Reducing the Risks of Emissions and Potential Loss of Production Due to Uncontrolled Off Spec Gas into Pipeline by Modification of the Logic of Shutdown Valve

摘要

Potential loss of production and gas emissions to flare constitute major problems in gas processing plant when off-spec gas cannot be controlled and may cause the entire gas to pipeline being off-spec and endanger liquefied natural gas (LNG) plant as the buyers have to burn the entire gas in gas pipeline to flare and, thus, there is an increase in emissions to environment. Normally, the gas impurity parameters to be maintained in a plant consist of Hydrogen Sulfide (H2S), Carbon Dioxide (CO2) and water content (H2O), which are monitored by the online analyzer transmitter installed after the purification units, such as acid gas removal unit and dehydration unit. The transmitter normally does not send the interlock signal to command the plant shutdown due to several factors which may affect the values of the analyzer. However, the off-spec gas shall not be allowed to enter the pipeline; otherwise, emissions and loss of production cannot be controlled. Among the methods to control off-spec gas is to shut the export gas to the pipeline remotely whenever there is confirmed off-spec sales gas. Modification of control of sales gas shutdown during an off-spec event can be done by adding a logic from the remote push button to the shutdown valve at the export gas line which can be operated by human intervention to prevent the off-spec gas from being delivered to the pipeline and buyers which may lead to an increase in emissions to environment and a loss of production.