Patent Application
20240060715
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French patent application No. JP2022-131511, filed Aug. 22, 2022, which is herein incorporated by reference in its entirety.
The present invention relates to a liquefaction system, and relates to a method for controlling an inlet temperature of a cold turbine used in a gas liquefaction system, for example.
A gas liquefaction system generally comprises a compression device, a cold turbine, and a heat exchanger. A liquefaction process generally involves liquefying a portion of the whole amount of supplied gas and feeding this portion to a product tank, with the remainder being circulated through the liquefaction system and re-treated together with newly supplied gas.
The cold turbine in the liquefaction system is operated so that a gas enters the cold turbine where it is used, and then exits as a gas. In order to avoid liquefaction at a cold turbine outlet, the system is controlled to output a warning or perform an emergency stoppage (turbine tripping), etc. on reaching a temperature at which liquefaction might occur. The temperature at which liquefaction might occur is calculated from a pressure difference between the turbine inlet pressure and the turbine outlet pressure. The liquefaction system is designed on the basis of normal operation, and is controlled so that the amount of gas fed to the cold turbine is maximized, while avoiding liquefaction by observing this temperature (the system is operated with the liquefaction process maximized).
JP H5-45050 A describes a liquefaction process comprising: one or more permanent gas compression devices, one or more permanent gas expansion turbines, and a heat exchanger for performing heat exchange between permanent gas and liquefied natural gas.
However, during start-up of the liquefaction system when it is being operated with the liquefaction process maximized, the gas pressure at the turbine inlet increases, and if the turbine inlet temperature reaches the warning output temperature or emergency stoppage temperature, the operator has to intervene each time this occurs. It would also be possible to respond to this situation by operating the turbine at low speed during start-up, but this would delay launching of the liquefaction process and cause lost time.
Furthermore, the warning output temperature and the emergency stoppage temperature are fixed to correspond to normal operation, and are therefore incompatible with start-up or abnormalities, etc.
The present disclosure provides a liquefaction system and a method for controlling a turbine inlet temperature of the liquefaction system, which enable a gas temperature at an inlet of a turbine to be measured and enable a warning output temperature set value and an emergency stoppage temperature set value to be varied correspondingly with an operating state.
The present disclosure relates to a liquefaction system (100) for liquefying a product gas provided from an air separation unit (A), the liquefaction system comprising: a temperature measuring unit (T5) for measuring an inlet gas temperature (T1) on entry to a cold turbine (ET22); a control valve (PV5) for controlling an amount of gas fed to the cold turbine (ET22), correspondingly with the inlet gas temperature (T1) measured by the temperature measuring unit (T5); and a control unit (200) which, from the beginning of start-up of the liquefaction system, compares the inlet gas temperature (T1) measured by the temperature measuring unit (T5) with a warning temperature set value plus a margin, and sets a first operating state when the inlet gas temperature (T1) 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 (T1) is greater than the warning temperature set value plus the margin, the control unit (200) performing control in response to the second operating state to make a degree of opening (OP1) of the control valve (PV5) greater than a degree of opening (OP2) during the first operating state in order to lower an inlet pressure of the cold turbine (ET22), and performing control in response to the first operating state to make the degree of opening (OP2) of the control valve (PV5) smaller than the degree of opening (OP1) during the second operating state in order to raise the inlet pressure of the cold turbine (ET22).
The first operating state means a normal operating state, and the second operating state means an operating state when the system is launched.
The control unit (200) may comprise: a state setting unit (201) which compares the inlet gas temperature (T1) measured by the temperature measuring unit (T5) with the warning temperature set value plus the margin, and sets the first operating state when the inlet gas temperature (T1) is equal to or less than the warning temperature set value plus the margin and also sets the emergency stoppage temperature set value at the warning temperature set value plus the margin, and sets the second operating state when the inlet gas temperature (T1) is greater than the warning temperature set value plus the margin; and a valve control unit (202) which performs control in response to the second operating state set by the state setting unit (201) to make the degree of opening (OP1) of the control valve (PV5) greater than the degree of opening (OP2) during the first operating state in order to lower the inlet pressure of the cold turbine (ET22), and performs control in response to the first operating state set by the state setting unit to make the degree of opening (OP2) of the control valve (PV5) smaller than the degree of opening (OP1) during the second operating state in order to raise the inlet pressure of the cold turbine (ET22).
The “warning temperature set value” is a temperature set value at a timing for warning of the possibility of gas liquefaction at the cold turbine outlet. The temperature is derived from a pressure difference in pressure measuring units provided at the turbine inlet and outlet, and a warning is output when this temperature reaches the “warning temperature set value”.
The “margin” is set while taking account of control responsiveness, and is set in a range from 1° C. to 3° C., for example.
The “emergency stoppage temperature set value” is a temperature set value at a timing for emergency stoppage of the cold turbine. The temperature is derived from the pressure difference in the pressure measuring units provided at the turbine inlet and outlet, and there is an emergency stoppage of the cold turbine when this temperature reaches the “emergency stoppage temperature set value”.
As used herein, the cold turbine is a turbine preferably located within a cold box and has an inlet temperature that is below zero degrees Celsius.
The liquefaction system (100) may comprise:
The control valve (PV5) is provided in the pipe (L412) downstream from the position of the pipe (L4121).
The temperature measuring unit (T5) is provided in the pipe (L4121).
The present disclosure relates to a method for controlling a turbine inlet temperature of a liquefaction system for liquefying a product gas provided from an air separation unit (A), the method comprising: a temperature measuring step in which an inlet gas temperature (Ti) on entry to a cold turbine (ET22) is measured; a setting step in which, from the beginning of start-up of the liquefaction system, the inlet gas temperature (T1) measured in the temperature measuring step is compared with a warning temperature set value plus a margin, and a first operating state is set when the inlet gas temperature (T1) is equal to or less than the warning temperature set value plus the margin, and an emergency stoppage temperature set value is also set at the warning temperature set value plus the margin, and a second operating state is set when the inlet gas temperature (T1) 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 (ET22), and control is performed in response to the first operating state to raise the inlet pressure of the cold turbine (ET22).
(1) There is no need for the turbine to be operated at low speed during start-up, which enables a rapid transition to normal operation.
(2) The need for operator intervention is eliminated.
(3) The transition from start-up to normal operation can be fully automated.
Other features and advantages of the invention will be further disclosed in the description that follows, and in several embodiments provided as non-limiting examples in reference to the appended schematic drawings, in which:
Several embodiments of the present invention will be described below. The embodiments described below illustrate examples of the present invention. The present invention is in no way limited by the following embodiments, and also includes a number of variant modes which are implemented within a scope that does not alter the gist of the present invention. It should be noted that not all of the components described below are essential components of the present invention.
Decompression devices 1 and 2 in a liquefaction system 100 according to embodiment 1 will be described with the aid of
The liquefaction system 100 utilizes a liquefaction cycle to liquefy a predetermined product gas provided from an air separation unit A, for example a nitrogen-rich gas, oxygen-rich gas, or argon-rich gas, etc.
The liquefaction system 100 according to this embodiment comprises: first and second compression devices C1, C2; first and second expander-compressors ET1, ET2; first and second heat exchangers E20, E21; first and second separator units V20, V21; and a liquefied gas tank (LIN TANK).
The nitrogen-rich gas fed from the air separation unit A passes through a pipe L1 and is compressed by the first compression device C1 then compressed by the second compression device C2. A decompression method in these compression devices will be described later.
A portion of the nitrogen gas compressed in the second compression device C2 is fed to a compressor ET11 of the first expander-compressor ET1 via a first branch pipe L41, then fed to a compressor ET21 of the second expander-compressor ET2 via a pipe L411, and is next fed to the first heat exchanger E20 via a pipe L412 where it is cooled, and a portion thereof arrives at the first separator unit V20. The remainder of this nitrogen gas is fed to an expander ET22 (corresponding to a cold turbine) of the second expander-compressor ET2 via a branch pipe L4121 branching from the pipe L412 partway through the first heat exchanger E20, and is then fed to the first separator unit V20 via a pipe L4122. A gas component drawn from a column top of the first separator unit V20 passes through the first heat exchanger E20 via a pipe L6, and is fed to a pipe L2 on an intake side of the compression device C2.
Liquefied nitrogen gas drawn from a bottom of the first separator unit V20 passes, via a pipe L5, through a portion of the second heat exchanger E21 where it is cooled, after which a portion thereof is fed to the liquefied gas tank (LIN TANK). The remainder of this liquefied nitrogen gas is fed to the second separator unit V21 via a pipe L51. A gas component drawn from a column top of the second separator unit V21 is fed to the second heat exchanger E21 via a pipe L52 and then returned to the second separator unit V21. A liquid component drawn from a bottom of the second separator unit V21 passes through a pipe L53 to function as cold in the second heat exchanger E21, then functions as cold in the first heat exchanger E20, and is fed to the pipe L1 on an intake side of the first compression device C1.
The remainder of the nitrogen gas compressed by the second compression device C2 passes through a portion of the first heat exchanger E20 via a second branch pipe L42 branching from a pipe L4, and is fed to an expander ET12 of the first expander-compressor ET1, then fed via a pipe L421 to partway through the first heat exchanger E20, merging with the pipe L6.
A first intake-side release pipe L11 for releasing gas, which branches from the pipe L1, is provided on the intake side of the first compression device C1, and a first intake-side release valve PV1 is provided in the first intake-side release pipe L11. A second intake-side release pipe L21 for releasing gas, which branches from the pipe L2, is provided on the intake side of the second compression device C2, and a second intake-side release valve PV21 is provided in the second intake-side release pipe L21.
A first bypass pipe L3 returning from a discharge side to the intake side of the first compression device C1 is provided, and a first bypass valve PV2 is provided in the first bypass pipe L3. A second bypass pipe L23 returning from a discharge side to the intake side of the second compression device C2 is provided, and a second bypass valve PV22 is provided in the second bypass pipe L23.
A control valve PV5 is provided in the pipe L412 downstream from the position of the pipe L4121. A temperature measuring unit T5 is provided in the pipe L4121.
After start-up, an inlet gas temperature T1 measured by the temperature measuring unit T5 is compared with a warning temperature set value plus a margin M (S201). During start-up, the inlet gas temperature Ti is greater than the warning temperature set value plus the margin M, and a second operating state is set.
In response to the second operating state, a valve control unit 202 makes a degree of opening OP1 of the control valve PV5 greater than a degree of opening OP2 during a first operating state in order to lower an inlet pressure of the expander ET22 (cold turbine) of the second expander-compressor ET2. As a result, the amount of gas fed to the first separator unit V20 is increased and the amount of gas fed to the expander ET22 (cold turbine) is reduced in relation to this, and it is possible to maintain a state of higher temperature than the warning temperature set value, making it possible to avoid operator intervention during start-up.
In step S201, the comparison is repeated until the measured inlet gas temperature T1 is equal to or less than the warning temperature set value plus the margin M. When the inlet gas temperature Ti is equal to or less than the warning temperature set value plus the margin M, the operating state transitions from the second operating state to the first operating state, and an emergency stoppage temperature set value is set at the warning temperature set value plus the margin (S202).
In response to the first operating state, the valve control unit 202 makes the degree of opening OP2 of the control valve PV5 smaller than the degree of opening OP1 during the start-up mode in order to raise the inlet pressure of the expander ET22 (cold turbine). As a result, the amount of gas fed to the first separator unit V20 is reduced and the amount of gas supplied to the expander ET22 (cold turbine) is increased in relation to this. This makes it possible to achieve a rapid transition from the state during start-up to operation in the normal state.
In this embodiment, the degree of opening (OP1) of the valve during the second operating state may be selected from a range of between 60% and 70%, for example. The degree of opening (OP2) of the valve during the first operating state may be selected from a range of between 50% and 60%, for example.
A method for controlling a turbine inlet temperature of a liquefaction system for liquefying a product gas provided from an air separation unit A comprises:
In another embodiment, a program for implementing the method for controlling a turbine inlet temperature causes a processor to implement each of the steps of the method for controlling a turbine inlet temperature.
(1) Functions of the mode setting unit 201 and the valve control unit 202 may be implemented by the single control unit 200.
(2) The control units may be configured to have one or more processors and a memory for storing a control program for operating the processor(s), or may be configured by combining one or more types of firmware, servers, high selectors, and low selectors, etc.
(3) The liquefaction system 100 is not limited to the configuration of embodiment 1, and other components may be added thereto. Furthermore, various types of measurement instruments and other pipes, etc. may also be provided.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP 2022-131511 | Aug 2022 | JP | national |
