GB2091779A - Apparatus for removing gas from landfill - Google Patents

Abstract

Apparatus for the recovery of useful fuel gas from landfill comprises a gas permeable standpipe (1) which is located in the landfill (9) and a seal (2 to 8) which is movable axially of the standpipe (1) to seal the standpipe (1) above the bottom of the seal. The bottom of the seal is located below the level of the landfill (9) and above the water level thereof so that gas can be pumped out of the landfill, into the standpipe (1) and to a storage or utilisation area. Preferably the standpipe (1) can be extended upwards to keep above the level of the landfill by adding sections onto fittings (16) on the top of sections already in place. <IMAGE>

Description

SPECIFICATION Apparatus for removing gas from landfill This invention relates to apparatus for removing gas from landfill, and in particular, but not exclusively, to apparatus which enables the recovery of useful fuel gas from the landfill.

Domestic refuse is generally collected for dumping, although in some instances the refuse is burnt in incinerators. A large proportion of the refuse is disposed of in disused quarries, sand pits and other excavations in order to reclaim the land for further exploitation as sites for building or agriculture. The refuse is laid down, compacted and covered with a layer of impermeable clay or other material. Then another layer of refuse is laid down and the process repeated until the excavation is filled in. The filled excavation should be leftfora number of years before it is re-used in order to allow the fill to settle adequately.

The refuse in the layers of the landfill is generally wet and is not exposed to the air. In these conditions, the refuse first decomposes aerobically to consume entrained oxygen and then decomposes anaerobically to form methane, carbon dioxide and other hydrocarbons. There may also be formed hydrogen sulphide and other organic and inorganic substances. The presence of these gases in the landfill can preventthe re-useofthe landforotherpur- poses. For instance, the gases will prevent agricultural cultivation by killing off any seeds planted on the landfill. If buildings are erected on the landfill, they may be at best subject to noxious fumes, and at worst subject to explosions caused by the ignition of the methane which accumulates in explosive concentrations in confined spaces.

A system whereby these gases are extracted from the landfill during its preparation is described in German Offenlegungsschrift No. 24 08 497 to AC Abfall - Consult GmbH. In this system a porous standpipe is inserted into a layer of refuse in the landfill and is connected to a pump which pumps gas out of the standpipe. The gas is passed through a series of condensers and collectors before being flared off. This system has various disadvantages.

As well as pumping out decomposition gases, the pump may also draw air from the top of the refuse layer which dilutes the decomposition gases and increases the amount of gas that has to be pumped.

Also, once the layer has been exhausted and another layer is to be placed on top of it, it is necessary to insert a new standpipe in the new layer. This process is inefficient due to the cost involved and the time spent not pumping.

It is an object of the present invention to provide apparatus for removing gas from landfill which at least in part overcomes the disadvantages of the known system.

Therefore, according to the present invention, apparatus for removing gas from landfill comprises a porous standpipe and a cylindrical seal movable axially along the standpipe for rendering the standpipe non-porous above the bottom of the seal.

Preferably, the standpipe has on its top a fitting for co-operation with a complementary fitting on the bottom of a second standpipe, whereby as the level of the landfill rises, the length of the apparatus is increased by adding further standpipes as necessary. The fitting may be a screw thread but is conveniently a spigot-type joint in which the bottom of the next standpipe is located.

The seal may be a tight-fitting cylindrical sleeve located inside or outside the pipe. Preferably, however, the seal comprises a second pipe co-axial with the standpipe and having on its bottom end an annular member which abuts tightly against the standpipe, the annular space between the standpipe and the pipe being filled with a flowable sealant material, such as clay or mud slurry. The annular member is preferably resilient but must be sufficiently strong to support the weight of the sealant and may comprise for instance a tyre inner tube.

If the seal is a cylindrical sleeve or if the second pipe is located outside the scandpipe, the stand pipe should be connected to a pump for pumping the gas out of the landfill. If a second pipe is located inside the standpipe, the second pipe should be connected to the pump.

The pump may be connected to a gas flare stack or to a gas storage tank. In either case the gas may be passed through a scrubbing system for removing noxious or incombustible constituents from the gas.

Preferably, the porous pipe has holes in it which are visible to the naked eye, although materials which are gas permeable without having visible holes can be used to form the standpipe.

In use, the apparatus is erected on a landfill site and the first layer of compacted refuse and clay or other material is formed around it. The position of the bottom of the seal is adjusted so that it is below the level of the clay layer but is above the water level of the landfill. A portion of the porous standpipe is thus left exposed at a depth in the refuse layer. As the refuse decomposes, the gas thus formed can be pumped into the standpipe with less risk of it being diluted by air coming in through the top surface of the refuse layer.

As more refuse is added to the landfill, further standpipes are added to those already located in the landfill so that the apparatus projects above the planned level of the landfill. A layer of clay or other material is placed over the new refuse layer. This may cause the water level of the fill to rise, and may cause it to rise above the original layer of refuse. The water level may also be raised by rainfall or other natural means. It may therefore be necessaryto adjust the position of the seal to leave a porous section of standpipe below the bottom of the seal and above the water levelm The process of adding further standpipes and adjusting the seal can be repeated as many times as necessary until the landfill reaches its planned level. This is not possible with the known system.

Since the gas emerging from the standpipe is not contaminated by air, it comprises mainl S m eahabn2 and carbon dioxide. If the carbon dioxides is removed, for instance in a quicklime scrubber, tilts emerging gas will be mainly methane, and can therefore be used as an efficient fuel or a chemical feedstock. This is another advantage over the known system.

The present invention also provides a landfill area including at least one apparatus according to the invention. Preferably, there is a plurality of such apparatuses connected to a central pumping and processing station.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa cross-sectional view of a landfill in which is located apparatus according to the invention; and Figure 2 is a schematic diagram of the landfill of Figure 1.

Referring now to the Figures, the apparatus comprises perforated concrete pipe sections 1 and a fle'.- ible plastic pipe 2 located inside the concrete pipe 1.

A cylindrical steel connector3 is held in the lower end of the plastic pipe 2 by clamps 4 and a T-piece 5 is held in the upper end thereof by clamps 6. The connector 3 has on its outside an inflated tyre inner tube 7 which is resiliently pressed against the inside of the concrete pipe 1. The annular volume defined by the concrete pipe 1, the plastic pipe 2, the T-piece 5 and the innertube 7 is filled with a flowable thick clay slurry 8, thereby rendering the concrete pipe 1 impermeable above the innertube 7.

The concrete pipe 1 has on its upper end a spigot 16 for supporting a second concrete pipe 17, (shown in dotted lines in Figure 1), which also has a support ing spigot 18.

The apparatus is located in a landfill and is sur rounded at least in its lower portion by refuse 9. the refuse 9 is compacted and covered by a layer of clay 10. The length of the plastic pipe 2 below the T-piece 5 is adjusted by use of clamps 6 so that the inner tube7 is located well below the surface of the landfill 10 but above the water level of the landfill. A portion of the concrete pipe 1 is therefore able to receive gas from the decomposing refuse 9 with less risk of dilution by air.

Figure 2 shows a landfill including several apparatuses as described above. Each T-piece 5 is connected by flexible hose or rigid pipework 11 to a central pumping station 12. The pumping station 12 extracts gas accumulating in the concrete pipe 1 through the plastic pipe 2 and flexible hose 11. Typically gas is withdrawn from each apparatus at a rate of about 50 to 100 ft34nin., although the rate of extraction will depend to a large extent on factors such as the rate of decomposition of the refuse 9, the conditions of the fill, the mangement of the filling operation, and the temperature of the surroundings.

The gas produced by decomposing domestic refuse comprises approximately 50 to 70% v/v methane, 30 to 40% v/v carbon dioxide and small proportions of nitrogen, oxygen, hydrogen sulphide, and higher hydrocarbons. The gas is pumped to a carbon dioxide scrubber 13 from which is produced gas con - ,n- ing about 90% v/v methane. This gas may be further scrubbed to remove noxious constituents, such as hydrogen sulphide, and is than pumped into astor- age tank 14 for use as a fuel gas.

When a new layer of refuse 15 (shown in dotted lines on Figure 1 ) is to be laid down on top of the clay layer 10, the inner tube 7 is deflated and the assembly comprising parts 2 to 8 is removed. A second, and if necessary further, section of pipe 17 are placed on top of one another using the spigot fittings until the apparatus is of sufficient length to extend above the planned new level of the fill 15. The assembly of parts 2 to 8 is replaced in the apparatus, and the position of the seal is adjusted so that its bottom is below the new level of the fill 15 and above the water level. The in ner tube 7 is reinflated the clay 8 repiaced to seal the standpipes above the inner tube 7. if the water level does not rise too much, it will be possible to extract gas from both layers of the refuse 9 and 15. The same process can be carried out each tin?'i a new layer of refuse is laid down, thus enabling gas of good quality to be oxtracted con tinuous'-.

The present invention the, before provides novel apparatus ' use in extracting gas from landfill which is easierto operate and producss better qual ity gas than the prnviosuly used systems.

Claims (11)

1. Apparatus for rerno sing gas from landfill, comprising a porous standpipe and a cylindrical seal movable axially along the standpipe for rendering the standpipe non-porous above the bottom of the seal.

2. Apparatus according to Claim 1, wherein the standpipe has on its top a fitting for co-operation with a complementary fitting on the bottom of a second standpipe.

3. Apparatus according to Claim 2, wherein the fitting is a spigot-type fitting.

4. Apparatus according to any one of Claims 1 to 3, wherein the seal is a tight fitting cylindrical sleeve.

5. Apparatus according to any one of claims 1 to 3, wherein the seal comprises a second pipe co-axial with the standpipe and having on its bottom end an annular member which abuts tightly against the standpipe, the annular space between the standpipe and the pipe being filled with a flowable sealant material.

6. Apparatus according to Claim 5, wherein the sealant material is a clay or mud slurry.

7. Apparatus according to either one of claims 5 and 6, wherein the annular member is resilent and sufficiently strong to support the weight of the sealant.

8. Apparatus according to any one of the preceding claims, wherein the standpipe is perforated.

9. Apparatus for removing gas from landfill, substantially as hereinbefore described with reference to the accompanying drawings.

10. An installation for removing gas from landfill, comprising at least one porous standpipe located in the landfill, a cylindrical seal movable axially along the standpipe for rendering the standpipe nonporous above the bottom of the seal and located with its bottom below the level of the landfill and above the water level of the landfill, and a pumping system for pumping gas out of the landfill, into the stand pipe and to a storage or utilisation system.

11. An installation for removing gas from landfill, substantially as hereinbefore described with reference to the accompanying drawings.