Landfill gas extraction constant flow control method and device

A landfill gas well extraction control system comprising:

• a. means for opening a differential pressure regulating valve in a complete wellhead assembly gas path to a nominal position,
• b. means for opening a second valve in the gas path,
• c. means for measuring the differential pressure across the differential pressure regulating valve,
• d. means for setting the second valve position to obtain the desired differential pressure across the differential pressure-regulating valve,
• e. means for measuring the differential pressure equivalent to the entire flow through the complete wellhead assembly gas path,
• f. means for maintaining the desired complete wellhead assembly gas path differential pressure at a constant value,
• g. means for obtaining a sample for measuring the gas composition on a periodic basis, and
• h. means for adjusting, if needed, the differential pressure equivalent to the entire flow through the complete wellhead assembly gas path.

A multiplicity of constant flow wellhead assemblies controlling flow through piping for a multiplicity of landfill gas extraction wells that use a common extraction vacuum source, each constant flow wellhead assembly comprising:

• a. a differential pressure-regulating valve,
• b. a second valve connected to the regulating valve by piping,
• c. a piping connection to the vacuum source,
• d. a multiplicity of pressure taps arranged such that the taps measure the differential pressure across the differential pressure-regulating valve and measure the differential pressure equivalent to the entire flow through the wellhead assembly,
• e. a control circuit providing display capability of the differential pressure between the pressure taps equivalent to the entire flow through the wellhead assembly, and display capability of the differential pressure between the pressure taps equivalent to the differential pressure across the differential pressure-regulating valve, and which positions the differential pressure-regulating valve to maintain a desired flow through the wellhead assembly, and
• f. a sample collection port located in the piping such that a sample of the well gas may be obtained.

A constant flow control wellhead assembly for a landfill gas well extraction system comprising:

• a. a manually controlled valve providing an open position, a closed position, and a multiplicity of partially open valve positions,
• b. a pressure-regulating valve,
• c. a multiplicity of pressure measurement taps in the piping arranged such that two taps may be used to measure the differential pressure across the pressure-regulating valve and such that two taps may be used to measure the differential pressure equivalent to the entire flow through the wellhead assembly,
• d. a sample tap such that a sample of the landfill gas passing through the wellhead assembly may be obtained, and
• e. a control circuit arranged such that the differential pressure across the pressure-regulating valve may be displayed to set the desired position of the manually controlled valve, and the differential pressure equivalent to the entire flow through the wellhead assembly may be displayed such that it may be used as a control parameter for the pressure-regulating valve.