http://www.age.uiuc.edu/bee/research/tcc/tccpaper1.htm
uiul-ENG-98-7009
Paper No.
984016
An ASAE Meeting Presentation
THERMOCHEMICAL CONVERSION OF SWINE MANURE: TEMPERATURE AND PRESSURE
RESPONSES
By
B.J. He Y. Zhang G. L. Riskowski T. L. Funk
Graduate Research Assistant Associate Professor Professor Assistant
Professor
ASAE Student Member ASAE Member ASAE Member ASAE Member
Department of Agricultural Engineering
University of Illinois at Urbana-Champaign
Urbana, Illinois, USA
Written for Presentation at the
1998 ASAE Annual International Meeting
Sponsored by ASAE
Disney's Coronado Springs Resort
Orlando, Florida
July 12-16, 1998
Summary: A bench-scale thermochemical conversion (TCC) processor was
developed to study the TCC of swine manure to oil and gases. The effects of
the process parameters, including temperature, pressure, solids content,
retention time, and pH, on the conversion of swine manure to oil and gases
were examined. In this preliminary study, the ranges of the process
parameters were 180-275¡C, 1.0-6.0 MPa, 20% total solids, 1.0 to 3.0 hours,
and pH 6, respectively. The COD of the post-processed water was
significantly reduced compared to the untreated slurry. Substantial heat was
generated during the process. Preliminary data showed that the TCC process
is promising and could be an attractive technology to treat swine manure.
Keywords: Thermochemical conversion, swine manure, renewable energy
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Thermochemical Conversion of Swine Manure: Temperature and Pressure
Responses
Bingjun He, Yuanhui Zhang, Gerald L. Riskowski, Ted L. Funk
Agricultural Engineering, University of Illinois at Urbana-Champaign
1304 West Pennsylvania Avenue, Urbana, IL 61801, USA
Abstract: A bench-scale thermochemical conversion (TCC) processor was
developed to study the TCC of swine manure to oil and gases. Theeffects of
the process parameters, including temperature, pressure, solidscontent,
retention time, and pH, on the conversion of swine manure to oil andgases
were examined. In this preliminary study, the ranges of the process
parameters were 180-275¡ C, 1.0-6.0 MPa, 20% total solids, 1.0 to 3.0 hours,
and pH 6, respectively. The COD of the post-processed water was
significantly reduced compared to the untreated slurry. Substantial heat was
generated during the process.Preliminary data showed that the TCC process is
promising and could be an attractive technology to treat swine manure.
Keywords:Thermochemical conversion, swine manure, renewable energy
Pork production is one of the most value-added agriculture sectors in the
United States. As the swine industry provides more pork products desired by
our society, an increasing amount of swine manure is produced. The impact of
swine production on the environment has increased concerns of the general
public, scientific communities, government agencies, and the pork industry.
Millions of dollars are spent annually on swine manure storage, transport,
and land application. In addition, odor emission from swine facilities has
caused more outcries from the public, and become another major concern of
the industry. Swine manure, once regarded as a valuable natural fertilizer,
has now become an expensive burden on the pork industry. However, livestock
manure is a plentiful source of biomass that has the potential to be
converted to renewable energy through biological and/or chemical processes.
The thermochemical conversion (TCC) process is a chemical reforming process
of organic matter in a heated enclosure with little or no oxygen present.
TCC technology was studied using primarily coal, peat, and lignocellulosic
materials, such as wood sludge, as feedstock during the 1970's and 1980's,
and most of this research focused on the process known as pyrolysis (Buekens
and Schoeters, 1980; Hirata, 1985; Overand et al., 1985; Bridgwater, 1994).
Pyrolysis requires dry feedstock before processing, which can be very energy
intensive. The research on livestock waste pyrolysis for energy production
focused mainly on cattle waste in the 1970's (Kreis, 1979). No literature is
available on the TCC process of swine manure. TCC technology has the
potential of being applied as a treatment of swine manure, a cost-negative
supply of biomass. The treatment of swine manure through the TCC process can
greatly reduce the typically high chemical oxygen demand (COD) of swine
manure. Also, the TCC process can produce bio-energy, combustible gases and
liquid fuel, which could be used as an energy source for the TCC process.
The goal of this research is to develop a technology to manage swine manure
efficiently using the TCC process. Experimental apparatus description and
preliminary results are presented in this paper.
MATERIALS AND METHODS
FEEDSTOCK
The feedstock, fresh swine manure, was collected from the floor of finisher
rooms at the Swine Research Farm, College of Agricultural, Consumer and
Environmental Sciences, University of Illinois at Urbana-Champaign. The
fresh manure was stored in a 5-gallon bucket at 4¡C for no more than 72
hours. The total solid and volatile solids content of the feedstock were
measured immediately after sampling. After the determination of the solids
content, the feedstock for the TCC processor was prepared by adjusting the
total solids content of the fresh manure to approximately 20% by weight with
de-ionized water. The prepared slurry was then weighed, and its pH measured
and recorded before fed into the TCC processor.
TCC PROCESSOR
The processor is made of T316 stainless steel with extreme operation
conditions of 13.1MPa and 350¡C. The capacity of the processor is two
liters. A spiral cooling coil inside the processor provides temperature
control. Two agitation propellers are driven by a 200W-motor through a
magnetic drive. A rupture disc and pressure relief valve were added to the
processor to ensure safety. A customized condensing-reflux unit is also
attached to the processor. A picture of the TCC processor and a diagram of
the processor setup with control system are shown in Figures 1 and 2.
Figure 1 TCC processor on a floor-stand cart.
Figure 2 Diagram of TCC processor.
In this study, temperature was the major control parameter. Pressure was
indirectly controlled through temperature control because the pressure was
coupled with temperature in such a psuedo-equilibrium slurry system. The
temperature controller features a three-term
Proportional-Integral-Differential control, high temperature limit shut-down
control, and thermocouple malfunction protection control. The resolution of
the control is 1¡C and accuracy is ± 2¡C. The cooling water to the cooling
coil is controlled by a solenoid valve. Agitation speed was controlled and
monitored continuously by a digital tachometer.
PROCESS PARAMETERS STUDIED
The parameters studied were operating temperature and retention time.
Temperature is important to the thermochemical process, because it affects
the conversion reactions involved. The temperature range for this study was
160~250¡C (the corresponding pressure range was 0.6~5 MPa). Volatile solids
content is another major parameter, which represents the highest potential
amount of the manure that can be converted to gases and oil.
In this study the total solids by weight in the fresh manure were
approximately 20%, of which 80-85% was volatile solids. Retention time is a
kinetic parameter of the TCC process. There were three levels of retention
time employed: 60, 120, and 180 minutes. Acidity (pH value) of the feedstock
affects the TCC process by serving as catalyst for the hydrolysis of
cellulose and many other carbohydrates and depolymerization reactions. In
this study, the pH value of the fresh manure (6 ± 0.3) was monitored but not
controlled.
PRODUCTS SEPARATION AND ANALYSES
The solid content of the feedstock was measured by the methods described in
the Standrad Methods for the Examinations of Water and Wastewater (1989).
Gases were produced during the process, which contribute to the pressure
increase after the reaction ceased. Gas product separation from the solids
and liquids was done readily after the operation ended and the processor was
cooled to room temperaturn when the final pressure and temperature readings
were recorded. The solids after the reaction are the char formed and inert
foreign materials such as dirt. Liquids include the post-processed water
with most of the soluble minerals and the oil produced. Solid/liquid
separation was achieved through two-stage filtration. Larger particles (char
and dirt, etc.) were filtered out through a 60-mesh metal screen filter. The
fine char particles were separated with a glass fiber filter (HACH company,
Loveland, Co.) under vacuum. Oil formed was separated from the
post-processed water through solvent extraction. Toluene was chosen as the
solvent and a multiple batch solvent extraction method was used. Oil product
isolation and solvent recovery was achieved by a batch rectification
operation. The rectification operation was finished when the boiling point
of the residue liquid was 150¡C or higher at a vacuum of -88 kPa. The
solvent evaporated at this temperature and pressure. The residual content
was the oil and other liquid organic compounds formed from the TCC process.
Several analyses were performed on the post-processed water, including COD,
nitrate, total phosphorus, and potassium contents. The chemical composition
of the oil and gas products have not been examined so far due to inadequate
information on the operating conditions of the process. Thus no rigid mass
balance has been performed.
RESULTS AND DISCUSSIONS
TCC PROCESSOR PERFORMANCE
Based on the power supplied to the TCC processor, the temperature increase
rate was controlled at 4¡C/min. While temperature was approaching the
pre-set point, the automatic control was in effect. Power was supplied to
keep temperature between the pre-set points. From the operation profile, as
shown in Figure 3, a large temperature overshoot at the early stage of the
operation was evident. While approaching the pre-set temperature (200¡C),
the temperature overshot by 45¡C. The temperature overshoot caused a
pressure overshoot as well. Furthermore, the pressure is much larger than
the water vapor pressure at the corresponding temperature. This phenomenon
was observed starting at 160¡C and most of the depolymerization reactions
occurred in the next 30~40 minutes. However, if the retention time was less
than 60 minutes, there was a significant amount of organic matter left
unreacted. The minimum retention time for complete conversion of the manure
was 120 minutes for the temperature of 250¡C.
Figure 3 Temperature and pressure responses at early stage of the TCC
process of swine manure. The pre-set temperature was 200¡C. Where: -o-
temperature, -?- pressure.
To examine the cause of this temperature/pressure overshoot, a set of tests
was conducted with water in the system. The results are summarized in
Figures 4 and 5.
As shown in Figures 4 and 5, low temperature increases over the pre-set
point were observed with water alone, which was solely from the heat inertia
of the processor system. It was concluded that the large
temperature/pressure overshoots from the TCC processing of swine manure were
not caused solely by the heat inertia, but instead from the reaction heat
produced by depolymerization of the swine manure. This was confirmed by
comparing this phenomenon with that of water (Figure 5). At the same
temperature increase rate, the pressures were much lower in the water system
than in the manure system. This exothermic reaction heat from
depolymerization caused the temperature overshoot of the TCC process.
Figure 4 Temperature increase (? T) of the system vs. the pre-set control
temperature in TCC process of swine manure and water systems. The
temperature increase rate was 4¡C/min. Where: -x- the TCC system, -?- tap
water system.
Figure 5 Operating pressure vs. temperature diagram for water and manure
sludge (20%TS). The pre-set temperature is 250¡C. Where: -x- operation
pressure in the TCC process of swine manure, -?- water vapor pressure of
water.
Because of the rapid reaction heat release, the temperature as well as the
pressure were uncontrollable. To operate the TCC processor safely and
smoothly, a two-stage temperature control strategy was adopted. Based on the
temperature overshoot at different pre-set temperatures (Figure 4), at first
the pre-set temperature was set lower than the desired operating
temperature. When the reaction occurred, the temperature increased to its
corresponding overshoot point. The final desired temperature was then re-set
when the temperature reached its highest point. This way we achieved a much
smoother operation temperature and pressure profile, as shown in Figure 6.
Figure 6 Temperature and pressure responses of the TCC process of swine
manure. The final expected temperature is 250¡C and the first pre-set point
was 200¡C. Retention time is 180 minutes. -o- temperature, -/- operation
pressure, --- water vapor pressure predicted, -?- gas pressure produced.
WASTE REDUCTION
The feedstock processed in this study was 20% of total solids by weight, of
which about 85% were volatile solids. The chemical oxygen demand (COD) of
this feedstock was 153,000 mg/L. After the TCC process, the COD of the
post-processed water after filtration was 8,500 ± 2,500 mg/L. This
represents a 94% reduction in COD. Some of the organic matter was converted
to char-like solids that can be easily separated from the liquids.
Approximately 80% of the post-processed solids by weight were volatile. An
example of product distribution is shown in Table 1.
Table 1 Products of a typical test of TCC process of swine manure. The
operating temperature was 250¡C, pressure 4.1 MPa, and retention time 180
minutes.
Quantity (g) Percentage of total input (%)
Input TS 195.4 20.0
VS 154.1 15.8
pH 5.92
COD, mg/L 153,000
Output Liquids (total) 859.9 88.2
Solids (dried) 22.9 2.35
Gases N.D. N.D.
Oil extracted 13.3 (8.63% of VS)
Post-processed water (before filtration)
TS (12.2% sample)
VS (10.2% sample)
Post-processed water (after filtration)
TS (5.92% sample)
VS (4.58% sample)
COD, mg/L 10,035
pH 6.06
N.D. = Not determined.
OIL PRODUCTION
The conversion process of swine manure is similar to many other biomass
sources. The process is even easier than others are because there is much
less lignin content in swine waste, which is very hard to decompose. On the
other hand, less lignin means less energy content (Humphrey, 1979; Glasser,
1985), resulting in less oil production. Swine manure has a high oxygen to
carbon ratio and low hydrogen to carbon ratio and it is quite different for
cattle manure (Zahn et al., 1997; Hrubant et al., 1978). These affect the
oil formation efficiency negatively because high oxygen content in organic
matter means low heating value. In this preliminary study, 8.5% of volatile
solids were converted to a low quality oil-like product. We are in the
process of increasing the oil production from the TCC process. Many
researchers have employed liquefaction, one type of TCC process, to increase
the yields of oil from different types of biomass (Appell et al., 1980;
Datta and McAuliffe, 1993) by applying reductive compounds (e.g., hydrogen
and carbon monoxide) to the de-oxygenation process. In our next stage
research, we will use hydrogen and/or carbon monoxide as reductants to
increase oil production.
SUMMARY
A preliminary study on the TCC process of swine manure has been carried out
with aims of reducing swine waste and odor emission, and producing oil. A
TCC bench processor has been developed and tested. COD levels of the swine
manure sludge were reduced by 94%. Approximately 8.5% of the volatile solid
were converted into oil product. The preliminary results show that the TCC
technology has the potential to be applied to swine manure treatment.
Further studies are in process to explore the optimum operating conditions
for maximum oil production and waste/odor reduction.
ACKNOWLEDGEMENT
The authors wish to acknowledge the financial support by Illinois Council on
Food and Agricultural Research (C-FAR).
REFERENCES
Appell, H.R., Y.C. Fu, S. Friedman, P.M. Yavorsky and I. Wender. 1980.
Converting Organic Wastes to Oil: A Replenishable Energy Source. Bureau of
Mines, U.S. Department of the Interior, Washington, D.C.
Bridgewater, A. V. eds. 1994. Advances in Thermochemical Biomass Conversion.
New York: Blackie Academic and Professional.
Buekens, A.G. and J.G. Schoeters. 1980. Basic principles of waste pyrolysis
and review of European processes. In Thermal Conversion of Solid Wastes and
Biomass, eds. J.L. Jonesand and S.B. Radding, 397-421. Washington D.C.
American Chemistry Society.
Datta, B.K. and C.A McAuliffe. 1993. The production of fuels by cellulose
liquefaction. In Proceedings of First Biomass Conference of the Americas:
Energy, Environment, Agriculture, and Industry. 2:711.
Glasser, W.G. 1985. Lignin. In Fundamentals of Thermochemical Biomass
Conversion. eds. R. P. Overend, T. A. Milne, and L. K. Mudge. 61-76. London
and New York: Elsevier Applied Science.
Hirata, T. 1985. Pyrolysis of cellulose: an introduction to the literature.
Washington, D.C.: U.S. Department of Commerce.
Hrubant, G.R., R.A. Rhodes, and G.H. Sloneker. 1978. Specific composition of
representative feedlot wastes: a chemical and microbial profile. Washington,
D.C.: Science and Education Administration, U.S. Department of Agriculture.
Humphrey, A.E. 1979. The hydrolysis of cellulosic materials to useful
products. In Hydrolysis of Cellulose: Mechanisms of Enzymatic and Acid
Catalysis, eds. R.D. Brown, Jr. and L. Jurasek, p27. Washington, D.C.:
American Chemical Society
Kreis, R. D. 1979. Recovery of by-products from animal wastes - a literature
review. EPA-600/2-79-142. Report for the US Environmental Protection Agency,
Cincinnati, OH.
Overend, R. P., T.A. Milne, and L.K. Mudge eds. 1985. Fundamentals of
thermochemical biomass conversion, Proceedings of International Conference
on Fundamentals of Thermochemical Biomass Conversion. New York: Elsevier
Applied Science.
Zahn, J.A., J.L. Hatfield, Y.S. Do, A.A. DiSpirito, D.A. laird, and R.L.
Pfeiffer 1997. Characterization of volatile organic emissions and wastes
from a swine production facility. J. Environ. Qual. 26:1687-1696.
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