Integrated Solutions for LNG Plants System Studies: Simultaneous Simulation of Electrical and Steam Systems

Abstract

Abstract In the last decades the importance of LNG (liquid natural gas) has been increasing continuously. Worldwide a large number of plants have been erected using classical compressor technology driven by direct-coupled gas turbines. This approach limits the availability due to maintenance restrictions and the missing spinning redundancy. Modern concepts are based on large full electrical compressors which allow controlling the process with reduced energy consumption. The corresponding maintenance concept improves the LNG plant availability significantly. LNG plants generally have no grid connection, i.e. the LNG plant must be supplied under island conditions. Guarantee a high availability of the electrical and steam generation is however necessary. Therefore it is primarily important not only to provide a suitable system design, but also to investigate its ability to dynamically withstand heavy events, taking into account the mutual interaction of electrical output of the steam turbine and the variation of the steam demand, the boiler capacity and the dynamics of the supplementary firing. Aim of this paper is to illustrate an integrated approach for the steady-state and dynamic study of LNG plants, in which both the electrical and the steam system are completely modeled and interfaced. After separate design, both systems are simulated with the same simulation tool, so operations and events are immediately incorporated and the two systems show the reciprocal interaction. Thus more realistic and significant system responses to events are obtained, with increase in the project efficiency and reduction of investment costs. To validate the approach, a typical LNG plant is modeled, including all relevant equipment and controllers, as well as process system units, with PSS®NETOMAC. The simulation of severe outage cases allows to optimize the basic electrical and steam control concept and to design the load or generation shedding sequences, depending on the outage severity.