fig 1: Thermodynamic analysis applied to bagasse boiler [7][8]
By using shell and tube type heat exchanger: [9]. Methodology is used for calculations are
shown in fig.1; we have done thermodynamic energy balance of input and output energy.

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
119
5.1. Feed water preheater
The flue gases leaving a modern 3-pass shell boiler are at temperatures of 200 to 300 °C.
Thus, there is a potential to recover heat from these gases. The flue gas exit temperature from a
boiler is usually maintained at a minimum of 200 °C, so that the sulphur oxides in the flue gas do not
condense and cause corrosion in heat transfer surfaces. When a clean fuel such as natural gas, LPG
or gas oil is used, the economy of heat recovery must be worked out, as the flue gas temperature may
be well below 200 °C.[1]
“m’w x Cpw x (Tw2-Tw1) = m’f x Cpf x (Tf2-Tf1) (1)”
Flue gases (Cpf-1.097kJ/kgO
C is when flue gas is at 200O
C ) come in to feed water heater at
200O
C and water at 30O
C. In order to decreased exhaust flue gas temperature we passed it through
feed water heater. By heat balance (equation no.1), we get temperature after feed water heater, water
at 100O
C with mass flow rate of water is 3kg/s and flue gas at 125O
C. Feed water preheater having
effectiveness of 0.411.
5.2. Preheat Combustion Air
Combustion air preheating is an alternative to feed water heating. In order to improve thermal
efficiency by 1%, the combustion air temperature must be raised by 20 °C. Most gas and oil burners
used in a boiler plant are not designed for high air preheats temperatures. Modern burners can with-
stand much higher combustion air preheat, so it is possible to consider such units as heat exchangers
in the exit flue as an alternative to an economizer, when either space or a high feed water return
temperature make it viable.
“m’a x Cpa x (Ta2-Ta1) = m’f x Cpf x (Tf2-Tf1) (2)”
Flue gases after passing through feed water heater, it comes in air preheater. Air having
temperature 25O
C and flue gases enter at 175O
C. By heat balance (equation no.2), we get
temperature after air preheater, air is at 50O
C with mass flow rate of air is 2.6kg/s and flue gas at
60O
C. Air preheater having effectiveness of 0.169.
Boiler efficiency is calculated by direct method. This is also known as ‘input-output method’
due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel-bagases) for
evaluating the efficiency. The gross calorific value of a biomass fuel, as determined with a bomb
calorimeter, can be written in most cases in the form:
“GCV = k x (1 – m – a) (3)”
GCV is 9204.8 kJ/kg. The efficiency can be evaluated using the formula (4) [2].
“η = {Q x (hg-hf)} x 100 / (q x GCV) (4)”
At 20 bar pressure and 333O
C enthalpy of superheated steam is 3093.16 kJ/kgO
C and
enthalpy of feed water is 419.1 kJ/kgO
C. Quantity of steam generated is 17 TPH [2] and quantity of
bagasse consumed is 8TPH [2]. By using equation no.(4) we get boiler efficiency as 61.73%.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
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6. RESULT TABLE
Table 1: Heat exchanger calculations
Temperature (O
C) Mass Temperature of flue
flow rate gases (O
C)
(kg/s)In Out In Out
Water 30 100 3 200 125
preheater
Air preheater 25 50 2.6 125 60
Table 2: Efficiency
Efficiency
Before (%) After (%)
53.31 61.73
7. CONCLUSION
• The efficiency of bagasse fired boiler was calculated using flue gases temperature leaving the
boiler and on the basis of total heat values of steam. The boiler efficiency found was 61.73 %
and previously it was 53.31 % under prevailing conditions of the boiler as shown in Table.2.
Steam from bagasse was 17 TPH at a pressure of 21 kg/cm2
and at a temperature of 333O
C.
• Through recovery of waste heat by installation of an economizer. Waste heat found in the
exhaust gas of various processes is used to preheat feed water and combustion air. After
recovery of waste heat we get 8.42% more efficiency than previous one at mass flow rate of
water and combustion air 3kg/s and 2.6kg/s respectively as shown in Table.1.
• By using water preheater and air preheater we decreased flue gas temperature up to 60O
c.
• Both the methods of efficiency calculations Direct and indirect gave similar results.
REFERENCE
[1] Bureau of Energy Efficiency, 2009.
[2] Energy Audit Report of MSSK Ltd. Boiler Efficiency, 2006, Malegoan, Pune
[3] A.D.Kiosova, G.D.Avrutskiib, Deep Recovering and Storing of the Heat of Flue Gases from
Boilers, ISSN 0040-6015, Thermal Engineering., 58(2), 2011, 948-952.
[4] Prateep Pattanapunt, Kanokorn Hussaro, Tika Bunnakand, Waste Heat Recovery From Boiler
Of Large-Scale Textile Industry, American Journal of Environmental Science, 9(3), 2013,
231-239.

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6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 115-121, © IAEME
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[5] J Barroso, H Amaveda, Antonio Lozano, On the optimization of boiler Efficiency using
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[8] P. Regulagadda, I. Dincer, G.F. Naterer, Exergy analysis of a thermal power plant with
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[9] Javier Uche, Luis Serra, Antonio Valero, “Thermoeconomic optimization of a dual-purpose
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[11] M. A. Khaustov, Experience Gained from Operation of an Individual Boiler House in a
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