This document summarizes research on developing a process model for steam treatment of biomass for pellet production. The researchers conducted a techno-economic assessment and energy analysis of steam pretreatment of straw and switchgrass. They developed a process model for the steam pretreatment using mass and heat balance calculations. The model was validated experimentally. Results showed that steam pretreatment improved pellet quality but increased costs. A plant size of 200,000 tonnes per year was optimal to realize economies of scale benefits from steam pretreatment. Sensitivity analysis showed the techno-economic model was most sensitive to transportation costs, moisture content, and internal rate of return.

1. Development of Process Model for Assessment
of Steam Treatment of Biomass for Pellet
Production
S M HASSAN SHAHRUKH, ADETOYESE OYEDUN, AMIT KUMAR
Department of Mechanical Engineering, University of Alberta
Edmonton, AB, Canada
2015 ASABE | ANNUAL INTERNATIONAL MEETING
July 26 – 29, 2015, NEW ORLEANS, LA, USA

2. Presentation Outline
 Background and Objective
 Pellet Production Supply Chain
 Model Development and Validation
 Mass and Heat balance of Steam
Pretreatment
 Techno-Economic Result
 Summary of Result
Presentation at ASABE, 26-29 July, 2015

3. Background
Presentation at ASABE, 26-29 July, 2015
•Pretreatment helps
producing high
quality pellets
•Energy density of
regular pellets is
1/8th of coal
•High transportation
cost of regular
biomass and pellets
•Need for higher
utilization of Biomass
Low
Utilization
Cost Issues
Pretreatment
Low Bulk
and Energy
density of
regular
pellets

4. Objectives
Conduct Techno-Economic Assessment
Cost curves Sensitivity & uncertainty
Conduct Energy Analysis
Net energy ratio (NER) Sensitivity & uncertainty
Develop process model for steam pretreatment of straw and switchgrass
Data intensive modeling Heat and mass balance
Presentation at ASABE, 26-29 July, 2015

5. Pellet Supply Chain
Biomass
collection
Bale
formation/
chipping
Transportation
to pellet plant
Pellet
production
Transportation
of pellet to
biorefinery
Used in
biorefinery
Supply chain of pellet to a biorefinery (Conventional method)
Used in
biorefinery
Biomass
collection
Transportation
to pellet plant
Pellet
Production
Transportation
of pellet to
biorefinery
Steam
pretreatment
Bale
formation
/chipping
Steam
Pretreatment
Supply chain of pellet (produced from pretreated biomass) to a biorefinery
Presentation at ASABE, 26-29 July, 2015

6. Experimental Material and
Method
Material
Straw and
switchgrass
Moisture content ~
10%-14%
Method
Pretreatment carried
in 2.6L StakeTech
Steam gun with 400g
of biomass treated at
different temperature
and time
Steam treated
biomass pelletized
Presentation at ASABE, 26-29 July, 2015

7. Model Input and Validation
1. Boiler unit: Supply of steam
at different time and
temperature
2. Steam Pretreatment
Unit: Biomass
is treated with high
pressure steam in batch
reactor (Yield reactor
considered)
logR = log exp(
T − 100
14.75
)dt
Governing
Equation:
Source: Lam et al.
2013
Presentation at ASABE, 26-29 July, 2015
Key Improvement: Improves
the calorific value by
increasing the Carbon
content and reducing
oxygen content.

8. Model Input and Validation
3. Pellet mill:
produces pellet of
20-30 mm long, 6
mm in diameter, has
a heating element
operating at 70-100
C.
2. Grinder: Kicks
energy constant
100KJ/kg, solid
recovery 95%
1. Dryer: operating
temperature at
80 C.
Presentation at ASABE, 26-29 July,2015
No grinder is required for
pellet production of straw and
switchgrass

9. Model Validation Result
Operation
Experimental Energy
Consumption (kJ)
ASPEN model Predicted Energy
Consumption (kJ)
Straw Switchgrass Straw Switchgrass
Steam
Pretreatment
749 678 760 710
Drying 6731 8979 6951 9045
Size reduction 0 0 0 0
Pelletization 330 318 352 325
Presentation at ASABE, 26-29 July,2015

10. Comparative Heat and Mass
balance
Presentation at ASABE, 26-29 July,2015
Dryer
Hammer Mill
Pellet Mill
1kg 0.95 kg 0.92kg 0.85 kg
17 MJ
0 MJ
0.3MJ 0.8 MJ
Dryer
Hammer Mill
Pellet Mill
1kg 0.95 kg 0.92kg 0.88 kg
17 MJ
0 MJ 0.3MJ 0.8 MJ
Straw Switchgrass
A. Regular Pellet A. Regular Pellet
B. Steam Pretreated Pellet B. Steam Pretreated Pellet
Dryer
Hammer
Mill
Pellet
Mill
3.0 kg 0.8 kg 0.8kg 0.72 kg
19 MJ
1kg
0.8MJ 6.7 MJ
0 MJ 0.42 MJ
Dryer
Hammer
Mill Pellet
Mill
3.4 kg 0.8 kg 0.8kg 0.71 kg
19.1 MJ
1kg
0.7MJ 8.9 MJ 0 MJ
0.4 MJ

11. Variation of NER with Pretreatment
Temperature and Level
Presentation at ASABE, 26-29 July,2015
0
0.5
1
1.5
2
2.5
3
140 160 180
NER
Steam Pretreatment Temperature
Straw Switchgrass
0
1
2
3
4
5
6
7
25% 50% 75%
NER
Pretreatment level
Straw Switchgrass
Process NER falls with increase of pretreatment level and temperature

12. Uncertainty Analysis
Presentation at ASABE, 26-29 July,2015
Straw Switchgrass
Straw NER at 95% confidence interval is 1.62±.0.10
Switchgrass NER at 95% confidence interval is 1.42±0.11

13. Techno-Economic Snapshot
Presentation at ASABE, 26-29 July,2015
Straw Forest residue Switchgrass
Regular Steam
pretreated
Regular Steam
pretreated
Regular Steam
pretreated
Optimum size
(t year-1)
190,000 250,000 190,000 290,000 190,000 230,000
Pellet cost ($ t-1) 122.04 188.34 116.01 183.14 116.20 192.41
-Capital recovery 9.56 15.31 10.83 20.34 13.74 21.53
- Maintenance cost 2.64 3.68 2.34 3.59 2.58 3.76
-Field cost 52.34 58.75 28.19 32.08 25.57 29.39
-Transportation cost 33.89 42.99 37.04 50.24 45.38 57.68
-Premium 0.00 0.00 6.39 5.50 5.34 6.13
-Employee cost 7.27 7.85 6.58 6.76 7.27 8.53
-Energy cost 5.41 48.91 14.74 53.79 5.41 54.50
-Consumable item cost 10.93 10.86 9.90 10.84 10.93 10.88
Pellet transportation 6.30 5.50 6.20 5.45 6.80 6.10
Total pellet delivery
cost
128.34 193.84 122.21 188.59 123.00 198.51

14. Variation of Transportation
cost
Presentation at ASABE, 26-29 July,2015

15. Variation of Capital Cost
Presentation at ASABE, 26-29 July,2015

16. Variation in Production Cost
Presentation at ASABE, 26-29 July,2015
Process scalability depends on maximum unit size available
and optimization between transportation and capital cost

17. Sensitivity Analysis- Straw
Presentation at ASABE, 26-29 July,2015
180.00
185.00
190.00
195.00
200.00
205.00
-20% -10% 0% 10% 20%
Totalcostofpellet($(t)-1)
% change
capital cost employee cost
Energy cost Transportation cost
188.00
190.00
192.00
194.00
196.00
198.00
200.00
-20% -10% 0% 10% 20%
% change
Moisture content
Feed stock material loss
Inflation
IRR
Techno-Economic model is sensitive to transportation,
moisture content and IRR parameter

18. Sensitivity Analysis - Switchgrass
Presentation at ASABE, 26-29 July,2015
186.00
191.00
196.00
201.00
206.00
-20% -10% 0% 10% 20%
Totalcostofpellet($(t)-1)
% change
capital cost employee cost
Energy cost Transportation cost
193.00
194.00
195.00
196.00
197.00
198.00
199.00
200.00
201.00
202.00
203.00
-20% -10% 0% 10% 20%
% change
Moisture content Feed stock material loss
Inflation IRR
% area
Techno-Economic model is sensitive to transportation,
moisture content and material loss parameter

19. Uncertainty Analysis
Presentation at ASABE, 26-29 July,2015
Straw Switchgrass
Straw and Switchgrass Production cost at 95% confidence interval is
$ 233-260 with standard deviation of $10

20. Summary of Result
Energy
•Energy ratio of regular pelletization process is higher than steam
pretreated pellet due to addition of steam as energy source
•Calorific value of pellet increases by 21% due to steam pretreatment
•Grinding energy input is zero for straw and switchgrass
Cost
•$/tonne cost of production for steam pretreated pellet is higher than
regular pellet due to increased capital cost
•$/GJ cost production of pellet for both steam treated pellet and
regular pellet is similar with approximately 30 cents difference
Scaling
•Steam pretreatment is more effective over a plant size of 200000
tonnes/yr plant capacity due to economy of scale benefits from the
scale of steam pretreatment unit operation
Presentation at ASABE, 13-16 July,2014

21. Acknowledgement
Bio Fuel Net
University of Alberta
Dr. Shahab Sokhansanj, Dr. Linoj Kumar and
Bahman Ghiasi, Department of Chemical
Engineering, University of British Columbia
Presentation at BFN 22-24 July,2015

22. THANKS
Contact Information:
Dr. AMIT KUMAR
Professor
NSERC/Cenovus/Alberta Innovates Associate Industrial Research Chair in Energy and
Environmental Systems Engineering
Cenovus Energy Endowed Chair in Environmental Engineering
Department of Mechanical Engineering, University of Alberta
Amit.kumar@ualberta.ca
www.energysystems.ualberta.ca
+1 780 492 7797 2015 CSBE | SCGAB Annual General Conference
July 5 – 8, 2015, Edmonton, AB, Canada