U.S. patent application number 09/938905 was filed with the patent office on 2003-02-27 for process for producing energy, feed material and fertilizer products from manure.
Invention is credited to Skinner, Richard, Stamper, Ken.
Application Number | 20030038078 09/938905 |
Document ID | / |
Family ID | 25472177 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038078 |
Kind Code |
A1 |
Stamper, Ken ; et
al. |
February 27, 2003 |
PROCESS FOR PRODUCING ENERGY, FEED MATERIAL AND FERTILIZER PRODUCTS
FROM MANURE
Abstract
A process for treating manure using anaerobic digestion includes
introducing manure into a mixing vessel containing a digester
liquid and agitating and filtering a slurry formed therefrom to
remove substantially all water insoluble solids, thereby leaving a
liquid containing ammonia and reactive organic materials. The
liquid is then heated and ammonia is removed therefrom to produce a
substantially ammonia-free liquid containing reactive organic
materials, which is cooled and placed in a digester containing
anaerobic bacteria to convert the reactive organic materials in the
liquid to biogas and to produce a digester liquid. The biogas is
withdrawn and utilized to generate electricity, and a small amount
of the digester liquid is withdrawn from the digester and recycled
back to the mixing vessel. The water insoluble solids and ammonia
removed during the process may be converted to ruminant animal feed
and concentrated liquid fertilizer, respectively.
Inventors: |
Stamper, Ken; (Norman,
OK) ; Skinner, Richard; (Bartlesville, OK) |
Correspondence
Address: |
DUNLAP, CODDING & ROGERS P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73114
US
|
Family ID: |
25472177 |
Appl. No.: |
09/938905 |
Filed: |
August 24, 2001 |
Current U.S.
Class: |
210/603 |
Current CPC
Class: |
Y02E 50/30 20130101;
Y02A 40/20 20180101; C02F 3/286 20130101; Y02P 20/145 20151101;
Y02W 30/40 20150501; C05F 17/40 20200101; C05F 3/00 20130101; C02F
11/04 20130101 |
Class at
Publication: |
210/603 |
International
Class: |
C02F 003/00 |
Claims
What is claimed is:
1. A process for treating manure using anaerobic digestion,
comprising the steps of: providing manure; introducing the manure
into a mixing vessel containing a digester liquid which is
substantially free of digestible organic materials and contains a
similar mineral content as the manure; agitating the manure and
digester liquid in the mixing vessel for an effective amount of
time to produce a pumpable slurry; withdrawing the pumpable slurry
from the mixing vessel; filtering the pumpable slurry to remove
substantially all water insoluble solids therefrom and provide a
resultant liquid containing ammonia and reactive organic materials;
heating the resultant liquid to a temperature in the range of from
about 150.degree. F. to about 230.degree. F. for an effective
amount of time to break chemical bonds and destroy active bacteria
present in the resultant liquid; removing ammonia from the heated
resultant liquid to produce a substantially ammonia-free liquid
containing reactive organic materials; cooling the substantially
ammonia-free liquid containing reactive organic materials to a
temperature in the range of from about 70.degree. F. to about
140.degree. F. to provide a cooled liquid stream containing
reactive organic materials; and passing the cooled liquid stream to
a digester containing anaerobic bacteria to convert the reactive
organic materials in the cooled liquid stream to biogas, thereby
producing a digester liquid substantially free of digestible
organic materials; withdrawing the biogas from the digester; and
withdrawing an effective amount of the digester liquid from the
digester and recycling the withdrawn digester liquid to the mixing
vessel for mixing with manure.
2. The process of claim 1 wherein, in the step of passing the
cooled liquid stream to the digester, the ammonia concentration in
the digester is maintained at a level below about 1500 ppm to
prevent inhibition of the anaerobic bacteria.
3. The process of claim 1 wherein the step of removing ammonia from
the heated resultant liquid is further defined as passing the
heated resultant liquid through a separator through which steam is
passed such that the ammonia present in the heated resultant liquid
is absorbed by the steam.
4. The process of claim 3 wherein the method further comprises
passing the steam containing the ammonia to a second separator
containing a dilute acid, wherein the ammonia is reacted with the
dilute acid to produce an ammonia salt which may be utilized as a
fertilizer.
5. The process of claim 1 wherein, in the step of passing the
cooled liquid stream to the digester, the biogas comprises methane
and carbon dioxide.
6. The process of claim 1 wherein, in the step of filtering the
pumpable slurry to remove substantially all water insoluble solids
therefrom, the water insoluble solids are collected and converted
to at least one of ruminant animal feed, a feed stock for
production of chemicals, and a fuel source to satisfy energy and
process heat requirements.
7. The process of claim 1 wherein, in the step of providing a
manure, the manure is poultry manure.
8. The process of claim 7 wherein the poultry manure is caged layer
manure.
9. The process of claim 1 wherein such process is conducted at a
facility in close proximity to a facility at which the manure is
produced.
10. The process of claim 1 wherein the process is continuous.
11. The process of claim 1 wherein the step of withdrawing the
biogas from the digester further includes utilizing the biogas for
generating electricity.
12. The process of claim 1 wherein the step of withdrawing the
biogas from the digester further includes collecting the
biogas.
13. A process for treating poultry manure using anaerobic
digestion, comprising the steps of: providing poultry manure;
introducing the manure into a mixing vessel containing a digester
liquid which is substantially free of digestible organic materials
and contains a similar mineral content as the manure; agitating the
manure and digester liquid in the mixing vessel for an effective
amount of time to produce a pumpable slurry; withdrawing the
pumpable slurry from the mixing vessel; filtering the pumpable
slurry to remove substantially all water insoluble solids therefrom
and provide a resultant liquid containing ammonia and reactive
organic materials; heating the resultant liquid to a temperature in
the range of from about 150.degree. F. to about 23020 F. for an
effective amount of time to break chemical bonds and destroy active
bacteria present in the resultant liquid; removing ammonia from the
heated resultant liquid to produce a substantially ammonia-free
liquid containing reactive organic materials; recovering the
ammonia removed from the heated resultant liquid such that the
ammonia may be utilized as a fertilizer; cooling the substantially
ammonia-free liquid containing reactive organic materials to a
temperature in the range of from about 70.degree. F. to about
140.degree. F. to provide a cooled liquid stream containing
reactive organic materials; and passing the cooled liquid stream to
a digester containing anaerobic bacteria to convert the reactive
organic materials in the cooled liquid stream to biogas, thereby
producing a digester liquid substantially free of digestible
organic materials, wherein the ammonia concentration in the
digester is maintained at a level below about 1500 ppm to prevent
inhibition of the anaerobic bacteria; withdrawing the biogas from
the digester and collecting the biogas for utilizing to generate
electricity; and withdrawing an effective amount of the digester
liquid from the digester and recycling the withdrawn digester
liquid to the mixing vessel for mixing with manure.
14. The process of claim 13 wherein the poultry manure is caged
layer manure.
15. The process of claim 13 wherein such process is conducted at a
facility in close proximity to a facility at which the manure is
produced.
16. The process of claim 13 wherein the process is continuous.
17. A process for treating poultry manure using anaerobic
digestion, comprising the steps of: providing poultry manure;
introducing the manure into a mixing vessel containing a digester
liquid which is substantially free of digestible organic materials
and contains a similar mineral content as the manure; agitating the
manure and digester liquid in the mixing vessel for an effective
amount of time to produce a pumpable slurry; withdrawing the
pumpable slurry from the mixing vessel; filtering the pumpable
slurry to remove substantially all water insoluble solids therefrom
and provide a resultant liquid containing ammonia and reactive
organic materials; recovering the substantially water insoluble
solids; heating the resultant liquid to a temperature in the range
of from about 150.degree. F. to about 230.degree. F. for an
effective amount of time to break chemical bonds and destroy active
bacteria present in the resultant liquid; removing ammonia from the
heated resultant liquid to produce a substantially ammonia-free
liquid containing reactive organic materials; recovering the
ammonia removed from the heated resultant liquid in the form of an
ammonia salt, an ammonia/water blend or anhydrous ammonia wherein
the ammonia salt, ammonia/water blend or anhydrous ammonia may be
utilized as a fertilizer; cooling the substantially ammonia-free
liquid containing reactive organic materials to a temperature in
the range of from about 70.degree. F. to about 140.degree. F. to
provide a cooled liquid stream containing reactive organic
materials; and passing the cooled liquid stream to a digester
containing anaerobic bacteria to convert the reactive organic
materials in the cooled liquid stream to biogas, thereby producing
a digester liquid substantially free of digestible organic
materials, wherein the ammonia concentration in the digester is
maintained at a level below about 1500 ppm to prevent inhibition of
the anaerobic bacteria; withdrawing the biogas from the digester
and collecting the biogas for utilizing to generate electricity;
and withdrawing an effective amount of the digester liquid from the
digester and recycling the withdrawn digester liquid to the mixing
vessel for mixing with manure.
18. The process of claim 17 wherein the poultry manure is caged
layer manure.
19. The process of claim 17 wherein such process is conducted at a
facility in close proximity to a facility at which the manure is
produced.
20. The process of claim 17 wherein the process is continuous.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates generally to bioconversion of
waste to useful products, and more particularly, but not by way of
limitation, to methods of treating manure using anaerobic
digestion.
[0005] 2. Brief Description of the Art
[0006] The number and size of concentrated animal feeding
operations, including agricultural operations which produce beef,
pork, poultry, milk or eggs, have been steadily increasing for the
past 50 years. The primary benefit of housing and feeding larger
numbers of agricultural animals at a single site is that the
consolidated operations give an economy of scale that lowers per
unit product operating costs and improves profitability. However,
as the number and size of concentrated, confined animal feeding
operations has grown over the years, the development of technology
to treat the waste material from these facilities has seriously
lagged. The majority of the waste material from existing operations
is land-applied with little treatment. Typically, manure disposal
is a net cost to the animal feeding operation, and there are
environmental concerns about direct application of raw manure to
the ground, including rainwater runoff of pollutants into surface
and ground waters and emissions of greenhouse gases to the
atmosphere.
[0007] In particular, chicken egg production in the United States
has undergone significant change in recent years. Such change is
characterized by modest growth of the producing flock, and
individual producing sites have become larger. For example, it is
estimated that there are currently more than 50 egg production
facilities in the United States which contain a minimum of one
million laying hens. Producers have been faced with the fact that
egg production and processing operations must become large and more
concentrated to improve economic performance in a competitive
business environment. However, of the known major producing
facilities with more than one million layers, none are known to use
any type of manure processing technology but rather simply apply
the manure to farm ground as a method of disposal, and, as
mentioned above, there are economic and environmental concerns with
this method of disposing of manure generated by the egg producing
operation.
[0008] Bioconversion refers to the conversion of organic matter
(such as waste material) into useful products (such as usable
energy) by bacterial decomposition of such organic matter.
Bioconversion is also known as anaerobic digestion, which is a
process utilized for pollution control in municipal sewage
treatment and livestock waste handling. For example, in some cases,
operators of animal feeding operations have constructed lagoons to
hold manure and to allow some anaerobic digestion of the waste
material before it is applied to the land. However, the condition
and operation of some of these lagoons has been the subject of
national news headlines, such as the breach of lagoon dikes in
North Carolina and Iowa. In addition, while research by
universities and government labs has shown that animal manure can
be effectively treated with anaerobic digestion, poultry manure has
been shown to be the most difficult to treat. Conventional
anaerobic digestion technology has certain limitations in terms of
reaction rates and the ability of the bacteria to be productive
when conditions (such as pH, temperature and concentration of
certain chemical constituents) in the digester are not optimum, and
current literature teaches that anaerobic treatment of poultry
manure can only be accomplished if the manure is diluted with water
at a ratio of between 4 to 1 and 10 to 1. While such dilution
allows for digestion of the manure, it also increases the volume of
waste that must be handled and ultimately sent to disposal. As a
result, this approach increases processing costs and is therefore
not economic.
[0009] In spite of the efforts of the government and the animal
feeding industry, there are no cost effective manure treatment
facilities in operation that are not a significant and direct
financial burden to the producer. Therefore, new and improved
methods of treating manure using anaerobic digestion technology
that overcome the disadvantages and defects of the prior art are
highly desired. It is to such methods of treating manure by
anaerobic digestion which not only eliminate the cost of manure
disposal but also result in the production of commercially viable
products that the present invention is directed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram of a process for treating
animal manure using anaerobic digestion constructed in accordance
with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention is directed to improved methods for
treating manure which involve anaerobic digestion. Conventional
anaerobic digestion technology has certain limitations in terms of
reaction rates and the ability of the bacteria to be productive
when conditions (such as pH, temperature and concentration of
certain chemical constituents) in the digester are not optimum. The
anaerobic digestion process depends on a collection of bacteria
collectively known as anaerobes, and such bacteria systematically
break down organic material into simple molecules. Pure organic
material (material that strictly consists of hydrogen and carbon)
is made into biogas, which consists primarily of methane and carbon
dioxide. Heteroatoms such as nitrogen and sulfur that may be
present in the organic material will be converted to ammonia and
hydrogen sulfide, respectively.
[0012] The four basic stages of anaerobic digestion are as follows:
(1) hydrolysis of large particulate solids; (2) fermentation of
large molecules into intermediates, i.e., acids and alcohols; (3)
conversion of such acids and alcohols into carbon dioxide, hydrogen
and small chain fatty acids, e.g. acetates; and (4) reduction of
carbon dioxide, hydrogen and acetates into methane. When viewing
this conversion, the anaerobic bacteria broadly operate in two
ways: (1) when converting the organic material into organic acids,
such as acetic acid, these bacteria are known as acetogens; and (2)
when converting the organic acids to methane, these bacteria are
known as methanogens. The methanogenic bacteria, responsible for
the final stage of anaerobic digestion, are only capable of
doubling their population at a very slow rate of about 192 hours.
On the other hand, the acetogenic bacteria involved in the
intermediate stage of anaerobic digestion have a doubling rate
about 60 times faster than that of the methanogenic bacteria. As
the productivity and reaction rate of the digester are strictly
dependent upon the productivity and reaction rates of the
population of bacteria in the digester, the deficient growth rate
of the methanogenic population of anaerobic bacteria must be
overcome by not only maintaining the methanogenic population but
also stabilizing the productivity and reactions rates of the
metanogenic population in the digester. The economics of the
process for treating manure using anaerobic digestion is dependent
upon the productivity and reaction rates of the digester, and
therefore high reaction rates mean that one can process more
material in a shorter amount of time. Thus, the capital costs of
any given operation can be reduced, since the size of the equipment
can be reduced for any given task/conversion.
[0013] There are a number of parameters that can affect
productivity of the bacteria and therefore the economics of the
operation. Among these are the digester temperature; the stability
of the digester temperature; intrusion of oxygen or air;
fluctuations in pH; and build up of toxic chemical constituents
such as ammonia, hydrogen sulfide or excess volatile fatty acids.
Parameters which lower the productivity of the anaerobic bacteria
are said to be "inhibitory".
[0014] It has been found that ammonia concentrations in excess of
1,500 ppm are inhibitory to anaerobic bacteria. As the
concentration of ammonia in fresh caged layer manure is typically
1% ammonia on a 70% moisture basis, it has been difficult to use
prior art anaerobic digestion processes on caged layer manure
without diluting the manure with significant amounts of water (4 to
10 times the original mass of manure). While this eliminates the
inhibitory effects of ammonia on the bacteria, the advantages of
high reaction rates are eliminated due to the larger volume of
material to be processed, and the economics of recovering valuable
primary plant nutrients becomes economically infeasible. In
addition, caged layer manure also contains about 1% organic
nitrogen (on a 70% moisture basis). As the organic nitrogen is
broken down to ammonia by the bacteria, it adds to the inhibitory
effect on the population of bacteria.
[0015] As stated previously herein, the methanogens are relatively
slow to reproduce. Therefore, any attempt to intervene in the
buildup of inhibitory materials must give consideration to the
potential deleterious effects of the methanogen population. The
present invention includes improved processes which deliver the
high reaction rates without diluting the feed material (i.e., caged
layer manure containing ammonia and organic nitrogen) and without
encumbering the bacteria with inhibitory conditions. By utilizing
the process technology of the present invention, manure can be
converted to commercial products and generate positive
economics.
[0016] Briefly, the present invention includes adding raw manure,
such as caged layer manure, to a mixing vessel containing a
digester liquid which has largely been depleted of digestible
organic materials but contains a similar mineral content as the raw
manure, and the raw manure and digester liquid are agitated to
produce a pumpable slurry. The pumpable slurry is withdrawn from
the mixing vessel and filtered to remove the majority of water
insoluble solids present in the pumpable slurry, thereby leaving a
resultant liquid containing ammonia and reactive organic materials.
The resultant liquid is then heated to a temperature in the range
of from about 15020 F. to about 230.degree. F. for an effective
period of time to break the bonds of certain compounds like
ammonium phosphate as well as to cause the subsequent shift in the
ionic state of ammonia from ammonium (NH.sub.4) to ammonia
(NH.sub.3). In addition, bacteria present in the resultant liquid
are destroyed during the heating of the pumpable slurry. The heated
resultant liquid is then passed through a first separator to remove
"free" ammonia, thereby producing a substantially ammonia-free
liquid and preventing inhibition of the anaerobic digestion step of
the process of the present invention by ammonia. The ammonia
separated by passing the heated resultant liquid through the first
separator can be recovered or passed to a second separator for
formation of an ammonia salt which can be utilized as a commercial
fertilizer product. The substantially ammonia-free liquid, which
contains reactive organic materials, is withdrawn from the first
separator, cooled to an appropriate digestion temperature and
passed to a digester for conversion of the reactive organic
materials to biogas. The biogas is withdrawn from the digester and
passed to a collection system, and the collected biogas is
desirably supplied to an electric operating plant for use in the
generation of electricity. A portion of digester liquid remaining
in the digester (which is substantially free of digestible organic
materials) is removed from the digester and recycled to the mixing
vessel for combining with manure in the first step of the process
of the present invention. The amount of digester liquid that is
recycled is sufficiently low so that the methanogen population in
the digester is not depleted over time. The concentration of
ammonia in the digester is thus maintained below the inhibitory
level, and therefore the anaerobic bacteria population present in
the digester is enhanced and is very productive. Therefore, the
process of the present invention has the following advantages over
the prior art: high reaction rates, small reactor volume, reacting
liquids with a relatively high concentration of salts and water
soluble solids, and low capital costs.
[0017] Shown in FIG. 1 is a schematic diagram illustrating one
embodiment of a process 10 for treating manure using anaerobic
digestion of the present invention. The process 10 for treating
manure is illustrated as being continuous, and such process 10 is
desirably conducted at a plant or facility which is in close
proximity to the source of the manure. Manure, such as caged layer
manure, is provided and passed through an inlet 12 into a mixing
vessel 14 containing a digester liquid which is substantially free
of digestible organic materials but contains a similar mineral
content as the manure, which will be described in more detail
hereinafter. The mixing vessel 14 is provided with an agitator or
stirrer 16, which agitates the manure and digester liquid for an
effective period of time to produce a pumpable slurry 18.
[0018] The volume of the mixing vessel 14 and conditions in the
mixing vessel 14 may vary, as long as the mixing vessel 14 is
capable of producing the pumpable slurry 18 as described herein.
The contents of the mixing vessel 14 are maintained at ambient
temperature and pressure, i.e., a temperature in the range of from
about 80.degree. F. to about 90.degree. F. and a pressure of about
14.7 psi.
[0019] The ratio of manure to digester liquid in the mixing vessel
14 may vary, depending upon the mass and percent moisture basis of
the manure. Desirably, the pumpable slurry 18 formed from the
manure and digester liquid will have a filterable solid content of
from about 5% to about 15%, and preferably, about 7%. To obtain
such a filterable solid content in the pumpable slurry 18, the
contents of the the mixing vessel 14 will be about 75% to about 85%
digester liquid and about 15% to about 25% raw manure. However, it
is to be understood that this does not result in a significant
dilution of manure in water (such as 4 to 10 times the original
mass of the manure as required by the prior art), as the digester
liquid contains a similar mineral content as the manure.
[0020] The amount of time required for the mixing vessel 14 to
produce the pumpable slurry 18 may vary, depending upon the amount
of digester liquid present in the mixing vessel 14, the amount of
manure introduced into the mixing vessel 14 and the moisture
content of such manure. Desirably, however, the amount of time
required for agitation of the mixture to produce the pumpable
slurry 18 will be in the range of from about 5 minutes to about 60
minutes.
[0021] The pumpable slurry 18 is withdrawn from the mixing vessel
14 and passed to a solid separator 20 via a conduit 22, a pump 24
and a conduit 26. Any pump capable of withdrawing the pumpable
slurry 18 from the mixing vessel 14 and passing the pumpable slurry
18 to the solid separator 20 via the conduits 22 and 26 may be
employed as the pump 24. Desirably, however, the pump 20 operates
in a pressure range of from about 0 psi to about 60 psi.
[0022] The solid separator 20 filters the pumpable slurry 18 to
remove substantially all water insoluble solids therefrom and
provide a resultant liquid containing ammonia and reactive organic
materials. The separated water insoluble solids, which may include
cellulosic materials, bran, feathers, and undigested grain, are
discharged from the solid separator 20 and passed via a conduit 28
to a collection vessel 29 for conversion into feed material as
described in more detail herein below. Any type of solid separator
capable of separating the water insoluble solids from the resultant
liquid may be utilized as the solid separator 20. Desirably, the
solid separator 20 is a "shale shaker" comprising a vibrating
screen shaker, a belt press with two rubber coated rollers and a
belt comprising a perforated material such as a 60 mesh stainless
steel screen. When employing such a shale shaker as the solid
separator 20, the pumpable slurry 18 is passed through the
vibrating screen shaker with the resulting solids going to the belt
press, which passes the wet solids between the two rubber coated
rollers which squeeze the resultant liquid therefrom so that only
the about 90% moisture to about 65% moisture solids remain thereon.
Desirably, the vibrating screen shaker is provided with a mesh size
in the range of from about 60 to about 80 mesh.
[0023] The resultant liquid containing ammonia and reactive organic
materials is withdrawn from the solid separator 20 and passed via a
conduit 30, a pump 32 and a conduit 34 through a heat exchanger 36
wherein the resultant liquid is heated to a temperature in the
range of from about 150.degree. F. to about 230.degree. F. for an
effective period of time to break chemical bonds of certain
compounds like ammonium phosphate, to cause the subsequent shift in
the ionic state of ammonia from ammonium (NH.sub.4) to ammonia
(NH.sub.3), and to destroy active bacteria present in the resultant
liquid. Preferably, the effective amount of time for maintaining
the resultant liquid at such temperature in the heat exchanger 36
is less than about 5 minutes.
[0024] Any pump capable of withdrawing the resultant liquid from
the solid separator 20 without causing damage to the solid
separator 20 or undesired withdrawal of the water insoluble solids
from the solid separator 20 can be employed as the pump 32.
Desirably, however, the pump 32 operates in a pressure range of
from about 0 psi to about 60 psi.
[0025] The heated resultant liquid is then passed, via a conduit
38, to a first separator 40 wherein ammonia present in the heated
resultant liquid is removed, thereby producing a substantially
ammonia-free liquid containing reactive organic materials.
Preferably, the method of removing the ammonia from the heated
resultant liquid in the first separator 40 includes passing a gas,
such as steam, through a conduit 42 into the first separator 40 and
withdrawn from the container 40 via a conduit 44. Thus, the flow of
the heated resultant liquid is in a counter direction to the flow
of the gas. The process of passing the gas through the heated
resultant liquid results in the absorption of the ammonia present
in the heated resultant liquid by the gas, thereby removing the
ammonia from the heated resultant liquid and producing a
substantially ammonia-free liquid containing reactive organic
materials. As previously stated herein above, ammonia
concentrations in excess of 1,500 ppm are inhibitory to anaerobic
bacteria; therefore, removal of ammonia at this point in the
process 10 prevents inhibition of downstream steps of the process
10 of the present invention by the presence of ammonia.
[0026] The first separator 40 is desirably a packed bed containing
standard inert packing materials such as raschig rings or"saddles"
(such materials being known to one of ordinary skill in the art).
The first separator 40 is depicted as having the conduit 38 through
which the heated resultant liquid passes connected to an upper end
thereof, the conduit 42 through which the gas enters the first
separator 40 connected to a lower end thereof, and the conduit 44
through which the gas containing the ammonia is removed connected
to the upper end thereof. By passing the heated resultant liquid
through the packed bed of the first separator 40, a maximum amount
of liquid surface area is created for interactions between the gas
and the heated resultant liquid, and the counter flow of the gas
relative to the heated resultant liquid results in optimum removal
of ammonia from the heated resultant liquid.
[0027] The ammonia-containing gas is withdrawn from the first
separator 40 via conduit 44 and passed to a second separator 46
containing a dilute acid, such as sulfuric acid, phosphoric acid,
citric acid or nitric acid, wherein the ammonia is removed from the
ammonia-containing gas and an ammonia salt is produced, which may
be utilized in the formation of a commercial fertilizer product.
The reaction of the dilute acid with ammonia in the second
separator 46 results in production of an ammonia salt which may be
utilized as a commercial fertilizer product. Such ammonia salt is
discharged from the second separator 46 via a conduit 48.
[0028] In another alternative of the present invention, the ammonia
may be captured from the ammonia-containing gas withdrawn from the
first separator 40 and recovered as an ammonia/water blend or as
anhydrous ammonia. Such ammonia-containing products could be used
to product a wide variety of products, including a commercial
fertilizer product.
[0029] The substantially ammonia-free gas remaining in the second
separator 46 is withdrawn via a conduit 50 and vented to the
atmosphere. Optionally, when steam is utilized as the gas, the
steam could be condensed to distilled water and utilized in the
facility at which the process 10 of the present invention is
conducted. In addition, waste heat may be captured in the form of
low pressure steam to aid in supplying process energy
requirements.
[0030] The substantially ammonia-free liquid containing the
reactive organic materials is then withdrawn from the first
separator 40 via a conduit 52 and passed through a second heat
exchanger 54, wherein the substantially ammonia-free liquid
containing the reactive organic materials is cooled to provide a
cooled liquid stream. Preferably, passage through the second heat
exchanger 54 provides a cooled liquid stream having a temperature
in the range of from about 100.degree. F. to about 140.degree. F.,
which temperature substantially corresponds to the temperature at
which digestion occurs.
[0031] The cooled liquid stream is then passed from the heat
exchanger 54 via a conduit 56 to a digester 58. In FIG. 1, the
passage of liquid from the first heat exchanger 36 to the first
separator 40 to the second heat exchanger 54 to the digester 58 is
illustrated as simply being by gravity flow through. However, if
desired, a pump may be utilized for delivery of the liquid from the
first heat exchanger 36 to the first separator 40 and/or to the
second heat exchanger 54 and/or to the digester 58.
[0032] The digester 58 contains anaerobic bacteria which convert
the reactive organic materials present in the cooled liquid stream
to biogas. The biogas generated has a high methane content (greater
than about 70%) and a low hydrogen sulfide content (less than about
0.4%). The digester 58 is maintained at an appropriate temperature
conducive to conversion of the reactive organic materials to biogas
by the anaerobic bacteria. The temperature of the digester 58 may
be maintained in the range of from about 32.degree. F. to about
80.degree. F. for a psychrophillic reaction (wherein a preferred
range is from about 70.degree. F. to about 80.degree. F.), in the
range of from about 100.degree. F. to about 108.degree. F. for a
mesophillic reaction, or in the range of from about 129.degree. F.
to about 137.degree. F. for a thermophillic reaction. Desirably,
the temperature of the digester 58 is in the range of from about
100.degree. F. to about 140.degree. F., and more desirably between
about 100.degree. F. to about 110.degree. F. The digester is
maintained at ambient pressure (i.e., about 14.7 psi).
[0033] The biogas so produced is withdrawn from the digester 58 and
passed via a conduit 60 to a collection system 62 for use in
generating electricity. The collection system 62 may be an electric
generator for directly generating electricity in conjunction with
the process 10 of the present invention. Optionally, the collection
system 62 may be a storage vessel for holding the biogas until
needed for use or until sold or transported to an electric plant.
Alternatively, the collection system 62 may be a treatment tower
for refining the biogas prior to passage to a storage vessel or an
electric generator or transported to an electric plant for use in
generating electricity or distribution of the biogas to purchasers.
The electricity so produced may be used to power requirements at
the egg laying operation and/or the facility at which the
continuous process 10 of the present invention is conducted, with
excess power being sold to an electric cooperative operation.
[0034] In a preferred embodiment of the present invention, the
biogas from the digester 58 will be delivered to a collection
system 62 via the conduit 60, wherein the collection system 62
comprises a low pressure compressor and a moderate volume storage
tank. From such a low pressure system, the biogas will flow through
a treatment tower for refining, which will include removing the
hydrogen sulfide from the biogas as well as passing the biogas
through a liquid knockout. The biogas will then flow to a
compressor that will raise the gas pressure to about 200 psi. This
moderate pressure gas will then be passed to a volume tank having
about
[0035] 2,000 cubic feet volume. Such moderate pressure gas can now
be utilized as fuel, which is distributed from the volume tank to
fuel consuming process equipment, which may include a spark-ignited
reciprocating engine, a fuel cell, a gas turbine, a boiler and a
rotary dryer. Steam generated from the boiler may also be utilized
to serve process energy needs as well as to produce fertilizer, as
described herein above with reference to the ammonia removed by the
process 10 of the present invention. Waste heat recovered from the
exhaust gases from the spark-ignited, reciprocating engine or the
gas turbine may be recovered to produce steam for use in the
process 10 of the present invention, to supplement the process
energy requirements.
[0036] A digester liquid remains in the digester 58 following
conversion of the reactive organic materials present in the cooled
liquid stream to biogas, and such digester liquid is therefore
substantially free of digestible organic materials. An effective
amount of the digester liquid is withdrawn from the digester 58 via
a conduit 64, a pump 66 and a conduit 68 and recycled back to the
mixing vessel 14 for combining with manure to repeat the process 10
of the present invention.
[0037] The term "an effective amount of the digester liquid" as
used herein is defined as an amount of digester liquid which is
large enough for admixing with manure to produce the pumpable
slurry 18 but sufficiently low enough to prevent the methanogen
population present in the digester 58 from being depleted over
time. It is to be understood that the effective amount of digester
liquid may be any volume of digester liquid which allows the
process 10 to function in accordance with the present invention.
Generally, such an effective amount of digester liquid will be
about 2% to about 8% of the total amount of digester liquid present
in the digester 58, and preferably about 5% of the total amount of
digester liquid present in the digester 58.
[0038] Any pump capable of withdrawing an effective amount of
digester liquid from the digester 58 but preventing excess digester
liquid from flowing out of the digester 58 and depleting the
methanogen population present in the digester 58 can be employed as
the pump 66. Desirably, however, the pump 66 operates in a pressure
range of from about 0 psi to about 60 psi.
[0039] As mentioned above, several useful products are generated
using the continuous process 10 for treating manure, especially
caged layer manure, using anaerobic digestion of the present
invention, wherein such useful products may be utilized to provide
a profit. First, the process 10 of the present invention generates
the biogas having a high methane content (greater than about 70%)
and a low hydrogen sulfide content (less than about 0.4%). Such
biogas is used to produce electricity as described herein before,
and excess power produced in such a manner can be sold to a third
party such as an electric cooperative operation and can be used to
support the power consumption requirements of the egg laying
operation. When the use of the biogas to generate electricity
becomes more efficient, the provider of the process 10 of the
present invention may become the power provider for the egg laying
operation. While analysis of competition in product pricing will
vary from site to site, it is estimated that electricity produced
by the process 10 of the present invention can be priced in the
range of from about 60% to about 70% of the market value and still
enable the facility using the process 10 of the present invention
to pay operating expenses, service debt and show a modest
profit.
[0040] Another product generated from the process 10 of the present
invention which may be utilized to produce a commercially viable
product is the ammonia salt collected from the second separator 46.
The ammonia salt will be used to produce a concentrated liquid
fertilizer which can be marketed to individuals and organizations
that have established relationships with local or area farmers.
Such concentrated liquid fertilizer will contain the ammonia salt
as collected from the second separator 46, and additives such as
minerals may be added to such concentrated liquid fertilizer,
depending upon local market demand and soil conditions. For
example, the concentrated liquid fertilizer containing the ammonia
salt may be supplemented with phosphorous, potassium, sulfur,
calcium and/or iron, depending upon local market demand. While
analysis of competition in product pricing will vary from site to
site, it is estimated that concentrated liquid fertilizer produced
in conjunction with the process 10 of the present invention can be
priced at about 85% of the market value.
[0041] The value of a fertilizer is dependent not only on the
contents of the fertilizer but also upon the physical form of the
fertilizer (i.e., gas, liquid or solid) and the cost of applying
the fertilizer. While anhydrous ammonia (a gas), is the lowest cost
form of ammonia, its application requires proper soil moisture
levels and is hazardous to personnel handling and applying the
material. The second lowest cost nitrogen fertilizer source is
urea; however, there is potential for nitrogen loss through ammonia
volatilization. The next least expensive form of nitrogen
fertilizer is a nitrogen solution ( such as 28%, 30% and 32%
nitrogen solutions), which offers ease of product transfer (via
pumps), and can be mixed and applied with pesticides. Liquid
fertilizers also offer the advantage of precision application in
conjunction with real time metering/global positioning and nozzle
selection, and the use of spray rigs with large booms can apply
liquid fertilizers to an entire section in a single day, while the
application rates of gaseous and dry fertilizer are much lower.
Therefore, liquid fertilizer appears to be the most competitive
form of nitrogen fertilizer available, and therefore concentrated
liquid nitrogen fertilizer may be produced in conjunction with the
process 10 of the present invention. In addition, the concentrated
liquid nitrogen fertilizer can be mixed and applied with
phosphorous, potassium and/or pesticides. Further, the concentrated
liquid nitrogen fertilizer produced in conjunction with the process
10 of the present invention will meet commercial specifications
required by state and federal laws for marketing as
fertilizers.
[0042] A third product which can be generated by the process 10 of
the present invention is the substantially water insoluble solids
separated from the liquid via the solid separator 24 and removed
from the solid separator 20 to the collection vessel 29. The solids
thus recovered from the solid separator 20 can be used as a feed
material to produce feed for ruminant animals. The protein content
of the feed material can be varied or tailored to meet specific
nutritional requirements, for example but not by way of limitation,
a cattle cube containing 15%, 20%, 25% or even 30% protein content
can be produced.
[0043] In addition, other materials may be combined with the
substantially water insoluble solids during formation of the feed
for ruminant animals, such as cattle cubes. Such materials include
bran, alfalfa, soybeans, cotton seeds, molasses, wheat mids, corn
gluten feed, yellow grease, rice hulls, peanut hulls, etc., as well
as animal by-products such as feather meal. Feed material formed
therefrom is sufficiently high in protein and minerals to supply
the nutritional requirements of cattle both during the early growth
phase of calves and for maintenance of mature cows during the
winter. In addition, vitamins (such as vitamins A and D), minerals
(such as salt and calcium supplements) and even antibiotics may be
blended therein to provide a feed that is specifically designed to
meet the nutritional needs of cattle.
[0044] The facility at which the process 10 of the present
invention is conducted may install blending, grinding and pelleting
equipment at the site to produce a feed product on site from the
bulk substantially water insoluble solids recovered from the solid
separator 20 of the process 10 of the present invention, or the
bulk substantially water insoluble solids recovered from the solid
separator 20 of the process 10 of the present invention may be sold
to an area feed mill for feed formulation, packaging, distribution
and sales. Optionally, the bulk substantially water insoluble
solids may be used in a gasifier or combusted directly to provide
energy in the form of steam or electricity. Also, use of the bulk
substantially water insoluble solids as a feed stock for production
of chemicals such as alcohols or diols may also be considered
within the scope of the present invention.
[0045] While the process of the present invention has been
described in detail herein for the bioconversion of manure and
especially caged layer manure, it is to be understood that such
processes are readily adaptable to other types of manure as well as
other waste products, including dairy manure, beef cattle manure
and concentrated swine waste. In addition, the process of the
present invention is not limited to the use of caged layer manure
but also includes all types of poultry manure, including broiler
manure and broiler litter. It is within the ability of one of
ordinary skill in the art to adapt such processes without undue
experimentation, and therefore the present invention is not limited
simply to the process described herein but also includes such
adaptable processes which are within the abilities of one of
ordinary skill in the art.
[0046] In addition, while the process 10 has been described herein
and illustrated in FIG. 1 as a continuous process, it is to be
understood that another embodiment of the process of the present
invention may be a batch process, in which excess digester liquid
is passed through an outlet for disposal, while a liquid, such as
water or a liquid containing a similar mineral content to that of
manure (i.e., a liquid containing potassium and phosphorous), is
combined with the manure in the first step of the process. Such a
batch process would have the advantage of allowing for isolation of
any methanogenic bacteria from the digester liquid removed from the
digester prior to disposal so that such methanogenic bacteria can
be recycled back to the digester, thereby preventing any depletion
of the methanogen population from the digester by removal of the
digester liquid. In addition, the digester liquid removed from the
digester may be stored until such a time that it is desired to mix
the digester liquid with the manure to repeat the process of the
present invention.
[0047] When the manure utilized in the process 10 of the present
invention is caged layer manure, the process 10 of the present
invention improves the profitability of the egg producer by
eliminating the cost of manure disposal and returning certain
commodities to the laying facility. The environmental liability of
the egg producer is also reduced since there is no application of
raw manure to the ground, thereby preventing rainwater runoff of
pollutants into surface and ground waters and significantly
reducing emission of greenhouse gases to the atmosphere. The net
environmental impact of the process 10 of the present invention on
the egg laying operation is very positive, and as a result, the
overall operation of the conversion plant utilizing the process 10
of the present invention will be fully compliant with current and
anticipated environmental laws and regulations.
[0048] From the above description, it is clear that the present
invention is well adapted to carry out the objects and to attain
the advantages mentioned herein as well as those inherent in the
invention. While presently preferred embodiments of the invention
have been described for purposes of this disclosure, it will be
understood that numerous changes may be made which will readily
suggest themselves to those skilled in the art and which are
accomplished within the spirit of the invention disclosed and as
defined in the appended claims.
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