United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-93/020 April 1993
i&EPA Project Summary
Rates of Reaction and Process
Design Data for the Hydrocarb
Process
Meyer Steinberg, Atsushi Kobayashi and Yuanki Dong
In support of studies for developing
the coprocessing of fossil fuels with
biomass (wood) by the Hydrocarb pro-
cess, experimental and process design
data are reported. The experimental
work includes the hydropyrolysis of bio-
mass and the thermal decomposition
of methane in a tubular reactor. The
rates of reaction and conversion were
obtained at temperature and pressure
conditions pertaining to a Hydrocarb
process design. A Process Simulation
Computer Model was used to design
the process and obtain complete en-
ergy and mass balances. Multiple feed-
stocks were also evaluated, including
biomass with natural gas, biomass with
coal, and sewage sludge (SL) and di-
gester gas (DG) as additional feed-
stocks.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key find-
ings of the research project that Is fully
documented In a separate report of the
same title (see Project Report ordering
Information at back).
Introduction
A feasibility study for the coprocessing
of fossil fuels with biomass by the
Hydrocarb process was performed for the
U.S. EPA (the related report is dated No-
vember 1991). Results of the study indi-
cated technical and economic feasibility
compared to conventional processes for
converting carbonaceous feedstocks such
as coal, natural gas, and biomass to clean
carbon and methanol fuels. For purposes
of mitigating the global greenhouse car-
bon dioxide (CO2) problem, coprocessing
fossil fuels with biomass, sequestering all
or part of the carbon and using the metha-
nol mainly as a power or transportation
fuel, presents the option of reducing and
eliminating CO emissions to the atmo-
sphere while still employing the world's
fossil fuel resources. The report recom-
mended that additional confirmation be
obtained of the kinetics of the major steps
in the Hydrocarb process, which includes
the hydropyrolysis of biomass and the ther-
mal decomposition of the methane-rich
process gas. To this end, an experimen-
tal study was undertaken using the
Brookhaven National Laboratory's Tubu-
lar Reactor Facility.
In addition to the experimental work, it
was recommended that further process
design studies be performed employing
the Process Simulation Computer Model
developed by the Hydrocarb Corporation
with alternative carbonaceous feedstocks.
This report describes the experimental and
process design work.
The report is divided into three sec-
tions. Part I deals with the hydropyrolysis
of biomass. Part II deals with the thermal
decomposition of methane in a tubular
reactor. Part III gives the results of an
analysis of the Hydrocarb process with
alternative and multiple feedstocks.
Part I. Hydropyrolysis of Bio-
mass
The pyrolysis and hydropyrolysis of bio-
mass in the form of poplar wood sawdust
having particle size less than 150 mm in
diameter was investigated in a 25 mm ID
and 2.5 m long tubular reactor facility at
Brookhaven National Laboratory. The tests
were conducted at temperatures up to
800°C and pressures between 30 and 50
atm.* The experiments were performed in
* 1 atm = l01.3kPa.
^/) Printed on Recycled Paper
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two different modes, depending on the
heat-up rate. In the low heat-up rate mode,
the biomass was first loaded in the reac-
tor at room temperature. Hydrogen was
then introduced into the system up to a
desired initial pressure level. The reactor
was slowly heated up at a rate of less
than 10°C/min. The change in the pres-
sure in the reactor and the composition of
the effluent gas were monitored with time.
In the higher heat-up rate mode, the reac-
tor was heated up and pressurized with
hydrogen up to the desired reaction con-
ditions before introducing the biomass. The
variations of pressure and gas composi-
tion versus time were then recorded and
analyzed. From these data, rates of reac-
tion and degree of conversion were deter-
mined. A typical run shown in Figure 1
indicates the calculated number of moles
of gas generated as a function of time.
At low heat-up rate, the reaction pro-
ceeds in two steps. First pyrolysis takes
place at temperatures of 300 to 400°C
and then hydropyrolysis takes place at
700°C and above. This is also confirmed
by experiments using pressurized
thermogravimetric analysis. Under condi-
tions of rapid heat up at higher tempera-
tures and higher hydrogen pressure,
gasification and hydrogasification of biom-
ass is especially effective in producing
CO and methane. An overall conversion
of 88 to 90 wt% of biomass was obtained.
This is in agreement with previous work
on flash pyrolysis and hydropyrolysis of
biomass under rapid heat up and short
reaction residence time conditions. Initial
rates of biomass conversion indicate that
the rate increases significantly with in-
crease in hydrogen pressure. At 800°C
and 51.3 atm the initial rate of biomass
conversion to gases is found to be 92%
per min.
Part II. Thermal Decomposition
of Methane
The reaction rate of methane decompo-
sition using the same reactor facility was
investigated in the temperature range of
700 to 900°C at pressures ranging from
28 to 56 atm. In these experiments, meth-
ane was fed into the reactor continuously.
Gas from upstream and downstream of
the reactor was analyzed on-line to calcu-
late the reaction rate. The variations in
methane concentration vs. residence time
under different operating conditions are
shown in Figure 2. It can be seen from
the experimental data that the gas resi-
dence time of about 2 min. is required for
the reaction to reach near equilibrium com-
position at 50 aim and 900°C. The rate is
represented by a conventional model,
dCKt
~"dt
kCcm
where C is the molar concentration and k
is the rate constant.
When the initial hydrogen concentration
is zero, the activation energy for methane
decomposition is 31.3 kcal/mol,* as deter-
mined by an Arrhenius Plot. This value is
lower than for previously published results
for methane decomposition and appears
to indicate that the high-surface-area sub-
micron carbon particles found adhering to
the inside of the reactor tend to catalyze
the methane decomposition reaction. The
* 1 kcal.4.l83kJ.
10
20 30 40
Time (min.)
50
60
Figure 1. Hydropyrolysis of poplar sawdust biomass. The change in number of moles in the reactor
with time at 800 °C and 52.4 atm of initial hydrogen pressure. Run No. 1152.
rate constant has been found to be ap-
proximately constant at 900°C in the pres-
sure range investigated, 28 to 56 atm.
The rate of methane decomposition in-
creases with methane partial pressure to
the first order. It is concluded that the rate
of methane decomposition is favored by
higher temperatures and pressures, while
the thermochemical equilibrium of meth-
ane decomposition is favored by lower
pressures. By extrapolating to higher tem-
peratures, the residence time to reach near
equilibrium at 50 atm would be 41 sec. at
1000°C and 12 sec. at 1140°C.
Part III. Design Analysis of the
Hydrocarb Process with
Alternate and Multiple
Feedstocks
The design performance of the
Hydrocarb process with alternative and
multiple feedstocks was investigated. The
alternative feedstocks studied for the
Hydrocarb process included biomass
(wood), Alaska Beluga coal, Kentucky (bi-
tuminous) coal, North Dakota (lignite) coal,
and Wyodak (subbituminous) coal. A ther-
modynamic-equilibrium-limited Process
Simulation Computer Model was used to
design the process and obtain complete
energy and mass balances. Boundary con-
ditions of pressure, temperature, and mass
balance for the cyclical process were de-
termined. Two cycles were investigated
depending on whether process gas from
the HPR goes directly to the MPR (cycle
1) or whether the HPR gas first goes to
the methanol synthesis reactor and con-
denser and then to the HPR (cycle 2).
Cycle 1 produces a higher ratio of metha-
nol to carbon and is preferred. The study
also included using sludge and digester
gas from sewage plants as additional feed-
stocks. It was found that these feedstocks
have to be coprocessed with either biom-
ass or coal to obtain a workable mass
balance. The effect of pressure and tem-
perature for both biomass and sludge feed-
stock was also investigated. Carbon
conversion efficiency ranges from 70 to
80% and thermal efficiency between 60
and 80%. Increasing the HPR and MPR
temperature improves methanol produc-
tion and thermal efficiency. The methanol
to carbon production rate decreases with
decreasing system pressure.
From this study it is concluded that a
most favorable operating conditions for
coprocessing biomass and methane is 50
atm system pressure, and 900°C for the
HPR and 1000°C for the MPR. Figure 3 is
a complete flowsheet showing the rates
and compositions of each stream to and
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from the major pieces of equipment in the
Hydrocarb process for coprocessing bio-
mass (wood) and methane (natural gas).
This process design and the experimental
rate data are being applied to the design
of reactors for an integrated 22.7 kg/h
Hydrocarb pilot plant.
Equilibrium Data
at 700°Cand56.1 atm
Equilibrium Data at
800°C and 56.1 atm
Equilibrium Data
at 900°C and 56.1 atm
20
40 60 80
Residence Time (sec.)
100
120
-0- 900°C 56.1 atm
-*- 900°C 28.1 atm
800°C 56.1 atm
900°C41.8atm
700°C 56.1 atm
Figure 2. Methane concentrations vs. residence time.
Hydrocarb Process (Cycle 1)
(Biomass + NG)
(P = 50 atm)
Wood 4630 kg/h
NG 694 kg/h
*
Char
212 kg/h
927 °C
900 °C
2298 kmol/h
CO 6.8
CO
CH
tf
0.7
30.1
6.8
55.7
1000°C
C 1222 kg/h
Off Gas
3 kmol/h
CO
CO,
CHA
H.O
2.7
3.0
24.0
0.1
69.5
50 °C
2167 kmol/h
257 °C
2540 kmol/h
CO 9.2
CO2 0.3
CH. 20.4
H2O 3.7
H. 66.4
H2O 620 kg/h
T
MeOH
3192 kg/h
260 °C
2304 kmol/h
CO 2.6
CO2 2.8
CH4 22.5
HO 1.6
n 65 4
MeOH 5.1
Carbon Conversion of Feedstock in HPR: 90%
Carbon Efficiency: 72.2%
Thermal Efficiency: 74.9%
Figure 3. Data summary with wood and CH4 as feedstocks.
'U.S. Government Printing Office: 1993 — 750-071/60224
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M. Steinberg and A. Kobayashi are with Brookhaven National Laboratory, Upton,
NY 11973; and Y. Dong is with Hydrocarb Corp., New York, NY 10018.
Robert H. Borgwardt is the EPA Project Officer (see below).
The complete report, entitled "Rates of Reaction and Process Design Data for the
Hydrocarb Process,"(Order No. PB93-155976; Cost: $27.00; subject to change)
will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
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POSTAGE & FEES PAID
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PERMIT No. G-35
EPA/600/SR-93/020
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