CN112145974B - Supercritical CO2 multistage throttling device and method - Google Patents
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D3/00—Arrangements for supervising or controlling working operations
- F17D3/01—Arrangements for supervising or controlling working operations for controlling, signalling, or supervising the conveyance of a product
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Abstract
The present disclosure provides a supercritical CO2Multistage throttling arrangement and method, relate to pipeline safety control technical field, including at least one choke valve and at least one heating mechanism, choke valve and heating mechanism alternate interval arrangement in proper order, and through blow-down pipe series connection in proper order and access pipeline, through the power of adjusting throttle valve opening and heating mechanism, so that the gas of blow-down pipe end discharge is higher than three phase point temperature, through controlling the change of fluid pressure in the gas transmission trunk, maintain the temperature of in-process of discharging, cooperate multistage choke valve, reduce the difference in temperature around the single-stage choke valve, cooperation heating structure, the pressure in the blow-down pipe discharges, effective control generates, reach the purpose of safe dry ice of discharging.
Description
Technical Field
The disclosure relates to supercritical CO2The technical field of pipeline safety control, in particular to supercritical CO2Provided are a multi-stage throttling device and a multi-stage throttling method.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Supercritical CO2Has the characteristics of high density and low viscosity, is in a state similar to gas and liquid, and is most of long-distance CO internationally2Pipelines are all conveyed in a supercritical state. However, due to supercritical CO2The pipeline and the long-distance gas transmission pipeline belong to a high-pressure pipeline and CO2Different from natural gas in physical property and phase property, has strong throttling effect, so that CO is produced2The throttling has specificity and certain potential safety hazard.
The inventor finds that when the pipeline is throttled, high-pressure CO in the pipeline2A strong throttling effect will be formed at the throttling orifice, if direct emptying is carried out as in fig. 1, the temperature field in the pipe will suddenly change, and when the pressure and the temperature are reduced to a certain value, CO will be generated2The phase change occurs to form dry ice, which may block the pipeline and seriously affect the normal transportation of the pipeline, and in addition, the strong low temperature also causes damage to the pipeline and the accessory equipment, and affects the safe discharge of the pipeline.
Disclosure of Invention
The purpose of the present disclosure is to address the existing prior artDefect, providing a supercritical CO2A multi-stage throttling device and method for controlling CO in gas pipeline2The fluid pressure changes, the temperature in the discharging process is maintained, the temperature difference between the front and the back of the single-stage throttle valve is reduced by matching with the multi-stage throttle valve, the pressure in the emptying pipe is discharged by matching with the heating structure, the generation of the dry ice is effectively controlled, and the purpose of safe discharging is achieved.
It is a first object of the present disclosure to provide a supercritical CO2The multi-stage throttling device adopts the following technical scheme:
including at least one choke valve and at least one heating mechanism, choke valve and heating mechanism alternate interval arrangement in proper order, and through blow-down pipe series connection in proper order and access pipeline, through the power of adjusting the throttle valve opening and heating mechanism to make the gas of blow-down pipe end discharge be higher than triple point temperature.
Furthermore, the opening of each throttle valve is respectively adjusted and is reduced to be above the critical pressure in a grading way, so that the temperature is maintained to be above the triple point.
It is a second object of the present disclosure to provide a supercritical CO2The multi-stage throttling method comprises the following steps:
determining throttle bleed supercritical CO2The minimum heat absorption capacity of dry ice is not generated in the process, and high-pressure CO is calculated2Throttling to a temperature above a critical pressure;
establishing a pipeline throttling and orifice throttling temperature calculation model, and judging whether the throttled temperature is lower than the triple point temperature or not, and determining the supercritical CO2Maintaining the temperature above the triple point temperature at the position above the critical pressure in a grading way;
determining the heating power required by each stage of throttling, carrying out parameter configuration according to the critical pressure ratio, and carrying out supercritical CO2Throttling to atmospheric pressure.
Further, when the temperature after throttling is judged to be higher than the temperature of the triple point, the heating power required by each stage of throttling is determined.
Furthermore, setting the throttling pressure according to the critical pressure, calculating the temperature after throttling, and configuring the heating power according to the required heating.
Further, the throttled temperature comprises the temperature at the throttle hole of the throttle valve and the temperature in the emptying pipe.
Further, the throttling process is controlled and the interstage heating is controlled by referring to the throttling stage number and the critical pressure ratio.
Further, for high pressure supercritical CO2And (4) emptying, adopting three-stage throttling, and heating between adjacent stages.
Further, in the first stage throttling, the pressure is throttled to the critical pressure, CO2Maintaining the original phase state for discharging.
And further, below the critical pressure range, arranging a second stage of throttling according to the critical pressure ratio, and distributing the heating quantity according to the balanced distribution principle.
Compared with the prior art, the utility model has the advantages and positive effects that:
(1) the temperature in the discharging process is maintained by controlling the pressure change of fluid in the gas transmission trunk line, the temperature difference between the front and the rear of a single-stage throttle valve is reduced by matching with a multi-stage throttle valve, and the pressure in the emptying pipe is discharged by matching with a heating structure, so that the generation of dry ice is effectively controlled, and the aim of safe discharging is fulfilled;
(2) the pressure and temperature change of the fluid in the gas transmission trunk line is controlled, so that the rapid expansion or evaporation of the fluid caused by rapid pressure reduction in the trunk line can not cause severe temperature reduction in the pipe, and the low-temperature damage process of the pipe and the pipeline instrument caused by the generation of dry ice is avoided;
(3) controlling the temperature change in the vent line connected to the atmosphere to prevent fluid from flowing through the vent valve at high pressure differential to prevent the problem of dry ice from clogging the vent line and causing dangerous accidents by introducing high pressure CO2The multi-stage throttling discharge method is adopted during the emptying of the pipeline, so that the front and back pressure drop of the throttling valve can be reduced, the temperature drop degree of the fluid is relieved, the fluid and surrounding media are given enough heat exchange time, the generation of dry ice is effectively controlled, the safe discharge is achieved, and the accident probability in the emptying process of the pipeline is reduced;
(4) at high pressure CO2The pipeline is discharged in the air by adopting multi-stage throttling discharge, so that the pressure drop before and after the throttle valve is reduced, the temperature drop amplitude of the fluid is relieved, and the pressure drop is reducedThe adverse effect of throttling and emptying on pipelines, equipment and the surrounding environment is realized, the pressure is released as soon as possible by using the least heating amount on the premise of not generating dry ice, and meanwhile, heating measures are taken, so that the generation of the dry ice can be effectively controlled, and the purpose of safe release is achieved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to be construed as limiting the disclosure.
Fig. 1 is a schematic structural diagram of a prior art bleed-off manner in the background art of the present disclosure;
fig. 2 is a schematic structural diagram of a throttling device in embodiments 1 and 2 of the present disclosure;
FIG. 3 shows the throttling process at CO in examples 1 and 2 of the present disclosure2A schematic diagram of evolution law in a pressure-enthalpy diagram;
fig. 4 is a schematic flow chart of the calculation of the temperature after the throttling of the pipeline in embodiments 1 and 2 of the present disclosure;
FIG. 5 is a schematic flow chart of the calculation of the temperature of the orifice of the pipe orifice in embodiments 1 and 2 of the present disclosure;
FIG. 6 shows supercritical CO in examples 1 and 2 of the present disclosure2And the multi-stage throttling emptying control flow diagram is shown.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof;
for convenience of description, the words "up", "down", "left" and "right" in this disclosure, if any, merely indicate that the directions of movement are consistent with those of the figures themselves, and are not limiting in structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present disclosure.
As described in the background section, the direct venting of the prior art causes a sudden change in the temperature field in the tube, and when the pressure and temperature are reduced, the CO2The phase change is carried out to form dry ice, which can block the pipeline and seriously affect the normal transportation of the pipeline; in view of the above problems, the present disclosure provides a supercritical CO2Provided are a multi-stage throttling device and a multi-stage throttling method.
Example 1
In an exemplary embodiment of the present disclosure, as shown in fig. 2-6, a supercritical CO is provided2Multistage throttling arrangement.
The device mainly comprises a throttle valve and a heating mechanism which are arranged on an emptying pipe, wherein the throttle valve and the heating mechanism are respectively arranged at least one, the throttle valve and the heating mechanism are alternately arranged on the emptying pipe at intervals, the emptying pipe is connected into a conveying pipeline, the throttle valve adjusts the flow conveyed by the emptying pipe, and the heating mechanism heats a medium in the emptying pipe.
For the prior art process of directly emptying the transfer line in FIG. 1, in CO2The line was depressurized to atmospheric pressure via a vent line. First at the blow valve, CO2The pressure in the pipeline is reduced to atmospheric pressure, and CO released thereby2The temperature is the same as its boiling point in the atmosphere, around-78.4 ℃, and the valve is also cooled to this temperature, so that dry ice is generated during the depressurization process. In addition, adiabatic expansion temperature drop occurs in the pipe due to mass loss in the fixed volume within the pipe. In addition, when the pressure drops below the critical pressure to produce steam, the heat of vaporization further cools the tubing.
In the present embodiment, as shown in FIG. 2, the heating mechanism is operated by a throttle valveCO formation in cooperation with a vent pipe2The pipeline multi-stage throttling emptying structure ensures that the gas discharged from the tail end of the emptying pipe is higher than the temperature of a three-phase point by adjusting the opening of the throttle valve and the power of the heating mechanism;
the opening of each throttle valve is respectively adjusted, and the opening is reduced to be above the critical pressure in a grading way, so that the temperature is maintained to be above the three-phase point.
The pressure and temperature change of the fluid in the gas transmission trunk line is controlled, so that the rapid expansion or evaporation of the fluid caused by rapid pressure reduction in the trunk line can not cause severe temperature reduction in the pipe, and the low-temperature damage process of the pipe and the pipeline instrument caused by the generation of dry ice is avoided;
controlling the temperature change in the vent line connected to the atmosphere to prevent fluid from flowing through the vent valve at high pressure differential to prevent the problem of dry ice from clogging the vent line and causing dangerous accidents by introducing high pressure CO2The multi-stage throttling discharge method is adopted in the pipeline emptying process, so that the front and back pressure drop of the throttling valve can be reduced, the temperature drop degree of the fluid is relieved, the fluid and surrounding media are subjected to sufficiently long heat exchange time, the generation of dry ice is effectively controlled, the safe discharge is achieved, and the accident probability in the pipeline emptying process is reduced.
Example 2
In another exemplary embodiment of the present disclosure, as shown in FIGS. 2-6, a supercritical CO is provided2A multi-stage throttling method.
Determining throttle bleed supercritical CO2The minimum heat absorption capacity of dry ice is not generated in the process, and high-pressure CO is calculated2Throttling to a temperature above a critical pressure;
establishing a pipeline throttling and orifice throttling temperature calculation model, and judging whether the throttled temperature is lower than the triple point temperature or not, and determining the supercritical CO2The temperature is maintained above the triple point temperature at the position above the critical pressure by stages;
determining the heating power required by each stage of throttling, carrying out parameter configuration according to the critical pressure ratio, and carrying out supercritical CO2Throttling to atmospheric pressure.
And when the temperature after throttling is judged to be higher than the temperature of the triple point, directly determining the heating power required by each stage of throttling.
As shown in fig. 3, the fluid is throttled on the pressure-enthalpy diagram in theory by the fact that the enthalpy of the fluid is the same before and after throttling through the pipe, and therefore the process of throttling the fluid should be an isenthalpic straight line perpendicular to the abscissa. As shown in the figure, the fluid directly throttled from point 1 and depressurized to point 3 passes through a gas-solid two-phase region to generate dry ice. And if the fluid absorbs heat after throttling from the point 1 to the point 2, or the fluid absorbs certain heat from the initial state of the point 1, so that the enthalpy of the fluid is increased, and dry ice is not generated in the throttling process. Minimum heat quantity Δ Q to be absorbedminIs exactly CO2Difference between enthalpy value (6-point enthalpy value) when dry ice is generated from gas phase under triple-point pressure and enthalpy value in initial state (1-point). It can also be seen in the figure that when point 1 is to the right of point 6, no dry ice is produced during throttling even without heat supply, due to the higher initial enthalpy value.
Due to CO2The pipeline is transported in supercritical state under the operating condition that CO is transported in supercritical state2When the pipeline is decompressed, measures such as heating and the like are generally needed to ensure that dry ice is not generated in the emptying pipeline. Because the pipeline still exchanges heat with the surrounding environment or medium in the process of emptying, the heat exchange quantity between the pipeline and the surrounding medium is calculated when the emptying and throttling pipelines are heated. It should be noted here that the insulation design of the flare throttle lines should be dependent on the ambient temperature conditions, since heat absorption is required at this time. If the ambient temperature is high and the fluid can absorb heat in the pressure reduction process, an insulating layer or a thermal insulating layer is not designed as much as possible; if the ambient temperature is low, a heat preservation design is required.
Specifically, the multistage throttling and emptying process of the pipeline in this embodiment is described in detail with reference to the accompanying drawings;
step 1, determining the minimum heat absorption capacity of the throttling process without generating dry ice.
Step 2, calculating high-pressure CO2Throttling to a temperature above the critical pressure.
And 3, judging whether the temperature after throttling is lower than the temperature of a three-phase point, if so, performing the step 4, and otherwise, directly performing the step 5.
Step (ii) of4, mixing the supercritical CO2The grading is reduced to the critical pressure, the specific required grade is determined according to the actual condition, and the temperature is not reduced to be below the triple point.
And 5, determining the heating power required by each stage of throttling.
And 6, setting throttling pressure according to the critical pressure ratio, calculating the temperature after throttling, judging whether heating is needed, calculating heating power if heating is needed, and finally throttling the pressure to atmospheric pressure to realize a safe and economic discharge process.
Further, step 1 minimum endotherm with CO2The P-H relationship is mainly considered in relation to the physical properties of (1).
Further, in the steps 2, 3 and 4, the temperature after throttling comprises the temperature in the pipeline and the temperature at the throttling hole, and the temperature is calculated according to a continuity equation, a momentum equation, an energy equation and a state equation respectively. In addition, because the kinetic energy difference between the front and the back of the throttling hole is large (the flow rate after throttling can be critical flow rate), the energy equation simplification processing of the inner temperature of the throttling pipe and the temperature at the throttling hole is different when the temperature in the throttling process and the temperature at the throttling hole are calculated.
Further, CO2There is a critical pressure ratio when the pipe is throttled, i.e. the ratio of the minimum pressure that can be achieved after throttling to the inlet pressure. The critical pressure ratio is determined by the material property, CO2The critical pressure ratio of (2) is 0.546. Thus, for higher inlet pressure CO2If one wants to control the throttling process or heat between stages, the critical pressure ratio should be considered when selecting the number of throttling stages.
In particular, due to supercritical CO2Has the characteristics of high pressure and good fluidity, and currently, CO2The pipeline is mostly operated in a supercritical phase state, however, the change or improper operation of the operating parameters in the pipeline operating process pipe or the flow parameters of the throttling emptying process is easy to cause CO2The phase state changes, the physical parameters change rapidly, and the safe operation of the pipeline is not facilitated. Thus for high pressure supercritical CO2In the emptying process, the following method can be selected:
(1) the first stage throttles the pressure to a critical pressure. In CO2Before the critical pressure is reached, the pressure is measured,the temperature drop is less along with the change of the pressure drop, and the throttling effect coefficient is less. In the throttling process, CO2Basically maintains the original phase state, changes of physical parameters such as density and the like are relatively smooth, and CO can be maintained2The pipeline realizes quick and stable discharge in a short time.
(2) Below the critical pressure range, a second stage of throttling is set, and the throttling pressure selection still takes into account the critical pressure ratio. Meanwhile, in order to reduce the number of throttling stages, heating measures are preferably applied after the first-stage throttling and before the second-stage throttling as much as possible.
(3) If the heating amount is too large, a third stage of throttling is arranged, and heating is carried out after the second stage of throttling. In the multi-stage throttling, if the heating amount is excessive, the distribution is carried out according to the equilibrium distribution principle.
The throttling series is not more than three, since the more throttling series, the more equipment and monitoring instruments are needed.
For low temperature liquid phase CO2And low temperature gas phase CO2Because of the low pressure, it is preferable to use one-stage or two-stage throttling in consideration of the amount of heating. For high temperature gas phase CO2Although the pressure difference between the front and the rear of the emptying valve is large, the initial temperature is high and the initial flow rate is large, the fluid behind the valve can be rapidly heated by the inlet fluid, dry ice deposition is not easy to generate, and therefore heating or multi-stage throttling is not needed, and the air can be directly emptied.
With reference to fig. 4, for the calculation of the temperature after the pipeline throttling, a pipeline throttling temperature calculation model is established;
for CO2Throttling of the pipe, if known CO2Composition, throttle inlet temperature T1And pressure P1And a throttle outlet pressure P2Can determine CO before throttling2Enthalpy of H1. Assuming an initial value T of the temperature after throttling2Considering the possibility of generating two-phase flow in the throttling process, phase equilibrium needs to be calculated through a thermodynamic equilibrium equation to obtain each phase fraction, and enthalpy H after throttling is solved through each phase fraction2Then adjusting T2Let H stand for1、H2Are equal. By such an iterative method, the CO can be determined2The temperature after throttling.
With reference to fig. 5, for the calculation of the temperature after orifice throttling, an orifice throttling temperature calculation model is established;
for CO2Throttling of the orifice, if known CO2Composition, throttle inlet temperature T1And pressure P1And a throttle outlet pressure P2Can determine the pre-throttle CO2Enthalpy of H1. And judging whether the throttling is critical throttling or not, and calculating the throttling pressure ratio by adopting a corresponding formula to obtain the kinetic energy difference. Assuming an initial value T of the temperature after throttling2Calculating the enthalpy H after throttling2Then adjust T2Let H stand for1And H2The following relationships are satisfied:
by such an iterative method, CO can be determined2The temperature after throttling.
In connection with FIG. 6, for supercritical CO2A multi-stage throttling emptying control process;
respectively adopting the established throttling temperature drop calculation method to calculate the temperature after throttling, respectively analyzing whether the throttling process reaches the critical pressure or not according to different throttling types, analyzing the throttling series and the minimum heat absorption capacity required to be adopted, and establishing a set of safe and economic supercritical CO2And (4) a multi-stage throttling emptying control scheme.
Suitable for supercritical CO2Analysis of flow characteristics in the process of pipeline throttling and emptying, supercritical CO under different initial conditions2The temperature change and the pressure change in the emptying process, the lowest temperature in the emptying process, whether hydrates are generated or not and the like are different, the model can accurately predict the temperature at different pressures after throttling, and the phenomenon that the pipeline is blocked by dry ice due to the fact that the temperature is too low is avoided;
the method is suitable for analyzing the minimum heat absorption capacity and throttling stages of the non-generated dry ice in the throttling process, the throttling control principle is to consume the least heating quantity and release the pressure as soon as possible on the premise of not generating the dry ice, namely, the dry ice is not generated, the heating quantity is as little as possible, the throttling stages are as few as possible, and a minimum heating quantity calculation method and a throttling stage selection method are provided.
Since the vent line is directly connected to the atmosphere, the CO is at high pressure2When the pipeline is released, the pressure and the temperature behind the valve are both greatly reduced due to overlarge pressure difference between the front and the back of the valve, and when the pressure in front of the valve is high enough, dry ice is easily generated and blocks an emptying pipeline. At high pressure CO2The pipeline is discharged in the air by adopting multi-stage throttling discharge, so that the pressure drop before and after the throttling valve is reduced, the temperature drop amplitude of fluid is relieved, and the adverse effect of throttling discharge on the pipeline, equipment and the surrounding environment is reduced.
At high pressure CO2The pipeline is discharged in the air by adopting multi-stage throttling discharge, so that the pressure drop before and after the throttling valve is reduced, the temperature drop amplitude of fluid is relieved, the adverse effect of the throttling discharge on the pipeline, equipment and the surrounding environment is reduced, the pressure is discharged as soon as possible by using the least heating quantity on the premise of not generating dry ice, and meanwhile, the generation of the dry ice can be effectively controlled by adopting heating measures, so that the aim of safe discharge is fulfilled.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims (7)
1. Supercritical CO2The multi-stage throttling method is characterized by comprising the following steps of:
determining throttle bleed supercritical CO2The minimum heat absorption capacity of dry ice is not generated in the process, and high-pressure CO is calculated2Throttling to a temperature above a critical pressure;
building a pipeline throttling and orifice throttling temperature calculation model, and judging whether the throttled temperature is lower than the triple point temperature or not, and adding supercritical CO2Reducing the temperature to a position above the critical pressure in a grading way, and maintaining the temperature above the triple point temperature;
determining the heating power required by each stage of throttling, performing parameter configuration according to the critical pressure ratio, and converting the supercritical CO into CO2Throttling to atmospheric pressure;
for high pressure supercritical CO2Emptying, adopting three-stage throttling, and heating between adjacent stages.
2. The supercritical CO of claim 12The multi-stage throttling method is characterized in that when the temperature after throttling is judged to be higher than the temperature of a triple point, the heating power required by each stage of throttling is determined.
3. The multi-stage throttling method of claim 1, wherein the throttling pressure setting is performed according to a critical pressure, the post-throttling temperature is calculated, and the heating power is configured according to the required heating.
4. The supercritical CO of claim 12The multi-stage throttling method is characterized in that the throttled temperature comprises the temperature at the throttle valve throttle hole and the temperature in a blow-down pipe.
5. The supercritical CO of claim 12The multi-stage throttling method is characterized in that the throttling process and the interstage heating are controlled by referring to the throttling stage number and the critical pressure ratio.
6. The supercritical CO of claim 12Multistage throttling method, characterized in that in the first stage throttling, the pressure is throttled to a critical pressure, CO2And maintaining the original phase state for releasing.
7. The supercritical CO of claim 62The multi-stage throttling method is characterized in that below a critical pressure range, secondary throttling is arranged according to a critical pressure ratio, and heating quantity is distributed according to a balanced distribution principle.
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| CN116036901B (en) * | 2022-12-22 | 2024-05-10 | 新疆敦华绿碳技术股份有限公司 | CO (carbon monoxide)2Emptying device |
| CN116146904B (en) * | 2023-02-08 | 2024-01-19 | 中国矿业大学 | CO (carbon monoxide) 2 Conveying safety emptying device |
| CN116105071B (en) * | 2023-02-15 | 2024-05-24 | 新疆敦华绿碳技术股份有限公司 | Supercritical carbon dioxide pipeline safety relief system and control method |
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