Optimization of Landfill Gas Production Using Vacuum Regulator
Since the gas production capacity and character of each well varies in landfills, each well needs to be vacuumed according to its capacity. However, when choosing vacuum pressure, applying vacuum below the capacity of the well will cause the full capacity of the well to be unavailable and the pressure inside the well will increase and leak methane into the atmosphere. Applying vacuum above the capacity of the well will cause the well to draw oxygen from the atmosphere and cause gas-producing anaerobic bacteria to die in an oxygenated environment, resulting in reduced gas production in the well. Therefore, the vacuum to be applied for each well should be optimized and kept constant with a certain error. Vacuum should not be allowed above and below these specified vacuum limit values.
There are already manually regulating valves at the head of each well to control the vacuum in the field. These valves fall into the throttle valve group and do not keep the vacuum value at a certain value, but provide some vacuum drop due to the well gas flow rate. Since this amount is related to the drop gas flow, both the flow rate changes and the changes in the blower inlet pressure cause changes in the vacuum applied to the well. In this way, the amount of gas produced by the well, and therefore the change of flow, causes the change of vacuum applied to the well.
The hand valve reduces the vacuum applied to the well to the set value. In this case, the pressure applied to the wells cannot be kept at the desired value in response to changes in operating conditions. As the blower pressure increases, the pressure applied to the wells increases proportionally. The flow drawn from the wells in relation to pressure changes also changes. Such variations in pressure and flow rate result in deviations from the optimized vacuum value for each well and require that each well be re-adjusted with the hand adjustment valve. This process is both difficult to manage and high in labor. In addition, in case of hand adjustment valve, all wells are affected by the vacuum changes in the system.
The vacuum to be applied to each well should be as constant as possible despite the variable blower pressures and should not change except for permissible deviations. In addition, a system that does not require human intervention as much as possible should be targeted in order to alleviate the labor force. For this purpose, the use of mechanical vacuum regulator instead of hand valve between the blower and the well is considered as a solution.
In the researches about vacuum regulator valve, it is concluded that there is no mechanical vacuum regulator suitable for pipe diameters used in the field. As a result of this, our company have had MADAS company to produce the vacuum regulator with the required features.
MADAS RGN DN65 VACUUM REGULATOR TECHNICAL REPORT
Madas RGN DN 65 vacuum regulator is produced by the factory by modifying the series positive pressure regulator. In this modification process, the ventilation inlet opening to the top of the diaphragm in the positive pressure regulator is taken to the bottom of the diaphragm; the impulse line inlet has been changed from the bottom to the top of the diaphragm and sealed with “o-rings” to prevent this part from coming into contact with the atmosphere.
Below is the technical document of the vacuum regulator Madas RGN DN 65.
The performance tests with various set values of this regulator are shown below.
It is an expected result that the vacuum starts to deviate from the set value in the yellow and red zones. This is because the pressure applied by the blower approaches or falls below the regulator setpoint, resulting in a certain amount of pressure drop due to the pressure loss within the regulator, depending on the gas flow.
RESULTS AND EVALUATION
As a result of the tests, it was seen that the regulators kept the well-side outlet pressure constant despite the pressure and flow changes in the system at the expected level within the frame of permissible deviations.
It is also seen in the table above (yellow and red zones) that deviations from the set value start to occur as the regulator inlet pressure approaches the set value.
In the region where the deviations do not exceed the permissible limits (green zone in the table), regulation is considered to be successful, although there are certain deviations as expected.
As a result; If vacuum regulators are used instead of manual adjustment valves for the landfill, it is concluded that the pressure to be applied to the wells will not change except for certain deviations and the wells will not be adversely affected by the change of the flow and pressure of the system. Thus, the gas production performance of the landfill will be improved.