(64c) Meet Environmental Challenges in Modern LNG Plant Design

MEET ENVIRONMENTAL CHALLENGES IN MODERN LNG PLANT DESIGN

George Hu, Senior Manager – LNG and Gas Processing, Technip USA, jihu@technip.com

Dr. Eliza Tsui, Senior Process Engineer, Technip USA, etsui@technip.com

Traditional Liquefied Natural Gas (LNG) facilities are typically located in remote areas, and they are usually required to follow the environmental standards set by the World Bank.  Many modern LNG liquefaction facilities, such as those in North America, are sited in populated location with nearby residential or recreational areas.  More stringent environmental regulations must be met to minimize the impact to the environment, local residents, fishery industry, etc.

Air emissions, waste water discharge, noises, plant safety in terms of explosion, vapor and liquid dispersion are of great concerns by the regulatory agencies and local communities.  Other environmental challenges throughout the life cycle of the LNG facility include dredging of seabed, destruction of vegetation, increased construction traffic, and increased ship traffic causing erosion.  In order to minimize the environmental impact, special consideration will need to be emphasized during design phases to select the Best Available Control Technology (BACT) or Best Available Techniques (BAT).

During process design of the LNG facility, emission points where contaminants are generated will be identified and various control technologies to mitigate the emissions will be evaluated.  Common contaminants such as NOx, sulfur, greenhouse gases including CO2 and VOCs, and particulate matters generated in the LNG facility require additional control technologies to reduce their concentration to the acceptable environmental standards.

Gas turbines that drive the refrigerant compressors and power generation are the major sources of NOx and CO2 emissions.  Using high-efficiency aero-derivative gas turbines can reduce fuel gas consumption as well as emissions.  To further reduce the NOx, CO2, and VOC emissions, Selective Catalytic Reduction (SCR) and Catalytic Oxidation (CO) can be installed to treat the gas turbine exhausts. 

Sulfur management is another important aspect in air emissions control during process design.  Acid gas that is removed in the Acid Gas Removal Unit (AGRU) could have high H2S content.  The acid gas must be first treated to remove the majority of H2S before it can be sent to the thermal oxidizer.  The thermal oxidizer will then convert the HAPs and VOCs into CO2 and H2O before the treated gas is released to the atmosphere.  Mercaptans could be an issue for some LNG facility depending on the LNG product specifications and process design.  When the LNG product specifications has very stringent mercaptans requirement, mercaptans can be removed with the condensate in the Natural Gas Liquids (NGL) removal unit.  However, if the condensate is used as a liquid fuel for the gas turbine, the high level of mercaptans in the condensate must be treated by mercaptans oxidation in order to reduce the sulfur emissions in the exhaust gas of the gas turbines.

Flaring is often minimized in traditional LNG facility due to economic reasons as valuable natural gas is being burnt.  Modern LNG facility has additional air, noise and visual emissions concerns during flaring as greenhouse gases and other contaminants will be released to the atmosphere.  Alternative designs in the flare system such as the use of High Integrity Pressure Protection System (HIPPS) can be applied to reduce the flare load in case of an emergency release.  Ground flare could also be considered to reduce the visual and noise impact.  Noise emissions generated by other equipment can be mitigated by applying proper insulations and adding shelters and enclosures.

Modern LNG facilities share good social responsibility with the local community by implementing process safety in design, using alternative design and Best Available Control Technology to ensure safe operation of the facility, and to minimize the environmental impact to the earth.