U.S. patent application number 10/854677 was filed with the patent office on 2005-02-24 for organic recycling with metal addition.
Invention is credited to Burnham, Jeffrey C., Dahms, Gary L..
Application Number | 20050039508 10/854677 |
Document ID | / |
Family ID | 33493338 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050039508 |
Kind Code |
A1 |
Burnham, Jeffrey C. ; et
al. |
February 24, 2005 |
Organic recycling with metal addition
Abstract
The invention is directed to methods for producing a granular
nitrogen fertilizer from an organic material comprising adding a
metallic salt to said organic material to form a slurry. Preferably
the organic material comprises dewatered biosolids and contains
water from a scrubber. Metallic salts that can be used comprise a
salt of iron, zinc, or a mixture thereof. Preferred iron salts
comprises ferric sulfate or ferric oxide, and preferred zinc salts
comprises zinc sulfate or zinc oxide. Preferably, the metallic salt
is mixed with an acid such as sulfuric acid to form an acidified
metal salt. Slurry pH ranges from approximately 2-2.5. The
acidified metal salt is added to the organic material in sufficient
quantity to lower viscosity of the slurry such that the resulting
fluid does not hinder fluid flow during operation. When the
metallic salt comprises acidified ferric sulfate or ferrous
sulfate, sufficient iron can be present to produce a fertilizer
product with 0.1 weight percent to 10 weight percent iron sulfate
calculated on a dry weight basis. The invention is also directed to
fertilizer products made by the methods of the invention. Preferred
products are granules and the metallic salt increases product
hardness. Fertilizer granules preferably contain metal that is
bioavailable to a plant when used as a fertilizer. Solubility of
the metal of the product in water is enhanced, and the product is
low staining.
Inventors: |
Burnham, Jeffrey C.;
(Naples, FL) ; Dahms, Gary L.; (Soda Springs,
ID) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD
SUITE 300
MCLEAN
VA
22102
US
|
Family ID: |
33493338 |
Appl. No.: |
10/854677 |
Filed: |
May 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60473197 |
May 27, 2003 |
|
|
|
60473198 |
May 27, 2003 |
|
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Current U.S.
Class: |
71/11 |
Current CPC
Class: |
C05C 3/00 20130101; C05C
3/00 20130101; C05F 3/00 20130101; C05B 7/00 20130101; C05F 5/008
20130101; C05B 17/00 20130101; C05B 17/00 20130101; C05B 7/00
20130101; C05C 3/00 20130101 |
Class at
Publication: |
071/011 |
International
Class: |
C05F 001/00 |
Claims
1. A method for producing a granular nitrogen fertilizer from an
organic material comprising adding a metallic salt to said organic
material to form a slurry.
2. The method of claim 1, wherein the organic material comprises
biosolids.
3. The method of claim 1, wherein the slurry comprises dewatered
biosolids.
4. The method of claim 3, wherein the dewatered slurry of biosolids
contains scrubber water.
5. The method of claim 1, wherein the metallic salt comprises a
salt of iron, zinc, or a mixture thereof.
6. The method of claim 5, wherein the iron salt comprises ferric
sulfate or ferric oxide.
7. The method of claim 5, wherein the zinc salt comprises zinc
sulfate or zinc oxide.
8. The method of claim 1, wherein the metallic salt is mixed with
an acid to form an acidified metal salt.
9. The method of claim 8, wherein the acidified metal salt is added
in sufficient quantity to lower viscosity of the slurry.
10. The method of claim 1, wherein the slurry is mixed at a
sufficient concentration and consistency to form a fluid that does
not hinder slurry flow during operation.
11. The method of claim 1, further comprising adding sulfuric
acid.
12. The method of claim 11, wherein the sulfuric acid is mixed with
the metallic salt prior to adding to said organic material.
13. The method of claim 11, wherein the sulfuric acid is mixed with
ferrous oxide to produce ferrous sulfate such that said slurry has
a resultant pH of approximately 2.0 to 2.5.
14. The method of claim 11, wherein the sulfuric acid is mixed with
ferric oxide to produce ferric sulfate such that said slurry has a
resultant pH of approximately 2.0 to 2.5.
15. The method of claim 11, wherein the metallic salt comprises
acidified ferric sulfate or ferrous sulfate which is mixed with the
organic material such that sufficient iron is present to produce a
fertilizer product with 0.1 weight percent to 10 weight percent
iron sulfate calculated on a dry weight basis.
16. The method of claim 15, wherein the fertilizer product has
between 0.5 weight percent and 5 weight percent iron sulfate
calculated on a dry weight basis.
17. The method of claim 15, wherein the fertilizer product has
between 1 weight percent to 3 weight percent iron sulfate
calculated on a dry weight basis.
18. The method of claim 11, wherein the sulfuric acid is added to
the organic material prior to reaching a mix tank and at a rate of
approximately 1.75 percent of a total feed rate to result in a pH
range of 3.0 to 3.5.
19. The method of claim 1, wherein the slurry is pumped into a
shear mix tank that contains a high shear rotary agitator which
turns at a speed sufficient to produce high shear.
20. The method of claim 19, further comprising passing the slurry
from said shear mix tank to a holding or equilibrium tank
containing an agitator.
21. The method of claim 20, wherein the holding or equilibrium tank
containing the agitator is capable of providing approximately 2
hours of storage for the slurry.
22. The method of claim 20, wherein the holding or equilibrium tank
is operated to maintain a pH of 3.0 to 4.0 with a solids content of
between 15 percent and 28 percent solids.
23. The method of claim 22, wherein the solids content is from 20
percent to 23 percent.
24. The method of claim 1, wherein the metallic salt chemically
bonds with one or more elements of the slurry.
25. The method of claim 24, wherein the metallic salt is an iron
salt that bonds with ammonium sulfate or ammonium phosphate present
in the slurry.
26. The method of claim 1, wherein the metallic salt comprises
acidified ferrous or ferric salts to reduce sulfur compounds in the
slurry.
27. The method of claim 26, wherein the acidified ferrous or ferric
salts reduce dust formation during operation.
28. The method of claim 26, wherein the acidified ferrous or ferric
salts reduce odor during operation.
29. The method of claim 1, wherein adding the metallic salt
enhances granulation formation of the slurry.
30. The method of claim 1, wherein the metallic salt initiates
chemical hydrolysis of organic molecules in the slurry.
31. The method of claim 1, wherein the metallic salt drives reduced
sulfur compounds out of the organic material reducing odorant
sources in a fertilizer product.
32. The method of claim 1, wherein the metallic salt is added to
said organic material in a pipe-cross reactor.
33. The method of claim 32, wherein the metallic salt enhances
reaction kinetics of the pipe-cross reactor.
34. The method of claim 32, wherein the metallic salt lowers
viscosity of the slurry such that operation of the pipe-cross
reactor is more controllable than without the metallic salt.
35. The method of claim 1, wherein the metallic salt is added in a
tubular reactor.
36. A fertilizer product produced by the method of claim 1.
37. The product of claim 36, wherein the metallic salt is acidified
ferrous or ferric salts.
38. The product of claim 37, wherein the acidified ferrous or
ferric salts increase product hardness.
39. The product of claim 36, which has a crush weight of greater
than 6 pounds.
40. The product of claim 39, which has a crush weight of greater
than 7 pounds.
41. The product of claim 36, wherein metal of the metallic salt is
available to a plant.
42. The product of claim 41, wherein solubility of the metal in
water is enhanced.
43. The product of claim 36, which is a low staining product.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 60/473,197 entitled "Organic Recycling with Metal
Addition," and U.S. Provisional Application No. 60/473,198 entitled
"Liquid Fertilizer Incorporating Biosolids and High Concentrations
of Ammonia," the entirety of which are both hereby incorporated by
reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] This invention is directed to systems, devices and methods
for converting organic material into fertilizer. More specifically,
the invention relates to adding iron sulfate or other metallic
salts to organic material prior to producing fertilizer from the
organic material.
[0004] 2. Description of the Background
[0005] The disposal of sewage sludge is a significant world-wide
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 land,
depositing it in a landfill, or granulating the sludge 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 a fertilizer, such fertilizers are
of relatively low analysis with regard to their plant nutrient
value.
[0006] 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 in U.S. Pat.
No. 3,050,383, 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 herein are
weight-based percentages (i.e. w/w).
[0007] 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 which are
entirely incorporated herein by 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.
[0008] 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 (e.g. U.S. Pat. No.
4,743,287, U.S. Defensive Publication T955,002, Norton et al. (Feb.
1, 1977), U.S. Pat. No. 5,466,273, U.S. Pat. No. 5,125,951, U.S.
Pat. No. 5,118,337, U.S. Pat. No. 5,393,317, and U.S. Pat. No.
5,422,015.
[0009] Tubular reactors are known in the art for producing ammonia
salts (e.g. U.S. Pat. No. 6,117,406, U.S. Pat. No. 2,902,342, U.S.
Pat. No. 2,755,176, and U.S. Pat. No. 2,568,901, the contents of
which are hereby incorporated by reference). Exothermic reactions
are carried out in the tubular reactors by reacting a base with an
acid in the reactor tube. European Patent Publication 770,586A1
also discloses that tubular reactors may be used for the treatment
of relatively low analysis organic waste material. This European
Patent Publication generally describes a process of treating such
organic waste by introducing the organic waste, ammonia, and an
acid into a tubular reactor, carrying out an exothermic reaction,
separating vapor from sludge, and then further processing the
sludge.
[0010] A component typically associated with tubular reactors is a
preneutralizer. The preneutralizer is typically used in conjunction
with tubular reactors to effect partial neutralization of the acid
prior to its introduction into the reactor. However, the use of a
preneutralizer poses various disadvantages including difficulty in
obtaining accurate control of flow rates. Additionally, operating
and equipment costs associated with the use of a preneutralizer
often represent a significant expense.
[0011] A reactor similar to the tubular reactor is the pipe-cross
reactor. Pipe-cross reactors similarly allow for an exothermic
reaction to take place, but typically involve the introduction of
one or two different acid solutions for reaction with a base in a
method to thoroughly mix the reagents. This is an important feature
of pipe-cross reactors as it eliminates the need for a
preneutralizer. At the first stage of the cross pipe reactor, the
base and/or scrubber water and organic material solution are
premixed. At the second step, pipe-cross reactors are formed with
up to two acid inlets configured such that the acid solutions are
introduced perpendicular to the pipe cross reactor as substantially
opposing streams. The perpendicular entry and opposing streams
allow for thorough mixing of the acids within the reactor, thus
eliminating the need for extraneous equipment such as a
preneutralizer.
[0012] Pipe-cross reactors are well-known and have been used in the
past to produce granular NPKS fertilizers from liquid chemicals
(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; U.S. Pat. No. 4,377,406; U.S. Pat. No.
4,134,750; 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)). More recently,
pipe-cross reactors have been successfully used to enhance the
plant nutrient value of relatively low analysis organic waste
material (e.g. U.S. Pat. Nos. 5,984,992 and 6,159,263, the entirety
of both of which is incorporated by reference herein).
[0013] One potential drawback of exothermically treating relatively
low analysis organic waste material with reactors, such as a pipe
cross reactor or tubular reactor, is the potential for exhausting
noxious odors during the process. The use of cross-pipe reactors
for treating such waste has helped to reduce the odors typically
associated with the treatment thereof. However, a need exists to
provide greater assurance that such potential odors are eliminated,
or at least reduced beyond current emission levels.
[0014] Additionally, a continued desire exists to improve the
efficiency of sludge treatment, both in terms of capital
expenditure as well as in operating costs.
[0015] There is a need in the art for relatively simple and
efficient processes for processing relatively low analysis organic
waste material to an enhanced plant nutrient value composition
without substantial emission of noxious odors. Preferably, such
processes would produce products that were sized and shaped to be
spread by commercially available commercial spreaders.
SUMMARY OF THE INVENTION
[0016] The present invention overcomes the problems and
disadvantages associated with current strategies and designs, and
provides new methods for the production of fertilizer from organic
materials such as, but not limited to biosolids. The invention
further provided fertilizers produced by methods of the
invention.
[0017] One embodiment of the invention is directed to methods for
producing a granular nitrogen fertilizer from an organic material
comprising adding a metallic salt to said organic material to form
a slurry. Preferably the organic material comprises dewatered
biosolids and contains water from a scrubber. Metallic salts that
can be used comprise a salt of iron, zinc, or a mixture thereof.
Preferred iron salts comprises ferric sulfate or ferric oxide, and
preferred zinc salts comprises zinc sulfate or zinc oxide.
Preferably, the metallic salt is mixed with an acid such as
sulfuric acid to form an acidified metal salt. Slurry pH ranges
from approximately 2-2.5. The acidified metal salt is added to the
organic material in sufficient quantity to lower viscosity of the
slurry such that the resulting fluid does not hinder fluid flow
during operation. When the metallic salt comprises acidified ferric
sulfate or ferrous sulfate, sufficient iron can be present to
produce a fertilizer product with 0.1 weight percent to 10 weight
percent iron sulfate calculated on a dry weight basis. When
sulfuric acid is added to the organic material, it is preferably
added prior to reaching a mix tank and at a rate of approximately
1.75 percent of a total feed rate to result in a pH range of 3.0 to
3.5.
[0018] Preferably the slurry is pumped into a shear mix tank that
contains a high shear rotary agitator which turns at a speed
sufficient to produce high shear. Slurry is passed from said shear
mix tank to a holding or equilibrium tank containing an agitator.
The agitator may provide approximately 2 hours or more of storage
for the slurry. Holding or equilibrium tanks can be operated to
maintain a pH of 3.0 to 4.0 with a solids content of between 15
percent and 28 percent solids. Metallic salt may chemically bonds
with one or more elements of the slurry. When using an iron salt,
the iron can bond with ammonium sulfate or ammonium phosphate
present in the slurry. This can enhance granulation formation, and
reduce sulfur compounds in the slurry, and odor and dust formation
during operation.
[0019] Preferably the metallic salt initiates chemical hydrolysis
of organic molecules in the slurry. This can drive sulfur compounds
out of the organic material reducing odorant sources in a resulting
fertilizer product.
[0020] Preferably the metallic salt is added to the organic
material in a pipe-cross reactor or a tubular reactor. The metallic
salt enhances reaction kinetics of the pipe-cross reactor and
lowers viscosity of the slurry such that operation of the
pipe-cross reactor is more controllable that without the metallic
salt.
[0021] Another embodiment of the invention is directed to
fertilizer products made by the methods of the invention. Preferred
products are granules and the metallic salt increases product
hardness. Product may have a crush weight of greater than 6 pounds
or preferably greater than 7 pounds. Granules of fertilizer
preferably contain metal that is bioavailable to a plant when used
as a fertilizer. Solubility of the metal of the product in water is
enhanced, and the product is low staining.
[0022] Other embodiments and advantages of the invention are set
forth in part in the description, which follows, and in part, may
be obvious from this description, or may be learned from the
practice of the invention.
DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 A process flow diagram of one embodiment of the
invention.
[0024] FIG. 2 A stylized view of a pipe-cross reactor.
[0025] FIG. 3 A partially cut away, perspective view of a
pipe-cross reactor in a rotary ammoniator-granulator.
[0026] FIG. 4 A stylized end view of a rotating bed of material in
a granulator.
[0027] FIG. 5 A side view of an orifice plate utilized with a
pipe-cross reactor.
[0028] FIG. 6 A process diagram of one embodiment of pre-treating
the sludge.
DESCRIPTION OF THE INVENTION
[0029] As embodied and broadly described herein, the present
invention is directed to systems and methods for treating organic
material. More specifically, the present invention relates to
systems and methods for treating sludge and converting sludge into
fertilizer.
[0030] As depicted in FIG. 1, a process for enhancing the plant
nutrient value of organic waste material generally involves mixing
the organic waste material with water 10. A preferred process for
mixing the organic material with water is described in FIG. 6.
Preferably, this process includes mixing the organic waste and a
fluid such as, but not limited to water with a metallic salt,
preferably iron. The water used in making the slurry may desirably
include scrubber water from the hereinafter described scrubber 38,
which may comprise waste acid. The slurry is mixed at a sufficient
concentration and consistency such that it will, preferably,
process the organic waste material as quickly as possible, but will
not clog or block a reactor during operation. A preferred reactor
is a pipe-cross reactor 12, but a tubular reactor might
alternatively be used, or even used, in a system, in conjunction
with a pipe cross reactor. The particular slurry concentrations and
consistencies may 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 reactor components.
However, as delivered to the pipe-cross reactor, the slurry
generally has a solids content of at least about 5 percent and
possibly as high as about 35%. Preferably, the solids content of
the slurry is from about 10% to 30% and more preferably from about
14% to 28%, and more preferably from about 15% to 22%.
[0031] As depicted in FIG. 1, 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.
[0032] 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 two moles 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 0.4:1 to 0.7:1, preferably 0.55
to 0.65:1, concerning the concentration of sulfuric acid, typical
molar ratios of N:S in the pipe cross reactor are between 0.5:1 and
0.8:1 preferably 0:65:1 to 0.72:1. 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.
[0033] Other acids which may be used with the invention comprise
nitric acid, acetic acid, citric acid and mixtures thereof, all of
which are well know to those skilled in the art (e.g, nitric acid
and an ammonia compound which might form ammonium nitrate in the
presence of organic materials which is explosive). 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).
[0034] 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 17.2 to 25.8 gpm) and phosphoric acid (at
a rate of from about 5.2 to 7.8 gpm). A third pipe 30 incorporates
the ammonia into or near the center of the reactor. The length of
this pipe 30 is desirably at least twenty to thirty inches to
ensure adequate mixing. A third cross pipe 32 incorporates the
slurry and additional water into the mixing chamber. Positioned
between the third cross pipe 32 and the first and second cross
pipes 26 and 28 is an orifice plate 33 which is utilized to
introduce turbulence into the flow of the slurry ensuring even
greater mixing.
[0035] A typical pipe-cross reactor for use with the invention has
a diameter of about three to ten inches, is from about seven to
about fifty feet long, and terminates in, for example, a two to
eight inch discharge pipe (or a slot of equivalent cross-sectional
area), preferably with a stainless steel insert or TEFLON.TM.
lining. The discharge pipe preferably discharges into a standard
rotating drum granulator 14, and 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 TEFLON.TM., ceramic, or other
corrosion-resistant lining may also be used in the pipe-cross
reactor. The temperature is preferably maintained below 204.degree.
C. (400.degree. F.).
[0036] The orifice plate 33, as shown in FIG. 5, includes a plate
formed from a material similar to the pipe-cross reactor 12 and
includes an orifice 35 or aperture which exhibits a smaller
diameter than that of the pipe-cross reactor 12. Thus, for example,
a pipe-cross reactor having a (6) inch diameter would employ an
orifice plate 33 having an orifice 35 which exhibited a diameter
less than inches, for example inches. In determining the size of
the orifice 35, various parameters may be considered including flow
rates of the slurry, acids and base, as well as the solid content
of the slurry. Thus, the size of the orifice 35 may be changed for
a given pipe-cross reactor 12 if the any process parameters are
altered.
[0037] Although FIG. 5 shows use of a circular orifice plate, it
was surprisingly discovered that adding a protuberance generally to
increase turbulence upstream of the two pipe cross reactor provides
greater heat recovery. In other embodiments, the turbulence is
created through use of a protuberance, such as a bump, multiple
bumps in series or parallel with respect to the flow stream, one or
more wires, input of pressurized gas such as air, use of a sonic
vibrator or vibrating wall at this position. For example, two,
three, four, five, six, seven, eight or more equally spaced bumps
that each protrude into the space towards the lumen middle, by, for
example, 0.02, 0.05, 0.1, 0.2, or 0.3 times the diameter at that
point may be used to create turbulence. In an embodiment a bump is
an annular thickening that forms a constriction within the pipe. A
sonic vibrator for example such as that offered by Advanced Sonics,
also may be used. A restriction, as shown in FIGS. 2 and 5, does
not have to be round but can be another cross sectional shape, such
as oval, square or irregular. An oval share is desirable,
particularly with the narrow ends pointed to the cross pipes such
that the larger oval axis extends across a line connecting the two
cross pipe openings. In another embodiment the short axis of the
oval extends across a line connecting the two cross pipes. The oval
shape with long matching axis provides a turbulence that more
closely matches the incoming flows from the perpendicular cross
reactors and is particularly desired when perpendicular cross pipe
reactors as shown in FIG. 2 are used.
[0038] The optimum placement of the protuberance(s) in many
embodiments is between 0.1 to 3 flow stream diameters upstream of
the average position of the cross reactor outlets (i.e. mean of the
cross reactor outlets, which may be staggered down the length of
the flow stream). More preferably the protuberances are located
between 0.3 to 1.5 diameters ahead of the cross pipe reactors.
Optimum placement will vary depending on the flow rate. For a very
high flow rate the protuberance(s) should be set further away or
the degree of protuberance into the flow path should be limited.
This embodiment may be carried out by an adjustable annular ring or
adjustable bumps that provide the ability to control the distance
away and the degree of flow path entry of the protuberance. An
annular ring may be adjusted for opening size and may be mounted at
alternative locations, for example. Multiple sonic vibrators, if
used may be placed at different locations and individually switched
to accommodate slower (vibrate closer to the cross pipes) or faster
(further away location) flow rate and/or lowered viscosity.
[0039] Adjustment of the cross pipe reactor itself may be optimized
for a given viscosity and flow rate. In many embodiments the cross
reactor pipes advantageously are exactly opposite each other, as
shown in FIG. 2. This placement is desirable when adding comparable
viscosity fluids at comparable flow rates. Also desirable, is the
use of multiple (3 or 4, or more) cross pipes. For example, a four
way (four perpendicular pipes) that administers two materials each
through two opposing sides, may be used if the viscosity is low
enough. Multiple cross reactor pipes may be switched to accommodate
changes in viscosity and/or flow rate. For example a less viscous
material or higher flow rate system may benefit by using one or
more cross reactor inlets that are further away (more downstream)
with respect to the protuberance(s) and that can be opened and
closed. Other combinations may be optimized upon routine
calibration, by changing the flow, and/or type of sludge material
and/or a reagent and then monitoring for heat recovery by measuring
temperature downstream at one or more points. By providing
adjustable protuberance(s), and/or cross pipe placements, and/or
flow rates optimized heat recovery may be obtained.
[0040] Yet another embodiment provides an automatic system that
constantly monitors temperature of mixed material at some point
downstream of the cross pipe reactor and adjusts protuberance
positioning, flow rate of sludge, flow rate of base, flow rate of
added water, flow rate of one or more acids, and switching of cross
reactor outlets for optimum effect. In a desirable embodiment flow
rate of base, and/or dilution water and/or an acid and/or a second
acid and/or sludge is adjusted up or down to obtain a higher
temperature. In another embodiment a switch selects between two or
more cross pipes to obtain a more desirable temperature. In yet
another embodiment some of the released heat is transferred in a
controllable way back to an input stream to obtain a more desirable
viscosity for adequate mixing. A control system may adjust heat
transfer up or down depending on the heat recovered, or depending
on another monitored variable, such as back pressure to the sludge
pump(s) or back pressure measured at a pipe-cross reactor
gauge.
[0041] Without wishing to be bound by any one theory of this
embodiment of the invention, a protuberance such as an orifice
plate or other mechanism or device allows greater mixing of the
slurry by inducing a zone of turbulence downstream of the orifice
plate 33 and generally in the vicinity of the first and second
cross pipes 26 and 28. The increased turbulence generated in many
cases increases heat production as measured as a higher melt
temperature. The temperature also can be measured at or downstream
of the last cross pipe addition of reagent, such as for example, 1
or 2 pipe diameters further downstream of the last cross pipe. It
has been observed that use of an orifice plate has effected an
increase of heat recovery, as much as approximately 30%, over
similar pipe-cross reactors lacking an orifice plate. An orifice
plate 33 may be changed for another orifice plate exhibiting a
different diameter orifice 35 if desired.
[0042] Referring to FIG. 2, ammonia is introduced into the
representative system depicted here 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 shown here typically operates at a gage
pressure of between fifteen and sixty psig.
[0043] A hot melt discharges from the pipe-cross reactor 12 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.
[0044] A preferred granulator (e.g. an ammoniator-granulator),
depicted in FIGS. 3 and 4, is a two to four meter diameter rotating
drum granulator having a length of from about five to about nine
meters. As shown in FIG. 3, the pipe-cross reactor 12 is oriented
vertically and includes a number of 90 transitions or bends prior
to entering the granulator 14. The shown position of the pipe-cross
reactor 12 is preferred as it provides greater mixing capabilities.
However, satisfactory results may be achieved with the pipe-cross
reactor 12 oriented horizontally without any transitions or bends
(e.g. U.S. Pat. Nos. 5,984,992 and 6,159,263).
[0045] In the depicted process, the granulator 14 includes an
ammonia sparger 20 operably positioned within the granulator 14 for
the addition of ammonia to the melt to complete the reaction of
acid and base for the final product. 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, as depicted in FIG. 1, 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. The vapors formed during
the reaction of the slurry with the acid and base (e.g. the flashed
off steam) are also collected and conveyed into the rotary dryer 16
for increasing the dew point vapors so as not to condense in the
plant equipment.
[0046] Passing such vapors directly into the dryer 16 is an
alternative process as compared to that of U.S. Pat. Nos. 5,984,992
and 6,159,263. Previous processes associated with pipe-cross
reactors have typically separated the granulated particles from the
vapor for independent processing prior to the drying of the
granulated particles. The presently depicted process eliminates the
need for additional particulate separation equipment and processing
of the air and ultimately results in a simpler and more efficient
process.
[0047] A preferred dryer for use with the invention is a two to
four meter diameter rotating drum dryer having a length of from
about seventeen to about thirty three meters, and having a heating
capacity of 30 to 70 million BTU/hour, with a lump crusher at the
discharge end.
[0048] The process further includes passing the dried granulated
particles to a granule separation apparatus, such as a screen 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, back into the process. 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.
[0049] During the process, fumes, which may contain ammonia,
particulates, and water vapor above its dew point, are collected
from the dryer 16 and passed through particulate separating
equipment, such as a dust cyclone 34. The dust cyclone 34 removes a
portion of the particulates from the air and recycles these
particulates (e.g. dust) with the fines and ground material. The
resultant fumes leave the dust cyclone 34 and are processed through
additional particulate separating equipment, such as a baghouse
filter 36. The baghouse filter serves to remove an additional
amount of particulates, particularly particulates which exhibit a
smaller size than those removed by the dust cyclone 34.
Particulates removed from the baghouse filter 36 are similarly
recycled with the fines and ground material for use in the
granulator 14.
[0050] The fumes leaving the baghouse filter 36 are subsequently
processed through a scrubber 38, such as a venturi scrubber or
packed bed scrubber, which includes water separation chambers for
collecting ammonia fumes and small dust particles. The invention
uses low pH water in the scrubber 38 to collect unreacted ammonia
vapors escaping the granulator 14. In one embodiment, small amounts
of sulfuric or phosphoric acid are added to the scrubber 38 to
maintain a low pH (e.g. 2 to 3) for proper ammonia vapor
scrubbing.
[0051] The process further includes oxidizing the air exiting the
scrubber, such as in a regenerative thermal oxidizer (RTO) 40. The
RTO 40 is used to destroy volatile organic compounds (VOCs) and
other gaseous hydrocarbon pollutants that would otherwise be
released into the atmosphere. The RTO 40 destroys such VOCs and
hydrocarbon fumes through a process of high temperature thermal
oxidation, converting the VOCs and fumes to carbon dioxide and
water vapor. The oxidation of the air further serves to
substantially eliminate any noxious odors that would otherwise be
exhausted into the atmosphere. Energy released from the oxidation
process can be recycled to reduce operating costs.
[0052] Air is drawn from the RTO 40 and exhausted into the
atmosphere through a stack 42. The process may advantageously
include using heat from the exhaust in the stack 42 to preheat the
base (e.g. ammonia) prior to its introduction into the pipe-cross
reactor 12 and/or the granulator 14 via the sparger 20.
[0053] Another aspect of the ventilation for the depicted process
includes collecting air from the screens 18. The process
contemplates two options, both of which involve particulate removal
and recycling of both particulates and air. The first option
includes processing the air through a dust cyclone 34 and recycling
both the particulates and the air back to the granulator 14. The
second option includes utilizing the dust cyclone 34, but further
includes processing the air through a baghouse filter 36, again
collecting the particulates for recycling in the granulator. The
air leaving the baghouse filter 36 is advanced to the dryer 16
instead of the granulator 14.
[0054] Other aspects of a ventilation system for use with the
invention preferably include fans for moving the air to and from
the various processing stages described above herein. Volume of air
moved is determined by the amount of moisture to be removed (above
dew point) and the melting point or disassociation temperature of
the fertilizer product.
[0055] NPK fertilizers preferably include the micronutrients iron
and zinc. In a preferred embodiment, spent acid from a hot dip
galvanizing or steel pickling process is used to maintain the low
pH of the scrubber water. These spent acids commonly are sulfuric
acid of five to ten percent strength, containing three to eight
percent iron. Galvanizing spent acid contains three to eight
percent zinc along with 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.
[0056] 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 preferably 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, and combinations thereof.
[0057] 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, environmental or industrial
biological materials, 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.
[0058] The following examples are offered to illustrate embodiments
of the present invention, but should not be viewed as limiting the
scope of the invention.
EXAMPLES
Example 1
[0059] In an agitation tank, 6700 kilograms/hour (7.4 tons/hour) of
sewage sludge were mixed with 37 liters per minute (ten
gallons/minute (gpm)) of scrubber water to form a slurry. The
slurry was of such a consistency (a solids content varying between
10% and 27%) 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 had a diameter of approximately four
inches and was forty feet long. The pipe-cross reactor terminated
in a rotating drum granulator. The rotating drum granulator was six
feet in diameter and twenty feet long.
[0060] The slurry was added to the pipe-cross reactor and 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) was maintained at about 149.degree. C. (300.degree.
F.) with moisture in the sludge. This temperature (above minimum
sterilization 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.
[0061] 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 flashed off as steam. An ammonia sparger is provided in the
granulator to add small amounts of ammonia to the granulation
mixture for reaction completion and final hardening of
granules.
[0062] Operating the pipe-cross reactor in such a manner
incorporated approximately 14.8 tons per hour of 20% solid sewage
sludge at a ten ton per hour production rate.
[0063] Granulated material exits the granulator at about 93.degree.
C. (200.degree. F.) and at about a five to fifteen percent moisture
content into a rotary dryer. The rotary dryer was approximately two
meters in diameter and has a length of about twenty meters. 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 was reduced to less than three percent by heated
forced air in the dryer.
[0064] Materials exiting the rotary dryer were run through the lump
crusher to reduce oversized material to less than one inch in
size.
[0065] Screens are used to separate the material into (a) fines,
(b) product and (c) oversized material. Fines are returned to the
granulator. Product went to a two meter diameter, twenty meter 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 tons (1800 kg) of fine material per
ton of product were required in the recycle stream.
[0066] Fumes from the granulator containing steam, ammonia and
particulate were collected by maintaining a negative pressure
inside the granulator with a fan pulling the fumes into the rotary
dryer to reduce the moisture content thereof. The air was drawn
from the granulator at a rate of 20,000 cubic feet per minute (cfm)
at a temperature of 92.degree. C. (198.degree. F.) and at 100%
relative humidity. This is roughly equivalent to conveying 34,200
pounds per hour (lbs/hr) of water and 296 pounds per minute
(lbs/min) of dry air.
[0067] The air from the rotary dryer was directed to a dust
cyclone, a baghouse filter, and then a scrubber. Air was drawn from
the dryer at a rate of 70,000 cfm at 45% relative humidity. The air
leaving the dryer had a dry bulb temperature of approximately
93.degree. C. (200.degree. F.) and a wet bulb temperature of
74.degree. C. (165.degree. F.). This is roughly equivalent of
conveying 56,100 lbs/hr water and 2,711 lbs/min of dry air. Air
entering the scrubber is scrubbed with low pH water (water at a pH
lowered by the addition of spent acid from a hot dip galvanizing
process). 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.
[0068] Air was directed from the scrubber to a regenerative thermal
oxidizer at a rate of 67,100 cfm at a temperature of 165.degree. F.
and at 100% relative humidity. Oxidized air was then drawn from the
regenerative thermal oxidizer and is exhausted through a stack
approximately one hundred (100) feet tall at a temperature of
93.degree. C. (200.degree. F.).
[0069] Dust-laden air is collected from the grinding mills and
screens by a fan maintaining negative pressure on the equipment.
The air is pulled through a cyclone system that removes about 97%
of the dust. From the cyclones, the air was passed back to the
rotary granulator and the dust added to the recycled fines.
[0070] The resulting fertilizer had an NPK value of 12-3-6 (12%
nitrogen, 3% phosphate, and 6% potash). It was also homogenous and
properly sized for standard application equipment.
Example 2
[0071] The process of Example 1 is repeated in a tubular reactor
rather than a pipe cross reactor. 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 to
form a slurry. The slurry is of such a consistency that it can be
pumped with a positive displacement pump or other suitable pump to
a tubular reactor equipped to receive ammonia, sulfuric acid,
phosphoric acid, sewage sludge, and water. The tubular reactor
preferably has a diameter of approximately 1.5 to 30 cm and a
length of 2 to 10 meters, preferably 5 to 8 meters. The reactor
terminates in a rotating drum granulator. The rotating drum
granulator is six feet in diameter and twenty feet long.
[0072] The slurry is added to the reactor and reacted with 8.6 gpm
99.5% ammonia, and an acid solution containing 8.6 gpm sulfuric
acid (93%) and 2.6 gpm phosphoric acid (54% P.sub.2O.sub.5). The
temperature of the reactor (due to the exothermic reaction between
the acid solution and the base) is maintained at about 149.degree.
C. (300.degree. F.) with moisture in the sludge.
[0073] The resulting melt from the 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 reaction completion and final hardening of the
granules.
[0074] Granulated material exits the granulator at about with a
moisture content into a rotary dryer. The rotary dryer is
approximately two meters in diameter and has a length of about
twenty meters. 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 less than three
percent by heated forced air in the dryer.
[0075] Materials exiting the rotary dryer are run through the lump
crusher to reduce oversized material to less than one inch in
size.
[0076] 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 diameter, twenty meter 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 tons (1800 kg) of fine material per
ton of product are required in the recycle stream.
[0077] Fumes from the granulator containing steam, ammonia and
particulate are collected by maintaining a negative pressure inside
the granulator with a fan pulling the fumes into the rotary dryer
to reduce the moisture content thereof. Air is drawn from the
granulator at a rate of 20,000 cubic feet per minute (cfm) at a
temperature of 92.degree. C. (198.degree. F.) and at 100% relative
humidity. This is roughly equivalent of conveying 34,200 pounds per
hour (lbs/hr) of water and 296 pounds per minute (lbs/min) of dry
air.
[0078] The air from the rotary dryer is conveyed to a dust cyclone,
a baghouse filter, and then a scrubber. Air is drawn from the dryer
at a rate of 70,000 cfm at 45% relative humidity. The air leaving
the dryer has a dry bulb temperature of 93.degree. C. (200.degree.
F.) and a wet bulb temperature of 74.degree. C. (165.degree. F.).
This is roughly equivalent of conveying 56,100 lbs/hr water and
2,711 lbs/min of dry air. Air entering the scrubber is scrubbed
with low pH water. The low pH water collects ammonia vapor present
in the fumes, as well as dust particles.
[0079] Air is conveyed from the scrubber to a regenerative thermal
oxidizer at a rate of 67,100 cfm at a temperature of (165.degree.
F.) and at 100% relative humidity. Oxidized air is then drawn from
the regenerative thermal oxidizer and is exhausted through a stack
approximately one hundred feet tall at a temperature of 93.degree.
C. (200.degree. F.).
[0080] Dust-laden air is collected from the grinding mills and
screens by a fan maintaining negative pressure on the equipment.
The air is pulled through a cyclone system that removes about 97%
of the dust. From the cyclones, the air is passed back to the
rotary granulator and the dust is added to the recycled fines. The
resulting fertilizer is determined to have an NPK value.
Example 3
[0081] FIG. 6 shows one preferred method of preparing and handling
the biosolids prior to their conversion into fertilizer.
[0082] In FIG. 6, municipal biosolids 620 are dispensed into 625
cubic yard boxes. These boxes are preferably placed on suitably
designed dumping vehicles and transported to the sludge handling
area. The boxes are opened and dumped into a receiving hopper 622.
The receiving hopper 622 preferably has a minimum containment
volume of about 47 cubic yards. The maximum volume of hopper 622 is
dictated by the available space and general physical arrangement of
the plant. The hopper 622 is preferably constructed of stainless
steel to protect against corrosion as a result of the wet
environment in the area. A large open grate is preferably installed
inside the hopper to capture any large tramp materials that may be
present in the sludge boxes. Preferably, this grating has openings
of approximately 1'.times.1'.
[0083] Sludge 620 passes through the grating into the bottom of the
hopper 622. At the bottom of hopper 622, horizontal double helix
screws 624 are used. The double helix screws initiate the transport
of the sludge 620 from the hopper 622 to the transfer pumps 626.
The number, size and arrangement of the screws are dictated by the
geometry of the hopper 622. In one embodiment, four screws are used
in an alternating manner to control the feed rate of the sludge
620. A variety of screws can be used. The screws are preferably
driven by direct drive gear motors operated at a speed sufficient
to provide the required quantity of sludge 620 for the process. The
delivery rate of sludge 20 can be further controlled by sequencing
the operation of the screws and controlling the operating versus
non-operating time for each.
[0084] The screws in the bottom of the hopper 620 discharge into a
horizontal, perpendicular collection screw 624 at one end of the
hopper. The collection screw 24 is used to collect the sludge 620
from the transport screws and transfer it to one of two sludge
pumps 626. This screw 624 can be of similar construction and motor
arrangement as the transport screws. The collection screw 624 is
preferably sized to provide the maximum required sludge delivery
rate. The collection screw 624 is preferably designed to operate in
either direction to provide movement of the sludge to different
pump suction locations. Ports are installed in the bottom of the
screw housing to direct the sludge to the currently operating
sludge pump 626.
[0085] Vertical piping (24") is preferably installed from the
collection screw 24 housing to the suction of the sludge pumps 626.
Preferably, a rotary lump breaker 628 is installed in this piping.
The lump breaker 628 is a rotary blade and grating system operated
at a speed suitable to facilitate the flow of the semi-solid sludge
620 to the pumps 626. The lump breaker has two primary functions:
1) to break any large lumps in the sludge 620 into smaller, more
manageable pieces and 2) to capture any small tramp materials
before they can reach the pumps 626. The lump breaker 628 has the
added benefit of imparting shear force to the sludge 620 to begin
the breakdown of polymeric binders in the sludge cake.
[0086] Water 630 is preferably injected into the sludge flow 620
prior to the lump breaker. This water 630 aids in the liquefaction
of the sludge 620 and is controlled so as to provide the final
sludge concentration desired. Preferably water 630 includes recycle
water the process venturi scrubber having a pH of about 2.5 to 4.0.
The water 630 is preferably added at a rate equal to at least 10%
of the desired reactor flow, more preferably at least 15%, and most
preferably at least 20%. In one embodiment the flow rate is
approximately 22.9% of the desired reactor flow.
[0087] In another embodiment, preferably, ferrous oxide 632 and
sulfuric acid 634 is also added to the water stream 630 in the
process sump 636. Such additions minimize the amount of water that
needs to be added to the sludge such that the slurry that is
created will not clog or block the pipe-cross or tubular reactor.
In one embodiment, process sump 636 is a stainless steel lined
concrete tank with dimensions of approximately
11'.times.11'.times.11'. In the sump 636, the sulfuric acid 634
reacts with the ferrous oxide 632 to produce ferrous sulfate such
that the mixture has a resultant pH of approximately 2.0 to 2.5
prior to its being added to the biosolids. Alternatively, ferric
oxide is used and reacts with the sulfuric acid to produce ferric
sulfate such that the mixture has a resultant pH of approximately
2.0 to 2.5 prior to its being added to the biosolids. The mixture
in the sump is agitated with a vertical agitator 638.
[0088] The sheared sludge discharges from the lump breaker 628 into
the suction of the sludge transfer pump 42. The sludge pumps 40
discharge into an 8" stainless steel header that flows to a high
speed mix tank 42. Prior to reaching the mix tank 644, sulfuric
acid 646 is injected into the flow stream to control the pH of the
final sludge mix at a range of 3.0 to 3.5. The sulfuric addition
rate is approximately 1.75% of the total reactor feed rate.
[0089] The sludge/acid mix flows into the bottom of the shear mix
tank 642. In one embodiment, tank shear mix tank 642 is an 890
gallon vertical cylindrical tank with a high speed, high shear
rotary agitator 648 sufficient to produce significant shear of the
acidified biosolids mixture.
[0090] In one embodiment, the slurry holding tank is a tank with a
volume of 14,800 gallons and is of stainless steel construction. It
contains a vertical agitator 650 with two sets of blades. The
holding tank 650 is designed to provide approximately 2 hours of
storage for the slurry feed, at maximum feed rates. It is operated
to maintain a pH of 3.0 to 4.0 with a solids content of between 15
percent and 28 percent solids and preferably at 20 percent to 23
percent.
[0091] Reactor feed is drawn continuously from the bottom of the
holding tank 50 into the suction of the slurry feed pump 652. The
sludge feed rate to the reactor is controlled by adjusting the
slurry feed pump 652 motor speed.
[0092] FIG. 6 shows a one process for adding iron (ferric) sulfate
into the sludge prior to reacting the sludge with acid and ammonia
to produce fertilizer as described in FIG. 1. In addition to adding
iron to the sludge in the form of iron (ferric) oxide, iron can be
added into the sludge in other forms as well including, for
example, iron sulfate, metallic iron, iron carbonate and iron
phosphate. Preferably, the iron is converted into iron sulfate
prior to being reacted with acid and ammonia to produce
fertilizer.
[0093] In one embodiment the iron (ferric) oxide is added as a
powder to a mixing tank containing water and sulfuric acid. The
water and sulfuric acid can include of the blowdown water from the
air emission scrubbing system which contains water, sulfuric acid
and ammonium sulfate. The addition of the sulfuric acid in this
mixing tank converts the iron oxide to an iron (ferric) sulfate.
This mixture of iron sulfate in water and ammonium sulfate is then
added to the biosolids slurry to facilitate product hardness and
odor.
[0094] In addition to iron, other metallic salts, for example zinc
oxide, can be added to the slurry prior to reaction to achieve
similar benefits as described herein.
[0095] It has been surprisingly discovered that by adding a metal
salt such as iron sulfate or zinc sulfate or magnesium sulfate,
into the sludge, a significant improvement to the sludge to
fertilizer process can be produced. Preferably, enough metal salt,
such as ferrous salt or ferric salt, is added to the sludge to
produce a fertilizer product with 0.1 wt % to 10 wt % metal salt,
such as iron sulfate. More preferably, the finished fertilizer
product has between 0.5 wt % and 5 wt % metal salt, such as iron
sulfate. Most preferably, 1 wt % to 3 wt % metal salt such as
ferrous or ferric sulfate. The addition of iron makes it easier to
control the process and provides a variety of other improvements to
the process. These improvements include:
[0096] a) Chemically bonded metal, such as iron, in the product.
The metal, such as iron is able to complex with components of the
organics in the mixture as well as the ammonium sulfate salt
present in the mixture.
[0097] b) Metal, such as iron or zinc, binding to reduce sulfur
compounds. The consequence of this binding is that these reduced
sulfur compounds are less able to volatize to the atmosphere or
environment therefore the perceived odor of the product is
significantly reduced.
[0098] c) Increased hardness of the product granule. The crush
weight of the product is increased significantly from approximately
4 to 5 pounds to over 6 pounds and more preferably over 7 pounds.
The invention has also been measured to create granules in the 8 to
9 pound hardness range.
[0099] d) Reduced dust associated with the product so that storage
and transport of the product is improved.
[0100] e) Reduced odor of the product will enhance the
marketability of the product in the commodity and specialty
fertilizer business.
[0101] f) Reduced volatility of nitrogen so that when the Unity
fertilizer product is used in the field on hard ground the amount
of nitrogen that is lost to the atmosphere is significantly
reduced, especially compared to the up to 40% volatility of urea as
used in commercial fertilizer practice.
[0102] g) Acid conversion of iron oxide to iron sulfate prior to
mixing with biosolids slurry.
[0103] h) Metal availability, such as iron or zinc, as increased
micronutrient. This is because of the addition of a metallic salt
to the mixture but also because of the binding of the metal to
organic components of the mixture such that the solubility of the
metal, such as iron, in water is enhanced.
[0104] i) Creates a lower staining product as compared to
conventional products. Metallic salt, such as ferrous or ferric
oxide or sulfate is preconditioned in a sump prior to its addition
to the biosolids slurry. This preconditioning converts the iron to
a black compound and avoids the red staining characteristic that
was associated with the ferric oxide form of the iron as previously
added.
[0105] The product as manufactured under this invention
incorporates a range of chemical conversions that are important
components of the finished fertilizer. The addition of iron in
combination of the sulfuric acid in the "preconditioning" of the
mixture prior to passing the mixture through the Pipe-cross reactor
causes a range of conditions in the mix which affect the operation
of the pipe-cross reactor and the chemical makeup of the final
product as follows:
[0106] a) it enhances the reaction kinetics of the pipe-cross
reactor.
[0107] b) it causes enhanced granulation.
[0108] c) Starts the chemical hydrolysis of the organic molecules
in the sludge slurry, e.g., the conversion of proteins to peptides
and amino acids, and/or the conversion of lipids to component
molecules such as fatty acids. The chemical hydrolysis of long
chain organic molecules, e.g., proteins, carbohydrates, lipids and
nucleic acids creates molecules that are more easily able to bind
to the iron; that can be more easily assimilated by the soil
microorganisms around the root zone of the target crop and that can
be more easily directly assimilated by the roots and root hairs of
the target crop such that the crop benefits with increased
vitality, growth and productivity. Further the hydrolysis of
organic molecules by the hydrolysis process associated with the
operation of the Pipe cross reactor renders the final product safer
than those products that would combine the biosolids organics
without such hydrolysis. An example of this would be the hydrolysis
of endocrine disrupter compounds which in the environment have been
shown to mimic endocrine hormones and affect the sexuality of
animals, e.g., alligators and frogs. The disruption of these
compounds will increase the public and scientific confidence that
the use of biosolids products is safe for public health.
[0109] d) Drives reduced sulfur compounds out of the biosolids
slurry such that these odorant sources are no longer a component or
are a reduced component of the finished product.
[0110] e) Lowers the viscosity of the biosolids slurry such that
the operation of the Pipe-cross reactor is more controllable.
[0111] f) Improves the mixing that occurs in the Pipe cross
reactor.
[0112] Other embodiments and uses of the invention will be apparent
to those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. All references
cited herein, including all U.S. and foreign patents and patent
applications, including U.S. Provisional Application No. 60/473,198
and the corresponding non-provisional application being filed
contemporaneously herewith and U.S. patent application Ser. Nos.
08/852,663, 09/735,768 and 09/416,370, are specifically and
entirely incorporated herein by reference. It is intended that the
specification and examples be considered exemplary only.
* * * * *