Liquefaction system and method for controlling turbine inlet temperature of liquefaction system

Abstract

A liquefaction system comprises: a temperature setting unit for setting an inlet gas temperature on entry to a cold turbine; a control valve for controlling an amount of gas fed to the cold turbine, correspondingly with an inlet gas temperature measured by the temperature measuring unit; and a control unit which compares the inlet gas temperature measured by the temperature measuring unit with a warning temperature set value plus a margin, and sets a first operating state when the inlet gas temperature is equal to or less than the warning temperature set value plus the margin and also sets an emergency stoppage temperature set value at the warning temperature set value plus the margin, and sets a second operating state when the inlet gas temperature is greater than the warning temperature set value plus the margin, the control unit performing control in response to the second operating state to make a degree of opening of the control valve greater than a degree of opening during the first operating state in order to lower an inlet pressure of the cold turbine, and performing control in response to the first operating state to make the degree of opening of the control valve smaller than the degree of opening during the second operating state in order to raise the inlet pressure of the cold turbine.

What is claimed is: 
     
         1 . A liquefaction system for liquefying a product gas provided from an air separation unit, the liquefaction system comprising:
 a temperature measuring unit configured to measure an inlet gas temperature on entry to a cold turbine;   a control valve configured to control an amount of gas fed to the cold turbine, correspondingly with the inlet gas temperature measured by the temperature measuring unit; and   a control unit which is configured to, from the beginning of start-up of the liquefaction system, compare the inlet gas temperature measured by the temperature measuring unit with a warning temperature set value plus a margin, and set a first operating state when the inlet gas temperature is equal to or less than the warning temperature set value plus the margin and also set an emergency stoppage temperature set value at the warning temperature set value plus the margin, and set a second operating state when the inlet gas temperature is greater than the warning temperature set value plus the margin,   wherein the control unit is configured to control, in response to the second operating state, a degree of opening of the control valve greater than a degree of opening during the first operating state in order to lower an inlet pressure of the cold turbine, and is further configured to control, in response to the first operating state, the degree of opening of the control valve be smaller than the degree of opening during the second operating state in order to raise the inlet pressure of the cold turbine.   
     
     
         2 . The liquefaction apparatus according to  claim 1 , further comprising:
 one or more compression devices for compressing the product gas fed from the air separation unit;   a compressor of a first expander-compressor to which a compressed gas fed from a post-stage of the compression device is introduced;   a compressor of a second expander-compressor to which a gas compressed by the compressor of the first expander-compressor is introduced;   a first heat exchanger to which the gas compressed by the compressor of the first expander-compressor is introduced via a first pipe;   a second pipe which branches from the first pipe and serves to feed a portion of the gas to the turbine which forms part of the second expander-compressor;   a first separator to which the remainder of the gas is fed via the first pipe; and   a third pipe for feeding the gas expanded in the turbine of the second expander-compressor to the first separator.   
     
     
         3 . The apparatus according to  claim 2 , wherein the control valve is disposed in the first pipe at a location that is downstream from the branching point of the second pipe. 
     
     
         4 . A method for controlling a turbine inlet temperature of a liquefaction system for liquefying a product gas provided from an air separation unit, the method comprising:
 measuring an inlet gas temperature on entry to a cold turbine;   comparing, from the beginning of start-up of the liquefaction system, the inlet gas temperature measured in the temperature measuring step with a warning temperature set value plus a margin, and setting a first operating state when the inlet gas temperature is equal to or less than the warning temperature set value plus the margin, and setting an emergency stoppage temperature set value at the warning temperature set value plus the margin, and setting a second operating state is set when the inlet gas temperature is greater than the warning temperature set value plus the margin; and   a control step in which control is performed in response to the second operating state to lower an inlet pressure of the cold turbine, and control is performed in response to the first operating state to raise the inlet pressure of the cold turbine.   
     
     
         5 . The method according to  claim 4  wherein the first operating state corresponds to a normal operating state, and the second operating state corresponds to an operating state when the system is launched. 
     
     
         6 . The method according to  claim 4 , wherein the product gas is nitrogen. 
     
     
         7 . The method according to  claim 4 , wherein the product gas is liquefied downstream of the turbine. 
     
     
         8 . The method according to  claim 4 , wherein the degree of opening of the valve during the second operating state is between 60% and 70% and the degree of opening of the valve during the first operating state is between 50% and 60%. 
     
     
         9 . The method according to  claim 4 , further comprising the step of liquefying a portion of the whole amount of product gas and feeding said portion to a product tank, with a remainder of the whole amount of product gas being circulated through the turbine and then being sent to the product tank.