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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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:

[0031] FIG. 1 illustrates a liquefaction system according to embodiment 1.

[0032] FIG. 2 is a flowchart showing a change of operating mode.

DETAILED DESCRIPTION OF THE INVENTION

[0033] 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.

Embodiment 1

[0034] Decompression devices 1 and 2 in a liquefaction system 100 according to embodiment 1 will be described with the aid of FIG. 1.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

(Turbine Inlet Temperature Control)

[0043] 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. FIG. 2 shows a flow of operating states.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] 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.

(Method for Controlling Turbine Inlet Temperature of Liquefaction System)

[0049] 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: [0050] a temperature measuring step in which an inlet gas temperature (Ti) on entry to a cold turbine (ET22) is measured; [0051] 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 [0052] 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 thereby relatively reduce the amount of gas supplied to 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) and thereby relatively increase the amount of gas supplied to the cold turbine (ET22).

[0053] 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.

Other Embodiments

[0054] (1) Functions of the mode setting unit 201 and the valve control unit 202 may be implemented by the single control unit 200.

[0055] (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.

[0056] (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.

[0057] 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.

[0058] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

KEY TO SYMBOLS

[0063] A Air separation unit [0064] 200 Control unit [0065] 201 Mode setting unit [0066] 202 Valve control unit [0067] T5 Temperature measuring unit [0068] PV5 Control valve