1. Department of Biosystems Engineering
University of Manitoba
BIOE 4440 Bioprocessing for Biorefining
__________________________________Due date: December 7th
, 2016
Design Project
Design of an Ethanol Production Run Using
a 95% Corn and 5% Wheat Mixture
Prepared by: Alain Lagasse โ 6773581
Vitaliy Solovyov โ 7688702
Abstract
The Husky Energy ethanol production process was analyzed to determine the required parameters
to produce 500,000 litres of ethanol from a 95% corn and 5% wheat blend. The required input
material was determined to be 1,164,200 kg of corn and 61,300 kg of wheat along with 3,120,700
kg of water, along with some enzymes and yeast. This mixture is fermented and mixed for 52
hours, which requires a 1.52 m diameter impeller operating at 2.22 rpm. This fermentation and
mixing process together require 415.4 GJ of energy. This product then passes through a distiller
which extracts the ethanol. The remaining solution is the centrifuged among 4 centrifuges which
run at 3000 rpm for durations of 128 seconds. This removes excess water and separates the
remaining product into thin stillage and insoluble cake fraction. The thin stillage is concentrated
from 5% solids to 30% solids in an evaporator. To achieve this 545,587 kg of steam at a
temperature of 110ยฐC must be passed through a 52.8 m2
heat exchanger at a flow rate of 0.592
kg/s. The concentrated thin stillage is then blended with the insoluble cake fraction previously
obtained from centrifugation and passed through a rotary dryer. The dryer takes room air heated
to 550ยฐC and passes it over the wet product for 4.85 minutes per batch at a rate of 19,992 m3
/h.
This process lowers the blendโs moisture content from 3.11 kg H2O/kg dry to 0.08 kg H2O/kg dry.
This process involves the removal of 429,454 kg of water and requires 1026.7 GJ of energy.
Several assumptions were made throughout the design process to simplify the design, this includes
perfect conversion of all starch to ethanol, the volume in the fermenter doesnโt change throughout
fermentation, the mixing should occur at a Reynoldโs number of 200, the temperature of the steam
used in the evaporator and the speed of the rotary drum dryer. Because of these assumptions the
values in these design may not be accurate, therefore this design should only be used as base design
for an ethanol production run, all calculations should be revisited by an expert as concrete design
decisions are made.
2. i
1 Introduction (Vitaliy Solovyov) _______________________________________ 1
2 Ethanol Production Design Analysis ___________________________________ 2
A. Production Overview (Alain Lagasse) ____________________________ 3
B. Mixing Operation (Vitaliy Solovyov) _____________________________ 8
C. Centrifugation Operation (Vitaliy Solovyov) ______________________ 12
D. Evaporation Operation (Alain Lagasse)__________________________ 13
E. Drying Operation (Alain Lagasse) ______________________________ 17
3 Conclusion (Alain Lagasse) ________________________________________ 22
4 References (Alain Lagasse) ________________________________________ 25
Table of Contents
3. 1
1 Introduction
Scope:
The Husky Energy plant in Minnedosa Manitoba specializes in the production of ethanol for
transportation fuel by breaking down wheat and corn and converting its mass into energy. The
major components of the process involve fermentation, mixing, centrifugation, evaporation and
drying; it is these 5 processes that will be analysed within this report. The amount of wheat and
corn utilized for the process of making ethanol depends on the harvesting yields during the years.
Four major wheat to corn ratios are implemented: 50% for both wheat & corn, 95% corn & 5%
wheat, 66.5% corn & 33.5% wheat, and finally 100% wheat. This report will focus on one specific
ratio of mass yields which is 95% corn & 5% wheat.
Purpose:
To determine the best utilized strategy for fermentation, mixing, centrifugation, evaporation, and
drying process in creating exactly 0.5-million-liter ethanol from 95% corn and 5% wheat.
A given amount of 0.5 million liters of ethanol is to be synthesized by the plant process. The
objective of this report is to determine how each of the five processes (fermentation, mixing,
centrifugation, evaporation, and drying) will be utilized properly if the plant is to meet this 0.5-
million-liter demand of ethanol. For the fermentation, it is imperative to determine the mass
quantity of both corn and wheat required, the amount of water needed for the fermentation (taking
into account the already present water content in the corn and wheat mass), how much glycerol
and lactic acid is produced as a by-product, and finally the amount of energy required to maintain
this process at a set temperature of 30o
C. The fermentation values are all based on already existent
data given. Using the determined fermentation data, the last 4 process can be analysed.
To better understand the mixing operation (the second process), the viscosity of the slurry must be
determined. Using this new information, it is important to determine the impeller speed and
diameter of the mixer. After which the required horsepower can then be determined for each mixer.
The fermented slurry undergoes mixing to evenly distribute the heat among the slurry mixture.
Centrifugation (the third process) requires the determination of the speed and quantity of an
industry scale centrifuge to be able to handle the slurry going from the mixer; this process uses
outside parameters from different centrifuge manufacturers to better suite the needs of the ethanol
plant. Once the centrifugation converts the slurry into thin stillage as well as cake, the thin stillage
is taken to the evaporation process (the fourth process) to further concentrate the particle content.
For this to work, the size of the evaporator must be determined as well as the amount of steam
required for the evaporation process to maintain a continuous production of ethanol. After the thin
stillage is concentrated in the evaporation process, it is again combined with the cake and is
targeted for drying (the last process) where the content is sent through a rotary dryer with given
parameters, where it is necessary to determine the optimum volumetric flow rate of drying air as
4. 2
well as the amount of energy needed in producing distillers dried grain with solubles (DDGS) as
a by-product. This report covers all of these processes in greater detail in the analysis portion of
the report.
2 Ethanol Production Design Analysis
A. Production Overview
i) Determining amount of corn and wheat required:
The provided handout, shown in Figure 1, states that corn produces 410 litres of ethanol per tonne
and wheat produces 370 litres of ethanol. The overall goal is to produce 500,000 L of ethanol using
a 95% corn and 5% wheat mixture.
Figure 1: Husky Energy ethanol production for corn and wheat
The calculate this the following equation calculation was used:
0.95 โ ๐ ๐ก โ 410
๐๐๐ก๐๐๐
๐ก๐๐๐๐
+ 0.05 โ ๐ ๐ก โ 370
๐๐๐ก๐๐๐
๐ก๐๐๐๐
= 500000 ๐๐๐ก๐๐๐
Where: mt = total mass of corn and wheat together (tonnes)
๐ ๐ก = 1225.5 ๐ก๐๐๐๐
๐ ๐๐๐๐ = 0.95 โ 1225.5 ๐ก๐๐๐๐๐ = 1164.2 ๐ก๐๐๐๐๐ = ๐, ๐๐๐, ๐๐๐ ๐๐ ๐๐๐๐
๐ ๐คโ๐๐๐ก = 0.05 โ 1225.5 ๐ก๐๐๐๐๐ = 61.3 ๐ก๐๐๐๐๐ = ๐๐, ๐๐๐ ๐๐ ๐๐๐๐๐
Therefore, 1,164,200 kg of corn and 61,300 kg of wheat are required to make 500,000 L of ethanol.
5. 3
ii) Determining the amount of water required:
Figure 2 shows that the percent solids of mash at the start of fermentation for 5% wheat and 95%
corn mixture is approximately 32% weight/volume of liquid (g/100mL). To determine the total
amount of mash solids the dry mass of the corn and wheat must be calculated.
Figure 2: Total mash solids in gram per liquid volume in 100 ml at the start of fermentation
Good quality corn has 14% wet basis moisture content, from this the corn water content can be
determined:
๐๐ถ๐๐๐๐ =
๐ ๐ป2๐ ๐๐๐๐
๐ ๐ก ๐๐๐๐
โ 100
Where: MCcorn = corn moisture content (%)
mH2O corn = amount of water in the corn (kg)
mt corn = total wet mass of corn (kg)
mdry corn = dry corn mass (kg)
14% =
๐ ๐ป2๐ ๐๐๐๐
1,164,200 ๐๐ ๐๐๐๐
โ 100
๐ ๐ป2๐ ๐๐๐๐ = 162,988 ๐๐ ๐ค๐๐ก๐๐
From here the dry mas of the corn can be calculated:
๐ ๐๐๐ฆ ๐๐๐๐ = ๐ ๐ก ๐๐๐๐ โ ๐ ๐ป2๐ ๐๐๐๐ = 1,164,200 ๐๐ โ 162,988 ๐๐ = 1,001,212 ๐๐ ๐๐๐ฆ ๐๐๐๐
6. 4
The wheat was assumed to have a 14.5% wet basis moisture content, this value was found on the
Ontario ministry of agriculture, food and rural affairs website. From this, the wheat water content
can be determined:
๐๐ถ ๐คโ๐๐๐ก =
๐ ๐ป2๐ ๐คโ๐๐๐ก
๐ ๐ก ๐คโ๐๐๐ก
โ 100
Where: MCwheat = wheat moisture content (%)
mH2O wheat = amount of water in the wheat (kg)
mt wheat = total wet mass of wheat (kg)
mdry wheat = dry wheat mass (kg)
14.5 =
๐ ๐ป2๐ ๐คโ๐๐๐ก
61,300 ๐๐ ๐คโ๐๐๐ก
โ 100
๐ ๐ป2๐ ๐คโ๐๐๐ก = 8,889 ๐๐ ๐ค๐๐ก๐๐
๐ ๐๐๐ฆ ๐คโ๐๐๐ก = ๐ ๐ก ๐คโ๐๐๐ก โ ๐ ๐ป2๐ ๐คโ๐๐๐ก = 61,300 ๐๐ โ 8,889 ๐๐ = 52,411 ๐๐ ๐๐๐ฆ ๐คโ๐๐๐ก
By adding the dry mass of corn and the dry mass of wheat, the total dry mass, mdry, can be obtained:
๐ ๐๐๐ฆ = ๐ ๐๐๐ฆ ๐๐๐๐ + ๐ ๐๐๐ฆ ๐คโ๐๐๐ก = 1,001,212 ๐๐ ๐๐๐๐ + 52,411 ๐๐ ๐คโ๐๐๐ก
= 1,053,623 ๐๐ ๐ ๐๐๐๐๐
By adding the water content of corn and the water content of wheat, the water provided by the corn
and wheat, minnate H2O, can be obtained:
๐๐๐๐๐ก๐ ๐ป2๐ = ๐ ๐ป2๐ ๐๐๐๐ + ๐ ๐ป2๐ ๐คโ๐๐๐ก = 162,988 ๐๐ + 8,889 ๐๐ = 171,877 ๐๐ ๐ค๐๐ก๐๐
Now everything required to determine the total liquid volume has been calculated. The total
required liquid volume is:
๐๐๐ก๐๐ ๐๐๐ โ ๐๐๐๐๐๐ =
๐ ๐๐๐ฆ[๐]
๐๐ป2๐[100 ๐๐ฟ]
โ 100
Where: Total Mash Solids = percentage of solids over liquid volume - 32% from Figure 2
VH2O = Amount of liquid volume required for fermentation (mL)
32% =
1,053,623 โ 103
๐
๐๐ป2๐
โ 100
๐๐ป2๐ = 3,292,571,875 ๐๐ฟ = 3,292,572 ๐ฟ = 3,292.6 ๐3
7. 5
Volume of water provided by the corn and wheat, assume density of water is 1000 kg/m3
:
๐๐๐๐๐๐ก๐ ๐ป2๐ =
๐โ20 ๐ก๐๐ก๐๐
๐โ20
=
171,877 ๐๐
1000
๐๐
๐3
= 171.9 ๐3
Where: Vinnate H2O = volume of water provided by corn and wheat (m3
)
ฯH2O = density of water (kg/m3
)
Therefore, the amount added water required for fermentation, VH2O add, would be:
๐๐ป2๐ ๐๐๐ = ๐๐ป2๐ โ ๐๐๐๐๐๐ก๐ ๐ป2๐ = 3,292.6 ๐3
โ 171.9 ๐3
= ๐, ๐๐๐. ๐ ๐ ๐
๐, ๐๐๐. ๐ ๐ ๐
๐๐๐๐๐ = ๐, ๐๐๐, ๐๐๐ ๐๐ ๐๐๐๐๐ ๐๐ ๐๐ ๐๐ ๐ ๐๐
Therefore, 3,120.7 m3
of water needs to be added to get the required 3,292.6 m3
of total water
From the engineering toolbox, the particle density of dry corn, ฯcorn, is 561 kg/m3
and the particle
density of dry wheat, ฯwheat, is 641 kg/m3
. Using these values the total volume of dry particles,
Vdry, in the fermenter can be calculated.
๐๐๐๐ฆ =
๐ ๐๐๐ฆ ๐๐๐๐
๐๐๐๐๐
+
๐ ๐๐๐ฆ ๐คโ๐๐๐ก
๐ ๐คโ๐๐๐ก
=
1,001,212 ๐๐
561
๐๐
๐3
+
52,411 ๐๐
641
๐๐
๐3
= 1,866.5 ๐3
Where: ฯcorn = particle density of dry corn (kg/m3
)
ฯwheat = particle density of dry wheat (kg/m3
)
Vdry = total volume of dry mass entering the fermenter (m3
)
From here, the total volume entering the fermenter can be determined as:
๐๐ก๐๐ก๐๐ = ๐๐๐๐ฆ + ๐๐ป2๐ = 1,866.5 ๐3
+ 3,292.6 ๐3
= 5159.1 ๐3
= 5.1591 ๐๐๐๐๐๐๐ ๐๐๐ก๐๐๐
With a maximum volume of 1.44 million litres per 52 hour run then the number runs would be:
# ๐๐ ๐๐ข๐๐ =
๐๐ก๐๐ก๐๐
๐๐ ๐ข๐
=
5.1591 ๐๐๐๐๐๐๐ ๐๐๐ก๐๐๐
1.44
๐๐๐๐๐๐๐ ๐๐๐ก๐๐๐
๐๐ข๐
= ๐. ๐๐ ๐๐๐๐
Therefore, three complete runs and one run at a 58% size half batch would produce the required
amount of ethanol form a 95% corn and 5% wheat mixture. Total fermentation time would be the
length of four batches, or 208 hours. Filling and emptying the fermenters also needs to be factored
in, it is assumed that emptying, cleaning and filling the fermenters takes about 12 hours, therefore
52 hour runs will actually take 64 hours, and the entire 4 batch run would take a total of 256 hours.
8. 6
iii) Determining the amount of glycerol produced:
Figure 3 shows that there is approximately 0.82 % glycerol as weight per volume in the solution
after a 52-hour fermentation run for 5% wheat and 95% corn mixture.
Figure 3: Glycerol, grams per total volume in 100 mL, produced after specific fermentation times
As previously established, the total volume pre-fermentation was s 5,159,100 L = 5,159,100,000
mL. Though only mass is conserved through the fermentation, not volume, it will be assumed that
the post-fermentation volume is approximately the same as the pre-fermentation volume.
Using this post-fermentation volume, the amount of glycerol produced can be determined as:
๐๐๐ฆ๐๐๐๐๐ ๐๐๐๐ก๐๐๐ก =
๐ ๐๐๐ฆ๐๐๐๐๐
๐๐ก๐๐ก๐๐
โ 100 = 0.82%
Where: mglycerol = mass of glycerol produced (g)
glycerol content = percentage of glycerol produced in gram over total volume (%)
Vtotal = total volume in the fermenter (mL)
0.82% =
๐ ๐๐๐ฆ๐๐๐๐๐
5,159,100,000 ๐๐ฟ
โ 100
๐ ๐๐๐ฆ๐๐๐๐๐ = 42,304,620 ๐ = ๐๐, ๐๐๐ ๐๐ ๐๐๐๐๐๐๐๐
Therefore, 42,304 kg of glycerol is produced during the total ethanol production run
9. 7
iv) Determining the amount of lactate (lactic acid) produced:
Figure 4 shows that there is approximately 0.08 % lactic acid as weight per volume in the solution
after a 52-hour fermentation run for 5% wheat and 95% corn mixture.
Figure 4: Lactic acid, grams per total volume in 100 mL, produced after specific fermentation times
Therefore, the amount of lactic acid produced can be determined as:
๐๐๐๐ก๐๐ ๐๐๐๐ ๐๐๐๐ก๐๐๐ก =
๐๐๐๐๐ก๐๐ ๐๐๐๐
๐๐ก๐๐ก๐๐
โ 100 = 0.08%
Where: mlactic acid = mass of lactic acid produced (g)
lactic acid content = percentage of lactic acid produced in gram over total volume (%)
Vtotal = total volume in the fermenter (mL)
0.08% =
๐๐๐๐๐ก๐๐ ๐๐๐๐
5,159,100,000 ๐๐ฟ
โ 100
๐๐๐๐๐ก๐๐ ๐๐๐๐ = 4,127,289 ๐ = ๐, ๐๐๐ ๐๐ ๐๐๐๐๐๐ ๐๐๐๐
Therefore, 4,127 kg of lactic acid is produced during the total ethanol production run
10. 8
v) Determining the energy requirements to maintain fermentation:
From the Husky Energy wheat and corn reaction formulas shown in Figure 1, each tonne of
fermented wheat produces about 0.31 GJ and each tonne of fermented corn produces about 0.34
GJ.
This ethanol production design calls for 1164.2 tonnes of corn and 61.3 tonnes of wheat. These
fermentations will produce the following amount of heat energy:
1164.2 ๐ก๐๐๐๐๐ ๐๐๐๐ โ 0.34
๐บ๐ฝ
๐ก๐๐๐๐
= 395.8 ๐บ๐ฝ ๐๐ ๐๐๐๐๐๐ฆ
61.3 ๐ก๐๐๐๐๐ ๐คโ๐๐๐ก โ 0.31
๐บ๐ฝ
๐ก๐๐๐๐
= 19.0 ๐บ๐ฝ ๐๐ ๐๐๐๐๐๐ฆ
Therefore, the total heat energy produced will be:
395.8 ๐บ๐ฝ + 19.0 ๐บ๐ฝ = ๐๐๐. ๐ ๐ฎ๐ฑ
Assuming steady state fermentation has been reached, then a total of 414.8 GJ of energy would
need to be removed from the fermenter to maintain the temperature at 30ยฐC.
B. Mixing Operation
*Note: This section was completed before the fermentation volume and number of runs were finalized,
therefore some values may not match
The mixing operation does not require the system to be scaled up since it is already done on the
industry scale.
It is assumed that the corn/wheat slurry will be highly viscous due to its particle content. Slurry
Viscosity, densities of corn and wheat must be known to determine Reynoldโs Number.
๐๐๐ โ % = 31.5% = % ๐๐๐๐๐๐ =
100 (๐ ๐ ๐๐ข๐๐๐ฆ โ ๐๐๐๐๐ข๐๐)๐ ๐๐๐๐ก๐๐๐๐
(๐ ๐๐๐๐ก๐๐๐๐ โ ๐๐๐๐๐ข๐๐) ๐ ๐ ๐๐ข๐๐๐ฆ
Water is used as liquid in this case that occupies same volume as slurry. Mass of slurry includes
water content.
๐ ๐ ๐๐ข๐๐๐ฆ = ๐ ๐๐๐๐ + ๐ ๐คโ๐๐๐ก = 1,164,200 ๐๐ + 61,300 ๐๐ = 1,225,500๐๐
(1,225,500๐๐ โ 171,900๐๐)๐ ๐๐๐๐ก๐๐๐๐
(๐ ๐๐๐๐ก๐๐๐๐ โ 1000๐๐/๐3) 1,225,500๐๐
= 0.315 ; ๐ ๐๐๐๐ก๐๐๐๐ = 578.26๐๐/๐3
11. 9
From Engineering Toolbox website, the particle density of corn (ground) is: ฯ = 561kg/m3
.
From Engineering Toolbox website, the particle density of wheat (ground) is: ฯ = 641kg/m3
.
It is expected that the density of the corn/wheat slurry will be somewhere between these two
numbers.
๐๐๐๐ข๐๐ ๐๐ ๐ท๐๐ฆ ๐๐๐ข๐๐๐ฆ ๐๐๐๐ก๐๐๐๐๐ = ๐๐๐๐ ๐ =
๐ ๐๐๐ฆ ๐ก๐๐ก๐๐
๐ ๐๐๐๐ก๐๐๐๐
=
298,632.2๐๐
578.26๐๐/๐3
= 516.43๐3
The volume of total innate water was previously calculated as 171.9m3
.
๐๐ =
๐๐๐๐ ๐
๐ ๐ค๐๐ก๐๐
=
516.43๐3
171.9m3
= 3.00 ๐คโ๐๐โ ๐๐ 300%
If Vp is greater than 10% (which was assumed to be the case) then the following equation is used
to find viscosity of slurry, ฮท.
From Engineering Toolbox website, the viscosity of water at 30o
C is: ฮทliquid = 0.798x10-3
Pas.
ฮท ๐ = ๐๐๐๐๐ก๐๐ฃ๐ ๐ฃ๐๐ ๐๐๐ ๐๐ก๐ฆ = 1 + 1.25๐๐ + 10.05๐๐
2
= 1 + 1.25(3) + 10.05(3)2
= 95.2 ๐๐๐ก๐๐
ฮท ๐ =
ฮท ๐ ๐๐ข๐๐๐ฆ
ฮท๐๐๐๐ข๐๐
= 95.2 =
ฮท ๐ ๐๐ข๐๐๐ฆ
0.798x10 โ 3Pas
; ฮท ๐ ๐๐ข๐๐๐ฆ = 0.0759 ๐๐๐ ๐๐ 75.9๐๐
Because the viscosity of slurry is not greater than 20Pas baffling is required (If viscosity would be
greater than 20Pas the liquid would be so thick that it can prevent vortexing by becoming a self-
baffled system due to large or large number of particles. In this case the system is still prone to
vortexing. Also, cells can get sheared from excess pressure and therefore Reynoldโs number should
be less than 300.
๐ ๐๐ฆ๐๐๐๐โฒ
๐ ๐๐ข๐๐๐๐ = ๐ ๐ =
๐๐ ๐๐ข๐๐๐ฆ โ ๐ โ ๐ท๐2
ฮท ๐ ๐๐ข๐๐๐ฆ
12. 10
From previous calculations, the total volume of slurry will be 516.43 + 171.9 = 688.33m3
.
688.33m3 is equivalent to 181,837.55 US gal; this value will be divided by 4 as it is assumed that
4 mixing containers will be needed for each fermentation reactor. Each mixer will be working on
45,459.4 US gal. It is assumed that because the fermentation process takes 2.29 runs during each
52-hour period, this mixing requirement will also be done in a 2.29 runs.
45,459.4
๐๐๐๐๐
๐๐๐ฅ๐๐
2.29 ๐๐ข๐๐
= 19,851.3 ๐๐๐๐๐/๐๐๐ฅ๐๐
On page 43 of textbook, Table 1 shows the next highest volume that will meet this US gal
requirement is a 20,000 US gal tank size which will have a standard impeller diameter size of 5ft.
Impeller diameter (Da) is therefore = 1.52m.
A medium agitation speed is favored as it is assumed that one (either pumping effect and shear
effect) should not be too high or too low. As discussed earlier shear effect cannot be high as this
will damage the cells. Normally when working with food mixing industry, Reynoldโs number
usually shows turbulent mixing conditions; this is to ensure even particle mixture. In the ethanol
production case, the mixing is done to evenly distribute heat across the mixture.
๐๐ ๐๐ข๐๐๐ฆ =
๐๐๐ก๐๐ ๐๐๐ ๐ ๐๐ ๐๐๐ข๐๐๐ฆ
๐๐๐ก๐๐ ๐๐๐๐ข๐๐ ๐๐ ๐๐๐ข๐๐๐ฆ
=
1,225,500๐๐
688.33๐3
= 1780.4๐๐
๐ ๐ =
๐๐ ๐๐ข๐๐๐ฆ โ ๐ โ ๐ท๐2
ฮท ๐ ๐๐ข๐๐๐ฆ
=
1780.4๐๐ โ ๐/60๐ ๐๐ โ (1.52๐)2
0.0759๐๐๐
= 903.25๐; ๐คโ๐๐๐ ๐ ๐๐ ๐๐ ๐๐๐
Tip Speed was also calculated along with Froude Number using the new Da value:
๐ฃ๐ก๐๐ = ๐(๐ท๐)๐ = ๐(5๐๐ก)๐ = 15.7๐ [
๐๐ก
๐๐๐
]
๐น๐ =
๐ท๐ ๐2
๐
=
(1.52) ๐2
9.81๐/๐ 2
= 0.155๐2
13. 11
Table 1 shows specific speed limits ranges for the 20,000 US gallon tank size: Low Speed
Conditions Example:
๐ ๐ = 903.25(๐) = 903.25 (32๐๐๐/60๐ ๐๐) = 481.7 (๐ฟ๐๐๐๐๐๐ ๐๐ฆ๐ ๐ก๐๐)
๐ฃ๐ก๐๐ = 15.7๐ = 15.7 (32๐๐๐) = 502.7 ๐๐ก/๐๐๐
๐น๐ = 0.155๐2
= 0.155(32๐๐๐/60๐ ๐๐)2
= 0.044
Regardless of Speed, all Re values, using Table 1 parameters, were greater than 300 which means
vortexing will occur and a baffled mixing tank will be needed. A baffled tank should not be used,
however, as this will create extra cleaning difficulties between runs. Also a baffled tank may
further create lysing of the cells.
Assuming having a Re number exactly 300 will start causing cell destruction from the shearing
force, Re was set to 200 to determine the impeller speed. The Impeller diameter will still be set to
1.52m as this is based on standard configuration of a tank.
๐ ๐ = 200 =
๐๐ ๐๐ข๐๐๐ฆ โ ๐ โ ๐ท๐2
ฮท ๐ ๐๐ข๐๐๐ฆ
=
1780.4 โ ๐/60๐ ๐๐ โ (1.52๐)2
0.0759๐๐๐
Impeller Speed (n) is therefore 2.22 rpm.
๐น๐ =
๐ท๐ ๐2
๐
=
(1.52) (
2.22
60๐ ๐๐
)2
9.81๐/๐ 2
= 0.00021
๐ฃ๐ก๐๐ = 15.7๐ = 15.7 (2.22๐๐๐) = 34.85 ๐๐ก/๐๐๐
Using this new Reynoldโs number on a charts found on page 48 in the textbook, the standard tank
condition is selected as it is believed to be the most likely scenario for industry scale. An unbaffled
tank vessel must be selected, but because of vortexing the Froude number will be used. 6-bladed
turbine is assumed. The power function (ฮธ) was found to be approximately 3.8.
ฮธ = 3.8 = Np =
๐
๐(๐/60)3 ๐ท๐5
=
๐
1780.4(2.22/60)31.525
=
๐
0.732
P =2.78x10-3
kW
1 hP = horsepower = 0.746kW
Power (P) = 3.73x10-3 hP (for standard configuration)
14. 12
C. Centrifugation Operation
*Note: This section was completed before the fermentation volume and number of runs were finalized,
therefore some values may not match
Given information:
- Removes 70% of water during centrifugation and separates solids into 2 fractions:
cake (insoluble 20%v/v), thin stillage (10%v/v).
- MCcake = 3.3kg/kg of dry basis
- MCthin stillage = 5.6kg/kg of dry basis (containing particle diameter of 0.2mm). This
corresponds to 5% total solids in thin stillage.
- Particle Density for liquid (thin stillage) is ฯp = 1200kg/m3
.
- Liquid Density is ฯ = 1040kg/m3
.
- Liquid Viscosity is ฮท = 1.0x10-3
Pas.
Goal is to determine the number of centrifuges needed to ensure a continuous production of
ethanol, which is to be controlled by the size of a single unit and its speed (i.e. all centrifuges must
have same parameters for each mixer). Some assumptions must first be considered, one of which
is the residence time is from t = 0 to t = tR, terminal settling velocity (vt) is reached when particles
move radially. Stokeโs Law must be satisfied.
๐ฃ๐ก =
๐2
๐(ฯ ๐ โ ๐)๐ท ๐
2
18ฮท
=
๐น๐(ฯ ๐ โ ๐)๐ท ๐
2
๐18ฮท
=
๐น๐(1200 โ 1040kg/m3
)0.00022
(
1,225,500๐๐
4
๐๐๐ฅ๐๐๐ )18(1.0x10โ3Pas)
= 1๐ฅ10โ9
๐น๐
An equation was found where Fc = kDn2
where k = 2ฯ2
/g. (Majekodunmi 2015). Speed ranges for
industrial scale centrifuges are typically between ranges of 1500 โ 3000rpm. For this case n value
will be set to 3000rpm.
Below is a link to TEMA Systems Inc. industrial centrifuge manufacturer which lists their
available sizes of centrifuges specializing in solid liquid separation. Assuming that industry scale
centrifuges are within the ranges listed, certain parameters will be taken from the link below such
as the length of the centrifuge (b) will equal to 3.2m and diameter of centrifuge (D) will be 1.4m.
http://www.tema.net/pdf/conturbex_cx2009.pdf
15. 13
๐น๐ = (
2๐2
๐
) ๐ท๐2
= (
2๐2
9.81๐
๐ 2
) (1.4๐)(3000๐๐๐)2
= 25,353๐๐; ๐ ๐๐ข๐ ๐ก ๐๐ ๐๐ ๐๐๐
๐ฃ๐ก = 1๐ฅ10โ9
๐น๐ = 1๐ฅ10โ9(7042.5) = 0.025๐/๐
Assuming that there will be at least 1 centrifuge after each mixer tank. V of slurry is 688.3m3
is
distributed among 4 mixers. The value b is the length of the centrifuge in meters. Assume A is
cross sectional area of the slurry being added to the centrifuge (not the cross sectional area of the
centrifuge which is ฯr2
, also assume that vt = v.
๐ = 172.075๐3
= ๐๐(๐2
2
โ ๐1
2) = ๐๐ด
๐ = ๐ฃ๐ด = ๐ฃ๐ก ๐ด = ๐(๐2
2
โ ๐1
2) ๐ฃ๐ก
๐
๐
= ๐ก ๐ =
๐๐ด
๐ฃ๐ด
=
๐
๐ฃ๐ก
=
3.2๐
0.025๐/๐
= ๐๐๐ ๐๐๐
There will be at least 1 centrifuge able to run a volume of 172.075m3
of slurry after each mixer
operation.
D. Evaporation Operation
The solution which leaves the fermenter is first distilled to remove the ethanol and then centrifuged
to separate the remaining portion into water, insoluble cake fraction and thin stillage. Only the thin
stillage passes through the evaporator to be concentrated. Therefore, the first task is to determine
how much solution is left once the ethanol is removed, the second task involves determining how
much thin stillage enters the evaporator.
1) Determining the amount of solution remaining after distillation:
As previously discussed, a total of 1,164,200 kg of corn and 61,300 kg of wheat is used to produce
500,000 L, or 500 m3
, of ethanol. From this, the volume entering the centrifuge can be determined
as:
16. 14
๐๐๐๐๐ก๐๐๐๐ข๐๐ = ๐๐ก๐๐ก๐๐ โ ๐๐๐กโ๐๐๐๐ = 5159.1 ๐3
โ 500 ๐3
= 4,659.1 ๐3
Where: Vcentrifuge = volume entering the centrifuge (m3
)
Vtotal = Total volume leaving fermenter (m3
)
Vethanol = volume of ethanol produced (m3
)
2) Determining the amount of thin stillage entering the evaporator:
The centrifugation process removes 70% of the incoming volume as water, 20% of the incoming
volume as insoluble cake fraction and 10% of the incoming volume as thin stillage. Using this, the
amount of thin stillage passing through the evaporator can be calculated as:
๐โ๐๐ ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐๐๐ก๐๐๐ =
๐๐กโ๐๐ ๐ ๐ก๐๐๐๐๐๐
๐๐๐๐๐ก๐๐๐๐ข๐๐
โ 100 = 10%
Where: Thin stillage percentage = the percentage of solution which is thin stillage, 10%
Vthin stillage = Volume of the thin stillage (m3
)
๐๐กโ๐๐ ๐ ๐ก๐๐๐๐๐๐ = 0.1 โ ๐๐๐๐๐ก๐๐๐๐ข๐๐ = 0.1 โ 4,659.1 ๐3
= 465.9 ๐3
Of the thin stillage, 5% is dry particles and 95% is liquid. Therefore, total density can be calculated
by:
๐๐ ๐ก๐๐๐๐๐๐ = 0.95 โ ๐ ๐๐๐๐ก๐๐๐๐ + 0.05 โ ๐๐๐๐๐ข๐๐ = 0.95 โ (1,200
๐๐
๐3
) + 0.05 โ (1,040
๐๐
๐3
) = 1,192
๐๐
๐3
Where: ฯstillage = density of the thin stillage (kg/m3
)
ฯparticle = particle density of the dry portion of the thin stillage (kg/m3
) โ from handout
ฯliquid = density of the liquid portion of the thin stillage (kg/m3
) โ from handout
Therefore, the total mass of thin stillage, mstillage, entering the evaporator can be calculated as:
๐ ๐ ๐ก๐๐๐๐๐๐ = ๐๐ ๐ก๐๐๐๐๐๐ โ ๐๐กโ๐๐ ๐ ๐ก๐๐๐๐๐๐ = 1192
๐๐
๐3
โ 465.9 ๐3
= 555,353 ๐๐ ๐กโ๐๐ ๐ ๐ก๐๐๐๐๐๐
i) Determining the amount of steam needed to maintain continuous production of ethanol:
It is assumed that the evaporator is running the entire length of the 4 fermentation runs, including
filling and emptying, therefore evaporation will occur over a total of 256 hours. Which means, to
maintain a continuous production of ethanol the evaporator feed rate can be calculated as:
๐ ๐ =
๐ ๐ ๐ก๐๐๐๐๐๐
๐ก๐๐ก๐๐ ๐๐ข๐ ๐ก๐๐๐
=
555,353 ๐๐
(256 โ๐๐ข๐๐ ) โ (3600
๐
โ
)
= 0.603
๐๐
๐
17. 15
Where: mf = incoming evaporator feed mass flow rate (kg/s)
mstillage = mass of thin stillage entering evaporator (kg)
total run time = total evaporator run time (hours)
Here are the known values for evaporation from the design handout:
๐ ๐ = 0.603
๐๐
๐
, ๐ฅ๐ = 0.05, ๐ฅ ๐ = 0.30, ๐ถ๐ ๐ = 4.2
๐๐ฝ
๐๐ โ ๐พ
, ๐ถ๐ ๐ = 3.9
๐๐ฝ
๐๐ โ ๐พ
, ๐๐
= 25 ยฐ๐ถ,
๐1 = 101.35 ๐๐๐, ๐ = 2500
๐
๐2 โ ๐พ
= 2.5
๐๐
๐2 โ ๐พ
, ๐๐๐๐๐๐๐๐๐๐ = ๐0
= 0 ยฐ๐ถ
Some other assumptions include that the incoming steam pressure is at 143.27 kPa, this way the
heat difference isnโt too large and wonโt cook/burn the product, and that the product boils at 100ยฐC
From the steam properties table, a pressure of 143.27 kPa gives:
๐๐ = 110 ยฐ๐ถ
Also, since the head space is at p1 = atmospheric pressure = 101.35 kPa then:
๐1 = 100 ยฐ๐ถ
Evaporator Calculations:
๐ ๐ โ ๐ฅ๐ = ๐ ๐ โ ๐ฅ ๐
๐ ๐ = ๐ ๐ โ
๐ฅ๐
๐ฅ ๐
= 0.603
๐๐
๐
โ
0.05
0.30
= 0.1005
๐๐
๐
๐ ๐ฃ = ๐ ๐ โ ๐ ๐ = 0.603
๐๐
๐
โ 0.1005
๐๐
๐
= 0.5025
๐๐
๐
๐ป๐ = ๐ถ๐ ๐ โ (๐๐ โ ๐0) = 4.2
๐๐ฝ
๐๐ โ ๐
โ (25 ยฐ๐ถ โ 0 ยฐ๐ถ) = 105
๐๐ฝ
๐๐
๐ป ๐ = ๐ถ๐ ๐ โ (๐1 โ ๐0) = 3.9
๐๐ฝ
๐๐ โ ๐
โ (100 ยฐ๐ถ โ 0 ยฐ๐ถ) = 390
๐๐ฝ
๐๐
๐ป๐ฃ = ๐ป๐@(100 ยฐ๐ถ โ 0 ยฐ๐ถ) = 2,676.1
๐๐ฝ
๐๐
Where: xf = feed solid concentration
mp = mass flow rate of concentrate leaving the evaporator (kg/s)
xp = concentrate solid concentration
mv = mass flow rate of vapor leaving the evaporator (kg/s)
Hf = enthalpy of feed (kJ/kg)
18. 16
Cpf = specific heat of feed (kJ/(kg*K))
Hp = enthalpy of concentrate (kJ/kg)
Cpp = specific heat of concentrate (kJ/(kg*K))
Hv = enthalpy of vapor (kJ/kg)
Hg = saturated vapor enthalpy (kJ/kg)
Tf = temperature of incoming feed (ยฐC)
T1 = temperature of concentrate and vapor leaving the evaporator (ยฐC)
T0 = reference temperature (ยฐC)
The incoming steam quality is assumed to be 1.0 and the outgoing steam quality is assumed to be
0.0, therefore, the steam enthalpy can be calculated as:
๐ป๐ = ๐ป๐@143.27 ๐๐๐ โ ๐ป๐@143.27 ๐๐๐ = 2,691.5
๐๐ฝ
๐๐
โ 461.3
๐๐ฝ
๐๐
= 2,230.2
๐๐ฝ
๐๐
Where: Hs = enthalpy of steam (kJ/kg)
Hf = liquid state enthalpy (kJ/kg)
Using the following heat balance equation, the steam mass flow rate can be calculated:
๐ ๐ โ ๐ป๐ + ๐ ๐ โ ๐ป๐ = ๐ ๐ โ ๐ป ๐ + ๐ ๐ฃ + ๐ป๐ฃ
Where: ms = steam mass flow rate (kg/s)
Therefore:
๐ ๐ =
๐ ๐ โ ๐ป ๐ + ๐ ๐ฃ โ ๐ป ๐ฃ โ ๐ ๐ โ ๐ป๐
๐ป๐
=
0.1005
๐๐
๐ โ 390
๐๐ฝ
๐๐
+ 0.5025
๐๐
๐ โ 2,676.1
๐๐ฝ
๐๐
โ 0.603
๐๐
๐ โ 105
๐๐ฝ
๐๐
2,230.2
๐๐ฝ
๐๐
= ๐. ๐๐๐
๐๐
๐
Since the evaporator would be running for 256 hours, the total amount of steam required would
be:
๐ ๐ ๐ก๐๐๐ = ๐ ๐ โ ๐ก ๐๐ข๐๐๐๐๐๐ = 0.592
๐๐
๐
โ 256 โ๐๐ข๐๐ โ 3600
๐
โ
= ๐๐๐, ๐๐๐ ๐๐ ๐๐ ๐๐๐๐๐
Therefore, to maintain a continuous production of ethanol a steam flow rate of 0.592 kg/s is
required over a span of 256 hours, this equals a total requirement of 545,587 kg of steam.
ii) Determining the size of the heat exchange area required:
To determine the size of the heat exchange area, the following energy balance equation will be
used:
19. 17
๐ = ๐ โ ๐ด โ (๐๐ โ ๐1) = ๐ ๐ โ ๐ป๐
Where: q = energy rate (J/s or W)
U = overall heat transfer coefficient (W/(m2
*K)
A = heat exchange area (m2
)
Ts = steam temperature (ยฐC)
๐ด =
๐ ๐ โ ๐ป๐
๐ โ (๐๐ โ ๐1)
=
0.592
๐๐
๐
โ 2,230.2
๐๐ฝ
๐๐
2.5
๐๐
๐2 โ ๐พ
โ (110 ยฐ๐ถ โ 100 ยฐ๐ถ)
= ๐๐. ๐ ๐ ๐
Therefore, to maintain a continuous production of ethanol an evaporator with a heat exchange area
size of 52.8 m2
is required.
E. Drying Operation
Two fractions are blended together and passed through the dryer, these are the concentrated thin
stillage coming from the evaporator and the insoluble cake fraction from the centrifuge. The ensure
continuous ethanol production, the drying process will take pace over 256 hours and will be
described over the next several steps. First, the total mass of concentrated thin stillage must be
calculated:
๐ ๐กโ๐๐ ๐๐๐๐ = ๐ ๐ โ ๐ก = 0.1005
๐๐
๐
โ 256 โ๐๐ข๐๐ โ 3600
๐
โ๐๐ข๐
= 92,621 ๐๐ ๐๐๐๐๐๐๐ก๐๐๐ก๐๐ ๐กโ๐๐ ๐ ๐ก๐๐๐๐๐๐
Where: mthin conc = mass of the concentrated thin stillage (kg)
mp = mass flow rate of the concentrated thin stillage (kg/s)
t = total running time (s)
Next, the moisture content of thin stillage needs to be calculated, the concentrated thin stillage has
70% liquid, assumed to be water, and 30% solids:
๐๐ถ๐กโ๐๐ =
๐ ๐กโ๐๐ ๐๐๐๐ ๐ป2๐
๐ ๐กโ๐๐ ๐๐๐๐ ๐๐๐ฆ
0.7 โ ๐ ๐กโ๐๐ ๐๐๐๐
0.3 โ ๐ ๐กโ๐๐ ๐๐๐๐
=
0.7 โ (92,621 ๐๐)
0.3 โ (92,621 ๐๐)
=
64,835 ๐๐ ๐ป2 ๐
27,786 ๐๐ ๐๐๐ฆ
= 2.33
๐๐โ20
๐๐ ๐๐๐ฆ
Where: MCthin = moisture content of the concentrated thin stillage (kg H2O/kg dry)
mthin conc H2O = mass flow rate of the concentrated thin stillage (kg/s)
mthin conc dry = mass flow rate of the concentrated thin stillage (kg/s)
Now, the total mass of insoluble cake fraction is calculated using pre-fermentation and post-
distillation mass balance:
20. 18
๐ ๐๐๐๐๐๐ ๐๐๐๐๐๐๐ก๐๐ก๐๐๐ = ๐ ๐๐๐ก๐๐ ๐๐๐ ๐ก๐๐๐๐๐ก๐๐๐
๐ ๐๐๐๐ + ๐ ๐คโ๐๐๐ก + ๐ ๐ป2๐ ๐๐๐๐๐ = ๐ ๐๐กโ๐๐๐๐ + ๐ ๐ป2๐ ๐๐๐๐๐ฃ๐๐ + ๐ ๐๐๐๐ + ๐ ๐กโ๐๐
๐ ๐๐๐๐ = ๐ ๐๐๐๐ + ๐ ๐คโ๐๐๐ก + ๐ ๐ป2๐ ๐๐๐๐๐ โ ๐ ๐ป2๐ ๐๐๐๐๐ฃ๐๐ โ ๐ ๐กโ๐๐ โ ๐ ๐๐กโ๐๐๐๐
๐ ๐๐๐๐ = ๐ ๐๐๐๐ + ๐ ๐คโ๐๐๐ก + ๐ ๐ป2๐ ๐๐๐๐๐ โ 0.7 โ ๐๐๐๐๐ก๐๐๐๐ข๐๐ โ ๐ ๐ป2๐ โ ๐ ๐ ๐ก๐๐๐๐๐๐ โ ๐๐๐กโ๐๐๐๐ โ ๐ ๐๐กโ๐๐๐๐
Where: mcorn = initial mass of corn (kg)
mwheat = initial mass of wheat (kg)
mH2O added = mass of H2O added to the fermenter (kg)
mcake = mass of insoluble cake fraction entering dryer (kg)
Vcentrifuge = volume entering centrifuge (m3
)
ฯH2O = density of water (kg/m3
)
mstillage = mass of thin stillage in the centrifuge (kg)
Vethanol = volume of ethanol removed by distillation (m3
)
ฯethanol = density of ethanol (kg/m3
) โ from online data sheet
๐ ๐๐๐๐ = 1,164,200 ๐๐ + 61,300 ๐๐ + 3,120,700 ๐๐ โ 0.7(4659.1๐3) โ (1000
๐๐
๐3
)
โ 555,353 ๐๐ โ (500๐3) โ (790
๐๐
๐3
)
๐ ๐๐๐๐ = 489,977 ๐๐
The water content of the insoluble cake fraction can now be calculated by using the given moisture
content of 3.3 kg H2O/kg dry:
3.3
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ
=
๐ ๐๐๐๐ โ20
๐ ๐๐๐๐ โ ๐ ๐๐๐๐ โ20
=
๐ ๐๐๐๐ โ20
489,977 ๐๐ โ ๐ ๐๐๐๐ โ20
,
๐ ๐๐๐๐ โ20 = 376,029 ๐๐ ๐ป2 ๐
๐ ๐๐๐๐ ๐๐๐ฆ = ๐ ๐๐๐๐ โ ๐ ๐๐๐๐ โ20 = 489,977 ๐๐ โ 376,029 ๐๐ = 113,948 ๐๐ ๐๐๐ฆ
Where: mcake H2O = mass of water in the cake fraction (kg)
mcake dry = mass of dry portion of cake fraction (kg)
1) Now that the cake and concentrated thin stillage components have been calculated the moisture
content of the blended product can be determined:
๐ ๐ป2๐ = ๐ ๐๐๐๐ ๐ป2๐ + ๐ ๐กโ๐๐ ๐๐๐๐ ๐ป2๐ = 376,029 ๐๐ + 64,835 ๐๐ = 440,864 ๐๐ ๐ป2 ๐
๐ ๐๐๐ฆ = ๐ ๐๐๐๐ ๐๐๐ฆ + ๐ ๐กโ๐๐ ๐๐๐๐ ๐๐๐ฆ = 113,948 ๐๐ + 27,786 ๐๐ = 141,734 ๐๐ ๐๐๐ฆ
๐๐ถ๐๐ =
๐ ๐ป2๐
๐ ๐๐๐ฆ
=
440,864 ๐๐
141,734 ๐๐
= ๐. ๐๐
๐๐ ๐ฏ ๐ ๐ถ
๐๐ ๐ ๐๐
21. 19
Where: MCin = moisture content of product entering dryer (kg H2O/kg dry)
mH2O = mass of water entering the dryer (kg)
mdry = mass of dry product entering the dryer (kg)
2) Since the final product leaves the dryer at a moisture content, MCout, of 0.08 kg H2O/kg dry, the
amount of moisture removed during drying can be calculated as:
๐๐๐๐ ๐ก๐ข๐๐ ๐ ๐๐๐๐ฃ๐๐ = ๐๐ถ๐๐ โ ๐๐ถ ๐๐ข๐ก = 3.11
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ
โ 0.08
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ
= ๐. ๐๐
๐๐ ๐ฏ ๐ ๐ถ
๐๐ ๐ ๐๐
3) The specific humidity of the air entering the dryer, Hin, can be determined using the
psychrometric chart:
From psychrometric chart, the specific moisture of air entering at 20ยฐC and 80% relative humidity
is:
๐ฏ๐๐ = ๐. ๐๐๐๐
๐๐ ๐ฏ ๐ ๐ถ
๐๐ ๐ ๐๐ ๐๐๐
4) The specific humidity of the air leaving the dryer can be determined using the equation provided
in the project handout:
๐ป ๐๐ข๐ก =
0.622 โ ๐๐ฃ
๐ โ ๐๐ฃ
=
0.622 โ (26.1 ๐๐๐)
101.35 ๐๐๐ โ 26.1 ๐๐๐
= ๐. ๐๐๐
๐๐ ๐ฏ ๐ ๐ถ
๐๐ ๐ ๐๐ ๐๐๐
Where: Hout = specific humidity of the air leaving the dryer (kg H2O/ kg dry air)
Pv = vapor partial pressure (kPa) โ in this case 26.1 kPa
P = total pressure (kPa) โ atmospheric pressure
5) The amount of specific humidity which can be removed by the dryer, Hremoved, is the difference
between Hout and Hin:
๐ป๐๐๐๐๐ฃ๐๐ = ๐ป ๐๐ข๐ก โ ๐ป๐๐ = 0.216
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ ๐๐๐
โ 0.0119
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ ๐๐๐
= ๐. ๐๐๐๐
๐๐ ๐ฏ ๐ ๐ถ
๐๐ ๐ ๐๐ ๐๐๐
6) The total amount of water to be removed, H2Oout, by the dryer can de determined as:
๐ป2 ๐ ๐๐ข๐ก = ๐๐๐๐ ๐ก๐ข๐๐ ๐ ๐๐๐๐ฃ๐๐ โ ๐ ๐๐๐ฆ = 3.03
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ
โ 141,734 ๐๐ ๐๐๐ฆ
= ๐๐๐, ๐๐๐ ๐๐ ๐ฏ ๐ ๐ถ
At a density of 1000 kg/m3
this represents: 429.5 ๐3
๐ป2 ๐
7) The cross section of the rotary drum, A, can be determined using its diameter, D:
๐ด = ๐ โ
๐ท2
4
= ๐ โ
(1.5 ๐)2
4
= ๐. ๐๐ ๐ ๐
22. 20
8) The required dry air flow rate, G, can now be calculated, but first the amount of dry air required
must be calculated:
๐ ๐๐๐ฆ ๐๐๐ =
๐ ๐ป2๐
๐ป๐๐๐๐๐ฃ๐๐
=
440,864 ๐๐ ๐ป2 ๐
0.2041
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ ๐๐๐
= 2,160,039 ๐๐ ๐๐๐ฆ ๐๐๐
Where: mdry air = mass of dry air required to properly dry the product (kg dry air)
Dividing the calculated amount of dry air required by the total run time provides the required dry
air flow rate, G:
๐บ =
๐ ๐๐๐ฆ ๐๐๐
๐ก๐ก๐๐ก๐๐
=
2,160,039 ๐๐ ๐๐๐ฆ ๐๐๐
256 โ๐๐ข๐๐
= ๐, ๐๐๐
๐๐ ๐ ๐๐ ๐๐๐
๐๐๐๐
9) The residence time, ฯ, in the rotary dryer should now be calculated, but first the dry product
flow rate, F, must be determined:
๐น =
๐ ๐๐๐ฆ
๐ก๐ก๐๐ก๐๐
=
141,734 ๐๐ ๐๐๐ฆ
256 โ๐๐ข๐๐
= 553.6
๐๐ ๐๐๐ฆ ๐๐๐๐๐ข๐๐ก
โ๐๐ข๐
To determine the dryer residence a drum rotation speed, rpm, is required. For this scenario, a speed
of 3 rpm has been chosen. This is a slow speed which should allow for consistent drying. The
residence time, ฯ, can now be calculated for concurrent flow:
๐ =
0.23 โ ๐ฟ
๐ท โ ๐0.9 โ ๐ก๐๐๐ผ
โ
๐ฟ โ ๐บ
102 โ โ ๐ ๐ โ ๐น
๐ =
0.23 โ (10 ๐)
(1.5 ๐) โ (3 ๐๐๐)0.9 โ tan(1ยฐ)
โ
(10 ๐) โ 8,438
๐๐ ๐๐๐ฆ ๐๐๐
โ๐๐ข๐
102 โ โ0.003 ๐ โ 553.6
๐๐ ๐๐๐ฆ ๐๐๐๐๐ข๐๐ก
โ๐๐ข๐
= ๐. ๐๐ ๐๐๐๐
Where: ฯ = residence time (minutes)
L = length of dryer (m) โ given as 10 m
D = diameter of dryer (m) โ given as 1.5 m
n = speed of dryer rotation (rpm) โ assumed to be 3 rpm
ฮฑ = angle of dryer (degrees) โ given as 1ยฐ
G = dry air flow rate (kg dry air/hour) โ previously calculated
F = dry product flow rate (kg dry product/hour) โ previously calculated
dp = equivalent diameter of spent grain particle โ assumed to be 3mm from sample in lab
10) Finally, the volumetric load and hold up of product in the dryer can be calculated based on the
previously obtained data. The volumetric load will be calculated first:
23. 21
๐๐ = ๐ ๐ โ
๐
๐ ๐
=
๐ ๐๐๐๐ + ๐ ๐กโ๐๐ ๐๐๐๐
๐ก๐ก๐๐ก๐๐
โ
๐
๐ ๐
=
489,977 ๐๐ + 92,621 ๐๐
256 โ๐๐ข๐๐
โ
4.85 ๐๐๐๐ข๐ก๐๐ โ (
โ๐๐ข๐
60 ๐๐๐
)
1200 ๐๐/๐3
๐ฝ ๐ = ๐. ๐๐๐ ๐ ๐
Where: Vp = volumetric load of product in dryer (m3
)
mp = mass flow rate of product (kg wet/hour)
ฯp = particle density of product (kg/m3
) โ given as 1200 kg/m3
The hold up of product in the dryer can now be calculated, but first the total drum volume, Vdrum,
is required:
๐๐๐๐ข๐ = ๐ด โ ๐ฟ = 1.77 ๐2
โ 10 ๐ = 17.7 ๐3
Finally, the product hold up, HU:
๐ป๐ =
๐๐
๐๐๐๐ข๐
=
0.153 ๐3
17.7 ๐3
= ๐. ๐๐๐๐
Now that the dryer steps have all been completed, the dryer requirements of drying air volumetric
flow rate and energy used by the drum dryer can be determined.
i) To begin, the volumetric flow rate will be determined by using the previously calculated dry air
flow rate using the following equation:
๐บ =
๐๐๐๐ก โ ๐
1 + ๐ป
Where: Vdot = drying air volumetric flow rate (m3
/s)
ฯ = density of air at 550ยฐC (kg/m3
) - found to be 0.4271 kg/m3
on engineering toolbox
H = specific humidity of air (kg H2O/ kg dry air) โ calculated 0.0119 kg H2O/ kg dry air
Therefore:
๐๐๐๐ก = ๐บ โ
1 + ๐ป
๐
= 8,438
๐๐ ๐๐๐ฆ ๐๐๐
โ๐๐ข๐
โ
1 + 0.0119
๐๐ ๐ป2 ๐
๐๐ ๐๐๐ฆ ๐๐๐
0.4271
๐๐
๐3
= ๐๐, ๐๐๐
๐ ๐
๐
This volumetric flow rate can be converted to an air velocity, Vair, by dividing the drum cross
section area:
24. 22
๐๐๐๐ =
๐๐๐๐ก
๐ด
=
19,992
๐3
โ
โ
โ
3600๐
1.77๐2
= ๐. ๐
๐
๐
Therefore, to dry the spent grain produced in a continuous ethanol production system to the above
given conditions the required volumetric flow rate of the drying air would need to be 19,992 m3
/h
which converts to an air velocity of 2.9 m/s. Though it was suggested that the air velocity be in the
range of 1.5 to 2.5 m/s, the velocity of 2.9 m/s is close enough to this range to be acceptable.
ii) Finally, the energy required to by the drum dryer to dry the spent grain can be calculated by
using the following energy equation:
๐ = ๐บ โ ๐ถ๐ ๐๐๐ โ (๐๐๐ โ ๐๐๐ข๐ก)
Where: Q = Energy rate (J/s or W)
Cpair = specific heat of air (kJ/(kg*K)) โ 1.105 kJ/(kg*K) at 550ยฐC engineering toolbox
Tin = Temperature of incoming air (ยฐC) โ given to be 550ยฐC
Tout = Temperature of outgoing air (ยฐC) โ given to be 120ยฐC
Therefore:
๐ = ๐บ โ ๐ถ๐ ๐๐๐ โ (๐๐๐ โ ๐๐๐ข๐ก) = 8,438
๐๐ ๐๐๐ฆ ๐๐๐
โ๐๐ข๐
โ 1.105
๐๐ฝ
๐๐ โ ๐พ
โ (550ยฐ๐ถ โ 120ยฐ๐ถ)
= 4,009,316
๐๐ฝ
โ๐
= 1114
๐๐ฝ
๐
= 1114 ๐๐ = ๐. ๐๐๐ ๐ด๐พ = ๐. ๐๐๐๐
๐ด๐ฑ
๐
This value will now be converted to joules required over a 256 hour runtime:
๐ธ๐๐๐๐๐ฆ = ๐ โ ๐ก = 1.114
๐๐ฝ
๐
โ 256 โ๐๐ข๐๐ โ 3600
๐
โ
= 1,026,662 ๐๐ฝ = ๐๐๐๐. ๐ ๐ฎ๐ฑ
Therefore, to dry the spent grain produced in a continuous ethanol production system to the above
given condition a total of 1.114 MW of power is required, over a 256 hour run time this translates
to 1026.7 GJ of energy required.
3 Conclusion
Large scale ethanol production is a complex and involved task, from a cost perspective, a time
perspective and an energy perspective. During the production of 500,000 litres of ethanol from a
95% corn and 5% wheat the fermentation process alone requires 256 hours to complete, this
includes four fermenter runs of 52 hours each and four emptying, cleaning and filling cycles of 12
hours each. To minimize down time the ethanol production line, all downstream processes are
designed to run concurrently with the fermentation process, but when a new production run is
25. 23
started there is some lag while the first batch undergoes fermentation and then passes through the
subsequent steps. Taking two of the longest processes into account, the evaporation and the drying,
adds a production lag equal to two complete fermentation runs, or 128 hours. The total ethanol
production time is now up to 384 hours, which comes out to 16 days. This production time doesnโt
consider other processes, such as distillation or centrifugation, neither does it factor any time losses
during the transition between processes or due to mechanical failure. A production time of at least
20 days is a safer assumption for the total production time of 500,000 litres of ethanol from a 95%
corn and 5% wheat blend.
The amount of material required to produce 500,000 litres of ethanol is quite substantial. Using a
95% corn and 5% wheat blend requires 1,164,200 kg of corn and 61,300 kg of wheat, a further
3,120,700 kg of water is also added to the fermenter to create adequate fermentation conditions.
Some enzymes and yeast are also required, but their mass is negligible compared to the other
components. This means that a total of 4,346,200 kg of matter is used in the production of the
ethanol. The 500,000 litres of produced ethanol only weighs about 395,000 kg, which means the
production of ethanol in the given condition requires approximately 11 times more initial matter
than amount of ethanol produced, this is a very large ratio. All this extra mass is taken up by the
production of by-products, such as 42,304 kg of glycerol, 4,127 kg of lactic acid, approximately
3,261,400 kg of water, 489,977 kg on insoluble cake fraction and 555,353 kg of thin stillage, as
well as some CO2. The thin stillage and cake fraction are further processed to produce distillers
dried grain.
The production of ethanol was also evaluated from a perspective of energy requirement, though
only the fermentation, mixing, and drying operations were examined. The fermentation process
creates an excess 414.8 gigajoules of heat energy, this heats needs to be dispersed to ensure a stable
fermentation and maximize the yield. The mixing operation requires 746 Watts of power, which
over the 208 hours of active fermentation corresponds to 559 megajoules of energy. The drying
process was determined to require 1.114 megawatts of power, which over a continuous operational
cycle of 256 hours corresponds to 1026.7 gigajoules of energy. Therefore, just these three
processes require 1442.1 gigajoules of energy, which doesnโt factor in any of the other processes,
nor any energy losses throughout the production. The actual energy requirement to produce
500,000 litres of ethanol from a 95% corn and 5% wheat mixture would be much higher than this
calculated amount.
To determine the design parameters of the ethanol production process several assumptions needed
to be made. In all these cases, assumptions were made which kept the process simple and which
could be supported which factual reasoning. These assumptions will be briefly listed and analysed.
The moisture content of the wheat was assumed to be 14.5% wet basis, which was found on
Ontario ministry of agriculture, food and rural affairs website. The initial fermenter volume and
final fermenter volume were assumed to be equal, this was chosen because it was unsure of
whether the produced CO2 was dispersed in the fermentation liquid or it escaped as gas, also the
density of the distillers spent grain would need to be calculated to determine the volume it
26. 24
occupies. Since these factors over-complicated the design they were omitted and the fermentation
volume was left constant. It was also assumed that the fermentation reaction was completely
successful, in other words all possible starch was converted to ethanol and its by-products, this
was also done to simplify the design, though in real life conditions these reactions are never 100%
perfect. For the mixing operation, the Reynoldโs number was pre-set to 200, this number was
chosen since it would prevent vortexing in the fermenter and therefore baffles can be omitted.
Baffles were purposely omitted since they add cleaning complexities. By assuming the Reynoldโs
number the speed of the impeller was determined. The centrifuge was assumed to be similar to a
standard industry scale centrifuge, this assumption provided the length and diameter of the
centrifuge, which was required in further calculations. During the operation process, the steam
used in the heat exchanger was assumed to have a pressure of 143.27kPa, which corresponds to a
temperature of 110ยฐC, this temperature was chosen since is low enough to prevent burning of the
incoming feed. Finally, two assumptions were made for the drying process. The first assumption
was in regards to the equivalent diameter of the solid particles entering the dryer. The particles
were assumed to have a diameter of 3 mm, which is approximately the diameter of the distillers
spent grain provided in Dr. Cenkowskiโs lab. The second dryer assumption involved the rotational
speed of the dryer. A speed of 3 rpm was chosen, this slow speed allows for consistent drying
conditions.
From all these factors, specific design parameters for the ethanol production were determined. The
mixing operation was found to require a 1.52 m diameter impeller with a power usage of 746
Watts. The centrifugation operation was found to be simplest if one centrifuge was available for
each fermenter, therefore, four centrifuges are required in this design. The evaporation process
requires a total of 545,587 kg of steam to properly concentrate the thin stillage, this heat exchange
occurs over a 52.8 m2
area. Lastly, the required volumetric airflow required during the drying of
the distillers spent grain was determined to be 19,992 m3
/h, this entire drying process requires
1026.7 gigajoules of energy. Throughout this design, simplifying assumption were made and
several processes were overlooked, which adds a level of uncertainty to the calculated parameters
of this ethanol production process design. That being said, this design is successful in
demonstrating the way in which each process affects the other processes, exposing the complexity
of the ethanol production process. For these reasons, this design could be used as a starting point
for designing an ethanol production process, but the steps should be reviewed by a qualified
professional and the calculations should be reworked as concrete decisions are made on assumed
values.
27. 25
4 References
Engineering Toolbox. 2016. Air Properties. http://www.engineeringtoolbox.com/air-properties-
d_156.html (2016/11/29).
Majekodunmi, S.O. 2015. A Review on Centrifugation in the Pharmaceutical Industry, American Journal
of Biomedical Engineering, 5(2): 67-78.
Ontario Ministry of Agriculture, Food and Rural Affairs. 2009. Cereal: Drying and Storing Wheat.
http://www.omafra.gov.on.ca/english/crops/pub811/4drying.htm (2016/11/29).