SK105195A3 - Method for exploitation of gas from waste disposal sites and device for its realization - Google Patents

Abstract

A method and a system for exploitation of gas from waste disposal sites is described, that is biogas being generated during anaerob decomposition of the waste deposited on the disposal site, and where the gas is recovered through a recovering system consisting of a number of drillings (10) and via MPR-module (measuring pump and adjusting module) is lead to boiler or gas engine-driven generator with transformer for sale of produced energy as electricity to the electricity company and heat to heating consumers, where the gas from each single drilling (10) is lead to the MPR-module through separate tubes, that the per cent content of methane (CH4) and oxygen (O2) in the gas and the gas quantity from each drilling (10) currently is measured and adjusted by means of a common measuring and adjusting equipment, whereto gas from each single drilling (10) in turn is lead, and that the O2-concentration in the gas continuously is measured on the suction side between the absorption manifold (12) and the compressor (34), for instance screw compressor.

Description

Technical field

The invention relates to a method for extracting gas from underground landfills. In particular, the extraction of biogas produced by the anaerobic decomposition of waste stored in underground landfills, the gas is taken from a sampling system comprising a number of wells and is further routed through a metering pump and control module to a gas boiler or heater or a gas engine a generator with a transformer for the sale of the recovered energy in the form of electricity to power companies and then in the form of heat to consumers.

BACKGROUND OF THE INVENTION

When depositing waste in a landfill, for example a so-called controlled landfill equipped with a membrane foil or the like, microbiological conversion of the waste occurs first by aerobic decomposition when oxygen is consumed and then by anaerobic decomposition when biogas is produced.

If the landfill reaches a stable anaerobic phase, the gas produced contains 30-60% methane, which gas can be extracted and recovered as an energy source for energy supply purposes.

A variety of landfill gas extraction systems are known, and the most efficient systems can produce more than 200,000 m of landfill gas per day, equivalent to about 100 tonnes of crude oil per day.

US-A-4,670,148 discloses an apparatus and method for evacuating gaseous decomposition products on tailings. The gas wells, located in different locations on the tailings heaps, are connected to the collecting device through the pumping pipe, from which the gas is taken for further use. Each evacuation line is equipped with one or more electronic sensors that transmit characteristic quantities of the gas flowing in each line to a metering and control unit that monitors the volume of the flowing gas as a function of comparing the sensor signals with preset thresholds.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved method of extracting gas from underground landfills, which allows optimum and safe operation of extraction, for example by means of a standard pump and control module.

The method according to the invention is characterized in that the percentage content of methane (CH ₄ ) and oxygen (O ₂ ) ^{in a2 and} °2 m m of gas and the amount of gas from each well is continuously measured and controlled by means of a common metering and control system. The concentration of oxygen in the extracted gas is continuously measured on the suction side between the intake manifold and the compressor.

With this relatively simple equipment, it is possible to ensure optimal and safe control of gas production when the quality of the gas from each well is continuously checked.

The percentage of methane in the extracted gas (its optimum thermal value) as well as the oxygen content (for safety reasons) are continuously measured and recorded. To prevent explosion safety, the measurement and recording of the oxygen concentration on the suction side of the system is performed just before the compressor.

Preferably, special extraction wells are used for gas extraction, each of which is provided with two tubes and a gravel filter, one of the tubes, the gas pumping tube being perforated or provided with slots, while the other, the so-called discharge tube, is adapted for connection of the submersible pump if the groundwater level in the landfill reaches too high and floods the suction filter of the gas pump pipe.

The damp and hot gas from the wells is routed via an underground pipeline to the metering pump and control module, and the underground pipeline is preferably inclined towards the wells so that condensing water automatically flows back into the well. Condensation water, which is possibly trapped in the pockets of the underground pipe, is blown back into the boreholes by means of the back blowing system of the metering pump and control module. Even if the underground manifold is located with a tendency towards the wells, a different arrangement of the wells in the landfill, due to the different degree of conversion of the deposited waste, can cause the formation of pockets in that pipe.

The invention further relates to a device used for extracting gas, in particular biogas, from underground waste dumps, the principle of which is that the metering pump and control module is housed in a standard tank which is divided into a control chamber and a pump chamber and is equipped with a metering and metering chamber. a control pipe unit for each borehole, for example, forty pipe units, each of which is connected to a manifold, and includes a flow meter, a motor valve, a side pipe branch with a solenoid valve and shut-off valves.

The device according to the invention is preferably arranged such that each metering and regulating duct unit can be connected to a common metering device comprising a methane indicator and an oxygen indicator by means of a short pipe branch with a solenoid valve.

The device according to the invention is further arranged such that each pipe between the measuring and control pipe unit and the well bore can be connected to the discharge side of the compressor, if necessary by means of shut-off or throttle valves, to return the water accumulated in the pipe back to the pipe. well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the accompanying drawings, in which:

Figure 1 shows a preferred embodiment of a gas extraction well used in the application of the method and apparatus of the invention.

Figure 2 shows a vertical cross-sectional view of the metering pump and control module (pumping chamber) in the reservoir in the direction of the suction line arrangement.

Figure 3 shows a vertical cross-sectional view of the metering pump and control module (pumping chamber) in the reservoir in the direction of the cooling system (right).

Figure 4 shows a vertical longitudinal section of the metering pump and control module (pumping chamber) in the container in a view of the pressure and cooling system.

Figure 5 shows a vertical longitudinal section of the metering pump and control module (pumping chamber) in the reservoir in the direction of the series of metering and control tubes for each well.

Figure 6 shows a sectional view connected to the rear contours of the measuring and control tube for a single well borehole; and

Figure 7 shows a partial vertical longitudinal section through the inspection chamber of the metering pump and control module.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, there is shown a well 10, which should be at most about six per hectare of landfill surface. The extraction well 10 is designed as a double well equipped with two plastic pipes, a perforated gas supply pipe 38 and slots equipped with a discharge pipe 40, both of which are surrounded by a suction filter 36 formed by a filter gravel.

Upwardly, the extraction well 10 is sealed against the ingress of atmospheric air through clay soil 42. The perforated gas supply pipe 38 is connected via an underground pipe 32 to a metering pump and control module.

On the surface, the borehole 10 is provided with a service shaft 44, by means of which, for example, a submersible pump can be lowered into the discharge pipe 40 if the groundwater level in the landfill reaches the level of the suction filter 36.

Each underground pipe 32 from each well 10 is introduced into a centrally located metering pump and control module that is housed in a standard container 2 and includes a control chamber 4 (see Fig. 7) and a pumping chamber 6 (see Fig. 2-5). The control chamber 4 and the pumping chamber 6 are separated from each other by an inner wall 46 with an inspection window 48 (see FIG. 2).

The underground conduit 32 is introduced into the metering pump and control module via a longitudinal inlet box 50 on a long side wall 52 with a long narrow inlet 54. Forty similar measurement and control tubes 8 are disposed along the long side wall 52 (see Figures 5 and 6). all of which are connected to a common intake manifold 12 and all of which are equipped with a flowmeter 14, an axial balancing device 16, a machine-controlled control valve 18, a short pipe branch 20 with a solenoid valve 22 and two shut-off valves 24 (choke valves), so that each measurement and control tube 8 serves both to continuously monitor the oxygen and methane concentration in the extracted gas from each well 10 by being connected to a common metering pump 26 containing a methane indicator 28 and an oxygen indicator 30 and to blowing water out from underground pipeline 32 sp T to the appropriate wells pressurisation so as to be connected to the discharge side of the compressor 34 (screw compressor - Fig. 4) via a return line 56.

From the intake manifold 12, gas is passed through the intake manifold 58, the gas filter 60, the valve 62, the flame retardant device 64 and the oxygen indicator 68 to the intake side of the screw compressor 34, the system being closed when the oxygen concentration exceeds 3, 5%, which corresponds to 20% for the upper explosion limit.

Before the gas leaves the metering pump and control module through the pipeline 66 towards the gas engine, boiler or heater, the gas passes through various filters, a cooling system, an oil separator, and so on. The gas is cooled down to the dew point, i. about 2 ’C to prevent condensation in the remote pipeline 66 and also to make this gas less aggressive to gas appliances.

In practice, a continuous gas control measurement is performed on each of the forty measuring and regulating tubes 8 by passing the gas from each tube 8 through a short pipe branch 20 and the following solenoid valve 22 to a common metering device 26 to determine the content. The metering pump 70 is the gas pumped from the pipe 8 through the methane indicator 28 and the oxygen indicator 30 directly to the intake manifold 12 for a period of time as long as the quality of the gas flow passing through the common metering device. In this way, the control measurement of the gas from each well and the recording of its results can be performed with a time interval of about one hour.

In the control chamber 4 there is a computer which, based on the measurement results, controls and controls the opening and closing functions of the machine-operated control valves 18 on the pipes 8 for the respective wells 10. The optimum percentage of methane and oxygen for each well 10 can be stored. For example, the percentage of methane may be pre-determined up to 45%. In such a case, the computer then opens the individual tube 8 pertaining to the well 10 when the methane percentage exceeds 45% and closes it when the methane percentage falls below 45%.

The result of repeated frequent measurements is that the extraction equipment can be controlled according to the actual changes in the extraction conditions, so that the optimum amount of gas and the energy stored therein is always pumped.

For example, the upper limit of the percentage of oxygen may be set to 1% so that the computer closes the individual tube 8 of the respective well 10 if the percentage of oxygen exceeds this limit. It is thus possible to prevent atmospheric air being sucked into the borehole, which would destroy the anaerobic bacteria producing the extracted gas.

Claims (6)

PATENT CLAIMS A method for extracting gas from an underground landfill, which is biogas produced by anaerobic decomposition of waste deposited in an underground landfill, where the gas is extracted by a multiple-well extraction installation (10) and directed to a gas boiler or to a metering pump and control module. gas engine driving the generator with transformer for sale of the produced energy as electricity utilities, is the gas from each drilling (10) is lead to the MPR-module through individual pipes (32), characterized in that the percentage of methane (CH ₄ ) and oxygen (0 ₂ ) in the gas and the amount of gas from each well (10) is continuously measured, controlled and controlled by a common measuring and control mechanism into which the gas from each well (10) is gradually introduced, and that the oxygen concentration (0) ₂ ) in the gas is continuously measured on the suction side between the intake manifold (12) and the compressor esor (34). Method according to claim 1, characterized in that bores (10) are used, each consisting of two tubes and a gravel filter (36), one of the tubes, the gas pumping tube (38) being perforated or equipped through the slots, while the second tube, the discharge tube (40), is adapted to receive the submersible pump if the liquid level in the landfill is too high and interferes with the suction filter (36) of the gas pump tube (38). Method according to claim 1, characterized in that the moist and hot gas from the wells (10) is fed to the metering pump and control module through an underground pipe (32) which is inclined towards the wells (10) and that the condensed water, trapped in the pockets of the pipe (32), it can be blown back into the boreholes (10) by a special back blowing device of the metering pump and control module. 4. A facility for extracting gas from an underground landfill, which is biogas produced by anaerobic decomposition of waste deposited in an underground landfill, where the gas is extracted by an offshore plant comprising multiple wells (10) and fed to a gas boiler via a metering pump and control module; to a gas engine driving a transformer generator for the purpose of selling the recovered energy in the form of electricity to power companies and in the form of heat to heat consumers, characterized in that the metering pump and control module is housed in a standard storage tank (2) divided into a control chamber ( 4) and a pumping chamber (6) and is provided with a measuring and regulating duct unit (8) for each borehole (10), for example forty duct units (8) each connected to the intake manifold (12) and equipped with a flow meter (14), machine-controlled control valve (16, 18), short a pipe branch (20) with a solenoid valve (22) and shut-off valves (24). Device according to claim 4, characterized in that each measuring and regulating duct unit (8) is adapted to be connected successively to a common measuring mechanism (26) with an indicator (28) by means of a short pipe branch (20) with a solenoid valve (22). methane and an oxygen indicator (30). Device according to claim 4 and 5, characterized in that each pipe (32) between the measuring and control pipe unit (8) and the borehole (10) can be connected to the discharge side of the compressor (34) by means of shut-off valves (24). ) to blow the water collected in the pipe (32) back to the borehole (10).