Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Utility Patent
1996-09-23
2001-01-02
Trammell, James F. (Department: 2764)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S050000, C073S019040, C073S019050
Utility Patent
active
06169962
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to landfills, and more particularly to systems and methods for controlling gas flow from landfills.
BACKGROUND
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, and because subsequent to recovery the gas can be used as a source of energy.
Accordingly, systems have been developed to extract the methane. One such system is disclosed in U.S. Pat. No. 4,026,355 to Johnson et al. As contemplated by Johnson et al., several wells are sunk vertically into a landfill, and gas seeps into the wells. A vacuum pump is in fluid communication with the wells to evacuate gas from the landfill.
As recognized by Johnson et al., as gas is evacuated from a landfill, oxygenated air can seep back in if gas pressure in the landfill near the surface is lower than atmospheric pressure. The inflow of oxygenated air, however, adversely affects the generation of methane. Accordingly, Johnson et al. teaches a trial and error method of establishing a maximum gas extraction rate while ensuring that landfill gas pressure near the surface remains about equal to atmospheric pressure. Johnson et al. contemplates that the gas extraction rate is established by appropriately establishing the speed of the vacuum pump.
Unfortunately, Johnson et al. cannot be used to control the gas flow rate through individual wells independently of the other wells, because Johnson et al. contemplates controlling only overall flow rate from the landfill by means of a single vacuum pump. As recognized by the present invention, however, gas production can vary throughout a landfill. Consequently, the present invention recognizes that it is sometimes desirable to control the flow rate on a well-by-well basis.
Additionally, the degree of flow rate control afforded by Johnson et al. is relatively coarse, in that the speed of a vacuum pump typically cannot be adjusted in fine increments. As recognized herein, it is desirable to afford a relatively fine degree of flow rate control, to optimize the extraction of methane while avoiding the seepage of air into a landfill.
Moreover, the present invention recognizes, as Johnson et al. does not, that under some circumstances it might be desirable to establish a particular flow rate in response to variables other than vacuum pressure in the landfill. Accordingly, such other variables must be measured, and flow rate established accordingly. Also, it is commonly required that many of these variables be recorded. Currently, the monitoring and recording of landfill variables is labor-intensive and must be done well-by-well. Consequently, current methods of landfill monitoring are costly and time consuming. Fortunately, the present invention recognizes that it is possible to monitor and record such variables, and in addition to control the flow rate of gas extracted from the landfill in response to the variables, without requiring labor-intensive well-by-well monitoring and control.
Accordingly, it is an object of the present invention to provide a landfill monitoring and control system for remotely monitoring and/or recording landfill variables. Another object of the present invention is to provide a landfill monitoring and control system that can control gas flow through a plurality of wells in response to gas flow variables. Still another object of the present invention is to provide a landfill monitoring and control system that can remotely control gas flow through wells in a landfill. Yet another object of the present invention is to provide a landfill monitoring and control system which is easy to use and cost-effective.
SUMMARY OF THE INVENTION
A landfill gas extraction system is disclosed for controlling the extraction of gas from a landfill that has a plurality of gas well cells, with each cell including one or more gas wells. A source of vacuum is in fluid communication with the cells. The present system includes a computer and a plurality of control valves in fluid communication with a respective cell, and each control valve is controllable by the computer for controlling gas extraction from the cell.
Preferably, for each cell, at least one sensor is provided for generating a feedback signal representative of a parameter from the group consisting of: pressure, temperature, flow rate, oxygen concentration, methane concentration, and carbon dioxide concentration. As set forth in detail below, the feedback signal is communicated to the computer and the computer controls the respective control valve in response thereto.
In the presently preferred embodiment the sensor is a flow rate sensor and the feedback signal represents flow rate through the cell. Consequently, the computer controls the respective control valve to establish a predetermined flow rate. If desired, the predetermined flow rate through each cell can be based on a predetermined landfill total flow rate. Also, in each cell a pressure sensor preferably generates a vacuum signal representative of pressure in the cell, and the computer includes computer readable code means for comparing the vacuum signal to a predetermined vacuum setpoint and controlling the control valve in response thereto.
Still further, in each cell an oxygen sensor generates an oxygen signal representative of oxygen concentration in the cell. The computer includes computer readable code means for comparing the oxygen signal to a predetermined oxygen setpoint and controlling the control valve in response thereto.
In addition to the above flow priority control structures, the present invention contemplates further controlling gas flow to minimize oxygen extraction and/or to maximize methane extraction from the landfill. Thus, the computer controls the control valve of each cell to maintain oxygen concentration below a predetermined oxygen concentration setpoint, while controlling the control valves such that the sum of the gas flow rates through all the cells is maintained within a predetermined field flow rate range. Moreover, the computer can control the control valve of each cell to cause relatively more gas to be extracted from cells having relatively high methane concentrations.
In an alternate vacuum priority control strategy, the sensor is a pressure sensor and the feedback signal represents vacuum pressure in the cell, and the computer controls the control valve of each cell to establish a predetermined vacuum pressure. In this alternate embodiment, each cell can include an oxygen extraction sensor for generating an oxygen extraction signal representative of oxygen extraction from the cell. The computer includes computer readable code means for comparing the oxygen extraction signal to a predetermined oxygen extraction setpoint and controlling the control valve in response thereto. Moreover, each cell can include a temperature sensor for generating a temperature signal representative of gas temperature in the cell, and the computer includes computer readable code means for comparing the temperature signal to a predetermined setpoint and controlling the control valve in response thereto.
Regardless of the particular gas extraction priority strategy, a respective vault is provided for holding each control valve. In accordance with the present invention, each vault includes a respective pressurized enclosure for holding the sensors of the present invention therein, with the control valve being external to the enclosure. Preferably, the control valve is a pneumatically-operated valve. Furthermore, a vault controller is disposed in the enclosure, and the vault controller is in communication with the computer. The vault controller can control its respective control valve in response to signals downloaded from the computer, such that in the event that communication between the computer and a vault controller is lost, the vault controller continues to operate its associated control valve in accordance with the logic discusse
Beach James Joseph
Brookshire Donald
Brookshire Ronald L.
Brookshire Travis
Kalantar-Nejad Seyed Mohammed Reza
Landfill Gas & Environmental Products, Inc.
Nguyen Cuong H.
Rogitz John L.
Trammell James F.
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