WO1997034679A1

WO1997034679A1 - Sludge drying apparatus and process

Info

Publication number: WO1997034679A1
Application number: PCT/US1997/004762
Authority: WO
Inventors: John R. Flaherty
Original assignee: Eco Technology, Inc.
Priority date: 1996-03-21
Filing date: 1997-03-21
Publication date: 1997-09-25
Also published as: AU2343897A

Abstract

Provided is an apparatus adapted for processing sewage sludge comprising: (a) a dewatering unit (100) for producing a sludge cake from a sludge, the dewatering unit (100) comprising a housing (110) and at least one screen (104) for filtering a sludge to collect a solids-enriched fraction on the screen; and (b) a vibrator for vibrating one or more screens, wherein the vibrator vibrates one or more screens with a vibratory frequency and amplitude effective, without any assist from gas flow through the screen, to maintain substantially all screen-applied sludge in constant motion. Sludge enters through an inlet (101) with sludge cake removed through one outlet (107) with filtrate removed from another outlet (108).

Description

Sludge Drying Apparatus and Process

The present invention is directed to systems for dewatering and drying sludge, particularly sludge from sewage plants.

The present application claims the priority of U.S. Application No. 60/013,821 , filed March 21 , 1996. Cities, particularly cities in the developed world, generate a tremendous amount of wastewater. The sludge-derived products that are thereby generated have economic potential for use as, for example, fertilizer or other form of nutrients, soil amendment or substitute, landfill cover or fuel. Such sludge-related processes can address the social and political pressure to more effectively recycle resources. A barrier to realizing this potential is the need for cost-effective systems to convert the sludge into forms that are readily transported, readily managed and readily usable for the intended purpose. The present invention provides cost- effective tools to remove the large amounts of water in sludge that interfere in the facile transport and handling of sludge. These tools further can process sludge into particularized granules that are readily handled by well- developed equipment for handling granular materials.

An average U.S. city of 600,000 population treats approximately 75 million gallons of wastewater daily. After a standard treatment process which concludes with a treatment in an anaerobic digestion system, about 400 gallons per minute flow from the digestion reservoirs to dewatering and drying systems. This in turn translates into approximately 10 tons of digested sludge at 25% (wt wt) solids] per hour. To produce a product containing 90% solids 7 tons of water must be removed from each 10 tons of sludge. This weight loss relationship varies from plant to plant depending on exact solids percentage and total hourly tons generated. The present invention, as described below, provides new tools, as well as a complete system, for cost-effectively addressing the task of removing such large amounts of water from sludge. Typically, the sludge produced by a waste treatment plant is dewatered or dried to a relatively low extent A large city, such as New York, often has to ship the waste to distant sites, and effectively pays for freighting about 75 tank cars of water for each 100 tank cars filled with the sludge waste The present invention presents economical methods of reducing the amount of water (and hence weight) which must be freighted to remote disposal sites Disposal fees are also reduced through the invention, both by reducing the weight of the waste, and by creating a more manageable form of the waste. Summary of the Invention

In a first embodiment, the invention provides an apparatus adapted for processing sewage sludge comprising: (a) a dewatenng unit for producing a sludge cake from a sludge, the dewatering unit comprising at least one screen for filtering a sludge to collect a solids-enriched fraction on the screen; and (b) a vibrator for vibrating one or more of the screens, wherein the vibrator can be operated to vibrate one or more screens with a vibratory frequency and amplitude effective, without any assist from gas flow through the screen, to maintain substantially all screen-applied sludge in constant motion. In one embodiment, the vibrator can be operated to vibrate screens so as to move the matenals applied thereto in a spiral pattern In one embodiment, the screen has a pore size of from about 270 mesh [53μm] to about 70 mesh [210μm], more preferably, from about 200 mesh [74μm] to about 100 mesh [149μm], still more preferably about 140 mesh [105μm]. In one embodiment, the dewatering unit further comprises- (a1 ) a sludge applicator for applying the sludge at about the center of a screen in the dewatering unit; and (a2) a first collection device for collecting material at an edge of that screen. The first collection device can further be for directing said collected material to a second screen for further dewatenng. Preferably, the sludge processing apparatus further comprises- (c) a dryer unit into which sludge cake produced by the dewatering unit is transferred and further dried. In a second embodiment, the invention provides an apparatus adapted for processing sludge comprising: (a) a dewatering unit for producing a sludge cake from a sludge, the dewatering unit comprising at least one screen for filtering a sludge to collect a solids-enriched fraction on the screen; (b) a first vibrator for vibrating one or more of the screens; and (c) a dryer unit into which sludge cake produced by the dewatering unit is transferred and further dried, which dryer unit comprises: (d ) at least one deck; (c2) a source of drying gas flow through the dryer unit; and (c3) a second vibrator for vibrating one ore more of the decks. Preferably the drying gas is air. In one embodiment, the second vibrator can be operated to vibrate decks with a vibratory frequency and amplitude effective to maintain substantially all deck-applied sludge cake in constant motion. In one embodiment, the second vibrator can be operated to vibrate decks, so as to move the materials applied thereto in a spiral pattern. In one embodiment, the drying gas flow from each source flows across the top of its respective deck. In another embodiment, each deck is a screen, such that drying gas can percolate from underneath the deck.

Preferably, the dryer unit further comprises: (c4) a sludge cake applicator for applying sludge cake at about the center of a said deck in the dryer unit; and (c5) a second collection device for collecting material at an edge of the deck. Preferably, the second collection device is further for directing said collected material to a second said deck for further drying. Preferably, the dryer unit has at least three said decks on which sludge cake-derived material is sequentially dried. Preferably, the at least one deck lacks filtration pores.

Preferably, the sludge processing apparatus further comprises: (d) a heater for heating the drying gas for the sources of drying gas to a temperature from about 300°F to about 500^βF, more preferably from about 350^βF to about 450^βF. Preferably, the sludge processing apparatus further comprises: (e) a conveyor for conveying sludge cake from the dewatering unit into the dryer unit; and (f) an output processing unit for dividing the dryer unit output into an output fraction and a recycle fraction and relaying the recycle fraction into the conveyer. Preferably, the output processing unit comprises one or more rotary valve airlocks to limit the amount of drying gas exiting the dryer unit via the output processing unit. In one embodiment, the sludge processing apparatus further comprises: (f) an output processing unit for dividing the dryer unit output into an output fraction and a fuel fraction. Preferably, for this embodiment, the sludge processing apparatus further comprises: (g) a grinding apparatus for grinding the fuel fraction to a more readily combustible size distribution, more preferably, grinding to an average particle size from about 300 mesh to about 400 mesh, yet more preferably about 350 mesh. Preferably, for this embodiment, the sludge processing apparatus further comprises: (d') a furnace for heating drying gas for the sources of drying gas, which furnace is fully or supplementally fueled by the fuel fraction. Preferably, the sludge processing apparatus further comprises:

(h) a heat recovery unit for (i) recovering heat from the drying gas from the source of drying gas after that drying gas exits the dryer unit, and (ii) transferring the recovered heat into drying gas for the source of drying gas prior to the introduction of that drying gas into the dryer unit. In a third embodiment, the invention provides a method of processing sludge comprising: (a) applying a sludge to at least one screen; and (b) vibrating the screen(s) to collect a solids-enriched material on the at least one screen, preferably wherein the screen(s) are vibrated with a vibratory frequency and amplitude effective, without any assist from gas flow through the screen, to maintain substantially all screen-applied sludge in constant motion. Preferably, the method comprises: (a¹) applying the sludge to about the center of a said screen; (b') vibrating the screen, or of the unit as a whole, such that material applied to that screen moves towards an edge of that screen; and (c) collecting a solids-enriched fraction from said edge. Preferably, the method of the third embodiment further comprises: (d) a drying step in which the solids-enriched material is further dried. Preferably, drying step (d) comprises: (d1) applying the solids-enriched material to at least one deck; (d2) applying an drying gas flow for drying the material applied to the decks; and (d3) vibrating each deck.

Preferably, the drying gas flow is over the top of each deck (particularly where the deck lacks pores). Alternatively or supplementally, the gas flow is introduced underneath the decks and percolates above the decks through pores in the deck. The method of the third embodiment can further comprise: (e) recovering a granularized product resulting from the drying step (d). The method of the third embodiment can also comprise: (d1') applying the solids-enriched material to about the center of such a deck; and (d3') vibrating that deck, or of the unit as a whole, such that material applied to that deck moves towards an edge of that deck; and (d4) collecting material from said edge. Preferably, the method further comprises: (d5) transferring the collected material for further drying on a second such deck. Preferably, the solids-enriched material is sequentially dried on at least three such decks. Preferably, the applied drying gas is preheated to a temperature from about 300^βF to about 500°F.

The method of the third embodiment can further comprise: (f) dividing the output of drying step (d) into an output fraction and a recycle fraction; and (g) relaying the recycle fraction into the solids-enriched material applied to step (d). Preferably, about 25% to about 75% (more preferably about 40% to about 60%, yet more preferably about 50%) of the output from drying step (d) is used as the recycle fraction.

In a fourth embodiment, the invention provides a drying device adapted for drying sludge cake comprising: (a) a chamber with at least one deck; (b) a vibrator for vibrating the one or more decks; and (c) a source of drying gas flow through the chamber. Preferably, the vibrator can be operated to vibrate the screen(s) with a vibratory frequency and amplitude effective to maintain substantially all screen-applied sludge- derived material in constant motion. In one embodiment, the vibrator can be operated to vibrate the screen(s) so as to move the materials applied thereto in a spiral pattern. In a fifth embodiment, the invention provides a method of drying sludge cake comprising: (a) applying the sludge cake to at least one deck; (b) applying an drying gas flow to dry the sludge cake applied to the deck(s); and (c) vibrating each deck. Preferably, the method further comprises: (f) dividing the output from drying on a said deck into an output fraction and a recycle fraction and relaying the recycle fraction into sludge cake applied to step (a).

In a sixth embodiment, the invention provides a sludge drying apparatus comprising: (a) an airlock input device for inserting a sludge or sludge cake; (b) a nozzle; and (c) a blower for providing a motive gas to push the sludge or sludge cake inserted via the airlock device through the nozzle. This aspect of the invention includes a method of drying a sludge or sludge cake comprising ejecting a sludge or sludge cake through the apparatus. Preferably, the sludge or sludge cake is ejected (i) into a vacuum chamber, (ii) into a chamber through which a drying gas is circulated, or (iii) onto a heated plate. Preferably, the nozzle comprises a coiled pipe.

Brief Description of the Drawings

The foregoing summary, as well as the following detailed description including preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

Figure 1 displays a dewatering unit. Figure 2 shows a dewatering unit linked by a screw conveyor to a dryer unit.

Figure 3 shows a dryer unit.

Figures 4A and 4B show a heat recovery system. Figures 5A and 5B show, respectively, a top view and a side view of a plow used in the invention.

Figure 6 shows a nozzle-based drying device. Definitions

The following terms shall have, for the purposes of this application, the meaning set forth below. In particular, for the purpose of interpreting the claims, the term definitions shall control over any assertion of a contrary meaning based on other text found herein:

^• maintain substantially all deck-applied solid in constant motion

The solids in a material applied to a deck (including a plate or screen) are substantially all in constant motion if at least about 70% of such solids is non-adherent to the deck, meaning that the solids are dislodged by any full upwards movement of the vibrating deck. ^■ sludge

"Sludge" refers to any form of biomass, biosolids, biowaste, residuals and the like that is in a form requiring water-content reduction to increase the material's value, for example as a fertilizer or other form of nutrients, soil amendment or substitute, landfill cover or fuel. Typically, the sludges that it is anticipated will be most often used with the present invention are those products of sewage treatment plants that are generally termed "sludges" within that industry.

^• sludge cake

"Sludge cake" refers to any dewatered sludge. Typically sludge cake is gelatinous, and is black and fibrous in appearance. Detaiied Description

A. The illustrated embodiments

The invention is described below with respect to a sludge-drying system of apparatuses of the invention. The sludge-drying system described below is illustrative of the invention, but the invention is not limited to these particular embodiments.

Illustrated in Figure 1 is vibratory separator or dewatering unit 100. Sludge is fed into dewatering unit 100 through inlet 101 , from which it falls onto a screen (not shown) located at the same level as the illustrated seam 104. Filtrate (i.e., effluent or "vibrate") passes through the screen and is funnelled through conduit 105 to liquid outlet 108. Filtrate can be dropped through an eductor venturi (not shown) to create a suction that can be connected to other discharge lines in an apparatus of the invention to facilitate drainage of condensed vapors. Due to the vibration of the screen, a material inserted into the dewatering unit 100 is repeatedly thrown upwards (i.e., fluidized), which helps minimize clogging of the screen and helps draw filtrate through the screen. Sludge cake collected on the screen moves laterally (preferably in a spiral pattern) as a consequence of the vibration of the dewatering unit 100. Plough 106 acts to aerate and agitate the collected sludge cake. Due to the lateral and vibratory movement of the sludge cake, a portion continually discharges through outlet 107. Optionally, anti-blinding sliders (not shown) are mounted beneath the screen to prevent clogging of the mesh of the screen. These sliders rotate as a consequence of the vibration of the dewatering unit 100. The dewatering unit 100 is mounted on springs 109 and is vibrated by a motor (not shown) found in housing 110. A preferred feature of a number of aspects of the invention is that the filtration screens or drying decks vibrate. Each screen or deck can be individually vibrated, but typically the entire apparatus housing the screen or deck is vibrated. Also illustrated in Figure 1 are inspection ports 102A and 102B. The discharge from outlet 107 is dropped onto screw conveyor 200, as illustrated in Figure 2. The spiral rotation of helical segment 201 moves the sludge cake upwards and towards the inlet 301 of vibrating dryer unit 300. Screw conveyor 200 also has a recycle inlet 202, the use of which is described further below. The spiral conveyor 200 is driver by motor 203. Screw conveyor 200 can be preheated, for example using jacketed steam, to insure that sludge cake is inserted into the vibrating dryer unit 300 at a temperature that facilitates the drying process conducted therein. Vibrating dryer unit 300 is shown in more detail in Figure 3. The inlet 301 can have associated with it a closure 302 (see Fig. 2), which can be used to prevent an outward flow of drying gas and heat from the vibrating dryer unit when the dryer unit is being pre-heated prior to operation. In one embodiment, not illustrated, the inlet 301 has for example an airlock or gate to allow the passage of sludge while limiting the outward flow of drying gas and heat. Sludge cake dropped into the vibrating dryer unit 300 through inlet 301 falls on first drying deck 303A. Heated drying gas flows through gas inlet 304A, over first drying deck 303A, and out first gas outlet 305A. Due to the vibration of the first dryer deck 303A, a material inserted into the vibrating dryer unit 300 is repeatedly thrown upwards (i.e., fluidized) and subjected to the drying action of the heat and lateral drying gas flow. Due to the vibrating movement, material migrates from the center of the first drying deck 303A to the periphery, where it drops onto the first funnel or feed tray 306A and is funneled so that it drops on the center of second drying deck 303B. Drying gas flow from second gas inlet 304B and out of second gas outlet 305B occurs as described above. Again, the vibratory action of second drying deck 303B results in material moving to the periphery and falling to second funnel 307A, which directs the material to the center of third drying deck 303C. Third drying deck 303C functions as described above (utilizing third gas inlet 304C and third gas outlet 305c), except that a material flowing to the periphery of third drying deck 303C is collected at dryer unit outlet 307, through which it is discharged from the vibrating drying unit 300 The vibrating dryer unit 300 is suspended on springs 308. A vibratory motor for vibrating the vibrating dryer is housed in housing 309 Also illustrated in Figure 3 are inspection ports 312A and 312B.

Preferably, the motor for vibrating the dryer unit 300 has two types of eccentric, adjustable weights for adjusting the oscillatory motion of the vibrating dryer unit 300 One weight type is used to adjust the horizontal oscillations of the vibrating dryer unit 300, while the other is used to adjust the vertical oscillations. Preferably, both the vertical and hoπzontal oscillations have an amplitude between about 1/16th inch and about th inch. The amplitude and oscillatory frequency are adjusted to provide for movement of the applied sludge or sludge cake as described further below. This frequency is substantially less than ultrasonic. In one preferred embodiment, the frequency is about 900 rpm. The motor for dewatering unit 100 preferably has these same characteristics.

The drying gas, preferably air, flowing through the system is preferably regulated in a number of ways, as will be described below with reference to Figures 4A and 4B The heat recovery system 400 has a distributing plenum 401 that divides the drying gas flow from a heater 402 into three drying gas streams, one stream each for first gas inlet 304A, second gas inlet 304B and third gas inlet 304C. After the drying gas flow passes through the vibrating dryer unit 300, a converging plenum 403 converges the three drying gas streams back into one. The converged drying gas stream passes through vortex damper 404 and is accelerated by balancing fan 405 (which also serves to draw drying gas from the vibrating dryer unit 300 and balance flow through the dryer unit 300) in the direction of conduit 406. The drying gas flow through conduit 406 passes through junction 407 and through shunt balancing damper 408 until it is injected into a heat recovery unit 409 which recovers heat from the drying gas and discharges the drying gas through heat exchange modules 410A-410F, which modules include stacks act to reduce the level of pollutants present in the discharged drying gas. The heat recovery unit can be, for example, a heat recovery unit available from Exothermic (Toledo, Ohio). Input drying gas is then heated with, one, heat from the heat recovery unit 409 and, two, heat from direct-fired heater 402. Second fan 411 acts to maintain and control drying gas flow. Drying gas flow from direct fired heater 402 proceeds to source conduit 412, with some drying gas flow proceeding via shunt conduit 413. Shunt conduit 413 acts to modulate supply air flow based on climatic conditions or closed loop requirements (such as a reduced need for heated drying gas in the dryer unit 300).

Illustrated in Figures 5A and 5B is a plow that can be can be applied over any of the vibrating decks of the invention, although the plow is most preferably applied to third deck 303C, as illustrated. The plow has a stainless steel tube 313, on which six mounting tubes 314 are affixed. On each mounting tube 314, a slotted, double-edged plow wedge 316 is mounted via a mount 315. The height of the mounts 315 on their respective mounting tubes 314 can be adjusted. The plow wedges 316 serve to flip or turn over material as it cycles about the surface of the associated third deck 303C (preferably in a helical pattern), thereby increasing the exposure of the material to enveloping gas. The arrows in Figure 5A indicated the clockwise movement of sludge-derived material which is preferably employed. (In the Southern hemisphere, counterclockwise motion may be more desirable.)

B. Operational Parameters for the Illustrated Embodiments 1. Dewatering Unit

The illustrated sludge-drying system is designed to accept 400 gallons per minute ("gpm") of, in a preferred example, a 2.2% (wt/wt) solids and 97.8% water slurry. This represents the sewage production from an urban population of 600,000. The 2.2% slurry is polymerized (as this term is understood in the sewage treatment arts) and then fed via a 6" diameter pipe into the illustrated 6' diameter, 3 horsepower, vibrating dewatering unit 100. The flow initially falls through a velocity reducer and will be dissipated over a 6' diameter, 140 mesh screen. The eccentric weights balanced on the output shaft of the motor cause an oscillation which keeps the solids in a perpetual fluidized bed mode and the dewatered sludge cake migrating in a spiral pattern (typically clockwise) to the outside diameter of the vibrating deck on which the screen 103 is mounted. From there the cake drops off the deck and out the discharge chute (8" x 20") into a shaftless, 12" diameter screw conveyor 200.

The resultant sludge cake preferably contains approximately 15% to 25% solids and preferably represents a minimum about 94% capture of the total flocculated solids from the initial 400 gpm (where the industry standard is 90% capture). The resultant sludge cake (a gelatinous material) drops into the screw conveyor 200 to be conveyed to the dryer unit 300, and preferably consists of a loosely aggregated material that has not been compressed or compacted. (The resultant cake thus contrasts with the output of the prevailing procedures of centrifugation or filter belt presses that squeeze the moisture from the flow and subject the sludge to compaction by high sheer forces, which type of output is more difficult to dry further due to the reduced surface area and relatively large particle size.)

The final product of the sludge-drying system is preferably particularized or singularized, meaning that the output of the dryer unit 300 is composed primarily of granules of clumped material, preferably having average diameter of between about 1/8" and about 1/4" and an average density of between about 25 to 30 Ibs./cu. ft. This particularization is enhanced by back feeding approximately two to three tons per hour of about 75% to about 95% dry finished material. This strategy permits about two to about three tons of about 75% to 95% dry material, preferably at 180°F, to be mixed in the screw (via recycle inlet 202) with about 10 to 12 tons per hour of the dewatered about 15%-25% solids cake resulting preferably in an about 30% solids cake, which solids content allows for bypassing a paste/glue phase drying process. 2. Dryer Unit

The sludge-drying system, in a preferred embodiment handles about 10 to about 12 tons per hour of about 15%-25% solid cake from the dewatering unit 100, which sludge cake typically has a temperature of about 70^βF. In a preferred mode of operation, about two to three tons per hour of about 180°F, about 75% to about 95% solids material recycled from the dryer unit 300 output, is dropped into the screw conveyor 200 through the recycle inlet 202. The combined about 15%-25% solid cake and the recycle about 75% to about 95% material are dropped into the 16" diameter spout on the dome of the dryer unit 300. The T diameter, triple-decked, three horsepower, vibrating dryer unit 300 receives the resulting about 12 to 15 tons per hour of 30% dry material (now somewhat granularized by the addition of the recycle material) and a traverse drying process begins. In this process, the following applies: Perpetual windrowing. Fluidized bed dynamics. - Multiple drying platforms. Radiant heat (all functional surfaces are preheated to an operational temperature, such as about 450^PF). Traverse hot drying gas flow is presented from the supply side across three 7' diameter, 14-gauge decks. Convection heating. Changes in vapor pressures.

In the dryer unit 300, the top two drying decks (303A and 303B) and conical feed trays (i.e., funnels) 306 are preferably coated with a material (such as a perfluorinated polymer material such as Teflon™, DuPont, Wilmington, DE) to prevent excessive adherence. The entire sludge-drying system, except for the six (6) exhaust stacks of the heat exchange modules 410, is insulated to reduce heat loss, comply to OSHA safety standards, and keep the moisture laden, saturated drying gas above the dew point or wet bulb temperature. Keeping the moisture in a gaseous state prevents premature condensation (prior to injection into the heat exchange modules 410A-410F) which may cause plugging of the drying gas filters.

Each of the three (3) supply-side drying gas vents (gas inlets 304) incorporates a wire mesh screen to diffuse the incoming drying gas and to slow down the drying gas velocity of 6,000 feet per minute. The hot, dry drying gas carries off approximately nine tons per hour of water vapor with the aid of a 40 horsepower balancing fan 405 (such as that available from Aerovent, Erie, PA). This fan 405 incorporates a vortex damper 404 that reduces the drying gas velocity to 300 feet per minute, which velocity reduction enables the larger, gas-suspended particles to drop to a bottom clean-out trough (not shown) of the converging plenum 403. The balancing fan modulates the drying gas flow within the dryer unit 300 and allows for a solids detention time, through the dryer unit 300 of approximately five (5) minutes. The effectiveness of the three drying decks (303A, 303B and 303C) in moving the applied material can be adjusted by varying the thicknesses of three 7-foot diameter decks based on the specific weights (i.e. densities) of the sludge on each of the successive decks. Thus, in one embodiment, the first deck 303A, which receives the most dense material, is one-inch steel plate; the second deck 303B, which receives a lower density material, is two-inch steel plate; and the third deck 303C, which receives a still lower density material, is three-inch steel plate. Preferably, prior to introducing hot drying gas into the system, ambient air is blown into and drawn across the entire system. Then 30,800 actual cubic feet of drying gas per minute at 350^βF is 450°F constantly introduced to bring the system up to an operational temperature. Strategically placed thermal couplers electronically feed operational parameters to a controller, which implements operations as appropriate, such as activating a sludge pump to initiate a flow of about 400 gpm. The first about two to three tons of finished about 75% to about 95% dry, Class A biosolids will be back-fed pneumatically to an orifice (recycle inlet 202) two-thirds of the length up the 16' screw conveyor 200. This bulking procedure is tantamount to "priming the pump" since the system output will be six tons per hour of a finished about 75% to about 90% dry product of which preferably about two to three tons are routed, for example to dump trucks, and about two to three tons are diverted back into the sludge-drying system.

A stainless steel T long, 2" diameter pipe with six slotted, double- edged plow wedges is, for example, utilized to further agitate and aerate the cake applied to first dryer deck (see Figs. 5A and 5B). The pipe and attached plow wedges are fixed to the frame of the dryer unit 300. Preferred operational parameters:

7,500,000 BTU Aerovent Burner (Aerovent, Erie, PA) with controls

Propane fuel (Natural gas optional) 100,000 BTU per gallon of propane 45 gpm propane consumption ($1.00 per gallon) Fuel vaporizer capacity = 120 gpm - line pressure 5 psi ^• 1 ,000 BTU to liberate one pound of water

75% of sensible and latent heat to be recovered Ambient air temperature = 30^βF ^■ Sludge Temperature = 70^βF 3. Heat Recovery, Emission Controls The heat recovery system 400 preferably condenses 30,800 cu.ft./min of drying gas and preferably recovers about 80% of sensible and latent heat. This process recovers approximately 5 x 10⁶ BTU to supplement the 7.5 x 10⁶ BTU provided to the sludge drying apparatus by the heater 402. The velocity of the drying gas exhausted from the dryer unit 300 is preferably reduced to less than 300 feet/min so that larger suspended sludge particles drop out of the drying gas stream into a cleanout trough (i.e., dropout box). To further reduce particulates, the exhaust drying gas passes through a Filtech filter chamber (Filtech, Pittsburgh, Pennsylvania) utilizing twenty-eight 2' x 2' Purolator filter panels (as supplied by Filtech, Pittsburgh, Pennsylvania). Each 2' x 2' panel has 28 feet of filtering capacity (784 total square feet) to capture 100% of ten micron particles and 97% of five micron particles. A Magnahelic gauge (as supplied by Filtech, Pittsburgh, Pennsylvania) with set points that can be used to switch off the sludge supply pump in the event of an drying gas pressure drop across the bank of filters.

An Exothermic Inc. (Toledo, Ohio) manufactured heat recovery unit is deployed to recover the exhaust heat (preferably at least about 75% of the exhaust heat). This system uses an air-to-air heat transfer system and incoming and exhaust drying gas are ducted through six heat exchange modules 410, each including a 14" exhaust, no-loss stack.

Odors are abated by adding potassium permanganate (Caras, Inc., Peru, IL) to the initial sludge slurry. The potassium permanganate oxidizes odor-causing sulfur compounds in the sludge.

Emissions absorption equipment utilizing activated carbon can be coupled to the sludge-drying system. Also, a catalyst afterburner to oxidize volatile organic compounds can be installed. Several known steam condensation approaches can be applied to reduce opacity problems, should such problems arise. The finished product and back fed material can be pelletized to reduce fugitive dust from the drying gas system. 4. Pneumatic Conveyance and Pelletizing

As for example six tons per hour of a 90% dry particle are discharged from the dryer unit 300, about three tons are diverted into a 3/4 horsepower, 4" diameter, 8 vaned rotary valve airlock (for example, from Production Sales Co., Lincoln, Nebraska) to be back fed into the screw conveyor. The other three tons per hour of biosolids are, for example, diverted into on-site 25-ton haul trucks. The motive air for this dilute phase air conveyance system is provided by a 30 horsepower, positive displacement blower capable of moving the dried sludge at a fly-speed velocity of 70 mph with minimal creation of fines or fugitive dust. An air velocity compensator is utilized to "quiet" the final particle discharge speed. Twenty foot lengths of galvanized pipe are clamped together with a maximum of three 90° sweeping bends per line.

Optionally, three horsepower, 4' diameter, agglomeraters (for example from Cason Union, New Jersey) are used to pelletize the dried particles. A mist of a binder material (such as a 2% starch solution) acts as the binder for, for example, a 75% dry sludge cake. Once pelletized, the 75% solid biosolids can be further dried to, for example, 90% dry and/or pneumatically conveyed to a spiral feeder or dump truck.

C. General Operational Parameters The above discussion in Sections A and B relate most directly to the illustrated embodiment. It will be recognized that parameters recited in those Sections A and B can be of general application to the invention as a whole. This section sets forth general parameters without reference to the particular illustrated embodiments. Preferably, the dewatering unit is effective to produce a sludge cake having at least about 15% to about 25% solids from a sludge having from about 1.5% to about 3% solids, more preferably about 2%. Preferably, the dryer unit is effective to process a sludge cake having from about 15% to about 30% solids to a sludge cake-derived product having from about 75% to about 95% solids more preferably 90%.

D. Nozzle-based Drying Processes

The invention also provides for drying apparatuses and processes utilizing nozzles that provide various spray patterns, where the spray pattern typically results from injecting a fluid through spiral piping and ejecting the fluid from the piping. Accommodations must be made so that a solids-containing material, instead of the typical fluid, can be ejected from such a nozzle. For instance, in Figure 6, the output of, for example, a dewatering unit is transferred via conduit 501 to airlock 502, and hence to hopper 503. A positive displacement blower provides motive gas (usually air) through conduit 504. The solids-containing material is accelerated towards nozzle 505, preferably a speed between about 60 and about 80 mph, more preferably about 70 mph. In the illustration, the nozzle ejects at the base of a stainless steel cone 506. The ejection of solids-containing material into a chamber through which drying gas flows increases the surface area of the solids that is exposed to the drying gas. The solids- containing material can be directed to collide with a heated surface to further enhance drying. The nozzle also acts to shred the solids in the input material.

In one embodiment, the nozzle is SpiralJet™ nozzle (available from Spraying Systems Co., Wheaton, IL), which ejects the solids- containing material in a "hollow cone" pattern in which the solids are enriched at the exterior portion of the cone, and the interior portion is substantially water. The solids-enriched portions and the water portions can be separately collected, for instance by aligning a drain pipe at the center of the hollow cone pattern. The extent to which the water portion contains solids will vary with the diameter of the drain pipe, with a larger diameter yielding a drier solids-enriched portion, but also leading to a greater solids content in the water portion.

A number of nozzles that can be used in the invention, such as nozzles that eject a 60°, 90" or 120" spray pattern, can be obtained from Spraying Systems Co., Wheaton, IL.

E. Alternative Specific Sludαe-Processinα System While the sludge-drying system outlined in sections A and B provides a complete processing system with only a few separate subsystems, other subsystems can be applied, for example to further improve one characteristic or another of the outputed solids and gases. Described in this Section is a sludge-processing system having a number of other subsystems.

Module #1: Dewatering & Polymer Reduction Equipment: -On-line flow measuring system.

-Floe mixer.

-Double decked, 72" diameter vibratory dewatering separator (3hp, 200 mesh, 74 micron screen, Kason Corporation, Clifton, NJ). -Fox eductor venturi (Fox Co., Newark, New Jersey).

The module is for drying, for example, a 2.5% solids material to a 13% solids material. The dewatering subsystem utilizes one or more vibrating separators with two 72" diameter decks supporting filtration screens. These vibrating screens receive the incoming flow of, for example, 300 - 450 gpm from a 12" diameter velocity reducer directly above a dome covering the top deck. This domed cover prevents splashing and contains odors. Antibinding sliders are mounted underneath the vibrating decks to keep the fine mesh screen from plugging. The anti-blinder sliders are rotated due to the oscillations of the unit. A 72" long pipe fixedly laid across the top drainage deck is mounted with a series of diamond shaped plows to create drainage troughs for enhanced water separation.

The amount of manic polymers used in polymerizing the 2.5% material prior to insertion into module #1 can be reduced since the oscillating movement of the screen allows for clear filtrate to drop through the screen orifices, while capturing for example 95% of the solids. Influent solids content of 2.5% is screened to 13% solids, with module #1 discharging dried material at an ambient temperature of 60^βF. Discharged from the lower vibrating deck is a wastewater effluent which is sent back to the head of the treatment plant through an existing sewer line. Oversized particles and wastewater grit larger than 1/2" are screened upon discharge from Module #1. The effluent wastewater flow drops through a eductor venturi creating a suction on subsequent discharge lines, which suction enhances the drainage of condensed vapors from Modules 2, 3, 4, and 5. Gravity discharge and screening of solids into Module #2 eliminate the need for costly sludge pumps to transport biosolids. Module #2: Mechanical Separation and Drying

Equipment:

-Blo-thru, 12" Rotary valve airlock (MAC Equipment, Inc., Sabetha, KS).

-Positive displacement blower (1 ,000 cfm @ 10 psi), 4" pipe, where the blower is for example a DuroFlow (as supplied by Pegos Airsystems, Nevato, California), Sutorbilt (as supplied by Pegos Airsystems, Nevato, California) or MAC Pneupro 420 Series (MAC Equipment, Inc., Sabetha, KS) blower. -120", 4" hollow cone nozzle SpiralJet Hollow Cone Spray

Nozzle, sold by Spraying System Co. of Wheaton, IL. -Fabricated mechanical separation chamber. -360" Air drying ring. -Low pressure, high volume blower. -Aero-vent dropout box (Aerovent, Inc., Erie, PA).

-Penn mist eliminator, 8" inlet line Penn Industries, Bradford, PA. Module #2 is for drying, for example, a 13% solids material to a 22% solids material. An energy dampening connection pipe connects the vibrating discharge spout of module #1 to a 12", 5 hp, Bio-thru rotary valve airlock. This airlock meters the sludge and presents 10 tons/hr of a gelatinous, dewatered biosolids through a 20 rpm, 8 vaned rotor. A positive displacement blower provides a drying gas to propel the sludge through a 4" stainless steel pipe into a 90° bend and into a cone-shaped chamber. The pipe exit is preferably at the bottom, narrowest portion of a 120° stainless steel cone, which exit is referred to as the tip of a static shreader nozzle. The sludge is blown through the pipe for example at 10 psi and 148 mph, and is discharged as a shredded sludge into the chamber at ^ΛA psi.

The upwards throw pattern of the solids is 12' wide at the top and 6' high from the tip of the nozzle. The nozzle functions as a static centrifuge without any moving parts. The solids are reduced in size such that the average particle diameter is less than 1/8th inch and are singular- ized. This singularization helps expose more surface area of the particles so the drying gas (preferably air) can make intimate contact with the particles. A resulting hollow cone shot pattern (solids-enriched material at the exterior of the shot pattern, and water-laden materials at the interior) allows for the moisture laden vapors to be exhausted from the center of the shot pattern without contaminating the incoming solids. The static shreader nozzle can mechanically separate the solids from the free, unbound moisture, and pass foreign debris up to V_".

The solids-enriched portion of the throw pattern falls over the edge of the 120° stainless steel cone. The solids drop that fall over the lip fall into a fabricated ring which receives an additional sweep drying gas from a second blower. This drying gas helps evacuate wet, saturated vapors from spray chamber. The wet vapors (distillate) are discharged to the head of the treatment plant through the fox venturi described above. A resulting material with, for example, 22% dry solids then is dropped through a rotary valve airlock to Module #3.

Module #3: Pre-Heat & Indirect Drying Equipment:

-Bio-thru, 12" rotary valve airlock (MAC Equipment, Inc., Sabetha, KS).

-Dual spiralfeeder jacketed, insulated 6" screw conveyors. -Insulated platen chamber (Customs Engineering, Erie, PA).

-Blo-thru, 12" rotary valve airlock. -Positive displacement blower (1 ,000 cfm @ 10 psi), 4" pipe.

-360° agitation loop, 4" pipe. -120°, 4" hollow cone nozzle. -Insulated spray drying, vacuum chamber.

-4 decked, 72" diameter Kason vibratory drying chamber (Kason Corporation, Clifton, NJ, 40 mesh, 420 micron screen), 3hp. Module #3 is for drying, for example, a 22% solids material to a 50% solids material. Sludge is pneumatically conveyed in a dilute phase from Modules #1 to #2, #2 to #3, and #3 to #5; thereby eliminating costly Schwing type, dense phase sludge pumps. Solids drop into dual screw conveyors for pre-heating, for example, from 70° F to 120^βF. The jacketed screw conveyors discharge the biosolids into an insulated platen chamber at 450°F and the sludge is gravity fed to the airlock underneath the chamber. A heater (for example an electric heater) is used (e.g., 30 Kw/hr) to maintain the process air at 450°F to raise the solids temperature up to 180°F or more while preheating the drying gas to be supplied to a positive displacement blower. Drying air is pre-heated to 180^βF and the blower further heats the drying gas temperature to 320^βF. Solids are now blown through a second static shredder nozzle and thrown into a vacuum chamber that maintains a temperature of 200°F or more. This static shredder nozzle functions as a static centrifuge. The moisture converts to vapors and is exhausted through a 12" exhaust port via a centrifugal fan. The reduced pressure of the vacuum chamber allows for water to boil at 180^βF. The process applied in Module #3 heats the solids up to at least about 180°F prior to discharge through the static shredder/centrifuge. The drying gas temperature is above 300^βF to further dry airborne particles of sludge. Material progresses from the vacuum chamber in the same way described above for the first static shredder nozzle of Module #2. - 23 -

Underneath the vacuum chamber is a 4 decked, vibrating chamber that accepts 320°F drying gas from a positive displacement blower and presents drying gas through a manifold into 4 plenum chambers under each deck. The decks are mounted with screens. Four exhaust ports draw wet drying gas from each deck and the saturated drying gas reports to Module #4. A material with 50% solids is sent via an airlock to a sludge hopper for hauling, or to Module #5 for further drying. Module #4: Vacuum/Compression & Heat Recovery Equipment: -Compressor or centrifugal fan

-Steam coil (Aerovent, Erie, PA) Vapors are compressed and condensed in a drop out chamber and the hot drying gas is recaptured as pre-heated supply drying gas for the above-described blowers. Distillate from the above-described modules runs through a steam coil to flow through jacketed screw conveyor.

Preferably, 80% of the purchased power is recycled through pre-heating the supply drying gas and solids with heat from the heat recovery module. Module #5: Final Drying Equipment: -4 decked, 72" diameter Kason vibratory drying chamber

(Kason Corporation, Clifton, NJ, 40 mesh, 420 micron screen).

-Positive displacement blower (1 ,000 cfm @ 10 psi), 4" pipe. Module #5 is for drying, for example, a 50% solids material to a

70% solids material. Solids drop through an airlock from Module #3 into a receiving spout on top of a domed dryer. A vacuum is pulled in an insulated, 72" vibrating dryer by a manifolded centrifugal fan. The vapors are exhausted from each deck level to prevent wet drying gas from passing through dried solids. The four decked vibratory dryer, similar to the unit in Module 3 is used to further dry biosolids from about 50% to about 70% dry. The decks are 40 mesh screens and a plenum chamber is mounted under¬ neath each vibratory deck to maintain a constant static pressure for the supply drying gas to permeate up through the fluidized bed of sludge. Pre-heated drying gas is blown under each deck from a 1 ,000 cfm, 10 psi, positive displacement blower. The drying gas temperature is, in one embodiment, 240^βF.

Module #6: Pelletizing Equipment:

-California Pellet Mill (Ingersoll-Rand, Indianapolis, IN) One - 150hp California pellet mill is utilized to receive a 70% (or more) dry solids material in a granular form less than 16 mesh (1/16"). The pellet mill will process 5 tons/hr of 40 lbs / cu. ft. material and produce a pellet V*" x 1 ". This pelletizing allows for further drying to 90%, while eliminating fugitive dust and other material handling problems. Any blending of organic supplements can be done in the pre-mixing chamber. A bagging system can be installed to facilitate down-stream uses of the processed sludge, such as for fuel or soil amendment.

As can be seen from a comparison of the sludge-drying system of Sections A and B with the sludge-processing system of this Section E, the invention is readily applied so as to minimize the number of processing steps required in processing sludge. However, this Section E illustrates that additional subsystems can be applied, as may sometimes be useful in particular contexts.

F. Some Benefits of Applying the Invention 1. The two major criteria of the Federal 503 Biosolids

Regulations can be satisfied:

Process to Significantly Reduce Pathogens (PSRP). Process to Further Reduce Pathogens (PFRP). 2. Volume reduction. 3. Elimination of high maintenance filter belt presses, sludge pumps, and centrifuges. 4. No make up or belt cleaning water required.

5. Modular design, which can be trailer mounted.

6. Low Energy Consumption.

7. Recycled heat. 8. Low maintenance (minimal moving parts).

9. Accelerated drying time.

10. Closed loop system.

11. Pelletized product could be recycled as fuel (especially in a cement kiln) or organic fertilizer. While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations in the preferred devices and methods may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the claims that follow.

Claims

What is claimed:

1. An apparatus adapted for processing sewage sludge comprising: (a) a dewatering unit for producing a sludge cake from a sludge, the dewatering unit comprising at least one screen for filtering a sludge to collect a solids-enriched fraction on the screen; and

(b) a vibrator for vibrating the screen(s), wherein the vibrator can be operated to vibrate the screen(s) with a vibratory frequency and amplitude effective, without any assist from gas flow through the screen, to maintain substantially all screen-applied sludge in constant motion.

2. The sludge processing apparatus of claim 1 , wherein the vibrator can be operated to vibrate the screen(s) so as to move the materials applied thereto in a spiral pattern.

3. The sludge processing apparatus of claim 1 , wherein the screen has a pore size of from about 270 mesh to about 70 mesh.

4. The sludge processing apparatus of claim 1 , further comprising a first collection device for collecting material at an edge of a said screen and for directing said collected material to a second said screen for further dewatering.

5. The sludge processing apparatus of claim 1 , further comprising:

(c) a dryer unit into which sludge cake produced by the dewatering unit is transferred and further dried.

6. An apparatus adapted for processing sludge comprising: (a) a dewatering unit for producing a sludge cake from a sludge, the dewatering unit comprising at least one screen for filtering a sludge to collect a solids-enriched fraction on the screen;

(b) a first vibrator for vibrating one or more decks; and (c) a dryer unit into which sludge cake produced by the dewatering unit is transferred and further dried, which dryer unit comprises: (d ) at least one deck;

(c2) a source of drying gas flow through the dryer unit; and (c3) a second vibrator for vibrating one or more decks.

7. The sludge processing apparatus of claim 6, wherein the second vibrator can be operated to vibrate one or more decks with a vibratory frequency and amplitude effective to maintain substantially all deck-applied sludge cake in constant motion.

8. The sludge processing apparatus of claim 6, wherein each deck is a screen.

9. The sludge processing apparatus of claim 6, wherein the dryer unit has at least two said decks on which sludge cake-derived material is sequentially dried.

10. The sludge processing apparatus of claim 6, wherein the at least one deck lacks pores.

11. The sludge processing apparatus of claim 10, further comprising:

(d) a heater for heating the drying gas for the source of drying gas to a temperature from about 300^βF to about 500?" F.

12. The sludge processing apparatus of claim 6, further comprising:

(e) a conveyor for conveying sludge cake from the dewatering unit into the dryer unit; and (f) an output processing unit for dividing the dryer unit output into an output fraction and a recycle fraction and relaying the recycle fraction into the conveyer.

13. The sludge processing apparatus of claim 6, further comprising:

(g) a grinding apparatus for grinding a fuel fraction of an output from the dryer unit to a more readily combustible size distribution.

14. The sludge processing apparatus of claim 6, further comprising:

(h) a heat recovery unit for (i) recovering heat from the drying gas from the source of drying gas after that drying gas exits the dryer unit, and (ii) transferring said recovered heat into drying gas for said source of drying gas prior to the introduction of that drying gas into the dryer unit.

15. A method of processing sludge comprising:

(a) applying a sludge to at least one screen; and

(b) vibrating the screen(s) to collect a solids-enriched material on the at least one screen, wherein the screen(s) are vibrated with a vibratory frequency and amplitude effective, without any assist from gas flow through the screen, to maintain substantially all screen-applied sludge in constant motion.

16. The method of claim 15, comprising: (a') applying the sludge to about the center of a said screen; (b') vibrating the screen, or of the unit as a whole, such that material applied to that screen moves towards an edge of that screen; and

(c) collecting a solids-enriched fraction from said edge.

17. The method of claim 16, further comprising:

(d) a drying step in which the solids-enriched material is further dried.

18. The method of processing sludge comprising: (a) applying a sludge to at least one screen;

(b) vibrating the screen to which the sludge is applied;

(c) collecting a solid-enriched, sludge-derived material from the screen;

(d) further drying the solids-enriched material by: (d1) applying the solids-enriched material to at least one deck;

(d2) applying an drying gas flow for drying the material applied to the decks; and

(d3) vibrating each deck while solids-enriched material is being dried by said drying gas.

19. The method of claim 18, further comprising:

(e) recovering a granularized product resulting from the drying step (d).

20. The method of claim 18, wherein the solids-enriched material is sequentially dried on at least three said decks.

21. The method of claim 18, wherein the applied drying gas is preheated to a temperature from about 300^βF to about 500^βF.

22. The method of claim 18, further comprising:

(f) dividing the output of step (d) into an output fraction and a recycle fraction; and

(g) relaying the recycle fraction into the solids-enriched material applied to step (d).

23. The method of claim 22, wherein about 25% to about 75% of the output from step (d) is used as the recycle fraction.

24. A drying device adapted for drying sludge cake comprising:

(a) a chamber with at least one deck;

(b) a vibrator for vibrating one or more decks; and

(c) a source of drying gas flow for drying sludge cake applied to the decks.

25. The sludge cake drying device of claim 24, wherein the drying device has at least two said decks on which sludge cake-derived material is sequentially dried.

26. The sludge cake drying device of claim 24,

(f) a heater for heating the drying gas of the sources of drying gas to a temperature from about 300^βF to about 500^βF.

27. The sludge cake drying device of claim 24, further comprising:

(g) a conveyor for conveying sludge cake into the chamber; and

(h) an output processing unit for dividing material that is processed through the chamber into an output fraction and a recycle fraction and relaying the recycle fraction to the conveyor.

28. A method of drying sludge cake comprising:

(a) applying the sludge cake to at least one deck;

(b) applying an drying gas flow to dry the sludge cake applied to the deck(s); and (c) vibrating each deck.

29. The method of claim 28, further comprising:

(a') applying the sludge cake to about the center of a said deck; and (c') vibrating that deck, or of the unit as a whole, such that material applied to that deck moves towards an edge of that deck; and

(d) collecting material from said edge.

30. The method of claim 29, further comprising: (e) transferring the collected material for further drying on a second said deck.

31. The method of claim 30, wherein the sludge cake is sequentially dried on at least three said decks.

32. The method of claim 29, further comprising:

(f) dividing the output from drying on a said deck into an output fraction and a recycle fraction and relaying the recycle fraction into sludge cake applied to step (a¹).

33. The method of claim 28, wherein the at least one deck is vibrated with a frequency and amplitude effective to maintain substantially all of the solids applied thereon in constant motion.

34. A sludge drying apparatus comprising: (a) an airlock input device for inserting a sludge or sludge cake,

(b) a nozzle, and

(c) a blower for providing a motive gas to push the sludge or sludge cake inserted via the airlock device through the nozzle

35 A method of drying a sludge or sludge cake comprising ejecting a sludge or sludge cake through an apparatus of claim 34

36 The method of claim 35, wherein the sludge or sludge cake is ejected (i) into a vacuum chamber, (n) into a chamber through which a drying gas is circulated, or (in) onto a heated plate