Controlling Liquefaction of Natural Gas

Abstract

A gas liquefaction process, especially for producing LNG, maintains product flow rate and temperature by controlling the refrigeration so that variation to reduce any difference between actual and required product temperatures is initiated before variation of the product flow rate to reduce any difference between actual and required flow rates.

Description

BACKGROUND OF THE INVENTION[0001]This invention relates to the field of control systems for production of liquefied gas (LG), and more specifically, to a process and system which controls LG production and LG temperature. It has particular but not exclusive application to liquefying natural gas (NG) to produce liquefied natural gas (LNG).[0002]Systems for the liquefaction of natural gas (NG) by refrigeration in heat exchange means, especially using a multicomponent refrigerant, are in use throughout the world. Control of the LNG production process is important to operate a plant efficiently, especially when attempting to meet demands for incremental production for downstream processing or when attempting to adjust to external process disturbances. Essentially simultaneous and independent control of both the LNG production flow rate and temperature is important for LNG plant operation. By fixing and maintaining the LNG production rate, plant operators can adequately plan and achieve ...

AI Technical Summary

Benefits of technology

[0012]varying the refrigeration provided by said heat exchange means in response to said LG flow rate and LG temperature comparisons to reduce any differences, characterized in that the refrigeration is varied to reduce any LG temperature difference before variation of the LG flow rate to reduce any LG flow rate difference. Thus, this aspect allows the LG flow rate and temperature to be independently set and refrigeration to be correspondingly adjusted to meet the set requirements with limited thermal stress on the heat exchange means. However, the control system concept of the invention is applicable to LG liquefaction processes in which the LG flow rate and temperature requirements are constant but from time to time some variation is required to the actual values in order to compensate for a change in other parameters, such as NG feed temperature and composition, MR composition, ambient air temperature, cooling water temperature, atmospheric pressure etc., that has caused the actual value to deviate from the required value.

[0017]means for varying the refrigeration provided by said heat exchange means in response to said LG flow rate and LG temperature comparisons to reduce any differences,

Problems solved by technology

However, if regulatory control is not adequate, even standard day to day operation is adversely affected.

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