Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~~VO 95/19327 ~ 15 g,~ 7 4 PCT/US94/00566
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SLUDGE TREATMENTSYSTE11Z
$ackground of the Invention
The present invention relates generally to a sludge treatment system for
treating
° sludge, such as sewage sludge received from a municipality, and more
particularly to an
improved sludge treatment system which produces a pelletized fertilizer or
soil amendment
product from the sewage sludge.
Other systems have been used to produce a pelletized product from sewer
sludge.
For example, U.S. Patent No. 4,872,998to Dausman et al. discloses an apparatus
and process
for forming a uniform pelletizable sludge product. The sludge is received by a
holding tank
which agitates the sludge to keep the solids in suspension with the liquid.
The sludge is
released from the holding tank through a control valve for mixing with
flocculation and
coagulation promoting chemicals and is then transported to a belt-type
dewatering press. After
the dewatering step, the sludge has 10 - 45 ~Y solids and is transported to a
temporary storage
tank. The sludge is fed from the temporary storage tank to an indirect dryer
which is heated
5 by either steam or hot oil from a boiler. Water vapor and other volatiles
are driven off during
the drying stage and pass from the dryer into a cyclone which removes the
airborne dust. The
resultant air and vapors are then pulled through a water jet scrubber to
remove any remaining
particles. This complete removal of all particulate matter is understood to be
critical to
subsequent process steps, and is believed to be a significant disadvantage of
this process. The
10 remaining particulate-free exhaust air is then passed to an odor control
system. Alternatively,
this remaining exhaust air may be returned to the boiler where the combustible
components
are ignited with the fuel used to heat the boiler. The dried sludge is fed
from the indirect
dryer to a storage tank or to a pelletizer. The pelletized material is then
fed to a pellet
storage tank. Thus, the Dausman et al. system processes the sludge without
recycling of any
previously heat-processed sludge.
U.S. Patent No. 3,963,471to Hampton discloses a method for pelletizing sewage
sludge for use as a fertilizer. Sludge is dewatered by adding coagulation and
flocculation
chemicals thereto and then passing the mixture through a dewatering press to
form sludge
cake. The dewatered sludge cake is mixed with a portion of the pellets
constituting the final
product which are in a hot, dried state. This mixing step lowers the heat
required in the dryer
to produce the final product and thereby prevents formation of clinkers and
ignition of the
organic material in the dryer. The larger the percentage of final product
returned to the
~ mixing chamber, the smaller in size are the resultant pellets formed in the
dryer.
U.S. Patent No. 2,977,214to Mcl:.ellan discloses a method for pelletizing
dried
sewage sludge. The dried sludge is compacted between two compacting rollers
into a rigid
highly frangible sheet. A rotating breaker fragments the sheet into gross
flakes or chunks.
The chunks are gravity fed from the compactor to a granulator. The granulator
includes two
sets of corrugated granulating rollers which grind the chunks received from
the compactor. A
WO 95/19327 PCT/US94/00566
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screening mechanism sorts the granulated sludge into undersized, oversized and
acceptable
sized granules. The undersized granules are recycled to the compactor, and the
oversized
granules are recycled to the granulator.
The reissued U.S. Patent No. RE.31,185 to Greenfield et al. discloses a
process
for dehydrating sewage sludges in a multistage evaporator. Oil is added to the
sludge in the
evaporator to yield a liquid pumpable mixture, which remains pumpable even
after water '
removal. Vapors are removed at each stage of the multistage evaporator and
used as a
combustion source for the preceding step in the process. A portion of the
anhydrous slurry
containing sludge and the oil removed from the last stage is recycled back to
a position
upstream of the first stage, thereby controlling the viscosity of the
evaporator feed. After the
final evaporator stage, the resultant dry solids and oil are passed through a
centrifuge for
separation, and the separated oil is recycled. The solids from the centrifuge
may be used for
fertilizer or to fuel the boiler-furnace which supplies steam to the
multistage evaporator.
U.S. Patent No. 4,321,151to McMullen discloses a process for converting sewage
sludge into energy useful for operating a sewage treatment plant. Raw settled
sludge is
withdrawn from the treatment stream early in the process sequence to preserve
the energy
content of the sludge. The withdrawn sludge is dewatered, caked and fragmented
for pyrolysis
to produce a combustible gas which may be used to fuel a gas turbine-generator
to power the
plant. The combustible gas is cleaned by removing the suspended tars and oils
therein. The
dried feed stock is pneumatically conveyed for pyrolyzing to a combustion
boiler-pyrolyzer, and
a portion is diverted to a rotary mixing device or blender. In the blender,
the dried feed stock
is blended with residual tar, oil and char (pyrolysis by-products) produced
from pyrolysis of
mixed and dried feed stock. The blended stock is directed to a pelletizing
unit to produce
pellets one inch in diameter and one and one-half inches long. The pellets are
pneumatically
conveyed to a combustion zone of the boiler-pyroIyzer.
U.S. Patent No. 3,960,725to Bjermo et al. discloses a method of converting
heavy-metal hydroxides into heavy-metal oxide powders or granules using
concentration
sintering. Before sintering, the sludge is dewatered and deposited on a media
carrier in a
1 - Smm thick film and the film is then dried. This method is useful for
eliminating the toxicity
of the metal hydroxy sludge for environmental considerations.
U.S. Patent No. 4,097,378to St. Clair discloses a method for removing water
from peat and various sludges. The sludge is mixed with oil and fed into a
condenser where it
is heated by direct contact with steam. Liberated uncondensed gases are routed
to a
conventional vent system.
U.S. Patent No. 4,402,834to Bastgen et al. discloses a continuous dewatering
process for sludges principally involving filtration. The raw sludge is mixed
with a flocculating
agent in a rotary filter drum. The thickened sludge is conveyed through a
filtering assembly
~VO 95/19327
PCT/US94/00566
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and subjected to dewatering forces including vacuum, centrifugal, static
pressure or pressure
while moving along the filter surfaces.
U.S. Patent No. 4,795,568to Chen discloses a waste water treatment system
using
excessive amounts of pressurized oxygen gas to oxidize the waste water
solution and increase
S the evaporation of waste therefrom. The oxidized liquid effluent undergoes a
series of flashing
steps to produce a saturated solution which crystallizes upon cooling.
U.S. Patent No. 3,342,731to Baumann discloses a method of dewatering fresh or
digested sludges or concentrate resulting from centrifuging fresh or digested
sludge. After
centrifuging, the sludge is further dewatered by filtering and the dewatered
sludge is then
incinerated. The ash resulting from the incineration of the dewatered sludge
is added to the
digested sludge or fresh sludge, along with lime for improved filterability.
The lime remaining
after incineration of sludge that has been treated with the ash and lime may
be recycled by
mixing it with the fresh lime and ash to be added to the sludge. U.S. Patent
No.
1,915,240to Putnam discloses a sewage purification system where lime and
ferric chloride are
mixed with the sludge to kill bacteria, oxidize and deodorize the treated mass
and to promote
flocculation. The sludge is centrifuged or otherwise dewatered then dried in a
sludge dryer
and ground for delivery to a storage bin. The resulting dried ground sludge
may be used as a
fertilizer or burned as fuel in the dryer. Alternatively, instead of
dewatering, drying and
grinding the sludge for fertilizing or heat, the sludge may be passed directiy
from a dewaterer
and processed through a retort to produce char or carbonized particles. This
resulting char
product is introduced into the raw sewage before the chemical treatment step
to absorb the
gases and putrescible matter and increase the speed at which the solids settle
from the liquid.
U.S. Patent No. 3,025,151to Berg discloses a method for digesting solids ,
separated from sewage sludge. The separated solids are mixed with a biological
culture and
aerated at a controlled temperature to decompose the fibrous cellulose, reduce
the grease
content of the sewage and remove objectionable odors from the solids. The
resulting product
may be pelletized for use as a fertilizer.
U.S. Patent No. 3,676,074to Shibayama et al. discloses a cylindrical rotary
tank
having an air pipe along the axis thereof. Organic materials are fed into the
cylindrical tank
and fermented using aerobic bacteria and thereby causing substantially no odor
nuisance. The
fermentation process also heats the tank to aid in drying the organic waste
and produce a solid
granular material which may be used as a fertilizer.
" U.S. Patent No. 4,660,628to Solberg et al. and No. 3,800,865to Onarheim et
al.
each disclose rotary heat exchangers wherein the heating or cooling medium is
passed through
~ 35 a hollow shaft having a plurality of fins extending outwardly therefrom.
The shaft is enclosed
within a container which receives the moist, solid or semi-solid materials
which are to be
heated or cooled.
,:
WO 95/19327 =. '"~~ ~ .. ~~: f ~ P ~ PCT/US94/00566
215 g 5'~
The Japanese Patent No. 5,439,372illustrates the method of adding aluminum
sulfate to waste sludge for settling, and thereafter adding a macromolecule
type aggregating
agent. The mixture is then centrifugally separated and the solid matter heated
for solidification
in a drying furnace at 200-SOOgbC to obtain a dried cake.
U.S. Patent No. 3,695,432to McCrink discloses a sewage disposal system which
pumps solid wastes separated from sewage through a heating retort. The solids
are mixed with '
a non-oxidizing gas such as ammonia, methane or propane which is injected
therein under
pressure, and the mixture is heated to produce a fine powdery ash. The gases
produced during
the process are passed through a flame curtain prior to exiting the system to
remove all odors
therefrom.
U.S. Patent No. 548,561 to Lamb discloses an apparatus for making fertilizer
from refuse. The refuse is filtered through sand and then evaporated using
steam passing
through a coil and then further dried using steam or hot air to produce a
fertilizer. Odors
produced by this system are conducted to the furnace for destruction therein.
U.S. Patent No. 659,503 to Wood discloses a sewage treating apparatus which
receives sludge solids in a vibrating and oscillating hopper comprising a
filter-bed holder.
Water is removed by the vibrating and oscillating hopper, and the resulting
solids entrapped
therein pass to a drying cylinder F where the material is thoroughly dried and
granulated by
heating and revolving the drying cylinder to produce a fertilizer.
U.S. Patent No. 3,909,410to Neukamm discloses a sewage sludge treating process
wherein the sludge slurry is continuously distributed in a rotating contactor
drum onto
preheated aggregate pieces which are continually fed into the drum. A portion
of the slurry
instantaneously adheres to the heated aggregate and the non-adhering slurry
exits the drum for
recycling. The coated aggregate is collected from the drum and heated during
travel to a
tumbler drum. In the tumbler drum, the sludge coating is broken away from the
aggregate
and pulverized into a powder or dust which is the product. The decoated
aggregate is recycled
into the rotating contactor drum.
None of the above sewage treatment systems are understood to process the
sewage sludge into a pelletized fertilizer having a long shelf life, such as
on the order of seven
months. Furthermore, none of these known systems are understood to make use of
waste oil,
such as transformer oil, crankcase oil, and other reclaimed oil in a heating
stage of the sewage
treatment process without venting significantly detectable amounts of gaseous
pollutants
thereby produced to atmosphere. Furthermore, none of the above sewage
treatment systems ~
are understood to fulfill such deficiencies with a minimal odor dispersing
apparatus which may
be used in a urban setting.
Thus, a need exists for an improved sludge treatment system for pelletizing
sewage sludge, such as may be used to produce a pelletized fertilizer or soil
amendment
product, which is not susceptible to the above limitations and disadvantages.
~WO 95/19327 r_ ~;~~ PCT/US94/00566
Summary of the Invention
It is an overall object of the present invention to provide an improved sludge
treatment system comprising a method and an apparatus for processing sludge,
such as waste
water sludge into a pelletized fertilizer.
A further object of the present invention is to provide an improved fertilizer
product made from a processed waste water sludge, with the fertilizer product
having an
improved shelf life.
An additional object of the present invention is to provide a sludge treatment
system which makes use of waste fuel, such as transformer oil, crankcase oil
and other
reclaimed oil, and which does not pollute the atmosphere.
A further object of the present invention is to provide an improved material
handling system for use in a sludge treatment system.
Another object of the present invention is to provide a sludge treatment
system
which may be used in an urban setting.
Still another object of the present invention is to provide a sludge treatment
system which is economical to operate and which produces a profitable final
product.
Yet another object of the present invention is to provide an improved sludge
treatment system capable of producing a pelletized fertilizer from digested
sludge, raw sludge,
waste-activated sludge, and a mixture of raw sludge and waste-activated
sludge.
A further object of the present invention is to provide an improved sludge
treatment system which produces a pelletized fertilizer meeting EPA (the
Environmental
Protection Agency) requirements relating to vector attraction reduction and
pathogen indicator
organism density for Class A sludge.
An additional object of the present invention is to produce from waste water
sludge a pelletized fertilizer having a nutrient value high in nitrogen and
phosphorous.
Yet another object of the present invention is to produce from waste water
sludge a pelletized fertilizer and to convert undesirable by-products in
exhaust gases produced
by a heat source during this production into a desirable fertilizer component
having a
beneficial nutrient value.
According to one aspect of the present invention, a method is provided of
converting sludge into fertilizer including the steps of mixing and sizing
dewatered sludge cake
solids with a recycled portion of sorted product to produce a solids mixture.
In a drying step,
the solids mixture is dried in a dryer to produce a dried solids. In a sorting
step, the dried
solids are sorted into a sorted product comprising oversize product,
undersized product, and
~ 35 standard sized product. In a recycling step, the oversized product is
recycled to serve as the
recycled portion of sorted product in the mixing and sizing step. In an adding
step, lime is
added to the standard sized product so as to produce a fertilizer from the
standard sized
product having an enhanced shelf life.
~15.85't ~
WO 95/19327 , PCT/US94/0056G
~~,~ a ' _6_
According to another aspect of the present invention a method of converting
sludge into fertilizer includes the mixing and sizing, drying, sorting and
recycling steps as
described above. This method also includes the step of providing heat energy
to the dryer
from a heat source. In a fueling step, the heat source is fueled with waste
oil to produce the
heat energy, and during the heat energy production the heat source also
producing an exhaust
gas containing undesirable by-products. In a filtering step, the undesirable
by-products from
the exhaust gas are filtered with a bag house prior to discharging the exhaust
gas to
atmosphere.
In an illustrated embodiment, prior to discharge to atmosphere, the exhaust
gas
from the filtering step may be used in preheating steps. Also, the undesirable
by-products
from the fueling step are converted during the filtering step into a desirable
fertilizer
component having a beneficial nutrient value.
According to a further aspect of the present invention, a method of converting
sludge into fertilizer includes the step of dewatering sludge to produce
dewatered sludge solids.
The method also includes the steps of drying the dewatered sludge solids in a
dryer to produce
dried solids, and providing heat energy to the dryer from a heat source. The
method includes
fueling and filtering steps, which may be as described above. In a
conditioning step, the
exhaust gas is conditioned by adding a conditioner additive thereto to aid in
the collection of
the undesirable by-products in the bag house and to facilitate removal of the
collected
by-products from the bag house.
In an illustrated embodiment, the conditioner additive comprises sodium
bicarbonate. With sodium bicarbonate as the conditioning additive, the method
may also
include the steps of adding either flyash or Portland Cement to the dried
solids to serve as a
binder, with the method furthering including a step of pelletizing the dried
solids afrer the
flyash or Portland Cement has been added thereto. In an alternative
embodiment, the
conditioning additive may be lime.
According to yet another aspect of the present invention, a method of
converting
sludge into fertilizer includes the mixing and sizing steps as described
above. In a drying step,
during the drying of the solids mixture a dryer vapor is produced having
condensable and
noncondensable vapors and particulate matter therein. The dried solids
produced in the drying
step are sorted in a sorting step into oversized product, undersized product
and standard sized
product, and in a recycling step, at least a portion of the sorted product is
recycled for use in
the mining and sizing step. Additionally, in a separating step, a substantial
portion of the
particulate matter from the dryer vapor is separated from the other vapors. In
a condensing
step, the dryer vapor is condensed to remove a substantial portion of the
condensable vapors
therefrom. In a destroying step, the noncondensable vapors, as well as any
condensable vapors
or particulate matter, remaining in the dryer vapor after the separating and
condensing steps
are destroyed through combustion at a temperature of substantially at least
1700° F in the heat
~'VO 95/19327 ~' I~ ' . PCT/US94/00566
7
source by containing the vapors and matter in the heat source for at least
approximately one to
two seconds. In this manner, the escape of odors from the system is minimized.
In an illustrated embodiment, the destroying step comprises the steps of
combusting the dryer noncondensable vapors, as well as any remaining
condensable vapors and
particulate matter, using a heat source with a firebox heated by a burner
having a flame with a
' prompt flame zone. In a providing step, fuel and primary air are provided to
the burner for
combustion. In a supplementing step, the primary air is supplemented with the
dryer
noncondensable vapors by injecting the noncondensable vapors, as well as any
remaining
condensable vapors and particulate matter, into the firebox substantially at
the prompt flame
zone.
According to a further aspect of the present invention, a method of converting
sludge into fertilizer includes the steps of promoting flocculation and
coagulation of the sludge
by adding a polymer to the sludge. In a dewatering step, the sludge is
dewatered afrer the
polymer has been added thereto to provide dewatered sludge solids. In a drying
step, the
dewatered sludge solids are dried in a dryer to produce dried solids. In an
adding step, lime is
added to the dried solids to produce a fertilizer therefrom having an enhanced
shelf life.
According to an additional aspect of the present invention, a sludge converter
is
provided for converting sludge into a fertilizer. The sludge converter
includes a mixer which
receives and mixes dewatered sludge cake solids and a recycled portion of
sorted product to
produce a solids mixture. A dryer receives and dries the solids mixture to
produce dried
solids. A sorter receives and sorts the dried solids into a sorted product
comprising oversized
product, undersized product and standard sized product. A screw conveyor
receives the
standard sized product and has a product outlet and a recycle outlet. The
product outlet is in
communication with storage means for storing the standard sized product. A
recycling screw
conveyor is in communication with the recycle outlet of the product screw
conveyor. The
recycling screw conveyor operates to recycle a portion of the standard sized
product to the
mixer to serve as the recycled portion of sorted product.
In an illustrated embodiment, the sludge converter includes a recycle
controller
responsive to sensors, analyzers and other meters which produce a dewatered
sludge cake solid
signal, a dried solids moisture signal, a dryer temperature signal, a dried
solids temperature
signal, and a horsepower signal which indicates the consistency of the sludge
within the dryer.
The recycle controller processes all of these signals and in response thereto
produces a recycle
conveyor controller signal. The recycling screw conveyor operates in response
to the recycle
control conveyor signal. The sludge converter may also include a heat source
which supplies
~ 35 heat energy to the dryer and produces an exhaust gas containing
undesirable by-products. To
remove these by-products from the exhaust gas prior to venting to atmosphere,
the sludge
converter also includes a bag house which receives and filters the heat source
exhaust gas.
During operation, the dryer produces condensable and noncondensable vapors and
particulate
WO 95/19327 = ~ A. PCT/US94/00566
i ' ~;s. ~ r
21~ ~5
matter. To remove these dryer by-products, the sludge converter may also
include a cyclone
which receives the dryer vapor from the dryer and separates a substantial
portion of the
particulate matter therefrom. A condenser in communication with the cyclone
and the heat
source is provided for condensing a substantial portion of the condensable
vapors from the ~
exhaust gas. The heat source receives the noncondensable vapors, as well as
any remaining
condensable vapors and particulate matter, from the condenser and combusts
these vapors and
matter at a temperature of substantially 1700° F by retaining them
within the heat source for
at least approximately one to two seconds.
The present invention relates to the above features and objects individually
as
well as collectively. These and other objects, features and advantages of the
present invention
will become apparent to those skilled in the art from the following
description and drawings.
Brief Description of the Drawings
Figs. 1 through 3 are portions of a schematic flow diagram which may be
interconnected in a side-by-side fashion, with Fig. 1 on the left, Fig. 2 in
the middle, and Fig. 3
on the right, to illustrate one form of a sludge treatment system according to
the present
invention.
Detailed Description of a Preferred Embodiment
Figs. 1 through 3 collectively illustrate an embodiment of a sludge treatment
system or sludge converter 10 constructed in accordance with the present
invention for
converting sludge, such as waste water sludge 12, into a fertilizer or soil
amendment product.
The sludge 12 may be, for example, digested sludge, raw sludge, waste-
activated sludge, or a
mixture of raw sludge and waste-activated sludge. The digested sludge may be
aerobically or
anaerobically digested sludge. The digested and the raw sludge may be, for
example, primary,
secondary or tertiary sludge. For convenience, the sludge converter 10 is
illustrated by
interconnecting Figs. 1-3 side to side, with a first portion of the sludge
converter designated
l0A shown in Fig. 1, an intermediate portion lOB being shown in Fig. 2, and a
final portion
lOC being shown in Fig. 3, such that the combination of items 10A, lOB and lOC
illustrate a
preferred embodiment of sludge converter 10.
The sludge 12, typically containing 3 to 6 ~ of solids, may be received from a
sludge generating entity, such as a municipality or metropolitan area, or an
industrial waste
water plant, for example in the paper industry. The sludge generating entity
from which sludge
12 is received hereinafter is designated as the "plant." A prototype sludge
converter 10 was
constructed in accordance with the present invention. Examples of the sludge
converter
components given herein are applicable to this prototype system. However, it
will be apparent
to those skilled in the art that suitable component substitutions may be made,
for example to
implement this system in accordance with the present invention on a larger
scale.
A sludge feed surge tank 14 receives the sludge 12 from the' plant through a
conduit 15. Tank 14 includes a sludge agitator or mixer 16, which agitates the
sludge by air
CA 02158574 2004-11-24
50358-1
9
mixing using compressed air received through conduit 18. A suitable sludge
mixer 16 is sold
under thetrade-mark"~ightnin Mixer",Model XJ1?4, manufactured by Mixing
Equipment
Company of Avon, New York 14414. 'The sludge flows through ,conduit 20 into a
grinder 22
for grinding. A suitable grinder 22 is sold under the trade-mark~'Muffin
Monster," Model No.
3-8-4, and is manufactured by Disposable Waste Systems, Inc., Santa Ana,
California 92707.
The sludge is pumped from grinder 22 through conduit 24 by a sludge pump 26. A
suitable
sludge pump is sold under the trade-mark"Moyno, "Model 1L8, manufactured by
MGI . Pumps,
Inc. of Bentsenville, Illinois 60106:
The sludge exits pump 26 through conduit 28, which has a T-fitting for
receiving
a polymer 30 through conduit 32. The polymer 30 may be of the type which
promotes
coagulation and flocculation of the sludge. A flow meter 34 has a transducer
36 monitoring
the sludge flow within conduit 28. The flow meter 34 produces a flow meter
signal 38 in
response to the flow through conduit 28 monitored by transducer 36. The flow
meter signal 38
is received by a recycle controller 40 (see Fig. 2). The recycle controller 40
receives a plurality
of sensor and monitor signals, which will be described further below along
with the meaner in
which the recycle controller 40 operates.
Dewatering means, such as a dewaterer which may be a centrifuge 42, receives
the sludge having polymer 30 therein from conduit 28. A variety of suitable
dewatering devices
are known in the art. The prototype of sludge converter 10 was constructed
using a centrifuge
sold under the trade-mark"Bird, "Model No. 2500, which in the prototype was a
mobile
completely self-contained test truck facility, manufactured by Bird Machine
Company of South
Walpole, Massachusetts 02071. The centrifuge 42 produces sludge cake solids
and centrate.
The centrate is delivered back to the plant through conduit 44. Of the total
recycle return load
or stream to the plant produced in the prototype sludge convener 10,
approximately 8596 was
produced by the centrifuge 42. The sludge cake solids produced by centrifuge
42 in the
prototype unit averaged from 26-326 total solids consuming 7-l5 pounds per ton
of polymer
with 95-9696 recovery of feed solids. The dewatering operation performed by
centrifuge 42
provides a consistent sludge production for an input to the balance of the
sludge converter 10.
The sludge cake solids exit centrifuge 42 through a turbulator feed conveyor
46,
which may be an enclosed shaftless screw conveyor. A suitable shaftless screw
conveyor may
be obtained from Purac Engineering, Inc. of Wilmington, Delaware 19808.
Several other
screw conveyors are described further below and such screw conveyors may also
be of the
shaftless variety such as those supplied by Purac Engineering, Inc. A solids
analyzer 48
monitors the flow of the sludge cake solids through conveyor 46 using
transducer 50. The
solids analyzer 48 produces a dewatered sludge cake solids signal 52 in
response to the
percentage of solids monitored by transducer 50. The recycle controller 40
also roceives the
CA 02158574 2004-11-24
50358-1
dewatered sludge cake solids signal 52. A suitable solids analyzer 48 may be
obtained from
Texas Nuclear of Austin, Texas, such as the TN Mark II Series SGD Density
Gauge.
Alternatively, instead of receiving sludge 12 from the plant, the plant may
provide
dewatered sludge cake solids or a centrifuged stock input 54. The centrifuged
stock input 54
5 may be delivered through an alternate turbulator feed conveyor 56 to
conveyor 46. The
intersection of conveyors 46 and 56 is shown schematically as a T-coupling to
illustrate the
principle that solids analyzer 48 would monitor and measure the percent solids
received from
the alternate source 54. If the alternate centrifuged stock input 54 is
received on a permanent
basis, then the above-described system upstream from the turbulator feed
conveyor 4b,
10 comprising items 12 through 44, would not be required.
Referring now to Fig. 2, the sludge cake solids are received from the
turbulator
feed conveyor 46 by sizing and mixing means, such as a sizing and mixing
turbulator or mixer
60. The prototype unit used a model 14T41-04 turbulator manufactured by Ferro-
Tech of
Wyandotte, Michigan 48192. The turbulator 60 serves to further mix and densify
the
emtrifuge cake. A solids mixture produced by the turbulator 60 exits through a
dryer feed
conveyor 62, which may be an enclosed shaftless screw conveyor. An optional
turbulator
bypass conveyor 64, which may be an enclosed shaftless screw conveyor,
interconnects the
turbulator feed conveyor 46 with the dryer feed conveyor 62.
A dryer 70 receives the solids mixture from conveyor 62. A suitable dryer 70
is
- sold under the trade-mark'Rotadisc,"Model No. TSTI.O,manufactured by Stord,
lnc. of
Greensboro, North Carolina 27409. This type of dryer has a sludge drying
chamber with a
hollow shaft rotatably mounted therethrough. The dryer 70 includes a motor
(not shown) for
driving the dryer by rotating the hollow shaft within the chamber. The hollow
shaft has a
plurality of hollow vanes extending outwardly therefrom and into the chamber
to agitate the
mixture during drying. A heating medium, such as steam or oil may be
circulated through the
hollow shaft and vanes while the shaft rotates, to dry the solids mixture to
produce dried solids.
A dryer 70 which operates at various temperatures is advantageous in drying
fibrous raw
sludges. For example, with a dryer 70 using oil as the heating medium,
successful operation of
the prototype system occurred at inlet oil temperatures of 350-500° F.
The temperature of dryer 70 is monitored by a dryer temperature sensor 72. The
dryer temperature sensor 72 produces a dryer temperature signal 74 in response
to the
temperature sensed within dryer 70. The recycle controller 40 receives the
dryer temperature
signal 74. The drying action within dryer 70 may be monitored by measuring the
amount of
horsepower required by the dryer motor (not shown) to rotate the dryer shaft.
To do this, an
ammeter 76 measures the current in amperes or amps drawn by the motor. The
ammeter 76
produces a horsepower signal 78 in response to the sensed dryer motor
amperage. The recycle
controller 40 receives the horsepower signal 78 from ammeter 76.
CA 02158574 2004-11-24
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11
A sorter, such as a sorting device comprising sorting screens 80, receives the
dried solids from dryer 70 through a dryer exit or sorter feed conveyor 82.
The sorter feed
conveyor 82 may be a screw conveyor, such as an enclosed shaftless screw
conveyor. The
temperature of the dried solids is measured by a dryer exit temperature sensor
84 having a
transducer 86 monitoring the temperature within conveyor 82. The dryer exit
temperature
sensor 84 produces a dried solids temperature signal 88 in response to the
temperature of the
dried solids exiting the dryer 70 through conveyor 82.
A moisture analyzer 90 includes a transducer 92 which senses and monitors the
moisture content of the dried solids in conveyor 82. The moisture analyzer 90
produces a
dried solids moisture signal 94 in response to the moisture content of the
dried solids
measured by transducer 92 in conveyor 82. The recycle controller 40 receives
the dried solids
moisture signal 94 from the moisture analyzer 90.
The sorting screens 80 receive and sort the dried solids into a sorted product
comprising: standard sized product which exits the screens through a standard
sized product
IS conveyor 96; undersized product which exits the screens through an
undersized product
conveyor 97; and oversized product which exits the screens through an
oversized product
conveyor 98. One suitable sorting device is sold under thetrade-mark"SWECO
Vibro-Energy
Separator," Model No. L5245444-3,manufactured by SWECO of Florence, Kentucky
41022.
Conveyors 96, 97 and 98 may be screw conveyors, such as shaftless screw
conveyors.
The conveyors 96, 97 and 98 deliver the respective standard, undersized and
oversized product to a recycle metering device 100. The recycle metering
device 100 may
select one or all of the dried standard sized, undersized and oversized
product to be recycled
through a turbulator recycle feed conveyor 102 which may be a screw
conveyor,such as an
enclosed shaftless screw conveyor. For example, during start-up of the sludge
converter 10, all
of the dried product sized may be recycled. The turbulator recycle feed
conveyor 102 joins the
turbulator feed conveyor 46. Thus, in the illustrated embodiment having this
recycle loop, the
turbulator 60 mixes the dewatered sludge cake solids with a recycled portion
of the dried
sorted product from the recycle metering device 100, to produce the solids
mixture.
The recycle metering device 100 typically recycles the undersized and
oversized
product through conveyor 102, and passes the standard sized product through a
dry product
storage feed conveyor 106, which may be a screw conveyor, such as an enclosed
shaftless screw
conveyor. Alternatively, the recycle metering device 100 may direct the
undersized or oversized
product to a disposal feed conveyor 104, to deliver such product to a
collection point for later
disposal.
The recycle metering device 100 responds to a recycle metering or conveyor
control signal 108 from the recycle controller 40. The recycle controller 40
rnay be of any type
of an analog or digital device, such as a microprocessor. Such a recycle
controller
microprocessor 40 receives the dewatered sludge cake solids signal 52, the
dryer temperature
CA 02158574 2004-11-24
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12
signal 74, the dried solids moisture signal 94, the dried solids temperature
signal 88, and the
horsepower signal 78. The controller 40 processes all of these received
signals according to a
control logic preprogrammed therein, and in response thereto produces the
controller signal
108. The controller 40 operates to maintain optimum operating conditions in
the turbulator,
S for example, to keep the consistency of the mixture therein within desired
limits, such as not
too gummy or gluey.
Referring now to Fig. 3, conveyor 106 delivers the standard sized product to a
dry
product storage container 110. During the prototype testing phase, three types
of sludges were
processed, i.e.,digested sludge, raw sludge, and a mixture of waste-activated
sludge and raw
sludge. The final dried product produced using the digested sludge, which may
be either
aerobically or anaerobically digested, was granular in nature so that it could
be used as a final
product without further processing. Digestion reduces the fiber content of the
sludge which
allows sufficient agglomeration to take place to produce this dried granular
product. In
contrast, the raw sludge and a 50:50 mixture of raw sludge with waste-
activated sludge was
converted into a fluffy dried product by the sludge converter 10. This fluffy
dried product
requires further treatment, such as pelletizing described below, to produce a
desired final
product. The waste-activated sludge should also require pelletizing, although
no testing was
performed during the prototype run.
Thus, if the sludge converter 10 receives raw sludge, waste-activated sludge,
or a
mixture of raw sludge and waste-activated sludge, an additional pelletizing
step is required to
produce the finished product. In this embodiment, a pelletizing conveyor 112,
which may be a
shaftless screw conveyor, delivers the standard sized product from the dry
product storage
container 110 to a palletizing device 114. The palletizing device 114 may
include a grinder,
roller compactor and granulator for compacting the standard sized product into
a finished
product. A suitable palletizing device 114 is manufactured by BEPEX .of
Minneapolis,
Minnesota 55413, with the grinder portion sold under thetrade-mark"Pulvocron
Primary
Grinder," Model No. P20; the compactor portion sold under the trade-
mark'Labpactor
Compactor," Model No. L200/50; and the granulator portion sold under the trade-
mark
"Frewitt Grartulator," Model No. MG800. A finished product 115 may exit the
palletizing
device 114 through a screw conveyor 116, or through a chute or other material
transfer device.
The finished product 115 may be delivered to finished product storage (not
shown), to a
vehicle (not shown) for immediate spreading as fertilizer, or to a packaging
apparatus (not
shown), such as for bagging the finished product 115.
To aid in the pelletizin~ operation, an additional material, such as flyash or
Portland Cement or lime, indicated as item 1 18, may he added to the
palletizing feed conveyor
112 through a metering device 119 as required. The flyash, Portland Cement or
lime may
serve as a binder to hold the compacted product into the palletized form
provided by the
palletizing device 114.
CA 02158574 2004-11-24
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13
Referring again to Fig. 2, a dryer heating and air handling system will be
described. The dryer 70 receives heat energy in the form of a heating medium,
such as steam
or hot oil, from a heat source 120 via conduit 122. A return path for the
heating medium from
the dryer to the heat source 120 is provided by conduit 124. A variety of
different types of
S devices are suitable to serve as the heat source 120 for use in the sludge
converter 10.
For example, the heat source 120 may comprise a steam generating boiler, with
steam serving as the heating medium. A suitable boiler mny be obtained from
Cleaver Brooks
of Milwaukie, Wisconsin 53201, under the trade-mark"G8 Packaged Boiler," Model
No.
15HP. Alternatively, the heat source 120 may be a thermal liquid heater, such
as as oil heater
with oil serving as the heating medium. A suitable oil heater may be obtained
from American
Hydrotherm Corporation of New York, New York 10016, under the trade-mark of .
"Hydrotherm Thermal Liquid Heater," model no. 25-2-24. Both of these heat
sources generate
the heat by combustion of fuel, and are particularly advantageously capable of
burning waste
oil, such as transformer oil, crankcase oil, or other reclaimed oil. This fuel
is roceived by the
heat source 120 througb conduit 126. The combustion flame may advantageously
be used for
the thermal destruction of noncondensable gases and particles produced during
the drying and
conveying processes in a manner discussed further below.
The heat source 120 used in the prototype was an oil heater supplied with the
Stord brand dryer 70, so the heat energy was supplied to the dryer via a hot
oil medium. The
prototype also had a boiler and a thermal destruction unit (TDU) which were
alternately run
during testing to thermally destroy noncondensable gases and particles,
mentioned above and
discussed in detail below. The boiler and TDU each provided a flame for the
thermally
destroying such noncondensates. In a permanent installation, a TDU may
advantagoously
provide the flame for thertaally destroying noncondensables when using a non-
combustion heat
source 120, such as an electric oil heater. The prototype boiler was a
conventional, hot water
boiler manufactured by Rite Engineering and Manufacturing Company of Downey,
California
90211. To facilitate combustion of the waste oil, a special burner was
installed in the Rite
boiler. This special burner is sold under the trade-mark".Clean Bum Air
Atomizer," model
no. 85 HS, utanufactur~ed by Clean Burn, lnc. of leola, Pennsylvania 17540.
The Clean Burn
sir atomizer used both a pressurized oil foed and compressed air to form a
final oil spray.
During drying, the dryer 70 produces a dryer vapor comprising condensable and
noncondensable vapors, as well as particulate matter. A conduit 128 delivers
the dryer .vapor
from dryer 70 to a main cyclone 130. A suitable cyclone is sold under the
trade-markql-ligh
Efficiency Wet Cyclone,"Model No. CY-230-8, manufactured by Stord, lnc. of
Greensboro,
North Carolina 27409. The cyclone 130 serves as a dust removal device to
separate and
remove a substantial portion of the particulate matter from the dryer vapor.
The cyclone l30
also aids in condensin' of the vapor pasts. The cyclone 130 draws a vacuum on
the conduit
128 to withdraw the dryer vapor from the dryer, and to provide a negative
pressure within the
CA 02158574 2004-11-24
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14
dryer 70. The running the dryer 70 at a negative pressure advantageously aids
in odor control
sad minimizes the escape of particulate matter to the surrounding environment.
The particular Stord brand cyclone used in the prototype system was a wet
cyclone which was modified by adding additional water injection nozzles. The
nozzles swept
the cyclone interior walls, promoting greater steam condensation and keeping
the cyclone
interior clean. In the prototype cyclone, two water injection nozzles (not
shown) were used
which roceived cool water through conduit 132. The flow and pressure of the
water was
metered (not shown). The cyclone under flow is delivered by conduit 134 to the
plant.
A conduit 136 delivers the remaining dryer vapor comprising condensable and
noncondensable vapors, as well as any remaining particulate matter, to a
condenser 140. The
condenser 140 receives cool water through conduit 142 which is used to
condense and remove
a substantial portion of the condensable vapors from the dryer vapor. The warm
water
produced during the condensing step leaves the condenser through conduit 144.
The
coadeasate containing the condensed components of the condensable vapors are
delivered form
the condenser 140 to the plant through conduit 146. A suitable condenser 140
is a tube and
shell heat exchanger, such as the shell tube cooler sold under the trade-
mark'~ieat
Exchanger," Model No. FTSSX-66, manufactured by Stord, inc. of Greensboro.
North Carolina
27409.
After condensing, the remaining dryer vapor noncondensate, comprising
noncondensable vapors, as well as any remaining condensable vapors and
particulate matter,
may be delivered through a conduit 148 to a .preheating device or preheater
150. A conduit
152 delivers this preheated remaining noncondensate to a blower unit or blower
154. The
blower 154 also serves to draw the noncondensate from condenser 140. A conduit
156 delivers
the noacondensate from blower 154 to the heat source 120. In the prototype for
the sludge
converter 10, a Stord mobile trailer test facility, Model No. TST-1 mobile
dryer unit supplied
by Stord Bartz Americas, Inc. of Greensboro, North Carolina 27409, was used.
This mobile
unit was a totally self-contained processing plant and included the dryer 70,
the oil heater
portion of the heat source 120 for supplying hot oil to the dryer as the heat
energy, the cyclone
130, the condenser 140 and the blower 154 each in communication with one
another as
described above.
The noncondensate, which may include compounds having foul-smelling odors, is
destroyed through combustion in the heat source 120. The combustion takes
place in the TDU
if used. Otherwise, the combustion takes place in the firebox of the portion
of the heat source
which heats the heating medium. Substantially total destruction of the
noncondensate in the
prototype TDU was accomplished by combusting the noncondensables at a
temperature of at
least 1700° F and by containing the noncondensate within the TDU for at
least approximately
one to two seconds. The destruction of the noncondensate is particularly
advantageous for a
sludge converter 10 used in an industrial or urban setting, since the
noncondensate typically
1
- z
~O 95/19327 , . PCT/US94/00566
-15-
comprises a variety of foul-smelling compounds. Thus, the escape of odors
associated with the
noncondensate from the sludge converter 10 is minimized using this odor
control system.
The odor control system of the present invention also includes several
auxiliary
cyclones which may be located along the various conveyors to provide a
negative pressure
within the enclosed conveyor system. The negative pressure enclosed conveyor
system serves
to draw particulate containing odorous vapor from the conveyors for disposal.
In this manner,
a relatively clean and a minimal odor dispersing sludge converter system 10 is
provided which
is compatible with an urban or industrial environment.
For example, an eductor-driven wet mixer cyclone 160 draws the particulate-
containing sludge cake vapor from the dewatered sludge cake solids within the
turbulator feed
conveyor 46. An eductor 162 removes these vapors from conveyor 46 and delivers
them
through conduit 164 to cyclone 160. The mixer cyclone 160 may also receive
particulate-
containing vapors from the solid mixture exiting the turbulator 60 through the
dryer feed
conveyor 62. An eductor 166 removes these vapors from conveyor 62 and delivers
them
through conduit 168 to cyclone 160. It is apparent that a separate mixer exit
cyclone (not
shown) may be included to receive the vapors drawn from conveyor 62 by eductor
166. The
mixer cyclone 160 functions in a similar fashion to the main cyclone 130 to
remove a
substantial portion of the particulate matter from the vapors received from
conduits 164 and
166. The cyclone 160 has a cool water supply (not shown) and may deliver the
mixer cyclone
under flow to the plant (not shown), in the manner described above for the
main cyclone 130.
The remaining condensable and noncondensable vapors, as well as any remaining
particulate matter, are delivered to a preheating device 170 from cyclone 160
through conduit
172. The preheating device 170 serves to prevent condensation of the vapors
during travel
through a conduit 174 which joins conduit 152 to deliver these vapors to the
heat source 120.
An eductor 176 draws particulate-containing vapors from the conveyor 82
exiting
the dryer 70 and delivers these vapors through conduit 178 to a dryer exit
cyclone 180. The
dryer exit cyclone 180 may operate in the same manner as described above for
the mixer
cyclone 160 to remove a substantial portion of particulate matter from these
vapors. A conduit
182 delivers the condensable and noncondensable vapors, as well as any
remaining particulate
matter, from cyclone 180 to a preheating device 184. The preheating device 184
serves to
prevent condensation of the vapors during travel through a conduit 186 which
joins conduit 152
to deliver the vapors to the heat source 120. Thus, running the enclosed
conveyors 46, 62 and
82 at a negative pressure advantageously aids in odor control and minimizes
the escape of
particulate matter to the surrounding environment.
Most other known heat source burners have a fan which forces air into the heat
source firebox through a plurality of air inlet apertures around the fuel
nozzle. A burner flame
has a prompt flame zone near the fuel nozzle where combustion originates, and
a late flame
zone near the tip of the flame. These known systems supply the noncondensable
vapors to the
CA 02158574 2004-11-24
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16
fire box in the late flame zone to avoid clogging of the sir inlet apertures,
as well as fouling of
the fan, and to prevent corruption of the flame. However, supplying these
vapors, which are
often cool, to the late flame zone disadvantageously quenches the flame. This
quenching of the
flaw roquires more fuel to be supplied to the burner to adequately maintain
the flame to heat
the heating medium. More inlet air for combustion of the additional fuel must
also be
supplied and of course heated by the flame, requiring yet more fuel.
The burner of the present invention combusts the dryer noncondensable vapors,
as well as any remaining condensable vapors and particulate matter, by
injecting these confined
vapors and matter into the prompt flame zone. These vapors and matter are a
s~ondary air
source which supplements the primary air delivered by the burner fan to the
fire box. By
preheating noncondensable vapors, as well as any remaining condensable vapors
and
particulate matter, with preheaters 150, 170 and 184, fouling of the fan is
substantially
eliminated. Furthermore, by using a burner having a substantially unrestricted
air inlet around
the fuel nozzle, clogging of the air inlet is substantially eliminated. A
suitable burner for heat
source 120 may be obtained by modifying one of several similar burners readily
available in the
marketplace.
Thus, these confined vapors and matter may be injected into the firebox, for
example with the primary inlet air, substantially at the prompt flame zone,
advantageously
conserving fuel. Burning the confined vapors and matter in the prompt flame
zone
advantageously provides more complete destruction than injection in the late
flame zone
because the prompt flame zone is at a higher temperature. As a further odor
control measure,
the primary inlet air may be collected from an enclosure or building
surrounding the sludge
converter l0,thereby
destroying a portion of any fugitive odorous compounds escaping from the
various equipment
described herein of the sludge converter 10.
During combustion of the waste oil fuel and vapors, the heat source 120
produces
as exhaust gas comprising undesirable by-products, such as by-products
containing sulfur which
may be in a gaseous state. To purify the heat source exhaust gas, the sludge
converter 10
includes an air cleaning system. A conduit 188 delivers the heat source
exhaust gases from the
heat source 120 to a bag house 190 (see Fig. 3). A suitable bag house may be
obtained from
Hosokawa. Micro of Summit, New Jersey 07901, under the trade name "Pulse-Jet
Bag House,'
Model 4B.
To aid in the air cleaning process, a conditioner additive, such as sodium
bicarbonate 192, may be added to the heat source exhaust gas. A conduit 194
delivers the
sodium bicarbonate to a dry feeder 196. A suitable dry feeder is sold under
the trade-mark
"AccuRate Dry Material Feeder," Model No. 302, manufactured by AccuRate, of
Whitewater,
Wisconsin 53190. A conduit 198 delivers the sodium bicarbonate from the dry
feeder 196 to
~i~VO 95/19327 ' - PCT/US94/00566
17
an eductor injector 200. Via a conduit 202, the eductor injector 200
distributes the sodium
bicarbonate into the heat source exhaust gas stream flowing in conduit 188.
The bag house 190 filters the undesirable by-products from the heat source
exhaust gas, and then discharges the now clean exhaust gas from conduit 204
and blower 206
and through a conduit 208 to atmosphere. Alternatively, before venting or
discharging the
clean exhaust gas to atmosphere, this gas may be used as a preheating heat
source in the
preheaters 150, 170 and 184. The clean exhaust gas is routed through conduits
(not shown).in
communication with conduit 208 and the preheaters 150, 170 and 184, and after
assisting in the
preheating step, is then vented to atmosphere.
Alternatively, the conditioner additive added to the heat source exhaust gas
may
be lime 210, which is initially supplied to the sludge converter 10 as raw
bulk lime in the
illustrated embodiment. The raw lime is delivered through conduit 212 to a
mill 214 where it
is ground into a fine powder. Conduit 216 delivers the ground lime to a lime
storage bin 218.
Alternatively, powdered lime may be fed directly into the storage bin 218. A
conduit 220
delivers the lime from storage bin 218 to the dry feeder 196. The sludge
converter 10 may use
as the conditioner additive either sodium bicarbonate 192 or lime 210
singularly, or as a
blended mixture thereof. The conditioner additive aids in the collection of
the undesirable
by-products in the bag house 190 and facilitates removal of the collected
undesirable
by-products from the bag house.
During the prototype testing, it was found that most of the sodium bicarbonate
192 is consumed during the precipitate-forming reaction within the bag house
190. During this
reaction, the sodium bicarbonate reacts with the sulfur components of the
undesirable
by-products to form sodium sulfate. In a system using sodium bicarbonate 192
as the
precipitate-forming catalyst for bag house 190, an additional binder, such as
the flyash or
Portland Cement or lime 118 is required for use by the pelletizing device 114.
In contrast to the sodium bicarbonate reaction in the bag house where most of
the sodium bicarbonate is consumed, a relatively large amount of the lime 210
is not consumed
during the bag house filtering process. Thus, the leftover lime 210 within the
bag house may
be reclaimed. This leftover or spent lime, along with the combustion dust and
calcium sulfate
produced during the bag house filtering action, is delivered through a conduit
222 to a valve
224. The valve 224 may be operated to send the spent lime, combustion dust and
calcium
sulfate through a conduit 226 for disposal. Alternatively, valve 24 may direct
the spent lime,
combustion dust and calcium sulfate through conduit 228 to the dry product
storage container
110. It is apparent that if sodium bicarbonate is used as the conditioner
additive, valve 224 and
conduits 226 and 228 direct the spent sodium bicarbonate (if any), the
combustion dust, and
sodium sulfate either to disposal or to storage container 110.
This reclaimed lime received by the dry product storage container 110 serves
several purposes. For example, the reclaimed lime may be used as a binder by
the pelletizing
WO 95/19327 PCT/US94/00566
-18
device 114 when pelletizing is required, such as when the sludge converter 10
receives raw
sludge, waste-activated sludge, or a mixture of raw sludge and waste-activated
sludge.
Additionally, the addition of lime to the standard sized product, be that
either reclaimed lime
from conduit 228 or additional lime received from source 118, advantageously
enhances and
increases the shelf life of the finished product 115. For example, by
providing a lime mix of
about 1016 by dry weight the finished product 115, the shelf life of the
finished product was '
found to be increased to at least seven months in duration. Furthermore, while
the sulfate
forms are not as useful for a binder as the lime, flyash or Portland Cement in
the pelletizing
step, the calcium sulfate and sodium sulfate advantageously enhance the
nutrient content of the
finished product 115.
This advantageously provides great flexibility to an operator of the sludge
converter 10, in that the finished product 115 may be stored on site and
removed only
periodically therefrom. Alternatively, the finished product 115 may be bagged
and distributed
for subsequent retail resale to consumers wishing to buy discreet quantities
of the finished
product, as opposed to bulk truckloads. However, if the consumer wishes to
immediately
spread the finished product 115, the addition of lime to the standard sized
product to enhance
the shelf life thereof is not required. Therefore, the system as shown in Fig.
3 having dual
inputs of sodium bicarbonate 192 and lime 210 may be particularly advantageous
where an
operator of the converter 10 has a variety of customers with different usage
requirements. For
example, if enhanced shelf life is required, the lime 210 may be added to the
bag house 190
and then reclaimed into dry product storage. .However, if the customer wishes
to immediately
spread the finished product 115, sodium bicarbonate 192 rnay be used in the
bag house 190.
In operation, the sludge converter 10 receives sludge 12 from the plant
through
conduit 15 which delivers the sludge to the sludge feed surge tank 14. The
operation of sludge
converter 10 will also be used to illustrate a method of converting sludge
into the pelletized
finished product fertilizer 115. The sludge 12 is typically received at a 3-6
9& solids
concentration.
The sludge received from the plant is mixed within tank 14 by an air mixing
device 16, which receives compressed air through conduit 18. Conduit 20
delivers the mixed
sludge from tank 14 to the grinder 22, which grinds the sludge. The conduit 24
delivers the
ground sludge from grinder 22 to the sludge pump 26. The conduit 28 delivers
the sludge from
pump 26 to the dewatering device, shown as the centrifuge 42. Prior to
delivery to the
centrifuge 42, the polymer 30 is added to conduit 28 via conduit 32. The
polymer may be any
of a variety of chemical compositions well known to those skilled in the art
to promote
coagulation and flocculation of sludge. The liquid centrate removed by the
centrifuge 42 is
delivered by conduit 44 to the plant.
The dewatered sludge cake solids produced by centrifuge 42 are fed through the
turbulator fwd screw conveyor 46 to the mixing and sizing device, shown as the
turbulator 60.
~i~VO 95/19327 '~~,~~' PCT/US94/00566
. - ~,.
-19-
Alternatively, the plant may provide the centrifuged stock input of previously
dewatered sludge
cake solids 54 through the screw conveyor 56 for delivery to the turbulator
60. The turbulator
60 sizes and mixes the dewatered sludge cake solids from centrifuge 42 with
recycled dry
product received through the recycle screw conveyor 102. The turbulator 60
produces the
solids mixture which is fed through the dryer feed screw conveyor 62 to the
dryer 70.
Optionally, the turbulator bypass screw conveyor 64 may be provided to bypass
the dewatered
sludge cake solids around the turbulator 60.
The dryer 70 dries the solids mixture to produce dried solids. The sorter feed
conveyor 82 delivers the dried solids from dryer 70 to the sorting device,
shown as the sorting
screen 80. The sorting screen 80 sorts the dried solids into standard sized
product, undersized
product and oversized product. The standard sized product, undersized product
and oversized
product are delivered via screw conveyors 96, 97 and 98, respectively to the
recycle metering
unit 100.
The recycle metering unit l~ operates in response to the recycle controller
signal
108 received from recycle controller 40. The recycle controller 40 generates
the control signal
108 by receiving and processing signals from various system monitors. These
system monitors
include the solids analyzer 48 with transducer 50 monitors the flow of
dewatered sludge cake
solids within conveyor 46, and in response thereto produces the dewatered
sludge cake solid
signal 52. The flow meter 34 with transducer 36 measures the sludge flow
through conduit 28,
and in response thereto produces the flow meter signal 38. The dryer
temperature monitor 72
produces the dryer temperature signal 74 in response to the dryer temperature.
The
consistency of the mixture within dryer 70 is measured by an ammeter 76 which
monitors the
current drawn by the motor turning the agitator shaft within the dryer 70. In
response to the
motor current draw, ammeter 76 produces the horsepower signal 78. The
temperature and
moisture of the dried solids mixture exiting the dryer through conveyor 82 are
monitored by
transducers 86 and 92 respectively. The temperature monitor 84 produces the
dried solids
temperature signal 88 in response to the temperature monitored by transducer
86. The
moisture sensor 90 produces the dried solids moisture signal 94 in response to
the percentage
of moisture measured by transducer 92. The recycle controller processes
signals 38, 52, 74, 78,
88 and 94 to produce the recycle controller signal 108.
The recycle metering device then directs the dried sorted product received
through conveyors 96, 97 and 98 through either conveyors 104 for disposal, 106
for final
product processing, or 102 for recycling. Typically, the standard sized
product is delivered
through conveyor 106 for finished product processing, and the undersized and
oversized
- 35 products are recycled through conveyor 102.
The dry product storage feed conveyor 106 delivers the standard sized product
from the recycle metering device 100 to the dry product storage container 110.
As mentioned
above, if the sludge received from the plant is digested sludge, the product
received by
WO 95/19327 ' PCTlUS94/00566
-20-
container 110 will already be granular in form, and not require further
processing by the
pelletizing device 114. However, if raw sludge, waste-activated sludge, or the
mixture of raw
sludge and waste-activated sludge is provided by the plant, the dried product
produced
therefrom is delivered by the pelletizing feed screw conveyor 112 to the
pelletizing unit 114.
The palletizing unit grinds, compacts, and granulates the product to form the
finished product
115 which is delivered from the pelletizer 114 through conveyor 116. During
storage in ,
container 110, the bag house precipitate of calcium sulfate or sodium sulfate
is added via
conduit 228 to the standard sized product to enhance the nutrient content of
the finished
product 115. Prior to the palletizing step, additional binder 118 which may be
flyash, Portland
cement or lime may be added through metering device I 19 into conveyor 112.
The finished
product 115 may be stored, bagged or immediately hauled away for spreading.
Referring again to Fig. 2, the heat source 120 supplies the drying medium,
such
as steam or hot oil, through conduit 122 to the dryer 70. The heat source 120
receives the
cooled drying medium from dryer 70 through conduit 124. The heat source 120
destroys
through combustion the conveyor and dryer vapors r~eived from preheaters 150,
170 and 184.
The conveyor vapors may comprise noncondensable vapors, as well as any
remaining
condensable vapors and particulate matter. The dryer noncondensate may
comprise
noncondensable vapors, as well as any remaining condensable vapors and
particulate matter.
During the destroying step, the dryer noncondensate and the conveyor vapors
are combusted
by providing them as a supplement to the primary air provided to the heat
source burner.
These supplementary conveyor vapors and noncondensate are injected into the
burner
substantially at the prompt flame zone of the burner flame.
The heat source 120 preferably burns fuel which is the waste oil, and during
this
burning generates an exhaust gas having undesirable by-products, such as
sulfur by-products
which may be in a gaseous state. Conduit 188 delivers the heat source exhaust
gas from heat
source 120 to the bag house 190. The eductor injector 200 feeds the
conditioner additive to
the heat source exhaust gas stream flowing through conduit 188 via conduit
202. Thus, the
exhaust gas has the conditioner additive dispersed therein upon entry into the
bag house 190.
The conditioner additive may be either sodium bicarbonate 192 or raw lime 120,
received from dry feeder 196 through conduit 198. In the illustrated
embodiment, the lime 210
is supplied as raw lime which may be in large chunks. These chunks of raw lime
are delivered
through conduit 212 to the mill 214 where they are powderized. Conduit 216
delivers the
powderized lime from mill 214 to the lime storage container 218.
Alternatively, powderized '
lime may be delivered directly to the storage container 218.
The bag house 190 filters the exhaust gas, so that clean exhaust gas is vented
to
atmosphere through conduit 204, blower 206 and conduit 208. Alternatively,
prior to venting
the clean exhaust gas in conduit 208 to atmosphere, this gas may serve as the
preheating heat
source for the preheaters 150, 170 and 184. The particulate matter entrapped
by bag house
~WO 95/19327 ,
~~~ PCT/US94/00566
-21-
190 may be delivered through conduit 222 to the valve 224. The valve 224 may
be adjusted to
direct this particulate matter for disposal through conduit 226.
Alternatively, this particulate matter may be reclaimed and delivered through
conduit 228 to the dry product storage 210. If the conditioner additive is
sodium bicarbonate,
the bag house produces sodium sulfate, whereas if lime is used, calcium
sulfate is formed in
the bag house. If sodium bicarbonate is used, typically most of the sodium
bicarbonate will be
consumed during the bag house reaction. However, if lime is used a significant
of lime may be
reclaimed from the bag house. This reclaimed lime is then added to the
standard sized
product to act as the binder, as well as to enhance the shelf life of the
finished product 115. If
sodium bicarbonate is used in the air cleaning process, an additional binder
of flyash, Portland
Cement or additional lime 118 may be added through the metering device 119 to
the
pelletizing feed conveyor 112.
Having illustrated and described the principles of our invention with respect
to a
preferred embodiment, it should be apparent to those skilled in the art that
our invention may
be modified in arrangement and detail without departing from such principles.
For example,
other dewatering devices, sizing and mixing devices, drying devices, sorting
devices, cyclones,
heat sources, condensers, recycle controllers, and pelletizing devices may be
used.
Additionally, suitable substitutions may be made for the arrangement and
location of the
various sensors which provide control signals to the recycle controller.
Furthermore, the use
and placement of conveyor cyclones will vary depending upon the particular
piping design of
the particular sludge converter 10 application. We claim all such
modifications falling within
the scope and spirit of the following claims.
