Download - Steve Peterson USDA – ARS – NCAUR
Comparison of gasification and pyrolysis methods for
preparing biochar from corn stover and wheat
straw
Steve PetersonUSDA – ARS – NCAUR
Applications of biochar
Uses beyond carbon sequestration◦ rubber composite filler – particle size a problem◦ filtration media
for filtration applications, particle size is not as important as surface area
Applications of biochar
Uses beyond carbon sequestration◦rubber composite filler◦filtration media
for composite fillers, large particles = poor
reinforcement
as filtration media, large, porous particles OK as long as they’re permeable to the medium
Applications of biochar
Uses beyond carbon sequestration◦rubber composite filler◦filtration medium◦peat moss substitute
Later in the program…
Pyrolysis vs. gasification
pyrolysis gasification
feedstock
Pyrolysis: pros and cons
heat
biochar(solid)
bio-oil(liquid)
+O2
(gas)(H2, CH4)
biomass
Cons:• batch method limits throughput• controlled environment = $$ • bio-oil can be problematic during processing
Pros:• oxygen is omitted, increasing the carbon yield• temperature control is accurate and variable
Gasification: pros and cons
open air system is cheaper and easier to run
can facilitate higher thoughput
scale up is easier and more cost-effecttive
side products are burned off
Pros:
Cons: no temperature control,
high temps are limited biochar typically has higher
ash contentimage courtesy of www.cleanstove.org
TLUD = Top Lit UpDraft
secondary air
primary air“AVUD” design by Paul Anderson
Feedstocks used
corn stover (CS) wheat straw (WS)
• both feedstocks are cheap and plentiful
• our collaborator has provided us with both glycerin and glycerin-free pelletized forms of WS
Feedstocks used
wheat straw + glycerin (WS+G)
corn stover (CS) wheat straw (WS)
Experimental design
Gasification (TLUD)Pyrolysis (retort oven)
400, 500, 600, and 700°C
temperature is not controlled;subject to gasification process
Feedstocks: CS, WS, WS+G
Biochar production method:
Temps:
Monitoring TLUD temperature
T1
T2
T3
T4
6:14:24 6:43:12 7:12:00 7:40:48 8:09:36 8:38:24 9:07:120
100
200
300
400
500
600
700
800
900T (
°C)
global time
Surface area/porosity
400 500 600 700 TLUD0
200
400
600
800
CS
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
400 500 600 700 TLUD0
100200300400500600700
WS
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
400 500 600 700 TLUD0
100200300400500600700800
WS+G
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
total surface area
micropore surfacearea
(micropore pore withd < 2 nm)
Surface area/porosity
400 500 600 700 TLUD0
200
400
600
800
CS
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
400 500 600 700 TLUD0
100200300400500600700
WS
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
400 500 600 700 TLUD0
100200300400500600700800
WS+G
pyrolysis temperature (deg C)
surf
ace a
rea (
m^
2/g
)
• CS surface area with T
• WS samples peak below 700°C
• micropore % roughly 55-70%
• WS+G TLUD markedly higher surface area
Observations
Water sorption trends
up
down
0 10 20 30 40 50 60 70 80 90 1000.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Moisture Sorption
Relative Humidity (% )
Mois
ture
Conte
nt
(g
of
wate
r/g o
f sam
ple
)
CS, 500°C
Water sorption trends
CS WS WS+G
g water per g sample
400°C 0.13 0.065 0.063
500°C 0.17 0.071 0.054
600°C 0.20 0.091 0.083
700°C 0.17 0.077 0.117
TLUD 0.14 0.069 0.050
CS significantly more water-sorptive than WS and WS+G
For CS and WS, water-sorption peaks at 600°C
Water-holding capacity is highest at 400°C and decreases with increasing temperature (not shown)
Ash content
CS WS WS+Gash content (%)
400°C 18 12 20
500°C 17 15 24
600°C 16 14 29
700°C 21 15 30
TLUD 35 27 25
Ash is an undesired component of biochar consisting of metal oxides; tends to dilute the effects of carbon
Assume limiting oxygen in the process will help reduce ash; retort > TLUD
Conclusions/Summary
Higher surface area & micropore SA with retort methods vs. TLUD
Lower ash content with retort method (except for WS+G sample)
Appears that the addition of glycerin to WS increases the biochar ash content
CS much more water sorptive than WS and WS+G
Bottom line: is the “lower quality” char from gasification a deal-breaker with the given
applications?
Acknowledgements
Paul Wever, Chip Energy
AJ Thomas & Ashley Maness
Mike Jackson
Steve Vaughn
HydroStraw, LLC
Jason Adkins
Nancy Holm, IBG, and ISTC