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Steam gasification of meat and bone meal in a two-stage fixed-bed reactor system.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
Published online 20 May 2010 in Wiley Online Library
(wileyonlinelibrary.com) DOI:10.1002/apj.454
Special Theme Research Article
Steam gasification of meat and bone meal in a two-stage
fixed-bed reactor system
Chirayu G. Soni,1 Ajay K. Dalai,1 * Todd Pugsley,1 and Terry Fonstad2
1
2
Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A9, Canada
Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A9, Canada
Received 11 December 2009; Revised 28 March 2010; Accepted 28 March 2010
ABSTRACT: Gasification of meat and bone meal (MBM) has been carried out using steam in single and two-stage
fixed-bed reactor systems. The first stage was used for the gasification, while the second stage allowed the thermal
cracking and reforming of tar as well as some additional secondary reactions to take place. The effects of temperature
(650?850 ? C) in both stages, steam/MBM (wt/wt) (0.4?0.8), and second-stage packed-bed height (40?100 mm) on
product distribution (char, liquid and gas) and gas composition (H2 , CO, CO2 , CH4 , C2 H4 , other H/C) were studied. It
was observed that a higher reaction temperature (850 ? C) favored high gas and hydrogen yields. Hydrogen yield was
increased from 36.2 to 47.1 vol% with an increase in steam/MBM (wt/wt), while an increase in the packed-bed height
increased gas (29.5?31.6 wt%) and hydrogen (45?49.2 vol%) yields. ? 2010 Curtin University of Technology and
John Wiley & Sons, Ltd.
KEYWORDS: steam gasification; meat and bone meal; two-stage reaction system
INTRODUCTION
The emergence of bovine spongiform encephthalophay
(BSE) in animals and its link with meat and bone meal
(MBM) shocked the rendering industries throughout
the world in the late 1980s. The issue became more
severe when Bruce et al .[1] discovered a link between
BSE and a new variant of the ?creutzfeldt-Jacob disease
(vCJD)? in humans. The immediate consequence was
a ban on the use of MBM in animal feed. The ban
created the significant issue of how to safely dispose
of the literally millions of tonnes of MBM material
produced annually throughout the world. In Canada,
landfill and incineration are accepted means of disposal
by the Canadian Food Inspection Agency (CFIA), while
mass composting is not.[2] Landfills that can accept
MBM are tightly regulated and subject to routine
inspection, leaving incineration as the main method
of MBM disposal. While incineration temperatures are
sufficiently high to destroy the pathogens present in
the MBM, there are operational issues associated with
ash stickiness and the production of hazardous dioxins
and furans at elevated temperatures. Hence, there is an
*Correspondence to: Ajay K. Dalai, Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan S7N
5A9, Canada. E-mail: ajay.dalai@usask.ca
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Curtin University is a trademark of Curtin University of Technology
ongoing need to develop alternative methods for the
safe disposal of MBM.
According to European Union regulations, the prions thought to be responsible for BSE can be destroyed
by thermal treatment at 850 ? C for at least 2 s.[3] . In
addition, MBM has a calorific value in the range of
17?20 MJ/kg, which is similar to some low-grade lignite and subbituminous coals. Hence, thermochemical
processes such as combustion, gasification, and pyrolysis represent promising alternatives to recover the MBM
fuel value while at the same time destroying the harmful
prions at high temperature.
Combustion and pyrolysis have received some attention in the literature,[3 ? 6] while gasification has received
far less. Our group has presented results of MBM gasification using various mixtures of nitrogen and oxygen
in a bench-scale (10.5 mm Inside Diameter (ID)) fixedbed reactor,[7] while Fedorowicz et al .[8] have reported
on the gasification of MBM in what appears to be a
bench-scale fluidized-bed reactor using steam as the
gasification medium. Both studies successfully showed
that a synthesis gas mixture containing primarily hydrogen and carbon monoxide with a high heating value
could be produced from the MBM fuel.
Our previous work[7] studied the effects of reaction
temperature, equivalence ratio, and packed-bed height
during gasification of MBM in a two-stage fixed-bed
reactor system using oxygen as a gasifying agent.
72
C. G. SONI ET AL.
Asia-Pacific Journal of Chemical Engineering
With the exception of Fedorowicz et al .,[8] scientific
investigations aimed at exploring the effects of the
important parameters in steam gasification of MBM
are limited in the open literature. In the present work,
the effects of the reaction temperature, steam/MBM
(wt/wt), and packed-bed height on product yield and
gas composition are studied using steam as a gasifying
agent in a two-stage fixed-bed reactor system.
EXPERIMENTAL
Material
The MBM used for the experiments was supplied in
powder form by Saskatoon Processing Ltd., Saskatchewan, Canada. The information on MBM related to
proximate analysis, C, H, N, S analysis, and particle
size was given in our previous work.[7] .
System description
Experiments were performed at atmospheric pressure
in single- and two-stage fixed-bed reactor systems.
The schematic diagram is shown in Fig. 1. The first
and second-stage reactors were made up of Inconel
tubing having 10.5 mm ID and lengths of 500 and
370 mm, respectively. The reactors were connected by
a 3-mm-diameter, 40-mm-long tube and placed inside
separate split tube furnaces (Applied Test Systems,
Inc.: Butler, PA, USA) with thermocouples located at
the midlength of the heating zone. The temperatures
of the reactors were monitored and controlled by a
temperature-controller system (Eurotherm models 2132
and 2416: Leesburg, VA, USA). Nitrogen as an inert
carrier was supplied at the desired flow rate from a
separate cylinder through a needle valve and mass flow
meter (Aalborg model GFM17: New York, USA), while
water was injected into the reactor by a syringe pump
(Kent Scientific, Genie Plus Model: Torrington, CT,
USA) at the desired flow rate. Two glass condensers
in series below the second-stage reactor, surrounded by
a mixture of ice and salt, were used to condense the
tar and cool down the product gases. The product gases
were collected in the saturated brine solution column
to prevent CO2 dissolution in pure water. The brine
solution column was further connected to the overhead
surge tank to receive the displaced brine solution.
Mass Flow Meter
Water
Vent
TIC
Syringe pump
First Stage Reactor
&
Furnace
Brine Solution
TIC
Second Stage Reactor
&
Furnace
N2 Gas
Gas Collector
Condensers
Figure 1. Schematic diagram of the experimental setup for steam gasification of MBM in a two-stage
fixed-bed reaction system. This figure is available in colour online at www.apjChemEng.com.
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Gas product analysis
The volume of the product gas collected was measured
on the basis of the displacement of the saturated brine
solution. The product gas composition was measured
using two different gas chromatographs: GCs HP 5880
and HP 5890. The detailed description of the program
used is available in our published article.[7] The volume percentage of each constituent compound in the
gas product was calculated on the basis of the total volume of the N2 -free gas collected at the end of each
run. The amount of condensed liquid (tar + water) in
the glass condensers and the char left inside the reactor
were measured by a weight difference before and after
the reaction.
Reproducibility
Selected experiments were repeated for each parameter
to check the reproducibility of the data. The percentage
difference observed in replicate runs is reported in each
figure. The variation observed in % difference is mainly
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
RESULTS AND DISCUSSION
Effect of temperature during the single-stage
operation
Numerous studies have been carried out on steam gasification of biomass and the temperature range studied
was 650?1000 ? C.[9 ? 12] Considering the literature range
and limitations of the experimental setup, the temperature range for the present study was chosen to be
650?850 ? C. The effect of the final temperature of the
first stage was studied by simply bypassing the secondstage reactor of Fig. 1. In this work, the final temperature of the first stage was varied from 650 to 850 ? C with
increments of 50 ? C while maintaining a steam/MBM
(wt/wt) ratio of 0.6 and a N2 flow rate of 45 ml/min.
The effect of the final temperature of the first stage on
the product (char, liquid and gas) yield and gas composition is presented in Figs 2 and 3, respectively. As
expected, char (from 21.7 to 14.1 wt%) and liquid (tar
+ water) (from 57.9 to 52.2 wt%) yields decreased,
whereas gas yield increased (from 8.7 to 18.1 wt%)
with an increase in temperature from 650 to 850 ? C.
It was also observed that, after 750 ? C, gas production
was rapid, which shows that MBM gasification reactions become significant after 750 ? C. This could be
explained by higher char conversion with steam and
the thermal cracking/steam reforming of tar at higher
temperatures. Similar trends were obtained by other
researchers.[9,13,14] .
12
60
Char
8
40
Liquid
Gas
4
20
GHV
0
550
Gross Heating Value (MJ/m3)
The first stage was used for gasification of MBM,
while the second stage was used for further cracking
of tar. The feed material was placed inside the firststage reactor and the inert packed-bed material (Ottawa
sand, particle size range: 152.2?1290.9 祄) was placed
inside the second-stage reactor. These materials were
supported on a plug of quartz wool, which was in
turn held in place by supporting pins welded to the
inside of both reactors. The sample size of MBM
was 2 g for all experiments, while the packed-bed
height of Ottawa sand varied from 40 to 100 mm
(3.46?8.65 cm3 ). The heating rate of the first-stage
reactor was kept at 25 ? C/min. The N2 flow rate was
maintained at 45 ml/min for all experiments unless
otherwise stated. Water injection was started when the
temperature of the first-stage reactor reached 110 ? C. It
took approximately 25?33 min from 30 ? C to reach the
final temperature of 650?850 ? C in the case of singlestage experiments. In the case of two-stage experiments,
the second-stage reactor was heated to the desired
temperature (650?850 ? C) with a nitrogen flow rate of
45 ml/min before heating of the first stage was initiated.
After attaining the final desired temperature of the first
stage, the reaction was allowed to continue for the next
30 min. Subsequently, the heating was stopped and the
reactor(s) were allowed to cool down. After each run,
the reactor and glass condensers were cleaned using
acetone and then dried with compressed air prior to the
next run.
due to the nonhomogeneity of MBM in the sample and
errors during products yield and gas analyses.
Weight (%)
Experimental Procedure
STEAM GASIFICATION OF MBM
0
650
750
850
Temperature (癈)
Figure 2. Effect of final temperature of first stage on
product yield (wt% yield) at steam/MBM (wt/wt) of 0.6 (%
difference in replicate run: char, � liquid, � gas, �.
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
DOI: 10.1002/apj
73
C. G. SONI ET AL.
Asia-Pacific Journal of Chemical Engineering
40
CO
CO2
CH4
20
C2H4
Other
H/C
0
550
650
750
850
Temperature (癈)
Figure 3. Effect of final temperature of first stage on gas
composition (vol% yield) at steam/MBM (wt/wt) of 0.6 (%
difference in replicate run: H2 , � CO, � CO2 , � CH4 ,
� other H/C, �.
The product gas was mainly composed of H2 , CO,
CO2 , CH4 , and other heavier hydrocarbon gases. The
H2 and CO yields increased from 42 to 52.2 and 10.2
to 26.8 vol% (N2 free basis), respectively, while that
of CO2 decreased sharply from 25.9 to 12.8 vol%
with an increase in temperature from 650 to 850 ? C.
Increased carbon conversion as well as the Boudard
reaction (C + CO2 ? 2CO) are partially responsible for
the observed increase in CO and the corresponding
decrease in content of CO2 at higher temperatures.
Methane (from 7 to 3.1 vol%) and other hydrocarbons
(from 2.7 to 1 vol%) showed a marginal decrease with
an increase in temperature. This could be explained by
the likelihood of some secondary reactions with CO2 as
well as the steam-reforming reaction of hydrocarbons
to produce CO and H2 . The gross heating value of
product gases was almost constant in the range of
11.2?11.5 MJ/m3 .
Effect of second-stage temperature during the
two-stage operation
The tar product observed above can be removed by
increasing the gas residence time, thus facilitating thermal cracking.[14] Hence, the second reactor stage was
introduced in series with the first stage for further cracking/reforming of tar and to increase the yield of H2 .
The second-stage reactor temperature was varied from
650 to 850 ? C in increments of 50 ? C while keeping the
first-stage temperature at 850 ? C, steam/MBM (wt/wt)
at 0.6, nitrogen flow rate at 45 ml/min, and secondstage packed-bed height at 60 mm. The effect of the
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Effect of steam to MBM ratio
In this set of experiments, the steam/MBM ratio (wt/wt)
supplied in the first-stage reactor was varied from 0.2
20
60
Char
15
40
Liquid
10
Gas
20
0
550
GHV
5
Gross Heating Value (MJ/m3)
H2
second-stage temperature on product yield and gas composition is presented in Figs 4 and 5. The liquid (tar +
water) yield decreased from 39.1 to 32.4 wt% and gas
yield increased from 27.4 to 32.1 wt% as the secondstage temperature increased from 650 to 850 ? C. After
introducing the second stage, the liquid (tar + water)
yield was 37.9% lower, while the gas yield was 77.3%
higher than that obtained using only a single-stage reactor system. CO and CO2 were almost constant over the
range of 23.6?23.9 and 10.5?9.8 vol% respectively.
The CH4 yield increased linearly with increase in temperature, while C2 H4 increased from 6.2 to 8.2 vol% up
to 800 ? C and then decreased to 5.9 vol%. Other heavier
hydrocarbons decreased sharply after 700 ? C. This phenomenon can be explained by the reforming/cracking
of heavier hydrocarbons into light gases. The gross
heating value initially increased up to 18.8 MJ/m3 at
700 ? C and then dropped down to 17.7 MJ/m3 with a
further increase in temperature to 850 ? C, which is consistent with the sharp decrease in the content of heavier hydrocarbons. Comparing steam gasification results
with those of MBM using O2 in our published work[7] at
identical operating conditions, it was found that the content of H2 in the case of using steam as a gasifying agent
(46.2 vol%) is more than double compared to that using
O2 (21.2 vol%). However, the gas yield in steam gasification (32.1 wt%) was less than when O2 was used as a
gasifying agent (52.2 wt %), which is largely due to high
amounts of CO and CO2 being present in the latter case.
Weight (%)
60
Volume (%)
74
0
650
750
850
Temperature (癈)
Figure 4. Effect of second-stage temperature on product
yield (wt% yield) at the first-stage final temperature
of 850 ? C, steam/MBM (wt/wt) of 0.6, and packed-bed
height of 60 mm (% difference in replicate run: char, �
liquid, � gas, �.
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
STEAM GASIFICATION OF MBM
60
50
H2
H2
CO
Volume (%)
40
Volume (%)
CO
CO2
CH4
CO2
25
CH4
C2H4
20
C2H4
Other
H/C
Other
H/C
0
0
550
650
750
Temperature (癈)
0
850
Char
Weight (%)
16
Liquid
25
Gas
8
GHV
Gross Heating Value (MJ/m3)
24
0
0
0
0.2
0.4
0.6
0.8
0.4
0.6
0.8
1
Steam/ MBM (wt./ wt.)
Figure 5. Effect of second-stage temperature on gas
composition (vol% yield) at first-stage final temperature of
850 ? C, steam/MBM (wt/wt) of 0.6, and packed-bed height
of 60 mm (% difference in replicate run: H2 , � CO, �
CO2 , � CH4 , � other H/C, �.
50
0.2
1
Steam/ MBM (wt./ wt.)
Figure 6. Effect of steam/MBM (wt/wt) on the product
yield (wt% yield) at final temperature of first stage and
second stage at 850 ? C, and packed-bed height of 60 mm
(% difference in replicate run: char, 0; liquid, 0; gas, �.
to 0.8 while keeping the final temperature of the first
and second stages at 850 ? C, N2 flow rate at 45 ml/min,
and packed-bed height of the second stage at 60 mm.
The effect of steam/MBM on product yield and gas
composition is presented in Figs 6 and 7. The char yield
decreased from 27 to 13 wt%, while liquid (tar + water)
and gas yields increased from 29.2 to 36.7 and 23.6
to 30 wt%, respectively. The increment in liquid (tar
+ water) is due to a large amount of unreacted steam
being present. Hydrogen increased from 36.2 to 47.1
vol%, while CH4 (23.2?14.5 vol%) and C2 H4 (8.7?5.3
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 7. Effect of steam/MBM (wt/wt) on gas composition
(vol% yield) at final temperature of first stage and second
stage at 850 ? C, and packed-bed height of 60 mm (%
difference in replicate run: H2 , � CO, � CO2 , � CH4 ,
� other H/C, �.
vol%) along with other hydrocarbons (0.4?0.3 vol%)
decreased gradually with an increase in steam/MBM.
The CO increased up to 23.8 vol% and then dropped
slightly to 23.3 vol%, while CO2 increased slightly
to 9.8 vol% and then remained constant with further
increase in steam/MBM. The char gasification and
reforming reactions are enhanced with an increase in
steam/MBM, which can be witnessed from the decrease
in char, CH4 , and other H/C content. The optimal
steam/MBM ratio for liquid and gas yields was 0.6;
however, the steam/MBM ratio of 0.8 was considered
to be suitable for H2 production. Similar trends were
observed by other researchers.[9,10] They found that
H2 and CO2 increased, while CH4 and CO decreased
with an increase in the steam flow rate during steam
gasification of lignin and refuse derived fuel in a fixedbed reactor system. Comparison of the results obtained
from steam and O2 as gasifying agents was made at the
same operating temperatures and packed-bed heights.
A higher content of H2 of 47.1 vol% was obtained
using steam at steam/MBM of 0.8, whereas the amount
was 21.2 vol% using O2 at ER of 0.2. H2 yield was
progressively increased in case of steam. However, the
gas yield was 30 wt% in the case of steam in comparison
to 52.2 wt% in the case of O2 .
Effect of packed-bed height
The packed-bed height of the second stage was varied
from 40 to 100 mm in increments of 20 mm while
keeping the final temperatures of the first and second
stages at 850 ? C, N2 flow rate at 45 ml/min, and
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
DOI: 10.1002/apj
75
C. G. SONI ET AL.
Asia-Pacific Journal of Chemical Engineering
in the case of the other H/C. They were constant in
the range of 6.3?6.1 vol%. These variations could be
due to reforming of CH4 and tar compounds with steam
and/or CO2 and water gas shift reactions.
45
40 mm
60 mm
30
Weight (%)
80 mm
100 mm
CONCLUSIONS
15
0
Char
Gas
Liq.
Figure 8. Effect of packed-bed height on the product yield
(wt% yield) at steam/MBM (wt/wt) of 0.8, final temperature
of first stage and second stage at 850 ? C (% difference in
replicate run: char, 0; liquid, � gas, �.
steam/MBM (wt/wt) at 0.8. Figures 8 and 9 show the
effect of the packed-bed height on product yield and gas
compositions. The liquid yield decreased from 38.6 to
34.9 wt%, while that of gas increased slightly from 29.5
to 31.6 wt%. H2 yield increased from 45 to 48.9 vol%
and CO and CO2 yields shifted up and down in the
range of 22.5?22.7 and 12.4?10.4 vol%, respectively
with an increase in the packed-bed height from 40 to
100 mm. CH4 showed a slight decrease from 14.5 to
13.3 vol%, while no significant variation was observed
MBM can be gasified using steam. Steam was found
to be an effective gasifying agent in comparison to
O2 to increase the hydrogen yield in the product
gases. A higher temperature of 850 ? C in both stages
was found to be favorable for higher gas yield and
hydrogen production within the temperature range studied. The two-stage process was found to be effective to reduce the liquid yield and increase gas yield.
It was also observed that with an increase in the
steam/MBM (wt/wt) ratio, hydrogen (36.2?49.2 vol%)
and gas (29.2?36.7 wt%) yields increased, while char
(27?13 wt%), CH4 (23.2?15.1 vol%), and other H/C
yields decreased. Gas (29.5?31.6 wt%) and hydrogen
(45?49.2 vol%) yields increased with increase in the
packed-bed height from 40 to 100 mm. There was no
significant variation observed in the case of yield of
heavier hydrocarbons.
Acknowledgements
The authors are grateful to the University of
Saskatchewan and the Province of Saskatchewan?s
60
Gross Heating Value (MJ/m3) & Volume (%)
76
40 mm
60 mm
40
80 mm
100 mm
20
0
GHV
H2
CO
CO2
CH4
Other H/C
Figure 9. Effect of packed-bed height on gas composition (vol% yield) and
gross heating value at steam/MBM (wt/wt) of 0.8, final temperature of first
stage and second stage at 850 ? C (% difference in replicate run: H2 , �
CO, � CO2 , � CH4 , � other H/C, 0).
? 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2011; 6: 71?77
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Agricultural Development Fund (ADF) for the financial
support for this project.
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