Operation on Process Off-Gas of a 24MW SGT-600 Gas Turbine on an LNG Plant in China

A privately owned LNG plant was taken into service at the Tuha Oil Fields in western China during 2004. The plant is the first of its kind and will produce Liquefied Natural Gas (LNG) from associated gas from the oil fields. The LNG is delivered to Central China by trucks. The plant was delivered by Tractebel with Linde AG being responsible for the LNG process design. The compression set of the refrigeration cycle consists of a three-stage Ebara compressor driven by a 24 MW Siemens SGT-600 gas turbine operating on the off-gas from the LNG plant. The operation of the gas turbine integrated in this plant is associated with some special challenges: • the ambient conditions out in the desert; • the fuel, that varies from natural gas to a process gas consisting of methane diluted with up to 28% nitrogen; • the refrigeration medium, which is circulated by the gas turbine driven compressor, changes in composition dependent on load; • the starting procedure with the compressor in the refrigeration loop. A combustion test was performed to verify that the DLE combustion system could accept the variations in gas composition. The control system was modified to handle the variable gas qualities in the fuel and in the refrigeration loop. Since the gas turbine/compressor set is an integrated part of the LNG process the commissioning was a long process governed by the LNG plant commissioning. It included some unexpected events. Now all is working well. It has been shown that a standard SGT-600 DLE unit can start and operate reliably and with low emissions on very much diluted natural gases. The paper contains a brief description of the LNG plant, definition of the special requirements on the gas turbine, a description of the combustion verification test on diluted gas, some events during commissioning and finally the engine verification test.