Progress on the generic
approach for modelling
production processes
covered in BREW
Morna Isaac, Martin Patel
The aim: Analysis of the manufacturing process of products
for which only basic data are available
Relevancy: Products in an early stage of development
and/or with data limitations due to competitive
sensitivity
Methodology: Available data are used to develop generic
elements of processes.
Focus: Energy use, as a first indication of environmental
impact, and costs
The main stages of a process:
1.
2.
3.
4.
Feedstock treatment (activation):
Biological conversion
Product separation
Waste treatment and utilities
Fermentation:
Theoretical
vs.
achieved Gluconic acid
Glycerol
yields
Sorbitol
Acetic acid
Lactic acid
Lactic acid
Citric acid
Citric acid
Citric acid
Propylene glycol
Itaconic acid, Pfizer
Itaconic acid, Von Fries
Lysine
cis, cis muconate
Ethanol, Z mobilis
Ethanol, batch
Ethanol, cellulose, BCI
Butanediol
Dehydroshikimic acid
P(3HB)
Theoretical yield Actual yield Actual yield
wt% of glucose
109%
102%
101%
100%
100%
100%
75%
106%
142%
84%
76%
76%
70%
54%
51%
51%
51%
50%
48%
48%
wt% of
glucose
% of theory
87%
77%
96%
90%
95%
91%
68%
90-100%
80%
75%
95%
90%
95%
91%
90%
85-94%
55%
47%
60-65%
42%
24%
48%
46-48%
46%
30%, 45%
27%
30-40%
65%
62%
85%
60%
44%
94%
90-95%
90%
60%, 90%
56%
63-83%
Productivity
and
yield of
fermentation
Product
L-lactic acid
Lactic acid (as sodium
lactate)
PDO
Succinic acid (as sodium
succinate)
Representative best practice
(yield of ethanol)
Ethanol (lignocellulose)
PHA
PHA (Case 9)
PHA (Case 2)
L-lysine
L-lysine
Glutamic acid (ammonium
glutamate monohydrate)
Itaconic acid
Citric acid (submerged)
Hypothetical bacterial
control agent
Gluconic acid (as sodium
gluconate)
alpha amylase
Porcine growth hormone
Penicillin G,
Cellulase
Immobilized cells for
acrylamide production
Recombinant intracellular
protein
Productivity Conc.
[kg/(m3*h)] [kg/m3]
Yield
[wt/wt%]
10
42
95%
5
6
120
100
95%
48%
2.5
1.92
95
115
100%
46%
1.38
50
47%
3.13
5
1.6
1.67
0.36
150
150
80
100
30%
37%
70%
40%
32%
1.36
1.06
0.69-0.75
0.39
56%
55%
87-92%
62
0.25
87%
103%
0.28
0.22
0.15
0.13
20
3.99
30
20%
4%
11%
33%
0.04
5
26%
0.03
0.8
1%
Estimating the critical aqueous conc.
When the product of a reaction is toxic, the
concentration beyond which the reaction stops or
Becomes too slow (Caqcrit) may be estimated using a
correlation with the aqueous solubility (saq):
aq
crit
log c
 0.79 log saq  0.74
(Straathof, 2003)
Theoretical energy consumption of
fermenters

Sterilization: for direct steam injection the mass of steam needed is:
Fs 




M mediumC p DT
DH vap  C p (Tsteam  Tster. )
If Cp=4.2 kJ/kg/ºC, initial medium temp. is 25ºC, sterilization temp. is
121ºC, steam temp. is 130ºC and DHvap=2180 kJ/kg,
the steam required is 0.2 kg steam/l medium.
Agitation and aeration: Can be in the range 1-10 kW/m3, usually 15 kW/m3. Larger fermenters have lower energy demands.
Aeration: 0.5-2vvm. For compressed air at 4 bar using 17 kJ/m3 this
consumes up to 0.6 kW/m3.
Agitation only (anaerobic processes): 1-3 kW/m3
Cooling: Heat production in microbial growth is 420-500 kJ/mol O2
consumed. Typically in fermenters OTR is 40-60 mol O2/m3/hr,
resulting in heat production of 5-8 kW/m3.
Theoretical energy consumption of
fermenters


Steam for sterilization: 0.135 kg steam/kg substrate
(converted to energy using 2.8 MJ/kg steam)
Electricity:
kWh/kg
substrate
Agitation
Aeration
Cooling
Total

Aerobic Anaerobic
0.096
0.096
0.381
0
0.228
0.046
0.705
0.142
Energy consumption for specific cases calculated
using yield and productivity figures for each case
(Lynd and Wang, 2003)
Energy consumption in fermentation
Anaerobic
AVG
Aerobic
STDEV
AVG
STDEV
Productivity
[kg/(m3*h)]
4.98
3.01
2.05
1.23
Heat [MJ/kg]
0.38
0.13
2.87
3.13
0.53
0.21
0.70
0.31
2.68
2.33
3.85
1.88
Theoretical
heat [MJ/m3.h]
2.46
1.55
1.55
1.42
Elect. [MJ/kg]
0.29
0.23
16.87
8.50
0.71
0.28
4.70
2.07
1.25
0.95
34.19
19.66
3.32
2.09
10.38
9.52
Theoretical
heat [MJ/kg]
Heat
[MJ/(m3.h)]
Theoretical
elect. [MJ/kg]
Elect.
[MJ/(m3.h)]
Theoretical
elect.
[MJ/m3.h]
Energy consumption in fermentation





Energy consumption per kg product and energy consumption
per fermentor volume and residence time both vary widely
between the different case studies.
The variation in these values is not due to differences in the
type of equipment between the cases.
In comparing calculated values based on generic energy
consumption as given in Lynd and Wang (2003) to energy
consumption of detailed designs, the calculated values for
aerobic processes are about three times too low.
In comparing the values for anaerobic processes, the
calculated steam use is close to the modelled use, but
electricity use is about double the modelled values.
Energy consumption for PHA production given in Akiyama et
al. (2003) is relatively high. This might be due to the
simulation program used to produce those values, SuperPro
designer.
Ethanol from corn stover:
electricity consumption
Comparison of two different simulations of the same
process design:
Battery
Electricity limits Section Section Section
(kW)
Total
100
200
300
NREL
model
5932
3200
1693
1038
SRI model
3708
981
2311
416
Difference
-37%
-69%
36%
-60%
Recovery


Biomass separation: Centrifugation, filtration, membranes
Product concentration
–
–
–
–
–
–
–
–


Distillation (ethanol)
Extraction (citric acid, lactic acid, acetic acid)
Precipitation (citric acid, lactic acid)
Direct crystallization/evaporation (gluconic acid, itaconic acid,
PDO)
Ion exchange (lysine)
Electrodialysis (succinic acid)
Adsorption
Ultrafiltration
Polishing: activated carbon, ion exchange, pH adjustment
Final purification: evaporation, crystallization, drying
A lot of research is being done on simultaneous
fermentation and separation.
Fermentation
product
Ethan Citric
ol
acid
Lactic Acetic Citric
acid
acid
acid
(extraction)
(extraction)
Lactic LSuccin Citric
acid
lysine ic acid acid
HCl
(conventional)
(conventional)
(ED)
PDO
Gluco Itaconi
nic
c acid
acid
Process step
Solid-liquid
separation
Evaporation
Liquid-liquid
extraction
Distillation
Precipitation
Acidification
Solid-liquid
separation
Ion exchange
Activated
carbon, pH
Electrodialysis
Evaporation
Crystallization
Drying
Distillation
Energy consumption of separation
operations
Operation
Rotary vacuum filter (Mycelium)
Centrifugation
(Yeast)
(Bacteria
Microfiltration
(Bacteria)
(Yeast)
(Mycelium)
Ultrafiltration
Nanofiltration
ED
Tower dryer
Units
MJe/m3
MJe/m3
MJe/m3
MJe/m3
MJe/m3
MJe/m3
MJe/m3 permeate
MJe/m3 permeate
MJe/m3
MJe/m3 removed
Crystallization
MJe/MJ transferred
(Cooling)
Evaporation
Distillation, spray drying
Value
Source
8.64
1
5.04
1
22.32
1
5.76
1
4.32
1
9.36
1
18
2
3.6
3
540
3
360
4
1.08
3
MJ steam/m3 water evaporated
800-2500
MJ steam/m3 water evaporated
5600
5
6
Waste treatment
Biomass waste: currently treated by inactivation,
heating to 80ºC for 30-60 min (Degussa).
It is then used as fertilizer.
Will this continue to be an acceptable approach in
future?
• The amount of waste produced by a growing
biotech. industry might be too large for this
approach to be feasible.
• Legislation might limit the possibilities.
In this case, the waste will have to be digested or
combusted.
Wastewater: wastewater treatment is dealt with in the
BREWtool.
SuperPro Designer




Process simulator specific to biochemical processes.
Includes unit operations specific to bioprocessing, and batch
as well as continuous processes.
Energy use of unit operations could be extracted from the
simulator for use in the generic approach.
Some process designs could be modelled and the results
used as a check for the results of the simplified generic
approach.
Costs




Investment costs for a set of representative
fermentation+recovery schemes will be estimated in
cooperation with DSM using their functional unit
method.
With this method an estimate of the investment
costs for a complete process is possible without
performing detailed process design.
The estimate is based on a specific mass balance.
The recovery schemes presented earlier will be
used for this.