A PILOT PLANT STUDY OF SYNTHESIS INTERMEDIATES
FROM FEEDLOT WASTE
by
ROGER LEE PETERSON, B. S. in Ch.E.
A THESIS
m
CHEMICAL ENGINEERING
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
MASTER OF SCIENCE
IN
CHEMICAL ENGINEERING
Approved
December, 1975
^0' r
ACKNOWLEDGMENTS
The Author wishes to thank Don Carlisile, Gerald Grusendorf
and the other undergraduates that helped during the construction
and operation of the project. My thanks also to Henry Burchett
for his help and advice.
The financial support of Pioneer Natural Gas CO., The
Environmental Protection Agency, and the Texas Cattle Feedlot
Association is gratefully acknowledged. A note of thanks also
to Phillips Petroleum Co. whose fellowship grant was greatly
appreciated.
n
CONTENTS
ACKNOWLEDGMENTS
ii
LIST OF TABLES
v
LIST OF FIGURES
vi
I. INTRODUCTION
1
II. LITERATURE REVIEW
3
III. CONSTRUCTION, MODIFICATIONS AND PROCEDURES
6
Concept
6
Reactor and Feed Hopper
6
^
'Char Hopper and Ram
Reactor Heaters
10
Preheater
11
Instrumentation and Controls
12
Down-Stream System
1^
Modifications
19
Feed Hopper
15
Cyclone and Filter
20
: Water-Gas Separation
23
Flow Measurement System
24
Operational Procedure
24
Analytical Procedures
25
Preparation of Feedstock
27
m
IV... DISCUSSION OF RESULTS
V.
VI.
28
Feed Considerations
28
Experimental Conditions and Results
31
Reactor Operating Characteristics
33
Downstream Operating Characteristics
51
Feed Particle Size
53
Char Characteristics
55
fluidized Bed and Char Hopper Characteristics
56
Reactor Temperature Control
57
Data Reliability
58
Early Runs
59
Proposed Modifications
61
CONCLUSIONS
65
RECOMMENDATIONS
66
LITERATURE CITED
67
APPENDIX
69
A..
Sample Calculations for Normalization of Data
70
B.
Discussion of Proposed Reactor Design
72
C.
Raw Data
74
D.
Supplemental Data
77
rv
LIST OF TABLES
Table
1.
Typical Operating Values and Results for the Pilot Plant
Reactor
32
2.
Mass Balances
46
3.
First Run Data
60
LIST OF FIGURES
Figure
1.
Dimensions of Reactor
7
2.
Char Hopper and Fluidization Plate
9
3.
Electrical System
15
4.
Original System Configuration
16
5.
Final System Configuration
17
6.
Cyclone Dimensions
22
7.
Temperature Profiles in Reactor
34
8.
Raw Gas Production
37
9.
Effect of Temperature on Normalized Gas Production
39
10.
Small Scale Reactor Normalized Gas Production
40
11.
Raw Gas Composition (Methane and Ethane)
42
12.
Raw Gas Composition (Hydrogen and Ethylene)
43
13.
Reactor Effluent Gas Composition
44
14.
Small Scale Reactor Gas Composition
45
15.
Average Temperature Comparison to Small Scale Reactor
49
16.
Effect of Particle Size on Degree of Reaction
54
17.
Wet Steam Condenser Design
64
18.
Proposed Reactor Design
73
VI
• INTRODUCTION
In the VJest Texas area almost 5 million head of cattle are fed
in feedlots annually.
manure a day.^
Each cow produces about 5 to 9 pounds of
Historically bovine wastes have been returned to
the soil by the farmer to act as natural fertilizer.
However, syn-
thetic fertilizers have become very attractive to the farmer because
of the ease of application, the absence of odor, the availability,
and the lack of insect pests and weeds.
At the same time feedlots
have become larger and more centralized so that it may be more eco-
f
nomical for the farmer to use the more expensive synthetic fertilizers than to pay for hauling the bulky manure to his fields.
Thus, the feedlot owner has experienced long periods in the past
when he had no economical way to dispose of his waste material depending upon the local price of synthetic fertilizer.
In common
practice, the manure accumulates in large piles on unused portions
of the feedlot.
Since the Environmental Protection Agency has pro-
mulgated a regulation stating that feedlot runoff cannot be discharged into the waters of the United States except runoff resulting
from chronic or catastrophic precipitation, it is probably more
economical for the feedlot owner to dispose of his wastes rather
than try to contain them.
The Chemical Engineering Department has a policy of trying to
solve problems of the people and industries within the area served
by the University.
Thus, an opportunity was seen to solve the feedlot waste problem because the increasing costs of energy have made alternate
souces of fuel and raw materials more attractive.
Ttris study is the second phase of the manure disposal scheme
which has come to be known as the Syn Gas project.
The first phase
was initiated in 1972 by a paper evaluating the possible uses for
manure from a thermochemical standpoint ^
. A project v/as then
f3)
funded to construct and operate a bench scale reactor^ .
The bench scale reactor produced very encouraging results
which indicated that the production of ammonia synthesis gas (a 1
to 3 ratio of Nitrogen to Hydrogen) was feasible from feedlot
wastes.
To determine the actual feasibility of operating on a
commercial basis and to provide scale up data, it was decided that
a relatively large demonstration plant would be required.
The details concerned with the construction and operational
characteristics of this reactor system are intended to give a
prospective design engineer an insight into the problems and behavior that can be expected in a commercial manure pyrolysis unit.
Also, the data obtained from this study indicate some guidelines
for the design of future solid waste reactors, along with new prospects for the utilization of manure.
^
LITERATURE REVIEW
There are many possible solutions to the cattle feedlot waste
problem.
(4)
A recent Environmental Protection Agency report ^ ' lists
approximately 30 different methods including land utilization, containment, various sewage treatment schemes, production of single
cell protein, feed recycling, chemical treatment and even production of protein from fly larvae.
The work of Herzog ^ ' formed the basis and design criteria for
this pilot plant project.
Herzog's work is discussed and used for
comparison later in this thesis.
Herzog concluded that the partial
oxidation of cattle manure if followed by desulfurization and reforming steps could result in a gas suitable for the synthesis of
ammonia.
There are several other studies concerning feedlot waste pyrolysis.
The most complete study surveyed was the work of Garner
and Smith ^
. This study imployed three, batch, bench-scale re-
actors with a maximum temperature of 400-500°C.
The mild heating
rates (5 to 40^F/min) resulted in a gas production of only 26.1%
by weight of the dry manure and 21.5% tarry volatile and low boiling organics.
The average gas analysis was 3.6% H2, 10.9% N^, 12.9%
CH., 16% CO, 38.9% CO^, 0.3% Zr^^^ and 1.8% CgHg.
A complete lab-
oratory analysis was done on the pyrolysates which resulted in the
identification of a wide variety of alcohols, aldehydes, ketones,
acids, amines and phenols as well as polyfunctional compounds.
ever, stearic acid was the only significant fraction of the
How-
4
pyrolysate recovered in pure enough form to enable positive identification.
One interesting fact discovered was the loss of weight
by pyrolysis was significantly inhibited when done in a vacuum as
compared to an inert atmosphere at 14.7 psia.
A cyclonic burner for manure-to-synthesis gas production was
built by Natour ^ K
The data generated from Natour's experiment
is not easily compared to this study because a significant percentage of the generated gas was burned to fuel the pyrolysis.
Natour did show that pyrolysis with partial oxidation could be
sustained without adding outside heat.
Grub
indicated that the dry portion of manure consisted
largely of undigested cellulose, hemicellulose, lignin and lignoprotein complexes.
The pyrolysis of cellulose was studied and
several mechanisms were proposed for its step by step degradation
(9 10)
^ '
\
With cellulose an aqueous distillate began to form at
200^C and tar and gases were formed at 230-240°C ^^K
tion
becomes exothermic at 270°C^ ^
The reac-
Gas production was greatest
between 270-350°C^^^
Lignin from spruce exothermically decomposed at a higher temperature range (350-450°C) than the cellulose ' '.
Pyrolysis of
this lignin yielded more carbon and tar and less aqueous distillate
than cellulose pyrolysis ^
. Young ^
' has compiled the pyrolysis
data for the various components of manure and shown that they can
easily be used to fit manure pyrolysis data over a wery wide temperature range.
Theoretical studies of manure pyrolysis have been
conducted by Young in a parallel investigation with the large
scale reector discussed in this thesis.
Oiher studies have been directly supported or associated with
the greater Syn-Gas project.
(12)
Khara ^
' investigated the utilizaf3)
tion and disposal of the char and ash obtained form Herzog's ^ '
small reactor.
Massie ^
' utilized a partial oxidation retort with
manure as feed in an earlier study.
Smith et al ^^^K
This work was continued by
Al-Haj-Ali ^^^' completed a study of the drying
characteristics of manure.
Thus, a considerable bulk of data has
been assembled toward the development of manure pyrolysis technology.
CONSTRUCTION, MODIFICATIONS AND PROCEDURES
As with most developmental projects, the equipment and procedures were in a constant state of change throughout the course
of the project.
As more data becaijje available on the operating
characteristics of the system various modifications were initiated
to increase reliability, improve the accuracy, remove limitations,
and enhance understanding of the data.
Concept
Manure was added into the top of the hot reactor where it fell
to the bottom countercurrent to a stream of steam and air introduced
through a distribution plate at the bottom.
Gases resulting from
tli'3 pyrolysis and partial oxidation of the manure exited with the
input gas stream out the top of the reactor.
The gas was stripped
of entrained solids, tars and condensables in stages and composition
and flow rate data were taken for the gas stream.
Char was removed
from the bottom of the reactor through an opening in the input
gas distribution plate.
Reactor and Feed Hopper
The reactor was made from schedule 40 stainless steel pipe
(see Figure 1). A 6 inch diameter, 5 foot long section composed the
main body of the reactor and an 8 inch diameter, 2 foot long section
was used at the top of the reactor for a fluidized bed expansion
section to allow separation of the solids and gas.
In order to
900- RF m flng.
stainless steel
schedule 40 pipe
stainless steel
STD. WT. weld cap
stainless steel
1'-
schedule 40 pipe
stainless steel
8" X 6" -
concentric reducer
stainless steel
8'-0"
schedule 40 pipe
stainless steel (316 L)
collar stainless steel
900- raised faced
weld neck flng.
w/blind stainless steel
Figure 1 . Reactor Diniensions
ullow for the more than 2 inch vertical heat expansion, the reactor
was welded to horizontal 8 inch I beams at the bottom and guided
at the top by triangular ears which moved in slots welded to another set of I beams.
A star feeder model R2-653 manufactured by Beaumont Birch Co.
was mounted between the manure hopper and the reactor using a Reliance VSD variable speed motor Model B56G3102 with a 12 to 48
sprocket gear ratio.
The inlet gas distribution plate at the bot-
tom of the reactor consisted of a 3/8th inch stainless steel plate
with concentric circles of l/16th inch holes drilled into it
around a 1 inch hole in the center.
This distribution plate was
welded to a thin collar which was welded to the bottom flange of
the the reactor in such a way as to provide even inlet gas flow to
the bottom of the distribution plate (Figure 2 ) . A one inch OD
stainless steel tube passed through the bottom flange and was then
welded to the central hole to allow char to exit the reactor.
This
tube extended about 6 inches through the outside of the bottom
flafje where it was connected with swedgelock fittings to the char
hopper.
The whole distribution plate system and flange was fitted
with yery close tolerance into the bottom of the reactor.
Char Hopper and Ram
The char hopper was constructed in such a way that solids
flow could be diverted from one side to the other by moving a
semicircular piece of metal (Figure 2 ) . This provided a method
reactor
fluidization plate
swedgelock
approximate
position of
ram in down
position
^*^^B
^^
inlet air and
steam
^-^ interior ring
semicircular
pi ate
side changing
lever
pipe guide
ram
dividing plate
between hoppers
flange
access
port
ports for
^ driving air
Figure L. Lhar hopper and
Fluidization Plate
of measuring the char flow rate.
10
The original design had a large
flange which formed the top of the hopper to provide access to the
interior.
Because of the awkwardness of removing the whole hojjper
after each run to remove solids, the difficulty in removing char
from each side without crossover, and the leaks in the thin homemade flange; the upper flange was cut off and a plate was permanently welded on.
Access was then provided to each side of the
hopper by 4 inch flanged nipples which could be easily removed for
cleaning the hoppers.
A pipe which served to guide the ram was installed through
the center of the hopper.
The ram was a polished rod, which in the up position, extended
through the distribution plate and effectively plugged the exit
port of the plate.
In the down position the top of the ram was
several inches below the entrance port to the char hopper allowing
free flow of solids from the reactor.
The ram cylinder was pressed
against a lead gasket at the bottom of the char hopper by chains
and turnbuckels to provide airtight seal.
V
Reactor Heaters
The heating section of the reactor consisted of two 24 inch
long sections.
Each section was constructed of 4 pre-formed pieces
which were fitted around the pipe and secured with external bands.
Each section was rated at 40 amps, 206 volts.
Circuit breaker
protection was provided for each of the 4 pieces in a section.
11
These heaters, model 50752 type 77-KSD, were manufactured by Lindberg Co.
In general, the performance of these heaters was less
than satisfactory.
Improper electrical installation was one pri-
mary cause for repeated failures.
The other primary cause was that
the heaters were damaged during the early runs by exceeding the
voltage and temperature design parameters of the heaters. As time
progressed, more and more elements burned out (2 elements to a
piece).
By the end of run 10, only one element in the lower sec-
tion, or 12.5% of the original capacity, was operating.
Only about
50% of the upper bank was still operating during the final runs.
About 25% of these failures were obviously due to mechanical breaks
in the nichrome lead-in wires in places where they could not be
repaired.
Some of the other failures were apparently due to ox-
idation and melting of the nichrome material.
Preheater
The preheater consisted of a U-shaped loop of stainless steel
tubing.
The first section was 16 feet of 3/4 inch tubing and the
remaining 17 feet was 5/8ths inch tubing.
This loop was connected
by 3/4 inch braided copper welding leads to a Hobart Model T-5005422, 500 amp welding generator.
A government surplus D.C. power
supply was originally purchased for this purpose, but was found to
be faulty and was used only for its magnetic contactor.
To pre-
vent a meltdown of the preheater piping, the contactor was controlled by a Thermo Electric model 32142-02-005 Mini Monitor Analog
12
Latching High Temperature Alarm triggered by a thermocouple clamped
to the top of the preheater.
The tubing of the preheater was en-
cased in a sandwich of block type insulation which was held together by duct tape.
Because of the large convection surface area
of the system and limited power supply, meltdown was not judged to
be a problem except in the case of no flow through the preheater.
Instrumentation and Controls
Type K thermocouples were used to monitor the temperature profiles in the reactor and were attached to a 24 point Leeds and
Northrup model number 547 recorder.
A Flexapulse pneumatic timer
manufactured by Eagle Signal Corp. was used to control the motion
of the ram.
This unit could be set to independently control both
the number of seconds the ram stayed up and the number of seconds
down.
To control the input air stream, a Brooks type 1110-06F1A1A
rotameter was installed.
. test meter.
The rotameter was calibrated using a wet
A Brooks type 1110-OlFlAlA rotameter was connected to
the helium input line to measure the flowrate to the feed hopper.
However, the helium flow rate required was shown to be beyond the
capability of this rotameter.
No replacement rotameter was in-
stalled because the flow rate was not critical to the operation.
The cold product gas exit rate was measured using a Rockwell 2
inch model TP-4 turbometer.
13
An Elison Eagle Eye flowmeter (mechanical manometer) with an
•Arnubar semi-pitot type sensor was purchased to measure the steam
f^ow rate.
This unit proved to be unreliable due to its slow re-
sponse time (measured in hours) and the relatively high air content
of the steam.
A roughly calibrated needle valve was finally in-
stalled and the flowrate was checked during each run by diverting
the steam flow through a hose placed in a bucket of cold water.
The increase in weight of the water bucket resulting from condensed
steam was used to calculate the steam flow rate.
Pressure taps were provided every six inches along the reactor
to measure the pressure drop across the fluidized bed.
These taps
were manifolded through three 5-way valves to a Honeywell Pneumatic Differential Pressure Transmitter.
mitter was hooked to two pressure gauges.
The output of the transOne gauge was located
on the main control panel and one v/as installed on the pressure
tap valve panel on the same level as the star feeder.
To provide control over the reactor heaters, tv/o model
1501AG-58-IK proportional temperature controllers were used to
drive model PAKlO-0-lX triac contactors.
manufactured by Victory Engineering Corp.
Both sets of units were
The controllers and
contactors were not capable of handling the severe load, voltage
and temperature conditions.
The units incorporated no protection
circuits, and had a limited life expectancy because of over heating
of the triacs.
The heater controls were the most signifi:ant pro-
blem encountered during the initial mechanical phase of the
14
operation.
After going through several attempts to bring the loads
down using large inductors, and a capacitive bypass for surge protection, the original triac contactors were discarded and new
silicon controlled rectifiers (SCR's) were ordered from Vectrol.
The rectifiers, model VSSC-1020-240-1FAC, were capable of handling
63 amps each at 240 volts with full surge protection.
The original
proportional controllers were retained and a 2500 ohm variable
center tap resistor was installed on the output stage of the controler.
The center tap was adjusted to provide voltage through a
rectifying bridge to the 15 volt D.C. control circuit of the Vectrol
SCR's (Figure 3 ) .
A Fisher type 657-ES pressure control valve with a built in
Fisher Wizard type 4100ZR controller was installed to regulate the
pressure in the system.
The sensing tap for pressure control was
located just above the reactor exit port for the hot gases in the
2 inch line leading to the cyclone.
Down Stream System
The configuration"of the downstream system was in a constant
state of change.
One can appreciate the sweeping nature of the
accumulated changes by referring to Figures 4 and 5 which represent the original construction and the present configuration of
the system.
15-
Vectrol SCR
^w\/w^- to
control
^ circuit
semicond
fuse
circuit
breaker
heaters
circuit
breaker
o—vV\A-c>
o v\AA-o%)-
2500j^
25 W
fuses
-•a>#-o
to
thermocouple
1i
I
control
circuit
zv
zr
5=^
Victory
Temperature
Controller
Figure 3. Electrical System
16
o
to
c
o
p::
(1)
c:
CD
O
QJ
cn
•r—
17
18
The filters for the exit gas stream shown in Figure 4 consisted of three AMF-Kuno catalog no 5224301 model 41-0403 cartridge type filters welded on a one inch O.D. stainless steel pipe.
These filters have an opening size of 40 microns.
Tv/o commercial impingers were used in the system.
One was
located just after the tar trap and the other was located in the
water/gas separation system.
These impingers consisted of a wire
screen impingment filter and a fixed vane centripetal separator.
MODIFICATIONS
Although the reactor system operated successfully on the first
r'^n, extensive modifications were required to allow a Wider range
0? operating conditions and to solve various problems that developed.
Feed Hopper
From the wery first run it was apparent that once steam entered the star feeder that the manure flow into the reactor
stopped almost immediately.
This was due to the moistened manure
being packed into a stiff paste by the mechanical action of the
star feeder or simply the moist manure particles adhered together
to form a plug in the hopper above the star feeder.
Initially it
was found that backflow could only be prevented by the use of
excessively high helium flowrates (one cylinder per hour).
A con-
centrated program to eliminate leaks was undertaken which
ultimately led to the redesign of the 4 inch feed inlet section
at the top of the hopper, building a new cone for the bottom of
the hopper, redrilling the homemade flange separating the top and
the cone of the hopper, rewelding all the joints on the hopper, and
silicon sealing the flanges.
It was also discovered that hot gas
backflow had destroyed the relatively low temperature seals in
the star feeder.
New seals had to be ordered and replaced before
further operation was possible.
19
20
These procedures cut the potential for backflow into the
hopper by an order of magnitude.
Unfortunately, it was soon ap-
parent that this was not enough.
During startup as the pressure
rose in the reactor because of generation of gas or filter loading,
backflow into the feed hopper occurred which equalized the pressure
in the dead air above the manure.
If backflow occurred faster
than the helium purge flow rate, plugging resulted.
run series the solution to backflow was found.
Later in the
A 3/8 inch bypass
line was installed between the top of the manure hopper and a
point just below the star feeder.
This line incorporated a 2 inch
by 15 inch water cooled condenser with a small reservoir and blow
down valve to condense any steam in the bypass stream.
Another problem related to backflow was the condensation of
water and tar on the sight glass which picked up manure dust and
made observation of the manure flow into the reactor impossible.
A second Thermo Electric Mini Monitor Latching High Temperature
alarm was ordered and installed with a warning buzzer which was
triggered by a type J thermocouple that was placed just below the
star feeder and opposite the bypass opening.
This alarm detected
when backflow was occurring and allowed more conservative helium
flow rates.
Cyclone and Filter
By the end of Run 4, it was apparent that the filter arrangement was not acceptable as a means of removing solids from the
21
product gas.
After a few runs, the filter was nearly permanently
clvigged with condensed tar and small particles, thus allowing only
a minimal flow at high differential pressures.
The clogging prob-
ably resulted from the small surface area, the dense packing of
particles, the unheated design and the large solids carryover.
A sample of the carryover scraped from the filter and the residue
in the filter housing were sieved,using this particle size distribution, a cyclone was designed (Figure 6 ) . The filter was retained
in a position immediately downstream of the cyclone and gas fired
heating jackets were provided for both.
The cyclone was moved as
close to the reactor as possible since heat transfer calculations
showed that it was impractical to insulate the original long
length of pipe to the degree required.
Run 5 proved that the fil-
ter problem had not been solved by the addition of the cyclone.
Subsequent removal and examination of the filter after the run
showed that the filter was covered with a white ash material having no visible porosity and closely resembling a coat of gray
latex house paint or fine paper. This material was judged to be
unfilterable and of a small enough volume not to cause plugging
in the tar trap or water cooled condenser.
Therefore, the filter
and filter housing were removed.
A rather thick accumulation of tar was noted inside the filter
cartridges when they were broken apart.
During the filter removal,
the two inch air cooled heat exchanger before the tar trap was
shortened to about 5 feet.
This exchanger was operated using
22
8" to 2" swedge
blind flange with 8" center
r
hole
3"
11V
4"
Figure 6.
Cyclone Dimensions
23
natural convection.
After solving the particle carryover problem, the poor tar
trap efficiency was investigated.
It was found that only small
quantities of the tar were condensing in the air cooled heat exchanger line or tar trap.
Almost all of the tar was being col-
lected in the impinger located immediately after the tar trap. A
rolled piece of aluminum screen was alternately dimpled and inserted into the 2h feet of the two inch air cooled line to act as
an impinger.
The effectiveness of this screen was not ascertained.
The impinger still collected most of the tar.
However, a certain
amount of a somewhat higher melting point tar did accumulate in
the tar trap.
Both sections of the tar collection system were
later steam traced and' a 4 inch diameter 12 inch long reservoir
was attached to the impinger.
Water-Gas Separation
The water-gas separation system was originally constructed
with a two inch knock out drum, a shop modified inverted bucket
type steam trap converted into a float type and another impinger
of the same type as used in the tar trap system (Figure 5 ) . The
steam trap did not have the volume throughout required, so it was
converted into an emergency overflow which was used frequently.
A
h inch needle valve was modified into a float valve and installed
as the primary valve.
This valve was not very successful because
the 24 x \h inch wooden float tended to stick in the gummy tar
24
residuals and required a great deal of tapping to reach an equilibrium condition.
After a tar trap fire in Run 10, live steam
had to be used to unplug tar in the water cooled exchanger.
The
steam cleared the water cooled exchanger, but it was found that
the whole water-gas separation system was filled with tar.
The
needle valve float assembly would have been very difficult to
clean and a larger commercial type float valve was ordered and has
been installed.
Flow Measurement System
It was discovered that oily organic condensates were fouling
the turbometer.
To prevent fouling, a small water cooled condenser
and a glass wool filter were installed.
In addition, a small 1%
inch diameter cyclone and a bypass around the meter run were
added (Figure 5 ) . The small cyclone was observed to have little
effect on entrained liquids in the gas. The filter was effective,
but the filter media had to be replaced every run.
In Runs 9 and
10, cotton was used instead of glass wool in the filter because
of availability.
Operational Procedure
1. The reactor was heated up to operating temperature using an air
purge rate of about 3 SCF/min.
2. After starting the helium purge, steam and air were added at the
rates to be used for the run.
3. Once the system became stabilized and the water removal system
25
was functioning, the manure feed was started.
A ram cycle of
3 seconds down and 10 seconds up was employed.
4. After the system reached thermal equilibrium the mass balance
period was started by switching the flapper in the char hopper sides, dumping the cyclone via the ball, valve, changing
the waste water container and drawing off any tar.
5. The mass balance period was ended by switching the flapper in
the char hopper back, and collecting the tar, water, and
cyclone samples for weighing.
6. Gas samples were taken by connecting a gas sampling bottle
across the sample loop (Figure 5) and adjusting the pressure
drop across the loop to about one psig.
7. The system was shut down by reversing steps 1, 2, and 3.
8. Char was removed and weighed after the reactor cooled.
Analytical Procedures
Gas samples were collected in 250 ml gas collection bottles.
These were then analyzed using a Varian Aerograph Gas Chromatograph with two columns.
One was a 12 foot long, l/8th inch
diameter column packed with 50/80 mesh Poropak Q.
A 4 foot pre-
column of l/8th inch tubing packed with 50/80 mesh Poropak R
was used in conjunction with the Poropak Q column.
These columns
were used to quanititatively measure hydrogen, methane, carbon
dioxide, ethylene, and ethane. A 12 foot long l/8th inch in
0
diameter column packed with 45/60 mesh 5 A molecular sieve was
26
used to quantitatively measure hydrogen oxygen, nitrogen, methane,
and carbon monoxide.
Runs 1 through 5 were analyzed through the
(II)
courtesy of Young ^ ' who was studying the theoretical aspects
of the pyrolysis process using a different chromatograph with
similar columns.
A ser.ies of one ml. volumes of air v/ere in-
jected before and after each sample series.
The air peaks were
averaged and a corrective factor was calculated from a standard
peak height which was used to correct the sample peak heights.
At least two injections on each column were made for each unknown
sample.
The peak heights were then converted to moles using stan-
dard curves.
Any oxygen present in the sample was assumed to be
due to air contamination and was subtracted out along with a
rationed amount of nitrogen.
The two columns were related by the
amount of methane measured on each side.
This procedure was re-
fined, and a computer program was written to calculate the
various results.
Because of the large sample injection volumes,
the program could only be used on runs 8, 9, and 10 because the
peak heights for the other runs fell beyond the linear portions of
the calibration curves.
Sieve studies were done by shaking samples through standard
sieves with an automatic sieve shaker for 10 minutes.
tions were then weighed.
The frac-
Moisture content of the manure was
found by heating samples in a weighed crucible at 104°C overnight,
desiccating, and then reweighing. Ash content was obtained by
heating the sample in an air environment at 950 C overnight and
27
then finding the weight differential.
Density was measured with
e-standard weighing bottle and calibrating the bottle with distiVied water.
Because of the small total volume of the weighing
bottle, the densities of the large particle sized samples may be
fractionally low.
Preparation of Feedstock
Manure was collected at Lubbock Feedlots located on the Old
Slaton Highway.
The large feedlot manure pile was surveyed using
visual examination and a shovel to find the driest, freshest,
loosest, manure that could be found in that order of preference.
The feedstock was collected in garbage cans and transported to
the Texas Tech Feedlot where a Wildcat Far Hammer Mill and tractor
was used to grind the manure.
A screen of 1 inch squares was used
in the hammer mill because it was the only size available.
The
manure used in runs 1 through 3 was sun dried for a few hours on a
large plastic sheet.
not require drying.
The manure used for the remaining runs did
In Runs 1 through 8 all manure was sieved
through a piece of metal lath to remove gross particles prior to
loading.
This hexagon shaped screen passed all particles smaller
than about 3/8ths inch in diameter.
For Runs 9 and 10, the manure
was sieved to pass through an l/8th inch hail screen.
This was
done in a hand operated tube sieve constructed for this purpose.
DISCUSSION OF RESULTS
The primary objective of this study was to provide scale up
information for the construction of a commercial plant and to determine the various operating parameters which must be considered
in the design and operation of a larger scale system.
The pilot
plant reactor involved a cross sectional area scale up over
(2)
Herzog's ^ ' small reactor of 14.2 to 1.
Feed Considerations
As was expected, the primary problem encountered in operation
was solids handling.
Extensive efforts were required to keep
steam from entering the feed material before it was introduced
into the reactor (See Construction, Modifications, Feed hopper).
It became apparent after working with this material that moisture
co'ttent was of primary importance.
The moisture content of manure
varies between about. 80% (fresh droppings) and about 3%.
It was
found that a feed with a moisture content of about 30% ground to
pass a l/8th inch screen could hold a perpendicular angle of
repose and compacted easily into clumps with applied pressure.
However, with vigorous tapping on the side of the hopper this
material would flow.
feeder pockets.
This feed tended to compact in the star
Drier feed material flowed without vibration and
was more resistant to compaction.
The ideal moisture content
appeared to be about 10% from a feeding standpoint.
From these
observations, it is the author's opinion that in a commercial
28
29
operation, once the manure- leaves the hammermill, it should be
handled by air transport rather than auger or drag chain.
Air
transport would help to dry the manure.
Drying the feedstock represents a major drawback and a potentially high cost.
There are several possible methods for achiev-
ing dry feedstock.
The first is a char fired rotary kiln or
similar arrangement.
This is not attractive because of its high
capital and operational costs. Also exhaust gases may be a problem.
The second alternative is spreading the raw feedstock over
a large area of land and allowing the arid weather of West Texas
to dry a thin layer.
several drawbacks.
This would be relatively cheap but has
The environmental impact of the manure stor-
age problem is intensified by increasing the surface area.
Flies,
watershed runoff and odor would be worse during wet weather.
During dry windy weather, particulate counts would be higher.
Ideally the manure would be left in the pens a few weeks
after the cattle have been shipped to market, allowing it to dry
and then removing it.
Unfortunately, the feedlot owner may not be
able to afford to keep his pens empty for long periods of time.
Finally, atmospheric drying puts the plant operator at the mercy
of the weather and requires the construction of large enclosed
storage areas to hold feedstock against a rainy day.
The author
is convinced that the present feedlot practice of piling manure
into 20 to 40 foot piles on the corner of the lot will not be able
30
to supply enough dry feedstock on a continuous basis.
Weathering
soon compacts the pile into a solid non-porous lump and anaerobic
bacterial action may generate enough water internally to keep up
with the drying rate deep in the pile.
This is supported in part
by the observation that very large slabs of manure (12" thick or
better) were usually too wet to hammermill at the core.
Also
it was the authors experience, while walking on an old pile of
manure at the feedlot where the surface manure was exceptionally
dry, to break through the surface crust and obtain a very wet
sample approximately knee deep.
Ground manure stored in gar-
bage cans gained noticeably in moisture content over a several
month period if the cans were covered with a tight lid.
Thus in
any large volume storage bin, air would have to be blown through
the material at a low rate to discourage anerobic activity.
Larger storage air flow rates would probably have a drying effect.
Waste heat from the reactor system could also be employed to
assist in drying.
A possible alternative to more costly drying schemes is
blending.
The author's solution to wet manure was to mix drier
manure with it during the hammermilling.
Since the Syn Gas
process should work equally well on any cellulosic material, if a
large amount of gin trash, ^'ck hulls, peanut shell, sunflower
trash, or many other possible feedstocks could be obtained, then
blending would be a very reasonable drying alternative.
In fact,
the hot char produced by the process could be used as an active
blending agent for the lower moisture contents.
•31'
It is anticipated that the most econonical drying scheme
will probably be a combination of two or more of the above methods.
Sun dryino is by far the cheapest method and would prob-
ably be employed to lower the moisture content as much as possible,
If required,one of the other schemes would probably be used to
reduce the dried manure to a moisture content that can be handled easily.
Some excess drying capacity might be desirable for
periods of wet weather.
It is doubtful if this process will be
economical in areas with extremely wet weather.
Experimental Conditions and Results
A summary of the range of operating conditions which were
employed by the pilot plant study is shown in Table 1.
Typical
raw gas compositions and densities for the feed and char are also
reported.
A complete listing of the data and results can be
found in the Appendix C.
a2
TABLE I
TYriCAL OPERATING VALUES
AND RESULTS FOR THE PILOT PLANT REACTOR
Typical Raw Gas Composition:
COr-^.POUND
h
MOLE %
29 to 11
h
41 to 13
CH4
15 to 7
CO
23 to 14
C02
20 to 11
C3H,
7 to 3.9
2.5to
^2^6
Temperature Range °C
Manure Feed Rate
Air Feed Rate
Steam Feed Rate
Raw Gas Production Rate
00.
Thermocouple #6
lb BDAF/hr
SCF/hr
Ib/hr
SCF/lb BDAF
810^
0
27
6
4
to
to
to
to
to
920°
40.1
150
10
17
Densities
3
Ib/fV
Char from hopper
22.4
(Run 8)
Char from Cyclone
17.7
(Run 8)
Fine sieved manure feed
30.
(10% H2O)
Course sieved manure
30. - 40.
33
Reactor Operating Characteristics
During the first run 3 to 6% ethylene concentrations were
noted in the produced gas stream.
This was attributed to the
temperature "quenching" effect caused by the lightly insulated
top of the reactor.
It was decided not to insulate the reactor
fir^tner as planned in order to possibly increase the production
of -:iiylene. As a result of this light insulation, tremendous
heat •osses were sustained which made a heat balance on the
system almost impossible.
However, studing the temperature pro-
files of the hot reactor just before adding manure and during
operation provided some insight into the actual operating
characteristics.
It appeared that most of the combustion was occuring just
above the distribution plate, perhaps confined to an area as little
as 12 inches high.
This can be shown by comparing the temperature
profiles of Run 8 and 9.
(see Fig. 7)
In both of these runs, only
one heating element was operational and was at maximum capacity
at all times.
Run 8.
Run 9 had an air feed ratio about 3 times that of
All other feed rates were the same.
The rapid temperature
rise in Run 9 can only be accounted for by the release of heat
through combustion.
The possibility of a fluidized bed evenly
distributing the heat within the lower section was judged to be
unlikely because of the noticable dip in the temperature profiles
between the heaters where the reactor was very poorly insulated.
The differences in the temperature profiles above the heaters
34
-o =
<D
•r- CO
"O
•r- O
to 4->
c:
fO =
S- UD
"O
cr
fcs
QX
LU
O
-r4-)
u
(D
CO
900
800
CJ
700
o
i_
c
600
500
400
_£^
Run 9
O
Run 8
|3
No Feed.Startup
Run 9
.a\
O
V'
300
H—h—I—I—I
4. 5 6
f—f
7
8
• • ^ \
^
-\
1
^
1
1
9 10 11 12 13
Ther-mocouple
ngiire 7. Temperature Profiles in Reactor
3;:.
CQjId be due to the higher total gas flowrate of Run 9 because of
the extra air.
Another possible cause was that the steam and
corbon dioxide concentrations varied between the runs, giving
the gaS a different emissivity for radiant heat transfer.
There appeared to be no clear correlation between air feed
rate and exit gas composition except for slight shifts in the
C0r>-C0 ratios^, provided the dilution effect of the air was removed mathematically.
Appendix.
This calculation is explained in the
This indicated that the desired synthesis gas reaction
was basically pyrolysis as was confirmed by the work of Young.
Young indicated that most of the pyrolysis reaction should be
over before the manure particle reached the typical highest
temperature zone in the reactor, provided that the particle was
not heat transfer limited.
for small particles.
Young indicated this was unlikely
This quick reaction theory was also sup-
ported by the pilot plant data in that the fines which were
collected in the cyclone appeared, on the basis of their ash
contents, to be as well or better reacted as the char collected
from the bottom of the reactor.
Thus the reactor was apparently divided into 3 zones of
reaction.
In the top zone pyrolysis occurred and in the bottom
zone combustion.
The middle zone could sustain a number of
reactions, the ones of primary interest being:
CiH20
->
CO+H-,0 ->
H2+CO
(1)
H2+CO2
(2)
36
(121
Reaction 1 is endothermic and probable not significant.^ '
Reaction 2 is exothermic and proceeds rapidly in the presence
(12)
of a catalyst.^
It is reasonable to assume, that in the steam
diluted atmosphere at the bottom of the reactor, a considerable
amount of the oxygen introduced with the air was converted to
carbon monoxide.
Also since some ashes act as catalysts,^
'
reaction 2 has potential for shifting the exit gas composition.
The gas analysis data did not provide any conclusive evidence regarding extent to which these reactions were occurring.
The very sizable scatter of the hydrogen percentages compared to
temperature could easily have resulted from analytical difficulties and shows no discernable trends. (See Figure 12)
From an analysis of the data reported in the Appendix the
reactor temperature appeared to be the most critical parameter
affecting the observed outputs.
The number of standard cubic
feet of gas produced per pound of bone-dry, ash-free (BDAF) manure
is given in Figure 8.
on the figures.
duction data.
were preferred.
Differences in feed particle size are noted
There were two methods for obtaining gas proDirect readings from the exit gas turbometer
However, fouling of the turbometer occured in
some runs so gas production was back calculated using a nitrogen
balance comparing the air input rate and the product gas analysis.
Turbometer readings were used for all plots in this thesis except
fir runs where these data were not available or obviously not
correct (Runs 1, 7 and 9 ) . The back calculated flow rate was used
for these runs.
37
ii course sieved data
17 - O "fii^e sieved data
ii
16
15 f
13
^
.o
12
^
LU
to
c
o
.a
<3P
O
n
10
£1
8
7 «
• I —
n.
©
il
ja.
6
O
£i
5
ja
4
3
j ^
1
i
800
850
900
Temperature
Figure 8.
C
950
Thermocouple # 6
Raw Gas P.oduction
1000
38
Reasonably good agreement can be shown between the calculated
and observed flow rates for the other runs. A complete listing
of values calculated by each method can be found in the Appendix.
In Figure 9 the gas production data were corrected for the
dilution effect of the added air and combustion products by removing the nitrogen and a ratioed portion of carbon monoxide
(See sample calculation in Appendix A).
This calculation assumed
that all the oxygen entering into the system with the input air
left the system as carbon monoxide.
Data which have been treated
in this way will be referred to as normalized data.
By normal-
izing the data the gas flow rates and compositions should only
result from the manure pyrolysis reaction which yields a better
correlation of the data. " Because several of the samples in
Herzog's data^ ' (Figure 10) contained less carbon monoxide than
was called for by the calculation, a second calculation was made
assumed that all the oxygen entering into the system leaves as
carbon dioxide.
Both these values were plotted on Figure 10.
The real volume correction due to combustion products should fall
between these points.
This second calculation was also done on
Runs 6 and 7 and the maximum difference between the two assumptions was less than 15% of the normalized gas flow rate.
Herzog's data obtained from the bench scale reactor were the
basis for the design of the large reactor.
Comparing Figures 9
and 10 it can be seen that Herzog's reactor potentially generated
39
10
ji Large Sieved Data
O Small Sieved Data
Q
CO
8
to
c
o
•T—
4r>
U
Z5
O
iDto
«3
CD
-Q.
-Q.
5 -
H £L
"O
OD
.Q.
£L.
o
0
750
800
850
900
Temperature Thermocouple #6
Figure 9.
Effect of Temperature on .formalized Gas Production
950
40
73
12
=3;
Q
CQ
-
11
10
to
§ 9
o
"§ 8
u
a.
(/>
fo
"a
7
'
M
E
o
.5
I
650
Figure 10.
700
CO2 assumption
CO assumption
750
800
Average Temperature, °C
850
Small Scale Reactor Normalized Gas Production
41
more pyrolysis gas per pound of manure.
However, the small scale
reactor temperatures probably may not be directly related to the
highest temperature in the large reactor (thermocouple #6). It
should be noted that Herzog's reactor was top fed through a standpipe into the top third of the reactor, and most of his solids
passed out with the exiting gas stream at the top rather than
the bottom as in the large reactor.
Herzog's reported temperatures
are the average of two thermocouples inserted into the middle of
his reactor.
The observed differences in gas yields between the large and
the small reactors could easily be the result of the gentler
temperature profiles in the large reactor.
As a manure particle
entered the reactor it encountered a temperature of only about
350°C.
The temperature rose as the particle fell.
Since any
volatile molecule resulting from the pyrolysis of the manure
particle would immediately be swept into a lower temperature
zone by the exiting gas, the large reactor naturally favored
large molecules which did not have time to be thermally cracked
in the gas phase.
This was verified by the larger hydrocarbon
percentages shown in Figures 11, 12 and 13 as compared to
Herzog's data in Figure 14. This also means that a very significant portion of the total hydrocarbons produced appeared as
condensables in the form of tar or lighter organics (see mass
balance. Table 2 ) . These tars and organics were not extensively
tested by the author, but Del La Garza^^^^ has undertaken this
42
^
15 r
n
J:I^
n
10
ii
o
n
ii
SI
%L
il^
o
O
o.
o
C3
eg <s>^og
H
Methane
O
Ethane
o
O
0
800
850
900
950
Temperature °C Thermocouple #6
Fiqure 11. Raw Gas Composition (Methane and Ethane)
1000
43
30^
JQ.
jQ.
XI
XI
ID.
^
20
XI
#
o
o
i?-
to
o
n.
JQL
XL
o
Hydrogen
O
Ethylene
ja
o
I 10
G
O^0
GO
G
G
0
800
850
900
950
Temperature Thermocouple -6
Figure 12
Raw Gas Composition (Hydrogen and Ethylene)
1000
44
C\ Methane
-^ Ethylene
Ethane
30
0-5
o
o
20.
to
o
EL
E
O
CJ
to
CD
"O
O)
M
ft3
E
S-
o
10
^c^o-cg
0
800
Figure 13.
850
900
950
1000
Temperature, °C Thermocouple #6
Reactor Effluerrt Gas Composition
45
30 r-
O Methane
Q Ethylene
o
o
20
to
o
CI.
to
CD
M
o
10
-
i^-
0
650
Figure 14.
±
700
750
800
Average Temperature, °C
Small Scale Reactor Gas Composition
850
46
TABLE 2
MASS BALANCES
RUN NO.
8
Inputs (lbs)
Wet Manure
Air
Steam
28.52
8.51
4.30
39.79
3.78
6.75
Total Input
41.33
50.52
29.43
Gas Out
H2O Out
15.60
10.75
12.66
14.19
5.84
7.25
Tar
Cyclone
Char
0.5
1.63
8.25
0.5
1.38
15.50
0.5
1.25
6.0
36.73
11.13%
44.23
12.45%
20.84
29.19%
% HpO
10.00
10.00
10.00
% Ash
19.59
21.54
21.54
46.5%
49.45%
50.24%
55.50%
53.27%
60.2%
22.28
2.88
4.27
Outputs (lbs)
Total Output
Unaccounted for
Other Measured Data
Manure Feed
Ash Contents
Char
Cyclone
47
MASS BALANCES(CONTINUED)
RUN NO.
Output Product Distribution (Mass Percent)
9
8
7
Np Free Gas
41.65
32.00
25.29
2.09
1.83
2.89
15.07
18.47
12.67
28.32
4.30
15.93
3.44
2.24
2.84
Tar
Light Organics & Produced HpO (input steam
subtracted)
Ash Free Char
Ash Free Char from
Cyclone
Accumulation and/or
experimental error
Totals
Total Char
Total possible produced tar and liquids
including accumulation
Np Free Gas
*SEE DISCUSSION
•k
19.29
22.90
48.79
100.01
100.01
99.99
21.91
30.56
18.77
*
36.45
41.65
37.40
32.00
55.93
25.29
48
project for his Master's thesis.
Preliminary results showed that
•further cracking of,the tar produces a variety of unsaturated
compounds of which ethylene, propylene, and various four carbon
compounds comprised a major portion.
Thus, while thetotal normalized
pyrolysis gas generation in the larger reactor may, in general,
lower than that produced by Herzog, the gas and tar produced in
the larger reactor may be potentially more valuable.
It should be noted that the differences in reported temperatures between the large and the small scale data were not
significant.
In the large scale reactor there were 12 thermo-
couples spaced evenly along the reactor.
Any of the thermocouples
in the upper section (6 through 12) could be used to relate the
data and a reasonable correlation was obtained.
However, thermo-
couple 6 seemed to relate the data as well as any of the others
and was considerably easier to read from the strip charts because it was usually the highest temperature in the reactor.
The average temperature of the pyrolysis zone would probably be
the best temperature to correlate the data.
Unfortunately the
exact location and length of this zone was unknown.
By averag-
ing all 12 thermocouple readings in the reactor and the temperature of the inlet gas through the distribution plate, the
raw,.large scale data can be shifted to nearly aline with Herzog's
raw gas production data (Figure 15).
49
XI Course Sieved Runs
O Fine Sieved Runs
Small Scale Reactor
30 t-
o
CQ
20
O
^^
A
o
u
-o
o
sQ_
lo
CD-
10
0
600
1.
700
Temperature, °C
800
Figure 15. Average Temperature Comparison to Small Scale Reactor
50
The increase in the normalized gas generation rate with
temperature, suggested that, at higher temperatures some of the
larger pyrolysis products did not have time to be generated and
escap- from the particle before it entered a higher temperature
zone that could cause secondary cracking.
A study of the effect
of higher fluidization gas velocities, which would further verify
this hypothesis, should be a part of the next phase of investigation.
The above analysis of the data indicated that the reactor as
it was operated, produced a significant amount of tars and liquids
at the expense of the total gas rate.
If the objective of the
process is to obtain unsaturated organic compounds, it may well
be that two stage pyrolysis would produce higher yields by allowing more precise control, and possibly the use of a catalyst
during the second cracking of the tars and organic liquids.
However, such an operation could require a considerable increase
in capital investment.
If the ethane and ethylene are removed
from the observed exit
gas stream and the CO2 is scrubbed out,
a producers gas with about 500 BTU/SCF (see appendix) still remains
which could be sold as fuel.
If ammonia synthesis gas is desired, then any production of
tars or liquids is undesirable.
The solution in this case would
be to very heavily insulate the reactor as was originally planned
for this study.
This would bring the top temperature of the
reactor to as high a value as possible.
By experimenting with
51
intermediate insulation thicknesses, it should be possible to
optimize the production of ethylene.
The data illustrated in
Figures 9 and 13 indicate that an increase in the exit gas
ethylene concentration is unlikely, but the volume of the gas
could be increased significiently.
(3)
From the development of the bench scale reactor^ '' it was
found that a manure feeding arrangement on top of the reactor was
much superior to all the other systems tried.
However, on a
larger scale it may be feasible to build a bottom fed reactor
which would increase the probability of complete cracking which
would require less reforming to produce ammonia synthesis gas.
A design and discussion of such a reactor has been included
in Appendix B.
Downstream Operating Characteristics
The gas stream produced in the large reactor contained
5 to 21% of the total solid char by weight.
These small particles
ranged in size from those caught in the cyclone (about 250ym to
20ym) down to sub micron sizes.
The appearance of the exit gas
was a dense grey smoke with a slightly green tinge and an unpleasant odor.
Tar began to condense significantly from this stream at
approximately 320^0.
The tar condensed at different temperatures
had a noticeably different appearance and characteristics.
The
highest boiling point tar was found to form grainy deposits which
did not flow well at steam tracing temperatures.
The grainy ap-
52
pearance could be due to fractional crystalization.
The observed
appearance of this tar was that of a nearly cold lava flow filling the bottom quarter of the pipe and consisting of 95% solids.
However, the ash content of this tar was considerably less than
one percent, so little char was present.
It was easier to use a ham.mer and chisel to shatter the high
temperature tar out of the tar trap than to melt it out using
steam tracing and positive pressure.
Only one large sample of
this tar was taken because it tended to accumulate in the lines
leading to the tar trap.
An internal fire in the downstream
system in Run 9 caused the accumulated tar to move down into the
tar trap.
A peak temperature of 900"c was registered just above
the tar trap during this fire.
The tar tended to condense on the entrained solids forming
an aerosol.
Thus, wery little tar was collected in the tar trap.
However, the tar impinger apparently worked well and removed a
large amount of the entrained tar from the gas.
There was a
noticableable relationship between pliancy of the tar and collection temperature.
This varied from a very soft material
similar to taffy at low temperatures (approx. 110°C) to a hard
and relatively brittle material at high temperatures, (approx.
300°C).
The product stream from the water-cooled condenser was a
brown to yellow, murky, foul-smelling liquor with a very high
total solids content and colloidal organics.
Over a period of
53
weeks, the liquid settled into three phases; a foamy organic
layer, a somewhat darker water layer, and a layer of solids.
Closer temperature control in the condensers would reduce the
amount of organics in the water stream by collecting the water
and light organic streams separately.
The waste water would
still be heavily polluted, but because the process produces a
potential activated-charcoal as a by-product, a serious problem
with organic-contaminated wastewater may not exist.
One major
problem was that the wastewater stream tended to cause severe
sticking problems with the float control valves.
The separated gas stream was clear of suspended solids,
but a problem was encountered with condensing liquids and
aerosols which tended to foul the turbometer.
Several of the
reported gas flow rates had to be back calculated form the nitrogen
content of the exit gas because of obviously faulty readings.
Feed Particle Size
Prior to Run 9 the char contained visibly unreacted manure
particles.
A representative sample of the char from Run 8 was
sieved using a set of standard sieves, and the ash content of
each fraction was determined (see Figure 16). If it is assumed
that the original ash content of all the various sized particles
was the same, then approximately one third of the reactable
mass of all the particles over 2 mm was unreacted.
Young's data^^^
indicated that raw manure particles smaller than about 0.25 mm
54
60
+->
CD
50
00
40
o
o
>>
t-J
o
I
o
r^
r^
o
I
o
A
I
I
o
C>J
Figure 16.
Effect of Particle Size on Degree of Reaction
55
show higher ash contents than larger particles.
This phenomenon
could explain the higher ash contents in the first and second
points on Figure 11.
Since the size distribution in any given ground manure
sample used in the large reactor varied considerably, it-was
decided finer sieving would be required.
The closest, com-
mercially available screen size was l/8th inch hail screen.
There-
fore this screen was used to construct a portable tube sieve which
could be transported to the grinding site which was located several miles away from the reactor.
The effect of particle size
is confirmed in part by examining Figure 9.
The finely sieved
runs show much less scatter between individual samples and apparently define a more precise relation.
Char Characteristics
Once a thoroughly reacted char had been obtained, the problem of unwanted fires arose.
The problem was not how easily this
char would burn, but how to keep it from burning.
In Run 9 the
hot char from the cyclone was ignited by a plastic bag left in
the collection bucket.
After noting the glowing fire on the sur-
face of the material, the fines were stirred with a steel pipe
and then dumped on a steel plate in a pile about 2 to 3 inches
deep.
This material which had an average particle size of about
70 ym continued to burn for hours and visually appeared to be converted to almost pure ash.
The combination of high heat cap-
.55
acity, low conductivity, and high porousity was thought to account
for such good combustion characteristics.
The char burns hot
av.i clean without any odor.
A siipplemental test of the char in a large, two-stage cotton-v;dste-furnace showed no problems with combustion other than
the large amount of ash left in the bottom of the furnace.
In
actual operation, some care will have to be taken to prevent exposing' the char to air until it has been cooled below its ignition
point.
Another small fire was maintained in the char hopper in
wery limited oxygen for longer than 24 hours after the run.
Fluidized Bed and Char Hopper Characteristics
There was no evidence to indicate that a fluidized bed was
ever obtained in the reactor.
The pressure tap system which was
designed to measure the pressure drop across the bed, never
showed more than a gentle pulsing which could be related visually
to the slugs of feed.
This further supports the rapid reaction
theory mentioned earlier.
What the instrumentation did show
strongly, was a large negative flow down the reactor which could
be related to the dropping of the ram.
the process involved.
It is easy to reconstruct
When the ram was in the up position, the
exit was essentially blocked.
Hot gas above the char had time to
cool through contact with the uninsulated walls creating a partial vacuum.
When the ram dropped, the hot char above the distri-
bution plate was carried downward with an explosive burst of gas.
57
As the char fell through the hopper it once again heated the gas
which equalized and the ram shut starting the cycle again.
This
w<i;i a very effective method for removing solids, but as a result
the whole process was more like a batch reactor cycling every 13
seconds than a fluidized bed.
No studies were made on the ef'ect
of the cycle time.
It is projected that for longer cycle times that a fluidized
bed of char would be built up, but this could be detrimental because of the accumulation and more complete combustion of some
of the particles.
This in turn could lead to the ash fusion
problems encountered by the cyclonic manure burning study. ^ ^
Reactor Temperature Control
Only a short range of temperatures were studied.
limit was set by the skin temperature of the reactor.
The upper
In the
early runs, the stainless steel skin temperature was not monitored and the temperature of the reactor was controlled by
attaching the top thermocouple in each bank of heaters to the
power controllers.
The thermocouples were not shielded and read
a composite of both radiation and gas temperature.
This pro-
vided a very loose coupling between the reactor's interior temperature and the heater control. As a result skin temperatures
very close to the softening point of the steel were obtained.
58
After analyzing the problems before Run 7, the control points
were shifted to thermocouples which monitored the skin temperature
of the steel beneath the heaters.
This change tightened up the
control linkage resulting in less temperature oscillation and
better control.
at 1000 C.
The maximum allowable skin temperature was set
This limited the internal temperature to approximately
900''C.
Data Reliability
The collection and anaylsis of data for this system was
difficult and time consuming.
The reliability of the data in-
creased significantly as this study progressed because of better
techniques and improved equipment.
For this reason Run 10 is
listed first in the data tables and the other runs follow in descending order.
The temperatures listed for the various gas
samples were estimated by approximating the residence time of the
gas in the system and then reading the appropriate temperature
off the recorder chart paper.
The residence time was usually
approximated by observing the lag time between an upset in temperature and the corresponding change in the recorded exit gas
flow rate.
This time varied from 10 to 15 minutes.
Because of
the difficulty in estimating lag time and averaging effects over
the sample period, the temperatures were very reliable for the
stable runs and were just rough estimates from the runs where the
temperature and the exit gas flow rate oscillated rapidly.
59
If the manure feed was subject to compaction or bridging the
manure feedrate became erratic due to local bridging and partial
plugging of the star feeder's pockets.
had this problem.
Run number one obviously
All the later successful runs used a dryer
manure which flowed easily.
Ash balances calculated for Runs 7
through 9 indicate that the listed feed rate was not more than
about 10% high on most runs.
However, Run number 7 which is listed
in the mass balance (table 2 ) , shows a large discrepancy between
calculated ash input and measured ash output.
Therefore the
actual manure flowrate in is probably much lower than what is
listed.
Early Runs
As with many experiments the least reliable data are always
the most critical.
The first run was also the highest tempera-
ture run (Table 3 ) . Data gathering was rather poor because of
typical start up problems such as leak detection, and trying to
determine the effectiveness and range of various equipment.
The
gas analysis was also somewhat in doubt as the chromatograph
was still being calibrated at the time. Most of the listed feedrates are just approximate values.
In spite of all this, the results show rather large effluent
gas rates.
In fact, the maximum rates listed could be conservative
since problems with the manure feed did cause sporadic flow.
Even
allowing for gross error, the data indicated that at higher upper
60
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61
and lower reactor temperatures a significant increase in gas production can be achieved.
The temperature at the top of the
reactor (thermocouple 12) during the first run varied from 400°
to 490° as compared to Run 9 which had a top temperature of
370 C.
All the other runs had lower measured temperatures at
the top of the reactor.
No data were reported for Runs 2 through 5.
In general
these were very short runs lasting from 8 to 60 minutes and were
characterized by feed problems, heater failures and plugged filters
The data were not judged to be of value since the reactor conditions were changing too rapidly to accurately measure.
Most
of the runs were not long enough to assure purging of the system.
Proposed Modifications
A major problem with the unit in its present configuration
was the accumulation of tars in various parts of the system.
A wet steam cooled condenser for the tar collection system has
been designed and construction is underway (Figure 17). This
vertical condenser employs an annular cooling tube design to
solve the expansion problems and to prevent plugging with the
high viscosity tar that might occur around any obstruction such
as a U tube connection.
Superheated steam from the Texas Tech
system will be mixed with an atomized water stream to obtain the
desired cooling media.
A boiling water condenser was rejected
upon the basis that it would slow down start up prohibitively.
62
In order to make the process capable of continuous operation
three two inch ball valves have been ordered.
Two will be in-
stalled on top of the feed hopper with a small vessel in between
to form a pressure tight lock hopper allowing manure to be added
to the hopper during operation.
The other valve will be in-
stalled in one of the inspection ports of the char hopper.
Internal pressure should force the char out similarly to the
operation of the ball valve dump on the cyclone.
However, it
may be necessary to install a manual ram that can be inserted
through the open valve to unstop any blockages.
At higher gas flow rates it will probably be necessary to
construct a larger knockout drum in the water gas separation
system.
The present drum was constructed of two inch pipe be-
cause it was the largest size that was readily available.
Since gas flow rates are so important, a backup flowmeter of
the pi tot type with a recorder would be useful. A reliable
flowmeter for the steam input should also be purchased, doing
away with the time consuming and error prone hose and bucket
teahnique.
As the amount of feed used during a single run will be in excess of 150 pounds at the higher feed rates, a large storage bin
has been designed and is under construction.
This bin has a
capacity of 96 ft^ or about 2800 lbs of ground manure.
The bin
will be equipped with an air distribution system to force air
through the stored manure which will prevent an aerobic decom-
63
position and probably do some drying.
The bin will be vented
through the stack of the steam plant.
This storage facility
should cut down the amount of time lost processing feedstock and
allow feed collection during drier periods of weather.
64
4" flange
TOP VIEW
swedgelock fittings^
fittings
^" tubing
exit
steam
4" flange
gas
from
cyclone
4" pipe
k" line to
J^" pipe
1^" rod plug
welded to end
DETAIL OF
END OF COOLING
TUBE
M
\•^r'J^
17
Steam Condens -r Design
CONCLUSIONS
1.
The operation of the large scale reactor demonstrated that the
basic partial oxidation technology developed on the small
scale reactor can be applied at a larger scale to produce a
useful synthesis gas.
2.
The composition of the effluent gas was influenced by the
reactor temperature profile.
3.
On the basis of average reactor temperatures, the raw gas
generation rates from the large and small reactors were
similar.
65
RECOMMENDATIONS
1.
The various modifications already initiated, such as the
installation of a wet steam tar condenser, modifications to
allow continuous operation, and storage facilities should be
completed.
2.
A series of runs should be made to define the maximum feedrate that the reactor system is capable of processing.
3.
A study on the effect of fluidization velocity on product
distribution should be undertaken.
4.
A study using reacted char as feed should be done to determine
the extent or importance of water gas shift.
5.
The properties and potential of the tar and water streams
should be investigated more thoroughly.
6.
An attempt should be made to determine the thermodynamics of
the system through measured heats of combustion, heat capacities, etc. of the reactants and products.
7.
The kinetics of the system should be studied by collecting
gas samples from the various zones of the reactor through
the pressure tap ports.
8.
In order to determine the effect of temperature gradient upon
the product distribution, experimentation with removable
sections of insulation on the upper part of the reactor should
be undertaken.
66
LITERATURE CITED
1.
Halligan, James E. and Sweazy, Robert M. "Thermochemical
Evaluation of Animal Waste Conversion Processes". Paper presented at the 72nd National AIChE Meeting, St. Louis, Mo.
(May 21-24, 1972).
2.
U. S. Congress. House. Control of Pollution from Animal Feedlots and Reuse of Animal Wastes. House Report 1012, 93rd
Congress, 1974.
3.
Herzog, Karl L. "Ammonia Synthesis Gas From Manure". M.S.
thesis, Texas Tech University, Lubbock, Texas (1973).
4.
U.S. Environmental Protection Agency, Feedlots, Point Source
Category, EPA-440/l-74-004-a, January 1974.
5.
Garner, William and Smith, Ivan C. The Disposal of Cattle
Feedlot Wastes by Pyrolysis. Environmental Protection Agency
Report, EPA-R2-73-096, January, 1973.
6.
Natour, Ibrahim, Parker, Harry M. and Halligan, James E.
"Production of Ammonia Synthesis Gas from Manure in a
Cyclonic Burner". Paper presented at 79th National Meeting
AIChE, Houston, Texas (March 16-20, 1975).
7.
Grub, W., Albin, R. C , Wells, D. M. and Wheaton, R. 1.
Animal Waste Management. Cornell University Conference on
Animal Waste Management, Ithaca, N. Y. (1969).
8.
Nilitin, N. I. Chemistry of Cellulose and Wood. New York:
Davey 1944.
9.
Coppick, S. "Degradation of Cellulose". Flameproofing Textile
Fabrics. New Yrok: Reinhold (1947) P.p. 13-75.
10. Shafizadeh, F. "Pyrolysis and Combustion of Cellulosic
Materials". Advances in Carbohydrate Chemistry. New York:
Academic pp. 419-474.
11. Young, Hall, Personal Communication on Thesis in Progress,
Texas Tech University, Lubbock, Texas (1975).
12. Hougen, Olaf: Watson, Kenneth; and Ragatz, Roland.
Process Principles. New York, John Wiley (1959).
67
Chemical
68
13. Khara, Bakulesh Hiralal, "By Product Utilization from processed Manure". M.S. thesis, Texas Tech University, Lubbock,
Texas (1975).
14. Mvssie, John Richard. "Continuours refuse Retort-A Feasibility Investigation". M.S. thesis, Texas Tech University,
Lubbock, Texas (1972).
15. Smith, G. L.; Albus, C. J.; and Parker, H. W. "Products and
Ooerating Characteristics of the TTU Retort". Paper 35e,
76th National AIChE Meeting, Tulsa, Okla. March 10-13 (1974).
16. Al-Haj-Ali, N. S. "Reaction Kinetics and Thermophysical
Properties of Feedlot Waste During Drying and Pyrolysis". M.S.
thesis, Texas Tech University, Lubbock, Texas (1974).
17. Del-La-6arza, Edward. Personal Communication on Thesis in
Progress. Texas Tech University, Lubbock, Texas (1975).
APPENDIX
A.
Sample Calculations for Normalization of Data
B.
Discussion of Proposed Reactor Design
C.
Raw Data
D.
Supplemental Data
69
70
APPENDIX A
Sample Calculations for Normalization of Data
Raw Gas Composit ion
(Mole %)
Correct Mole %
COp assumption
Correct Mole %
CO assumption
H^
27.43
44.14%
39. 97
CO
17.57
7.07
25. 60
CO^ 17.62
31.55
18 97
CH,,
7.82
12.58
11 39
CpHyj 2.89
4.65
4 .21
99.99
100.14
N^
24.78
100.1
CO assumpt ion
1.
24.78 (N2 Cone.)
2C+02->2C0
.21O2AIR
2C0
.79N2AIR
0,
Calculated CO
= 13.17 due to combustion
Subtracting out the nitrogen and the CO due to combustion &
recalculating percentages
9
^'
(
17.57-13.17 ) 100% = 7.08% Corrected CO
percentage
(100.1-(13.17+24.78) )
Corrected , H,
^-\iMk^r^)^^^°''-''-^'°''
percentage
and so forth to yield column 2 in the above table
C + 0^ -> 002
for the CO2 assumption
thus
4. 24.78 (N^conc.)
.2IO2AIR
.79N2AIR
CO 2
0,
calculated C0«
= 6.59
due to combustion
71
The nitrogen and the CO2 generated through combustion are then
subtracted out and the composition percentages recalculated in a
manner similar to the CO assumption to yield column 3 in the
above table.
It should be noted that except for the percentages of CO2
and CO there is not a drastic change in the percentages from
column 2 to column 3.
Combustion corrected flow rates
For simplicity only the CO assumption will be demonstrated,
from equation 1
Total nitrogen & CO subtracted = 24.78 + 13.17 = 37.95
^ • .
. .
fraction remaining
100.1 - 37.95
-.
_= .6209
^..^Q
100.1
observed gas rate = 12.96 SCF/lbBDAF
normalized gas rate = (12.96) .6209 = 8.05
^^^^IbBDAF
72
APPENDIX B:
DISCUSSION OF PROPOSED REACTOR DESIGN
This bottom fed design (Figure 13) depends upon heat transfer
through relatively small (2 to 6 inch) stainless steel riser tu^dS.
It is not anticipated that heat transfer will be a great problem
since at 900°C most of the heat transfer will be by radiation.
The external firing allows more control and flexibility in that
the BTU's which are added by combustion are not rigidly linked
to the nitrogen percentage in the exit gas.
High temperature
pyrolysis in the reactor with concurrent flow in the presence of
steam should convert most of the organics to gas resulting in a
higher hydrogen content with less extra processing required.
Heat economy is obtained by immediately using the hot char, which
has a high heat capacity, in the external furnace. All flows
through the reactor are well above the minimum transport velocity
to avoid buildup of dense particles.
The feed would have to be
ground very fine to allow good heat transfer.
The actual size
distribution needed would probably be a function of residence
time and temperature gradient.
One possible problem area is at
the bottom of the reactor where the manure transport line makes
a bend into the reactor.
This bend would have to be a much
gentler bend than is shown or impingement and build up of manure
could occur.
73
CO,
Condensers
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Figure 18.
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LENGTH OF RUNS
Run Number
Total Length of Time
Manure Added
hours
1
0.60
6
2.13
7
1.62
8
2.27
9
2.08
10
2.08