IES20060487A2 - A waste treatment system - Google Patents

Abstract

Waste material having a solids content of less than about 22% is treated by first directing waste having a solids content of less than 22% into an infeed tank. Waste from the infeed tank is delivered into a holding tank and then onto a conveyor. Waste on the conveyor is exposed to microwaves and heat is applied to the waste on the conveyor to evaporate moisture. The dried waste is discharged from the heater into a trailer for onward transportation. <Figure I)

Description

The invention relates to a method an apparatus for treating sludge-type waste material having a solids content of from 6% to 25%.

Large quantities of sludge with low levels of solids present major treatment and disposal problems for a wide range of industries and public authorities. Various treatment systems are used, however in general these are either very costly or do not efficiently and effectively deal with the waste material.

This invention is directed towards providing an improved method and apparatus to effectively and efficiently treat such waste materials.

Statements of Invention According to the invention there is provided a method for treating waste material having 20 a solids content of less than about 22% comprising the steps of: directing waste having a solids content of less than 22% into an infeed tank; conveying the waste in the tank to an outlet from the infeed tank; conveying the waste from the outlet of the infeed tank to a feed hopper; delivering the waste from the feed hopper onto a conveyor; IE 0 6 0 4 8 7 -2exposing the waste on the conveyor to microwaves; applying heat to the waste on the conveyor to evaporate moisture; collecting the evaporated moisture; filtering the evaporated moisture; and discharging the dried waste.

In one embodiment the waste has a solids content of at least 10%. Usually the waste has a solids content of about 15%.

In one embodiment the waste is directed from a trailer into the infeed tank. Preferably the waste is directed from a trailer by gravity into the infeed tank.

In one embodiment the method comprises coarse filtering the waste prior to delivery into the infeed tank.

The waste in the infeed tank may be conveyed to the infeed tank outlet by a screw conveyor. The waste in the infeed tank may be conveyed to the infeed tank outlet by a plurality of screw conveyors.

In one embodiment the waste from the outlet of the infeed tank is conveyed to the feed hopper by a screw conveyor.

The method may comprise spreading the waste across the conveyor for exposure to microwaves. In one arrangement the conveyor comprises an infeed conveyor and a main conveyor and the method comprises spreading the waste across the infeed conveyor. -3ln one embodiment the method comprises the step of in-line cleaning the conveyor after discharge of dried waste. The conveyor is preferably cleaned by leading the conveyor over a brush means. ln one embodiment the evaporated moisture is passed through a filtration bed. The method preferably comprises collecting condensate from the filtration bed and treating the collected condensate. In one arrangement the filtration bed is supported on a mesh floor through which evaporated moisture is led.

In one embodiment dried waste is discharged into a trailer. Dried waste may be discharged directly from the heater into a trailer.

In another aspect the waste has a solids content of less than 15% and the method comprises the steps of:15 delivering the waste into a separator; and separating the proportion of the moisture from the waste to increase the solids content of the waste prior to delivery into the infeed tank.

In this case the solids content of the waste from the separator may be at least 18%. Waste may be delivered to the separator from a tanker. In one case waste is delivered directly from the tanker into the separator.

In a further aspect the invention provides a waste treatment system for treating waste material with a solids content of less than about 22% comprising:an infeed tank for waste having a solids content of less than 22%, the infeed tank having an inlet and inlet feed conveying means for conveying waste to an outlet of the tank; IE 06048 7 -4a feed hopper: waste conveying means for conveying waste from the infeed tank outlet to the feed hopper; delivery means for delivering waste from the feed hopper to a conveyor; microwave means for exposing waste on the conveyor to microwaves; heating means for heating the microwaved waste; filtration means for filtering evaporated moisture removed from the waste; and discharge means for discharge of dried waste. ln one embodiment the inlet feed conveying means comprises a screw conveyor. The inlet feed screw conveyor may be located at a base of the tank for delivery of waste to the outlet of the infeed tank.

In one embodiment the inlet feed conveying means comprises a plurality of screw conveyors.

In one embodiment the infeed tank comprises a base, sidewall means extending upwardly from the base, and a top defining a waste inlet opening which is closable by a lid. The sidewall means adjacent the top opening is preferably sloped to direct waste to the base of the infeed tank.

In one embodiment a coarse filter is provided at the infeed tank inlet.

IE 06 0 4 8 7 -5The system may comprise ram means for operating the !id and interlock means to prevent unauthorised opening of the lid.

In one embodiment the base is sloped upwardly from the inlet end to the outlet from the infeed tank.

The invention also provides an infeed tank for a waste treatment plant, the infeed tank having at least some of the features herein described.

The invention also provides dried waste when treated by a method of the invention.

Brief Description of the Drawings The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, in which: Fig. 1 is a plan view of a waste treatment system according to the invention; Fig. 2 is a side cross sectional view of an infeed tank used in the system of the invention; Fig. 3 is a top plan view of portion of the infeed tank of Fig. 2; Fig. 4 is a perspective view of portion of the inlet of the infeed tank; Fig. 5 is a perspective view of waste being delivered to a conveyor for exposure to microwaves; IE 06 0 4 8 7 -6Fig. 6 is a perspective view illustrating the cleaning of the microwave conveyor belt; Fig. 7 is a perspective view illustrating the discharge of dried waste; and Fig. 8 is a perspective view of an evaporated moisture treatment unit used in the system of the invention.

Detailed Description Referring to the drawings and initially to Fig. 1 there is illustrated a system I and method for treating waste material with a high moisture content. The solids content of the waste sludge is typically less than 22% and may be as low as 6%.

In the case of waste with a solids content of typically 15% to 22% the waste is delivered to the treatment facility by a trailer 2 which discharges the waste into an infeed tank 3. Dried waste material treated by the system and method of the invention is preferably discharged directly into an outfeed trailer 4 to be transported to a disposal or further treatment location. The system 1 ensures that the waste is quickly and efficiently handled and treated and is processed without a requirement for storage facilities at the treatment location.

The waste is processed by first treatment in multiple stages with microwaves which kill substantially all pathogens and the waste is then dried in a direct heater 10 prior to discharge directly into the output trailer 4. Steam generated in the microwave and drying stages is directed to a separation and filtration unit 15.

Referring to Fig. 2, the infeed tank 3 a large capacity tank (about 45 tons) and is generally retilinear in plan view and comprises a base 20 and side walls which define a top at the upper edge thereof. The top has a sludge inlet 22 closable by a ram operated lid IE 0 6 0 4 8 7 -723. An interlock is provided to prevent unauthorised opening of the lid such as by operation of the ram. Sludge is delivered into the infeed tank 3 in the direction of the arrows from a tipper trailer 2. The tank 3 is below ground level so that the truck 2 can reverse up to the top of the tank and, an opening of the lid 23, deliver sludge into the tank 3. The sludge inlet 22 is covered by a coarse filter 21 to ensure that no debris enters the infeed tank 3. The side wall 25 closest to the sludge inlet 23 is sloped to ensure free flow of sludge to the base of the tank 3. The base 20 is sloped upwardly from the inlet end towards the outlet 28. Six discharge screw conveyors 27 are located at the bottom of the tank 3 to deliver the sludge to a discharge outlet 28 from which the sludge is delivered on demand by another series of screws 29a, 29b, 29c to an intermediate feed hopper 30 from which the sludge is delivered to the treatment system.

Waste from the feed hopper 30 is delivered onto an infeed conveyor belt 31 by a screw conveyor 32. The waste is spread evenly across the infeed conveyor belt 31 which delivers the waste onto a main conveyor belt 33. The waste on the conveyor 33 is led through multiple, in this case six, microwave treatments 35. A microwave treatment system is described in detail in US 6,618,957. The microwaves subject the waste material to high frequency radio waves in the ultra high frequency band. The pathogens and polar water molecules in the waste material attempt to align themselves with the oscillating electric field at a frequency of 915 MHz. However, the pathogens or molecules within the pathogens cannot align themselves synchronously with a resultant atmosphere of excitement which causes the pathogens to explode structurally. Water molecules attached to the pathogens are released in the form of water vapour into a heated chamber.

After microwave treatment as described, the conveyor 33 delivers waste to the direct heating station 10 at which heat is directed to the waste to dry the waste.

IE 0 6 0 4 8 7 -8The main conveyor 33 is in the form of a belt comprising a number of interlinked sections for ease and economic replacement. After discharge of dried waste the belt is cleaned by passing it over brushes 50 [Fig. 6], Referring in particular to Fig. 8. there is illustrated the separation and filtration unit 15 used in the waste treatment system of the invention. Steam generated during the treatment process is collected and delivered by a delivery pipe 55 to the bottom of the filtration unit 15. A filtration medium in the form of a bed of activated carbon is supported on a mesh floor (not shown) above a lower steam inlet 56. Condensate is collected for further treatment.

In the case of sludge with a solids content of 6% to 15%, the sludge is delivered by a pump directly from a tanker into a pre-treatment separator which may be in the form of a decanter or centrifuge. The separator processes the sludge to increase the solids content to above 15%, typically from 16% to 22%. The pre-treated waste is discharged from the separator onto a conveyor which delivers the waste into the infeed tank 3.

The invention provides a waste treatment system and method which is highly efficient at killing pathogens and drying the waste. The system is capable of handling waste with a wide range of solids content and the resultant waste is substantially free from pathogens and is dried to typically an 80% solids content. Incoming untreated waste and outgoing treatment waste is quickly and efficiently received and discharged, respectively so that on-site storage is minimised.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims (2)

1. A method for treating waste material having a solids content of less than about 22% comprising the steps of:directing waste having a solids content of less than 22% into an infeed tank; conveying the waste in the tank to an outlet from the infeed tank; conveying the waste from the outlet of the infeed tank to a feed hopper; delivering the waste from the feed hopper onto a conveyor; exposing the waste on the conveyor to microwaves; applying heat to the waste on the conveyor to evaporate moisture; collecting the evaporated moisture; filtering the evaporated moisture; and discharging the dried waste.

2. A method as claimed in any preceding claim wherein the waste is directed from a trailer into the infeed tank, preferably the waste is directed from a trailer by gravity into the infeed tank, the method may comprise coarse filtering the waste prior to delivery into the infeed tank. IE 06 0 4 8 7 -10A method as claimed in any of claims 1 to 2 wherein the waste in the infeed tank is conveyed to the infeed tank outlet by a screw conveyor, preferably the waste in the infeed tank is conveyed to the infeed tank outlet by a plurality of screw conveyors, the waste from the outlet of the infeed tank may be conveyed to the feed hopper by a screw conveyor. A method as claimed in any preceding claim comprising spreading the waste across the conveyor for exposure to microwaves, the conveyor may comprise an infeed conveyor and a main conveyor and the method comprises spreading the waste across the infeed conveyor, the method may also comprise the step of inline cleaning the conveyor after discharge of dried waste, the conveyor may be cleaned by leading the conveyor over a brush means. A method as claimed in any preceding claim wherein the evaporated moisture is passed through a filtration bed and the method may comprise collecting condensate from the filtration bed and treating the collected condensate, the filtration bed may be supported on a mesh floor through which evaporated moisture is ted.