Upload
others
View
10
Download
0
Embed Size (px)
Citation preview
Process integration studies on Kraft pulp
mill biorefineries producing ethanol Rickard Fornell 1,2
Thore Berntsson 1, Anders Åsblad 3 1 Heat and Power Technology, Chalmers University of Technology
2 SP Technical Research Institute of Sweden 3 CIT Industriell Energi AB
Introduction
Different biorefinery concepts connected to kraft pulp mills have been studied in this project. Three different process
combinations have been assessed; a repurposed kraft pulp mill to ethanol and electricity or lignin production, a
repurposed kraft pulp mill to ethanol and DME production, and finally co-locating an ethanol plant with a state-of-the-art
kraft pulp mill. The focus of the project has been on finding opportunities for improving energy efficiency by means of
heat integration of different parts of the processes, and then to assess the economics of the different concepts.
Results and Conclusions
Methodology
Computer simulations of all processes have been used for extraction of stream
data used in a pinch analysis (WinGEMS, Aspen Plus, OptiVap).
Several different pinch methods have been used in the project, e.g. GCC and
Composite Curves, Advanced Composite Curves, Split GCCs, TSA.
Techno-economic analyses of the different alternatives has been performed
using Aspen IPE, Vendor quotations, and reference literature.
Acknowledgements
The work presented here has been funded by the Swedish Energy Agency and Chalmers
Energy Initiative. The work has been carried out in collaboration with Innventia.
Repurposing unprofitable pulp mills
in traditionally strong pulping countries
(Scandinavian example)
Ethanol production co-located with
state-of-the-art mills (Brazilian example)
460
500
540
580
620
660
700
Turbines Lignin
€/m
3 E
tOH
New turb/lign HEN + turb/lign
HI + turb/lign HP + turb/lign
Base case production cost 635 €/m3 EtOH
31 €/m3
84
€/m
3
0
200
400
600
800
0 200 400 600 800
EtO
H p
rod
co
st
[€/m
3]
DME price [€/m3]
EtOH production cost interval
for the repurposed mill
Base-case in
EtOH-DME
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 1.0 2.0 3.0 4.0 5.0 6.0
∆ R
eve
nu
e [
M€
/yr]
∆Investment [M€]
The energy inputs and outputs for the different studied
processes are shown in the figure below. In the repurposed pulp mill
investing in larger turbines or lignin extraction in order to make use of
excess steam can improve the energy balance, but improved heat
integration (reducing steam demand with ~35%) combined with new
turbines/lignin almost doubles the output of electricity or lignin. If DME
and ethanol are produced, the steam demand will be low but the
electricity demand high. The conversion efficiency to biofuels will be high
(>65%). An ethanol plant co-located with a large pulp mill gives
opportunities to reduce steam demand to a very low level (approx. 50%
lower than the best case for the stand-alone ethanol plant).
The profitability of producing ethanol in a
repurposed, typical Scandinavian, kraft pulp
mill can be improved by implementing heat integration
measures. For the studied mill, where 120 000 m3 of
ethanol is produced, the increase in annual earnings
compared to a case where only minimum number of
investments are made is approximately 10M€/yr.
Producing both DME and ethanol has the potential of
high profitability. The results are however very sensitive to
the price of the products. The large amounts of fairly pure
CO2 (~400ktonnes CO2/yr) leaving this type of biorefinery
also makes for an interesting alternative if CCS is
implemented. A high value for CO2 would improve the
profitability of the concept considerably.
Finally, if an ethanol plant is co-located with a state-
of-the-art kraft pulp mill, further improvements can be
made compared to the best process design in the repurposed
mill. Several different alternatives with low PBP have been
found, mainly connected to innovative heat integration of
evaporation plants, and redesign of the hot and warm water
system in the pulp mill in order to increase and make use of
available excess heat.
A 120 000m3/yr ethanol plant and a 1 400 000ADt/yr
hardwood kraft pulp mill.
Process integration => Cooking chemicals, hot and cold
utilities, waste water treatment.
A 120 000m3/yr ethanol plant from a 326 600ADt/yr, old
and inefficient, softwood kraft pulp mill.
Alt 1) Improved energy efficiency by investing in a
condensing turbine, new back-pressure turbines, or a
lignin separation unit, and increased heat integration.
Alt 2) Improving conversion efficiency by investing in a
thermochemical process for DME production (replacing
the recovery boiler), in combination with ethanol
production.
Process integration => Hot and cold utilities. DME process
is a heat source, Ethanol process is a heat sink.
-40 -30 -20 -10 0 10 20 30 40 50 60
Heat integrated
Original
Heat integrated
Heat integrated and Lignin
Heat integrated and Electricity
Lignin
Electricity
No investments
Energy inputs and outputs (MJ/l EtOH)
Ethanol export
Power export
Lignin export
DME export
Power demand
Steam demand
EtO
H in
re
pu
rpo
sed
m
ill
Co
-lo
cate
d
EtO
H a
nd
mill
EtOH-DME