Thesis on Biodiesel Engergy Consumption

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Thesis on Biodiesel Engergy Consumption

  1. 1. CHG-4300 STUDY THE EFFECT OF DRY VS. WET WASHING ON ENERGY BIODIESEL CONSUMPTION AND OPERATING COST AT DIFFERENT SOLVENT RATIOS Prepared by: Parag B. Kadakia Student ID: 4332788 Session: Fall 2008 Professor: Dr. Andre Y. Tremblay Department of Chemical Engineering University of Ottawa Ottawa, ON. Canada
  2. 2. Abstract Search for renewable fuels are escalating due to the rising concern of CO2 emission. Biodiesel is one such carbon neutral source of fuel becoming popular. High cost of manufacturing biodiesel and limitations due to cold flow properties makes it a less favourite renewable fuel. Therefore, the purpose of this study was to assess the possibility of reducing energy consumption and thereby, increasing profit by implementing dry washing (ion exchange) of crude biodiesel instead of water washing at different solvent to oil molar ratios. Both the processes (water washed and dry washed) were simulated in HYSYS at six different solvent to oil molar ratios (6:1, 9:1, 12:1, 15:1, 18:1, and 20:1). Preliminary equipment design was carried out from material balance data derived from HYSYS and fixed cost was estimated to be $10.15 m for water washed process and $ 7.52 m for dry washed process at 6:1 methanol to oil molar ratio. Energy consumption, after preliminary heat integration, was estimated to be 3390 MJ/h for water washed and 1024 MJ/h for dry washed processes at the same ratio. Operating cost of the plant for both processes were estimated and found to be $ 53.08 m and $ 52.16 m for water washed and dry washed processes respectively. It was found that the absence of water in the system reduces equipment cost because methanol-water recovery and recycle is energy intensive process requiring additional equipment such as- distillation column, reboiler and a condenser. For dry washed process, methanol can be flash separated from glycerol but the ion exchange resin and tower are required to purify crude biodiesel which incurs additional cost of $ 370,000. Vapour re-compression cycle was implemented for methanol separation stage in dry washed process to conserve 12% of the overall heat energy requirement. The net profit generated by water washed process is in the range of $ 3.4 to 0.98 m whereas by dry washed process is $4.3 to 3.7 m for ratios ranging from 6:1 to 20:1. Additional profit in dry washed process clearly represents the savings due to decrease in energy consumption when compared with water washed process. Therefore, dry washed process is preferred over water washed process even at increased methanol to oil molar ratio of 20:1. Some challenges were also identified such as- consumption of vegetable oils for biodiesel production may create food crisis, higher crystallization temperature limits the use of biodiesel and the price of vegetable oils is the major limiting factor in biodiesel profitability. 2
  3. 3. Contents I.Abstract..................................................................................................................................2 II.List of Figures.......................................................................................................................4 III.List of Tables.........................................................................................................................4 1.0Introduction..................................................................................................................................5 1.1 History.......................................................................................................................6 1.2 Definition.......................................................................................................................6 1.3 Transesterification of oils and fats....................................................................7 1.4 Advantages and disadvantages of biodiesel......................................................8 2.0 Literature Review....................................................................................................................11 2.1 Choice of the catalyst........................................................................................11 2.2 Effect of methanol to oil molar ratio...............................................................12 2.2Washing of crude biodiesel...............................................................................13 2.4 Effect of reaction temperature...................................................................................15 3.0 Process Description........................................................................................................17 3.1 Design basis........................................................................................................17 3.2 Typical process for water washing..................................................................18 3.3 Proposed process without water washing.......................................................20 4.0 Energy consumption......................................................................................................23 4.1Vapour re-compression................................................................................................23 5.0 Cost Analysis.............................................................................................................................28 5.1 Fixed Cost Index (FCI).....................................................................................28 5.1.1 Water Washing......................................................................................28 5.1.2 Dry washing (ion exchange)..................................................................31 5.2 Cost of Manufacturing (COM).........................................................................33 5.2.1 Direct Manufacturing Cost (DMC)......................................................33 5.2.2 Fixed Manufacturing Cost (FMC)........................................................36 5.2.3 General Manufacturing Expenses (GE)...............................................37 5.3Revenue generated.............................................................................................38 6.0 Conclusion and Recommendations..............................................................................40 6.1 Conclusion..........................................................................................................40 6.2 Recommendations..............................................................................................41 6.2.1 Vegetable oils- part of the food chain..................................................41 3
  4. 4. 6.2.2 Expensive Raw material........................................................................41 6.2.3 Cold flow properties..............................................................................42 6.2.4 Less incentive (profit margin)...............................................................43 7.0 References......................................................................................................................44 7.1 Web references..................................................................................................46 Appendix-I.....................................................................................................................47 II List of Figures 2.1 Wash water required to remove NaOH/HCl from biodiesel stream...........................14 2.2 Effect of temperature on biodiesel yield and reaction time..............................16 3.1 Process flow diagram for biodiesel production (Haas et al., 2006)..................18 3.2 Process flow diagram for biodiesel production (no washing)...........................21 3.3 HYSYS simulation of biodiesel production........................................................22 4.1 Comparison for energy consumption between washing and no-washing options........................................................................24 4.2 Schematics for vapour re-compression for no-washing option.......................25 4.3 Methanol recovery and power consumption as a function of operating pressure.................................................................................................................26 4.4 Comparison of energy consumption between vapour re-compression and no- washing cycles for methanol separation stage...............................................................27 5.1 Equipment cost break up for 6:1 molar ratio washing option (Appendix-I).............31 5.2 Cost of manufacturing Distribution (6:1 ratio washing option).................................38 5.3 Net profit at different molar ratios.................................................................................39 III List of Tables 1.1Advantages of biodiesel..........................................................................................8 1.2Major disadvantages of biodiesel..........................................................................9 3.1 Feed and product flow rates................................................................................17 4.1 Nett heating required after integration (washing option- 6:1 molar ratio)....23 4.2 Nett cooling required after integration (washing option- 6:1 molar ratio)....23 4.3 Nett heating required after integration (no washing option- 6:1 ratio)..........23 4.4 Nett cooling required after integration (no washing option- 6:1 ratio)..........24 5.1 Fixed cost of the plant excluding land (6:1 molar ratio, wet washing)......................29 5.2 Fixed cost of the plant excluding land (6:1 molar ratio, dry washing)......................31 5.3 Grass route cost of equipment for different molar ratios...........................................32 5.4 Break up for yearly raw material cost..........................................................................33 5.5 Utilities cost break up for 6:1 molar ratio....................................................................34 4
  5. 5. 5.6 Other Costs (6:1 ratio washing option).........................................................................36 5.7 Fixed manufacturing cost (FMC) (6:1 ratio washing option)....................................37 5.8 General manufacturing cost (GE) (6:1 ratio washing option)...................................37 1.0 Introduction With the rising concern of global warming and thus green house gas (GHG) emission, mainly caused by the combustion of limited quantity of fossil fuel, the need for exploring renewable sources of energy has been increasing rapidly. On the other hand, biomass use is becoming more popular due to its sort span of life cycle which makes it a carbon-neutral source (Dowaki et al., 2007). Biodiesel is one such renewable fuel made from biomass used for diesel engines and compression-ignition engines (CIGs). Biodiesel is briefly defined as the monoalkyl esters of vegetable oils or animal fats. Biodiesel is the best candidate for diesel fuels in diesel engines because it burns like petroleum diesel with better efficiency than gasoline. Biodiesel also exhibits great potential for CIGs. Biodiesel is now mainly being produced from soybean, canola, rapeseed, and palm oils. The higher heating values (HHVs) of biodiesels are relatively high. The HHVs of biodiesels (39 to 41 MJ/kg) are slightly lower than those of gasoline (46 MJ/kg), or petroleum diesel (43 MJ/kg), but higher than coal (32 to 37 MJ/kg) (Sheehan et al., 1998). One of the most popular ways of manufacturing biodiesel is by trans-esterification of vegetable oils as discussed in detail in Section1.3. The reaction requires higher then theoretically required solvent to oil ratio and water washing of biodiesel. Separation and recycle of these liquids in the process are energy intensive and require additional equipment. Therefore, the purpose of this report is to study the effect of varying solvent to oil ratio and removing water washing step on overall energy consumption and the operating cost of biodiesel manufacturing facility. 5
  6. 6. Literature review was done (Section 2.0) in order to form the design basis required to compare with the proposed modifications in biodiesel manufacturing. 1.1History Although, the process of making fuel from biomass is as old as it can be e.g. burning of wood, dried cow dumping etc. is still in practise in India since ancient times, biodiesel dates back to 1853 when Duffy and Patrick attempted trans-esterification of triglycerides content in vegetable oils and in animal fats. During 1893, the name “biodiesel” had been given to trans- esterified vegetable oil to describe its use as a diesel fuel (Demirbas et al., 2002) in diesel engines invented by German scientist Dr. Rudolph Diesel. Since the 1980s, biodiesel plants have opened in many European countries, and some cities have run buses on biodiesel, or blends of petro and biodiesels. In 1991, the European Community (EC) proposed a 90% tax deduction for the use of biofuels, including biodiesel. Biodiesel plants are now being built by several companies in Europe; each of these plants will produce up to 1.5million gallons of fuel per year. The European Union accounted for nearly 89% of all biodiesel production worldwide in 2005. 1.2 Definition In general terms, biodiesel may be defined as a domestic, renewable fuel for diesel engines derived from natural oils like soybean oil that meets the specifications of ASTM D 6751. In technical terms (ASTM D 6751) biodiesel is a diesel engine fuel comprised of monoalkyl esters of long-chain fatty acids derived from vegetable oils or animal fats, designated B100 and meeting the requirements of ASTM D 6751(Demirbas et al., 2009). Biodiesel, also referred to as methyl ester or fatty acid methyl ester (FAME), in application as an extender for combustion in 6
  7. 7. CIEs (diesel), possesses a number of promising characteristics, including reduction of exhaust emissions (Dunn et al., 2001). 1.3 Trans-esterification of oils and fats In order for vegetable oils and fats to be compatible with the diesel engine, it is necessary to reduce their viscosity. This can be accomplished by breaking down triglyceride bonds, with the final product being referred to as biodiesel. There are at least four ways in which oils and fats can be converted into biodiesel (Ghadge and Raheman et al., 2006): 1. Tran-sesterification, 2. Blending, 3. Microemulsions, 4. Pyrolysis. Among these processes, trans-esterification is the most commonly used method. The trans- esterification process is achieved by reaction of a triglyceride molecule with an excess of alcohol in the presence of a catalyst to produce glycerine and a fatty acid methyl ester ‘‘FAME’’ which is the biodiesel. As shown in Figure 1.2, trans-esterification reaction consists of a sequence of three consecutive reversible reactions where triglycerides are converted to diglycerides and then diglycerides are converted to monoglycerides followed by the conversion of monoglycerides to glycerol. In each step an ester is produced and thus three ester molecules are produced from one molecule of triglycerides. The transesterification reaction requires a catalyst such as sodium hydroxide to split the oil molecules and an alcohol (methanol or ethanol) to combine with the separated esters. It also 7
  8. 8. gives glycerol as a co-product which has a commercial value. A catalyst is usually used to improve the reaction rate and yield (Demirbas et al., 2009). Because the reaction is reversible, excess alcohol is used to shift the equilibrium to the product side. 1.4 Advantages and disadvantages of biodiesel Some of the advantages of biodiesel are listed in Table 2.1. One of the major advantage of biodiesel is that it is a renewable source of energy i.e. amount of carbon dioxide it emits upon combustion is captured by the materials used to produce biodiesel and therefore, carbon dioxide emission to atmosphere is negligible. Also, its low sulphur content (Knothe et al., 2006) is very important property because, upon combustion, the sulphur content in the fuel gets oxidised to form oxides of sulphur which stays in atmosphere and further reacts with water vapours present in air to form sulphuric acid which is the major cause of acid rain. Biodiesel is more biodegradable then petroleum diesel (Zhang et al., 2003) which is to decompose and does not stay in the environment for a longer period. Table 1.1 Advantages of biodiesel •Portability •Readily available •Renewability •High combustion efficiency and low sulfur and aromatic content. •Higher cetane number, and higher biodegradability •Helps reduce a country’s dependency on imported petroleum, 8
  9. 9. The use of biodiesel is however limited despite its significant environmental benefits. Table 2.2 lists some of the disadvantages of biodiesel. Operating disadvantages of biodiesel in comparison with petrodiesel are cold start problem, lower energy content, higher copper strip corrosion, and fuel pumping difficulty due to higher viscosity. The major disadvantage of biodiesel is its high crystallization temperature (cold flow properties) due to its saturated fatty acid content. various methods are applied to improve the cold flow properties such as; by mixing with petroleum diesel fuel, by elimination of methyl esters of saturated fatty acids with high crystallization temperature through chemical combinations into stable solid compounds, or by winterization process (using solvent) or dry fractionation (without solvent). However, according to some authors (Srivastava et al., 2008), there is no reason to eliminate saturated methyl esters from biodiesel fuel, since it possesses better properties related to ignition quality and calorific value (Kazancev et al., 2006). Another approach could be to convert saturated fatty acid into unsaturated ones by applying acid treatment. Table 1.2 Major disadvantages of biodiesel..... •Higher viscosity. •Lower energy content. •Higher cloud and pour points. •Higher NOx emission. •Higher price. •Cold start problems. Low energy content of biodiesel increases fuel consumption when biodiesel is used instead of pure petroleum diesel, in proportion to the share of the biodiesel content. Taking into account the higher production value of biodiesel as compared to petroleum diesel, this increase in fuel consumption raises in addition the overall cost of application of biodiesel as an alternative 9
  10. 10. to petroleum diesel. Biodiesel has a higher cloud point and pour point compared to conventional diesel (Prakash, 1998). Neat biodiesel and biodiesel blends increase nitrogen oxide (NO2) emissions compared with petroleum-based diesel fuel used in an unmodified diesel engine (EPA, 2002). Peak torque is lower for biodiesel than petroleum diesel but occurs at lower engine speed and generally the torque curves are flatter. Biodiesels on average decrease power by 5% compared to diesel at rated loads (Demirbas et al., 2006). 10
  11. 11. 2.0Literature Review 2.1Choice of the catalyst Alkaline catalysts are the preferred choice for the trans-esterification reaction because it increases the rate of reaction which, otherwise, could last up to many hours. However, the alkaline-catalyzed process is sensitive to FFA content of the feedstock oils. Many published papers [9–11] suggested that alkaline catalysts could only be applied when FFA content in the oils or fats is less than 1.0% (Leung et al., 2006). Three alkaline catalysts viz. sodium hydroxide (NaOH), potassium hydroxide (KOH) and sodium methoxide (CH3ONa), are the most common choices. Leung et al., 2006 studied the effects of these three catalysts used on the transesterification through examining the ester content in the biodiesel. As shown in the Table 2.1, the amount of NaOH used was smaller than those of KOH and CH3ONa for the same mass feedstock oil, since NaOH has the smallest molar mass (40 g/ mol), followed by CH3ONa (54 g/ mol) and KOH (56 g/mol). Table 2.1 Comparison of alkaline catalysts used in trans-esterification reaction (Leung et al., 2006) Catalyst Concentration Ester content Biodiesel yield (wt% by weight of crude oil) (wt%) (wt%) NaOH 1.1 94.0 85.3 KOH 1.5 92.5 86.0 CH3ONa 1.3 92.8 89.0 However, in terms of molar concentrationCH3ONa was about 10% lesser than that of NaOH and KOH. Moreover, the biodiesel yields with NaOH and KOH as catalyst were lower than that of CH3ONa. This happens because during the preparation of the catalyst NaOH (or 11
  12. 12. KOH) will be added and dissolved in the anhydrous methanol forming sodium (or potassium) methoxide together with a small amount of water. Therefore, NaOH is selected as compared to KOH because it is cheaper and easily available. 2.2 Effect of methanol to oil molar ratio Methanol was chosen to be the solvent because methanol has the lowest boiling point and least specific heat as compared to ethanol and butanol. Theoretically, 3moles of methanol are required for each mole of oil but since the reaction is reversible, it is necessary to maintain reactant concentration higher than product concentration in the reactor. Also, it is important to get complete conversion of the oil because the mono, di and tri-glycerides cannot be washed with water and they end up in the final product (Kotrba et al., 2006). When the trans-esterification is complete, there should be no or only small traces of monoglycerides and only a small amount of diglycerides in the reaction product stream (Vicente et al. 2004; Gerpen et al. 2004; Leung and Guo 2006). Leung et al., 2006 also conducted experiments to study the effect of molar ratio on ester content and yield of the transesterification for canola oil. Maximum ester yield was obtained at a molar ratio of 6:1 for neat Canola oil. This higher molar ratio than the stoichiometric value resulted in a greater ester conversion and could ensure complete reaction. When the ratio was increased from 3:1 to 6:1, the ester content raised from 80.3% to 98.0%, while the yield rose from 78.7% to 90.0%. Therefore, the reaction was incomplete for a molar ratio less than 6:1. On the other hand, there is very little effect on the biodiesel yield and purity for molar ratio beyond 6:1. The results showed that the molar ratio of alcohol to oil is another important parameter 12
  13. 13. affecting the biodiesel yield and biodiesel purity, apart from catalyst concentration and reaction time (Myint et al., 2009). As stated above, a 6:1 methanol/oil molar ratio was optimal for the trans-esterification of neat Canola oil. It resulted in the highest ester content in the product (98%) and maximum product yield (90.4%). This result is in line with the reports of many investigations based on neat vegetable oils (Dube et al., 2003, Freedman et al., 1984, Boocock et al., 1996), and this ratio has actually been normally adopted in commercial operations. 2.3 Washing of crude biodiesel There are two generally accepted methods to purify biodiesel: wet and dry washing. The more traditional wet washing method is widely used to remove excess contaminants and left over production chemical from biodiesel. In the biodiesel production, it is well known that the vegetable oils/fats used as a raw material for the transesterification should be water-free since the presence of water has negative effects on the reaction (Komers et al., 2001) and it also increases the cost and production time. Dry washing replaces water with an ion exchange resin or amagnesium silicate powder to neutralize impurities. Both dry washing methods are being used in industrial plants (Gonzalez et al., 2003). Whilst it has been proved for some time that it is possible to meet the specifications by water washing, this process gives rise to some disadvantages. A highly polluting liquid effluent is generated as it is shown in Table 2. Significant product loss can be carried out for retention in thewater phase. Furthermore, emulsions formation when processing used cooking oils or other feeds with high FFA content can happen due to the soap formation (Leung et al., 2001). 13
  14. 14. Water is the main cause for side reactions besides alcoholysis – saponification of the trans-esterified oil and/or alkyl esters produced. Therefore it is also responsible for the reduction in the concentration of the catalyst. Water can consume the catalyst and reduce catalyst efficiency (Komers et al., 2001). The presence of water has a greater negative effect than that of the free fatty acids. So, the water content should be kept below 0.06% (Ma et al., 1998), much lower than the allowable free fatty acids content. Only as little as 0.1% of water added led to some reduction of the yield of methyl esters and the conversion was significantly reduced to 6% when only 5% of water was added (Canakci and Gerven et al., 1999). These problems may hinder the most efficient utilization of waste vegetable oils and crude oils since they generally contain water and free fatty acids (Tomasevic and Marinkovic, 2003). Therefore, the proposed study also compares the effect of both, dry and wet, washing on energy consumption and operating cost of the biodiesel plant. The quantity of water required was assumed from Figure 2.1 (Myint et al., 2009). Figure 2.1 Wash water required to remove NaOH/HCl from biodiesel stream (Myint et al., 2009) In order to decrease the amount of NaOH and HCl in the product stream, water washing is used along with adiabatic decantation. It can be seen that the amount of NaOH and HCl in the 14
  15. 15. biodiesel stream decreases significantly as the amount of water used in the washing process increases. However, after it reaches 300 mol of water, the catalyst amount removed from the biodiesel stream becomes less significant. Therefore, 300 mol of water is considered to be the practical amount of water needed for the washing step. 2.4 Effect of reaction temperature In general, higher temperatures increases rate of reaction and reduces conversion. But higher temperature could also accelerate the saponification of triglycerides affecting negatively the product yield. On the other hand, higher temperature could lead to a drastic decrease in viscosity which is favourable to increase the solubility of the oil in the methanol and improve the contact between oil and methanol molecules, thereby reaching a better conversion of triglycerides. Therefore, the optimum reaction temperature has to be found. Leung et al., 2006 conducted experiments to determine the effect of reaction temperature on methyl esters formation by carrying out trans-esterification reaction was carried out keeping 6:1 methanol/oil molar ratio and 1.0 wt% NaOH concentration for neat oil. The experiments were conducted at temperatures ranging from 30 to 70 °C. The effect of reaction temperature on the product yield and reaction time is shown in Figure 2.2. 15
  16. 16. Figure 2.2 Effect of temperature on biodiesel yield and reaction time (Leung et al., 2006) Experimental results showed that the trans-esterification reaction could proceed within the temperature range studied but the reaction time to complete the reaction varied significantly with reaction temperature. It can be seen that a high product yield could be achieved even at room temperature but the reaction time would be substantially increased. It was also observed that for neat oil the maximum yield occurred at a lower temperature range between 40 and 45 °C. When temperature was reduced from 70 °C to 45 °C, the product yield can be increased from 90.4% to 93.5%, enhanced by about 3%, but the reaction time for completion of the trans- esterification was prolonged from 15 min to 60 min due to a lower reaction rate at 45 °C. This significant increase in ester yield at a lower temperature indicated that higher temperature had a negative impact on the product yield for the trans-esterification of neat oil. The reason for this is that higher temperature accelerates the side saponification reaction of triglycerides. But, obviously, the temperature effect was smaller than that of catalyst concentration. 16
  17. 17. 3.0Process Description 3.1Design basis As stated earlier, two scenarios were considered; one with water washing (wet washing) and another without water washing (dry washing) while methanol to oil molar ratios were varied from 6:1 to 20:1 for each scenarios. The process plant is designed for 10.5 million gallons of biodiesel per year (39,800 m3/year) based on 8,000 operating hours/year. Input data of the feed and product flow rates are shown in the Table 3.1. Table 3.1 Feed and product flow rates Mass flow (kg/h) Molar flow (kmol/h) Canola oil 4260.00 4.81 Methanol (for 6:1 ratio) 924.88 28.86 NaOH 42.60 1.07 HCl 38.57 1.06 Biodiesel 4260.00 14.43 Glycerol 443.10 4.81 Water for washing 540.00 300.00 Water formation 26.59 1.48 It was also assumed that all the free fatty acid will react with NaOH and form soap. In order to account for the presence of free fatty acids in the feedstock, 0.05 wt% of free fatty acid [oleic acids (C18H34O2)] in the feed was assumed. This number corresponds to maximum amount of free fatty acid in refined vegetable oil (Gerpen et al., 2005). According to the previous assumptions, there is soap formation from both fatty acid saponification and triglyceride saponification. A strong acid is added to reverse the saponification process and prevent soap interference in the separation process. In this process, hydrochloric acid is used to reverse soap formation and obtain free fatty acids and sodium chloride. HCl- the amount of hydrochloric acid required for neutralization is equivalent to the number of moles of NaOH remaining in the mixture, which is 1.06 kmol/h. 17
  18. 18. 3.2Typical process for water washing Figure 3.1 shows the PFD for biodiesel production. Three sequential trans-esterification reactions were modeled. The first reactor was continuously fed with canola oil and a 1.78% (wt/ wt) solution of sodium methoxide in commercial grade methanol. MeOH NaOH Water vapours Evaporator LP steam in Water wash tank Biodiesel reach Oil CSTR-3 CSTR-1 CSTR-2 Biodiesel LP steam in Condensate out MeOH recycle Decanter-1 Decanter-2 Centrifuge-1 Centrifuge-2 Glycerol+MeOH reach Water recycle HCl in Neutalizer Water- MeOH Glycerol distillation distillation Free fatty acid Glycerol removal Centrifuge-3 Figure 3.1 Process flow diagram for biodiesel production (Haas et al., 2006) Product was removed from the reactor at a rate equal to the rate of charging with reactants and catalyst in such a manner as to give a residence time of 1 h in the reactor. Glycerol, a co-product of trans-esterification, separates from the oil phase as the reaction proceeds. Following the first trans-esterification reaction, continuous centrifugation is employed to remove the glycerol-rich 18
  19. 19. co-product phase, which is sent to the neutralizer. The methyl ester stream which also contains un reacted methanol, oil and catalyst, is fed into a second steam jacketed, CSTR where a continuous stirred reaction is conducted at 60oC, with the crude ester product being removed from the reactor at a rate equal to that of reagent addition and in such fashion as to produce a reactor residence time of 1 h. A trans-esterification efficiency of 90%, well within the range of reported values (Freedman et al., 1984; Noureddini and Zhu, 1997), was assumed for each of these three trans-esterification reactions, for an overall efficiency of 99%. The mixture of methyl esters, glycerol, unreacted substrates and catalyst exiting the third CSTR reactor was fed to a continuous decanter. The glycerol-rich aqueous stream from this operation is sent to the neutralizer while the impure methyl ester product goes to the water wash tank for purification and dehydration. The crude methyl ester stream is washed with water at pH 4.5 to neutralize the catalyst and convert any soaps to free fatty acids, reducing their emulsifying tendencies. Then biodiesel is separated from the aqueous phase in the decanter-2. The latter is cycled to the neutralizer. The crude, washed methyl ester product may contain several percent of water. This must be lowered to a maximum of 0.050% (v/v) to meet United States biodiesel specifications. Water is removed in the evaporator from an initial value of 2.4% to a final content of 0.045%. The glycerol liberated during trans-esterification has substantial commercial value if purified to USP grade. However, this process is expensive. Small and moderately sized operations, including those of the scale modeled here, often find it most cost effective to partially purify the glycerol, removing methanol, fatty acids and most of the water, and selling the product (90% glycerol by mass) to industrial glycerol refiners. This impure, dilute, aqueous glycerol streams exiting the trans-esterification reactors and the biodiesel wash process are treated with hydrochloric acid to convert contaminating soaps to free acids, allowing removal by 19
  20. 20. centrifugation. This fatty acid waste is presumed to be destined for disposal. Methanol is recovered from this stream by distillation and is recycled into the trans-esterification operation. Finally, the diluted glycerol stream is distilled to reduce its water content. At this point the glycerol concentration is 90% (w/w), suitable for sale into the crude glycerol market. Water recovered during drying of the ester and glycerol fractions is recycled into wash operations. The model includes maximum recovery of the heat present in condensates, transferring it via heat exchangers to the material feed streams entering reactors. Since environmental pollution regulations vary from location to location, no precise calculation of waste stream treatment costs was attempted. However, the lump sum of $500,000 was allocated for waste stream disposal charges. 3.3Proposed process without water washing Figure 3.2 shows the proposed PFD for no washing (ion exchange) process. The trans- esterification step remains unchanged while crude biodiesel stream is directly fed to the dry wash tower to remove any traces of catalyst and HCl using ion exchange technique before feeding it to the evaporator whereas methanol distillation column has also been removed since it can be flash separated from glycerol because there is only trace amount of water present in the system. This approach saves cost of equipment (distillation columns) and reduces energy in absence of water because water has higher boiling point and specific heat which requires more energy to separate. 20
  21. 21. MeOH NaOH Water vapours Evaporator LP steam in Biodiesel reach Oil CSTR-3 CSTR-1 CSTR-2 Biodiesel LP steam in Condensate out MeOH recycle Decanter-1 Centrifuge-1 Centrifuge-2 Glycerol+MeOH reach Water vapours HCl in Neutalizer MeOH Glycerol Flash Tank Flash Tank Free fatty acid removal Centrifuge-3 Glycerol Figure 3.2 Proposed PFD for biodiesel production without water washing Both models were simulated in HYSYS for the methanol to oil molar ratios of 6:1, 9:1, 12:1, 15:1, 18:1 and 20:1. Figure 3.3 shows the PFD generated in HYSYS for water (wet) washing option. Triolein was declared as the hypothetical component since it is not included in the HYSYS component database. Simple spreadsheet function was used for reaction and decanter separation steps. Required data were assumed from design basis (Section 3.1). Material and energy balance data obtained from HYSYS were used for equipment sizing and energy consumption estimation which, in turn, was used to find the operating and fixed cost of the plant. This is discussed in following sections in detail. 21
  22. 22. 22
  23. 23. Figure 3.3 HYSYS simulation of biodiesel production 23
  24. 24. 4.0Energy Consumption Energy required for both scenarios were derived from HYSYS simulation and after the preliminary heat integration, total energy consumption was estimated as shown in Tables 4.1 through 4.4. Table 4.1 Nett heating required after integration (washing option- 6:1 molar ratio) Heating Heat required Balance heat required required (oC) MJ/h Heat Provided by (refer Table 4.2) (MJ/h) HE-102 25 to 60 135.874 Glycerol cooler- 37.363 MJ/h 98.510 HE-103 25 to 60 285.800 FAME cooler- 285.800 MJ/h 0 Heater-1 60 to 100 458.893 458.893 Q-100 60 to 100 1921.585 1921.585 Reboiler 932.818 932.818 Total 3734.970 3390.897 Table 4.2 Nett cooling required after integration (washing option- 6:1 molar ratio) Cooling Energy to be Cooling provided to Balance cooling Heatsource required (oC) removed (MJ/h) (refer Table 4.1) required (MJ/h) FAME cooler 100 to 25 702.415 HE-103 285.800 MJ/h 416.651 Glycerol cooler 100 to 25 89.238 HE-102 37.363 MJ/h 51.875 MeOH recycle 65 to 60 8.625 8.625 Water recycle 65 to 60 12.285 12.285 Total 812.563 489.437 While the heat integration reduces both heating and cooling requirements to some extent, not all the heating requirement can be offered by the process due to temperature cross over. Therefore, external heating in terms of low pressure steam and cooling in terms of the circulating cooling water will have to be provided. Table 4.3 Nett heating required after integration (no-washing option- 6:1 molar ratio) Heating Heat required Balance heat required required (oC) MJ/h Heat Provided by (refer Table 4.2) (MJ/h) HE-102 25 to 60 135.874 Glycerol cooler- 37.363 MJ/h 98.510 HE-103 25 to 60 285.800 FAME cooler- 285.800 MJ/h 0 Heater-1 60 to 100 393.369 393.369 Q-100 60 to 100 532.569 532.569 Reboiler 0 0 24
  25. 25. Total 1374.603 1024.440 Table 4.4 Nett cooling required after integration (washing option- 6:1 molar ratio) Cooling Energy to be Cooling provided to Balance cooling Heatsource required (oC) removed (MJ/h) (refer Table 4.1) required (MJ/h) FAME cooler 100 to 25 702.415 HE-103 285.800 MJ/h 416.651 Glycerol cooler 100 to 25 89.238 HE-102 37.363 MJ/h 51.875 MeOH recycle 65 to 60 8.625 8.625 Water recycle 65 to 60 0 0 Total 800.287 477.151 It can be noted that cooling requirement for both washing and no-washing options are almost identical except that the recycle water cooling is not require in no-washing option. Whereas, heating requirement is less than one third for no-washing option than for washing option. This is because distillation and reboiler are not required in no-washing option. This results in cost and energy savings. On the other hand, no-washing option incurs additional cost which is discussed in the following sections. Figure 4.5 shows the comparison of energy consumed by washing option with no-washing for different molar ratios ranging from 6:1 to 20:1. Figure 4.5 Comparison for energy consumption between washing and no-washing options 25
  26. 26. Clearly, it can be seen that wet washing option consumes a lot of heat energy than no-washing option. As stated earlier, this is due to the distillation column required to separate water from methanol and glycerol. Whereas, for no-washing option the methanol and glycerol can be simply separated by flashing which results in energy economy. Even at the highest molar ratio of 20:1, no-washing option consumes heat energy almost same as washing option 6:1 molar ratio. Therefore, it can be said that the presence of water in the system elevates energy consumption greatly. Another alternative is to discard water rather than recycling it but this imposes the loss of biodiesel because wash water carries some biodiesel while leaving the decanter. 4.1Vapour re-compression To further reduce the energy consumption in no-washing option, vapour re-compression cycle was implemented in HYSYS as shown by Figure 4.6. Figure 4.6 Schematics for vapour re-compression for no-washing option Vapour re-compression is widely used technique for recovering low temperature heat energy. Reducing pressure also reduces boiling point of the liquid requiring less heating while the vapour stream leaving the flash tower, which needs to be cooled, preheats the methanol and glycerol feed stream entering the flash separator. 26
  27. 27. In order to design the optimum operating pressure, a plot of vacuum pump power consumption and methanol recovery was made as a function of operating pressure as shown in Figure 4.7. The lower the operating pressure, higher the methanol recovery and so is the power consumption. In order to keep the power consumption lower, some compromise will have to be made. Therefore, 70 kPa pressure was selected to keep power consumption of 50 kW and methanol recovery of 2557 kg/h. This results in 12% reduction of total heating requirement for no-washing option. The additional equipment require for vapour re-compression is the liquid ring vacuum pump which was estimated to cost $ 20,000. This additional cost of equipment can be recovered by the amount of heating it saves within 15 weeks of operation (Appendix-I). Figure 4.6 Methanol recovery and power consumption as a function of operating pressure Next, the energy consumption from vapour re-compression was compared with no- washing option for the methanol separation stage as shown in the Figure 4.7. It can be seen that for 6:1 molar ratio, at least 75% of energy can be saved using vapour re-compression. 27
  28. 28. Figure 4.7 Comparison of energy consumption between vapour re-compression and no-washing cycles for methanol separation stage. This reduction in energy consumption would positively affect the profitability of the plant which is discussed in the following section in detail. 28
  29. 29. 5.0 Cost Analysis After the technical evaluation of the process, it is necessary to analyse the impact of molar ratios and wet/dry washing on the economic feasibility of the plant in terms of profit/loss and the amount of funds required to be invested. In order to estimate the initial investment, it is important to analyse the fixed cost index (FCI) while rate of return and profitability requires to estimate the cost of manufacturing against expected revenue from the selling of the proposed two options (water washing and no-washing). Some of the major contributors for fixed cost are land, equipment and interconnecting piping and instrument costs while cost of manufacturing includes raw material, utilities costs, cost of waste disposal/treatment, cost of raw material, and other costs such as- cost involved in labour, taxes, research and development, sells and distribution, etc. the preliminary analysis would indicate whether it is profitable to enter into the project or not. If preliminary analysis indicates possibility of generating profit then further economic analysis in detail is necessary to include interest factors, pay-back period, rate of return, net present worth of future income, etc. 1.1Fixed Cost Index (FCI) 1.1.1Water Washing Table 5.1 shows the grass route cost of the equipment. Purchased cost (Cp) for equipment in cast steel material and at atmospheric pressure condition was calculated using equation 5.1 where the values for constants where K1, K2 and K3 were derived from course notes of CHG-4244 (plant design) (Thibault et al., 2008) and the capacity (A) was estimated from HYSYS simulation e.g. (A) in the equation 5.1 represents heat transfer area for heat exchangers (in m2) and power (in kW) for pumps and turbines, etc. 29
  30. 30. 5.1 CBM, from Table 5.1, represents bare module cost (equation 5.2) that includes direct and indirect costs for each equipment such as- material of construction of equipment, operating pressure, etc.; CTM represents the total module cost of the equipment (equation 5.3) such as- freight, duties & taxes, etc.; while CGR is the grass route cost (equipment 5.4) accounting for equipment erection, interconnecting piping and instruments, etc. 5.2 Where constant FBM is chose from plant design notes. 4.3 5.4 Costs of centrifuges, vacuum pumps and ion exchange tower (no-washing only) have been estimated online (Web-1,4). Total fixed cost for the plant was estimated to be $ 10.15 m. Rotating equipment such as- pumps and fans will have to be bought in pairs assuming one each will be kept as a back-up therefore, FCI includes double the cost of such machinery. Table 5.1 Fixed cost of the plant excluding land (6:1 molar ratio, wet washing) Equipment: Quantity CP ($) CBM0($) CTM($) CGR($) CSTR s 3 102280.0447 184104 217243 309295 Centrifuges 3 53100 175230 206771 294386 Triolein heater 1 2463 15625 18438 26251 Wash tank 1 86511.13125 155720 183750 261610 MeOH Pre-heater 1 2393 15179 17912 25501 Oil-Heater 1 3033 19241 22705 32325 Flash Dryer 1 71797.197 237984 280821 399812 MeOH Flash Tank 1 116344.2826 383936 453045 645013 Glycerol separator 1 72334 564207 665764 947868 MeOH Flash Heater 1 3086 19580 23104 32894 Equipment: Quantity CP ($) CBM0 CTM CGR MeOH Distillation column 1 128377 963094 1136451 1617998 Condensor 1 3643 15937 18806 26774 Reboiler 1 3146 13761 16239 23119 30
  31. 31. Equipment: Quantity CP ($) CBM0($) CTM($) CGR($) Glycerol cooler 1 2480 15735 18567 26435 Triolein Feed pumps 2 6257 33788 39870 56764 MeOH Feed Pumps 2 4511 20301 23956 34107 MeOH storage tank 1 31063 102508 120960 172214 Triolein storage tank 1 67730 528297 623391 887540 Glycerol storage tank 1 73294 571693 674598 960445 Water Wash pumps 2 5152 27822 32829 46740 FAME separator 1 90057 702444 828884 1180106 FAME-water decanter 1 89684 699533 825449 1175215 Distillation Pumps 2 3534 19085 22520 32063 Pure FAME cooler 1 3607 22884 27003 38444 FAME storage tank 1 162528 536343 632885 901056 Total 10 153 975 Cp-equipment cost, CBM0-bare module cost, CTM-total module cost, CGR-grass route cost Similarly, equipment cost for all other ratios were estimated. Table 5.3 shows the total cost for each ratio. It can be seen that the cost increases steadily as the molar ratio increases. This is mainly because of the cost involved in methanol distillation column. As it can be seen from the pie chart (Figure 5.1), major cost contributor is the storage tanks (34%), next major contributor is other process vessels (32%) such as decanters, evaporators, etc. decanters cost more because one hour of residence time was assumed for design purpose which increased the size of the equipment. Next major cost involved is the cost of distillation column (19%). This cost will rise steadily for higher molar ratios whereas storage cost will not be directly proportional to increased molar ratios because the plant capacity is constant for all molar ratios. 31
  32. 32. Figure 5.1 Equipment cost break up for 6:1 molar ratio washing option (Appendix-I) Cost of land was assumed to be $ 2 m arbitrarily. Then total FCI including land cost was estimated to be $ 12.15 m from 6:1 molar ratio including water washing 1.1.2Fixed Cost Index (FCI): No-Washing (Ion exchange) Most of the equipment cost is the same as that of the washing option such as- reactors, storage tanks and pumps because the production capacity is constant for both scenarios. The major reduction in cost is due to the absence of distillation column and connecting equipment. Whereas the additional cost of ion exchange tower was added. Table 5.2 shows the equipment cost break up for 6:1 molar ratio for dry washing option. Table 5.2 Fixed cost of the plant excluding land (6:1 molar ratio, dry washing) Equipment: Quantity CP ($) CBM0($) CTM($) CGR($) CSTR s 3 102280 184104 217243 309295 Centrifuges 3 53100 175230 206771 294386 Triolein heater 1 2463 15625 18438 26251 MeOH Pre-heater 1 2393 15179 17912 25501 Oil-Heater 1 3033 19241 22705 32325 Flash Dryer 1 71797 237984 280821 399812 MeOH Flash Tank 1 116344 383936 453045 645013 Glycerol separator 1 72334 564207 665764 947868 MeOH Flash Heater 1 3086 19580 23104 32894 Equipment: Quantity CP ($) CBM0 CTM CGR Glycerol cooler 1 2480 15735 18567 26435 Triolein Feed pumps 2 6257 33788 39870 56764 MeOH Feed Pumps 2 4511 20301 23956 34107 MeOH storage tank 1 31063 102508 120960 172214 Triolein storage tank 1 67730 528297 623391 887540 Glycerol storage tank 1 73294 571693 674598 960445 FAME separator 1 90057 702444 828884 1180106 Pure FAME cooler 1 3607 22884 27003 38444 FAME storage tank 1 162528 536343 632885 901056 Ion exchange towers 2 383168 Total 7 518 120 32
  33. 33. Two ion exchange towers were considered keeping one stand by to be used during the regeneration of first tower. The cost for resin was estimated online (Web-2) and the tower cost was assumed using equation 5.1. The total cost of equipment for dry washing option has been found to be $ 7.52 m. Table 5.3 compares the grass route cost of equipment for washing and no- washing options. Worth noting that the equipment cost of highest molar ratio for no-washing option is less than that of 6:1 ratio for water washing option. Therefore, even is the methanol to oil molar ratio is increased to more than three folds, the cost of equipment will still be at least 20% less. Table 5.3 Grass route cost of equipment for different molar ratios Molar ratio Washing ($ m) No-washing ($ m) 6:1 10.15 7.52 9:1 10.71 7.66 12:1 11.24 7.80 15:1 11.75 7.93 18:1 12.25 8.06 20:1 12.58 8.14 5.2 Cost of Manufacturing (COM) Cost of manufacturing plays important role in assessing profitability of the plant. While COM higher then revenue generated is definitely not recommended, further reducing COM is advantageous even when it is lesser than the revenue generated. Manufacturing costs can be further divided into three categories: direct manufacturing costs, fixed manufacturing costs, and general manufacturing expenses. 5.2.1 Direct Manufacturing Cost (DMC) DMC mainly includes costs of; •Raw materials 33
  34. 34. •Utilities •Waste treatment •Operating labor •Other costs involved in maintenance, lab charges, operating supplies and patents. Each section is explained in detail as follows. Raw Material Cost The raw materials require in the plant are canola oil, methanol, catalyst NaOH and HCl which were estimated to be $ 14.48 m per year (Web-3). Table 5.4 shows the detail break up of raw material cost. Table 5.4 Break up for yearly raw material cost Raw material Hourly consumption Unit cost ($) Total yearly cost ($) rate (kgéh) Canola oil 4260 0.90/L 34 014 489 MeOH 462 0.192/kg 770 447 NaOH 42.13 0.19/kg 64 178 HCl 38.14 0.215/kg 64 744 Total raw material cost 34 913 860 Therefore total raw material cost, including transportation cost, for the plant was estimated to be $ 34.91 m per year. The raw material cost remains unchanged for all molar ratios and for both the options (washing and no-washing). Although, methanol consumption, in terms of the system loss, will slightly increase for higher molar ratios but the same can be neglected when compared with the cost of canola oil. Utilities Major utilities include power, low pressure steam and cooling water for the plant. However, required heating loads will be partly provided by the process heat, low pressure steam will be 34
  35. 35. required and so is the cooling water to provide adequate cooling. Table 5.5 shows the cost of utilities required for biodiesel processing for washing and no-washing options at 6:1 molar ratio. However, the cost of cooling water will be less during winter as more amount of heat/kg of water can be removed due to low temperature as a result of natural cooling of the water. Table 5.5 Utilities cost break up for 6:1 molar ratio Utility Washing No-Washing MJ/h Yearly cost ($)* MJ/h Yearly cost ($)* Cooling water 489.436 2300 477.151 1353 LP steam 3390.897 343122 1024.440 142976 Power 241.200 114271 241.200 114271 Total 459693 258600 *Cost were estimated using CHG-4244 course notes (Thibault et al., 2008) Wastewater Treatment Major waste stream leaving the plant containing FFAs and some water vapours. However, as discussed earlier, some literatures mention FFA as adviceable compound in biodiesel for combustion, it can be treated to convert into biodiesel. But for the purpose of this report, it was assumed that the FFAs be discarded. Therefore, the lump sum cost of $ 500,000 was assumed for waste disposal. It was further assumed that the cost of waste treatment does not change on varying molar ratio or for no-washing option. Manpower Requirements Following steps were used to estimate the number of operators required and the cost of labour for the manufacturing cost (Thibault et al., 2005): 1 operator = 8h/shift * 5 shifts/week * (52-2) weeks of work/year = 2000h/yr = 250shifts/yr 35
  36. 36. 52 - 2 weeks of maintenance per year = 50 weeks of work/year 1 position = 1 shift/8h * 24 h/day * 365 days/yr = 1095 operating shifts/yr 1095 shift/yr / 250 shifts/operating year = 4.38 operators ~ 4.5 operators Cost of Labour =NOL*4.5 operators/position*40 h/operator week*52 weeks/year*Wh$/h = 9360 NOL Wh ($/yr) Wh = $25/h = $52 000/year NOL = (6.29 + 31.7*P2 + 0.23Nnp)1/2 7.5 P = 2 for liquid and gas handling. Nnp = 10 for our process NOL = 11.6 ~ 12 Total operators = NOL * 4.5 = 54 COL = 54 * 52000 = $ 2,808,000 Therefore total labour cost for the plant was estimated to be $ 2,808,000 per year. The labour cost remains constant for all ratios and for no-washing option. Other Costs Table 5.6 shows the break-up of each cost. Table 5.6 Other Costs (6:1 ratio washing option) Cost Type Equation (Thibault et al, 2008) $/year Direct Supervisory 0.18COL 505 450 Maintenance 0.06FCI 609 239 Operating Supplies 0.009FCI 91 386 36
  37. 37. Lab Charges 0.15COL 421 200 Patents 0.03COM 1 588 230 Total 3 215 495 Therefore, direct manufacturing cost (DMC) was obtained by summing up the costs of raw material, utilities, waste treatment, operating labour and other costs to get $ 41 346 632. 5.2.2 Fixed Manufacturing Cost (FMC) FMC includes costs of depreciation, local taxes and plant overheads as shown in the Table 5.7. Major part of FMC is contributed by depreciation cost of equipment assuming straight line method. However, considering double declining method, cost of depreciation will be reducing every year because double declining method assumes that major depreciation occurs during early years of operation. In that case, FMC will be changing every year based on depreciation therefore, best thing is to exclude depreciation from fixed manufacturing cost for the purpose of generating cash flows here yearly depreciation can be added separately. Table 5.7 Fixed manufacturing cost (FMC) (6:1 ratio washing option) Cost Type Equation (Thibault et al, 2008) $/year Depreciation 0.1 FCI 1 015 387 Local Taxes 0.032 FCI 324 927 Plant Overheads 0.708 COL + 0.036 FCI 2 353 607 Total 2 678 534 5.2.3 – General Manufacturing Expenses (GE) GE involves costs of administration, distribution and selling, and research and developments as shown in the Table 5.8 below. 37
  38. 38. Table 5.8 General manufacturing expenses (6:1 ratio washing option) Cost Type Applicable relation $/year Administration 0.177 COL + 0.009 FCI 588 402 Distribution 0.11 COM 5 823 512 R&D 0.05 COM 2 647 051 Total 9 493 555 Therefore the cost of manufacturing excluding depreciation (COMd) was obtained by summing up the DMC, FMCd and GE to get $ 52.94 m. Figure 5.2 shows the percentage contribution on each of these costs to the COMd. 70% of the COMd is contributed by raw material cost. Therefore, utilizing raw material to get optimum return per kilogram of residue is important. On the contrary, utilities account for less than 1% of total cost of manufacturing. Figure 5.2 Cost of manufacturing Distribution (6:1 ratio washing option) 5.3 Revenue generated Total revenue generated comes from selling of char and power. It was assumed that there is an increasing demand for charcoal because major application for charcoal is water filtration which will keep increasing since water is used for human consumption. 38
  39. 39. 5.6 Where M is the mass flow rate in kg/h and P is the prize of the compound in $/kg. Equation 5.6 was used to calculate yearly revenue generated by the plant where sell price of biodiesel was assumed to be $ 4.95/gallon (Web-3) and that of glycerol was assumed to be $ 0.96/kg to get gross revenue of $ 56.49 m. The revenue minus the expenses results in net profit of $ 3.41 m. Similarly, Figure 5.3 shows the amount of profit generated at different molar ratios and for no-washing option. Figure 5.3 Net profit at different molar ratios Amount of profit is inversely proportional to the expenses. As the molar ratio increases, the expenses increases and profit decreases. In case of water washing option, cost of separating water from methanol and glycerol is a major factor reducing the profit from $ 3.4 to 1 m. On the other hand, no washing option uses ion exchange resin which does not change upon increasing molar ratios and therefore, the expenses does not increase very much as is the case for water washing option. Although, utilities contribute less than 1% of the total cost of manufacturing, it plays a decisive role profitability criteria because every dollar saved on any energy consumption is directly result in profit. Moreover, savings on equipment cost as a result of process modification is also an important factor which increases the profit margin. 39
  40. 40. 6.0 Conclusion and Recommendations 6.1 Conclusion This report dealt with studying the effect of varying methanol to canola oil molar ratio for water wash and dry wash (ion exchange) options on energy consumption and profitability of the biodiesel plant. The two models were considered; one with widely used cycle implementing water washing of biodiesel and second, implementing dry washing i.e. biodiesel purification using ion exchange rather than water washing. Both the models were simulated in HYSYS for 10 million gallons of biodiesel production capacity per year using canola oil and methanol. For each of the two models, methanol to oil molar ratio was varied from 6:1 to 20:1 in six stages. Energy consumption was estimated from HYSYS energy balance and two scenarios were compared to study the effect. It was found that the energy consumption, when no water present in the system, is much less (1024 MJ/h) than the one using water washing cycle (3309 MJ/h). Therefore, biodiesel plant be operated without water washing mainly because methanol separation from water being difficult task requiring distillation column involving energy intensive step. Energy consumption can be further reduced by implementing vapour re- compression cycle for separating methanol and glycerol. Vapour re-compression recovers low 40
  41. 41. temperature heat which, otherwise, would be wasted in cold sink incurring additional cost of cooling. 12% of overall energy consumption can be saved using vapour re-compression cycle. In order to compare the profitability of both scenarios (washing and no-washing), fixed cost of the plant for each molar ratio was calculated along with other applicable costs and subtracted from revenue to find the net profit. Cost of equipment were found to be $10.15 m for the process using water washing compared to $ 7.52 m from dry washing option. No washing option requires less number of equipment and due to the absence of water, methanol can be easily flash separated from glycerol. The net profit generated by the water wash plant was found to be $ 3.4 m compared to $ 4.3 m for dry wash process. Therefore, in order to conclude, it can be said that biodiesel manufacturing process would be more beneficial if water washing step can be replaced by dry washing (ion exchange). 6.2 Recommendations Although, proposed project appears to be a profitable and technically sound, there are certain challenging factors involve which needs to be discussed. 6.2.1 Vegetable oils- part of the food chain Biodiesel is made using vegetable oils and most vegetable oils are a part of human food chain. This is a serious issue of creating global food crisis because if oils are directed to biodiesel production, the price hike would be more likely which may create difficult for general public to buy oils for consumption. Therefore, using alternative to vegetable oils could be a good option e.g. used frying oils from fast food industries. Another option could be to grow more oil seeds dedicated for biodiesel production leaving the food chain intact. 6.2.2 Expensive raw material 41
  42. 42. As discussed earlier, vegetable oil constitutes more than 70% of the total operating cost. Profit margin is directly affected by the raw material cost. Therefore, alternatives to expensive raw material can be explored. Used frying oil can be very cheaper in price but this requires additional processing and energy consumption increasing expenses as well as the biodiesel yield is much less (~90%) which reduces the profit. 6.2.3 Cold flow properties One of the major limitations of biodiesel is its cold flow property. Cold flow properties are a major concern when the temperature of operation goes below 10 °C. Problems with biodiesel often develop from plugged fuel lines and filters, and these problems are caused by the formation of crystals (Yori et al., 2006). Methyl and ethyl esters of fatty acids have considerably higher crystallization temperatures than diesel fuel. Crystal growth inhibitors for diesel fuel, also known as pour point depressants (PPD), are available commercially (Huang et al., 2000). Though they have been reported to reduce the pour point of biodiesel, these additives usually do not reduce the cloud point (CP) nor improve the filterability of biodiesel at low temperatures. CP and cold flow plug point (CFPP) temperatures for biodiesel are higher than that of petroleum diesel. As it can be seen from the Table 6.1 that CP and CFPP of biodiesel is almost 15-20oC higher than petroleum diesel. Table 6.1 Comparison of cloud point (CP) and cold flow plug point (CFPP) and pour point (PP) temperatures for pure biodiesel and petroleum diesel (Yori et al., 2006). CP (oC) CFPP (oC) PP (oC) Pure biodiesel -3 -10 to -14 -9 to -16 Petroleum diesel -17 -31 -24 Since the cloud point is highly related to the fatty acid composition of biodiesel (Imahara et al., 2006), (Knothe et al., 2005), higher amount of saturated free fatty acids (FFAs) of long and 42
  43. 43. linear chains are responsible for higher cloud points. Therefore, removing or reacting excess fatty acid might cause the CP to lower. Also, unconverted mono and di glycerides increases the crystallization temperature of biodiesel. Upon acid esterification the FFA can be converted to methyl ester to bring down the CP and glycerides can be converted to glycerol which can be separated from biodiesel (Sheehan et al., 1998). For additional details on cold flow properties, refer Appendix-I. Improvements, to some extent, can also be made through chemical combinations into stable solid compounds, or by winterization process (using solvent) or dry fractionation (without solvent). Each additional step is energy and cost consuming which would result in the loss of profit margin. 6.2.4 Less incentive (profit margin) Currently fossil energy is most widely used because it is a cheaper alternative than renewable energy. The higher cost of biodiesel (limited profit margin) makes it less popular then fossil diesel business venture. Therefore, government should intervene and offer certain benefits to biodiesel producers and consumers such as- CO2 tax credits, tax rebate, cheaper (duty/tax free) raw material, offer to buy biodiesel at a set price, make people aware of the importance of renewable energy with respect to CO2 emission. Also, when finite amount of fossil fuels will extinct, energy consumption by human will have to come from renewable sources. Therefore, it is very important that biodiesel (renewable fuels) be made popular and attractive choice. 43
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  46. 46. Zhang Y, Dub MA, McLean DD, Kates M. Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresour Technol 2003;90:229–40. “Survey of Diesel Fuels and Aviation Kerosene’s From U.S. Military Installations”, Paper by Steven R Westbrook (SwRI) and Maurice E. LePera (US Army TARDEC), Presented at the 6th International Conference on Stability and Handling of Liquid Fuels, October 13-17, 1997, Vancouver, B.C., Canada. 7.1 Web references Web-1 http://www.matche.com/EquipCost/Centrifuge.htm Web-2 http://www.arborbiofuelscompany.com/Biodiesel_Dry_Washing_Questions_and_Answers.html Web-3 www.icis.com Web-4 http://www.gnsolidscontrol.com/decanting-centrifuge/ Web-5 http://www.nrel.gov/docs/fy04osti/36240.pdf) Web-6 http://ezinearticles.com/?Cold-Soak-Filtration-Test-Mandated-For-Biodiesel-Testing&id=1735307 Web-7 http://www.biodieselexpertsintl.com/Default.aspx?tabid=414 Web-8 http://www.uiweb.uidaho.edu/bioenergy/Bioshortcourse/Diesel_Fuel_Props.htm 46
  47. 47. Appendix-I I.1 Additional information on Cold Flow Properties (literature review) As discussed briefly in the report (Section 9.2.3), one of the main reasons for using biodiesel in blend with petroleum diesel is its high crystallization temperature. Three important cold weather parameters that define operability for bio and petroleum diesel are cloud point (CP), pour point (PP) and cold flow plugging point (CFPP) temperatures. Each one of them is discussed briefly. Over the years, so many efforts has been made to understand how to deal with the cold flow properties of diesel fuel—or the low temperature operability—of existing diesel fuel. The cloud point and the cold filter plugging point (CFPP) or the low temperature filterability test (LTFT) commonly characterize the low temperature operability of diesel fuel. I.1.1 Cloud Point A fuel property that is particularly important for the low temperature operability of diesel fuel is the cloud point. The cloud point is the temperature at which a cloud of wax crystals first appears in a liquid upon cooling. Therefore, it is an index of the lowest temperature of the fuel’s utility under certain applications. Operating at temperatures below the cloud point for a diesel fuel can result in fuel filter clogging due to the wax crystals. As described in ASTM D2500, the cloud point is determined by visually inspecting for a haze in the normally clear fuel, while the fuel is cooled under carefully controlled conditions. The apparatus used for this test is shown in Figure 2.1. The cloud point is an important property for biodiesel since biodiesel fuels typically have higher cloud points, i.e., crystals begin to form at higher temperature, than standard diesel fuel. This feature has implications on the use of biodiesel in cold weather applications. An alternative procedure for measuring the cloud point of diesel/biodiesel fuels is ASTM 47
  48. 48. D5773. A summary of the procedure steps is 1) the sample is cooled in a Peltier device at a constant rate, 2) the sample is continuously monitored by optical detectors, and 3) the temperature is recorded that corresponds to the first formation of a cloud in the fuel. The repeatability of the cloud point test is <0.5°C and the reproducibility is <2.6°C. Figure 2.1 Scehmatic diagram of the apparatus used for cloud point measurement (Web-5) I.1.2 Pour Point A second measure of the low temperature performance of diesel/biodiesel fuels is the pour point. The pour point is the lowest temperature at which a fuel sample will flow. Therefore, the pour point provides an index of the lowest temperature of the fuel’s utility for certain applications. The pour point also has implications for the handling of fuels during cold temperatures. The standard procedure for measuring the pour point of fuels is ASTM D97. A summary of the procedure steps is 1) the sample is cooled at a specified rate, 2) the sample is examined at 3°C intervals for flow, and 3) the lowest temperature at which sample movement is 48
  49. 49. observed is noted. The repeatability of the pour point test is <3°C and the reproducibility is <6°C. I.1.3 Cold Flow Plug Point (CFPP) The temperature at which a fuel will cause a fuel filter to plug due to fuel components, which have begun to crystallize or gel. When diesel fuels start to solidify, they initially form microscopic crystals. If allowed to agglomerate, these crystals will grow large enough where they can plug fuel filters and fuel lines. Anti-gelling additives can be used to disrupt the agglomeration process. The CFPP is less conservative than the cloud point, and is considered by some to be the true indication of low temperature operability. The shows CFPP results for biodiesel and Number 2 diesel fuel at various concentrations. The University of Missouri prepared the fuel blends and they were analyzed at Cleveland Technical Center in Kansas City. The data suggests that the fuel mixture starts to gel sooner as the concentration of biodiesel increases. High concentrations of biodiesel (i.e. blends over 20%) may not be appropriate for use in cold climates without blending extreme percentages of kerosene combined with proven cold flow improvers specific to conventional diesel fuel. Figure I.1 CFPP for biodiesel blends (Survey of Diesel Fuels) 49
  50. 50. I.1.4 Analysis I.1.4.1 Cold Soak Filtration The newest testing requirement for biodiesel fuel testing is the cold soak filtration test. The procedure was added to the ASTM Method in October 2008. Figure I.2 shows the picture of typical cold soak filters developed by Biodiesel Experts International in association with Schroeder Biofuels. A new proprietary multi-stage separation technology designed specifically to ensure that biodiesel products conform to ASTM 6517 standard for cold flow properties. The Cold Clear TM system consists of a three-stage bank of housings using a combination of filtration and adsorption principles to capture compounds that could cause plugging or crystallization in biodiesel fluids. It is designed to improve purity standards in alternative fuels for consumers (Web-6). In the past, substandard biodiesel has been known to precipitate material out of solution when exposed to cold temperatures. If a solid material were to precipitate out of the biofuel when it is used in an engine, it can lead to extensive damage. Therefore, legislators took action to prevent such substandard product from making it to the market. In scientific terms, cold soak filtration measures time in seconds it takes for cold soaked biodiesel to pass through two 0.8 micron filters. It also measures the amount of particulate matter collected on the filter. This works to ensure that end users will not have clogged filters or worse problems with their engines when using biodiesel in cold temperatures. It also ensures that producers will maintain a high level of brand integrity as guaranteed by their customer’s satisfaction with their product. 50
  51. 51. Figure I.2 Picture of typical cold soak filters (Web-7) The schematic diagram of lab scale CFPP test method is shown in the Figure I.3. It determines the lowest temperature where 20 ml of fuel can be drawn through a 45 micron screen in 60 seconds with 200 mm of water (1.96 kPa) of vacuum. Figure I.3 Schematic diagram of lab scale CFPP test method (Web-8). I.2 Material Balance (from HYSYS) 51
  52. 52. The following data represents 6:1 no-washing option. Refer “hysys-data” file for data pertaining to all other ratios. The following Tables should be refer with Figure 3.3 for stream identifications. Name 1.00 2.00 3.00 4.00 5.00 6.00 Vapour Fraction 0.00 0.60 0.00 1.00 0.00 0.00 Temperature [C] 65.00 120.00 25.28 120.00 120.00 65.53 Pressure [kPa] 500.00 101.30 500.00 101.30 101.30 250.00 Molar Flow [kgmole/ h] 29.56 15.98 4.81 9.63 6.35 14.47 Mass Flow [kg/h] 5042.46 1017.64 4259.95 305.82 711.82 4246.17 Std Ideal Liq Vol Flow [m3/h] 5.64 1.05 4.79 0.38 0.67 4.84 Heat Flow [kJ/h] -15762951.50 -5722629.82 -9066841.60 -1908430.09 -3814199.74 -10128432.46 Molar Enthalpy [kJ/kgmole] -533245.49 -358046.25 -1884606.44 -198182.57 -600351.42 -699941.11 (M-Oleate) [kg/h] 4236.59 211.83 0.00 0.33 211.50 4236.59 (Methanol) [kg/h] 330.62 330.62 0.00 300.27 30.35 3.31 (Glycerol) [kg/h] 428.00 428.00 0.00 0.73 427.27 0.86 (triolein*) [kg/h] 42.60 42.60 4259.95 0.00 42.60 4.26 (H2O) [kg/h] 4.64 4.59 0.00 4.50 0.09 1.16 Heat CapacitykJ/kg-C 2.23 2.32 1.61 1.61 2.63 2.07 Heat Capacity [kJ/kgmole-C] 380.20 147.99 1425.95 51.00 295.01 608.43 Name FAME-2 FAME-21 FAME-2-2 fameL glyce Glycerol Out Vapour Fraction 0.00 1.00 0.00 0.00 0.00 0.00 Temperature [C] 65.00 120.00 25.00 120.00 120.00 65.00 Pressure [kPa] 101.30 101.30 101.30 101.30 101.30 500.00 Molar Flow [kgmole/ h] 14.29 0.00 0.71 0.79 5.56 4.65 Mass Flow [kg/h] 4236.59 0.00 211.83 247.85 463.97 428.00 Std Ideal Liq Vol Flow [m3/h] 4.83 0.00 0.24 0.28 0.38 0.34 Heat Flow [kJ/h] -10075694.81 0.00 -520672.65 -556595.77 -3257603.96 -3104795.42 Molar Enthalpy [kJ/kgmole] -705152.74 -198182.57 -728790.92 -703705.54 -585654.72 -668067.75 (M-Oleate) [kg/h] 4236.59 0.00 211.83 210.96 0.54 0.00 (Methanol) [kg/h] 0.00 0.00 0.00 1.13 29.23 0.00 (Glycerol) [kg/h] 0.00 0.00 0.00 0.39 426.89 428.00 (triolein*) [kg/h] 0.00 0.00 0.00 35.38 7.22 0.00 (H2O) [kg/h] 0.00 0.00 0.00 0.00 0.09 0.00 Heat Capacity [kJ/kg- C] 2.07 1.61 1.92 2.24 2.84 2.65 52

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