Two systems designed for the thermal combustion and abatement of hydrocarbon emissions from two natural gas fractionation trains have been installed at a Southwest midstream natural gas processing facility. Designed and manufactured by Catalytic Products International (CPI), Lake Zurich, Ill., the identical Thermal Combustor Systems (TCSs) were installed to eliminate hydrocarbon emissions from an acid gas stream and a disulfide oil (DSO) separator gas stream.

The combustion systems are part of an expansion at the fractionation complex. The gas streams contain methane, ethane, propane, butanes, nitrogen, carbon dioxide (CO2) and dimethyl sulfide, among other compounds. The thermal combustion systems will destroy the hydrocarbon emissions with 99.9 percent destruction rate efficiency (DRE), according to CPI.

CPI worked closely with the gas processing facility’s engineering consultant providing the design, supply and startup of the two systems. The TCSs were custom designed for the particular gas trains and included auxiliary devices to aid in performance and safety. Custom features include electrical components designed for Class 1 Division 2, oxygen (O2) analyzers and a temperature safety system.

Custom Thermal Oxidation Systems Have Wider Use

Raw natural gas contains water, CO2, sulfur compounds and heavy hydrocarbons that must be removed before it is sent to the pipeline. Natural gas sources with large amounts of acid gases, also known as sour gases, must be treated and sweetened to meet natural gas pipeline specifications and sale contracts.

CPI’s TCS units are designed to burn or combust hydrocarbon vapor mixtures that have varying energy content. Often used where enclosed flares may fail, the TCS approach combines aspects of both an enclosed flare and a thermal oxidizer. They are custom designed for a particular process stream and can include forced draft or a drafted system along with auxiliary devices to aid in performance and safety.

During operation, the TCS sequence begins with a fresh-air purge of the system. After purging, the pilot and main burners are ignited and held in place until appropriate flame scanning safeties are met, after which process gas is introduced to the oxidation system. This increases the internal temperature within the combustion chamber. To control the temperature and facilitate combustion, fresh air is added via natural aspiration or forced-draft introduction.

The thermal combustion system is capable of automatically adjusting to the process gas volumes, concentrations and heat values. If the process gas cannot support combustion, natural gas may be added as a support fuel.