3. 3
VIABILITY.................................................................................................................................. 25
POSSIBLE IMPROVEMENTS............................................................................................................. 25
REFERENCES............................................................................................................................... 25
APPENDIX.................................................................................................................................. 28
APPENDIX I ............................................................................................................................... 28
APPENDIX 2: THROUGHPUT CALCULATIONS........................................................................................ 28
APPENDIX 3:NUMBER OF PONDS NEEDED FOR GROWTH AND CULTIVATION................................................ 30
APPENDIX 4: MASS BALANCE CALCULATIONS:PRE-TREATMENT............................................................... 30
APPENDIX 5: ENERGY BALANCE CALCULATIONS:PRE-TREATMENT........................................................... 32
APPENDIX 6: THE THEORETICAL MAXIMUM STEAM REQUIRED FOR EVAPORATOR........................................ 33
APPENDIX 7: EVAPORATOR SIZING.................................................................................................. 34
APPENDIX 8: HEXANE RECYCLE LOOP CALCULATIONS........................................................................... 35
APPENDIX 9: TANKSIZING............................................................................................................. 36
APPENDIX 10: HEATER AND COOLER SIZING....................................................................................... 37
APPENDIX 11: OVERALL HEAT AND MATERIAL BALANCE FOR HEXANE RECYCLE LOOP.................................... 38
APPENDIX 12: CO2 CONSUMPTION OVER INSTALLATION....................................................................... 38
APPENDIX 13: WASTE WATER STREAM MASS BALANCE........................................................................ 39
APPENDIX 14: WASTE WATER STORAGE TANK SIZING CALCULATION........................................................ 39
APPENDIX 13: MASS BALANCE....................................................................................................... 40
.............................................................................................................................................. 40
APPENDIX 14: ENERGY BALANCES................................................................................................... 40
APPENDIX 12: START-UP COSTS..................................................................................................... 41
APPENDIX 13: ANNUAL COSTS ....................................................................................................... 42
APPENDIX 14: ANNUAL INCOME..................................................................................................... 42
APPENDIX 15: RISK MATRIX .......................................................................................................... 42
APPENDIX REFERENCES.............................................................................................................. 43
Table of Figures and Tables
Figure 1: Block Diagram ................................................................................................................ 7
Figure 2: Overall Flow Diagram......................................................................................................8
Figure 3: Growth stage flow diagram ........................................................................................... 10
Figure 4: Combustion Traingle..................................................................................................... 18
Figure 5: Cradle to grave............................................................................................................. 22
Figure 6: Start up Cost Distribution.............................................................................................. 23
Figure 7: Annual Cost Distribution ............................................................................................... 23
Figure 8: Breakeven Curve........................................................................................................... 24
Figure 9: Hexane Recycle Loop .................................................................................................... 35
Figure 10: Aspen hexane Calculation............................................................................................ 36
4. 4
Table 1: Oil content of plant sources (Dao Energy, n.d)....................... Error! Bookmark not defined.
Table 2: Open and Closed pond comparison................................................................................. 11
Table 3: Comparisonof biodiesel purificationmethodstakenfrom(DennisY.C.Leung,XuanWuand
M.K.H. Leung) ..................................................................................................................... 28
Table 4: Heat and mass balance for hexane loop .......................................................................... 38
Table 5: CO2 Consumption.......................................................................................................... 38
Table 6: Waste water mass balance............................................................................................. 39
5. 5
Remit
To produce 5000 barrelsof biodieselfromcultivatingthe microalgaeorganism Chlorella vulgarissp.
througha closedpondsystem.
Background
The purpose of this project is to produce 5,000 barrels per day of biodiesel from a specific; aquatic;
photosyntheticorganism, which is called Chlorella vulgaris. This type of the algae strain has a great
potential as a source for biodiesel production (Marudhupandi, Gunasundaria and Kumara). In this
sectionthe growthprocessof Chlorella vulgaris and the size of the pondsneededforthe processwill
covered.
Biodiesel can be produced from different resources, such as edible seed crops (sunflower, palm,
rapeseed, soybean, coconut, etc) and non-edible seed crops (jatropha, karanja, jojoba, mahua,
cookingoil,animal fats,etc).Those are the first two generations of feedstock, where microalgae is
the third.Using microalgae hasa fewadvantagesrelatingtothe environment. The first advantage is
that microalgae reducescarbondioxide,CO2,andconvertsitintosugars;andfinallyinto fuel using a
biochemical process. The second advantage is that microalgae can grow anywhere in water
(freshwater or wastewater), demanding less water and nutrients for the growth in comparison to
edible and non-edible seed crops (BLINOVÁ, BARTOŠOVÁ and GERULOVÁ).
TABLE 1: OIL CONTENT OF PLANT SOURCES (DAO ENERGY, N.D)
Cultivation is the first step in producing biodiesel by growing algae. Microalgae can be cultivated
usingdifferentmethods; suchasopenand closed pond systems. The algae require light to grow for
biomass production. Cultivation can be also done by a heterotrophic method; that is where algae
grow without light, but instead fed sugars to produce biomass (BLINOVÁ, BARTOŠOVÁ and
GERULOVÁ).However,forthisproject, the closed pond system was chosen in order to produce the
biomass. The principle behind this method is to have raceway ponds covered with a greenhouse
(Algae Basics:ClosedSystems),where itiseasilyexposedtosunlight.Forsuchponds,paddle wheels
are used in order to move the water. This causes the algae to circulate and encourages the the
natural light to be spread equally. For this project, there are 209 ponds with a depth of 30 cm
(Rogers, Rosenberg and Guzman) and a pond size of 100 m2
(giving a total surface area of growth:
20,900 m2
). The volume of each pond is 30000 L. In order to produce 671721 kg (5,000 barrels per
year) of biodiesel in one year, the amount of biomass harvested in one day is 8329.09 kg with
6. 6
assumptiontooperate withnodowntime.Perday,42pondswouldbe harvestedandcleaned,while
167 ponds continued growing.
There are several factorsthataffectthe growthof the algae.Those factorsinclude temperature, pH,
and light.Temperature isone of the importantelements.Itinfluencesthe chemical composition,the
fixation of carbon dioxide and uptake of nutrients needed for the growth. Under increasing
temperatures the growth rate of the algae will increase, however only up until its optimum point.
Once the optimum value is reached, the growth rate will start to decrease. For the strain of the
algae chosen for this project, Chlorella vulgaris, the optimum temperature range is from 25⁰C to
30⁰C (Cassidy). Light is another factor, providing the essential energy source for the microalgae
growth. (Maryam Al-Qasmi).Asitisan endothermicreaction, the light provides the energy needed
for carbon fixation. The energy enables microalgae call to undergo the process of photosynthesis,
which utilises carbon dioxide and converts it into compounds such as carbohydrates and proteins,
while releasing oxygen as waste. (BLINOVÁ, BARTOŠOVÁ and GERULOVÁ). The final element
concernedwiththe growthof microalgae,ispH.For this algal strain, Chlorella vulgaris, the pH range
is from 7 to 9. The optimum range is from 8.2 to 8.7 (BLINOVÁ, BARTOŠOVÁ and GERULOVÁ).
Location
For this process, location is an important choice that has a number of requirements needing
fulfilling.The chosenlocationforthisreportisbasedatSan JuanPowerStationin New Mexico, USA.
To determine this location, the following ideas were developed:
- The best climate for algae development
- Closeness to market
- Closeness to raw materials
- Transport links
Algae are knownto growbestin relativelywarmclimateswithplentyof sunshinetoprovide energy
for the algae to grow. It is therefore important that the final location has a Mediterranean like
climate that will allow for growth all year round. New Mexico has an average temperature of
around 64°F or roughly 18°C. In Summertime temperatures can reach the high 30’s (°C) and in
winteraround10°C withfreezingconditionspossible.Fortunately,the growingpondswill be closed
off whichshouldpreventthe temperature beingafactor. Sunlight in the state is typically very high
sitting at 70-80% of sunlight being fully received with 90% common. This makes New Mexico
particularly ideal as like any biological plant process, light is a major factor (New Mexico State
University ).
Climate change fearsandthe gradual move awayfrom traditional fossil fuelshasfuelledthe growth
of the marketconcernedwithbiodiesel andother renewable fuels. With the USA being one of the
major CO2 contributors in the world there is strong pressures to tackle the progression of climate
change.Biodiesel consumptionhasgrownfrom25 million gallonsper year in the early 2000’s to 1.7
billiongallonsin2014. It is clearto see there isplentyof opportunityforbiodiesel in the country of
production (National Biodiesel Board).
The locationwasprimarilychosen due toits closeness to a large coal fired power plant which could
feedthe CO2 needsof the algae.Itis alsoa low cost way, as takingflue gasfrom the powerplant will
occur mimimal costs, as it would otherwise be a waste product. Whilst New Mexico is a rather arid
climate, it does have a significant agricultural industry with production value sitting at around $4
billionin2014, a large portionof thatbeingdairyfarming.Thismeansthere will be plentyof sources
7. 7
of waste water that can be used for the process. San Juan PS is also close to route 64 which runs
throughthe north of New Mexico to surrounding states (New Mexico Department of Agriculture ).
Process Overview
Please refer to Figure 2, when pipelines or equipment are mentioned.
The algae to biodieselprocessiscomprisedof four main areas. The growth stage, the pretreatment
stage,and the transesterificationandpurification processes. These four areas are identified on the
block diagram, Figure 1. The initial inputs required for growth are waste water and flue gas.
FIGURE 1: BLOCK DIAGRAM
9. 9
Algae Cultivation
Process Description
In order to achieve the conditions needed for the algae biomass to grow, for further downstream
processing certain feed streams need to be defined and process equipment determined. This will
therefore be the main objective of this section- to define how to create these conditions through
process design.
CO2 Stream Definition
One of the key condition requirements of algae like any other plant is a source of carbon dioxide
(CO2). Higher concentrations are needed to stimulate high growth, so treated flue gas from a coal
powerstationwill be utilisedinorderto obtain this stream. However, this stream cannot simply be
pumped through the algae culture without having certain controls in place. As seen from Table 2,
hydrodynamic stress is something that should be considered during the design of the ponds along
with good mixing and mass transfer of CO2. Therefore, a balance of factors needs to be achieved-
although mass transfer coefficients are considered to be low due to the raceway pond set up so
maximizing the other variables is an important part of the process.
The CO2 stream will be a gas stream, and therefore will utilise a centrifugal fan/compressor
arrangementtosupplythe closedracewayponds.Initiallyflue gas exiting the power station will be
veryhot (following the combustion conditions) and this gas must be cooled to be suitable for both
storage and inprovidingalgae culture input(GP-1).Thispresentsanopportunityforheatrecoveryas
shown by the process prior to storage (EX-1). The heat from this flue gas will be picked up by a
cooling water stream (SP-1) which will be vaporised to steam for use in the first stage of the
processing plant (SP-2) thus improving economy. A storage tank has been proposed (STOR-1) to
store flue gas to ensure supply is always available in case of any power plant shut-down and
preventing a poor algae harvest.
Waste Water Stream Definition
Another key condition requirement is providing macro/micro nutrients to algae. This will be
achievedusingawaste waterstreamwhichthe algae can be used to remove the nutrients allowing
safe disposal of the water. Agricultural waste water will be transported in (LP-1) and then will be
diluted (by LP-2) to reduce turbidityi
. A recycle biomass (RECY-1) stream will add further nutrition
from already processed algae mass, which in turn, will reduce the need for as much waste water.
Aftermixingfromamixingvalve (CV-1) the stream will be piped through (LP-3) to a stirred storage
tank (STOR-2) whichwill keep the mixture evenly distributed until draining to the Closed Raceway
Pond(s).
Choice of Vessel Type
The idea proposed for the growth process involves using raceway ponds, as used in open pond
systems,butclosingitoff fromthe elements. This gives the controller much greater influence over
whatfactors can affectthe algae- negative orpositive.Thistype of vessel is known as a closed pond
system and derives a lot of the advantages of open pond-ways and photo-bioreactors (PBR’s). To
getan ideaof the parametersof these systems, the table below gives some description of the two
pond types (S. Judd).
11. It can be seen closed pond has a number of advantages over open pond other than the higher
capital and operational costs involved. However, these are still significantly lower than scaled up
PBR’s.
Product Stream
There are a total of three expectedoutputsrunningfrom the Raceway Pond which include effluent
gas; effluentwater;andalgae biomass.The effluentgasisthe remainingflue gasafterbeingbubbled
through the algal biomass. It is expected that around 50% of the CO2 from the flue stream will be
removedreleasingharmless O2 in its place. This will be vented off as a treated effluent gas stream
(GP-5) to the atmosphere.
Nextisthe effluentwaterstream,whichisusedtograduallydrythe biomass during the flocculation
process prior to moving the final biomass to processing. This water will need to be filtered and
recycledbackintothe processto reduce water consumption. This will run through the PS-2 stream.
Finally,the biomass product stream will transport the partially dried algae slurry to the processing
plant downstream for further processing and the separation of the final products and bi-products.
This will move through the PS-1 stream.
Parameter Open Closed
Design complexity Lower Higher
Control Poor Good
Cost Lower Higher
Water losses High Low
Typical biomass concentration Low<comma> 0.1–0.2 g/l High: 2–8 g/l
Temperature control Difficult Easily controlled
Species control Difficult Simple
Contamination High risk Low risk
Light utilisation Poor Very high
CO2 losses to atmosphere High (up to 38%a) Almost none
Typical growth rate (g/m2/day) Low: 10–25 Variable:1–500
Area requirement Large Smaller
Depth/diameter of water 0.3 m 0.1 m
Surface: volume ratio ∼6 60–400
Cleaning None Required
Bimass quality Variable Reproducible
Harvesting efficiency Low High
Harvesting cost Higher Lower
Most costly operating function Mixing Oxygen and temperature control
Hydrodynamic stress on algae Very low Low-moderate
Gas transfer control Low High
TABLE 2: OPEN AND CLOSED POND COMPARISON
12. Pre-treatment
Please referto Figure 2 for identification of streamsand equipment.
Dewatering operation
Since the algae growin the suspensionof the water,alarge surface area of water is required for the
cultivation and growth. However, this complicates algae harvesting as large volumes of water are
neededtobe removedbeforethe oil withinthe algae cellscanbe extracted.Withinthe ponds algae
culturesare verydilute,typicallycontaining0.02-0.06% dry solid.Therefore meaningharvesting 1 kg
of algal biomassrequires separating 2,000-5,000 kg of water (Gouveia).The harvesting operation is
split into three steps the bulk process harvesting and the thickening, which is then followed by
drying. In previous microalgae studies the energy costs for pre-treatment, including drying, are
estimated to make up 20-30% of the total production costs. This is a major limiting factor on a
commercial scale,andwill need to be overcome in order for the project to become viable. (Grima)
Bulk harvesting E-101
As the algae are growninthe ponds,E-101, the nutrientandcarbon dioxide supplyare slowlyleaned
off.Notonlydoesthisenhance the growthandoil contentof the algae,butit concentratesthe algae
water slurry to around 4-7% dry solids (Gouveia). This process of causing carbon dioxide/nutrient
stressiscalledauto-flocculation. Chemicalandinorganicflocculation,meaningthe thickeningof the
algae water suspension, was not used due to the impact adding additional chemicals may have on
the transesterificationprocess.Overall the additionof chemical flocculantsiscurrentlynota method
of choice forcheapand sustainable production,as recent developments involve encouraging auto-
flocculation which can occur during carbon dioxide limitation (Gouveia).
Filtration E-102
A tangential membrane Micro Filter is shown as E-102 on the flow diagram. The 7% algae slurry, P-
101, passes through the filter, resulting in an outlet dry solid percentage of 15%, P-102. The water
removed is recycled back to the pond system, as shown by P-108. Microfiltration membranes can
meetthe needsof small sizedmicroalgaeharvesting.Cell diametersof 2–40 µm. (Ching-LungChena)
The diameterof ChlorellaVulgaris,10 µm fallswithin thiscriteria(Havard).Microfiltersrequire little
investmentandare simple inconstructionwhichallow foreasyoperation (Gouveia).The problem of
membrane fouling can be reduced by the use of turbulent inlet flows and shear forces on the
membrane surface (Ching-Lung Chena). However, too much shear stress can lead to the algal cell
wall bursting prematurely, resulting in lost algae oil. Therefore a balance must be struck. Another
disadvantage isthatitis veryenergyintensivetoachieve highfiltrationratios.However,Larzarovaet
al has shown that the cost of micro filtering river water can be as low as 0.2 kWh/m3
of water
processed (Lazarova V). Nevertheless a more realistic scope for power consumption for these
operations is 0.3–2 kWh/m3
(Grima).
Centrifugation E-105
The 15% algae slurry, P-102, is then pumped to a spiral plate centrifuge, E-105, where the slurry is
concentrated to 25%, P-104. Centrifugation uses the centrifugal force to replace gravity for the
separation of microalgae from the water (Ching-Lung Chena). Once again the water removed is
recycled back to the pond system through P-107. The centrifuge recommended for this process is
developedbyEvodosspecificallyfordewatering algae. It is able to achieve 31.5 % dry algae weight,
consuming 0.95 kWh/m3
of algae slurry while processing up to 40 m3
of slurry/hr (Algae Industry
13. Magazine). Although centrifugation has been successfully applied to microalgae harvesting in
previousstudies,itstill hassome disadvantagesassociated.
(Gouveia). The energy consumption and
capital cost of centrifugation is very high and similarly to filtration, the cell structure may be
destroyed under the high gravitational and shear forces, resulting in lost algae oil (Ching-Lung
Chena).
Evaporator E-106
Afterthe microalgae dewateringprocesseshave beencarriedout,the dry solid content of the algae
slurryisstill low.Therefore,adryingprocessisneededinordertoremove all traces of water before
the algae oil can be extracted from the dry biomass. A convective oven dryer could be used for
process,howeverthisisveryenergyintensive.Anotheroptionis solar drying, however this method
was discounteddue tothe longprocesstimesanda large dryingsurface requirement.Moreover,itis
difficulttomaintainthe qualityof the endproduct with a slow drying rate due to low temperatures
encouraging biomass degradation and the growth of bacteria (Ching-Lung Chena).
A possible solutionthatcould reduce the energy costs of the drying process is the recycling of heat
fromthe flue gasfeed,whichisthe carbondioxide supplyrequiredforalgae growthinthe ponds. By
using this waste heat, to produce steam, an evaporator can be used to dry the algal biomass. The
evaporatorwill be operatedat60 ºC to preventdegradationof the algal cells. P-601 to P-602, is the
flue gas stream from the nearby power station which provides the carbon dioxide supply to the
algae ponds. The hightemperature flue gas is used to heat up water, producing a steady supply of
steam,P-604, whichcan be easilyutilisedacrossthe plant.Forexample inthe n-hexanerecycle loop
and the transesterificationprocess.Calculationsbasedonthe sizingon the evaporator can be found
in Appendix 6, along with the maximum theoretical steam required, based on a single effect
evaporator.Fromthe calculations,itishighlyrecommendedthata multipleeffectevaporatorisused
in the process, to reduce the initial volume of steam required and to increase the overall steam
economy.
Algae oil extraction
The algae oil extraction is split into two processes in order to achieve the highest extraction
percentage of oil available algal oil. A mechanical pressing stage, followed by a solvent extraction.
These twostagestogetherwill be able toderive up to 95% of the total oil (Oilgae).The algae strain,
Chlorella Vulgaris, has an oil content of 29% (Saddam H. Al-lwayzy).
Mechanical crushing E-201
The firststage of the oil extractionisthe mechanical crushing of the dry algae biomass. An oil press
was selectedasthe methodtoextractthe oil fromthe driedalgae.Thismethodisbe able to remove
up to 70% of the oil.The PacificOil Type 90 oil pressrequires0.05kWh/kgof dry biomass (PacificOil
Presses).The pressproducesacrude oil productand a de-oiledalgal meal containing approximately
8-12% residual oil (Oilgae). The pressing is under 'cold' conditions, which means at 25 ºC.
Solvent Extraction and Recycle Loop
The de-oiledalgae meal,producedfromthe pressing,containsresidualoil whichisthensubjectedto
a solventextractionprocess. The residual algae oil dissolvesinthe solvent,whichisn-hexane.Thisis
done in the mixing unit, E-202, at a pressure of 5 bar. The remaining pulp is then filtered out from
the n-hexane,algae oil mixture,E-203.The pulpisrecycledbackintothe ponds, to provide nutrition
for the growingalgae.The algae oil,n-hexane mixture,P-204, proceeds to a pressure relief valve, E-
204, which reduces the pressure from 5 bar to 1 bar. Following the pressure reduction, the outlet
streamof the valve,P-205,entersa pre heaterbefore entering the flash separator. The pre-heater,
E-205, heatsthe algae oil,n-hexane mixtureto200 ºC, causingthe vaporisationof the n-hexane.The
algal oil and the n-hexane vapour are then separated by a flash separation, E-206. The algae oil
14. extracted proceeds to storage, E-210, while the n-hexane vapour is recycled in the solvent recycle
loop. P-207 transports the n-hexane vapour to cooler, E-207, where it is cooled to 25 ºC. Following
that the n-hexane liquid is pumped back up to 5 bar, E-208, before entering the n-hexane storage
tank,E-209. The highboilingpointof the algae oil, 554.2 °C compared, to the low boiling point of n-
hexane,67 °C,alongwithits highsolubility in n-hexane are the properties exploited in the solvent
extraction process (PubChem), (Oilgae). The n-hexane recycle loop is based on work by (Ronald
Halim), with various modifications (U. Schuchardt).
Solvent selection
The propertiesof n-hexane allow it to be an ideal solvent, as it has a high specificity towards lipids
and isvolatile enoughtoensure alowenergyseparationof the lipidfromsolvent (M. Mubarak). The
non-polar n-hexane acts by disrupting the hydrophobic interactions between the non-polar and
neutral lipidspresentinthe algal biomass (M.Mubarak). The use of n-hexanetoextractthe algae oil
is a fairly cheap and efficient method, however several drawbacks are also associated. Long
executiontimespose aproblem,however,operatingthe extractionprocessathigher temperatures,
50 to 200°C, and pressures can combat this issue (M. Mubarak). The high pressure ensures that the
solvent always remains in a liquid state which ensures not only a rapid extraction but the safe
storage of the n-hexane.
Althoughthe n-hexane recycleloopisaverysmall process,it contributes significantly to the overall
percentage recovery of algae oil extraction. It accounts for 20% of the overall algae oil recovered,
therefore it was modelled on Aspen Plus software. The sizing of equipment calculations based on
AspenPluscanbe foundin Appendix 8-11. Since low of volumes of n-hexane solvent are used the
minimum heat transfer areas for the cooling and heating are extremely small, as a result double
pipe heat exchangers are recommended, in order to keep the process simple yet cost effective.
Oil production
Transesterification (E-304)
Assumption:The feedstockisnon-acidic,meaningthatthe free fattyacid(FFA) contentis<2.5wt% of
oil.
The algal oil extracted will be converted to biodiesel (denoted as fatty acid methyl ester (FAME))
througha transesterificationreaction,more informationonthe chemistry of reactions can be found
inAppendix 1.Thisreactionwill have methanol react with the algal oil and have sodium hydroxide
(denoted as NaOH) as the homogenous catalyst. The NaOH itself does not catalyse the reaction, it
has to be mixedwithmethanolto produce methoxide which reacts readily with algal oil. The NaOH
comesinsolidformand doesnotreadilydissolve with the methanol. Therefore, NaOH needs to be
slowly added and mixed carefully (E-303) with methanol before mixing with the oils (ISTC). The
reaction mixture is immiscible, separating into two phases, oil phase and methanol phase. It has
beenshownthatstirringor agitatingthe mixture doesnotprove tobe effective enough to facilitate
the reaction.Newresearchshowsthatif passedthroughan ultrasonictransducer,the oil emulsifies
intothe alcohol phase formingsmall bubblesthatincreasesmasstransfersignificantly (StavaracheC,
VinatoruMand NishimuraR) (ThanhLT, OkitsuKand SadanagaY). The optimal operatingconditions
for this reaction will be at 1 atm and 50o
C, with methanol to oil ratio of 5:1, 50 minutes reaction
time. This gives a maximum yield of 99% (Thanh LT, Okitsu K and Sadanaga Y).
Product Separation
The transesterificationproductswouldbe a mixture of FAME and glycerol which can be completely
separatedina settlingchamber(E-305) for4 hours (Thanh LT, Okitsu K and Sadanaga Y) (Dennis Y.C.
15. Leung,XuanWu and M.K.H. Leung).Owingtothe large difference in densities causing immiscibility
of glycerol andFAME.However,FAMEand glycerol are both contaminated by unreacted methanol,
soapsand catalystthat needtobe furthertreated. The majority of these contaminants concentrate
in the glycerol phase rather than the FAME.
Purification of Crude Diesel
Dennis Y.C. Leung et al. (Dennis Y.C. Leung, Xuan Wu and M.K.H. Leung) has made a comparison of
the multiple ways to treat the contaminants in crude diesel in terms of current technology and
productstandards.Water washingwouldbe the methodused to purify the crude diesel, because it
is the most effective method in terms of removing contaminants – see Appendix 1 for the full
comparison. Water (distilled warm water) will readily dissolve with the contaminants, especially
glycerol andmethanol.Also,waterisimmiscibleindiesel allowingthe use of acentrifuge. Therefore,
crude diesel willbe waterwashed(E-401) forseveral cyclesuntil the water is clear of contaminants.
The water and diesel are then separated using a centrifuge (E-403) where the refined diesel will
leave inP-404 and the waste waterwill leave via P-405. The waste water that is left will need to be
further treated to remove the free methanol.
Re-neutralisation (E-501)
The basic catalyststend to concentrate inthe glycerol phase,andmustbe neutralized (VanGerpenJ,
Shanks B and Pruszko R). The crude glycerol will be neutralized using sulphuric acid (H2SO4) to
produce sodium sulphate salts (Na2SO4) which in turn can be separated to produce agricultural
fertilizers (J).
Vacuum Separation (E-503)
The neutralised crude glycerol is flash separated in a vacuum drum and an evaporators is used to
separate the water and methanol. The evaporated water and methanol can then be liquefied (E-
504) to be further separated using a distillation column.
Recycling Unreacted Alcohol
Once liquefied,the water and methanol mixture will then be separated in a distillation column (E-
504) with pure methanol as the distillate and waste water as the bottoms product. The methanol
distillate(P-505) can be recycled back into the transesterification process with the waste water (P-
506) being sent to the local municipal sewer system for further processing.
Market
With the company located in the north west of New Mexico, San Juan, the main market for the
company will be the north of New Mexico and surrounding states; Texas, Colorado and Arizona.
There are already several fuel companies across America that sell biodiesel as an alternative to
diesel.Namely“Loves Travel Store” which has several stations located in the north of New Mexico
alongInterstate 40, roughly 2 hours from San Juan. (National Biodiesel Board) New Mexico’s other
main biodiesel producer and the main competitor “Rio Valley Biofuels” is located in the far south
meaning there is an open market in the north of the state for a new biofuels producer. Although
there are currentlyonlya fewretailersof biodiesel inNew Mexico,the biofuelmarketisexpected to
grow drastically over the next 5 years with a predicted consumption of 5717.7 million litres in
Americaby2020 (LaisGalileuSperanza).Thisisconsistent with the growth in the industry over the
past 15 years,the productionof biodiesel hasgrown rapidly throughout America in the early 2000’s
with an increase from 2 million gallons in 2000 to around 250 million gallons in 2006 growing at a
pace of roughly 113 million gallons per year from 2004 to 2006 (Centre for Agriculture and Rural
Development).Thisgrowthmeansthe numberof retailersthroughoutNewMexicoselling biodiesel
16. is also expected to continue to increase, by producing 5,000 barrels of biodiesel per year the
company will capitalize on this expansion by supplying a number of consumers within the target
area.A recentpublicationquotesthe currentprice of biodiesel on the gulf coast as $3.21 per gallon
givingthe business an annual income of $561316.80 from biodiesel sales alone (U.S Department of
Energy ). As well as biodiesel the process also produces a large amount of glycerol as a byproduct.
This can also be sold on to other companies for the possible production of methanol, ethanol,
hydrogen, fuel additives and animal feed as well as being a component used for waste treatment
(Alexandre Bevilacqua Leoneti). However due to the rapid increase in the production of biodiesel,
the market price of crude glycerol plummeted in recent years to around $66 per ton. This measn
that for the glycerol being produced per year, the annual income would be only $1252.44. (César
Quispe)
Health and Safety Report (HAZAN)
Bio-refineries can present a number of potential health and safety (H&S) issues much like any
refinery.Usingavarietyof chemicalsandprocesses, resulting hazards must be identified; analysed
to findwhomightbe affected;evaluatedsothatitcan be eliminatedorcontrolledsufficiently(using
a risk matrix to determine whether enough has been done, matrix used can be found in the
appendices); and determine how frequently the findings should be reviewed (IChemE).
Energy Recovery Process
Thisprocessacts to achieve a bettereconomyforthe plant.Itisbeneficial inreducingthe amountof
fuel required to raise the appropriate amount of steam to supply drying operations further
downstreampreparingthe algae forprocessing.However,itdoespresentsafetyissueswhichcannot
be eliminated entirely. High temperature (up to 400°C) and allowing for poor equipment health
couldpresenta considerable problem.Hightemperature will make pipe walls become very hot thus
closingoff thisproblemis the bestoption.Usinginsulationisbeneficialbothwithprotectingworkers
and any persons on site from burning and scalding (which would give a 4-6 in severity) and also
improvespreventionof heatlosses to the surroundings. Maintaining the health of pumps and heat
exchangersusedinthe processisessential.Muchlike pipes,equipmentcanhave rupturesasa result
of corrosion and continued mechanical use, thus potentially allows for scalding hot steam to be
releasedintoareaswhere the workforce may come intocontact (likelihood is high if manufacturers
recommendationisnotfollowedmakingitlikely).Therefore,routine safetychecksshouldbe carried
out with maintenance as often as recommended by manufacturers (This lowers the likelihood to
around a 2 which gives adequate control). Due to the nature of this process, it should be regularly
reviewedintermsof H&Sand absolutelymustbe revisitedinthe eventof any slight modification to
the system during plant optimisation.
Growing Process
This is the backbone of the refinery process, and problems here will represent issues further
downstream. Fortunately, the process itself doesn’t pose much risk to surrounding areas as it is
closed off as a matter of optimizing the product. However, work will need to be done inside the
closedoff area’ssuchas cleaningandrestockingtasks.The processutilizeslarge amountsof flue gas,
which as a product of combustion, contains little oxygen and high concentrations of CO2 and trace
amounts other harmful by-products (such as Sulphur and Nitrogen oxides). Therefore, the
atmosphere fora large amountof time,will notbe suitable foranypersons.Onsite workerswhoare
17. permittedtowork inside the vessels will be at greatest risk and so it should be a requirement that
onlytrainedandresponsiblepersons be allowed to work in these areas. This gives the potential of
multiple deathsif notcontrolledgivingthe highestseverity.The recommendedapproachwouldbe a
control system that determines when the vessel is in operation and must signal this to persons on
site. Any irregular works should be put through a permit to work system and any regular works
carried out during operation will need breathing equipment. To ensure total safety, the ponds
should be aired between batches that way cleaning can be done safely. Of course a safety system
mustbe presenttosignal whetherthe vessel is safe for persons to work in it. This should lower the
likelihoodtoa1 givingadequate control.Thisprocessdoesnotnecessarilyneedregularreviews and
so every few years is acceptable. Any modifications will require a review.
Pre-treatment and Drying
Drying makes up the majority of this area of the process. As covered previously, steam is raised to
bringthe requiredheatneedtoconcentrate the algal biomassandremove anywaterthat is brought
withit.Withoutthisstep,the standardof the productsimplywouldn’t be possible. Steam will be at
just about 100°C and at 1 bar gauge. The vessel will operate at 60°C and again 1 bar gauge. As the
pressures are relatively low, it does not present too much of an issue. The temperatures are high
and could cause damage to the surroundings giving a severity that could range up to a 6 if burns
were significant.Properinsulation and design of the mass transfer lines and vessels should control
the immediate riskenoughagainbringingdownlikelihood.Whilstrupture islesslikely, it should still
have controlsinplace of proper maintenance as per manufacturer’s instructions. Yearly reviews of
thisarea isrecommended,andof course anymodificationwillrequireacomplete review of thisarea
of the process.
Hexane Treatment Stage
Withthisstage,maximisingrecovery of the algal constituents is the key goal, which maximises the
amountof productthat can be sold.However,the introductionof hexane presentsthe mostnotable
hazard of its flammability and toxicity. The hexane is mostly confined to this area of the process
thanks to the recycle loop in use. It will be pressurised to keep it as a liquid (5 barg) up until the
hexane recovery unit where it will be depressurised to atmospheric level to allow flash off. It is
therefore essential that this stage be fully evaluated.
Firstly, hexane is highly flammable and so the combustion triangle must be looked at to eliminate
one but preferably two of the sides (shown fig. 1). Here heat is suggested as one of the sides,
however any ignition source is sufficient with hexane. A fire inside the system would result in a
sudden increase in pressure (above the already high pressure) and would eventually cause an
explosive rupture inanysystemweakpointssuchasvalvesandvessels.Thiscouldhave the potential
to spread to other parts of the plant which could make a fire uncontrollable and affect more than
just the site. The process does not use a lot of hexane, reducing the potential severity however
fatalitiescouldhappengivingaseverityof 8.In termsof the closedoff processthe easiesttoremove
isoxygen.Todo this,a purging system is by far the best option as it completely removes all air and
replaces it with non-reactive nitrogen. This brings the likelihood down to a 2. To avoid fires in the
eventof a spill ora purgingsystemfailure,anyformof ignitionmustbe bannedatall times when on
site (removing ignition). To further prepare for any system failures, a last resort is recommended
ensuring firefighting equipment is available with trained personnel that can contain any outbreak
until local emergency services arrive.
18. Hexane isalsoverytoxic.Inhighconcentrationsitcan cause symptomsranging from headaches and
nausea all the way to brain damage and ultimately death. Persons on site are by far at the highest
risk,as hexane wouldsimplyflashoff inthe eventof aspill whichwill affect the immediate area but
will eventually dissipate in the air (of course the speed is dependent on local conditions) thus a
severity of 8 is appropriate. On the basis routine safety checks are made with scheduled
maintenance the likelihoodof spillsis verysmall atabout1. However,it would be inappropriate not
to have a response toa spill.There shouldbe trainedpersonnel available to contain any spill, along
withPPEspecific to the event such as breathing apparatus. The findings should be reviewed every
fewmonthsinitiallytoensure preventionsystemsare effective.After this it may not be appropriate
to review as regularly unless modifications are made to the process.
FIGURE 4: COMBUSTION TRAINGLE
Fuel Treatment and Processing Stage
Thisis the final stage inthe productionof bio-dieselandutilisesharmful chemicals in achieving that
goal. There are three chemicals in use during this process that can’t be eliminated or a safer
alternative found with the information gathered. These chemicals include:
- Methanol
- Sodium Hydroxide (Solid)
- Sulphuric Acid
These chemicalswillbe inrelativelyhighconcentrationswheninstorage andwill be present in large
parts of this process.
Methanol isusedas a reactant inthe reaction stage which causes transesterification of the algal oil
resultinginthe refinedbiodiesel. It takes part in a reaction maintained at approx. 1 barg, 50°C. This
createsacidicconditionswhich is catalysed by the sodium hydroxide. This makes for many hazards
taking into account toxicity and stream conditions. For all these chemicals it is important first aid
response is fast and effective, using wash stations and appropriate first aid kit as well as signage
around areas of high severity if spills and outbreaks were to occur.
Methanol isbothflammable andhighlytoxic.ThisismixedwithNaOHprior to entering the reaction
vessel.Methanol hasbothprovenlinksto short-term and long-term health conditions on repeat or
long-term exposure. It has a flash point of 12°C. There is potential for severe health effects along
withfireswhichcoulddamage equipmentaswell asfurtherthreatsto health so the severity will be
givena 6. The processisclosedoff solikelihoodisrelatively low on the basis proper maintenance is
done.Anypersonstaskedwiththismaintenance will likelybe exposedhowever,therefore permit to
19. worksystems(whichincludeaspill clean-upplan) andproperPPEsuchas fire retarded suits and gas
masksare necessary. Thisshould give adequate control of this hazard by lowering likelihood of an
event to a 2.
The sodiumhydroxide will be storedasasolidandlatermixedintosolutionwithmethanol.Being an
alkali it has a high toxicity, often more extreme than acid counterparts due to its reactivity with
many substances including a large number of carbon based compounds. It can cause major injury
whichcouldpresentlong-termaftereffectsand in extreme cases could result in fatalities. Working
aroundthissubstance will require thoroughtrainingandfull riskassessmentas part of the permit to
worksystem.Pipingandvesselsshouldbe designedwithappropriate materialstoprevent corrosion
of buildingmaterials.A spill response planisabsolutelynecessaryshouldothercontrolsfail.Thiswill
give adequate control forthissubstance.Reviewsmayneedtobe regularduringplantstart-up stage
but once fully operational may not be as often. Again reviews are important if modifications are
made to the process.
Sulphuricacid is highly toxic. As it is also a di-acid, it is much more potent than other popular acids
such as hydrochloricacid.Athighconcentrations,fumescan develop with reactions with water and
oxidising agents being violent. This puts the site, particularly around the input of acid to the crude
glycerol productionvessel athighriskasseveritycouldleavemajorinjuriesandburns. Similar to the
hydroxide discussed earlier, designing appropriate vessels; piping; and equipment is important as
thisacid isverycorrosive.Anyworksdone where contactwiththissubstance ispossible,will require
trained persons with proper risk assessing (Permit to Work) and mandatory PPE. This will give
enough control to present a low risk and reviews should be regular.
Noise and Vibration Pollution
As with most mechanical units and certain vessels, the high amounts of kinetic energy result in
vibrationandnoise whichcanpresent issues to the chronic health of persons exposed, resulting in
conditions such as deafness and arteritis. This gives a severity that could be as high as a 6 as a
disablingillnessispossible.On-site personsare the mostat riskas continual exposure over time can
developtoreduce life qualityinlateryears.Forbothof these factors, they cannot be eliminated, or
controlledtoa great enough degree as the likelihood is at the highest value of ten on the scale (as
the units are operating regularly). Along with insulation to take the edge off, PPE on site must be
mandatory,includingearprotection.Clearsignage isnecessary to warn workers of these hazardous
areas and any works that must be done during operation should go through the permit to work
systemso that all risks and exposure limits have control measures in place prior to starting. Whilst
PPE is the last resort, it should bring down likelihood to a 2. Reviews should be done yearly.
Furthermore, these vessels can pose a lot of physical hazards to persons performing any
maintenance oroptimizingwork.Areascontainingsystemsof piping;instrumentation;andelectrical
systems are the main hazards with all vessels along with heights for any larger vessels. This is a
considerationthatmustbe taken on board in all areas of the plant. These can result in injuries that
can be majorand affectlife qualityforworkers.Therefore,thiscollectionof hazardswill be given a 6
on the severityfactor.Priortocontrol,thisisverymuch likely,especially for those not experienced
withthe plant. Proper permit to work preparation with full risk assessment and clear toolbox talks
are vital forany worksof thistype.PPE of course should be standard whenever on plant but should
be adjusted dependent on the work and what risk assessments may determine.
20. Sustainability
The principle of the three pillars of sustainability states that to achieve a completly sustainable
process, the three elements: environment, social and economics must be satisfied (Sustainability
Problem).
Environmental Sustainability
Today,businesses take environmentintoconsiderationandtry to prevent pollution. Environmental
sustainability is the first pillar, and it defines how the ecosystem, air quality and sustainability of
other resourses that impact on the environment, can be protected (What Is Sustainability?).
A fuel like petroleumwhichisanon-renewable, has been used for decades and its usage continues
to increase today. This is one of the influences in the increase of greenhouse gases, contributing
greatly towards global warming. In order to meet environmental sustainability, renewable and
carbon neutral fuelsare needed.Thus, microalgae is the key for the production of biodiesel. There
are factorsthat provide more environmental benefits,thusithasgained a lot of attention (Monford
Paul Abishek).
In order to produce any type of fuel, input resources are first required. Thus, for production of
biofuel from microalgae, water, nutrients and land are needed. As this project is based on the
production of biodiesel from algae, it is important that the environmental impact is sustainable.
(Moheimani).
Water is one of the main factors needed for the growth of algae, there is a large amount of water
required.Since freshwaterislimited,itisessentialthatwastewatersourcesare usedtocultivate the
algae. Algae can grow in efficiently wastewater, and also purify the water, which can then be
recycled back into the ponds for the further growth of more algae. Thus, it is unlikely that large
volumesof freshwaterare neededto be usedto grow the algae.Bearinginmind,the strain of algae,
which will be able to grow succesfully in such water conditions, in this case Cholrella Vulgaris.
(Moheimani).
Algae take upcarbon dioxide (CO2) throughphotosynthesislike anyotherplant,helpingtooffsetthe
productionof greenhouse gases,which are released during production of non-renewable fuels. As
previously described, the location of ponds will not be far from an emission source, the coal fired
power plant. As carbon dioxide is also one of the factors needed for the growth of algae, it is
importantto maintainrequiredamountof carbondioxide (CO2) as it can affect the growth of algae.
Land isanotherfactor that isimportantforthe growthof algae. As the land required for the growth
of algae issignificantlylessincomparisontoothercrops such as Jatropha. A major advantage is that
the land used for algae growth can be unsuitable for agriculture. (Moheimani).
Social Sustainability
Social sustainability includes aspects such as liveability, human rights, labour rights, social
responsibilitiesand community development. Being a socially sustainable means being reputable
and respectable business with fewer economic and enviromental risks. (Bowden).
Due to the large total area of closedpondsthe plantwill be locatedoutside the inhabitanted zones,
inorder to control the noise pollutionandhelptomitigate the climaticeffects of the power station.
Also,inorderto control carbon dioxide consumption the type of the growth process was chosen to
be closed pond system. This gives the added ability to control the carbon dioxide in the outside
environment, which can affect the people within the community.
21. The production of biofuel from algae will have great benefits on the social side of this project.
Starting a new plant will provide job opportunities within the local area. This will increase the
employment rate and level of infrastucture within the community. (Algae Basics).
Another important aspect of social sustainability is to make sure the employees are well looked
after,overall benefittingfromworkinginthe company. This means there will be safety precautions
in place such as; the company by providing the personal protective equipment. The employees
wouldbe alsoprovidedwith adequatetrainingonthe safety of the process.Byprovdingthis level of
commitment to employees, the business will appear very attractive to potential job applicants.
Economic Sustainability
Economicsustainabilityisthe thirdpillarof sustainabilityanditisimportantforthe development of
economic growth with in the business, partners, consumers, suppliers and employees (THE
IMPORTANCE OF ECONOMIC SUSTAINABILITY).
In orderto make the projectviable,the firststep was to choose the system for the growth of algae.
In thiscase the closedpondsystemwaschosen instead of bioreactors, due to the fact that raceway
ponds appear to be only type of system which is sustainable not only in terms of environmental
aspect, but also economical. This is due to the fact that the bioreactors are far too expensive to
construct in comparison to closed pond system. They also have very high-energy demand, which
cannot be economically viableforthe productionof low value of biodiesel production (Moheimani).
For the closedpondsystem,onthe otherhandthe waterwaste andcarbon dioxide will be supplied
by a powerplant,whichwill be located near to the plant. Both water waste and carbon dioxide are
insignificant in teams of cost, which makes the project economical sustainable.
One of the otherfactorsin orderto keepthe economyof the company stable is the land that would
be usedfor the growthof algae.The landwill be unsuitable foragriculture,makingthe landcheaper.
The equipmentcostisanotherfactor,whichcan make the economysustainable with in the process.
For the pretreatmentprocess,the type of the equipment was changed from oven to an evaporator
as an evaporated is cheaper and steam used for drying will be raised with an energy recovery
process from flue gas sourced from the nearby power plant.
22. FIGURE 5: CRADLE TO GRAVE
Economic Appraisal
It was assumedthatforthisprocessthat start up would take six months and so during the first year
there would only be 50% of the target annual production of 5000 barrels. The start up costs for the
processcame to a total of $1,457,504 withthe highestcontributorto the costs being the cost of the
processequipment,namelythe operation units and storage equipment including the algae growth
ponds.
As well asequipmentaninitial inoculumof the algae speciesisneededto initiate growth within the
ponds. An assumption of 1 litre of culture per pond meant that 209L of culture is required. Rather
than renewthisculture for every batch (as the inoculum is much too expensive) a small amount of
algae grown in the previous batch will be kept during the harvest of each pond to be used as the
newculture tostart the growingforthe nextbatch.As well asthe pondsa greenhouse isrequired to
ensure thata closedpondgrowthsystemisachieved,alongwiththe costof the waste water storage
tank (2500m3
) the growth stage of the process has the highest initial cost.
23. The secondlargestcapital cost fallstothe pre-treatmentstage,thisislargelydownto the volume of
fluidandsolidsbeingmanoeuvredthroughthe process before the algae oil is obtained, because of
thisthe machine usedduringthissectionof the processmustbe able to deal with much higher flow
rates than that of the treatment stage.
Due to the large initial investment, the breakeven point for this process is longer than anticipated,
however,asthisprojectisproducingamore environmentallysustainable fuel source,it is likely that
there are several grants available that could help towards the initial capital investment.
The main annual running costs consist of labour, energy and raw materials; although the CO2 and
waste water required for the growth process may be obtained for no cost, methanol, hexane,
sodiumhydroxideandsulphuricacidare requiredforthe pre-treatmentandtreatmentstagesof the
process. However, the cost of these material if not high and the the greatest part of the annual
expense is the in the labour.
51%
31%
18%
Process Start up Cost Distribution
Growth Pre-Treatment Treatment
9%
6%
2%
83%
Annual Running Costs
Raw Materials Energy Maintenance Labour
FIGURE 6: START UP COST DISTRIBUTION
FIGURE 7: ANNUAL COST DISTRIBUTION
24. Owingtothe fact that the processwill be running 24 hours a day 365 days a year, with 4 employees
working at any on time and an average wage of $11 per hour the annual wages (United States
Departmentof Labor ) make up over80% of the runningcosts.The energy required for each section
of the process was calculated and a cost of 0.107$/kWh was assumed. The annual income from the
biodiesel andglycerol produced was calculated to be slightly higher than the annual running costs,
however, the large start up costs means that the breakeven point for the process is 20 years after
the initial startup.However, this is partially due to the assumption that the mechanical operations
such as evaporators and distillation columns, will be replaced after ten years, 3 months of
maintenance and installation time was predicted for this.
This, however, is not a completely accurate representation of the time taken for the process to
breakeven as the oil market fluctuates dramatically and regularly and thus the price that the
biodiesel will be sold for will change from year to year and so it may not be accurately predicted.
Consequently,the process,althoughprofitable aftera20-yearperiod,cannotcurrentlybe described
as economically viable due to the small proportion of profit compared to the initial investment as
well as the time scale for return on investment. However, by increasing the amount of biodiesel
producedperyear,the annual income may be greatly increased without increasing the annual cost
by too much.
-1600000
-1400000
-1200000
-1000000
-800000
-600000
-400000
-200000
0
200000
0 5 10 15 20 25
CumulativeCashReturn($)
Year
Breakeven Point
FIGURE 8: BREAKEVEN CURVE
25. Overview
Viability
Initiallythe remitsetforthisprojectwastoproduce 5000 barrelsof Biodieselthroughthe cultivation
of microalgae in a closed pond system, however, the process chosen achieve this objective is not
completelyviable.Environmentallyandsocially,the processissustainable,the algae consumptionof
CO2 and waste water, the recycling of many components within the process and the fact that the
plantmay be situatedonnonarable landfar from inhabitedareasmeansthatthere isminimal effect
on the environment and surrounding area. In spite of this, the current remit is not economically
feasible, using the process chosen, although a profit can be made eventually, 20 years is an
impractical time frame for the small amount of profit that will be achieved. The small annual net
profit is not enough to pay back the large initial investment within a reasonable period of time.
Possible Improvements
Several improvements could be made to the process to increase the economic feasibility of the
project.The mostobviousimprovementwouldbe toexpandthe algae pondsystemandincrease the
annual productionof biodiesel, as this will not increase the annual costs by too much (the majority
of annual runningcostsare due to labour),thusincreasing the annual profit and decreasing the pay
back time.
However,there are otherfactorswhichwhichmayenhance the viabilitywithoutchangingthe initial
remit. The by-products of the process are currently not creating a sufficient income, by selling the
proteinsinthe biomass for uses such as fertiliser could provide another income source. Glycerol is
also being sold as a byproduct, however due to the growing biodiesel industry, the value of crude
glycerol has plummeted in recent years. The further treatment of glycerol to form other products
such as ethanol and succinic acid could increase the value, $100 and $500 per ton respectively.
(National Chemical Database Service ) Advancements in technology could also make the process
more economical, as there is the possibility of performing the transesterification reaction on wet
algal biomass, which would cut out the entire drying stage of the pre-treatment process (Ji-Yeon
Park). However,the wet transesterfication process, is very innovative, as it has only recently been
developed. Finally, the process location could be moved to a country with a similar climate, but
provides cheaper labour, for example Mexico. This is because labour makes up 84% of annual
running costs amd decreasing this cost would once again increase the annual net profit.
References
1. 17 Feb 2016. <http://www.algaeindustrymagazine.com/evodos-expanding-product-
line/>.
2. Algae Basics: Closed Systems. 6 Febuary 2016 <http://allaboutalgae.com/closed-
systems/>.
26. 3. BLINOVÁ, Lenka, Alica BARTOŠOVÁ and Kristína GERULOVÁ. "CULTIVATION OF
MICROALGAE (Chlorella vulgaris) FOR BIODIESEL PRODUCTION." RESEARCH PAPERS
FACULTY OF MATERIALS SCIENCE AND TECHNOLOGY IN TRNAVA 23.36 (2015).
4. Cassidy, Keelin Owen. "EVALUATING ALGAL GROWTH AT DIFFERENT
TEMPERATURES." University of Kentucky, 2011.
5. Ching-Lung Chena, Jo-Shu Changabc & Duu-Jong Leed. "Dewatering and Drying
Methods for Microalgae." (2015): Volume 33, Issue 4.
6. Dennis Y.C. Leung, Xuan Wu and M.K.H. Leung. "A review on biodiesel production
using catalyzed transesterification." Applied Energy 87.4 (2009): 1084-1092.
7. Gouveia, Dr. L. Microalgae as feedstock for biofuels. Dordrecht London New York:
Springer Heidelberg , 2011.
8. Grima, Molina. Recovery of microalgae biomass, and metabolites: process options
and economics. Biotechnol Adv., 2003.
9. Havard. Bionumbers. 17 Feb 2016
<http://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101481&ver=7>.
10. IChemE. Hazop and Hazan: identifying and assessing process industry hazards.
IChemE, 1999.
11. ISTC. Feasibility report, small scale biodiesel production. Center IST: Waste
Management and Research Center, 2006.
12. J, Duncan. Cost of biodiesel production. New Zealand: Energy Efficiency Conserv
Auth, 2003.
13. Lazarova V, Phillippe R, Sturny V, Arcangell JP. "Evaluation of economic viability and
benefits of urban water reuse and its contribution to sustainable development."
Water PracTechnol (2006): 1:1–11.
14. M. Mubarak, A. Shaija, T.V. Suchithra. "Review on the extraction of lipid from
microalgae for biodiesel production." (2014).
15. Marudhupandi, Thangapandi, et al. "Influence of citrate on Chlorella vulgaris for
biodiesel production." Biocatalysis and Agricultural Biotechnology 3.4 (2014): 386-
389.
16. Maryam Al-Qasmi, Nitin Raut Member, IAENG, Sahar Talebi, Sara Al-Rajhi, Tahir Al-
Barwani. "A Review of Effect of Light on Microalgae Growth." Proceedings of the
World Congress on Engineering 1 (2012).
17. National Biodiesel Board. Biodiesel Basics. 2016. 2016 <biodiesel.org>.
18. New Mexico Department of Agriculture . "2014 New Mexico Agriculture Statistics
Bulletin ." (2014).
19. New Mexico State University . "S. Engle in NMSU: New Mexico Climate Center."
(2016).
20. Oilgae. Feb 2016. <http://www.oilgae.com/algae/oil/extract/che/che.html>.
21. Oilgae. <http://www.oilgae.com/ref/glos/hexane_solvent_oil_extraction.html>.
22. Pacific Oil Presses. Feb 2016. <http://pacificoilproducts.com/type90.html>.
23. PubChem. <https://pubchem.ncbi.nlm.nih.gov/compound/Triolein>.
24. Rogers, Jonathan N., et al. "A critical analysis of paddlewheel-driven raceway ponds
for algal biofuel production at commercial scales." Algal Research (2013).
25. Ronald Halim, , Michael K. Danquah, Paul A. Webley. "Extraction of oil from
microalgae for biodiesel production: A review." (2012).
26. S. Judd, L. J. P. van den Broeke, M. Shurair, Y. Kuti and H. Znad,. Water Research . 87
vols. 2015.
27. 27. Saddam H. Al-lwayzy, Talal Yusaf and Raed A. Al-Juboori. "Biofuels from the Fresh
Water Microalgae Chlorella vulgaris (FWM-CV) for Diesel Engines." (2014).
28. Stavarache C, et al. "Fatty acids methyl esters." Ultrason Sonochem 12 (2005): 367-
372.
29. Thanh LT, et al. "Ultrasound-assisted production of biodiesel fuel from vegetable oils
in a." Bioresour Technol 101.2 (2009): 639-645.
30. U. Schuchardt, S.R. Ricardo, R.M. Vargas. "Transesterification of vegetable oils: a
review." J. Braz. Chem. Soc. (1998): Vol. 9, No. 1, 199-210. .
31. Van Gerpen J, et al. Biodiesel production technology: August 2002–January 2004.
Iowa State University: Renewable Products Development Laboratory, 2004.
28. Appendix
Appendix I
Chemical Reactionstakenfrom (DennisY.C.Leung, XuanWuand M.K.H. Leung)
Transesterification
Hydrolysis
Saponification
TABLE 3: COMPARISON OF BIODIESEL PURIFICATION METHODS TAKEN FROM(DENNIS Y.C.LEUNG,XUAN WU AND
M.K.H. LEUNG)
Appendix 2: Throughput calculations
Remit: To produce 5000 barrels of biodiesel from cultivating the microalgae organism Chlorella vulgaris sp.
through a closed pond system.
5000 oil barrels =794.9365 m3 [1]
Density of biodiesel =845 kg/m3 [2] -- EN 590:2004 STANDARDS
Mass of biodiesel needed to be produced = 794.9365 × 845
= 671721.3425 kgper year
29. Time for one batch = 4 days + 1 day cleaning(assumingno algaeharvestingduringcleaning,also allows
growth.)
Batches in a year = 365 / 5
= 73
=> 73 batches in a year.
Mass of biodiesel produced in each batch = 671721.3425 / 73
= 9201.66 kg
Transesterification
To produce 1 kg of biodiesel: [3]
1.05 kg of algaeoil is required.
0.1249 kg of methanol
0.0105 kg Sodiumhydroxide (Catalyst)
0.113 kg of glycerol produced alongsidebiodiesel
Therefore for each batch => 9201.66 × 1.05
= 9661.75 kg of algaeoil required per batch
Algae oil content per 1 kg of dry biomass =29 %
29 % = 9661.75 kg
1 % = 333.2 kg
100% = 33316.36 kg of dry biomass per batch
8329.09 kg of dry biomass needed to be processed per day.
Mass of methanol for each batch = 9201.66 × 0.1249
= 1149.3 kg
Per day = 287.32 kg (2-3 barrels of methanol a day, if not recycled)
Mass of NaOH for each batch = 0.0105 × 9201.66
= 96.62 kg (under 1 barrel of catalysta day,if not recycled)
Per day = 24.155 kg
Mass of n-hexane for each batch = 0.00295 × 9201.66
= 27.15 kg
Per day = 6.8 kg
Mass of glycerol for each batch = 9201.66 × 0.113
= 1039.79 kg
Per day = 259.95 kg
30. Appendix 3: Number of ponds needed for growth and cultivation
Pond area = 100 m2
Pond depth = 0.3 m
Pond volume = 30 m3
Algae growth = 0.5 kg /m2.day (dry biomass in water) [3]
Per pond = 100 × 0.5 = 50 kg /day produced
The same pond can be harvested 4 times duringthe batch process.
Pond productivity per batch = 4 × 50 = 200 kg dry algaebiomass.
Number of ponds harvested duringbatch = 33316.36 / 200 = 167
Number of ponds harvested per day = 42 ponds.
Total number of ponds = 42 + 167
= 209 ponds.
Appendix 4: Mass balance calculations: Pre-treatment
Basis:8329 kgof dry biomass produced a daily
Auto flocculation: Mass of water after auto flocculation step
- Assumption algae solid = 7%
7 % = 8329 kg
1 % = 8329 / 7 = 1189.87 kg
100 % = 1189.87 × 100 = 118987 kg
Mass of water = 118987 - 8329
= 110657.91 kg
Filtration: Mass of water after filtration step
- Assumption algae solid = 10%
10 % = 8329 kg
1 % = 8329 / 10 = 832.91 kg
100 % = 832.91×100 = 83290.9 kg
Mass of water = 83290.9 - 8329
= 74961.81 kg
31. Centrifuge: Mass of water after centrifugation step
- Assumption algae solid = 25%
25 % = 8329.09 kg
1 % = 8329.09 / 25 = 333.16 kg
100 % = 333.16 × 100 = 33316.36 kg
Mass of water = 33316.36 - 8329.09
= 24987.27 kg
Oil extraction stage
Assumptions:
- Algal strain: Chlorella vulgaris
- Oil content: 29 % of dry biomass.
Mass of oil in dry algal biomass=0.29 × 8329
= 2415.44 kg
Mass of oil left to be extracted after mechanical pressing
- Assumption 75 % efficiency
=> (1 - 0.75) × 2415.44
= 603.85 kg
Mass of oil left after hexane solvent extraction.
- Assumption 80 % efficiency
=> (1 - 0.8) × 603.85
= 120.77 kg residual oil in biomass.
Residual oil left in de-oiled algal biomass = 120.77/ [8329 × 0.71]
= 0.02
= 2 %
Overall extraction efficiency = [(2415.44 - 120.77) / 2415.44] × 100
= 95 %
Total algae oil produced per day = 2415.44 × 0.95
= 2294.7 kg
32. Appendix 5: Energy Balance Calculations: Pre-treatment
- Please refer to the mass balance for mass flow rates
Basis:8329 kgof dry biomass produced a daily.
Example calculation: Entry to centrifugation stage
Density of algal slurry: [4]
ρm = 100 / [cw / ρs + [100 - cw] / ρl]
Where:
cw is the concentration of solids :10%
ρs is the density of the solids.Algal biomass[5] :1100 kg/m3
ρl is the density of the liquid.Water[6] :998 kg/m3
ρm = 1007 kg/m3 The densities of various slurry concentrationscan befound in the Energy balance.
Energy requirement for centrifugation
Assumption - 0.95 kWh/m3 power requirement [7]
Volumetric flow rate into centrifuge = ρm × mass
= 83291 kg/day / 1007 kg/m3
= 83 m3/day
Power consumption:0.95 × 83
= 79 kWh/day
Energy requirement for micro filtration
.Assumption - 1 kWh/m3 power requirement [8]
Volumetric flow rate into micro filter = ρm × mass
= 127316 kg/day / 1005 kg/m3
= 127 m3/day
Power consumption:1 × 127
= 127 kWh/day
Energy requirement for pumping duty in the dewatering stage
The energy required for all pumping processes in the pre-treatment, dewatering stage was 9.2 kWh/day. [9]
This value is based from a journal article, dealing with a similar process of dewatering algal biomass.
998
10100
1100
10
100
m
33. Energy requirement for mechanical crushing
Assumption - 0.05 kWh/kg power requirement [12]
Mass flowrate into mechanical press =8329 kg/day
Power consumption:0.05 × 8329
= 416 kWh/day
Energy requirement for mixing unit
Assumption - 0.01 kWh/kg power requirement [12]
Mass flowrate into mixingunit= 6404 kg/day
Power consumption:0.01 × 6404
= 64 kWh/day
Energy requirement for pumping in hexane recycle loop
Sincehigher pressures arerequired in the hexane recycle loop the pumping duty required in the dewatering
stage is multiplied by three.
Power consumption: 9.2 × 3
=27.6 kWh/day
Appendix 6: The Theoretical Maximum Steam Required for Evaporator
- Please refer to the mass balance for mass flow rates.
Assumptions: - The evaporator has a single effect.
- The heat capacity of the slurry is assumed to be that of waters due to low
concentrations.
- No heat loss to the surroundings.
- Steam is supplied at 1 bar.
Energy balance over evaporator:
wf : mass flowrate of feed = 33316 kg/day
cp : heat capacity of feed = 4.181 kJ/ kg K
).(. 1 FpFvvss TTcwww
34. wv : mass flowrate of vapour produced = 24987 kg/day
Latent heats: Steam tables used [10]
λs : latent heat of steam = 2257.9 [At 1 bar and 99.7 ºC]
λv : latent heat of vapour = 2308.8 [Assumption that vapour leaves at temperature, T1]
Temperatures and Pressures:
T1 : temperature of evaporator = 60 ºC
High evaporator temperatures will destroy the algaecell walls releasingthe oil prematurely.
Referring to steam tables gives an evaporator pressureof 0.2 bar.
TF : temperature of feed = 25 ºC
Mass flow rate of steam [ws]
ws = 27709.8 kg/day
This is the maximum theoretical steam needed to operate the evaporation. It is highly recommend that a multi
effect evaporation system is implemented as this will significantly reduce the mass flow rate of steam
required.
Appendix 7: Evaporator Sizing
- Please refer to the mass balance for mass flow rates.
Assumptions: - The evaporator has a single effect.
-Constant evaporation, 24 hours a day.
- No heat loss to the surroundings.
- Heat transfer coefficient [11]:1.7 W/m2 K
Q = ws × λs
Q = 27709.8 × 2257.9
Q = 62565964.59 kJ/day
=> 2606915.19 kJ/h
s
FpFvv
s
TTcww
w
).(. 1
9.2257
)2560(181.4333168.230824987
sw
35. => 724.14 kJ/s
Ts, temperature of the steam, 99.7 ºC.
A = Q / [U × (Ts - T1)]
= 724.14 / [1.7 × (99.7 - 60)]
= 10.72 m2
Steam economy: Mass of vapour produced / Mass of steam required
=> 24987 / 27709.8
= 0.9
The steam economy can be increased by addingmore evaporation effects to the system.
Appendix 8: Hexane Recycle Loop Calculations
Assumptions:
- The algaeoil was taken as triolein,[vegetable oil],due to similar properties.
- All algaeoil is extracted.
- There is no heat loss to surroundings.
- The solid biomassparticles were neglected in the process design.
The fluid packageused was NRTL. Aspen Plus contained no data on the ideal gas heatcapacity of triolein at
various temperatures, therefore experimental data was inputted, as shown below. [13]
TUAQ
FIGURE 9: HEXANE RECYCLE LOOP
36. Appendix 9: Tank sizing
Volume of mixingunit:
Volume entering tank:
- Hexane: 4 L/hr
- Algae oil:19 L/hr
- Total : 23 L/hr
Volume exitingtank: 35 L/hr [After absorption]
Volume of tank required = 50 L [To accountfor solid biomassparticles in the mixture]
Volume of hexane storage tank:
Volume entering tank: [S-09] = 4 L/hr
Volume exitingtank: [S-03] = 4 L/hr
Volume of hexane lostdownstream = 0.3 L/hr
Volume of hexane lostdownstream = 172.8 L/month
6 batches in a month = 6 × 27.15 = 162.9 kg/month
= 79.2 L/month required.
Minimum volume of tank required = 172.8 + 79.2 = 252 L
Volume of hexane storagetank = 300 L [To allowfor sufficientspacefor bulk purchases]
Volume of flashseparator:
Volume entering: [S-06] = 1246 L/ hr
Volume exiting:
Vapour: [S-07] = 1116 L/hr
Bottoms: [S-10] = 77 L/hr
FIGURE 10: ASPEN HEXANE CALCULATION
37. Minimum volume of tank required = 2000L. [For safety]
Volume of algae storage tank:
Mass of algaeoil produced = 2294.6 kg/day
Density of algaeoil [4] =900 kg/m3
Volume = 2.549 m3
=2549.6 L
Volume of algaeoil storagetank = 3000 L
Appendix 10: Heater and Cooler sizing
Preheater
Duty = 0.568 kJ/s [From Aspen Plus]
ΔT = 200 – 22.4 = 178.6 ⁰C
U [11] =0.06 kW/m2 K
A = Q / U × ΔT
A = 0.568 / [0.06 × 178.6]
A = 0.053 m2
Cooler
Duty = 0.48 kJ/s [From Aspen Plus]
ΔT = 190 – 25 = 165 ⁰C
U[11] = 0.06 kW/m2 K
A = Q / U × ΔT
A = 0.48 / [0.06 × 165]
A = 0.048 m2
Flow rate of steam required for Preheater before separation.
Q = Ws × λs
TUAQ
TUAQ
38. Q = 0.568 kJ/s [From Aspen Plus]
λs: latent heat of steam = 2257.9 [At 1 bar and 99.7 ºC]
Ws = Q / λs
Ws = 0.568 / 2257.9
Ws = 0.000252 kg/s
Ws = 0.9 kg/hr
Appendix 11: Overall heat and Material balance for Hexane Recycle Loop
Appendix 12: CO2 Consumption Over Installation
TABLE 5: CO2 CONSUMPTION
TABLE 4: HEAT AND MASS BALANCE FOR HEXANE LOOP [ASPEN PLUS]
39. Appendix 13: Waste Water Stream Mass Balance
Appendix 14: Waste Water Storage Tank Sizing Calculation
𝑇𝑜𝑡𝑎𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝑅𝑒𝑞′ 𝑑 = 2,500 𝑚3
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐶𝑦𝑙𝑖𝑛𝑑𝑒𝑟 = 𝜋𝑟2ℎ = 2,500 𝑚3
In termsof height(h):
ℎ =
2,500
𝜋𝑟2
To findthe surface area of the tank and hence optimise:
𝑆𝐴 = 2𝜋𝑟ℎ + 2𝜋𝑟2
Subin (h) above…
𝑆𝐴 = 2𝜋𝑟(
2500
𝜋𝑟2
) + 2𝜋𝑟2
Withsimplification…
𝑆𝐴 =
5000
𝑟
+ 2𝜋𝑟2
Performingdifferenciation:
𝑆𝐴′ = 4𝜋𝑟 −
10000
𝑟2 = 0
Equalszeroto findminimumturningpointhence smallestsurface area.Thisgives:
4𝜋𝑟3 = 10000 ( 𝑚𝑢𝑙𝑡𝑖𝑝𝑙𝑖𝑒𝑑 𝑡ℎ𝑟𝑜𝑢𝑔ℎ𝑜𝑢𝑡 𝑏𝑦 𝑟2)
Hence radiusand heightare:
𝑟 = 9.27𝑚, ℎ = 9.26𝑚
Andthe final surface areawhensubingthese valuesintothe surface areaequationgives:
𝑆𝐴 = 1,079.3 𝑚2
For economiccostingforthe sizing,a1000 m2
storage tank isrequired
TABLE 6: WASTE WATER MASS BALANCE
40. Oil extraction stage
StreamID P-105 P-201 P-212 P-202 P-203 P-204 P-205 P-206 P-207 P-208 P-209 P-210 P-211
MassFlowRate (kg/day)
Dry Biomass 5913.65 5913.65 0.00 5913.65 5913.65 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Algae Oil 2415.44 603.86 1811.58 483.09 120.77 483.09 483.09 483.09 0.00 0.00 0.00 0.00 483.09
N-Hexane 0.00 0.00 0.00 6.80 0.00 6.80 6.80 6.80 6.80 6.80 6.80 6.80 0.00
Total 8329.09 6517.51 1811.58 6403.54 6034.43 489.89 489.89 489.89 6.80 6.80 6.80 6.80 483.09
Temperature () 25.00 25.00 25.00 25.00 25.00 25.00 25.00 200.00 190.00 25.00 25.00 25.00 190.00
Pressure (Bar) 1.00 1.00 1.00 5.00 1.00 5.00 1.00 1.00 1.00 1.00 5.00 5.00 1.00
PRE treatment
Stream ID P-101 P-102 P-108 P-103 P-107 P-104 P-105 P-106
Mass Flow Rate (kg/day)
Algae 8329.09 8329.09 0.00 8329.09 0.00 8329.09 8329.09 0.00
Water 118987.01 74961.82 44025.19 74961.82 49974.54 24987.27 0.00 24987.27
Total 127316.10 83290.91 44025.19 83290.91 49974.54 33316.36 8329.09 24987.27
Percentage solids 7.00 10.00 0.00 10.00 0.00 25.00 100.00 0.00
Temperature () 25.00 25.00 25.00 25.00 25.00 25.00 60.00 25.00
Pressure (Bar) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
PRE treatment
Equipment ID E-102 E-105 E-105 E-103 & E-104
Equipment Microfiltration Centrifudge Evaporator Pumps
% concentration of solids 7 10 25 -
Density 1005 1007 1022 -
Total mass flow rate into equipment (kg/day) 127316 83291 33316 -
Total volumetric flow rate (m3/day) 127 83 33 127
Energy input PER DAY(kWh) 127 79 - 9.2
Oil extraction stage
Equipment ID E-201 E-202 E-208
Equipment Mechanical crushing Mixing unit Pump
Total mass flow rate into equipment (kg/day) 8329 6404 -
Temperature 25 55 25
Energy input PER DAY(kWh) 416 64.04 27.6
Appendix 13: Mass Balance
Appendix 14: Energy Balances
