WO2003073001A1

WO2003073001A1 - Method and arrangement for combusting landfill gas, and a burner

Info

Publication number: WO2003073001A1
Application number: PCT/FI2003/000135
Authority: WO
Inventors: Juhani Hintikka
Original assignee: Greenvironment Oy
Priority date: 2002-02-27
Filing date: 2003-02-26
Publication date: 2003-09-04
Also published as: FI20020374A0; AU2003206985A1

Abstract

The present application describes a decentralized method, system and burner (2), the burner being mounted directly in a suction well (14) bored in waste dumping (1) or on a gas discharge opening implemented with earth-moving technology of a small landfill and sucking the gas with a blower (9) of its own, generating in a pressure chamber (11) the pressure needed for combustion taking place in a combustion chamber (25). Since the combustion is carried out in the apparatus locally and suction-well-specifically, it is not necessary to construct large gas pipelines, and device investments are not wasted.

Description

METHOD AND ARRANGEMENT FOR COMBUSTING LANDFILL GAS, AND A

BURNER

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method according to the preamble of claim 1 and to an arrangement according to the preamble of claim 3 for combusting landfill gas suction-well-specifically. The invention also relates to a burner according to claim 11 , intended to be mounted in a suction well in a landfill for combusting landfill gas (LFG) suction-well-specifically.

[0002] In this context, "LFG" refers to landfill gas and "burner" refers to a burner of a flare burner type.

[0003] In known LFG combustion methods, the landfill gas is conveyed from suction wells in the dumping of a landfill to a pumping station by means of underpressure generated by a centralized pumping station, the pressure being raised on the secondary side of the pumping station and conveyed, in general, to a flare burner to be combusted, which is the minimum procedure in destroying the methane contained in the LFG. In the known system, a separate suction pipeline must be dug from each suction well to the pumping station, which suction pipeline must be constructed in accordance with the legislation on natural gas concerning underground pipelines. Therefore, conveying LFG to a centralized pumping station causes expensive earth-moving work at the mounting stage.

[0004] A disadvantage of the known LFG combustion method is also that the gas generation estimate for a landfill is usually based on calculation or incomplete test pumping. Since the gas production estimate is only indicative, it is necessary, just in case, to use overdimensioning in designing the pumping station and the flare burner, which increases the apparatus size and therefore also the acquisition price of the whole plant. Overdimensioning also makes the use of the plant more difficult and deteriorates the negative energy balance of the plant even more. [0005] Experimentally, it can also be noted that in most landfills 20 to 60% of the suction wells do not generate LFG at all or generate it in such small amounts that it is not worthwhile to suck gases from the well site at all. As regards such wells, not only the suction well but also the transport pipeline to the pumping station and, at the same time, working time and material used for constructing the well and the pumping station go to waste in the known centralized system. Likewise, the high degree of humidity in LFG causes disturbances, particularly in cold seasons when constructions freeze.

[0006] Further, there are no known apparatus for controlled combustion of discharging gases in small, closed landfills.

BRIEF DESCRIPTION OF THE INVENTION

[0007] An object of the invention is to provide a method, a system and a burner, wherein suction-well-specific burners can be mounted simply; the burners can be moved later away from a landfill part generating only small amounts or no LFG, either to a landfill part generating more LFG or to another landfill; the costs caused by the closing of the landfill are reduced; the usability is improved; and the combustion process is improved owing to more accurate dimensioning.

[0008] In accordance with the invention, these objects can be achieved by constructing a self-sucking and suction-well-specific, electrically controlled burner generating the overpressure required for the combustion, only the electric connection contained in the gas sampling pipe being conveyed to a centralized control unit.

[0009] In a preferred embodiment of the invention, the burner is surrounded by a protective casing made of steel which functions, at the same time, as a support and basic structure of the burner. The lower part of the burner comprises an acid-resistant pipe which is directed perpendicularly downwards and fits into the upper part of the suction well with dimensional accuracy. The pipe is connected by its upper part to a blower, above which there is the pressure-balancing chamber of the burner. The connection leading from the blower to the pressure-balancing chamber is inside the chamber above the bottom, and there is a drain pipe provided with a magnetic valve leading from the bottom of the chamber back to the suction pipe leading to the blower. The pressure chamber comprises temperature and pressure sensors required for measuring gas, and a gas sample pipe fitting. Beginning from the upper part of the pressure chamber, there is a pipe connected to the magnetic valve, after which there is a gas quantity indicator. An actual gas jet pipe leads upwards from the gas quantity indicator, there being holes bored in the upper part of the pipe, dimensioned for a suitable gas flow. Around the holes, there is an adjustable throttling band. Around the gas jet pipe, there is a short pipe which functions as a gas and an air premixing pipe. The jet around the pipe and the premixing pipe is a steel pipe the inside of which is insulated, functioning as the actual combustion chamber. The lower and upper ends of the pipe are open, supported against a protective casing and made of acid- resistant steel. The upper part of the pipe comprises two truncated cones the inner diameters of which are the same. The temperature control sensor of the combustion chamber is in the upper part of the combustion chamber.

[0010] In a preferred embodiment of the invention, the control centre of the burner is embedded in the protective casing. The cables from the burner, containing the sampling pipe, are connected to the landfill monitoring room, where there are the computer-based remote monitoring and alarm systems of the decentralized combustion system according to the invention.

[0011] The burner according to the invention can also function independently in small closed landfills, being responsible for the LFG combustion of these landfills that generate small amounts of gas but form the majority of all landfills.

[0012] A simplified operating principle of a decentralized burner system can be as follows. The blower of the burner sucks the LFG from the suction well and transfers it to the pressure chamber, where the temperature and pressure of the LFG are measured. When the pressure of the LFG in the chamber has risen above the set limit value, the magnetic valve leading to the combustion is opened, allowing the gas to flow through the quantity indicator to the jet pipe, and the LFG flows further to the premixing pipe through holes bored in the jet pipe. In the premixing pipe, the LFG is mixed with the air being absorbed from the lower part of the pipe, forming thus a combustible gas mixture, which is ignited with ignition electrodes attached to the outer periphery of the mixing pipe, the electrodes generating an arc at the level of the upper edge of the mixing pipe by means of high voltage caused by an electric transformer. When being released from the mixing pipe, the gas mixture ignites and the whole of it burns when travelling to the upper part of the actual combustion chamber, where the combustion gases are released to the air. The temperature of the combustion chamber is measured with a limit value sensor located in the upper part of the combustion chamber. The burner system is controlled with a logic-controlled electric system provided with burner-specific flame control, which electric system receives measuring information on the gas pressure and the temperature of the gas and the combustion chamber, the limit value settings of which function together with a flame control electrode as a safety system required of burners by the legislation on natural gas. The structure of the burner is such that there is no risk that people would, even in winter conditions, get close to the hot areas of the burner without auxiliary structures. [0013] A drain pipe provided with a magnetic valve leads from the lower part of the gas pressure chamber back to the suction pipe of the blower.

[0014] The LFG sampling pipe of the burner and the electric measuring messages are taken via the same integral cable to the computer- aided alarm and remote monitoring unit located in the monitoring room of the landfill. There is also supply cabling required by the burner in the measuring cable. The remote monitoring system collects the required information from different burners for requirements of the operating and maintenance staff.

[0015] More specifically, the method, system and burner according to the invention are characterized by what is stated in the characterizing part of the independent claims.

[0016] Preferred embodiments of the invention are described in the dependent claims.

LIST OF FIGURES

[0017] The invention will now be described in more detail in connection with preferred embodiments, with reference to the attached drawings, of which

Figure 1 shows a decentralized suction-well-specific system of a whole western landfill for about 40 000 inhabitants; and

Figure 2 shows a suction-well-specific burner.

DETAILED DESCRIPTION OF THE INVENTION

[0018] In the following, the invention will be described in more detail with reference to Figure 1 , which shows a decentralized suction-well-specific system of a whole western landfill for about 40 000 inhabitants, and with reference to Figure 2, which shows a suction-well-specific burner. [0019] Once a remote monitoring unit 5 in a monitoring room 4 has given an electric start-up command to suction-well-specific burners 2 via cables 3, logic-controlled control units 6 provided with flame control relays, belonging to each burner 2 separately, start up the burner 2. The prerequisite for the start-up is that a flame control electrode 24 has not detected a flame in a combustion chamber 25 before the start-up and that the temperature of the combustion chamber 25 does not exceed the upper limit value of temperature measurement 29.

[0020] If the mentioned prerequisites are fulfilled, a blower 9 connected to the suction well 14 of the burner 2 with a pipe 8 is started, and at the same time, the magnetic valve 13 of the drain pipe 12 that has been open during the downtime is closed, and an arc is generated in the gap of ignition electrodes 23. When the pressure of the LFG in a chamber 11 has risen above the limit value of pressure measurement 32, a magnetic valve 17 connected to a pipe 16 in the upper part of the pressure chamber 11 is opened, allowing the LFG to flow into the jet pipe 19 through the quantity indicator 18. From holes 21 in the jet pipe 19, throttled with a control band 20 affecting the gas pressure, the gas is discharged into a space surrounded by a mixing pipe 22, where the LFG is mixed with the air absorbed from below, forming thus a combustible gas mixture. The gas mixture ignites when it encounters the arc between the tips of the ignition electrodes 23. A flame must be generated and the flame control electrode 24 must detect it within one second from the opening of the magnetic valve 17. When the flame has been detected, the arc goes out after about ten seconds from the ignition. The actual combustion of the gas mixture takes place in the thermally insulated 26, steel-structured 27 combustion chamber 25, into which the actual combustion air flows from the lower part of the combustion chamber 25 from an opening between the casing 27 and the protective casing 7. The temperature in the combustion chamber 25 is controlled by a temperature sensor 29. The combusted gas is discharged into the air from the upper part of the combustion chamber 25 and is further mixed with the air flowing through openings between truncated steel cones 28 in the upper part to ensure the combustion.

[0021] If the flame control electrode 24 loses contact with the flame during the use, the burner 2 goes to a quick-closing state, whereby the magnetic valve 17 is closed within a time of less than one second from the generation of the disturbance information and prevents the access of the gas via the jet pipe 19 into the combustion chamber 25. When the burner 2 has been in the flame disturbance state for 10 seconds, it makes a new start-up attempt, which functions as described above. If the flame is generated and the flame electrode 24 gets permanent contact with it, the flame burns in the burner 2 until the working command from the monitoring room 4 is interrupted, or the temperature of the combustion chamber 25 exceeds the limit value of about 1 100°C, or the pressure in the pressure chamber 11 is reduced below the set value of about 50 mbar, or the methane content of the gas sample sucked along a gas sampling pipe 31 at the analysis devices of the monitoring room 4 is reduced below 30 per cent by volume, or the oxygen content in the gas sample exceeds 3 per cent by volume. In all of these cases, the burner 2 sends an alarm to the monitoring room 4 and/or from the monitoring room 4 further to the telephone of the person on call for remote alarm.

[0022] In accordance with the inventive idea, a decentralized suction-well-specific LFG combustion apparatus and method have been provided which are easy to implement and do not require extensive earth- moving work in the landfill due to construction of gas pipelines, saving thus manpower and costs. Also, it is easy and inexpensive to apply the apparatus and the method specifically to such landfill parts that generate LFG. Since the burner is only in one size and several of them are needed per one landfill, large-scale production reduces the manufacturing costs. According to the inventive idea, excessive burner/s can be transported or sold elsewhere when LFG generation is reduced in the landfill. Further, the inventiveness is fulfilled as improved efficiency, because the burner is dimensioned particularly for the requirements of a suction well and no possible overdimensioning needs to be taken into account.

[0023] It will be obvious to a person skilled in the art that as the technology advances, the basic idea of the invention can be implemented in a plurality of ways. The invention and its embodiments are thus not limited to the above examples, but can vary within the scope of the claims.

Claims

1. A method of combusting landfill gas (LFG), comprising forming a suction well (14) in a landfill; sucking landfill gas (LFG) from the suction well (14); and combusting the landfill gas sucked from the suction well (14) with a burner (2); characterized by combusting the landfill gas (LFG) suction- well-specifically (14) by means of the burner (2) mounted at least partly in the suction well.

2. A method according to claim 1, characterized by the monitoring and starting of the burner (2) taking place in a central monitoring room (4).

3. A system for combusting landfill gas (LFG), comprising a suction well (14) in a landfill; suction means for sucking landfill gas (LFG) from the suction well

(14); and combustion means for combusting the landfill gas sucked from the suction well (14); characterized in that a burner (2) has been mounted at least partly in the suction well (14) for combusting the landfill gas (LFG) suction-well-specifically.

4. A system according to claim 3, characterized in that the burner (2) comprises suction means (8, 9, 10) for sucking the landfill gas (LFG) from the suction well (14) into a pressure chamber (11) in the burner (2), the pressure chamber comprising measuring means (32) for measuring the landfill gas pressure prevailing in the pressure chamber (14); that the measuring means (32) are functionally connected to valve members (17) in the burner (2), the valve members being connected to the pressure chamber (11 ); that the measuring means (32) are arranged to transmit a signal to the valve members (17) when the pressure in the pressure chamber (11) has risen above a preset limit value and that the valve members (17) are arranged, as a response to said signal, to open and discharge landfill gas (LFG) from the pressure chamber; that the burner (2) comprises mixing members (20, 21, 22) for mixing the landfill gas (LFG) discharged from the pressure chamber (11) through the valve members (17) with the air to form a combustible mixture; and that the burner (2) comprises ignition members (23) for igniting said combustible mixture.

5. A system according to claim 4, characterized in that the burner (2) comprises flame control means (24) arranged to measure the temperature in the burner (2) and functionally connected to the valve members (17) in such a way that the valve members (17) remain closed if the temperature measured by the flame control means exceeds a preset limit value.

6. A system according to claim 5, characterized in that the flame control means (24) are arranged to continuously measure the temperature in the burner in such a way that if there is an interruption in the measurement, the flame control means (24) are arranged to transmit a signal to the valve members (17), which are, as a response, arranged to close the valve members (17).

7. A system according to claim 4 or 5, characterized in that the burner (2) comprises flame control means (24) arranged to measure the pressure in the burner (2) and functionally connected to the valve members (17) in such a way that the valve members (17) remain closed if the pressure measured by the flame control means exceeds a preset value.

8. A system according to claim 7, characterized in that the flame control means (24) are arranged to continuously measure the pressure in the burner in such a way that if there is an interruption in the measurement, the flame control means (24) are arranged to transmit a signal to the valve members (17), which are, as a response, arranged to close the valve members (17).

9. A system according to claim 3 to 8, characterized in that it comprises means for remote-starting and remote-monitoring the burner (2).

10. A system according to claim 3 for combusting landfill gas suction-well-specifically, characterized in that the apparatus compπses: a pipe (8) connected to a suction well (14), the pipe being connected to a blower (9), from which a connecting pipe (10) leads to a pressure chamber (11), to which a drain pipe (12) provided with a magnetic valve (13) is connected; a sampling pipe (31) leading to a monitoring room (4); a temperature sensor (33); a pressure sensor (32) and a connecting pipe (16) leading to a magnetic valve (17); a quantity indicator (18) being connected to the magnetic valve (17), to which quantity indicator a jet pipe (19) provided with holes (21 ) throttled by a control band (20) is connected, the jet pipe being surrounded by a premixing section casing (22), to which ignition electrodes (23) are attached, above which there is a thermally insulated (26) combustion chamber (25) with a steel casing (27), in the upper part of which combustion chamber there is temperature measurement (29); and truncated steel cones (28), whereby the steel casing (27) of the combustion chamber (25) is attached to the protective and support casing (7) of the burner with steel fasteners (30), and whereby a control centre (6) made of steel and containing the logic and electric control devices is arranged in the protective and support casing (7).

11. A burner (2) intended to be mounted in a suction well (14) in a landfill for combusting landfill gas (LFG) suction-well-specifically, c h a r a c t e r i z e d in that the burner (2) is dimensioned and designed to be mounted partly in the suction well (14); and that the burner (2) comprises suction means for sucking the landfill gas (LFG) from the suction well (14); and combustion means for combusting the landfill gas sucked from the suction well (14).

12. A burner according to claim 11 , c h a r a c t e r i z e d in that the burner (2) comprises suction means (8, 9, 10) for sucking the landfill gas (LFG) from the suction well (14) to a pressure chamber (11 ) in the burner (2), the pressure chamber comprising measuring means (32) for measuring the pressure of the landfill gas in the pressure chamber (14); that the measuring means (32) are functionally connected to valve members (17) in the burner (2), the valve members being connected to the pressure chamber (11 ); that the measuring means (32) are arranged to transmit a signal to the valve members (17) when the pressure in the pressure chamber (11 ) has exceeded a preset limit value and that the valve members (17) are arranged, as a response to said signals, to open and discharge landfill gas (LFG) from the pressure chamber; that the burner (2) comprises mixing members (20, 21, 22) for mixing the landfill gas (LFG) discharged from the pressure chamber (11) through the valve members (17) with the air to form a combustible mixture; and that the burner (2) comprises ignition members (23) for igniting said combustible mixture.

13. A burner according to claim 11 or 12, characterized in that the burner (2) comprises flame control means (24) arranged to measure the temperature in the burner (2) and functionally connected to valve members (17) in such a way that the valve members (17) remain closed if the temperature measured by the flame control means exceeds a preset limit value.

14. A burner according to claim 13, characterized in that the flame control means (24) are arranged to continuously measure the temperature in the burner in such a way that if there is an interruption in the measurement, the flame control means (24) are arranged to transmit a signal to the valve members (17), which are arranged, as a response, to close the valve members (17).

15. A burner according to claim 11 or 12, characterized in that the burner (2) comprises flame control means (24) arranged to measure the pressure in the burner (2) and functionally connected to the valve members (17) in such a way that the valve members (17) remain closed if the pressure measured by the flame control means exceeds a preset limit value.

16. A burner according to claim 15, characterized in that the flame control means (24) are arranged to continuously measure the pressure in the burner in such a way that if there is an interruption in the measurement, the flame control means (24) are arranged to transmit a signal to the valve members (17), which are arranged, as a response, to close the valve members (17).

17. A burner according to claim 11 to 16, characterized in that it comprises means for remote-starting and remote-monitoring the burner

(2).

18. A burner according to claim 11 for combusting landfill gas suction-well-specifically, characterized in that the apparatus comprises: a pipe (8) connected to a suction well (14), the pipe being connected to a blower (9), from which a connecting pipe (10) leads to a pressure chamber (11), to which a drain pipe (12) provided with a magnetic valve (13) is connected; a sampling pipe (31) leading to a monitoring room (4); a temperature sensor (33); a pressure sensor (32) and a connecting pipe (16) leading to a magnetic valve (17); a quantity indicator (18) being connected to the magnetic valve (17), to which quantity indicator a jet pipe (19) provided with holes (21 ) throttled by a control band (20) is connected, the jet pipe being surrounded by a premixing section casing (22), to which ignition electrodes (23) are attached, above which there is a thermally insulated (26) combustion chamber (25) with a steel casing (27), in the upper part of which combustion chamber there is temperature measurement (29); and truncated steel cones (28), whereby the steel casing (27) of the combustion chamber (25) is attached to the protective and support casing (7) of the burner with steel fasteners (30), and whereby a control centre (6) made of steel and containing the logic and electric control devices is arranged in the protective and support casing (7).