U.S. patent application number 12/625210 was filed with the patent office on 2010-03-18 for sewage sludge recycling with a pipe cross-reactor.
This patent application is currently assigned to Unity Envirotech LLC. Invention is credited to Gary L. Dahms, Gary D. Greer.
Application Number | 20100064747 12/625210 |
Document ID | / |
Family ID | 25313922 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100064747 |
Kind Code |
A1 |
Greer; Gary D. ; et
al. |
March 18, 2010 |
Sewage Sludge Recycling With A Pipe Cross-Reactor
Abstract
An improved process for enhancing the plant nutrient value of
relatively low analysis organic waste material (e.g., sewage
sludge) involves treating the waste material with an acid and base
in a pipe-cross reactor. The process more particularly involves
mixing the waste material with water to form a slurry (or initially
taking the waste material as a slurry); pumping the slurry to a
pipe-cross reactor for reaction with a base, acid, and water to
form a melt: spraying the melt onto a recycling bed of fines in a
granulator and flashing off the water contained in the melt as
steam; rolling the melt onto recycled fine particles in a
granulator to form granulated particles; and drying these
granulated particles to form an enhanced plant nutrient value
composition (e.g., a fertilizer or soil conditioner having a
greater "NPK" value than the original relatively low analysis
organic waste material). The invention also includes fertilizers
produced according to the improved process, which fertilizers are
of the same size and shape and density of commonly used
fertilizers. The method advantageously utilizes the heat generated
by the exothermic acid-base reaction in the pipe-cross reactor to
remove the approximately 80% water from sludge, thus saving large
amounts of energy normally used in conventional drying or burning
methods, while, at the same time, conserving the intrinsic values
of the nutrients and humates contained in the sludge. In one
embodiment, the process includes a method of disposing of spent
acid from a hot dip galvanizing process or a steel pickling process
involving incorporating the spent acid to maintain the low pH of a
venturi scrubber used in the improved process.
Inventors: |
Greer; Gary D.; (Soda
Springs, ID) ; Dahms; Gary L.; (Soda Springs,
ID) |
Correspondence
Address: |
DRINKER BIDDLE & REATH;ATTN: INTELLECTUAL PROPERTY GROUP
ONE LOGAN SQUARE, 18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Assignee: |
Unity Envirotech LLC
|
Family ID: |
25313922 |
Appl. No.: |
12/625210 |
Filed: |
November 24, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11635193 |
Dec 7, 2006 |
|
|
|
12625210 |
|
|
|
|
10884856 |
Jul 6, 2004 |
7169204 |
|
|
11635193 |
|
|
|
|
09735768 |
Dec 12, 2000 |
6758879 |
|
|
10884856 |
|
|
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|
09416370 |
Oct 12, 1999 |
6159263 |
|
|
09735768 |
|
|
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08852663 |
May 7, 1997 |
5984992 |
|
|
09416370 |
|
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Current U.S.
Class: |
71/11 |
Current CPC
Class: |
C05F 3/00 20130101; Y02W
30/40 20150501; Y02P 20/145 20151101; Y02A 40/20 20180101; Y02W
30/43 20150501; Y02A 40/205 20180101; C05F 7/00 20130101; Y02P
20/133 20151101; Y02P 20/136 20151101; C05D 9/02 20130101; C05G
5/12 20200201; Y02A 40/213 20180101; C05F 3/00 20130101; C05F 5/00
20130101; C05F 7/00 20130101; C05F 7/02 20130101; C05F 7/00
20130101; C05F 7/02 20130101; C05D 9/02 20130101; C05F 3/00
20130101; C05F 7/00 20130101 |
Class at
Publication: |
71/11 |
International
Class: |
C05F 7/00 20060101
C05F007/00 |
Claims
1. A granular fertilizer of relatively low analysis organic waste
material having an enhanced plant nutrient value composition, said
fertilizer produced by the process comprising: mixing said
relatively low analysis organic waste material with water to form a
slurry capable of being pumped; pumping said slurry to a pipe-cross
reactor for reaction with a base, acid, and water to form a melt;
spraying said melt onto a recycling bed of fines in a granulator,
and flashing off water contained in the melt as steam: rolling said
melt onto fine particles in the granulator to form said granular
fertilizer; and drying said granular fertilizer to reduce the
moisture content thereof to form dried granular fertilizer
comprising an enhanced plant nutrient value composition.
2. The granular fertilizer of claim 1, wherein said granular
fertilizer is substantially homogenous.
3. The granular fertilizer of claim 1, wherein said granular
fertilizer is sized and shaped for application by standard granular
fertilizer application equipment.
4. A granular fertilizer having a plant nutrient value composition
of 12% nitrogen, 3% phosphorous, and 6% potassium, said fertilizer
produced by the process comprising: mixing low analysis organic
waste material with water to form a slurry capable of being pumped;
pumping said slurry to a pipe-cross reactor for reaction with a
base, an acid, and water to form a melt; spraying said melt onto a
recycling bed of fines in a granulator and flashing off water
contained in the melt as steam; rolling said melt onto fine
particles in the granulator to form said granular fertilizer;
drying said granular fertilizer to reduce the moisture content
thereof to form dried granular fertilizer; and collecting fumes
from the granulator containing steam, ammonia and particulate by
maintaining a negative pressure inside the granulator by pulling
the fumes through a venturi scrubber having a venturi throat with
water having a pH of about 2 to about 3 as scrubber water sprayed
into the venturi throat.
5. The granular fertilizer of claim 4, wherein the pH of the
scrubber water is kept at about 2 to about 3 by incorporating spent
acid from a hot dip galvanizing process into the scrubber
water.
6. The granular fertilizer of claim 5, wherein said spent acid from
said hot dip galvanizing process contains about three percent to
about eight percent zinc.
7. The granular fertilizer of claim 6, wherein said spent acid from
said hot dip galvanizing process contains about three percent to
about eight percent iron.
8. The granular fertilizer of claim 4, wherein the pH of the
scrubber water is kept at about 2 to about 3 by incorporating spent
acid from a steel pickling process into the scrubber water.
9. The granular fertilizer of claim 8, wherein said spent acid from
said steel pickling process contains about three percent to about
eight percent iron.
10. The granular fertilizer of claim 4, wherein said granular
fertilizer is substantially homogenous.
11. The granular fertilizer of claim 4, further comprising an
ingredient selected from the group consisting of lime, dolomite,
calcite, hydrobiotite, gypsum, phosphates, potash, urea, soil
clays, calcium peroxide, ammonium nitrate, vermiculite, humic acid,
iron, manganese, magnesium, boron, copper, zinc, and combinations
thereof.
12. A granular fertilizer having a plant nutrient value composition
of 12% nitrogen, 3% phosphorous, and 6% potassium, said fertilizer
produced by the process comprising: mixing low analysis organic
waste material with water to form a slurry capable of being pumped:
pumping said slurry to a pipe-cross reactor for reaction with a
base, acid, and water to form a melt; spraying said melt onto a
recycling bed of fines in a granulator, and flashing off water
contained in the melt as steam; rolling said melt onto fine
particles in the granulator to form said granular fertilizer: and
drying said granular fertilizer to reduce the moisture content
thereof to form dried granular fertilizer comprising an enhanced
plant nutrient value composition.
13. The granular fertilizer of claim 12, wherein said granular
fertilizer is substantially homogenous.
14. The granular fertilizer of claim 1, further comprising an
ingredient selected from the group consisting of lime, dolomite,
calcite, hydrobiotite, gypsum, phosphates, potash, urea, soil
clays, calcium peroxide, ammonium nitrate, vermiculite, humic acid,
iron, manganese, magnesium, boron, copper, zinc, and combinations
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. Ser.
No. 11/635,193, filed Dec. 7, 2006, which is a continuation of U.S.
Ser. No. 10/884,856, filed on Jul. 6, 2004, now U.S. Pat. No.
7,169,204, which is a continuation of U.S. Ser. No. 09/735,768,
filed on Dec. 12, 2000, now U.S. Pat. No. 6,758,879, which is a
continuation of U.S. Ser. No. 09/416,370, filed on Nov. 12, 1999,
now U.S. Pat. No. 6,159,263, which is a continuation of U.S. Ser.
No. 08/852,663, filed on May 7, 1997, now U.S. Pat. No.
5,984,992.
TECHNICAL FIELD
[0002] This invention relates generally to a method of treating
organic material to create a fertilizer. More specifically, the
invention relates to the treatment of organic material, such as
sewage sludge, with an acid and base in a pipe-cross reactor.
BACKGROUND
[0003] The disposal of sewage sludge is a problem. Current methods
of disposing of sewage sludge include incineration, direct land or
ocean application, heating and drying the sludge for sterilization
and then applying it to the land, depositing it in a landfill, or
granulating it with a standard rotary granulator, with heating and
drying being provided by exogenous heat sources (e.g. by burning
purchased fuel). While some of these methods result in what is
termed a "fertilizer", such fertilizer is of relatively low
analysis with regard to its "plant nutrient value".
[0004] Methods of expressing a fertilizer's "plant nutrient value"
involve identifying the fertilizer's "NPK" value, wherein N relates
to the amount of nitrogen, P relates to the amount of phosphorus
(expressed as P.sub.2O.sub.5), and K relates to the amount of
potassium (expressed as K.sub.2O). Thus, as reported by Wilson in
U.S. Pat. No. 3,050,383 (Aug. 21, 1962), sewage sludge with a
2.5-2.5-0 value contains two and a half percent nitrogen, two and a
half percent phosphorous as P.sub.2O.sub.5, and zero percent
potassium as K.sub.2O. Except as otherwise indicated by usage, all
percentage values used herein are weight-based percentages (i.e.,
w/w).
[0005] Fortunately, methods exist for enhancing the nutrient value
of relatively low analysis organic waste material. For instance, in
the aforementioned Wilson patent (the contents of the entirety of
which are incorporated by this reference), a method is disclosed
for treating dried animal manure and sewage sludge with controlled
amounts of an acid, such as sulfuric acid, phosphoric acid (or an
equivalent phosphorous compound, the strength of which is expressed
as phosphoric acid), or mixtures thereof, and an aqueous ammoniacal
solution, such as aqueous ammonia or ammoniacal nitrogen
salt-containing solutions and tumbling the resulting reaction mass
to form fertilizer granules having an "upgraded" or "enhanced"
plant nutrient value.
[0006] Other methods of enhancing the plant nutrient value of
relatively low analysis organic waste material with acids, bases,
or mixtures thereof have also been described. See, e.g., U.S. Pat.
No. 4,743,287 (May 10, 1988) to Robinson, U.S. Defensive
Publication T955,002 (Feb. 1, 1977) to Norton et al., U.S. Pat. No.
5,466,273 (Nov. 14, 1995) to Connell, U.S. Pat. No. 5,125,951 (Jun.
30, 1992) to Lahoda et al., U.S. Pat. No. 5,118,337 (Jun. 2, 1992)
to Bleeker. U.S. Pat. No. 5,393,317 (Feb. 28, 1995) to Robinson,
and U.S. Pat. No. 5,422,015 (Jun. 6, 1995) to Angell et al.
[0007] A further drawback of sludges treated in conventional
manners (e.g., by drying and screening) is that they are usually of
insufficient size and shape to be spread by commonly used
agricultural fertilizer spreaders, and cannot be used in the newer
pneumatic spreaders.
[0008] It would be an improvement in the art if a relatively simple
process existed for processing relatively low analysis organic
waste material to an enhanced plant nutrient value composition,
especially if such a process yielded a product which was sized and
shaped to be spread by presently commercially available
spreaders.
DISCLOSURE OF THE INVENTION
[0009] The invention includes an improved process for enhancing the
plant nutrient value of relatively low analysis organic waste
material, such as sewage sludge. The improvement involves
exothermically treating the relatively low analysis organic waste
material with an acid and a base in a pipe-cross reactor.
[0010] More particularly, the improved process involves mixing the
relatively low analysis organic waste material with water to form a
slurry (or taking the waste material as a slurry): pumping the
slurry to a pipe-cross reactor for reaction with a base, acid, and
water to form a melt; spraying the melt onto a recycling bed of
fines, and flashing off the water contained in the melt as steam.
The melt is then rolled onto a substrate such as recycled fine
particles in a granulator to form granulated particles, causing the
granulated particles to grow in size (e.g., to form granules).
These granulated particles are then dried (e.g., with a rotary
dryer) to reduce their moisture content, and form an enhanced plant
nutrient value composition (e.g., a fertilizer or soil conditioner
having a greater NPK value than the original relatively low
analysis organic waste material).
[0011] Generally, the process will also include passing the dried
granulated particles to a separation apparatus and separating the
dried granulated material into fines, product, and oversized
material, and further includes grinding the oversized material and
returning the fines and oversized material to the granulator for
use as a granular substrate. Potash and other micronutrient
materials may be added as dry material to the returning fines for
further enhancement of the product.
[0012] The invention also includes fertilizer produced according to
the improved process. Fertilizers produced by the instant invention
are of the same size and shape and density of commonly used
fertilizers.
[0013] An advantage of the method is that it uses the heat
generated by the exothermic acid-base reaction in the pipe-cross
reactor to remove the approximately 80% water from sludge, thus
saving large amounts of energy normally used in conventional drying
or burning methods, while, at the same time, conserving the
intrinsic values of the nutrients and humates contained in the
sludge. The method also handles the processed material as a slurry,
thus avoiding the nuisance of conveying and handling dry or solid
materials. The method also achieves high temperatures which aids in
the destruction of pathogens.
[0014] In one embodiment, the process includes a method of
disposing of spent acid from a hot dip galvanizing process or a
steel pickling process comprising incorporating the spent acid to
maintain the low pH of a venturi scrubber used in the improved
process thus producing a micronutrient enriched fertilizer.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 is a process flow diagram, showing a process
according to the invention.
[0016] FIG. 2 is a stylized view of a pipe-cross reactor for use
with the invention.
[0017] FIG. 3 is a partially cut away, perspective view of a
pipe-cross reactor in a rotary ammoniator-granulator for use in
practicing the invention.
[0018] FIG. 4 is a stylized end view of a rotating bed of materials
in a granulator for use with the invention.
BEST MODE OF THE INVENTION
[0019] As depicted in FIG. 1, an improved process for enhancing the
plant nutrient value of organic waste material generally involves
mixing the organic waste material with water in an agitation tank
or sludge slurry tank 10 to form a slurry. The water used in making
the slurry preferably includes scrubber water from the hereinafter
described scrubbers 22, which includes waste acid. The slurry is
mixed at a sufficient concentration and consistency that it will
optimally process the organic waste material as quickly as
possible, but will not clog or block the pipe-cross reactor 12
during operation. Of course, the particular slurry concentrations
and consistencies will depend, to some extent, on the size and
amount of insoluble particulate material contained in the
particular organic waste material, and the size and length of the
pipe-cross reactor components.
[0020] The slurry is pumped from the agitation tank 10 to a
pipe-cross reactor 12 for an exothermic reaction with, for example,
a base such as ammonia, and an acid or acids such as sulfuric acid,
phosphoric acid, and mixtures thereof, with or without extra water
to form a melt.
[0021] Pipe-cross reactors are well-known, and have been used in
the past to produce granular NPKS fertilizers from liquid
chemicals. See, e.g., Energy Efficient Fertilizer Production with
the Pipe-Cross Reactor, (U.S. Dept. of Energy, 1982) (a pipe-cross
reactor fit into the granulator drum of a conventional
ammoniation-granulation system); Achorn et al., "Optimizing Use of
Energy in the Production of Granular Ammonium Phosphate Fertilizer"
(1982 Technical Conference of ISMA, Pallini Beach, Greece); British
Sulfur Corp. Ltd., "TVA modifies its pipe reactor for increased
versatility". Phosphorus & Potassium, No. 90, pp. 25-30 (1977);
Achorn et al., "Efficient Use of Energy in Production of Granular
and Fluid Ammonium Phosphate Fertilizers" (1982 Fertilization
Association of India Seminar. New Dehli, India): Salladay et al.
"Commercialization of the TVA Pipe-Cross Reactor in Regional NPKS
and DAP Granulation Plants in the United States" (1980
Fertilization Association of India Seminar, New Dehli, India); U.S.
Pat. No. 4,619,684 (Oct. 28, 1986) to Salladay et al.; U.S. Pat.
No. 4,377,406 (Mar. 22, 1983) to Achorn et al.; U.S. Pat. No.
4,134,750 (Jan. 16, 1979) to Norton et al.; U.S. Defensive
Publication T969,002 (Apr. 4, 1978) to Norton et al; and Salladay
et al. "Status of NPKS Ammoniation-Granulation Plants and TVA
Pipe-Cross Reactor" (1980 Fertilizer Industry Round Table, Atlanta,
Ga., US).
[0022] Amounts of acid and base used in the exothermic process can
be determined by one of skill in the art. However, for guidance in
the neutralization of ammonia, approximately one mole of sulfuric
acid, or of phosphoric compounds expressed as phosphoric acid, is
used for each two moles of ammonia. Concerning the concentration of
phosphoric acid, typical molar ratios of N:P in the pipe-cross
reactor are between 1.3:1 to 1.8:1, preferably 1.4:1 and 1.5:1,
taking into consideration water dilution of the phosphoric acid to
between about forty-two to forty-seven percent (42 to 47%)
P.sub.2O.sub.5. The molar amount of nitrogen should take into
consideration not only the amount of ammonia being added, but the
typical amount of ammoniacal nitrogen contained in the particular
organic waste material.
[0023] Other acids which may be used with the invention include
nitric acid, hydrochloric acid, acetic acid, citric acid and
mixtures thereof. Certain combinations (e.g., nitric acid and an
ammonia compound which might form ammonium nitrate which may be
explosive) need to be carefully considered before use however.
Whatever the acid or acids chosen, the strength of one of the acids
used in the process will preferably be equivalent to 90% sulfuric
acid (e.g., 93 to 100 percent sulfuric acid).
[0024] As depicted in FIG. 2, the pipe-cross reactor 12 is
preferably provided with two cross pipes 26, 28 to receive sulfuric
acid (at a rate of about 8.6 gpm) and phosphoric acid (at a rate of
from about 2.6 gpm). A third pipe 30 incorporates the ammonia into
the center of the reactor. The length of this pipe 30 should be at
least twenty (20) to thirty (30) inches to ensure adequate mixing.
A third cross pipe 32 incorporates the slurry and additional water
into the mixing chamber. A typical pipe-cross reactor for use with
the invention has a diameter of approximately three (3) to ten (10)
inches, is from about seven (7) to about fifty (50) feet long, and
terminates in a, for example, two (2) to eight (8) inch discharge
pipe (or a slot of equivalent cross-sectional area), preferably
with a stainless steel insert or TEFLONT.TM. lining. The discharge
pipe preferably discharges into a standard rotating drum granulator
14. It is preferably made of a steel pipe (e.g., HASTELLOY C-276 or
316L stainless steel (with HASTELLOY C or B for the reaction
tube)). A TEFLONT.TM., ceramic, or other corrosion resistant lining
may also be used in the pipe-cross reactor. The temperature is
preferably maintained below 149.degree. C. (300.degree. F.).
[0025] The ammonia is introduced into the system at a rate of from
about 4.3 gpm. Organic waste material (e.g., sewage sludge) and
water are incorporated at a rate of from about 30 to about 40 gpm
of slurry. The pipe-cross reactor is typically operated at a gage
pressure of between fifteen (15) and sixty (60) psig.
[0026] A "hot melt" discharges from the pipe-cross reactor tube
into the granulator 14, while water flashes from the reactor
product as it issues into the granulator 14. Steam is generated by
the exothermic reaction conducted within the pipe-cross reactor
12.
[0027] A preferred granulator (also commonly known as an
"ammoniator-granulator") is a two (2) to four (4) meter (e.g., six
(6) to twelve (12) feet) diameter rotating drum granulator having a
length of from about five (5) to about seven (7) meters. In the
depicted process, the granulator 14 includes an ammonia sparger 20
operably positioned within the granulator 14 for the addition of
small amounts of ammonia to the melt to for example, control or
adjust the pH of the granulated material.
[0028] The melt is rolled onto recycled fine particles within the
granulator 14 to form granulated particles, thus causing the
granulated particles to grow to a desired size. Afterwards, these
granulated particles are passed into a rotary dryer 16 for a
sufficient amount of time to reduce their moisture content, thus
forming a fertilizer having an enhanced plant nutrient value.
[0029] A preferred dryer for use with the invention is a two (2) to
three (3) meter (e.g., six (6) to eight (8) feet) diameter rotating
drum dryer having a length of from about fifteen (15) to about
seventeen (17) meters, and having a heating capacity of 30 to 45
million BTU/hour, with a lump crusher at the discharge end.
[0030] The depicted process further includes passing the dried
granulated particles to a separation apparatus or screens 18 and
separating the dried granulated material into fines, product and
oversized material. Oversized material is reduced in size to be
incorporated, as a fine, into the process.
[0031] The fines are returned to the granulator 14 (along with
potash or any micronutrients required for the desired final product
analysis) for incorporation into the process. The product from the
separation process is preferably cooled in a product cooler (from
two (2) to three (3) meters in diameter, and fifteen to seventeen
(17) meters long) or a suitable fluid-bed type cooler.
[0032] During the process, fumes from the granulator 14 containing
steam, ammonia, and particulate are collected by maintaining a
negative pressure inside the granulator 14 by pulling the fumes
through a venturi scrubber 22 having low water as scrubber water
sprayed into the venturi throat.
[0033] Other aspects of a ventilation system for use with the
invention preferably include fans (e.g., ones capable of moving
about 60,000 cubic feet per minute of air), dry cyclones for dust
collection, and venturi scrubbers with water separation chambers
for collecting ammonia fumes and small dust particles.
[0034] The invention uses low pH water in the venturi scrubbers to
collect unreacted ammonia vapors escaping the granulator. In one
embodiment, small amounts of sulfuric or phosphoric acid are added
to the venturi scrubbers to maintain a low pH (e.g., 2 to 3) for
proper ammonia vapor scrubbing in the venturi scrubbers.
[0035] NPK fertilizers generally, however, preferably include the
micronutrients iron and zinc. In a preferred embodiment, therefore,
spent acid from a hot dip galvanizing (EPA/RCRA hazardous waste
designation D002, D006, D007 and D008) or steel pickling process
(EPA/RCRA hazardous waste designation K062) is used to maintain the
low pH of the scrubber water. These spent acids commonly are
sulfuric acid or hydrochloric acid of five (5%) to ten percent
(10%) strength, containing three (3) to eight (8) percent iron.
Galvanizing spent acid contains three (3) to eight (8) percent zinc
along with the previously described iron. The iron and zinc are fed
with the ammonia-laden scrubber water from scrubbing to the sludge
slurry tank, and on to the pipe-cross reactor for incorporation as
iron and zinc micronutrients in the final NPK fertilizer. In the
case of spent sulfuric acid, the sulfur also becomes a nutrient in
the resulting fertilizer, since it reacts in the pipe-cross reactor
to form ammonium sulfate (while hydrochloric acid goes to form
ammonium chloride).
[0036] Other micronutrients or additional ingredients may be
incorporated into the resulting fertilizer by adding them with a
weigh feeder as a dry solid to the fines recycle stream.
"Micronutrients" or "additional ingredients" include lime,
dolomite, calcite, hydrobiotite, gypsum, phosphates (e.g., rock
phosphate or ammonium phosphate), potash, urea, soil clays, calcium
peroxide, ammonium nitrate, vermiculite, humic acid, and trace
minerals such as iron, manganese, magnesium, boron, copper, and
zinc.
[0037] Although the invention has been most particularly described
for the processing of municipal sewage sludge, the inventive
process may also be used to enhance the plant nutrient value of
other relatively low analysis organic waste material such as
poultry manure, food processing wastes, wastes from paper
manufacturing, swine manure sludge, mixtures thereof, and the like.
In such a case, the particular relatively low analysis organic
waste material is substituted for the sewage sludge in the process,
and the process parameters are accordingly modified.
[0038] The invention is further explained by the following
illustrative example:
Example
[0039] In an agitation tank, 6700 kilograms/hour (7.4 tons/hour) of
sewage sludge are mixed with 37 liters per minute (ten
gallons/minute (gpm)) of scrubber water from a venturi scrubber to
form a slurry. The slurry is of a consistency that it can be pumped
with a positive displacement pump or other suitable pump to a
pipe-cross reactor equipped to receive ammonia, sulfuric acid,
phosphoric acid, sewage sludge, and water. The pipe-cross reactor
has a diameter of approximately four (4) inches, and is forty (40)
feet long. The pipe-cross reactor terminates in a rotating drum
granulator. The rotating drum granulator is six (6) feet in
diameter, and is twenty (20) feet long.
[0040] The slurry is added to the pipe-cross reactor, and is
reacted with 8.6 gpm 99.5% ammonia, 8.6 gpm sulfuric acid (93%),
and 2.6 gpm phosphoric acid (54% P.sub.2O.sub.5). The temperature
of the pipe-cross reactor (due to the exothermic reaction between
the acid and the base) is maintained at about 149.degree. C.
(300.degree. F.) with moisture in the sludge. This temperature acts
to kill Salmonella, E. coli, and other pathogens which may be found
in the slurry. This temperature also acts to deodorize the material
somewhat.
[0041] The resulting melt from the pipe-cross reactor is sprayed
onto a recycling bed of fines, along with 2000 pounds of added
potassium chloride (60% K.sub.2O) while the water contained in the
melt flashes off as steam. An ammonia sparger is provided in the
granulator to add small amounts of ammonia to the granulation
mixture for control.
[0042] Operating the pipe-cross reactor in such a manner
incorporates approximately 14.8 tons per hour of 20% solid sewage
sludge at a ten (10) ton per hour production rate.
[0043] Fumes from the granulator containing steam, ammonia and
particulate are collected by maintaining a negative pressure inside
the granulator with a fume fan pulling fumes through a venturi
scrubber with low pH water (water at a pH lowered by the addition
of spent acid from a hot dip galvanizing process) sprayed into the
venturi throat. (If galvanizing acid is unavailable, the pH may be
controlled with phosphoric or sulfuric acid). The low pH water
collects ammonia vapor present in the fumes, as well as dust
particles.
[0044] Granulated material exits the granulator at about 93.degree.
C. (200.degree. F.) and at about a five (5) to fifteen (15) percent
moisture content into a rotary dryer. The rotary dryer is
approximately two meters (e.g., six (6) feet) in diameter and has a
length of about twenty meters (e.g., sixty (60) feet). It has a
heating capacity of 30 million BTU/hour, and is associated with a
lump crusher or lump breaker at the discharge end. The moisture in
the material is reduced to about three percent (3%) by heated
forced air in the dryer.
[0045] Materials exiting the rotary dryer are run through the lump
crusher to reduce oversized material to less than one (1) inch in
size.
[0046] Screens are used to separate the material into (a) fines.
(b) product and (c) oversized material. Fines are returned to the
granulator. Product goes to a two meter (six foot) diameter, twenty
meter (sixty foot) long cooler and then on to storage, while the
oversized material is passed through a grinding mill, and reduced
to fines for recycling to the granulator. About two (2) tons (1800
kg) of fine material per ton of product are required in the recycle
stream.
[0047] Dust-laden air is collected from the dryer, grinding mills,
and screens by a fan maintaining negative pressure on all of the
equipment. The air is pulled through a cyclone system that removes
about 97% of the dust. From the cyclones, the air is passed through
a venturi scrubber to remove the remaining dust particles. Air from
the venturi scrubber is sent to a large separator chamber, along
with the air from the granulator fume scrubber to remove any
condensed moisture. The air from these venturi scrubbers is
combined and passed through a secondary venturi scrubber. The air
then exits through a stack approximately one hundred (100) feet
tall. The air is saturated at around 66.degree. C. (150.degree.
F.).
[0048] The resulting fertilizer is determined to have an NPK value
of 12-3-6 (12% nitrogen, 3% phosphate, and 6% potash). It is also
homogenous and properly sized for standard application
equipment.
[0049] References herein to a specific Example or specific
embodiments should not be interpreted as limitations to the
invention's scope which is determined by the claims.
* * * * *