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