CN111426113B - Flow control method for cold source liquefied natural gas of cold energy supply system - Google Patents
Flow control method for cold source liquefied natural gas of cold energy supply system Download PDFInfo
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- CN111426113B CN111426113B CN202010392930.1A CN202010392930A CN111426113B CN 111426113 B CN111426113 B CN 111426113B CN 202010392930 A CN202010392930 A CN 202010392930A CN 111426113 B CN111426113 B CN 111426113B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
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Abstract
The invention discloses a flow control method of liquefied natural gas of a cold source of a cold energy supply system, which is used for regulating the cold energy supply system. When the change value of the heat exchange amount of the downstream heat exchanger within a certain time is not more than a preset value, controlling the flow of the liquefied natural gas to be constant, setting the temperature of the liquefied natural gas at the liquefied natural gas inlet and the temperature of the liquefied natural gas outlet to be constant, and setting the flow of the secondary refrigerant to be constant, so that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃; and when the change value of the heat exchange amount of the downstream heat exchanger within a certain time is larger than a preset value, adjusting the flow of the secondary refrigerant and the flow of the liquefied natural gas, and keeping the flow of the secondary refrigerant and the flow of the liquefied natural gas unchanged to ensure that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃. The method stores the cold energy of the liquefied natural gas through the temperature change of the refrigerating medium and provides stable cold energy for downstream facilities with variable cold loads.
Description
Technical Field
The invention relates to the technical field of liquefied natural gas cooling, in particular to a flow control method of liquefied natural gas as a cold source of a cold energy supply system.
Background
Natural gas has become a good safe and clean energy source for countries in the world due to its excellent properties such as high efficiency, high quality, cleanliness and wide use. The liquefied natural gas is liquefied and then reduced in volume to 1/600, long-distance transportation is facilitated, after the liquefied natural gas is transported to a station by a ship, the liquefied natural gas needs to be converted into a gaseous state, and in the process, cold energy of about 830-860 MJ/t is released. However, when the cold energy of the lng is used for the cold load demand of the downstream facility, the cold load of the downstream facility varies greatly at different times, and the variation frequency is fast and the variation range is wide, so that the flow demand of the corresponding lng fluctuates greatly, thereby affecting the normal operation of the upstream receiving station.
To this end, there is a need for a method of regulating the flow of lng that can meet the changing cooling load of downstream facilities without affecting the upstream receiving station.
Disclosure of Invention
The invention aims to provide a flow control method of liquefied natural gas of a cold source of a cold energy supply system, which can ensure that the flow change of the liquefied natural gas can meet the change cold load of downstream facilities and can not influence the normal operation of an upstream receiving station.
In order to achieve the technical effects, the technical scheme of the flow control method for the cold source liquefied natural gas of the cold energy supply system is as follows:
a flow control method of liquefied natural gas as a cold source of a cold energy supply system, the cold energy supply system comprising: the heat exchange piece comprises a liquefied natural gas inlet, a liquefied natural gas outlet, a secondary refrigerant liquid return port and a secondary refrigerant liquid supply port; a downstream heat exchanger comprising a coolant inlet and a coolant outlet; the secondary refrigerant inlet is connected with the secondary refrigerant liquid supply port, and the secondary refrigerant outlet is connected with the secondary refrigerant liquid return port; the method is characterized in that:
when the change value of the heat exchange amount of the downstream heat exchanger within a certain time is not greater than a preset value, controlling the flow of the liquefied natural gas to be constant, wherein the temperature of the liquefied natural gas at the liquefied natural gas inlet and the temperature of the liquefied natural gas outlet are constantly set, and the flow of the secondary refrigerant is constantly set, so that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃;
and when the change value of the heat exchange amount of the downstream heat exchanger within a certain time is larger than a preset value, adjusting the flow of the secondary refrigerant and the flow of the liquefied natural gas, and keeping the temperature of the liquefied natural gas at the liquefied natural gas inlet and the temperature of the liquefied natural gas outlet constant, so that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃.
In some embodiments, when the change value of the heat exchange amount in a certain time of the downstream heat exchanger is larger than the preset value, the flow rate of the liquefied natural gas is adjusted to enable the water supply temperature of the refrigerating medium to be between-21 ℃ and-27 ℃ through the following steps:
s1, keeping the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas constant;
s2, adjusting the operation quantity of the heat exchange pieces to adjust the flow rate of the secondary refrigerant and ensure that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃;
s3, calculating a first theoretical value of the flow of the liquefied natural gas according to the adjusted water supply temperature of the secondary refrigerant, the adjusted flow of the secondary refrigerant and the adjusted return water temperature of the secondary refrigerant;
s4, adjusting the flow rate of the liquefied natural gas to the first theoretical value obtained in the step S3.
In some embodiments, the theoretical value of the flow rate of the liquefied natural gas is QLiquefied natural gasSaid Q isLiquefied natural gasSatisfy the relation: qLiquefied natural gas＝[(TGo back to-TFor supplying to)×QSecondary refrigerant×C]/(HGo out-HInto) Wherein:
Qliquefied natural gas: a flow rate of the liquefied natural gas;
Tgo back to: the return water temperature of the secondary refrigerant;
Tfor supplying to: the water supply temperature of the secondary refrigerant;
Qsecondary refrigerant: the flow rate of the secondary refrigerant;
c: the mass heat capacity of the secondary refrigerant;
Hgo out: an enthalpy of the liquefied natural gas at the liquefied natural gas outlet;
Hinto: an enthalpy of the liquefied natural gas at the liquefied natural gas inlet.
In some embodiments, a thermometer is disposed at the coolant outlet to detect the current outlet temperature of the coolant, predict the current supply water temperature of the coolant after heat exchange is performed on the coolant, and adjust the flow rate of the liquefied natural gas so as to make the adjusted supply water temperature of the coolant in the range of-21 ℃ to-27 ℃, which includes the following specific steps:
step Q1, according to the relational expression, taking the current outlet temperature of the secondary refrigerant as the TGo back toThe current flow rate of the liquefied natural gas is QLiquefied natural gasThe current flow rate of the secondary refrigerant is QSecondary refrigerantThe mass heat capacity of the secondary refrigerant is C, and the enthalpy value of the liquefied natural gas at the liquefied natural gas outlet is HGo outSaid liquefied natural gas at said liquefied natural gas inlet has an enthalpy of said HIntoCalculating the water supply temperature of the secondary refrigerant after the heat exchange of the current secondary refrigerant in the heat exchange piece as a predicted value of the water supply temperature of the secondary refrigerant;
step Q2, if the predicted value is in the range of-21 ℃ to-27 ℃, then no treatment is carried out;
step Q3, if the predicted value is not in the range of-21 ℃ to-27 ℃, adjusting the current operation quantity of the heat exchange elements to adjust the current flow rate of the refrigerating medium, so that the predicted value is in the range of-21 ℃ to-27 ℃;
step Q4, according to the relational expression, using the adjusted predicted value as the TFor supplying toThe flow rate of the secondary refrigerant after being adjusted is QSecondary refrigerantThe outlet temperature of the secondary refrigerant is TGo back toObtaining said QLiquefied natural gasThe flow rate of the liquefied natural gas is adjusted to the second theoretical value.
In some embodiments, the thermometers are positioned at set intervals on a return line through which the coolant is transported from the downstream heat exchanger to the heat exchange member to detect the coolant temperature at different locations in the return line, and steps Q1-Q4 are repeated to ensure that the predicted value is in the range of-21 ℃ to-27 ℃.
In some embodiments, after the liquefied natural gas enters the heat exchange member to complete heat exchange, the liquefied natural gas is gasified from liquid liquefied natural gas into gaseous liquefied natural gas and is reheated to 1 ℃ by an air-temperature gasifier to return to a natural gas pipeline network of the liquefied natural gas receiving station.
In some embodiments, the coolant is a 48% aqueous ethylene glycol solution.
In some embodiments, the heat exchange element is an intermediate medium heat exchanger, the intermediate medium heat exchanger includes an intermediate medium channel, an intermediate medium flows in the intermediate medium channel, the intermediate medium transfers the cold energy of the liquefied natural gas to the secondary refrigerant, the temperature of the intermediate medium is not lower than-35 ℃, and the intermediate medium is propane.
In some embodiments, the downstream heat exchanger comprises a plate heat exchanger in which the coolant exchanges heat with secondary water used for refrigeration of the commercial facility, the plate heat exchanger controlling the outlet temperature of the secondary water by a three-way valve on the coolant side.
In some embodiments, the plate heat exchanger comprises an ice and snow making plate heat exchanger and a venue air conditioner plate heat exchanger, and the coolant has a temperature of-14 ℃ to-16 ℃ at a water outlet of the ice and snow making plate heat exchanger and a temperature of-6 ℃ to-8 ℃ at a water outlet of the venue air conditioner plate heat exchanger.
The invention has the beneficial effects that: in a time period when the change value of the heat exchange amount in a certain time of the downstream heat exchanger is relatively stable, the cold load change of downstream facilities can be met and the cold energy of the liquefied natural gas can be stored only by adjusting the water supply temperature of the secondary refrigerant within the range of-21 ℃ to-27 ℃, so that the problem that the cold energy released by the liquefied natural gas is not matched with the cold load of the downstream facilities is avoided, the change value of the heat exchange amount in the certain time of the downstream heat exchanger has stable flow, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas, the influence of the cold load change of the downstream facilities on the operation of an upstream receiving station is avoided, the upstream receiving station can provide the cold energy for the downstream facilities under the condition of stable operation, and the cold energy source of the liquefied natural gas is saved.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 is a schematic diagram of a cold energy supply system according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for controlling the flow rate of liquefied natural gas from a cold source of a cold energy supply system according to an embodiment of the present invention;
fig. 3 is another flow chart of a flow control method for liquefying natural gas by a cold source of a cold energy supply system according to an embodiment of the invention.
Reference numerals:
1. a heat exchange member; 11. a liquefied natural gas inlet; 12. a liquefied natural gas outlet; 13. a secondary refrigerant liquid return port; 14. a secondary refrigerant liquid supply port;
2. a downstream heat exchanger; 21. a secondary refrigerant inlet; 22. and a secondary refrigerant outlet.
Detailed Description
In order to make the technical problems solved, the technical solutions adopted and the technical effects achieved by the present invention clearer, the technical solutions of the present invention are further described below by way of specific embodiments with reference to the accompanying drawings.
In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, removably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.
In the description of the present embodiment, the terms "upper", "lower", "right", "left", and the like are used based on the orientations and positional relationships shown in the drawings only for convenience of description and simplification of operation, and do not indicate or imply that the referred device or element must have a specific orientation, be configured and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used only for descriptive purposes and are not intended to have a special meaning.
The following describes specific contents of the flow control method of the liquefied natural gas as the cold source of the cold energy supply system according to the embodiment of the present invention with reference to fig. 1 to 3.
As shown in fig. 1 to fig. 3, a flow control method of liquefied natural gas of a cold source of a cold energy supply system according to an embodiment of the present invention includes: the heat exchange piece 1 comprises a liquefied natural gas inlet 11, a liquefied natural gas outlet 12, a secondary refrigerant liquid return port 13 and a secondary refrigerant liquid supply port 14; the downstream heat exchanger 2, the downstream heat exchanger 2 includes the coolant inlet 21 and coolant outlet 22; the secondary refrigerant inlet 21 is connected with the secondary refrigerant liquid supply port 14, and the secondary refrigerant outlet 22 is connected with the secondary refrigerant liquid return port 13; wherein:
when the change value of the heat exchange amount of the downstream heat exchanger 2 within a certain time is not more than a preset value, controlling the flow of the liquefied natural gas to be constant, setting the temperature of the liquefied natural gas at the liquefied natural gas inlet 11 and the temperature of the liquefied natural gas outlet 12 to be constant, and setting the flow of the secondary refrigerant to be constant so as to enable the water supply temperature of the secondary refrigerant to be in the range of-21 ℃ to-27 ℃;
when the change value of the heat exchange amount of the downstream heat exchanger 2 within a certain time is larger than a preset value, the flow rate of the secondary refrigerant and the flow rate of the liquefied natural gas are adjusted, and the temperature of the liquefied natural gas at the liquefied natural gas inlet 11 and the temperature of the liquefied natural gas outlet 12 are kept constant, so that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃. The direction of the arrows in fig. 1 indicates the direction of coolant flow.
As shown in fig. 1, in the cold energy supply system, a coolant enters the heat exchange member 1 from a coolant return port 13, lng enters the heat exchange member 1 from an lng inlet 11, the coolant and the lng complete heat exchange in the heat exchange member 1, the lng completes heat exchange and is output from an lng outlet 12, the coolant is output from a coolant supply port 14 after heat exchange, the coolant is transported from the coolant supply port 14 to a coolant inlet 21, the coolant enters the downstream heat exchanger 2 from the coolant inlet 21 to provide cold energy for downstream facilities and is transported from a coolant outlet 22 to the coolant return port 13, the coolant is transported to the heat exchange member 1 to exchange heat with the lng again and to provide cold energy for the downstream facilities through the downstream heat exchanger 2. In addition, temperature sensors are arranged at the coolant supply port 14, the coolant return port 13, the liquefied natural gas inlet 11, the liquefied natural gas supply port, the coolant inlet 21 and the coolant outlet 22 to test the temperatures of the liquefied natural gas and the coolant. In the operation process of the cold energy supply system, the temperature of the secondary refrigerant at the secondary refrigerant liquid return opening 13 is the water return temperature of the secondary refrigerant, the temperature of the secondary refrigerant at the secondary refrigerant liquid supply opening 14 is the water supply temperature of the secondary refrigerant, the temperature of the secondary refrigerant at the secondary refrigerant inlet 21 is the inlet temperature of the secondary refrigerant, the temperature of the secondary refrigerant at the secondary refrigerant outlet 22 is the outlet temperature of the secondary refrigerant, the temperature of the liquefied natural gas at the liquefied natural gas inlet 11 is the inlet temperature of the liquefied natural gas, and the temperature of the liquefied natural gas at the liquefied natural gas outlet 12 is the outlet temperature of the liquefied natural gas.
It should be noted that, in this embodiment, the heat exchange amount of the downstream heat exchanger 2 in a certain time refers to the heat quantity that needs to be transported or taken away by the downstream heat exchanger 2 in a certain time in the actual working process. In some applications, the amount of heat exchanged over time may be replaced by the cold or heat load of the downstream heat exchanger 2. Specifically, the constant value of the change in the heat exchange amount in a certain period of time is equivalent to the constant cold load or heat load of the downstream heat exchanger 2.
It will be appreciated that the coolant provides cooling energy to the downstream facility in the downstream heat exchanger 2, and in the case that the cooling load of the downstream facility frequently changes and the change range is large, the change value of the heat exchange amount of the downstream facility in a certain time will be greatly changed, so that the flow demand of the liquefied natural gas also needs to be changed correspondingly. If the flow rate of the liquefied natural gas is adjusted every time the heat exchange amount of the downstream facilities changes, the normal operation of the upstream receiving station of the liquefied natural gas is extremely easily influenced. In order to meet the varying cooling load of the downstream facility without affecting the normal operation of the receiving station upstream of the lng, the present embodiment stores the cold energy of the lng through the temperature variation of the coolant so that the cold energy of the coolant can provide the downstream facility with the cold energy meeting the demand of the downstream facility in the downstream heat exchanger 2 for a period of time when the flow rate of the lng is constant.
In a time period when the change value of the heat exchange amount in a certain time of the downstream heat exchanger 2 is relatively stable, the flow rate of the liquefied natural gas, the inlet temperature of the liquefied natural gas, the outlet temperature of the liquefied natural gas and the flow rate of the secondary refrigerant are not adjusted, and the cold energy of the liquefied natural gas can be stored through the change of the water supply temperature of the secondary refrigerant. Specifically, the supply water temperature of the coolant is controlled within the range of-21 ℃ to-27 ℃, and when the variation value of the downstream heat exchanger 2 in the time period is high, the supply water temperature of the coolant is also greatly changed so as to provide enough cold energy for downstream facilities or store the cold energy of the liquefied natural gas; when the variation value of the downstream heat exchanger 2 is low in this period, the supply water temperature of the coolant is changed little to maintain the functions of supplying cold energy to the downstream facilities and storing the cold energy of the lng. Through the arrangement, in the time period when the change value of the heat exchange amount within a certain time of the downstream heat exchanger 2 is relatively stable, the cold load change of the downstream facility can be met and the cold energy of the liquefied natural gas can be stored only by adjusting the water supply temperature of the secondary refrigerant, so that the problem that the cold energy released by the liquefied natural gas is not matched with the cold load of the downstream facility is avoided, the liquefied natural gas is enabled to have stable flow, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas in the time period when the change value of the heat exchange amount within the certain time of the downstream heat exchanger 2 is relatively stable, the influence on the operation of the upstream receiving station due to the change of the cold load of the downstream facility is avoided, the upstream receiving station is facilitated to provide the cold energy for the downstream facility under the condition of stable operation, and the cold energy source of the liquefied natural gas is saved.
In some embodiments, as shown in fig. 2, when the variation value of the heat exchange amount in a certain time of the downstream heat exchanger 2 is greater than the preset value, the flow rate of the liquefied natural gas is adjusted to make the supply water temperature of the coolant in the range of-21 ℃ to-27 ℃ by the following steps:
s1, keeping the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas constant;
s2, adjusting the operation number of the heat exchange pieces 1 to adjust the flow rate of the secondary refrigerant and ensure that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃;
s3, calculating a first theoretical value of the flow of the liquefied natural gas according to the adjusted water supply temperature of the secondary refrigerant, the adjusted flow of the secondary refrigerant and the adjusted return water temperature of the secondary refrigerant;
s4, the flow rate of the lng is adjusted to the first theoretical value obtained in step S3.
It can be understood that when the change value of the heat exchange amount of the downstream heat exchanger 2 in a certain time is greater than the preset value, the cooling load of the downstream heat exchanger 2 is greatly changed, and at this time, if the flow rate of the liquefied natural gas is not adjusted, the supply water temperature of the coolant is no longer in the range of-21 ℃ to-27 ℃. When the water supply temperature of the secondary refrigerant is lower than-27 ℃, the secondary refrigerant can affect the heat exchange element 1 to damage the heat exchange element 1; when the supply temperature of the coolant is above-21 ℃, the coolant will not provide enough cooling energy to the downstream facilities and affect the normal operation of the downstream facilities. In addition, in the actual operation process of the downstream facility, the change value of the heat exchange amount of the downstream heat exchanger 2 within a certain time period is relatively stable within a certain time period after exceeding the preset value, in order to meet the cooling load requirement within the certain time period, the flow rate of the secondary refrigerant and the flow rate of the liquefied natural gas need to be adjusted and constantly set, and the flow rate of the secondary refrigerant and the flow rate of the liquefied natural gas after being adjusted can enable the supply water temperature of the secondary refrigerant after being adjusted to be within the range of-21 ℃ to-27 ℃, so that the requirement of the cooling load of the downstream facility within the time period after the change value of the heat exchange amount of the downstream heat exchanger 2 within the certain time period exceeds the preset value can be met, and the cooling energy can be stably provided for the downstream facility without adjusting the flow rate of the liquefied natural gas when the cooling load of the downstream facility is changed within the time period.
Specifically, the adjustment of the flow rate of the coolant and the flow rate of the liquefied natural gas is performed by the following steps. In the first step, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas are kept stable. In this example, the inlet temperature of the liquefied natural gas was-145 ℃ and the outlet temperature of the liquefied natural gas was-15 ℃. And secondly, only adjusting the operation number of the heat exchange pieces 1 to adjust the flow of the secondary refrigerant, and returning the temperature of the secondary refrigerant at the secondary refrigerant liquid supply port 14 of the heat exchange pieces 1 to the range of-21 ℃ to-27 ℃. And thirdly, calculating a first theoretical value of the flow of the liquefied natural gas according to the adjusted water supply temperature of the secondary refrigerant, the adjusted flow of the secondary refrigerant and the adjusted return water temperature of the secondary refrigerant in order to provide enough cold energy for the secondary refrigerant with the changed flow to meet the cold load requirement of downstream facilities. And fourthly, adjusting the flow of the liquefied natural gas according to the obtained first theoretical value of the flow of the liquefied natural gas. After the flow of the secondary refrigerant and the flow of the liquefied natural gas are stable, the cold energy supply system can enable the secondary refrigerant to provide stable cold energy for downstream facilities by adjusting the water supply temperature of the secondary refrigerant in the time period.
In some embodiments, the theoretical value of the flow of liquefied natural gas is QLiquefied natural gas，QLiquefied natural gasSatisfy the relation: qLiquefied natural gas＝[(TGo back to-TFor supplying to)×QSecondary refrigerant×C]/(HGo out-HInto) Wherein:
Qliquefied natural gas: a flow rate of liquefied natural gas;
Tgo back to: the return water temperature of the secondary refrigerant; t isFor supplying to: the water supply temperature of the secondary refrigerant;
Qsecondary refrigerant: the flow rate of the secondary refrigerant; c: mass heat capacity of the secondary refrigerant;
Hgo out: the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12;
Hinto: the enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11.
It will be appreciated that the first theoretical value at which the lng flow should be adjusted after a change in coolant flow needs to be accurately determined to ensure stable operation of the cold energy supply system. Because the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas are constantly set, the enthalpy value of the liquefied natural gas at the liquefied natural gas inlet 11 and the enthalpy value of the liquefied natural gas at the liquefied natural gas outlet 12 are both constant, and because the secondary refrigerant generally does not change in the operation process of the cold energy supply system, the mass heat capacity of the secondary refrigerant is also constant, the return water temperature of the secondary refrigerant and the supply temperature of the secondary refrigerantThe water temperature can be obtained by measurement, and the flow rate of the liquefied natural gas and the flow rate of the secondary refrigerant can be directly obtained, so that the relationship Q is obtained according toLiquefied natural gas＝[(TGo back to-TFor supplying to)×QSecondary refrigerant×C]/(HGo out-HInto) The theoretical value of the fourth data can be determined according to the numerical values of any three data in the four data of the flow of the liquefied natural gas, the flow of the secondary refrigerant, the return water temperature of the secondary refrigerant and the water supply temperature of the secondary refrigerant, so that the theoretical value can be quickly adjusted according to the obtained theoretical value to meet the requirement of a cold energy supply system. Specifically, when the change value of the heat exchange amount of the downstream heat exchanger 2 in a certain time is greater than a preset value and the flow of the secondary refrigerant needs to be adjusted, the current return water temperature of the secondary refrigerant is taken as TGo back toThe adjusted water supply temperature of the secondary refrigerant is TFor supplying toThe flow rate of the adjusted secondary refrigerant is QSecondary refrigerantThe mass heat capacity of the secondary refrigerant is C, and the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12 is HGo outThe enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11 is HIntoCalculated according to the relation, QLiquefied natural gasThe value of (A) is the theoretical value of the flow of the liquefied natural gas, so that the flow of the liquefied natural gas can be adjusted according to the calculated first theoretical value, the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃, and the purpose of enabling the secondary refrigerant to provide stable cold energy for downstream facilities is achieved.
In some embodiments, as shown in FIG. 3, a thermometer is disposed at the coolant outlet 22 to detect the current coolant outlet temperature, predict the coolant feed temperature after heat exchange with the current coolant, and adjust the flow rate of liquefied natural gas to adjust the coolant feed temperature to be in the range of-21 ℃ to-27 ℃, which comprises the following steps:
step Q1, according to the relation, the current outlet temperature of the refrigerating medium is TGo back toThe current flow rate of liquefied natural gas is QLiquefied natural gasThe current flow rate of the coolant is QSecondary refrigerantThe mass heat capacity of the secondary refrigerant is C, and the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12 is HGo outThe enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11 is HIntoCalculating the water supply temperature of the secondary refrigerant after the heat exchange of the current secondary refrigerant in the heat exchange piece 1 as a predicted value of the water supply temperature of the secondary refrigerant;
step Q2, if the predicted value is in the range of-21 ℃ to-27 ℃, then no treatment is carried out;
step Q3, if the predicted value is not in the range of-21 ℃ to-27 ℃, adjusting the current running quantity of the heat exchange elements 1 to adjust the current flow of the refrigerating medium so as to enable the predicted value to be in the range of-21 ℃ to-27 ℃;
step Q4, according to the relation, the adjusted predicted value is taken as TFor supplying toThe flow rate of the adjusted secondary refrigerant is QSecondary refrigerantThe outlet temperature of the secondary refrigerant is TGo back toObtaining QSecondary refrigerantThe flow rate of the liquefied natural gas is adjusted to the second theoretical value.
It can be understood that, in the operation process of the cold energy supply system, the flow rate of the liquefied natural gas, the flow rate of the coolant, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas are kept constant in most of the time periods, so that the theoretical water supply temperature of the coolant after the heat exchange of the coolant in the heat exchange member 1 can be calculated according to the above relation and the return water temperature of the coolant. Meanwhile, in the foregoing time period, the cooling load of the downstream facility is relatively stable, and therefore it is considered that the change in the cooling load of the downstream facility can directly change the temperature of the water outlet of the coolant. The transport of the coolant from the coolant outlet port 22 to the coolant return port 13 takes a period of time and the temperature change during transport is much less than the temperature change of the coolant after heat exchange in the downstream heat exchanger 2. By integrating the characteristics of the cold energy supply system in the operation process, it can be considered that the change of the cold load of the downstream facility can be preliminarily judged by using the current outlet temperature of the secondary refrigerant, and the water supply temperature of the secondary refrigerant after the heat exchange of the current secondary refrigerant in the heat exchange member 1 is completed is predicted under the condition that the flow rate of the liquefied natural gas, the flow rate of the secondary refrigerant, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas are kept constant according to the current outlet temperature of the secondary refrigerant and the relational expression, so that the corresponding adjustment is performed according to the predicted value.
Specifically, the prediction and the corresponding adjustment of the supply water temperature of the secondary refrigerant are completed through the following steps. The first step, according to the relation, the current outlet temperature of the secondary refrigerant is taken as TGo back toThe current flow rate of liquefied natural gas is QLiquefied natural gasThe current flow rate of the coolant is QSecondary refrigerantThe mass heat capacity of the secondary refrigerant is C, and the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12 is HGo outThe enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11 is HIntoAnd calculating the water supply temperature of the current secondary refrigerant after the heat exchange of the secondary refrigerant in the heat exchange member 1 as a predicted value of the water supply temperature of the secondary refrigerant. Second, if the predicted value is within the range of-21 ℃ to-27 ℃, no treatment is performed. Thirdly, if the predicted value is not in the range of-21 ℃ to-27 ℃, adjusting the current running quantity of the heat exchange pieces 1 to adjust the current flow rate of the secondary refrigerant, and taking the adjusted flow rate of the secondary refrigerant as Q according to the relational expressionSecondary refrigerantThe current coolant outlet temperature is TGo back toThe current flow rate of liquefied natural gas is QLiquefied natural gasThe mass heat capacity of the secondary refrigerant is C, and the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12 is HGo outThe enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11 is HInto，TFor supplying toNamely the predicted value of the adjusted water supply temperature of the secondary refrigerant, and the predicted value is in the range of-21 ℃ to-27 ℃. And fourthly, after the flow of the secondary refrigerant is changed, the flow of the liquefied natural gas also needs to be changed according to the changed flow of the secondary refrigerant. According to the relational expression, the adjusted predicted value is taken as TFor supplying toThe flow rate of the adjusted secondary refrigerant is QSecondary refrigerantThe current coolant outlet temperature is TGo back toThe mass heat capacity of the secondary refrigerant is C, and the enthalpy of the liquefied natural gas at the liquefied natural gas outlet 12 is HGo outThe enthalpy of the liquefied natural gas at the liquefied natural gas inlet 11 is HIntoObtaining QLiquefied natural gasSecond theoretical value ofAnd adjusting the flow rate of the liquefied natural gas to a second theoretical value.
Through the adjustment of the steps, the flow rate of the secondary refrigerant and the flow rate of the liquefied natural gas can be adjusted when the current secondary refrigerant is not transported to the heat exchange member 1, the water supply temperature of the secondary refrigerant after the heat exchange of the heat exchange member 1 is completed by the current secondary refrigerant is within the range of-21 ℃ to-27 ℃, and the cold load after the change of the downstream facilities can be met, so that the cold energy supply system can be immediately adjusted after the cold load of the downstream facilities is changed, the secondary refrigerant can meet the cold load of the downstream facilities within the maximum time range, the influence on an upstream receiving station can be avoided, and the cold energy resource of the liquefied natural gas is saved.
In some embodiments, thermometers are provided at regular intervals on the return line from the downstream heat exchanger 2 to the heat exchange member 1 to detect the temperature of the coolant at different locations in the return line, and steps Q1-Q4 are repeated to ensure predicted values in the range of-21 ℃ to-27 ℃.
It can be understood that, because the temperature change of the coolant in the process of being transported from the water outlet of the downstream heat exchanger 2 to the water return port of the heat exchange member 1 inevitably occurs, although the temperature change is much smaller than the temperature change of the outlet temperature of the coolant caused by the change of the cold load of the downstream facility, there is still a certain error in directly using the current outlet temperature of the coolant to predict the future supply water temperature of the coolant. In order to adjust the flow rate of the secondary refrigerant and the flow rate of the liquefied natural gas in the existing time before the secondary refrigerant enters the secondary refrigerant return port 13 and also accurately predict the future supply water temperature of the secondary refrigerant, thermometers are provided at set intervals on a return line through which the secondary refrigerant is transported from the downstream heat exchanger 2 to the heat exchange member 1. Specifically, thermometers are arranged every 500m on a water return line of the coolant to detect the temperature of the coolant. After the temperature of the secondary refrigerant is obtained, the temperature of the secondary refrigerant is taken as TGo back toAnd repeating the foregoing steps of Q1-Q4 to ensure predicted values in the range of-21 ℃ to-27 ℃. It should be added that the arrangement of the thermometer on the water return line can be adjusted according to the actual situation,in the cold energy supply system, the adjustment of the flow rate of the coolant and the flow rate of the liquefied natural gas according to the temperature of the coolant at the location of the return line may also be determined according to actual conditions, and is not particularly limited in this embodiment.
In some embodiments, after the lng enters the heat exchange member 1 to complete heat exchange, the lng is gasified from the liquefied lng to gaseous lng and reheated to 1 ℃ by an air-temperature gasifier and returned to the natural gas pipeline network of the lng receiving station.
It can be understood that the cold energy of the lng after heat exchange in the heat exchange member 1 is utilized, and in order to use the lng without available cold energy, the lng is converted from liquid to gas, and is reheated to 1 ℃ by an air-temperature vaporizer, so that the gas can be delivered to a natural gas pipeline network of an upstream receiving station and transported to other areas.
In some embodiments, the coolant is a 48 wt% aqueous ethylene glycol solution.
It can be appreciated that the aqueous solution of ethylene glycol in the coolant has the characteristics of good stability, small specific gravity and small viscosity, can bear lower temperature in the cold energy supply system and does not corrode the transportation pipeline of the cold energy supply system, thereby prolonging the service life of the cold energy supply system. It should be added that the mass ratio of the glycol in the glycol aqueous solution will affect the freezing point of the glycol aqueous solution, and in this embodiment, a 48 wt% glycol aqueous solution is preferred, but in other cold energy supply systems, the coolant can be selected from glycol aqueous solutions with other glycol mass ratios to achieve better heat exchange effect and cold supply effect.
In some embodiments, the heat exchange member 1 is an intermediate medium heat exchanger, the intermediate medium heat exchanger includes an intermediate medium channel, an intermediate medium flows in the intermediate medium channel, the intermediate medium transfers the cold energy of the liquefied natural gas to the secondary refrigerant, the temperature of the intermediate medium is not lower than-35 ℃, and the intermediate medium is propane.
It will be appreciated that the use of an intermediate medium heat exchanger can improve the efficiency of heat transfer between the coolant and the lng. Specifically, the intermediate medium is arranged in the intermediate medium channel of the intermediate medium heat exchanger, and the heat exchange efficiency can be improved by using propane as the intermediate medium. The present embodiment does not limit the specific type of the intermediate medium, as long as the heat exchange member 1 has high heat exchange efficiency, such as an alcohol-water solution. In addition, the temperature of the intermediate medium cannot be lower than-35 ℃ in order to ensure the temperature operation of the heat exchanger 1.
In some embodiments, the downstream heat exchanger 2 comprises a plate heat exchanger in which the coolant exchanges heat with secondary water used for refrigeration of the commercial facility, the plate heat exchanger controlling the outlet temperature of the secondary water by a three-way valve on the coolant side.
It can be understood that the plate heat exchanger used in the downstream heat exchanger 2 can improve the cooling efficiency of the coolant to the downstream arrangement, and has the advantages of large adaptability, compact structure, low price, easy access to people and easy disassembly and washing. Because the cooling loads of different scenes in the downstream facilities are not completely consistent, the plate heat exchanger is provided with a three-way valve for flow control so as to control the outlet temperature of secondary water for cooling the downstream facilities, thereby further improving the adaptability of the downstream heat exchanger 2.
In some embodiments, the plate heat exchanger comprises an ice and snow making plate heat exchanger and a venue air conditioner plate heat exchanger, and the coolant has a temperature of-14 ℃ to-16 ℃ at a water outlet of the ice and snow making plate heat exchanger and a temperature of-6 ℃ to-8 ℃ at a water outlet of the venue air conditioner plate heat exchanger.
It will be appreciated that in this embodiment, the cooling load usage of the downstream facilities includes ice making and snow making and venue air conditioning. For this reason, the plate heat exchanger of the downstream heat exchanger 2 comprises an ice-making and snow-making plate heat exchanger and a plate heat exchanger for a venue air conditioner, and in order to meet the cooling load requirement of downstream facilities, the temperature of the water outlet of the secondary refrigerant at the ice-making and snow-making plate heat exchanger is-14 ℃ to-16 ℃, and the temperature of the water outlet of the plate heat exchanger for the venue air conditioner is-6 ℃ to-8 ℃, so that the secondary refrigerant can provide cooling energy for the ice-making and snow-making plate heat exchanger and the plate heat exchanger for the venue air conditioner to the maximum extent.
Example (b):
a flow control method of liquefied natural gas as a cold source of a cold energy supply system according to an embodiment of the present invention will be described with reference to fig. 1 to 3.
As shown in fig. 1, in the cold energy supply system in this embodiment, a 48 wt% ethylene glycol aqueous solution is used as the coolant, the distance between the heat exchange member 1 and the downstream heat exchanger 2 is 3900m, and the two complete the transport of the coolant through buried pipelines of the underground DN 600. The direction of the arrows in the figure is the direction of coolant transport. After entering the downstream heat exchanger 2 from the water inlet of the downstream heat exchanger 2, the secondary refrigerant is used as primary water supply to exchange heat with secondary water in the ice and snow making plate heat exchanger and the air conditioning plate heat exchanger in the downstream heat exchanger 2 of the downstream facility respectively. In the heat exchange process, the temperature of the secondary refrigerant at the water outlet of the ice and snow making plate type heat exchanger is-14 ℃ to-16 ℃, and the temperature of the water outlet of the plate type heat exchanger for the air conditioner in the venue is-6 ℃ to-8 ℃; after heat exchange is finished, the secondary refrigerant is transported to the heat exchange part 1 through the water return pipeline to exchange heat with the liquefied natural gas, is output from the water supply port of the heat exchange part 1, provides cold energy for the downstream heat exchanger 2 through the transport pipeline again, and the water supply temperature of the heat exchange part 1 is in the range of-21 ℃ to-27 ℃. The liquefied natural gas provides cold energy for the refrigerating medium, enters an air temperature type vaporizer to be heated to more than 1 ℃, and returns to an external transmission pipe of an upstream receiving station to be transmitted to the outside.
Specifically, in the downstream facility in this embodiment, the maximum cooling load of the ice and snow making plate heat exchanger is 9340KW, the water supply temperature of the secondary refrigerant in the ice and snow making plate heat exchanger is-21 ℃, the water return temperature in the ice and snow making plate heat exchanger is-14 ℃, the water supply temperature of the secondary water in the ice and snow making plate heat exchanger is-18 ℃, and the water return temperature in the ice and snow making plate heat exchanger is-13 ℃; when the secondary refrigerant is output to the venue air-conditioning plate heat exchanger from the ice-making and snow-making plate heat exchanger, the water supply temperature of the secondary refrigerant in the venue air-conditioning plate heat exchanger is the return water temperature of the secondary refrigerant in the ice-making and snow-making plate heat exchanger, namely-14 ℃, the outlet temperature of the secondary refrigerant in the venue air-conditioning plate heat exchanger is-6 ℃, the water supply temperature of the secondary water in the venue air-conditioning plate heat exchanger is 5 ℃, and the inlet temperature of the secondary water in the venue air-conditioning plate heat exchanger is 13 ℃.
Meanwhile, the cold load change coefficient in the downstream facility for 24 hours per day is as follows, where the cold load of the downstream facility for each hour is the maximum daily cold load multiplied by the cold load change coefficient for that hour. The cooling load change coefficients between 0 and 2 are all 0.16, the cooling load change coefficients between 2 and 5 are all 0.25, the cooling load change coefficient between 6 is 0.5, the cooling load change coefficient between 7 is 0.59, the cooling load change coefficients between 8 and 9 are all 0.67, the cooling load change coefficient between 10 is 0.75, the cooling load change coefficient between 11 is 0.84, the cooling load change coefficient between 12 is 0.9, the cooling load change coefficients between 13 and 14 are all 1, the cooling load change coefficient between 15 is 0.92, the cooling load change coefficients between 16 and 17 are all 0.84, the cooling load change coefficients between 18 and 19 are all 0.74, the cooling load change coefficients between 20 and 21 are all 0.5, the cooling load change coefficient between 22 is 0.33, and the cooling load change coefficients between 22 and 24 are all 0.16.
According to the above coefficient of change of the cold load of the downstream facility, it can be observed that the cold load of the downstream facility between the previous day 22 and the current day 22 changes 14 times in total, and if the flow rate of the liquefied natural gas is adjusted every time the cold load changes, the change of the flow rate load is large, which will negatively affect the upstream receiving station and is not beneficial to the normal stable operation of the upstream receiving station. Therefore, the method divides the previous 22 days to the current 22 days into four time periods according to similar cold load change coefficients, constantly sets the flow of the secondary refrigerant, the flow of the liquefied natural gas, the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas in each time period, stores the cold energy of the liquefied natural gas by changing the water supply temperature of the secondary refrigerant within-21 ℃ to-27 ℃ so as to solve the problem that the cold energy released by the flow of the liquefied natural gas between the previous 22 days to the current 22 days is not matched with the cold application of downstream facilities, finally solves the problem of the flow fluctuation of the liquefied natural gas caused by frequent change of the cold load of the downstream facilities, and is beneficial to providing the cold energy for the downstream facilities by an upstream receiving station under the condition of stable operation. Wherein, the relation Q is usedLiquefied natural gas＝[(TGo back to-TFor supplying to)×QSecondary refrigerant×C]/(HGo out-HInto) The flow rate of the liquefied natural gas over the four time periods is determined.
Specifically, in the cold energy supply system of the present embodiment, there are a plurality of heat exchange members 1, the flow rate of the coolant in each heat exchange member 1 is constantly set to 541t/h, and the flow rate of the coolant is adjusted by the different operation numbers of the plurality of heat exchange members 1 in different time periods; the pressure of the liquefied natural gas was 7.5MpaG, the inlet temperature of the liquefied natural gas was-145 deg.C, the outlet temperature of the liquefied natural gas was-15 deg.C and was set constantly. The water supply temperature of the secondary refrigerant, the inlet temperature of the secondary refrigerant, the outlet temperature of the secondary refrigerant and the return water temperature of the secondary refrigerant are obtained through temperature sensors arranged in the cold energy supply system. The flow rate of the liquefied natural gas is determined by the measurement data and the relational expression. After the setting, the flow rate of the liquefied natural gas is stably set in each of the four periods, so that the influence of the change of the flow rate of the liquefied natural gas caused by the change of the downstream cooling load on the operation of the upstream receiving station can be greatly reduced. In addition, in the present embodiment, the data of the important parameters in the cooling energy supply system between the previous day 22 and the current day 22 are as follows.
The first time interval is from the previous 22 days to the current 5 days, wherein the running number of the heat exchange pieces 1 in the first time interval is 1, the flow rate of the liquefied natural gas is 25t/h, and the flow rate of the refrigerating medium is 541 t/h;
in the period from 22 days before to 23 days before, the water supply temperature of the secondary refrigerant is minus 24.06 ℃, the water return temperature of the secondary refrigerant is minus 14.34 ℃, the inlet temperature of the secondary refrigerant is minus 21 ℃ and 73 ℃, the outlet temperature of the secondary refrigerant is minus 16.7 ℃, and the cold load change coefficient is 0.16; in the period from 23 days before to 24 days before, the water supply temperature of the secondary refrigerant is minus 24.06 ℃, the water return temperature of the secondary refrigerant is minus 14.34 ℃, the inlet temperature of the secondary refrigerant is minus 21 ℃ and 69 ℃, the outlet temperature of the secondary refrigerant is minus 16.66 ℃, and the cold load change coefficient is 0.16; in the previous 24 days to this day 1, the feed water temperature of the coolant was-24.02 ℃, the return water temperature of the coolant was-14.3 ℃, the inlet temperature of the coolant was-21 ℃ and 69 ℃, the outlet temperature of the coolant was-16.66 ℃, and the cooling load variation coefficient was 0.16; in the present 1 and present 2 days, the water supply temperature of the coolant is-24.02 ℃, the water return temperature of the coolant is-14.3 ℃, the inlet temperature of the coolant is-21 ℃ and 65 ℃, the outlet temperature of the coolant is-16.62 ℃, and the cold load variation coefficient is 0.25; in this 2 to this 3 day, the coolant feed temperature was-25.74 deg.C, the coolant return temperature was-12.66 deg.C, the coolant inlet temperature was-24.02 deg.C, the coolant outlet temperature was-16.62 deg.C, and the cooling load coefficient of variation was 0.25; in the present 3 to present 4, the feed temperature of the coolant was-25.74 ℃, the return temperature of the coolant was-14.37 ℃, the inlet temperature of the coolant was-21 ℃ and-76 ℃, the outlet temperature of the coolant was-16.66 ℃, and the coefficient of variation of the cooling load was 0.25; in the present 4 to present 5, the feed water temperature of the coolant was-23.48 ℃, the return water temperature of the coolant was-10.41 ℃, the inlet temperature of the coolant was-21 ℃ and 76 ℃, the outlet temperature of the coolant was-14.37 ℃, and the cooling load variation coefficient was 0.25;
the second time interval is from 5 days to 10 days, wherein the running quantity of the heat exchange elements 1 in the second time interval is 2, the flow rate of the liquefied natural gas is 78t/h, and the flow rate of the refrigerating medium is 1082 t/h;
in the present 5 to the present 6, the water supply temperature of the coolant is-25.83 ℃, the water return temperature of the coolant is-10.41 ℃, the inlet temperature of the coolant is-23.48 ℃, the outlet temperature of the coolant is-11.37 ℃, and the cold load variation coefficient is 0.5; in the present 6 to the present 7, the water supply temperature of the coolant was-25.83 ℃, the water return temperature of the coolant was-11.37 ℃, the inlet temperature of the coolant was-25.83 ℃, the outlet temperature of the coolant was-12.03 ℃, and the cooling load variation coefficient was 0.59; in the current 7 to the current 8 days, the water supply temperature of the coolant is-26.05 ℃, the water return temperature of the coolant is-10.28 ℃, the inlet temperature of the coolant is-25.33 ℃, the outlet temperature of the coolant is-12.03 ℃, and the cold load variation coefficient is 0.67; in the present 8 to present 9, the feed water temperature of the coolant was-26.05 ℃, the return water temperature of the coolant was-10.28 ℃, the inlet temperature of the coolant was-24.29 ℃, the outlet temperature of the coolant was-10.94 ℃, and the cooling load coefficient of variation was 0.67; in the present 9 to present 10 days, the water supply temperature of the coolant is-24.95 ℃, the water return temperature of the coolant is-7.437 ℃, the inlet temperature of the coolant is-24.29 ℃, the outlet temperature of the coolant is-10.94 ℃, and the cold load variation coefficient is 0.75;
the third time period is from 10 days to 18 days, wherein the running quantity of the heat exchange pieces 1 in the third time period is 3, the flow rate of the liquefied natural gas is 116t/h, and the flow rate of the refrigerating medium is 1623 t/h;
in this time 10 to this day 11, the feed water temperature of the coolant was-24.95 ℃, the return water temperature of the coolant was-7.437 ℃, the inlet temperature of the coolant was-21 ℃ to 07 ℃, the outlet temperature of the coolant was-12.26 ℃, and the cooling load coefficient of variation was 0.84; in this 11 and present 12 days, the feed water temperature of the coolant was-25.93 ℃, the return water temperature of the coolant was-7.437 ℃, the inlet temperature of the coolant was-21 ℃ to 07 ℃, the outlet temperature of the coolant was-12.26 ℃, and the cooling load coefficient of variation was 0.9; in this day 12 to this day 13, the feed water temperature of the coolant was-24.95 ℃, the return water temperature of the coolant was-7.53 ℃, the inlet temperature of the coolant was-21 ℃ and-17 ℃, the outlet temperature of the coolant was-10.89 ℃, and the cold load coefficient of variation was 1; in this day 13 to this day 14, the feed water temperature of the coolant was-24.55 ℃, the return water temperature of the coolant was-6.167 ℃, the inlet temperature of the coolant was-21 ℃ and-17 ℃, the outlet temperature of the coolant was-10.89 ℃, and the cold load coefficient of variation was 1; 14 this day to 15 this day, the feed water temperature of the coolant was-24.55 deg.C, the return water temperature of the coolant was-6.167 deg.C, the inlet temperature of the coolant was-21 deg.C, 08 deg.C, the outlet temperature of the coolant was-10.7 deg.C, and the cooling load coefficient of variation was 0.92; in the present 15 to 16 days, the feed temperature of the coolant was-25.65 ℃, the return temperature of the coolant was-8.417 ℃, the inlet temperature of the coolant was-21 ℃ to 08 ℃, the outlet temperature of the coolant was-10.7 ℃, and the coefficient of variation of the cooling load was 0.84; in this day 16 to this day 17, the coolant feed water temperature was-25.65 ℃, the coolant return water temperature was-8.417 ℃, the coolant inlet temperature was-23.07 ℃, the coolant outlet temperature was-12.96 ℃, and the cooling load coefficient of variation was 0.84; in the present 17 to present 18 days, the feed temperature of the coolant was-25.93 ℃, the return temperature of the coolant was-11.86 ℃, the inlet temperature of the coolant was-23.07 ℃, the outlet temperature of the coolant was-12.96 ℃, and the cooling load variation coefficient was 0.74;
the fourth time period is from 18 days to 22 days, wherein the running quantity of the heat exchange elements 1 in the fourth time period is 2, the flow rate of the liquefied natural gas is 70t/h, and the flow rate of the refrigerating medium is 1082 t/h;
in the present 18 to present 19, the coolant feed temperature was-25.93 ℃, the coolant return temperature was-9.284 ℃, the coolant inlet temperature was-24.47 ℃, the coolant outlet temperature was-11.86 ℃, and the cooling load coefficient of variation was 0.74; at the time of 19 today, in 20 days, the water supply temperature of the secondary refrigerant is-24.47 ℃, the water return temperature of the secondary refrigerant is-9.284 ℃, the inlet temperature of the secondary refrigerant is-21 ℃ and 88 ℃, the outlet temperature of the secondary refrigerant is-13.11 ℃, and the cold load change coefficient is 0.5; in this day 20 to this day 21, the feed water temperature of the coolant was-24.32 ℃, the return water temperature of the coolant was-10.53 ℃, the inlet temperature of the coolant was-21 ℃ and 88 ℃, the outlet temperature of the coolant was-13.11 ℃, and the cold load coefficient of variation was 0.5; at this time 21 to this day 22, the coolant feed temperature was-24.32 deg.C, the coolant return temperature was-10.53 deg.C, the coolant inlet temperature was-21 deg.C, 73 deg.C, the coolant outlet temperature was-16.7 deg.C, and the cooling load coefficient of variation was 0.33.
In the description herein, references to the description of "some embodiments," "other embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above description is only a preferred embodiment of the present invention, and for those skilled in the art, the present invention should not be limited by the description of the present invention, which should be interpreted as a limitation.
Claims (7)
1. A flow control method of liquefied natural gas as a cold source of a cold energy supply system, the cold energy supply system comprising: the heat exchange device comprises a heat exchange piece (1), wherein the heat exchange piece (1) comprises a liquefied natural gas inlet (11), a liquefied natural gas outlet (12), a secondary refrigerant liquid return port (13) and a secondary refrigerant liquid supply port (14); a downstream heat exchanger (2), the downstream heat exchanger (2) comprising a coolant inlet (21) and a coolant outlet (22); the secondary refrigerant inlet (21) is connected with the secondary refrigerant liquid supply port (14), and the secondary refrigerant outlet (22) is connected with the secondary refrigerant liquid return port (13); the method is characterized in that:
when the change value of the heat exchange amount of the downstream heat exchanger (2) within a certain time is not greater than a preset value, controlling the flow of the liquefied natural gas to be constant, wherein the temperature of the liquefied natural gas at the liquefied natural gas inlet (11) and the temperature of the liquefied natural gas outlet (12) are constantly set, and the flow of the secondary refrigerant is constantly set, so that the water supply temperature of the secondary refrigerant is in the range of-21 ℃ to-27 ℃;
when the change value of the heat exchange amount of the downstream heat exchanger (2) in a certain time is larger than a preset value, adjusting the flow rate of the refrigerating medium and the flow rate of the liquefied natural gas, keeping the temperature of the liquefied natural gas at the liquefied natural gas inlet (11) and the temperature of the liquefied natural gas outlet (12) constant, so that the water supply temperature of the refrigerating medium is in the range of-21 ℃ to-27 ℃, and adjusting the flow rate of the liquefied natural gas so that the water supply temperature of the refrigerating medium is between-21 ℃ and-27 ℃ by the following steps:
s1, keeping the inlet temperature of the liquefied natural gas and the outlet temperature of the liquefied natural gas constant;
s2, adjusting the operation quantity of the heat exchange pieces (1) to adjust the flow rate of the secondary refrigerant, and enabling the water supply temperature of the secondary refrigerant to be in the range of-21 ℃ to-27 ℃;
s3, calculating a first theoretical value of the flow of the liquefied natural gas according to the adjusted water supply temperature of the secondary refrigerant, the adjusted flow of the secondary refrigerant and the current return water temperature of the secondary refrigerant;
s4, adjusting the flow rate of the liquefied natural gas to the first theoretical value obtained in the step S3;
the theoretical value of the flow of the liquefied natural gas is QLiquefied natural gasSaid Q isLiquefied natural gasSatisfy the relation: qLiquefied natural gas＝[(TGo back to-TFor supplying to)×QSecondary refrigerant×C]/(HGo out-HInto) Wherein:
Qliquefied natural gas: a flow rate of the liquefied natural gas;
Tgo back to: the return water temperature of the secondary refrigerant; t isFor supplying to: the water supply temperature of the secondary refrigerant;
Qsecondary refrigerant: the flow rate of the secondary refrigerant; c: the mass heat capacity of the secondary refrigerant;
Hgo out: an enthalpy value of the liquefied natural gas at the liquefied natural gas outlet (12);
Hinto: an enthalpy value of the liquefied natural gas at the liquefied natural gas inlet (11);
a thermometer is arranged at the secondary refrigerant outlet (22) to detect the current outlet temperature of the secondary refrigerant, the water supply temperature of the secondary refrigerant after the heat exchange of the current secondary refrigerant is predicted, and the flow of the liquefied natural gas is adjusted to enable the adjusted water supply temperature of the secondary refrigerant to be in the range of-21 ℃ to-27 ℃, and the method specifically comprises the following steps:
step Q1, according to the relational expression, taking the current outlet temperature of the secondary refrigerant as the TGo back toThe current flow rate of the liquefied natural gas is QLiquefied natural gasThe current flow rate of the secondary refrigerant is QSecondary refrigerantThe mass heat capacity of the secondary refrigerant is C, and the enthalpy value of the liquefied natural gas at the liquefied natural gas outlet (12) is HGo outSaid liquefied natural gas at said liquefied natural gas inlet (11) having an enthalpy value of said HIntoCalculating the water supply temperature of the secondary refrigerant after heat exchange of the current secondary refrigerant in the heat exchange piece (1) as a predicted value of the water supply temperature of the secondary refrigerant;
step Q2, if the predicted value is in the range of-21 ℃ to-27 ℃, then no treatment is carried out;
step Q3, if the predicted value is not in the range of-21 ℃ to-27 ℃, adjusting the current running quantity of the heat exchange elements (1) to adjust the current flow of the refrigerating medium so that the predicted value is in the range of-21 ℃ to-27 ℃;
step Q4, according to the relational expression, using the adjusted predicted value as the TFor supplying toThe flow rate of the secondary refrigerant after being adjusted is QSecondary refrigerantThe outlet temperature of the secondary refrigerant is TGo back toObtaining said QLiquefied natural gasThe flow rate of the liquefied natural gas is adjusted to the second theoretical value.
2. The method for controlling the flow of liquefied natural gas as a cold source of a cold energy supply system according to claim 1, wherein the thermometers are provided on a return line for transporting the coolant from the downstream heat exchanger (2) to the heat exchange member (1) at set intervals to detect the temperature of the coolant at different positions of the return line, and the steps Q1-Q4 are repeated to ensure that the predicted value is in the range of-21 ℃ to-27 ℃.
3. The method for controlling the flow rate of the liquefied natural gas as the cold source of the cold energy supply system according to claim 1 or 2, wherein the liquefied natural gas enters the heat exchange member (1) to complete the heat exchange, and is gasified from the liquefied natural gas into the liquefied natural gas in a gaseous state, and is reheated to 1 ℃ by the air temperature type gasifier to be returned to the natural gas pipeline network of the liquefied natural gas receiving station.
4. The method for controlling the flow rate of the liquefied natural gas as the cold source of the cold energy supply system according to claim 1 or 2, wherein the coolant is a 48% glycol aqueous solution.
5. The method for controlling the flow rate of the liquefied natural gas as the cold source of the cold energy supply system according to claim 1 or 2, wherein the heat exchange member (1) is an intermediate medium heat exchanger, the intermediate medium heat exchanger comprises an intermediate medium channel, an intermediate medium flows in the intermediate medium channel, the intermediate medium transfers the cold energy of the liquefied natural gas to the secondary refrigerant, the temperature of the intermediate medium is not lower than-35 ℃, and the intermediate medium is propane.
6. A cold energy supply system cold source lng flow control method according to claim 1 or 2, characterized in that the downstream heat exchanger (2) comprises a plate heat exchanger in which the secondary water used for commercial facility refrigeration is heat exchanged with the coolant, and the plate heat exchanger controls the outlet temperature of the secondary water by a three-way valve on the coolant side.
7. The method for controlling the flow rate of liquefied natural gas as a cold source of a cold energy supply system according to claim 6, wherein the plate heat exchanger comprises an ice-making and snow-making plate heat exchanger and a plate heat exchanger for a venue air conditioner, and the coolant has a temperature of-14 ℃ to-16 ℃ at a water outlet of the ice-making and snow-making plate heat exchanger and a temperature of-6 ℃ to-8 ℃ at a water outlet of the plate heat exchanger for the venue air conditioner.
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| CN106122760A (en) * | 2016-06-22 | 2016-11-16 | 中国天辰工程有限公司 | The control system of a kind of LNG gasification process cold energy use and control method thereof |
| CN207894080U (en) * | 2018-01-30 | 2018-09-21 | 中国科学院广州能源研究所 | A kind of LNG cold energy recycling energy storage ice maker |
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| CN110513932A (en) * | 2019-09-05 | 2019-11-29 | 浙江紫明科技有限公司 | LNG cold energy recycles ice-making system |
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| CN106122760A (en) * | 2016-06-22 | 2016-11-16 | 中国天辰工程有限公司 | The control system of a kind of LNG gasification process cold energy use and control method thereof |
| CN207894080U (en) * | 2018-01-30 | 2018-09-21 | 中国科学院广州能源研究所 | A kind of LNG cold energy recycling energy storage ice maker |
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