GB2141732A

GB2141732A - Method and apparatus for gas production

Info

Publication number: GB2141732A
Application number: GB08315342A
Authority: GB
Inventors: David Charles Pike; Peter H Prior
Original assignee: SUMMERLEAZE GRAVEL CO Ltd
Current assignee: SUMMERLEAZE GRAVEL CO Ltd
Priority date: 1983-06-03
Filing date: 1983-06-03
Publication date: 1985-01-03
Also published as: GB8315342D0; GB2141732B

Abstract

Methane is produced from a domestic waste tip (10) by spraying the tip (10) with water and collecting the resultant leachate from the bottom of the tip. The leachate is pumped up through a heater (30) by a pump (26) and then fed to an anaerobic reactor (28) where bacteriological reaction produces methane gas. The treated leachate is cooled and returned to the tip for recycling. The cooled leachate in turn cools the waste and so inhibits the formation of gas from the tip itself. Gas can thus be produced and collected in a controlled manner. <IMAGE>

Description

SPECIFICATION Methane production The present invention relates to the production of methane, and is particularly applicable to the production of methane from domestic waste landfills or tips.

An established (i.e. 1-2 years old) open domestic waste tip will produce a liquid called leachate which is produced as a result of rainfall impinging on the tip and of bacterial action on the waste. The leachate consists of aqueous solutions (95% water) of volatile acids which are subsequently attacked by bacteria to produce methane. Both the production of leachate and methane are dependent upon the temperature of the tip; if the tip is below 7-1 5'C the reactions will cease and if above 45"C the bacteria will be killed.

There have been earlier schemes to collect the methane generated from domestic waste tips and to use it for industrial heating purposes; such schemes have the disadvantage that the methane is produced at widely varying and uncontrollable rates, due to variations in rainfall amounts, temperature of the tip, and leachate extraction from the tip, and therefore does not equate to the energy demand at any one time.

It is an aim of the invention to provide an improved method of methane production from domestic waste tips, in which the methane is produced at a controlled and determined rate.

According to the present invention, the improved method includes the steps of cooling the waste contents of the tip to reduce or prevent the formation of methane therein, extracting leachate from the tip, and generating methane from the leachate.

Conveniently the methane is produced by heating the extracted leachate in an upflow anaerobic sludge blanket reactor, surplus leachate being cooled before being returned to the tip.

The heating and cooling of the leachate may take place in a heat pump.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic view of apparatus for carrying out the method of the invention to produce methane in a controlled manner from a domestic waste tip.

Referring to the drawing, there is shown a domestic waste landfill or tip 10 which may be partly covered by a waterproof sheet 1 2 to control the amount of rainfall impinging on the waste contents of the tip, excess clean rain water being directed to a sump 1 4 where it is pumped by pump 1 6 to a water course 18; clean rain water is also collected in interceptor channels 20 provided in the side walls 22 of the tip.

At the base of the tip is a layer 24 of gravel which acts as a sump to collect leachate produced by the tip. From this layer leachate is pumped by pump 26 to an upflow anaerobic sludge blanket (UASB) reactor 28 which operates at a warm temperature (say 35"C) to produce from the leachate methane gas in a controlled chemical reaction analogous to the production of carbon dioxide during the anaerobic fermention of sugars by yeast during the production of ethyl alcohol. To increase the temperature of the leachate from say 1 5 C (the temperature on leaving the tip) to a temperature of 35"C (required by the reactor), the leachate is passed through a heat pump 30. Methane produced by the reactor is directed by outlet pipe 32 to industrial users of the methane.To allow for the case where the required temperature increase is beyond the capacity of the heat pump, a methane burner 34 may be provided which is supplied with methane from branch line 36 of pipe 32 and which supplies additional heat to the leachate.

A valve 38 may also be required in outlet pipe 32 in accordance with local authority requirements to permit the exhaust of surplus methane gas from the reactor.

Effluent (treated leachate) leaving the reactor is directed back through the heat pump 30 where it is cooled (down to say 5"C) before being sprayed back onto the waste contents via pipe 39 to control the temperature of the tip. By keeping the tip at a sufficiently low temperature, the production of methane within the tip can be prevented or at least substantially reduced. If additional cooling fluid is required, a bypass circuit 40 may be required to bypass some of the leachate from a point upstream of the reactor direct to the heat pump, thereby increasing the flow of cooled effluent back to the tip. In the event of excess leachate being produced, pipe 39 is provided with a valved branch 42 to enable the excess to be directed to a sewer.

Operation of the heat pump is expected to produce surplus heat, and this heat could be used locally to heat for example greenhouses etc.

It will be apparent that the above described method permits the production of methane gas from a domestic waste tip at a controlled rate to suit the users demand for the gas. In the absence of demand, or in the event of low demand, excess methane produced by the reactor may be liquified and stored for future use.

1. A method of methane production comprising the steps of cooling the waste contents of a waste tip to reduce or prevent the formation of methane therein, extracting leachate from the tip and treating the extracted leachate to produce methane therefrom.

2. A method according to claim 1, including the step of returning the treated leachate

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Methane production The present invention relates to the production of methane, and is particularly applicable to the production of methane from domestic waste landfills or tips. An established (i.e. 1-2 years old) open domestic waste tip will produce a liquid called leachate which is produced as a result of rainfall impinging on the tip and of bacterial action on the waste. The leachate consists of aqueous solutions (95% water) of volatile acids which are subsequently attacked by bacteria to produce methane. Both the production of leachate and methane are dependent upon the temperature of the tip; if the tip is below 7-1 5'C the reactions will cease and if above 45"C the bacteria will be killed. There have been earlier schemes to collect the methane generated from domestic waste tips and to use it for industrial heating purposes; such schemes have the disadvantage that the methane is produced at widely varying and uncontrollable rates, due to variations in rainfall amounts, temperature of the tip, and leachate extraction from the tip, and therefore does not equate to the energy demand at any one time. It is an aim of the invention to provide an improved method of methane production from domestic waste tips, in which the methane is produced at a controlled and determined rate. According to the present invention, the improved method includes the steps of cooling the waste contents of the tip to reduce or prevent the formation of methane therein, extracting leachate from the tip, and generating methane from the leachate. Conveniently the methane is produced by heating the extracted leachate in an upflow anaerobic sludge blanket reactor, surplus leachate being cooled before being returned to the tip. The heating and cooling of the leachate may take place in a heat pump. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic view of apparatus for carrying out the method of the invention to produce methane in a controlled manner from a domestic waste tip. Referring to the drawing, there is shown a domestic waste landfill or tip 10 which may be partly covered by a waterproof sheet 1 2 to control the amount of rainfall impinging on the waste contents of the tip, excess clean rain water being directed to a sump 1 4 where it is pumped by pump 1 6 to a water course 18; clean rain water is also collected in interceptor channels 20 provided in the side walls 22 of the tip. At the base of the tip is a layer 24 of gravel which acts as a sump to collect leachate produced by the tip. From this layer leachate is pumped by pump 26 to an upflow anaerobic sludge blanket (UASB) reactor 28 which operates at a warm temperature (say 35"C) to produce from the leachate methane gas in a controlled chemical reaction analogous to the production of carbon dioxide during the anaerobic fermention of sugars by yeast during the production of ethyl alcohol. To increase the temperature of the leachate from say 1 5 C (the temperature on leaving the tip) to a temperature of 35"C (required by the reactor), the leachate is passed through a heat pump 30. Methane produced by the reactor is directed by outlet pipe 32 to industrial users of the methane.To allow for the case where the required temperature increase is beyond the capacity of the heat pump, a methane burner 34 may be provided which is supplied with methane from branch line 36 of pipe 32 and which supplies additional heat to the leachate. A valve 38 may also be required in outlet pipe 32 in accordance with local authority requirements to permit the exhaust of surplus methane gas from the reactor. Effluent (treated leachate) leaving the reactor is directed back through the heat pump 30 where it is cooled (down to say 5"C) before being sprayed back onto the waste contents via pipe 39 to control the temperature of the tip. By keeping the tip at a sufficiently low temperature, the production of methane within the tip can be prevented or at least substantially reduced. If additional cooling fluid is required, a bypass circuit 40 may be required to bypass some of the leachate from a point upstream of the reactor direct to the heat pump, thereby increasing the flow of cooled effluent back to the tip. In the event of excess leachate being produced, pipe 39 is provided with a valved branch 42 to enable the excess to be directed to a sewer. Operation of the heat pump is expected to produce surplus heat, and this heat could be used locally to heat for example greenhouses etc. It will be apparent that the above described method permits the production of methane gas from a domestic waste tip at a controlled rate to suit the users demand for the gas. In the absence of demand, or in the event of low demand, excess methane produced by the reactor may be liquified and stored for future use. CLAIMS

2. A method according to claim 1, including the step of returning the treated leachate to the tip.

3. A method according to claim 2, wherein the cooling step is effected by cooling the treated leachate before returning it to the tip.

4. A method of producing gas from a domestic waste site comprising the steps of directing water over the waste at the site, extracting the aqueous solution produced at the site when the water has passed through the waste, heating the extracted aqueous solution to produce gas therefrom, cooling the treated aqueous solution and returning it to the site to cool the waste and so inhibit the production of gas at the site.

5. A method according to claim 4, wherein the heat extracted from the cooling of the treated aqueous solution is applied to heat the untreated extracted aqueous solution.

6. Apparatus for the production of gas comprising a domestic waste tip containing domestic waste, means for extracting an aqueous solution from the tip, means for heating the extracted aqueous solution, an anaerobic reactor for treating the heated aqueous solution to produce gas therefrom, cooling means for cooling the treated solution and returning it to the tip to cool the waste therein to a level such that production of gas from the tip itself is inhibited.

7. Apparatus according to claim 6, wherein the cooling means comprises a heat exchanger for extracting heat from the treated solution and transferring it to the untreated solution.

8. Apparatus according to claim 6 or to claim 7, including an impervious cover covering the waste to direct rainwater away from the tip.

9. A method of methane production substantially as hereinbefore described, with reference to the accompanying drawing.

10. Apparatus for the production of methane substantially as hereinbefore described, with reference to the accompanying drawing.