Waste treatment apparatus and method

Abstract

In apparatus and method for waste treatment by pyrolysis, treated waste is flushed through a grid (18) to trap recyclable material in the pyrolysis chamber (24). Pyrolysis is carried out at a temperature of from 400-700° C. and off-gases are dissolved in a solution in scrubber (13) for disposal in a water course. Water is introduced into the chamber as superheated steam via pipes (5) so as both to flush away treated material and clean the chamber. Recyclable waste is separated from non-recyclable by treating non-recyclable waste by pyrolysis, and flushing treated non-recyclable waste away through liquid exhaust (8). Apparatus is made as a modular, free-standing unit and comprises plugs for connection to an electricity supply, to a water supply, and to a sewerage system (16) and has a chamber with a volume in the range 0.01-0.5 m.sup.3.

Claims

1. A process for waste treatment comprising: introducing waste into a chamber; heating the waste to an elevated temperature to effect pyrolysis of the waste, then as the next step; introducing oxygen into the chamber to effect combustion of the waste; after combustion is completed, admitting water and/or steam in pulses into the chamber to cool the chamber, and flushing the combusted waste from the cooled chamber with water; wherein the temperature to effect pyrolysis is from 400-700° C. and the temperature to effect combustion is at least 400° C.

2. A process according to claim 1, wherein the temperature to effect pyrolysis is from 500-600° C.

3. A process according to claim 1, comprising holding the waste at the elevated temperature until 50% or more of the waste is degraded by pyrolysis.

4. A process according to claim 1, wherein the temperature to effect combustion is at least 450° C.

5. A process according to claim 1, wherein the temperature to effect combustion is at least 500° C.

6. A process according to claim 1, wherein the temperature to effect combustion is not more than 800° C.

7. A process according to claim 1, wherein the combusted waste is flushed through a grid to trap recyclable material.

8. A process according to claim 7, wherein the grid is moveable, and the method comprises moving the grid between a first position in which the grid traps the recyclable material and a second position in which the recyclable material can be transferred into a receptacle.

9. A process according to claim 1, comprising flushing the combusted waste from the chamber into a sewage system.

10. A process according to claim 1, wherein the maximum volume of the chamber is 0.5 m.sup.3.

11. A process according to claim 1, wherein waste gases produced during the process are passed through a wet scrubber.

12. A process according to claim 1, wherein waste gases produced during the process are passed through an aqueous agitation system.

13. A pyrolysis and combustion apparatus, comprising: a sealable chamber; a waste treatment zone in the chamber; a port for introducing waste into the chamber; a port for the exit of treated waste; a heating element; an injector for cooling the chamber using water and/or steam injected in pulses; a port for admitting water to flush the chamber; and a control system configured to carry out a process according to claim 1.

14. An apparatus according to claim 13, wherein the chamber comprises an output for connection to a sewer so that the treated waste can be flushed into the sewage system.

15. An apparatus according to claim 13, further comprising a tank to contain a gas treatment solution, an exhaust port for exit of gases from the chamber and a conduit arranged in combination with the tank and the exhaust port to contact the gases with the solution.

16. An apparatus according to claim 13, further comprising a grid between the waste treatment zone and the exit port.

17. An apparatus according to claim 13, wherein the maximum volume of the chamber is 0.5 m.sup.3.

18. An apparatus according to claim 13, wherein waste gases produced during the process are passed through at least one of a wet scrubber and an aqueous agitation system.

19. A process for waste treatment comprising: introducing waste into a chamber, wherein the maximum volume of the chamber is 0.5 m.sup.3, heating the waste to an elevated temperature to effect pyrolysis of the waste, then as the next step introducing oxygen into the chamber to effect combustion of the waste, after combustion is completed, admitting water and/or steam in pulses into the chamber to cool the chamber, and flushing the combusted waste from the chamber with water.

20. A pyrolysis and combustion apparatus, comprising: a sealable chamber, wherein the maximum volume of the chamber is 0.5 m.sup.3, a waste treatment zone in the chamber, a port for introducing waste into the chamber, a port for the exit of treated waste, a heating element, means for cooling the chamber using water and/or steam injected into the chamber in pulses; means for admitting water to flush the chamber; and a control system configured to carry out a process according to claim 1.

Description

(1) The invention is now illustrated in the following specific embodiment with reference to the accompanying drawings in which:—

(2) FIG. 1 shows a schematic cross-sectional view of a pyrolysis apparatus; and

(3) FIG. 2 shows schematic isometric view of the apparatus.

(4) Referring to the drawings, a pyrolysis apparatus has the following features:—

PARTS LIST AND KEY

(5) 1. Storage Chute 2. Loading Door Mechanism 3. Loading Door 4. Lid 5. Air/water tubes 6. Heating Plates 7. Access Drawer 8. Chamber Exhaust (liquid) 9. Gas Exhaust Control Valve 10. Gas Cooling Radiator 11. Liquid Bleed Valve 12. Liquid Exhaust Control Valve 13. Wet Scrubber 14. Filtration System 15. Filtration Return-Protection Valve 16. Exit to Foul Water 17. Cage 18. Mesh 19. Treatment zone 20. Hinges 21. Exit Port for Liquid 22. Exit Port for Gas 23. Access Door to Cage 24. Chamber 25. Sealing Plate Loading Sensor (not shown) Seals (not shown) Lid Cooler (not shown) Insulation for chamber (not shown) Water Jacket on Chamber (not shown) Air Compressor (not shown) Air tank (not shown) Water Pump (not shown) Water Header Tank (not shown) Gas Flare (not shown)
Main Components:
Heating Chamber

(6) The chamber (24) is manufactured from stainless steel (Austenitic Chromium-Nickel Steel) grade 316. Other materials, e.g. titanium, can be used. The weld material used in fabrication retains the corrosion resistant properties of the main body of the chamber. The chamber is resilient to the frequent heating/cooling cycles, and the material requires a heat treatment and finishing process within its manufacture.

(7) The chamber has dimensions of 450×450×700 mm, with a wall thickness of 1.5 mm (the walls can also be up to 4 mm thick). On the top face of the chamber is a flat sealing plate (25) which is ground to a flat surface (+/−0.1 mm max) across the top surface. The chamber also features two outlets, an exit port (21) leading to an exhaust (8) at the base for liquid waste (approx 60 mm dia) and an exit port or outlet (22) at the top of one of the sides for the gas and vapour (approx 38 mm dia).

(8) Lid

(9) The lid (4) is manufactured from a similar material as the heating chamber, although it is manufactured from a flat plate. The surface is finished so the lid and chamber form a critical sealing surface. The lid is also reinforced on its rear to avoid any warping or distortion due to repetitive heating and cooling cycles. The lid is designed to be as robust as possible. The lid houses the hinge mechanism (20) on its rear and gives a mating surface for sealing on its underside. The lid also contains the seals (discussed below). The lid features an integrated water cooling surface (not shown) which runs around the rim of the lid, directly above the seals. This prolongs the product life cycle.

(10) Seals

(11) PTFE coated silicone rubber seals (not shown) are used to seal any non-permanent mating faces, such as the chamber lid and access drawer. All other mating surfaces feature a soft metal gasket arrangement.

(12) Access Drawer

(13) The drawer (7) is used to remove any incompatible materials that have not been decomposed by the process. The drawer features a water cooling circuit (not shown) similar to the lid that is used to cool the mating surfaces of the seat. The working surface of the drawer is a fine mesh (18) of a 3 mm aperture (up to a 5 mm aperture can also be used) which allows movement of solids, liquids and gases in the system. The drawer also features a sensor that informs the operator that the drawer has reached a certain predetermined capacity, and requires emptying.

(14) Heating Elements

(15) Flat plate heaters (6) are used on all four vertical sides of the chamber. The heaters are assembled to give maximum contact with the outside of the chamber.

(16) Air/Water Tubes

(17) The tubes (5) are used to pass water and air around the outer surfaces of the chamber. This is performed to preheat the waste prior to direct injection of the superheated air and steam at the latter phases of the process. The tubes are manufactured from Stainless Steel material (Inconel™ material can also be used), of 5 mm diameter.

(18) Heat Insulation

(19) On the outside of the heaters are many efficient insulating layers (not shown) which work to both reflect heat back into the chamber and reduce heat emissions to the outer surfaces of the assembly. This insulation ensures that all heating energy is used in a useful way to directly heat the waste product.

(20) On the underside of the lid is a layer of ceramic plate (not shown) (5 mm thick) which is bonded onto the stainless steel lid. This reduces external heat loss and increases the product lifespan of seals etc.

(21) Cooling Radiator

(22) The radiator's primary function is to cool the gas which has been emitted from the product, prior to any filtration. The cooling prolongs the life and retains maximum efficiency of the filtration equipment.

(23) The radiator (10) consists of a 38 mm tube (or same diameter as the chamber gas exhaust), which is bent in 2 axes. Fine horizontal fins are welded to the outside of the tube to increase heat loss of the passing gases. This reduces the exhaust gases from temperatures in the region of 600° C. down to 200° C. or below.

(24) Wet Scrubber

(25) The wet scrubber (13) is placed after the gas radiator in the system and removes particulate matter from the passing gases and dissolves gases in the scrubbing liquid for disposal subsequently. Inside the scrubbing device is a series of stacked jets producing a very fine mist of water. The mist attracts particulates to the outer surfaces of the mist droplets, and these are ‘pulled out’ of the gas flow and into the liquid waste stream. Within the scrubber is a series of openings which guide the flow of the waste gases directly past the mist jets.

(26) Purification Systems

(27) A ceramic filter (14) is preferably used. This cleans the exhaust gases prior to release to the foul water system. The filter screws onto a fixed manifold having a rubber seal which mates onto the manifold. Gases pass into the centre of the filter via a tube with an external thread which secures the filter to the manifold. The gases pass through the porous membrane of the filter and through to the return tube in the manifold. In normal use, the filter is replaced approximately every year. In alternative embodiments an actived carbon filter is used, this is replaced approximately every 90 days.

(28) Waste Gas Flare

(29) After the purification systems there is optionally a small gas flare outlet to burn off any flammable gas by-products from the waste. The flare is sited and specified so that it does not compromise safe and secure operation of the unit. However, in preferred embodiments a waste gas flare is not required due to the combination of low processing temperatures and gas cleaning systems.

(30) Other Key Components:

(31) Loading Chute

(32) The chute (1) is fabricated from a corrosion resistant material. It has a storage capacity less than the chamber, eliminating the possibility of overloading.

(33) There is a sensor (not shown) within the chamber which records the level that the waste has been loaded to, and when this level has been reached a separate solenoid/mechanism arrangement (not shown) locks off access to the system via the external chute. The chute also features an access door (not shown) which allows an operator to manually load the system on demand.

(34) Cage

(35) The system is housed within a cage (17). The framework has castors (not shown) to allow the unit to be removed easily due to a breakdown etc. The cage also has fixed outlets (not shown) for all services needed—foul water, fresh water and 3 phase (single phase may be used if feasible) electricity. Services are simply plugged in and are easily disconnected.

(36) There is a lockable front access door (23) which allows an operator to perform basic maintenance tasks. The cage also protects equipment from vandalism.

(37) Chamber Water Jacket

(38) On the outside of the chamber and lid insulation there is a water jacket (not shown). This ensures that the insulation and chamber do not overheat and it gives the system the ability to cool rapidly on demand.

(39) Control Electronics

(40) A programmable logic controller (PLC) (not shown) controls the operation of the system, and monitor sensors (not shown) that are positioned throughout most mechanisms and active components within the system. All electronics are housed within a weatherproof enclosure (not shown), and positioned at a low point in the cage.

(41) Air Compressor

(42) An air compressor (not shown) is used to run the pneumatic cylinders (not shown) that open and close the lid and chute door and to provide air to be injected for combustion. The compressor is also used in transporting air through the tubes on the outside of the chamber for the air injection phase in the cycle. The compressor feeds a reservoir tank (not shown) which allows the system to have a certain capacity of stored air. This means that the compressor is not constantly running, which improves the life cycle of the unit. The compressor is also housed in a sealed enclosure (not shown) to ensure low noise emissions.

(43) Water Pump

(44) A pump is used to move water from a header tank and around the system, feeding components such as the cooling circuit, water jacket and the water injection feed into the heating chamber (24).

(45) Valves

(46) A network of high spec valves (9, 11, 12, 15) is used to control and throttle the flow of liquid and gas between the chamber, exhaust, radiator, wet scrubber and purification systems and to enable periodic change of water in the scrubber. These are controlled remotely by the programmable logic controller.

(47) Process Cycle

(48) 1. Loading of Waste

(49) The chamber lid is opened and the waste enters the chamber (which is at ambient temperature) via the storage chute. The lid is then closed and the chamber is sealed.

(50) 2. Heating

(51) The panel heaters are activated and the interior temperature is raised to between 500-550° C. The liquid exhaust valve is closed and the emitted gases during the heating phase are passed through the cooling and purification system.

(52) The temperature ramping period takes approximately 5-10 minutes, after which time the temperature is maintained via a thermostat. Due to the efficiency of the chamber insulation the power applied to the heaters is throttled to maintain the interior chamber temperature.

(53) The gases produced by the waste are monitored and the moisture in the waste is emitted as a vapour and passed to the exhaust. The mass of a full load of typical waste reduces by approximately 70%.

(54) The temperature is held for approximately 30 minutes.

(55) 3. Air Injection (Also Known as the Combustion Phase)

(56) After the heating phase has completed the external panel heaters are turned off and air is passed through the tubes around the outside of the chamber (which preheats the air to a superheated temperatures) and injected into the top of the chamber. The injectors are such that the air is sprayed as a widely dispersed stream, as opposed to a concentrated jet. The air is initially pulsed to reduce stress in the system, and after a certain period the air is injected constantly.

(57) The flow rate of the air is kept to around 50 l/min (rates of from 25 to 100 i/min, and also outside these ranges may be used, depending on system size and configuration). This low rate is maintained to ensure that internal pressure levels within the chamber are not increased too rapidly, as this will compromise the effectiveness of the seals.

(58) With the introduction of air, the waste begins to glow. The volume of the waste decreases further, typically reaching around 5% of its original volume. The waste is converted to a very fine ash.

(59) Smoke and particulate levels in the system increase during the air injection phase. All gaseous exhausts are passed through the wet scrubber and through the purification system. The combustion phase lasts approximately 15 minutes.

(60) 6. Steam Injection

(61) When the combustion phase has completed the air injection is turned off, the gas exhaust valve is closed, the liquid exhaust valve is opened and water flows through the same tubes as the air, around the outside of the chamber and is injected as superheated steam. The steam is initially injected in a series of pulses, then as a constant stream. The pulses are 1 second on, 3 seconds off for 30 pulses, then continuously on for 3 minutes. The water is injected at approximately 2 l/min.

(62) The steam both flushes the ash out through to the exhaust, and cleans the internal faces of the chamber. The steam has a cooling effect on the chamber, and after approximately 1 minute the internal temperature of the chamber drops to below 100° C. After the steam injection has completed the lid opens and the system is ready for its next cycle. Any incompatible waste that has not been decomposed by the cycle is held in the drawer, and can be removed and recycled.

EXAMPLE 1

(63) Apparatus of the invention was tested for its ability to treat domestic waste whilst ensuring that gas and water emissions did not exceed the limits imposed by environmental legislation.

(64) A mixed bag of waste was prepared, based on analysis of typical breakdown of domestic waste, containing 100 g garden waste, 100 g paper and cardboard, 200 g PVC, 300 g meat by-products and table salt and 100 g polyester, making a total weight of 800 g mixed waste.

(65) This mixed waste was treated in apparatus of the invention using parameters determined to provide waste destruction in a relatively short period of time, these parameters being a pyrolysis temperature of 550° C. for 75 minutes followed by combustion with an air flow of from 40-50 liters/min for 15 minutes followed by steam injection to wash the ash residue into the water collection tank (the tank being used in the emissions test instead of a sewer connection).

(66) This treatment was found to destroy all of the mixed waste, i.e. convert it all to ash which was flushed from the chamber with the steam/water.

(67) Testing of the off-gases gave the following results:—

(68) TABLE-US-00001 TABLE 1 Off-gas data NO (NOx) SOx HCL mg/m.sup.3 mg/m.sup.3 mg/m.sup.3 Ex. 1 6 185 <47 Limit stipulated by 400 200 60 environmental legislation

(69) Separately, the wet scrubber water, to be discharged to the sewer in normal operation, was tested for levels of heavy metals and dioxins with the following results:—

(70) TABLE-US-00002 TABLE 2 Off-water Data Thallium Mercury Arsenic Cadmium Chromium Lead Nickel Dioxins Ex. 1 0.002 0.04 38.5 1.4 25.7 125 127 0.01 Limit stipulated by 0.05 0.03 150 50 500 200 500 0.3 environmental legislation

(71) Hence, the off-gases and the off-water were inside the emissions limits stipulated in the environmental legislation.

(72) The invention hence provides treatment of waste by pyrolysis and apparatus for doing so.