JPH04203397A - Method for cooling intermediate gas in multi-state compressor and multi-stage compressor having intermediate gas cooler - Google Patents

Abstract

PURPOSE:To prevent the increasing of a tube wall surface temperature and liquefaction of handling gas by a method wherein intermediate gas cooled by an intermediate heat exchanger is heated up to such a temperature as one not liquefied even under an expansion at a labyrinth part and supplied to a compressor at a high pressure. CONSTITUTION:CO2 gas compressed by a compressor 1 is supplied by an intermediate heat exchanger 3, a part of this gas is mixed with gas bypassed through the intermediate heat exchanger 3 and cooled by it, adjusted to show a certain specified temperature and further sent to a high pressure side compressor 2. An amount of cooling water and an amount of bypassed gas are adjusted by a temperature controller 5 and a temperature controller 7 in such a way as a temperature of the cooling gas becomes a certain temperature. The temperature controller 5 sets CO2 temperature to a minimum temperature not generating any liquefaction and the temperature controller 7 sets its temperature to a minimum temperature not generating any liquefaction even if CO2 gas is expanded. With such an arrangement, it is possible to prevent any occurrence of stress corrosive cracking of the heat exchanger tube and further to extend a life of the tube.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for cooling intermediate gas in a multi-stage compressor in which discharged gas from a front-stage compressor is cooled and guided to a rear-stage compressor, and a method for cooling intermediate gas. The present invention relates to a multi-stage compressor equipped with a cooling device, and is particularly suitable for use in carbon dioxide compressors used in corrosive environments where chloride stress corrosion cracking may occur.

[Conventional technology]

As a conventional technology of this kind, Hitachi Hyoron vO ] 960 N
3 (March 1978 issue).

The device described in this document is a multi-stage compressor that compresses carbon dioxide gas (hereinafter referred to as CO2 gas). ) and sent to the next stage side (later stage side or high pressure side) compressor.

(Problem to be solved by the invention) Generally, when compressing gas with a compressor, the relationship between the amount of work per unit mass (head) given to the gas by the drive machine and the change in the state of the gas is as shown in equation (1). is expressed in

Here, Hth = Theoretical head η = Polytropic index R = Gas constant Ts - Suction temperature Pd = Discharge pressure Ps = Suction pressure ηpal: Volitropic efficiency As shown in formula (1), the same pressure rise can be achieved by lowering the suction temperature Ts. (Pressure ratio P, 1/Ps) The amount of work (Hth) required per unit mass is small. Therefore, it is generally desirable that the gas temperature at the outlet of the heat exchanger be lower, since the shaft power (energy) of the drive machine can be reduced. For this reason, a heat exchanger is provided between the right groups to cool the CO2 gas.

On the other hand, since CO2 gas has the property of liquefying if the pressure is high even at a temperature above room temperature, the gas temperature at the outlet of the heat exchanger must be above a temperature at which this liquefaction does not occur. Furthermore, after the C02 gas is sucked into the compressor, a portion of it leaks from the shaft seal to the outside of the machine.

The pressure outside the machine is always lower than the pressure inside the compressor.

Therefore, if the CO2 gas leaking while expanding to the outside of the machine liquefies during the process (for example, inside the shaft sealing labyrinth), an erosion attack will occur, causing harmful damage to the compressor. If the intake CO2 gas temperature is low, it will expand and liquefy. Taking these things into consideration, the temperature at the outlet of the CO□ gas heat exchanger is controlled.

Furthermore, when manufacturing a heat exchanger, since cooling water contains corrosive factors such as chlorine ions, the heat exchanger tube material, tube temperature, and cooling water speed must be carefully considered when designing the heat exchanger. ing.

In addition, the tube heat transfer capacity is designed with a margin in advance for heat exchange capacity in consideration of contamination caused by cooling water during operation.

The heat exchanger is already manufactured in such a way that there is no shortage of heat exchangers even for long-term continuous operation.

Generally, the heat transfer rate of a heat exchanger is expressed by equation (2).

] Here, K = heat transfer coefficient α □ = gas side (tube side) heat transfer coefficient α2 = water side (shell side) heat transfer coefficient f, = fouling coefficient In formula (2), the fouling coefficient fv is the initial operating value. sometimes 0
．． 0001 or less, but in manufacturing, taking into consideration contamination on the cooling water side due to long-term operation, it is generally set to about 0.0004.

On the other hand, the amount of heat transfer Q is expressed by equations (3), (4), and (5).

Q=KXAXΔTm - Old= (3) Q=G, jX
Cp%, XATw ++++++++ (4) Q=GriX
C,,XΔTI+ (5) Here, Q=heat transfer amount A=heat exchange area ΔTm=logarithmic average temperature difference G=flow rate and thus the temperature of the heat exchanger tube increases. In other words, in the conventional system that adjusts the amount of cooling water so that the temperature of the cooled gas at the heat exchanger outlet is constant, there is insufficient cooling water at the beginning of operation, causing a rise in the temperature of the heat exchanger tubes, and scaling due to the cooling water flow rate source. There was a risk of chloride stress corrosion cracking due to adhesion of chloride and an increase in tube wall temperature.

The purpose of the present invention is to prevent the tube wall temperature from increasing.
Another object of the present invention is to provide a method for cooling an intermediate gas in a multi-stage compressor that does not cause liquefaction of the handled gas, and a multi-stage compressor equipped with an intermediate gas cooling device.

[Means to solve the problem]

The first feature of the present invention for achieving the above object is to cool the intermediate gas compressed by the low-pressure side compressor by exchanging heat with cooling water in an intermediate heat exchanger, and then to The present invention provides a method for cooling an intermediate gas in a multistage compressor in which the gas is heated to a temperature at which it does not liquefy even if the labyrinth portion expands and is supplied to a high-pressure compressor.

A second feature of the present invention is to bypass a portion of the intermediate gas discharged from the low-pressure side compressor, cool the remainder of the intermediate gas by exchanging heat with a cooling fluid in an intercooler, and then, In order to heat this cooled gas to a temperature at which it does not liquefy even if it expands in the labyrinth part of the next-stage compressor, it is mixed with the bypassed intermediate gas and supplied to the next-stage compressor. Cooling of the intermediate gas in the multi-stage compressor It's in the method.

The third feature of the present invention is to bypass a part of the intermediate gas discharged from the pre-stage compressor, and heat exchange the remaining intermediate gas with the cooling water in the intercooler through the heat exchanger tube. The gas is cooled to near the gas-liquid critical point, and then a part of the cooled gas flows into the labyrinth seal portion of the next stage compressor and is cooled to a temperature near the vapor-liquid critical point at which it does not liquefy even if it expands. In order to heat the cooled gas, the bypassed intermediate gas is mixed and supplied to the next stage compressor.

A fourth feature of the present invention is a low-pressure side compressor, a high-pressure side compressor, a gas line that guides intermediate gas discharged from the low-pressure side compressor to the high-pressure side compressor, and a gas line provided in this intermediate gas line. In a multi-stage compressor equipped with an intercooler for cooling the intermediate gas with cooling water via a heat exchanger tube, the intermediate gas line is provided with a bypass line for the intercooler, and the bus pass line is provided with the intercooler. A control valve that controls the amount of bypass gas, and controls the opening degree of the control valve so that the temperature is such that the gas after the merging of the intermediate gas line and the bypass line does not liquefy even if it expands in a labyrinth part of the high-pressure side compressor. A fifth feature of the present invention resides in a multi-stage compressor equipped with an intermediate gas cooling device having a control means for controlling the intermediate gas discharged from the former stage compressor and the latter stage compressor. In a multi-stage compressor equipped with an intermediate gas line leading to a compressor, and an intercooler provided in the intermediate gas line to cool the intermediate gas with a cooling fluid, a pipe line for sending cooling fluid to the intercooler. a control valve provided on the outlet side of the intercooler to control the flow rate of the cooling fluid; a first temperature detection means provided on the outlet side of the intercooler for detecting the temperature of the gas discharged from the intercooler; a first control means for controlling the control valve based on the detected temperature; a means for heating intermediate gas downstream of the first temperature detection means; a second temperature detection means for detecting the gas temperature; and a second control for controlling the heating means based on the second temperature detection means so that the heated gas does not liquefy even if it expands in the labyrinth part. and a multi-stage compressor with an intermediate gas cooling device.

A sixth feature of the present invention is that the first stage compressor, the second stage compressor, an intermediate gas line that guides intermediate gas discharged from the first stage compressor to the second stage compressor, and this intermediate gas line, In a multi-stage compressor equipped with an intercooler installed in the intermediate gas line and configured to cool the intermediate gas with cooling water via a heat exchanger tube, a pipe line for sending chilled water to the intercooler. a first control valve provided on the outlet side of the intercooler to control the flow rate of the cooling water; a first temperature detection means provided on the outlet side of the intercooler for detecting the temperature of the gas discharged from the intercooler; a first control means for controlling the control valve to cool the intermediate gas to a temperature close to the critical point of the intermediate gas based on the temperature detected by the detection means; a bypass gas line provided to join downstream of the first temperature detection means; a second control valve provided in the bypass gas line for controlling the amount of bypass gas; and a joining side of the intermediate gas line and the bypass line. a second temperature detection means for detecting the temperature of the gas;
The present invention provides a multi-stage compressor equipped with an intermediate gas cooling device and a second control means for controlling the opening degree of the second control valve based on the temperature detection means.

A seventh feature of the present invention is that the gas handled in the multi-film compressor having each of the above features is carbon dioxide gas (CO2 gas).

[Effect]

With the above configuration, there is no need to reduce the flow rate of the cooling fluid even in the initial operation of the heat exchanger, as long as it is not close to the gas-liquid critical point. By mixing the supercooled portion with the heating means or bypassed hot gas, the temperature of the gas taken into the downstream compressor can be raised to a level that does not liquefy when the labyrinth portion expands.

Therefore, sufficient cooling fluid can always flow so that the heat exchanger tubes of the intercooler are always kept at a temperature that does not cause stress corrosion cracking.

〔Example〕

FIG. 2 is a diagram showing the overall configuration of the carbon dioxide compressor.

Generally, compressors are pressurized from atmospheric pressure to approximately 260 atmospheres. CO2 gas inhaled at atmospheric pressure is
For example, the first group is about 5 atm, the second group is about 25 atm.
The pressure is increased to approximately 90 atmospheres in the third group, and the discharge pressure is increased to approximately 260 atmospheres in the fourth and final group.

FIG. 3 shows a state diagram of CO2 gas. In FIG. 3, for example, when the second group outlet pressure of the CO2 compressor is 25 atm, the point of intersection with the liquidus line is approximately -11°C, and the CO□ gas will not liquefy unless the temperature falls below this temperature. Generally, water coolers are not cooled below 0° C., so no matter how much the first and second coolers are cooled, they will not liquefy. However, if the third group outlet pressure is 90 atm, the intersection with the gas-liquid critical line will be approximately 40 degrees Celsius, and if the temperature drops below this temperature, it will liquefy.
'C or higher).

Furthermore, even at temperatures above 45°C, liquefaction occurs due to expansion when leaking out of the compressor. (For example, in the case of 45°C, it crosses the liquidus line due to expansion and liquefies. Therefore, even if CO2 gas expands, it does not cross the liquidus line (for example, 68°C
) It is necessary to control the compressor group 4 inlet temperature. In this way, the temperature at the outlet of the CO2 gas heat exchanger is controlled in consideration of energy reduction, supercooling, and prevention of liquefaction due to expansion.

Further, the same applies to gases other than CO2 gas when they are handled near the liquidus line or the gas-liquid critical line.

A specific embodiment of the present invention will be described with reference to FIG. 1, taking as an example a case in which it is applied to a carbon dioxide (CO2) compressor. Front side (
(Low pressure side) The CO2 gas compressed by the compressor 1 passes through the intermediate gas line 10 and is cooled by the intermediate heat exchanger and the intermediate cooler 3. At the same time, some gas is transferred to the intermediate gas line 1-1. It bypasses the heat exchanger 3, mixes with the cooled gas, adjusts it to a certain arbitrary constant temperature, and sends it to the next stage high pressure side (second stage side) compressor 2.

In the heat exchanger 3, the intermediate gas is cooled by cooling water via the heat exchanger tubes 3a.

The temperature of the cooling gas is detected by a first temperature detector 5a downstream of the heat exchanger 3, and a temperature controller (first control means) 5 detects the temperature of the cooling gas.
control valve 4 to maintain a certain temperature.
control and adjust the amount of cooling water.

Next, the amount of bypass gas is determined by detecting the gas temperature after mixing with a second detector 7a, and controlling the temperature of the mixed gas by a temperature controller (second control means) 7 so that the temperature of the mixed gas reaches a certain constant temperature. control) to the roll valve 9. The set temperature of the temperature controller 5 is set lower than the set temperature of the temperature controller 7. The set temperatures of the temperature controllers 5 and 7 will be explained with reference to FIG. The temperature controller 5 is set to the lowest temperature at which the CO□ gas does not liquefy (for example, about 45° C. when the CO2 gas is at 9 degrees atmospheric pressure) in FIG.

Further, the set temperature of the temperature controller 7 is set to the lowest temperature at which liquefaction does not occur even if the CO2 gas expands (for example, about 98° C. when the CO□ gas is at 90 atmospheres).

According to this embodiment, by providing the hot gas bypass line 11, the amount of cooling water can be made sufficiently larger than when the bypass is not provided. This will be explained next.

Since the gas temperature at the outlet of the heat exchanger 3 is controlled to be lower than the gas temperature after mixing, it is necessary to perform a hot gas bypass. Therefore, the amount of gas passing through the heat exchanger 3 is reduced. In this case, the heat transfer coefficient α1 on the gas side decreases in proportion to about the 0.8th power of the flow rate. on the other hand,
Even if a hot gas bypass is performed, the overall amount of heat exchange between the gas side and the water side is the same as when there is no such bypass6, that is, there is almost no change in the heat transfer rate of the heat exchanger. Even if the gas side heat transfer coefficient α1 becomes smaller, in order to keep the heat transfer coefficient K the same, either increase the water side heat transfer coefficient α2 or
It is necessary to remove dirt from the heat exchanger tubes. That is, when the heat exchanger is designed with a certain fouling coefficient in consideration of long-term continuous operation and is operated without initial fouling, it is not necessary to reduce α2 by using the hot gas bypass.

The heat transfer coefficient α2 on the water side changes in proportion to the amount of cooling water to the 0.6th power, so reducing α2 means reducing the flow rate, which increases the outlet temperature of the cooling water and heats up. If the temperature on the outlet side of the exchanger tube 3a increases and the cooling water contains corrosive factors (if normal water is used as the cooling water), corrosion will be accelerated and cause stress corrosion cracking. . According to the system of the present invention,
By reducing the heat transfer coefficient α2 on the water side, it is possible to prevent stress corrosion cracking from occurring.

The operation of the present invention will be explained in more detail using FIGS. 4 and 5.

Even if the hot gas bypass line 1]- is provided as in the present invention, the required amount of heat exchanged by the heat exchanger 8 is the same as when the bypass line 11 is not provided. FIG. 4 is a schematic configuration diagram in the case where there is no bypass line, and FIG. 5 is a schematic configuration diagram of the present invention. When the heat exchange portion is surrounded by the inspection spaces 8 and 9, the amount of heat exchange between the gas and water is generally the same in both the conventional method and the present invention. In addition, hot gas bypass is required to reach the target gas temperature, but the amount passing through the heat exchanger is reduced by the amount of gas bypass. Then, the gas side root transfer coefficient α□ of the heat exchanger tube is approximately 0 of the flow rate.
．． Since it is proportional to the eighth power, α1 becomes smaller.

In order to make the amount of heat exchanged the same, it is necessary to make the heat transfer rate K shown in the above equation (3) almost the same. Therefore,” No. 1 (2
), as the gas side heat transfer coefficient α becomes smaller, the water side heat transfer coefficient α2 increases accordingly. In order to increase α2, it is necessary to increase the amount of cooling water Gl as described above. The fact that the amount of cooling water can be increased with the same amount of heat exchanged means that the temperature difference of the cooling water can be reduced, as is clear from equation (4), and the outlet temperature of the cooling water can be lowered. By being able to lower the temperature of the cooling water in the tubes 3a of the heat exchanger 3, the temperature of the tubes 3a can be lowered.

In the above embodiment, the bypass gas line 11 is provided to allow the gas cooled by the intermediate heat exchanger 3 to join the hot gas, so that the cooled gas flows into the labyrinth seal of the downstream compressor and expands. The cooling gas is heated to a predetermined temperature so that it does not liquefy even when
Instead of providing the bypass gas line, another intermediate gas heating means may be provided to heat the gas coming out of the intermediate heat exchanger 3 to the predetermined temperature.

〔Effect of the invention〕

According to the present invention, the temperature of the tube wall surface of the heat exchanger can be kept low and at the same time the handled gas is prevented from liquefying, so that it is possible to prevent the occurrence of stress corrosion cracking in the heat exchanger tubes and to extend the life of the tubes. The advantage is that a method for cooling intermediate gas in a multi-stage compressor that can be extended and a multi-stage compressor equipped with an intermediate gas cooling device are obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is a CO
A configuration diagram showing the entire system of a two-gas compressor, Figure 3 is C
A state diagram showing the relationship between the temperature of O2 gas and changes in entropy, FIGS. 4 and 5 are configuration diagrams of main parts explaining the present invention in detail, FIG. 4 is a diagram without a bypass line, and FIG. 2 is a diagram showing a device provided with a bypass line. 1...Low pressure side (previous stage side) compressor, 2...High pressure side (later stage side) compressor, 3...Intermediate heat exchanger (intercooler), 4
... 1st control valve, 5 ... temperature controller (
first control means), 5a... first temperature detector, 6...
- Second control valve, 7. Temperature controller (second control means), 7a... Second temperature detector, 10.. Intermediate gas line, 11.. Bypass gas line. =23=

Claims (1)

[Claims] 1. Cooling intermediate gas compressed by a low-pressure side compressor by exchanging heat with cooling water in an intermediate heat exchanger,
A method for cooling an intermediate gas in a multi-stage compressor, characterized in that the cooled gas is then heated to a temperature at which it does not liquefy even if it expands in a labyrinth section, and is then supplied to a high-pressure side compressor. 2. A part of the intermediate gas discharged from the low-pressure side compressor is bypassed, and the remaining intermediate gas is cooled by exchanging heat with the cooling fluid in the intercooler, and then this cooled gas is transferred to the next A method for cooling an intermediate gas in a multi-stage compressor, characterized in that the intermediate gas is heated to a temperature at which it does not liquefy even if expanded in a labyrinth portion of the stage compressor, and is mixed with the bypassed intermediate gas and then supplied to the next stage compressor. 3. A part of the intermediate gas discharged from the pre-stage compressor is bypassed, and the remainder of the intermediate gas is heat exchanged with cooling water in the intercooler through a heat exchanger tube to cool the gas near the gas-liquid critical point. After that, a part of this cooled gas flows into the labyrinth seal part of the next stage compressor and heats the cooled gas close to the critical point of the compressor to a temperature at which it does not liquefy even if it expands. A method for cooling intermediate gas in a multistage compressor, characterized in that the bypassed intermediate gas is mixed and supplied to a next stage compressor. 4. A low-pressure side compressor, a high-pressure side compressor, a gas line that guides the intermediate gas discharged from the low-pressure side compressor to the high-pressure side compressor, and a heat exchanger installed in this intermediate gas line to transfer the intermediate gas. In a multi-stage compressor equipped with an intercooler cooled by cooling water via a tube, an intermediate gas bypass line provided in the intermediate gas line so as to bypass the intercooler, and this bypass a control valve provided in the line to control the amount of bypass gas; and a control valve configured to maintain a temperature at which the gas after the merging of the intermediate gas line and the bypass line does not liquefy even if it expands in the labyrinth portion of the high-pressure side compressor. 1. A multistage compressor equipped with an intermediate gas cooling device, characterized in that the compressor is equipped with a control means for controlling the opening degree of the intermediate gas cooling device. 5. A front-stage compressor, a rear-stage compressor, an intermediate gas line that guides the intermediate gas discharged from the front-stage compressor to the rear-stage compressor, and a cooling fluid provided in the intermediate gas line to direct the intermediate gas to the rear-stage compressor. In a multi-stage compressor equipped with an intercooler configured to perform cooling, a control valve for controlling the flow rate of the cooling fluid is provided in a pipe line for sending cooling fluid to the intercooler, and a control valve is provided on the outlet side of the intercooler. a first temperature detection means for detecting the temperature of the gas discharged from the provided intercooler; a first control means for controlling the control valve based on the temperature detected by the temperature detection means; means for heating intermediate gas downstream of the temperature detection means; second temperature detection means for detecting the temperature of the gas after being heated by the heating means; and a second temperature detection means for detecting the temperature of the gas heated by the heating means; and second control means for controlling the heating means based on the second temperature detection means so as not to liquefy the compressor even if the gas is heated. 6. An upstream compressor, a downstream compressor, an intermediate gas line that guides the intermediate gas discharged from the upstream compressor to the downstream compressor, and an intermediate gas line installed in the intermediate gas line that heats the intermediate gas. In a multi-stage compressor equipped with an intercooler that is cooled by cooling water via an exchanger tube, a first compressor is provided in a pipe line that supplies cooling water to the intercooler and controls the flow rate of the cooling water. a control valve; a first temperature detection means provided on the outlet side of the intercooler for detecting the temperature of the gas discharged from the intercooler; a first control means for controlling the control valve so as to cool the gas to near the critical point; and a first control means provided in the intermediate gas line so as to bypass the intercooler and join downstream of the first temperature detection means. a bypass gas line, a second control valve provided in the bypass gas line to control the amount of bypass gas, and a second temperature detection means to detect the temperature of the gas after the intermediate gas line and the bypass line merge. , controlling the opening degree of the second control valve based on the second temperature detection means so that the gas after the merging flows into the labyrinth seal portion of the downstream compressor and is at a temperature at which it does not liquefy even if it expands; A multi-stage compressor equipped with an intermediate gas cooling device, characterized in that it is equipped with a second control means. 7. A multistage compressor equipped with an intermediate gas cooling device according to any one of claims 4 to 6, wherein the gas to be compressed is carbon dioxide gas (CO_2 gas).