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• Mark Anthony Caro

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Material Balance Calculations

For the engineering aspect of the research, material balance calculations and preliminary costing analysis were done. Material balance calculation was employed on the following processes: centrifugation, fermentation, distillation and dehydration. The amount of sugarcane juice, nutrients, yeast and media to be used were calculated and considered in the preliminary costing. The efficiencies of the equipment used in the calculations are based on either existing studies or existing industrial equipment. The amount of retentate (isoluble solids), filter cake, carbon dioxide and water vapor produced were also calculated. On the other hand, fermentation yield was calculated based on the literature value of glucose to ethanol conversion. In all the component balance calculations, only the sugar, ethanol and insoluble solids contents are specified to simplify the calculations. All other parameters which are deemed to be unnecessary to the calculations are classified under “others”.

The over-all process block diagram is

presented in Figure 4-13. A capacity of 1000 L of sugarcane juice is used as the basis of the material balance calculations. All units of values presented in the material balance are in per hour basis. The sugar cane juice density used in the calculations is based on the study of Astolfi-Filho, et al.(2011). Equation 4-1 shows the over-all material balance equation for the centrifugation of the sugarcane juice while Equation 4-2 presents the component mass balance for insoluble solids. Figure 4-14 shows the flowsheet for the said process. In the operations, it is assumed that the equipment (disc centrifuge) has a maximum separation efficiency of 66.97% (Kumar, V., Vijay, V.K., & Agarwal, U.S., 2008).

Figure 4-14. Flowsheet for the centrifugation of the sugar cane juice.

SCJ =CJ + IS (Equation 4-1) IS=η × IS i

(Equation 4-2)

where: SCJ CJ ISi IS η

is the flowrate of sugarcane juice (kg/h) is the flowrate of the clarified juice (kg/h) is the initial flowrate of the insoluble solids (kg/h) is the final flowrate of the insoluble solids (kg/h) is the disc centrifuge efficiency (%)

The clarified juice will undergo continuous fermentation. Figure 4-15 shows the flowsheet for the continuous fermentation of the clarified sugarcane juice. The clarified juice shall be mixed with nutrients, yeast and media, the amount of which are calculatedbased on the protocols presented by Del Rosario, et al. (1987) for nutrients, and

Martinez, et al. (2007) for yeast and media. The conversion of sugar to ethanol was assumed to be 0.514 (www.livestrong.com/article/126363-glucose-ethanol/). The fermentation shall be carried out in a Continuous Stirred Tank Reactor at temperature ranging from 25 °C to 32 °C. This range is adopted from the findings of this research. Equation 4-3 presents the over-all material balance equation for the fermentation process.

Figure 4-15. Flowsheet of the continuous ethanol fermentation of clarified sugarcane juice.

CJ + M +N +Y =CO 2+ FB

where: CJ M N Y CO2 FB

is the flowrate of clarified juice (kg/h) is the flowrate of the medium used (kg/h) is the amount of the nutrients (kg) is the amount of yeast (kg) is the amount of evolved carbon dioxide (kg/h) is the flowrate of the fermented broth (kg/h)

(Equation 4-3)

The fermented broth has an ethanol content of 67.2598 kg/h, which is equivalent to 6.1951%. In order to increase the concentration of ethanol. The fermented broth shall undergo distillation process. However, the broth should be filtered first to remove unnecessary debris and materials prior to distillation. The filtration will be carried out in a rotary filter with filtration efficiency of 99.7% (http://www.abbess.com/vac/filterexhaustandinlet.html). Figure 4-16 shows the flowsheet for the filtration of the fermented broth. Equation 4-4 shows the material balance equation around the rotary filter.

Figure 4-16. Flowsheet for the filtration of the fermentation broth.

FB=S+ FFB

(Equation 4-4)

where: FB S FFB

is the flowrate of the fermentation broth (kg/h) is the flowrate of the solids (filter cake) (kg/h) is the flowrate of the filtered fermentation broth (kg/h)

The filtered fermented broth is now ready to undergo distillation. Figure 4-17 shows the block diagram for the distillation process while Equation 4-5 presents the overall material balance equation. On the other hand, Equation 4-6 shows the component balance equation for ethanol. According to Baticados, E.J., et al. (2010), the mass fractions of bottoms and distillate are 0.0025 and 0.9560, respectively.

Figure 4-17. Flowsheet for the distillation of the clarified fermentation broth.

F=B+ D

(Equation 4-5)

F X F =B X B + D X D (Equation 4-6) where: F B

is the fermentation broth (kg/h) is the bottoms (kg/h)

D XF XB XD

is the distillate (kg/h) is the mass fraction of ethanol in fermentation broth is the mass fraction of ethanol in bottoms is the mass fraction of ethanol in distillate

The resulting product from the distillation is hydrous ethanol (95.6% w/w). In order to further increase the ethanol concentration to 99.5% (w/w), the product shall be subjected dehydration by use of molecular sieves in a pervaporator system. Figure 4-18 shows the flowsheet for the pervaporator system. Equation 4-7 shows the material balance equation around the pervaporator system.

Figure

4-17.

Flowsheet for the dehydration using molecular sieves in a pervaporator system.

D=E+W (Equation 4-7) where: D E W

is the distillate (kg/h) is the 99.5% ethanol solution (kg/h) is the water removed from the distillate (kg/h)