The present invention relates generally to landfills, and more particularly to systems and methods for disposing of liquid condensate from landfill gas recovery systems.
Waste products decompose in landfills, and after the free oxygen in the landfill is depleted, the waste product decomposition generates methane gas. It is desirable to recover this methane gas for environmental and safety reasons. To this end, landfill gas recovery systems have been introduced which collect the gas generated in landfills and burn the gas in flares on the landfill.
Occasionally, gas in the recovery system condenses with other fluids such as water. This methane-based condensate, like the gas, must be removed from the landfill for safety and environmental reasons, and to ensure that blockage of gas piping and damage to the flare system does not occur. Typically, the condensate is simply pumped out of the gas recovery system and transported to a hazardous waste dump site, where it is disposed of.
As recognized herein, transporting hazardous condensate to another waste facility for disposal is not only expensive, it does not solve the environmental problem of disposing of the condensate, but rather only moves the problem to a hazardous waste disposal facility. With this in mind, the present invention recognizes the desirability of economically disposing of the condensate at the site at which it is recovered in an environmentally benign way.
As recognized herein, one method for disposing of the condensate is to burn it in the flare chamber that is used to burn the methane gas. Typically, a landfill gas recovery flare chamber includes a ring of vertically-oriented burners located near the bottom of the chamber, and methane gas is piped through the burners and oxidized, with the hot oxidation products exhausting upwardly up through the flare chamber and out of the open top end of the chamber. In such a flare chamber, the condensate can be injected radially into the flare chamber above the burners by entraining the condensate in a pressurized high velocity air stream above the flame of the flare.
Such a system, as understood by the present invention, unfortunately requires a relatively expensive air compressor to generate the pressurized air stream. Also, a portion of the high velocity condensate stream tends to impinge on the wall of the flare chamber that is opposite the condensate injection point, damaging the wall.
Alternatively, the present invention understands that condensate can be pumped upwardly into the flare chamber through a vertical pipe that is centrally located in the flare chamber below the ring of burners. As the condensate moves upwardly past the burners, it flashes into vapor. As recognized by the present invention, however, the injection rate of condensate sometimes must undesirably be limited to avoid excessively cooling the flare chamber as the latent heat of vaporization of the condensate is overcome. Excessively cooling the flare chamber could reduce the ability of the flare to burn the methane gas and condensate. Moreover, the present invention understands that landfill process controls, including those related to condensate injection systems, preferably be automatic, to more accurately control the processes and to avoid the necessity of personnel undertaking time consuming and repetitive process monitoring and adjustment.
As further recognized herein, it is possible to provide a condensate injection system having a relatively high condensate injection rate without excessively cooling a flare chamber, and to automatically control the condensate injection rate as appropriate for the particular energy level of the flare. Accordingly, it is an object of the present invention to address one or more of the abovenoted considerations.
A compressorless condensate injection system is disclosed for a landfill having a flare chamber including at least one wall that is heated when the flare chamber burns methane gas extracted from the well. The system includes a condensate reservoir and a condensate pump in fluid communication with the reservoir to pump condensate into the chamber at a high pressure, preferably 40-250 pounds or more. At least a first injection line is in fluid communication with the condensate pump but not with an air compressor. The first line terminates in a first nozzle that is positioned on the flare chamber for directing condensate into the chamber such that condensate from the nozzle is vaporized when it is sprayed into the chamber without requiring the use of compressed air.
In a preferred embodiment, the first line has a heat exchange segment that is curved, e.g., the segment can extend partially or completely around the flare chamber before terminating in a nozzle. In this way, fluid in the first line can be heated when the flare chamber burns gas extracted from the well.
A first control valve preferably is in fluid communication with the first injection line for selectively blocking fluid flow therethrough, with the first control valve being responsive to electrical control signals. Indeed, secondary injection lines with respective solenoid valves and nozzles can be provided for selectively injecting even greater amounts of condensate into the chamber, depending on vaporization conditions. These secondary nozzles can be oriented to direct condensate upwardly and radially inwardly into the flare chamber. If desired, a ring line can communicate with the condensate pump, and the ring line terminates in a ring line nozzle disposable adjacent the burners of the flare.
Additional features can include a methane gas inlet line and a methane sensor for measuring a methane concentration in the inlet line, a flow sensor for measuring gas flow rate in the inlet line, and a temperature sensor for sensing temperature in the flare chamber. Also, condensate temperature and pressure can be measured in each heat exchange segment. Electrical control signals for controlling the solenoid valves can be generated by a computer based on these signals.
In another aspect, a computer program device can include a computer program storage device readable by a digital processing system, and a computer program on the program storage device and including instructions executable by the digital processing system for performing method steps for controlling at least one control valve disposed in at least one condensate injection line in a landfill flare chamber. The method undertaken by the computer includes determining a gas volume burn rate based on a combination of methane concentration in gas to be burned in the chamber, flow rate of gas, and flare chamber temperature. Also, the computer generates one or more control signals to control the valve or valves in response to the determination of gas volume burn rate.
In still another aspect, a condensate injection nozzle includes a nozzle body defining a pathway therethrough, and an orifice element disposed in the pathway. An diversion plate is also disposed in the pathway. In accordance with present principles, the diversion plate causes turbulent flow of the condensate, prior to the condensate passing through the orifice element and being injected into the flare chamber.
The details of the present invention, both as to its structure and its operation, can best be appreciated in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: