Chemical Technology March 2016

LNG vaporisers selection based on site ambient conditions – Part 2

by John Mak, Senior Fellow and Technical Director, Nick Amott, Curt Graham, Dhirav Patel, Fluor, USA

Part 1 of this article appeared in the August 2015 issue of Chemical Technology . Today’s LNG landscape is changing. Many of the newer LNG import terminals are smaller in size and are mainly located in South East Asia and South America. These new terminals place a strong emphasis on energy efficiency, environmental impacts and emissions.

Heat integration with power plant Simple cycle power plant W heretheregasificationplantislocatedclosetoapowerplant, a hybrid type systemusingwaste heat fromthe gas turbine and Submerged Combustion Vaporisers (SCVs) for LNG heating can increase the thermal efficiency of the integrated facility. The heat integration scheme for a simple cycle power plant can be illustrated as shown in Figure 7. In this configuration, hot water is used as an intermediate fluid. The circulating water is heated by the hot exhaust gas from the gas turbine in a direct contact heating tower. When waste heat recovery is operated, the fuel gas burners of the SCVs are not required; the LNG vaporisation duty is supplied by the circulating hot water. Fuel firing with SCVs is only required when the power plant is not operating or when the quantity of waste heat is insufficient to support the regasification duty. With the use of waste heat, there are significant energy savings, in addition to the reduction in CO 2 and NOx emissions from the facility. In addition, the chilled water from the LNG plant can be used to lower the gas turbine inlet temperature using an exchanger. This is particularly advantageous when operating during hot summer days when the gas turbine output typically drops due to higher ambient temperature. Lowering the gas turbine inlet temperature can significantly increase the power output as shown in Figure 8. Typically, for each degree centigrade drop in air temperature, power output can be increased by 0,7 to 1,2 % depending on the gas turbine aerodynamic design characteristics. Typically, aero- derivative gas turbines are designed with a higher compression

Figure 7: Simple cycle power plant integration

ratio and higher efficiency than industrial gas turbines, and would benefit more with inlet air chilling, as shown in Figure 8. Combined cycle power plant For combined cycle power plants, low pressure steam is condensed in the surface condenser in the steam cycle using cooling water. The cooling water return can be used to supply heating to the LNG plant as shown in Figure 9. This integration method is cur- rently employed in the large Grain CHP station to increase thermal efficiency and reduce emissions. The thermal efficiency of an

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Chemical Technology • March 2016