uilu # 99-7021
Paper No. 994062
An ASAE Meeting Presentation
THERMOCHEMICAL CONVERSION OF SWINE MANURE: A PROCESS
TO REDUCE WASTE AND PRODUCE LIQUID FUEL
by
B. J. He Y. Zhang Y. Yin G. L. Riskowski T. L. Funk
Research Assistant Associate Professor Visiting Scholar Professor Assistant Professor
ASAE Student Member ASAE Member ASAE Member ASAE Member
Department of Agricultural Engineering
University of Illinois at Urbana-Champaign
1999 ASAE/CASE Annual International Meeting
Toronto, Ontario, Canada
July 18-21, 1999
Summary:
A thermochemical conversion (TCC) process was applied to the treatment of swine manure slurry for energy
production and waste reduction. The objectives of this first stage study were to explore the feasibility of oil production
from swine waste and to determine the waste reduction rates through this process. A bench TCC reactor was
developed and tested. The operating temperature ranged from 250C to 305C. The retention time was two hours. A
reducing agent, CO, was added to promote oil product conversion. Operating pressure ranged from 6.9 to 10.3 MPa
and pH was monitored but not controlled. The oil product was evaluated through element analysis, heating value, and
benzene solubility. The waste reduction rate was evaluated by chemical oxygen demand (COD) before and after the
TCC process. The operating temperature and CO addition were the important factors affecting oil yield and quality.
At temperatures of 285ºC or above with CO addition, the carbon content was typically 65% to 68%, and hydrogen
content 8% to 10%. The oil yield was as high as 63% of the initial volatile solids in the input. The benzene solubility
of the oil product was as high as 90%. The average heating value of the oil product was 30,500 kJ/kg. The COD
reduction rate was as high as 72% through this TCC process.
Keywords:
Swine manure, thermochemical conversion, liquefaction, renewable energy, biomass
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THERMOCHEMICAL CONVERSION OF SWINE MANURE: A PROCESS
TO REDUCE WASTE AND PRODUCE LIQUID FUEL
B. J. He, Y. Zhang, Y. Yin, G. L. Riskowski, T. L. Funk
Agricultural Engineering, University of Illinois at Urbana-Champaign
1304 West Pennsylvania Avenue, Urbana, IL 61801, USA
ABSTRACT. A thermochemical conversion (TCC) process was applied to the treatment of swine manure slurry
for energy production and waste reduction. The objectives of this first stage study were to explore the feasibility
of oil production from swine waste and to determine the waste reduction rates through this process. A bench
TCC reactor was developed and tested. The operating temperature ranged from 250 C to 305C. The retention
time was two hours. A reducing agent, CO, was added to promote oil product conversion. Operating pressure
ranged from 6.9 to 10.3 MPa and pH was monitored but not controlled. The oil product was evaluated through
element analysis, heating value, and benzene solubility. The waste reduction rate was evaluated by chemical
oxygen demand (COD) before and after the TCC process. The operating temperature and CO addition were the
important factors affecting oil yield and quality. At temperatures of 285ºC or above with CO addition, the
carbon content was typically 65% to 68%, and hydrogen content 8% to 10%. The oil yield was as high as 63%
of the initial volatile solids in the input. The benzene solubility of the oil product was as high as 90%. The
average heating value of the oil product was 30,500 kJ/kg. The COD reduction rate was as high as 72% through
this TCC process.
KEYWORDS. Swine manure, thermochemical conversion, liquefaction, renewable energy, biomass
S
wine manure management for large materials are converted to liquefied products through a
confinement operations is a major concern of complex sequence of changes in physical structure and
both the public and pork industry. Many chemical bonds (Chornet and Overend, 1985). In this study, a
researchers have initiated studies to explore thermochemical conversion process, liquefaction, was applied
effective and efficient ways to solve this problem. to the treatment of swine manure slurry for energy production
Application of a thermochemical conversion process for and waste reduction. The objectives of this study are to (1)
swine manure treatment is one of the possible solutions explore the feasibility of oil production from swine waste, (2)
(He et al., 1998). Studies on livestock waste conversion determine the waste reduction rates through this process, and
processes were mainly conducted during the 1970’s and (3) examine the operation parameters that affect the swine
concentrated on pyrolysis and/or gasification of cattle manure liquefaction process.
manure to produce combustible gases. Swine manure
was rarely the feedstock for the thermochemical
conversion process. However, swine manure is a MATERIALS AND METHODS
biomass rich in cellulose and lignin. It has the potential PROCESS AND FEEDSTOCK
to be converted to a liquid oil product.
The process setup and control scheme of the
Ligno-cellulosic wastes can be converted to various thermochemical conversion (TCC) reactor were described by
forms of energy through numerous thermochemical He et al. (1998). The TCC processor was upgraded to operate
conversion processes, depending upon the at an extreme operating condition of 375C and 35 MPa for an
characteristics of the raw materials and the type of extended investigation range. A high-pressure cable tubing
energy desired. Among the thermochemical conversion connects the CO cylinder to the inlet of the TCC processor.
processes, liquefaction was one of the most studied and The reactor was housed in a closed chamber. The chamber
widely used (Minowa et al., 1995; Datta and McAuliffe, was under a slightly negative pressure and exhausts out to
1993; Gharieb et al., 1993; Chornet and Overend, 1985; ensure no CO leaks into room.
Kranich, 1984; Kaufman and Weiss, 1975).
The collection of the feedstock, fresh swine manure, was
Liquefaction was historically linked to hydrogenation
from the same source and follows the same processing
and other high-pressure thermal decomposition
procedures as in the preliminary research (He et al., 1998).
processes that employ reactive hydrogen or carbon
The chemical analysis results show that the characteristics of
monoxide (CO) to produce a liquid fuel from organic
the swine manure, such as carbon and hydrogen content,
matter. In the liquefaction process, the carbonaceous
CONTACT AT: (217) 333-5243, FAX: (217) 244-0323, E-MAIL: BHE@UIUC.EDU 1
volatile solids, and pH value were consistent from batch at a constant speed of 200 rpm and kept constant for all
to batch. experiments in the study.
The outputs from this TCC process include gases, liquid
PROCESS PARAMETERS oil, post-processed water, and solid products. Gases were
released after the run. Gas samples were collected in 100-ml
Temperature was determined as the most important
serum bottles for laboratory analysis. The oil product was
parameter in the process, because the equilibrium was
readily separated from the post-processed water after the run,
established between water vapor and liquid water in the
since it is lighter and floats to the top of the post-processed
closed system, and water vapor contributes to the
water. The solid product consists of inert materials and char
pressure increase and the gas production. The total
particles. The char particles are so fine that they remained
operating pressure is coupled with operating
suspended in the liquid. The separation of solids and post-
temperature and changes during the course of the
processed water was conducted using vaccum filtration with a
feedstock decomposition. CO serves as a reducing agent
glass fiber filter (pore size 1.2 m. HACH company,
in the process. The amount of CO affects the oxygen
Loveland, Co.).
content in the depolymerized products, or the quality of
the oil product. In the closed system, the initial pressure
of CO is proportional to the initial amount of CO added, ANALYTICAL ASSAYS
therefore, after determining the amount of feedstock
The analysis of gas product composition was performed
(total volatile solids), the CO initial pressure determines
by a gas chromatography (GC) designed for simple gas
the initial ratio of CO to total volatile solids.
analysis (Model 580, GOW-MAG Instrument Company,
Solids content is another major parameter affecting Bridgewater, NJ). The GC is equipped with a column of
the TCC process. Based on preliminary tests, about 87% porous polymer and molecular sieve 5 Å in the size of 80~100
of the total solids are volatile. Since the volatile solids meshes. The column is 8 centimeters in diameter and 1.2
are the fraction of the manure that can be converted to meters in length. The amount of gaseous product was
oil products, high volatile solids content is desirable. estimated by using the Starling modified Benedict-Webb-
However, manure with 25% (by weight) or more total Rubin gas equation of state (Starling, 1971). This equation
solids content is difficult to pump. Manure with less was mainly used for the thermal property calculations of
than 10% total solids is easier to pump, but may not be hydrocarbons. The error range is 0.5%~2.0% for light
economical. Initially, the level of total solids content hydrocarbons, CO2, H2S, and N2. In the preliminary study of
was chosen to be 20% in this study. this TCC process, the major component of gas product was
Retention time is a kinetic parameter of the TCC carbon dioxide. When the equation was tested with known
process. It affects the organic conversion rate or product CO2 data, the results showed a very good prediction with an
yields. Inadequate retention time of the reactants will error less than ±1% as pressure ranged up to 4 MPa.
lead to an incomplete conversion process. However, The elemental analyses were performed on the oil product
excessive retention time may result in over-reacting of and post-processed water. These included carbon, hydrogen
the oil products and formation of char. The retention and nitrogen (CHN) analysis, and metallic element analysis
time was set to 120 minutes in this study based on using carbon-hydrogen-nitrogen analyzer (CE440 by Exeter
preliminary work. The natural pH (6.50.3) of the fresh Analytical, Inc. N. Chelmsford, MA) and Inductively Coupled
manure was monitored but not controlled. Plasma (Plasma II by Perkin Elmer Norwalk, CT),
respectively.
EXPERIMENTAL PROCEDURES The quality of the TCC oil product was evaluated by the
The TCC processor was operated in a batch mode. carbon and hydrogen content, the heating values, and the
After introducing the initial CO, the reactor was heated benzene solubility. The carbon and hydrogen content were
up to a pre-set temperature. The rates of temperature obtained from the CHN analysis. Heating values of oil
increase were 5-10C/min. It took 40-50 minutes to product were estimated based on the complete oxidation of
reach this pre-set temperature. The highest temperature carbon and hydrogen elements and considering the oxygen
increasing rate occurred between 220ºC to 250ºC, when content in the oil product. A set of calculations on more than
exothermic reactions start. The temperature and ten known heating value compounds showed that the errors of
pressure responses of the TCC process were discussed the estimated heating values were within 5%. Solubility of
by He et al. (1998). After each run, the reactor was the oil products in benzene solvent was also conducted, which
cooled down to about 150ºC or lower at which time the is another accepted method to evaluate pyrolysis oils (Appell
reactions all terminated in 5 minutes. When the reactor et al., 1980).
was further cooled to ambient temperature, the The procedures of chemical oxygen demand (COD),
temperature and residual pressure were recorded for gas volatile solids and total solids, and pH values measurements
product estimation. The agitation is assumed to have a were the same as in the preliminary study (He et al., 1998).
minor effect on the TCC process. The agitation was set
2 ASAE/CSAE ANNUAL INTERNATIONAL MEETING
The procedures of chemical oxygen demand depolymerization reactions did not occur until 220C. The
(COD), volatile solids and total solids, and pH values depolymerization reaction did not proceed to completion and
measurements were the same as in the preliminary study some of the feedstock remained intact at 220C or below. In
(He et al., 1998). this study, the reaction temperature range was 250C to
The solubility of oil product, oil product yield, and 305C. The corresponding pressures were 5.5 MPa to 11
COD reduction rate are defined as following, MPa. These were lower than those in liquefaction processes
respectively: of wood sludge where temperature was as high as 400C and
oil residue (g) pressure was as high as 24 MPa (Meier & Rupp, 1991).
Oil so lub ility (%) (1 ) 100% (1)
total oil sample (g) Within this temperature range, the volatile solids conversion
rates to oil product ranged from 11% to 63% (Table 1). It was
total oil product (g)
Oil yield (%) 100% (2) obvious that operating temperature substantially affected the
total volatile solids input (g)
conversion process, though there is a variation in the oil
COD of post processed water product yields. One of the notable phenomena was that at
COD reduction (%) (1 ) 100% (3)
COD of raw manure 275C or below, the oil product did not form successfully in
The standard errors were within 5% for solids every run. This was presumably due to the complexity of the
measurements, oil solubility, elemental analysis, and swine manure composition and the slight variation from batch
total mass balance in this study. The standard error for to batch.
the COD measurement was within 8%. The quality of TCC oil product is evaluated by an
element analysis, its benzene solubility, and heating value.
Based on the chemistry principle that “like dissolves like”,
RESULTS AND DISCUSSION benzene solubility is another parameter to characterize the oil
product quality. The more the oil product dissolves in
The focus of this study is on the TCC oil product benzene, the more oil-like components it contains, thus the
and waste strength reduction of swine manure. The
better quality of the oil. The oil product samples at 285C to
process yields four products: oil, the post-processed
water, gases, and solid residues. The results of ten 305C had a benzene solubility of 81.6% to 89.8%. The oil
example experiments are summarized in Table 1. products at 270C or below had a low solubility as the result
of incomplete depolymerization. Portions of the feedstock
OIL PRODUCTION remained un-reacted, but contained in the oil layer. Therefore,
The conversion process of swine manure to oil is from the oil product yield and quality point of view, the
similar to other biomass liquefaction processes. The operating temperature needs to be 285C or higher.
biomass conversion in this study is even easier in the
sense that swine manure contains less lignin, which is CARBON AND HYDROGEN CONTENT OF THE OIL PRODUCT
very difficult to decompose. The biomass has been The contents of carbon and hydrogen are important
“pre-processed” by the pigs to such a uniform size that it indicators of the quality of the TCC oil product. For high
is suitable for liquefaction. On the other hand, less quality oil, the content of carbon and hydrogen must be
lignin means less energy content (Humphrey, 1979; sufficiently high and oxygen content should be as low as
Glasser, 1985) resulting in less oil yield. Swine manure possible. Besides carbon and hydrogen, the oil product also
has a high oxygen to carbon ratio and low hydrogen to contains many other elements, such as oxygen, nitrogen,
carbon (Zahn et al., 1997; Hrubant et al., 1978). These sulfur, and minerals. The carbon content in the study ranged
affect the oil formation efficiency negatively because from 63% to 71%, the hydrogen 8% to 10%, and nitrogen
high oxygen content in organic matter implies low 3.8% to 4.6%. The average ratio of carbon to hydrogen is
heating value. According to preliminary test results, 7.4:1 (by weight). A review of the literature shows the
there was little organic carbon converted to oil without carbon and hydrogen content is equivalent to or better than the
the addition of a reductant. The oil yield was less than pyrolysis oil made from wood sludge liquefaction, where the
8% (by weight) (He et al., 1998). In a liquefaction carbon content ranged from 50% to 67%, hydrogen from 7%
process, some sort of reductive chemical reagent, e.g., to 8%, and nitrogen 8% to 10% (Rick and Vix, 1991).
hydrogen or CO, is needed to increase the oil production Oxygen content was not analyzed, but it was assumed to be a
rate (Datta and McAuliffe, 1993; Appell et al., 1980). major component besides the carbon and hydrogen. The TCC
In this study, CO was employed as the reductant. The oil product has a relatively high nitrogen content, about 4-
experimental results showed that the addition of the CO 4.5%wt as a result of the high nitrogen content in the
improved the organic carbon conversion to oil product. feedstock. A typical analysis of dry raw swine manure sample
Temperature had a substantial effect on the oil showed that the nitrogen content was 3.74%wt, while the
formation, as expected. The depolymerization reactions carbon and hydrogen contents were 47%wt and 6.5%wt,
of organic matter could not occur until the temperature respectively. Based on the C:H ratio and assuming the
reached such a degree that the activation energy was remainder is oxygen, the heating value of the TCC oil product
overcome. It was observed from preliminary work that was estimated as 30,500 kJ/kg.
the reactions initiated from 160C, but the
JULY 18-21, 1999 TORONTO, ONTARIO, CANADA 3
Table 1 Summary of the experiment results of the TCC process. The retention was 120 minutes for all the experiments.
Operating Conditions Oil Product Post-processed Water CO
No. Temp Pressure VS:CO yield Solubility C H N N P K COD COD re- conversion
(C) (MPa) (wt) (%) (%) (%wt) (%wt) (%wt) (ppm) (ppm) (ppm) (mg/L) duction (%) (%)
1 250 4.5 0.1 7.5 33.0 52.2 71.5 8.5 4.6 6,300 4,196 1,130 115,850 52.0 1.0
2 250 6.9 0.2 3.8 33.5 51.6 68.7 8.2 4.5 6,300 4,330 1,471 119,950 50.3 0.0
3 270 5.5 0.2 7.5 11.1 49.5 68.6 8.1 4.5 6,300 4,062 1,200 107,600 55.1 0.0
4 270 10.5 0.3 1.5 48.6 71.6 65.8 9.5 3.9 7,300 4,089 1,352 124,300 48.3 16.4
5 285 8.6 0.5 7.5 38.3 83.7 63.6 10.4 n.d. n.d. 4,657 938 94,700 63.9 76.7
6 285 11 0.7 1.8 43.9 81.6 68.6 9.3 4.1 n.d. 4,552 929 90,350 65.3 26.7
7 295 9.6 0.5 7.5 32.0 81.6 n.d. n.d. n.d. n.d. n.d. n.d. 89,900 62.7 n.d.
8 295 9.6 0.5 7.5 51.8 86.6 n.d. n.d. n.d. n.d. n.d. n.d. 66,400 71.9 80.6
9 305 11 0.7 7.5 63.0 87.4 n.d. n.d. n.d. n.d. n.d. n.d. 83,800 65.2 89.0
10 305 11 0.7 7.5 51.1 89.8 n.d. n.d. n.d. n.d. n.d. n.d. 67,300 71.7 78.0
n.d. = not determined.
WASTE STRENGTH (COD) REDUCTION This is because the minerals from the feedstock remained
The waste strength in the post-processed water was essentially in aqueous solution. The major portion of the
substantially reduced in the TCC process. The nitrogen in the feedstock was in nitrate form that dissolved in
feedstock swine manure slurry processed in this study the aqueous solution. The NPK value is still too high to be
was controlled at 20% (by weight) of total solids, of discharged to a wastewater treatment system. If diluted, it
which approximately 85% to 88% was volatile solids. could be used for irrigation under some specific conditions.
The COD of this feedstock was 237,4001,200 mg/L.
After the TCC process, the COD range of the post- GAS PRODUCTION AND CARBON MONOXIDE CONVERSION
processed waters was from 66,400 mg/L to 124,300
mg/L and the sample mean and standard deviation were Carbon dioxide (CO2) was the sole gas by-product in the
96,020 and 20,610 mg/L, respectively. The TCC process. The GC analysis showed no methane or other
corresponding volatile solids contents in the post- gases. Carbon dioxide was formed when the depolymerization
processed water ranged from 3.27% to 6.76%. The COD occurred and the carbonyl groups were thermally cleaved.
of the post-processed water were 28% to 50% of those CO2 was also released as the result of decarboxylation
in the original manure slurry. More than 50% of the reactions. It was observed that more CO2 was produced and
organic matter was converted to oil product that can be more char formed if no CO was added as a reductant at high
readily separated from the liquid. operating temperatures. The CO addition consumption
becomes an indication of oil product formation, i.e., CO
It was also observed that the runs with higher oil reduced the feedstock, eliminating elemental oxygen and
yields also had higher COD reduction rates. The runs releasing carbon dioxide.
with operating temperature of 285C or higher had an The results showed that 76.7% of the CO was converted
average oil product yield of 46.7%. The average COD to CO2 in Run #5. It had about the same oil product quality as
for the runs was 82,080 mg/L with a standard deviation Run #6 but 5.6% less oil yield. The CO conversion rate,
of 12,300 mg/L. The corresponding COD reduction rate however, was 50% higher than that in Run #5. This was
was 65.4%. This was 15% more COD reduction rate because four times more CO added in Run #6. In terms of
than that of the runs with operating temperature lower consumption of CO per unit weight of volatile solids input,
than 285C, of which the average oil product yield was the values were 0.125 g CO/g VS and 0.095 g CO/g VS for
31.5%. This is because less organic matter remained in the runs #6 and #5, respectively, excluding the amount
the post-processed water when the oil conversion rates consumed by the free oxygen in the head space. The
were high. Therefore, temperature is the most important difference of these values was not as significant as CO
operating parameter that affects the oil production and conversion rate only. Although excessive CO addition
waste reduction. resulted in a better oil yield, it is not economical in terms of
the operation cost.
NUTRIENT CONTENTS IN POST-PROCESSED WATER
In the study, the nutrient content, nitrogen (N),
phosphate (P), and potassium (K), of the post-processed SOLID PRODUCT
water were measured for some runs. The NPK Solid product was only a small portion of the total input,
concentrations in the post-processed water were usually less than 5% (by weight). It contained inert materials,
basically constant regardless of the operation conditions. such as dust, and some char formed. Depending on the
4 ASAE/CSAE ANNUAL INTERNATIONAL MEETING
operation conditions, the volatile solids content in the and L. K. Mudge, 967-1002. Elsevier Applied Science, New
solid product ranged from 30% to 70% by weight. York, NY.
Datta, B.K. and C.A McAuliffe. 1993. The production of fuels
by cellulose liquefaction. In Proceedings of First
EFFECTS OF OPERATING PARAMETERS Biomass Conference of the Americas: Energy,
Determining the role of each operating parameter is Environment, Agriculture, and Industry. 2:711.
very important for the optimization of the TCC process.
Gharieb, H.K, S. Faramawy, and F.A. El-Amrousi. 1993.
The effects of operating parameters on the oil formation,
Liquefaction of cellulosic wastes: production,
waste reduction, and oil product quality were
characterization and evaluation of pyrolysis oils, Journal of
investigated systematically. The optimum operation
Chemical Technology and Biotechnology, 58(4):395-402
conditions were determined through a set of orthogonal
experiments. The results are discussed in separate paper He, B. J., Y. Zhang, G. L. Riskowski, T. L. Funk. 1998.
(He et al., 1999). Thermochemical conversion of swine manure:
temperature and pressure responses. ASAE Annual
CONCLUSIONS International Meeting, Paper No. 984016. Orlando, FL.,
July 12-16.
The TCC process was applied to the treatment of
swine manure slurry to produce liquid oil and reduce He, B. J., Y. Zhang, G. L. Riskowski, T. L. Funk. 1999.
the waste strength. The oil yield was as high as 63% of Thermochemical conversion of swine manure: effects of
the total volatile solids of the feedstock. The COD in operational parameters on oil conversion rates and waste
the post-processed water after the TCC process had a reduction rates. Manuscript in preparation
reduction rate as high as 72%. The TCC oil product had Hrubant, G. R., R. A. Rhodes, and G.H. Sloneker. 1978.
a similar quality to that of pyrolysis oil from wood Specific composition of representative feedlot wastes: a
sludge. The average heating value of the oil product chemical and microbial profile. Washington, D.C.:
was estimated a 30,500 kJ/kg. It was concluded that the Science and Education Administration, U.S. Department
TCC processing of swine manure is feasible. The of Agriculture.
application of the TCC process to the treatment of swine Kaufman, J.A. and A. H. Weiss. 1975 Solid waste
manure not only can reduce the waste strength, but also conversion, cellulose liquefaction. EPA 670/2-75-031.
can produce useful energy in the form of liquid fuel. Report for the U.S. Environmental Protection Agency,
Further research is needed in improving the oil Cincinnati, OH.
conversion efficiency and utilization of the oil product. Kranich, W. L. 1984. Conversion of sewage sludge to oil by
hydroliquefaction. EPA-600/2-84-010. Report for the
ACKNOWLEDGMENTS U.S. Environmental Protection Agency, Cincinnati, OH.
The Illinois Council on Food and Agricultural Meier, D. and M. Rupp. 1991. Direct catalytic liquefaction
Research is acknowledged for providing financial technology of biomass: status and review. In Biomass
support for this preliminary study. Thanks are extended Pyrolysis Liquids Upgrading and Utilization. A. V.
to Mr. Peter G. Stroot, a research engineer of the Bridgewater and G. Grassi (eds). 177-218. Elsevier
Department of Agricultural Engineering, University of Applied Science, New York, NY.
Illinois at Urbana-Champaign, for his great thoughts and Minowa, T., S. Yokoyama, M. Kishimoto, and T. Okakura.
discussions. The authors would like to thank Dr. Joanne 1995. Oil production from algal cells of Dunaliella
Chee-Sanford of the Department of Animal Sciences, Tertiolecta by direct thermochemical liquefaction. Fuel.
University of Illinois at Urbana-Champaign, for her kind 74(12):1735-8.
assistance in gas analysis.
Rick, F. and U. Vix. 1991. Product standards for pyrolysis
products for use as fuel in industrial firing plants. In
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