CZ217895A3 - Process and apparatus for gas extraction from underground refuse dump - 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. Specifically, the extraction of biogas produced by the anaerobic decomposition of waste stored in underground landfills, which gas is taken by a sampling system comprising a number of wells, and is then fed to a gas boiler or heater via a metering pump and control module. a gas engine driving a transformer generator for the purpose of selling the generated energy in the form of electricity to energy 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 provided with a membrane foil or the like at the bottom, microbiological conversion of the waste occurs first by aerobic decomposition when oxygen is consumed and then by anaerobic decomposition to produce biogas.

If the landfill reaches a stable anaerobic phase, the produced gas 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 ^{3 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 pumping gaseous decomposition products on tailings heaps. The gas wells, located at different locations on the tailings heaps, are connected via a pumping pipe to a collecting device from which gas is taken for further use. Each evacuation line is provided with one or more electronic sensors that transmit characteristic quantities of gas flowing in each line to a measuring and control unit that monitors the volume of gas flowing as a function of comparing the sensor signals with preset thresholds.

SUMMARY OF THE INVENTION

The purpose of the present invention is 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 of methane (CH) and oxygen (O ₂ ) in the extracted gas and the amount of gas from each well is continuously measured and controlled by means of a common metering and control system to which gas is supplied from each well wherein the concentration of oxygen in the gas to be extracted is continuously measured on the suction side between the intake manifold and the compressor.

By means of this relatively simple measure, it is possible to ensure an optimal and safe control of gas production, where the quality of gas from each well is continuously monitored.

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 avoid the risk of explosion, the measurement and recording of the oxygen concentration on the suction side of the system is performed just before the compressor.

Preferably, special gas wells are used for gas extraction, each of which is provided with two pipes and a gravel filter, one of which pipes, the gas pumping pipe, is perforated or slotted, while the other, the so-called discharge pipe, 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, the underground pipeline preferably inclined towards the wells so that condensing water automatically flows back into the well. The condensed water, which is possibly trapped in the underground pipe pockets, 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 inclined 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 the pipeline.

The invention further relates to a device used for the extraction of gas, in particular biogas, from underground waste dumps, characterized in that the measuring pump and control module is located in a standard container, which is divided into a control chamber and a pumping chamber and provided with a measuring and a control pipe unit for each borehole, for example, forty pipe units each connected to the intake manifold and comprising 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 measuring and regulating pipe unit can be connected to a common measuring device comprising a methane indicator and an oxygen indicator by means of a short pipe branch with a solenoid valve.

The apparatus according to the invention is further arranged such that each piping between the measuring and regulating 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 pipeline back 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 practice 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 as viewed towards the intake manifold arrangement;

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

Figure 4 shows a vertical longitudinal section of the metering pump and control module (pumping chamber) in the reservoir as viewed from the pressure and cooling system,

Figure 5 shows a vertical longitudinal cross-section of the measuring shaft and control module (pumping chamber) in the reservoir in a view of a series of measuring and control pipes for individual drilling wells,

Figure 6 shows a sectional view associated with a view of the rear contours of a measuring and control tube for a single well borehole

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

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a logging well 10, which should be at most about six per hectare of landfill surface. The borehole 10 is a double borehole provided with two plastic pipes, a perforated gas pump 38 and slots provided with a discharge pipe 40, both of which are surrounded by a suction filter 36 formed by a filter gravel.

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

On the surface, the borehole 10 is provided with a service shaft 44, by which a submersible pump can be lowered, for example, 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, which is arranged in a standard reservoir 2 and includes a control chamber 4 (see Fig. 7) and a pumping chamber 6. (see Figs. 2-5). . The control chamber 4 and the pumping chamber 6 are separated from each other by a gas-tight inner wall 46 with an inspection window 48 (see FIG. 2).

The underground pipe 32 is introduced into the metering pump and control module through an elongated inlet box 50 on a long side wall 52 with a long narrow inlet opening 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 metering and control tube 8 serves, on the one hand, to continuously monitor the concentration of oxygen and methane in the extracted gas from each well 10 by being connected to a pump 70 of a common metering device 26 comprising a methane indicator 28 and an oxygen indicator 30; on the other hand, to blow water out of the computer duct 32 to the boreholes by generating an overpressure so that it is connected to the discharge side of the compressor 34 (screw compressor - see FIG. 4) via a return discharge line 56.

From the intake manifold 12, the 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 is closed when the concentration oxygen exceeds 3.5%, which corresponds to 20% for the upper explosion limit.

Before the gas exits the metering pump and control module via a long pipe 66 towards the gas engine, boiler or heater, the gas passes through various filters, a cooling system, an oil separator, etc. The gas is cooled down to the dew point, i.e. the gas. at about 2 ° C to prevent condensation in the pipeline 66 and also to make this gas less aggressive to gas appliances.

In practice, a continuous gas control measurement is carried out on each of the forty measuring and regulating tubes 8 by passing the gas from each of the tubes 8 through a short pipe branch 20 and the following solenoid valve 22 to a common metering device 26 for determining the methane and oxygen content of the gas from the well borehole 10. Through the pump 70, the gas is pumped from the tube 6 through the methane indicator 28 and the oxygen indicator 30 directly to the intake manifold 12 for a period of time until the quality of the gas flowing through the common metering device 26 is certain 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-controlled control valves 18 on the tubes 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 can be pre-determined 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 if the methane percentage falls below 45%.

As a result of repeated frequent measurements, the extraction equipment can be controlled in fact, depending on 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 6 of the respective well 10 if the percentage of oxygen exceeds this limit. This prevents atmospheric air being sucked into the borehole that 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 an extraction facility comprising multiple wells (10) and is fed via a pump and control module to a gas boiler or a gas engine driving a transformer generator to sell the generated energy in the form of electricity to power companies, the gas from each well (10) being fed to the metering pump and control module through a separate line (32), characterized in that the methane (CH) percentage and oxygen (O) in the gas; and 4 2 the amount of gas from each well (10) is continuously measured, controlled and controlled by a common measuring and control device into which the gas from each well (10) is gradually introduced, and that the oxygen concentration (O) in the gas is continuously measured at suction between the intake manifold (12) and the compressor (34). Method according to claim 1, characterized in that boreholes (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 provided 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 boreholes (10) is fed to the measuring pump and control module through an underground pipe (32) which is inclined towards the boreholes (10), and that the condensed water, trapped in the pockets of the pipe (32) may be blown back into the boreholes (10) by a separate back blowing device of the metering pump and control module. 4. Equipment 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 extraction facility comprising multiple wells (10) and fed through a metering pump and control module to a gas a boiler or 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 arranged in a standard storage tank (2) a chamber (4) and a pumping chamber (6) and is provided with a measuring and regulating pipe unit (8) for each borehole (10), for example forty pipe units (8), each of which is connected to the intake manifold (12) and is equipped with a flowmeter (14), a machine - controlled control valve (16,1 8), a short pipe branch (20) with a solenoid valve (22) and shut-off valves (24). Device according to claim 4, characterized in that each measuring and control unit (8) is adapted to be connected successively to a common measuring device (26) with an indicator (28) by means of a short pipe branch (20) with a solenoid valve (22). methane and an oxygen indicator (30). Apparatus according to claims 4 and 5, characterized in that each pipe (32) between the measuring and regulating pipe unit (8) and the borehole (10) can be connected to the discharge side of the compressor (shut-off valves) if necessary. 34) to blow the water accumulated in the pipe (32) back to the borehole (10).