EPA/600/A-97/010
BIOMASS REACTIVITY IN GASIFICATION
BY THE HYNOL PROCESS
Yuanji Dong
Acurex Environmental Corporation
4915 Prospectus Drive
Durham, NC 27709
Robert H. Borgwardt
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
Keywords: biomass gasification; gasification kinetics; biomass-to-methanol.
INTRODUCTION
Methanol has many advantages to be considered as an alternative fuel. About 75% of
methanol production uses natural gas as feedstock. Use of biomass as feedstock to produce
methanol is of current interest because it offers substantial benefits for reduction of greenhouse gas
emissions. The research and development of biomass-to-methanol processes, one of which is called
Hynol, are now in progress.
The Hynol process was proposed to utilize biomass as a feedstock and natural gas as a
cofeedstock to increase methanol yield and reduce costs (Steinberg and Dong, 1994). The process
consists of three reaction steps: (1) gasification of biomass with the Hj-rich gas recycled from
methanol synthesis, (2) steam reforming of the produced gas with an addition of natural gas
feedstock, and (3) methanol synthesis from the H2 and CO produced by the reformer. A schematic
flow diagram of the process is shown in Figure 1. Since the reaction of biomass with the H2 in the
recycle gas to form CH4 is exothermic, the heat so generated is able to offset the energy required
for other endothermic reactions in a Hynol gasifier. As a result, no expensive 02 plant or external
heat source is needed for gasification. The use of natural gas as cofeedstock eases the requirement
for a consistent composition of biomass feedstock. The integrated cyclical process configuration
helps ensure the completion of overall conversion and increases thermal efficiency. CO shifting is
not necessary and the requirement for acid gas removal is reduced, which lowers capital and
operating costs.
A theoretical evaluation of the Hynol process conducted by the Air Pollution Prevention and
Control Division (APPCD) of the National Risk Management Research Laboratory,
U.S.Environmental Protection Agency (EPA), showed that the Hynol process represents a promising
technology for maximizing fuel production inexpensively and with minimum greenhouse gas
emissions (Borgwardt, 1995). Consequently, the APPCD established a laboratory to further assess
the process feasibility. In the first phase of the study, a thermobalance reactor (TBR) was installed
and used to evaluate biomass reactivity in gasification at the operating pressure, temperature, and
feed gas composition specific for the Hynol process. The experimental work also attempted to
improve understanding of the variables affecting Hynol gasification and identify needs for process
development. This article summarizes the TBR results.
EXPERIMENTAL
A flow diagram of the TBR system is detailed in Figure 2. The reactor is electrically heated
and consists of a 35-mm I.D. stainless steel reactor pipe, a 305-mm O.D, pressure vessel, and a
topwork which accommodates a weight transducer for measurement of sample weight during
reaction. A pulley assembly is used to raise and lower a sample basket between the topwork and
the reaction zone.
To initiate an experimental run, a basket with known weight of biomass sample was placed
into the topwork through.the removable window. A constant helium flow was introduced to the
topwork to protect the wood sample from contact with process gas prior to entry in the reaction
zone. Mass flow controllers were used to control the flow rates of H2, CH,, CO, and CQ from
individual gas cylinders to obtain the desired feed gas composition. Steam was added to the feed
gas from a steam generator fed with distilled water by a metering pump. The gas mixture was
further heated by a superheater and then entered the reactor. The reactor exit gas was cooled in a
condenser to remove moisture, and then depressurized through a back-pressure regulator before it
was vented to atmosphere. When pressure and temperature in the reactor system were stabilized at
the desired levels, the sample basket was lowered into the reaction zone and the change in sample

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weight was automatically recorded by the transducer as a function of reaction time. A computer was
used to control the TBR system and log experimental (tea. After gasification, the basket was raised
back into the topwork and the reactor was depressurized and cooled. The discharged char was then
weighed to determine the final sample weight. Because changes in gas composition across the
sample are negligible, the reaction can be considered to take place at constant operating conditions.
In this study, the Hynol feed gas refers to a composition — H2 = 65.83%; CH4 = 11,63%; CO
= 8.95%; CO, = 2.32% and steam = 11.27% - which is based on the results of a Hynol process
simulation. Poplar wood, which is considered a primary candidate for large scale production as an
energy crop for fossil fuel displacement (Wright, 1995), was used as a representative biomass
sample. It was grown in North Carolina and cut to desired sizes and dried before its use.
Composition is presented in Table I.
KINETIC MODEL AND DATA TREATMENT
The weight transducer output was recorded as a function of reaction time during a test. The
records were converted into the data of variation in sample weight with time. The biomass
conversion, X, on an ash-free basis was then calculated by:
W0 - W
X -- 	2		/J)
w - w c
^0 OA
where W0 is the initial sample weight, W is the sample weight at any reaction time, CA is the weight
fraction of ash obtained from the ultimate analysis of the original sample, and X is thus also a
function of reaction time.
General observation of the reaction behavior revealed that biomass gasification under Hynol
conditions involves two types of reactions: a rapid reaction, which may complete in a few seconds,
involving devolatilization and pyrolysis reaction of the volatile matter in biomass with H2 and steam;
and a veiy slow reaction of residual carbon with the process gas which requires hours to finish. To
quantitatively describe the rate of gasification, these two reactions are assumed to be first order with
respect to the remaining solid reactants. The rate of the rapid reaction can be expressed as:
- K <*c " *,)	(2)
and the rate expression for the slow reaction is:
-1=^(1 -Xc- X2)	(3)
where X, and X2 are the conversions by the rapid and slow reactions at time t, Xc is the maximum
attainable conversion by the rapid reaction, and k, and k2 are the reaction rate constants for the rapid
reaction and the slow reaction, respectively.
By integrating Equations (2) and (3), the total biomass conversion can be expressed by:
X = X, + X2 = 1 - Xc exp(-V) " (1 " Xc) exp(-V)	(4)
The model involves three parameters: Xc, k„ and k2, which are functions of operating conditions
such as biomass properties, reaction temperature, pressure, and feed gas composition. They can be
determined by fitting Equation (4) to the experimental conversion data obtained from TBR tests.
RESULTS AND DISCUSSIONS
The above model was used to correlate the experimental data obtained from TBR tests.
Figure 3 is a typical example of curve fitting results by the model, showing good agreement between
the experimental data and the model regression over the entire reaction period.
Four different sizes of poplar particles were used to investigate the effects on gasification:
7/16-in diameter cylinders, 1/4-in diameter cylinders, 1/8-in cubes, and 20 to 30 mesh sawdust. The

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rate of [he rapid reaction increased significantly as a result of higher heat transfer and intraparticle
diffusion rates when particle size was reduced from 7/16- to 1/8-in. Agglomeration during
gasification was observed for the particles larger than 1/8-in, which inhibited gas diffusion within
the particles. Sawdust heated up more quickly, and no agglomeration was observed. Experimental
results showed that, at 30 atm and 800°C, about 87% of the 1/8-in poplar particles and 90% of the
sawdust can be gasified by the Hynol feed gas in 60 min.
The analysis of the charred samples obtained from 7/16-in poplar particles showed that some
of the volatile matter remains after gasification. However, for 1/8-in poplar particles or sawdust,
nearly all of the H and O were converted into product gas in 20 min.
The agglomerates of residual chars formed in the TBR were fragile. If a fluidized bed
gasifier is used, agglomeration is not likely to occur as a result of attrition; therefore, higher reaction
rate and conversion than observed in TBR testing arc expected in such systems.
The rapid-reaction stage of poplar gasification was found to be essentially completed in less
than 0,2 to 0.3 min, contributing most of the biomass conversion. A small additional conversion
is contributed by the slow reaction. To achieve high biomass conversion, sufficient gasification time
must be provided. Tests showed that biomass conversion increased from 85 to 90% when
gasification time extended from 20 to 150 min. The comparison between the compositions of chars
after 20 and 150 min gasification indicated that there was virtually no further conversion of H and
O in the char after 20 min and that the additional conversion resulted from the reaction of carbon
with the process gas.
Experimental results of 60-min gasification with sawdust and 1/8-in poplar particles at
different reaction temperatures showed great increase in biomass conversion and gasification rates
when temperature increased from 750 to 950°C as shown in Figure 4. The rate constants for the
rapid and slow reactions, k, and k2> at different reaction temperatures were determined by fitting
the experimental data for gasification of 1/8-in poplar particles. The rate constants thus obtained
were plotted against the reciprocal of the absolute temperature, as shown in Figure 5, and expressed
as functions of reaction temperature by the Arrhenius equation:
where subscript i is 1 for the rapid reaction and 2 for the slow reaction. E, is the activation energy.
The results obtained were: k10 = 108.85 min'1, E, = 3.78 kcal/mol, ka = 22925 min"1, and E2 = 34.1
kcal/mol. The maximum attainable conversion by the rapid reaction, Xg, was also correlated as a
function of temperature for gasification of 1/8-in poplar particles by:
where T is the reaction temperature in °C. With Equations (4), (5), and (6) and the values of k10,
Ej, kg* and Ej, the conversions of 1/8-in poplar particles at different temperatures and gasification
times were predicted. Figure 6 compares the prediction with the conversion data obtained from the
separate experimental tests at different temperatures and gasification times. The comparison covers
a temperature range of 750 to 950°C and a gasification time range from 0.2 to 150 min for 1/8-in
poplar particles gasified by the Hynol feed gas at 30 atm. The activation energy obtained for the
rapid reaction was low, implying that heat transfer dominates the rates of devolatilization and
pyrolysis of biomass in the TBR.
The effect of feed gas composition on poplar gasification was investigated by varying the
flow rates of individual gas components under constant system pressure. Helium was used as an
inert "make-up" gas for this purpose. At 30 atm and 800°C, the final conversion of poplar wood
gasified by pure helium after 60 min was about 6% lower than that obtained under pure H2, If the
conversion obtained after 60 min of gasification is plotted against H2 partial pressure (PH2), a linear
relationship, conversion = 0.0017 x P»«. was found. When steam partial pressure in the feed gas was
varied from 7 atm to zero while the partial pressures of other gas components remained constant,
the conversion was proportional to steam partial pressure or 0.003 x PH20. Negligible effects on the
gasification conversion and reaction rate of 1/8-in poplar particles were observed as the CH« in the
feed gas was reduced from the simulated Hynol composition, 11.63%, to zero. Replacing CO and
C02 in the feed gas with helium did not affect the gasification rate. The conversion and reaction
rates of 1/8-in poplar particles gasified by the Hynol feed gas were nearly the same as those
observed by the feed gas containing no CO and C02.
E,
(5)
Xc = 0,9611 - 0.0001497
(6)

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REFERENCES
Borgwardt, R. (1995): The Hvnol Process. Presented at Symposium on Greenhouse Gas Emissions
and Mitigation Research, Washington, DC. June 27-29.
Steinberg, M. and Dong, Y. (1994):;
Condensed Carbonaceous Material. U.S. Patent 5,344,848.
Wright, L. (1995): Demonstration and Commercial Production of Biomass for Energy. Proceedings,
Second Biomass Conference of the Americas, NREL/CP-200-8098, National Renewable Energy
Laboratory, Golden, CO, pp. 1-10.
TABLE 1. COMPOSITION OF POPLAR WOOD USED
Carbon (wt.%) 51.52
Hydrogen (wt.%) 6.20
Oxygen (wt.%) 41.37
Ash (wt.%) 0.47
Sulfur (wt%) 0.02
Nitrogen (wt.%)	0.42
Volatile (wt%)	91.38
Fixed carbon (wt.%)	8.15
Higher heating value
(Btu/lb dry wood)	8768.
CWlTlwl IHwIMimI
Cuban OjQM mol ^
O-
Figure 1. Schematic flow diagram of the Hynol process.
H2
CH4
CO
CC2
Heat Tracing #1,
H20
Staam
Oooarator
Figure 2. Flow diagram of the TBR system.
4

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X
tz
I
RUN NO. AS5040?
Poplar Mwtfu#
30 a&n end 800°C
HpwHeedgas
0,4
0.2
—-— Model correlation
0.0
0.0
0.1
50.0
00.0
Tune (mln)
Figure 3. Example of TBR experimental data fitting by the model.
Sample: 1/8' Popia/cubes
Pressure: 30 aim
0.95
£
6
s
0.90
0.85
0.80
850
900
950
750
800
Temperature (°C)
Figure 4. Effect of reaction temperature.
3.2
3.0
2.8
- -6
2.4
1/T(K')
Figure 5. Antienius plots of the rate constants.
0.95
0.90
j;
0.85 ¦
0.80 -
0.80	0.85	0.90	0.95
Figure 6. Comparison of the model prediction
with experimental conversion data.

5

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T TECHNICAL RETORT DATA 	-
JN K MKL" K i Jr~ F~ llu (Please read Instructions on the reverse before completini
' REP|RPTa7600/A-97/010
3. R!
4. TITLE AND SUBTITLE
Biomass Reactivity in Gasification by the Hynol Pro-
cess
5. REPORT OATE
6. PERFORMING ORGANIZATION COOE
7. AUTHOR(S)
Yuanji Dong (Acurex) and Robert H. Borgwardt (EPA)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND AODRESS
Acurex Environmental Corporation
4915 Prospectus Drive
Durham, North Carolina 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D4-0005, W. A. 32
12. SPONSORING AGENCY NAME ANO ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper: 11/94-5/95
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notes ^ppcD author Borgwardt's mail drop is 63; his phone number is
919/541-2336. For presentation at ACS Symposium on CO2 Capture, Utilization, and
Disposal, Orlando, FL. 8/25-29/96.
The paper discusses the use of a thermobalanee re-
actor to evaluate the reactivity of poplar wood in gasification under the operating con-
ditions specific for the Hynol process (30 atm and 800 C). The gasification involved
a rapid devolatilization and pyrolysis reaction of the volatile matter in biomass and
a slow reaction of residual carbon with the process gas. Nearly 86% of 01/8-in. (0.3
2m) diameter poplar particles and 90% of sawdust could be converted into gas pro-
ducts by a feed gas corresponding to the Hynol process (66% hydrogen) in 60 min.
About 4% additional conversion of 1/8-in, particles was obtained when gasification
time was extended to 150 min. Gasification rate and biomass conversion were strong-
ly affected by reaction temperature and particle size. The conversion was propor-
;ional to the partial pressures of hydrogen and steam in the feed gas. A kinetic model
vas developed to correlate the experimental data and quantitatively express gasifica-
tion rates and biomass conversion as functions of reaction time. The activation ener-
gies for the rapid and slow reactions were estimated to be 3.8 and 34 kcal/mol, re-
spectively.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IOENTIPIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Kinetics
Fuels Carbinols
Biomass
Gasification
Poplar Wood
Sawdust
Pollution Control
Stational Sources
Hynol Process
Modeling
13 B 20K
21D 07C
08A.06C
13H, 07A
UL
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report}
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)

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