(72d) Lng Pump Applications with Variable Speed Motor Controls at Lng Regasification Terminals

Due to the increased demand in natural gas, number of new LNG re-gasification terminals will be constructed in the U.S. These terminals supply gas to the gas transmission lines where the demand of natural gas varies from season to season and also during the day resulting in wide variation of pipeline delivery pressure and export gas rate from the terminal.

Presently most the LNG terminal cryogenic pump applications running in high pressure LNG re-gasification typically run on fixed speed motors and produce a single flow versus head curve at that speed. Control of these pumps is accomplished by throttling the discharge pressure with a control valve or bypass of a portion of the discharge flow to a secondary flow stream. Pumps that are run at a fixed speed have a single Best Efficiency Point (BEP) at which the pump is designed to run at the rated production point. Pump flows that are throttled by reduction of the discharge pressure run off of the BEP and therefore will reduce the efficiency.

The efficiency and range of operation for pumps in cryogenic service can be improved by use of variable speed controls. Adjustment of the speed allows the user to accurately control the operating characteristics of the pump over a greater range with better overall efficiency. Efficiency of pump operation at flow points that are off design can be improved by varying the pump speed to a point on the pump hydraulic curve which matches the BEP for the desired flow.

The paper will discuss how The variable speed operation of cryogenic pumps will result in improved operating costs with more effective control of the output flow and head In addition the paper will also discuss various other design, control and economic benefits of utilizing variable speed motors at LNG terminals.