CN202082623U

CN202082623U - Aftercondenser control system

Info

Publication number: CN202082623U
Application number: CN 201120161026
Authority: CN
Inventors: 白改玲; 王红; 安小霞; 赵月峰; 宋媛玲; 李艳辉
Original assignee: China Huanqiu Engineering Co Ltd
Current assignee: China Huanqiu Engineering Co Ltd
Priority date: 2011-05-19
Filing date: 2011-05-19
Publication date: 2011-12-21
Anticipated expiration: 2021-05-19

Abstract

The utility model relates to an aftercondenser control system, which comprises a liquid level sensor respectively connected with the top and the bottom of a shell through two pipelines to detect the height of the liquid level of mixed liquid in the shell, an NG (Natural Gas) input pipe converged with the liquid level sensor in the middle of a BOG (Boil Off Gas) input pipe, an NG switch valve positioned on the NG input pipe, a second controller connected with the liquid level sensor to receive the output liquid level height and a first controller respectively connected with the second controller and a BOG compressor to control and reduce BOG output by the BOG compressor when the liquid level output by the second controller is lower than the information of liquid level lowest value information. The second controller is connected with the NG switch valve to control the NG switch valve to open under a condition that the liquid level height is higher than a liquid level highest valve. The aftercondenser control system can maintain both air pressure and liquid level in the aftrercondenser shell in a certain range stably under a premise that aftercondenser lower equipment (such as LNG (Liquefied Natural Gas) pump) is not subject to cavitation and operates safely.

Description

Recondensor control system

Technical Field

The utility model relates to a liquefied natural gas stores and carries the field, especially relates to a control system of recondensor.

Background

Liquefied Natural Gas (LNG) is a high-quality energy source and has the characteristics of high calorific value and small combustion pollution. The primary function of an LNG receiving station is to receive, store and vaporize ocean-transported LNG to obtain gaseous Natural Gas (NG) products, which are fed to power plants and city gas users through a natural gas pipeline network.

In the production process of the LNG receiving station, due to various factors such as leakage of ambient heat, volume replacement during ship unloading, flash evaporation, and rapid reduction of atmospheric ambient pressure, a certain amount of Boil Off Gas (BOG) is released from LNG in an LNG storage tank, other LNG facilities, and an LNG pipeline, and is a combustible Gas, and direct discharge of the BOG may cause accidents such as explosion and fire, as well as air pollution.

Typically, the BOG is processed by the LNG receiving station in a recondensation method, in which the BOG is compressed to a low pressure (typically 0.5MPa to 1.0MPa) by a BOG compressor, and then mixed with LNG pumped from the LNG low-pressure feed pump in a recondensor, and the BOG is condensed into a liquid state by the cold energy of the LNG to form a mixed liquid output. The recondensation method can utilize the cold energy (the existing concept corresponding to the heat quantity) of the LNG, and reduces part of power consumption required for directly compressing the BOG to reach the output pressure requirement, so that the use of energy sources can be further saved on the premise of safely and effectively processing the BOG.

Fig. 1 is a block diagram of a recondenser and its control system as provided by the prior art. As shown in fig. 1, the recondenser includes a shell 101, a BOG inlet pipe 102 communicating with the top of the shell 101, an LNG inlet pipe 103 communicating with the upper portion of the shell 101 and partially entering the interior of the shell 101, an inlet pipe 104 communicating with the end of the LNG inlet pipe 103 located in the interior of the shell 101 to allow LNG to be discharged from both outlets thereof, a liquid distributor 111 located in the interior of the shell 101 below the inlet pipe 104 to uniformly distribute LNG, a packed bed 105 located in the interior of the shell 101 and below the liquid distributor 111, a mixed liquid outlet pipe 106 communicating with the bottom of the shell 101, and a vortex breaker 112 located at the bottom of the shell 101 and at the inlet of the mixed liquid outlet pipe 106.

In FIG. 1, the BOG input pipe 102 is connected at its beginning to the output pipe of the BOG compressor and receives the compressed BOG output therefrom; the initial end of the LNG input pipe 103 is connected with an output pipe of the LNG low-pressure delivery pump and delivers all the LNG output by the LNG input pipe; the LNG passes through the outlet of the inlet pipe 104 to the upper surface of the liquid distributor 111 and then flows along the thin pipes in the liquid distributor 111 to the packing bed 105 where the LNG is thoroughly mixed with the BOG and condensed into a mixed liquid which is discharged through the mixed liquid outlet pipe 106. The end of mixed liquor outlet pipe 106 may be connected to an LNG pump to deliver mixed liquor to the user. The vortex breaker 112 prevents the mixed liquid from generating vortex and bubbles when entering the inlet of the mixed liquid outlet pipe 106, which may cause cavitation of the LNG pump.

The amount of cold per unit amount of LNG pumped into the housing 101 by the LNG low pressure pump is determined and therefore its ability to condense BOG is also determined, and if the amount of BOG fed into the housing 101 is excessive, it will cause an inconsistent ratio of LNG to BOG amounts, such that there will be more BOG in the housing 101 and thus a greater gas pressure, which in turn will cause the level 107 of the mixture in the housing 101 to drop below the surface of the packing bed 105, further affecting the mixing and condensing rate of LNG and BOG. Meanwhile, the mixed liquid output through the mixed liquid output pipe 106 is in a saturated state in this case, and once the mixed liquid output pipe is affected by external factors (for example, the temperature of the mixed liquid output pipe is high due to the rise of the ambient temperature), BOG is released again, which may cause "cavitation" of the LNG pump of the downstream equipment. Therefore, both the gas pressure and the liquid level 107 within the recondensor housing 101 need to be maintained within certain limits to ensure that the mixed liquor pressure in the mixed liquor takeoff pipe 106 is stable and that the LNG is in a somewhat subcooled state to prevent "cavitation" of downstream equipment, such as the LNG pump of fig. 1.

The control system shown in fig. 1 controls the level of liquid (i.e., liquid level 107) within the housing 101. As shown in fig. 1, the liquid level sensor 108, which is respectively communicated with the top and the bottom of the casing 101 through two pipes, can detect the liquid level 107 of the mixed liquid in the casing 101 in real time, and after sending the liquid level 107 to the controller 109, the controller 109 determines whether the liquid level 107 at this time is equal to a set value (the set value is slightly higher than the height of the packing bed 105), and if not, controls to increase or decrease the opening degree of the regulating valve 110 on the LNG input pipe 103 to increase or decrease the flow rate of the LNG input into the casing 101, so as to gradually restore the liquid level 107 in the casing 101 to the set value.

However, in the control system of the prior art, which only controls the liquid level 107 in the shell 101 to be kept constant, only adjusts the opening of the adjusting valve 110 on the LNG input pipe 103, and does not take into account the flow rate of BOG input into the shell and the supercooling degree of the output mixed liquid, so that the pressure at the mixed liquid outlet cannot be kept stable and the mixed liquid can meet the supercooling degree requirement, because: when the liquid level drops due to the large pressure in the housing, the control system of the prior art will increase the opening of the regulating valve 110 on the LNG input pipe 103 to increase the LNG input, thereby increasing the liquid level, but this will also cause the gas pressure in the housing to increase further after the liquid level increases, causing material loss and environmental pollution due to overpressure discharge of the gas in the housing, and at the same time, as the pressure in the housing 101 increases, the condensation amount of BOG increases, which may cause the output mixed liquid to be in a saturated state, which is a challenge for the safety of the equipment downstream of the recondenser (e.g. the LNG pump in fig. 1 may be subject to cavitation). On the contrary, when the liquid level rises due to the small pressure in the shell, the control system of the prior art reduces the opening of the regulating valve 110 to reduce the LNG feed rate and thus lower the liquid level in order to prevent the mixed liquid from flowing back to the BOG compressor due to the excessively high liquid level, but this causes the gas pressure in the shell to further reduce after the liquid level is lowered, and at the same time, the pressure of the discharged mixed liquid is further reduced due to the lowered liquid level in the shell, which adversely affects the safety of the equipment downstream of the recondenser (e.g., the LNG pump may generate cavitation).

SUMMERY OF THE UTILITY MODEL

The utility model aims to solve the technical problem that a control system of recondenser is provided, can be under the prerequisite of guaranteeing to mix liquid output pipeline and low reaches equipment safety, keep atmospheric pressure and liquid level in the recondenser shell all to stabilize in the certain limit.

The utility model provides an above-mentioned technical problem's technical scheme as follows: a recondenser control system, said recondenser comprising a shell, a Boil Off Gas (BOG) inlet communicating with a top of said shell, a Liquefied Natural Gas (LNG) inlet communicating with an upper portion of said shell and partially entering an interior of said shell, an inlet communicating with an end of said LNG inlet located within said shell, a liquid distributor located within said shell below said inlet for uniform distribution of LNG, a packed bed of packed material located within said shell below said liquid distributor, a mixed liquor outlet communicating with a bottom of said shell, a vortex breaker located at a bottom of said shell and located at an inlet of said mixed liquor outlet, a subcooled LNG transfer line for transferring subcooled LNG; the tail end of the mixed liquid output pipe and the supercooled LNG conveying pipe are converged into a total output pipe; the initial end of the BOG input pipe is connected with the output pipe of the BOG compressor and receives the BOG output by the BOG input pipe; the starting end of the LNG input pipe is connected with an output pipe of the LNG low-pressure delivery pump and receives the output LNG; at the filler bed layer, mixing and condensing the LNG input into the shell and the BOG input into the shell into a mixed liquid, and further mixing the mixed liquid with the supercooled LNG in the supercooled LNG conveying pipe in the total output pipe through the mixed liquid output pipe to obtain a final mixed liquid; the control system includes: the liquid level sensor is respectively connected with the top and the bottom of the shell through two pipelines to detect the liquid level of the mixed liquid in the shell, the natural gas NG input pipe is converged with the natural gas NG input pipe in the middle of the BOG input pipe, the NG switch valve is positioned on the NG input pipe, the second controller is connected with the liquid level sensor to receive the liquid level output by the liquid level sensor, and the first controller is respectively connected with the second controller and the BOG compressor to control and reduce the flow of BOG output by the BOG compressor when the liquid level output by the second controller is lower than the liquid level minimum value information;

the second controller is connected with the NG switch valve to control the NG switch valve to be opened under the condition that the liquid level is higher than the highest liquid level value.

The utility model has the advantages that: in the utility model, because the liquid level in the shell that level sensor detected is less than under the condition of the minimum value of liquid level, it is higher to explain the air pressure in the shell, at this moment, the second controller will send the liquid level to the first controller and be less than the minimum value of liquid level information, make its BOG compressor that control links to each other reduce the flow of output BOG, thereby reduce the flow that BOG input shell, like this, BOG in the shell will be along with the lapse of time and the LNG condensation that is input gradually becomes mixed liquid, thereby make the proportion of LNG and BOG's volume reach coordination ratio gradually, the air pressure in the shell reduces gradually, and the liquid level rises gradually; under the condition that the liquid level height is higher than the liquid level maximum value in the shell that level sensor detected, it is lower to explain atmospheric pressure in the shell, and at this moment, the second controller will direct control open continuous NG ooff valve, and like this, NG will follow in the NG input tube gets into the shell to improve the atmospheric pressure in the shell, reduce liquid level height gradually. Therefore, the utility model discloses can keep atmospheric pressure and the liquid level in the recondensor shell all to stabilize at certain extent. And the stability of the air pressure in the shell also ensures that the pressure of the mixed liquid in the mixed liquid output pipeline (comprising the mixed liquid output pipe and the total output pipe) and downstream equipment (such as an LNG pump in figure 2) is not too small, thereby ensuring the safety of the mixed liquid output pipeline and the total output pipe. In addition, the mixed liquid output pipe and the supercooled LNG conveying pipe for conveying the supercooled LNG are combined into the total output pipe, so that the final mixed liquid obtained by mixing in the total output pipe is necessarily unsaturated mixed liquid, downstream equipment can be fully prevented from being damaged by cavitation, and the safety of the downstream equipment is guaranteed.

On the basis of the technical scheme, the utility model discloses can also do as follows the improvement:

further, still include: the BOG flow meter, the first temperature sensor and the second pressure sensor are respectively connected with the BOG input pipe to respectively detect BOG flow, BOG temperature and BOG pressure in the BOG input pipe; the standard volume flow calculator is respectively connected with the BOG flowmeter, the first temperature sensor and the second pressure sensor so as to calculate and obtain BOG standard volume flow according to the BOG flow, the BOG temperature and the BOG pressure which are respectively input by the three; a first pressure sensor connected to the main output pipe to detect a final mixture pressure therein; a fourth controller connected to the first pressure sensor to receive the final mixture pressure as input thereto; the first calculator is respectively connected with the standard volume flow calculator and the fourth controller to calculate a set value of LNG input flow according to the BOG standard volume flow and the final mixed liquid pressure which are respectively input by the standard volume flow calculator and the fourth controller; an LNG flow meter connected to the LNG input pipe to detect an LNG input flow rate therein; the LNG input adjusting valve is positioned on the LNG input pipe; and the third controller is respectively connected with the first calculator, the LNG flowmeter and the LNG input regulating valve so as to compare the LNG input flow set value and the LNG input flow which are respectively input by the first calculator and the LNG flowmeter, thereby controlling and regulating the opening degree of the LNG input regulating valve.

Further, still include: a second temperature sensor connected with the total output pipe for detecting the temperature of the final mixed liquid therein; a pressure difference calculator which is respectively connected with the second temperature sensor and the fourth controller, calculates the saturation vapor pressure corresponding to the final mixed liquid temperature according to the final mixed liquid temperature input by the second temperature sensor, and subtracts the saturation vapor pressure from the final mixed liquid pressure input by the fourth controller to obtain a pressure difference; a sixth controller connected to the differential pressure calculator and the first controller, respectively, comparing a differential pressure set value with the differential pressure input from the differential pressure calculator, and transmitting a comparison result to the first controller; and the first controller controls to reduce the BOG compressor output BOG flow under the condition that the comparison result shows that the pressure difference is smaller than the pressure difference set value.

Further, the system also comprises a supercooling LNG conveying pipe regulating valve positioned on the supercooling LNG conveying pipe; and the supercooling LNG conveying pipe regulating valve is connected with the fourth controller, and the opening degree of the supercooling LNG conveying pipe regulating valve is increased under the control of the fourth controller under the condition that the fourth controller judges that the final mixed liquid pressure is lower than the final mixed liquid pressure set value.

Further, the recondenser further comprises a subcooled LNG transfer leg in parallel with the subcooled LNG transfer tube; the control system further comprises a subcooled LNG transfer branch regulating valve positioned on the subcooled LNG transfer branch; and the supercooling LNG conveying branch pipe regulating valve is connected with the fourth controller, and under the condition that the fourth controller judges that the supercooling LNG conveying pipe regulating valve reaches the maximum opening and the pressure of the final mixed liquid is lower than the pressure set value of the final mixed liquid, the opening of the supercooling LNG conveying branch pipe regulating valve is increased according to the control of the fourth controller.

Further, still include: a subcooled LNG flow meter on the subcooled LNG transfer line to detect a flow rate of subcooled LNG therein; a seventh controller which is connected to the subcooled LNG flow meter and the first controller, determines whether the subcooled LNG flow input from the subcooled LNG flow meter is less than a subcooled LNG flow set value, and transmits a determination result to the first controller; and the first controller controls to reduce the BOG compressor output BOG flow under the condition that the judgment result shows that the subcooled LNG flow is smaller than the subcooled LNG flow set value.

Further, said recondenser further comprises a gas output tube in communication with a top of said enclosure; the control system further comprises: the gas output regulating valve is positioned on the gas output pipe; a third pressure sensor connected to the gas output tube for detecting a gas pressure within the housing; and the fifth controller is respectively connected with the third pressure sensor and the gas output regulating valve and controls the opening of the gas output regulating valve under the condition that the air pressure in the shell sent by the third pressure sensor is judged to be larger than a first set value of the air pressure in the shell.

Further, said recondenser further comprises a gas output tube in communication with a top of said enclosure; the control system further comprises: and the air pressure safety valve is positioned on the gas output pipe and is opened under the condition that the air pressure in the shell is higher than a second set value of the air pressure in the shell.

Further, the tail end of the gas output pipe is connected with a BOG recovery main pipe or a flare system.

Further, the packing is Raschig rings or pall rings.

Drawings

FIG. 1 is a block diagram of a recondenser and its control system as provided by the prior art;

FIG. 2 is a block diagram of the level control portion of the recondenser and its control system provided by the present invention;

fig. 3 is a structural diagram of an LNG input flow control portion, a differential pressure control portion, a pressure control portion, and a subcooled LNG output flow control portion in the recondenser and its control system according to the present invention.

Detailed Description

The principles and features of the present invention are described below in conjunction with the following drawings, the examples given are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

Fig. 2 is a block diagram of the level control portion of the recondenser and its control system provided by the present invention. As shown in fig. 2, the recondenser of the prior art is modified by the present invention, which comprises a housing 201, a BOG inlet pipe 202 communicating with the top of the housing 201, an LNG inlet pipe 203 communicating with the upper portion of the housing 201 and partially entering the inside of the housing 201, an inlet pipe 216 communicating with the end of the LNG inlet pipe 203 located inside the housing 201, a liquid distributor 214 located inside the casing 201 and below the liquid inlet pipe 216 to uniformly distribute the LNG flowing to the upper surface thereof (the LNG is uniformly distributed by vertically penetrating thin pipes inside the liquid distributor 214 shown in fig. 2), a packed bed 205 filled with a packing and located inside the casing 201 and below the liquid distributor 214, a mixed liquid outlet pipe 213 communicating with the bottom of the casing 201, a vortex breaker 215 provided at the bottom of the casing 201 and located at an inlet of the mixed liquid outlet pipe 213, and a supercooled LNG transfer pipe 212 for transferring supercooled LNG. The mixed liquor output line 213 of the recondenser merges at its end with the subcooled LNG transfer line 212 into a total output line 206; the initial end of the BOG input pipe 202 is connected with the output pipe of the BOG compressor and receives the BOG output by the BOG input pipe; the LNG input pipe 203 is connected at its initial end to an output pipe of the LNG low-pressure feed pump, and receives LNG outputted therefrom. Thus, at the packing bed 205 inside the housing 201, LNG fed into the housing 201 and BOG fed into the housing 201 are mixed and condensed into a mixed liquid, and the mixed liquid is further mixed with the supercooled LNG in the supercooled LNG feed pipe 212 in the total output pipe 206 through the mixed liquid output pipe 213 to be a final mixed liquid.

Since the supercooled LNG transferred in the supercooled LNG transfer pipe 212 in fig. 2 is LNG in an unsaturated state, the final mixed liquid obtained after mixing is in an unsaturated state regardless of whether the supercooled LNG is mixed with a mixed liquid in a saturated state or a mixed liquid in an unsaturated state, which sufficiently ensures that the final mixed liquid is in an unsaturated state without releasing BOG even if the environment outside the recondenser is changed to some extent, such as temperature rise of ambient air, and the like, thereby preventing the final mixed liquid from corroding downstream equipment (such as an LNG pump in fig. 2).

As shown in fig. 2, the start of the subcooled LNG transfer pipe 212 and the LNG input pipe 203 can be connected to the output pipe of the LNG low-pressure transfer pump outputting LNG, i.e. the LNG transferred by the two is a part of the LNG outputted by the LNG low-pressure transfer pump, all the LNG transferred by the LNG low-pressure transfer pump is required to enter the recondenser shell 201 in the prior art, but the utility model discloses only a small part of LNG is required to enter the recondenser shell, so that under the condition of using the LNG low-pressure transfer pump with the same flow rate, the capacity of the recondenser shell 201 is much smaller than the prior art, and thus its volume and weight are also smaller than the prior art. The reduction in volume and weight means that the amount of manpower and material required to set the recondenser in a higher position than the LNG pump and to design the complex piping to accommodate the position of the LNG pump is much smaller than in the prior art, and the cost of the recondenser housing itself, which is smaller in volume and weight, is much lower, and thus the overall cost is much lower.

Of course, the beginning of the subcooled LNG transfer pipe 212 may not be the output pipe of the LNG low-pressure transfer pump as the beginning of the LNG input pipe 203, but a separate subcooled LNG output line may be provided.

The utility model provides a control system includes five major parts, is respectively: the LNG refrigeration system comprises a liquid level control part, an LNG input flow control part, a pressure difference control part, a pressure control part and a supercooled LNG output flow control part.

Fig. 2 shows a liquid level control portion of the control system provided by the present invention. As shown in fig. 2, the control system includes: a level sensor 208 connected to the top and bottom of the housing 201 through two pipes to detect a liquid level 207 of the mixed liquid in the housing 201, a Natural Gas (NG) input pipe 204 merged with the BOG input pipe 202 at a middle portion thereof (any position in the middle other than the beginning and end is referred to as a middle portion thereof), an NG on-off valve 210 provided on the NG input pipe 204, a second controller 209 connected to the level sensor 208 to receive a liquid level outputted therefrom, and a first controller 211 connected to the second controller 209 and the BOG compressor, respectively, to control to reduce a flow rate of the BOG outputted from the BOG compressor when receiving information that the liquid level 207 outputted from the second controller 209 is lower than a liquid level minimum;

the second controller 209 is connected to the NG on-off valve 210 to control the NG on-off valve 210 to be opened in the case where the liquid level 207 is higher than the liquid level maximum value.

The liquid level sensor 208 in fig. 2 may be implemented by a conventional height sensor, the first controller 211 and the second controller 209 may be implemented by various devices having control functions, such as a microprocessor, a programmable logic device (PLC), an FPGA, and the NG switching valve 210 may be an electric or pneumatic valve.

Therefore, in the utility model, because the liquid level in the shell detected by the liquid level sensor is lower than the lowest liquid level value, the air pressure in the shell is higher, at the moment, the second controller sends the information that the liquid level is lower than the lowest liquid level value to the first controller, so that the BOG compressor connected with the second controller is controlled to reduce the flow of the output BOG, thereby reducing the flow of the BOG input into the shell, therefore, the BOG in the shell can be gradually condensed into mixed liquid along with the lapse of time, thereby gradually achieving the coordination ratio of the amounts of the LNG and the BOG, gradually reducing the air pressure in the shell, and gradually increasing the liquid level; under the condition that the liquid level height is higher than the liquid level maximum value in the shell that level sensor detected, it is lower to explain atmospheric pressure in the shell, and at this moment, the second controller will direct control open continuous NG ooff valve, and like this, NG will follow in the NG input tube gets into the shell to improve the atmospheric pressure in the shell, reduce liquid level height gradually. Therefore, the utility model discloses can keep atmospheric pressure and the liquid level in the recondensor shell all to stabilize at certain extent. And the stability of the air pressure in the shell also ensures that the pressure of the mixed liquid in the mixed liquid output pipeline (comprising the mixed liquid output pipe and the total output pipe) and downstream equipment (such as an LNG pump in figure 2) is not too small, thereby ensuring the safety of the mixed liquid output pipeline and the total output pipe. In addition, the mixed liquid output pipe and the supercooled LNG conveying pipe for conveying the supercooled LNG are combined into the total output pipe, so that the final mixed liquid obtained by mixing in the total output pipe is necessarily unsaturated mixed liquid, downstream equipment can be fully prevented from being damaged by cavitation, and the safety of the downstream equipment is guaranteed.

Fig. 3 is a structural diagram of an LNG input flow control portion, a differential pressure control portion, a pressure control portion, and a subcooled LNG output flow control portion in the recondenser and its control system according to the present invention. As shown in fig. 3, the recondenser has the same structure as that of fig. 2, that is, it has a housing 301, an LNG inlet pipe 303 and a liquid inlet pipe connected to the end thereof, a liquid distributor located inside the housing 301 and below the liquid inlet pipe, a BOG inlet pipe 302, a subcooled LNG transfer pipe, a mixed liquid outlet pipe, and a total outlet pipe 305, and a vortex breaker 329 disposed at the bottom of the housing 301 and located at the inlet of the mixed liquid outlet pipe 305, wherein the LNG inlet pipe 303 and the subcooled LNG transfer pipe are connected to the outlet pipe of the LNG low-pressure transfer pump at the beginning thereof, the BOG inlet pipe 302 and the total outlet pipe 305 are connected to the BOG compressor and the LNG pump at the end thereof, and the subcooled LNG transfer pipe and the end of the mixed liquid outlet pipe are combined into the.

The utility model provides a recondensor's control system, in addition to having the liquid level control part that fig. 2 shows, still include LNG input flow control part, this part includes: a BOG flow meter 308, a first temperature sensor 324, and a second pressure sensor 325, which are connected to the BOG input pipe 302, respectively, to detect a BOG flow rate, a BOG temperature, and a BOG pressure therein, respectively; a standard volume flow calculator 309 connected to the BOG flow meter 308, the first temperature sensor 324, and the second pressure sensor 325, respectively, for calculating a BOG standard volume flow according to a BOG flow, a BOG temperature, and a BOG pressure input from the three, respectively; a first pressure sensor 307 connected to the overall output pipe 305 to detect the final mixture pressure therein; a fourth controller 313 connected to the first pressure sensor 307 to receive the final mixture pressure inputted thereto; a first calculator 310 connected to the standard volume flow calculator 309 and the fourth controller 313, respectively, for calculating an LNG input flow set value according to the BOG standard volume flow and the final mixture hydraulic pressure inputted thereto, respectively; an LNG flow meter 326 connected to the LNG input pipe 303 to detect an LNG input flow therein; an LNG import regulating valve 312 on the LNG import pipe 303; and a third controller 311 connected to the first calculator 310, the LNG flow meter 326 and the LNG input regulating valve 312, respectively, to compare the LNG input flow set value and the LNG input flow inputted from the first calculator 310 and the LNG flow meter 326, respectively, thereby controlling the opening of the LNG input regulating valve 312.

Here, the standard volume flow is a common physical concept, and refers to a volume flow per unit time at 0 ℃ and one atmosphere, and since the measured value by the BOG flowmeter 308 in the LNG receiving station is only the BOG flow value in the BOG inlet pipe 302 under the current temperature and current pressure conditions, it is necessary to measure the current BOG temperature and the current BOG pressure in the BOG inlet pipe 302 by using the first temperature sensor 324 and the second pressure sensor 325, respectively, to obtain the standard volume flow of the BOG, so as to convert the current BOG flow in the BOG inlet pipe 302 measured by the BOG flowmeter 308.

If the LNG input flow rate set value calculated by the first calculator 310 is greater than the LNG input flow rate measured by the LNG flow meter 326, the third controller 311 controls to increase the opening degree of the LNG input adjusting valve 312, thereby increasing the flow rate of LNG in the LNG input pipe 303 to gradually reach the LNG input flow rate set value. On the contrary, if the LNG input flow rate set value is smaller than the LNG input flow rate, the third controller 311 controls to decrease the opening degree of the LNG input adjusting valve 312, thereby decreasing the flow rate of the LNG in the LNG input pipe 303 to gradually reach the LNG input flow rate set value.

Here, the BOG flowmeter 308 and the LNG flowmeter 326 may be implemented by conventional flow sensors, the first temperature sensor 324 may be a conventional temperature sensor, the first pressure sensor 307 and the second pressure sensor 325 may be implemented by pressure sensors, the standard volume flow calculator 309 and the first calculator 310 may be implemented by circuits having calculation functions, the third controller 311 and the fourth controller 313 may be implemented by devices having control functions such as a PLC, a microprocessor, and the like, and the LNG input regulating valve 312 may be an electric or pneumatic regulating valve.

Utilize foretell LNG to input flow control part, the utility model discloses can guarantee that the flow in LNG and the BOG input shell 301 is harmonious, keep a harmonious proportion to guarantee the stability of mixed condensation speed, atmospheric pressure, liquid level in the recondenser, guarantee the stability of the pressure of final mixed liquid in the total output tube 305.

The differential pressure control section in the control system described above includes: a second temperature sensor 320 connected to the main output pipe 305 to detect the temperature of the final mixture therein; a differential pressure calculator 321, which is connected to the second temperature sensor 320 and the fourth controller 313, respectively, and calculates a saturation vapor pressure corresponding to the final temperature of the mixture according to the final temperature of the mixture input by the second temperature sensor 320, and subtracts the saturation vapor pressure from the final pressure of the mixture input by the fourth controller 313 to obtain a differential pressure; a sixth controller 322 connected to the differential pressure calculator 321 and the first controller 211, respectively, comparing the differential pressure set value with the differential pressure input from the differential pressure calculator 321, and transmitting the comparison result to the first controller 211; the first controller 211 may not output the control signal when the comparison result is that the differential pressure is greater than the differential pressure set value, and may control to decrease the flow rate of the BOG output from the BOG compressor when the comparison result is that the differential pressure is less than the differential pressure set value.

The first controller 211 is the first controller 211 in fig. 2.

Normally, a pressure difference of about 0.1MPa should be provided between the final mixture pressure and the saturated vapor pressure at that temperature, and thus the pressure difference setting value here may be set to 0.1 MPa. If the pressure difference between the final mixed liquid pressure and the saturated vapor pressure at the temperature is greater than the pressure difference set value, it indicates that the cold quantity of the LNG input into the shell 301 is enough to meet the cold quantity required by the condensation of the BOG in the shell 301, and the flow rate of the BOG output by the BOG compressor is not reduced, and if the pressure difference is less than the pressure difference set value, it indicates that the cold quantity of the LNG in the shell 301 is insufficient and the corresponding BOG amount is excessive, and at this time, the flow rate of the BOG compressor should be reduced to reduce the amount of the BOG output to the shell 301, so as to prevent the liquid level 306 from being reduced due to the high air pressure in the shell 301, and further, the pressure difference between the final mixed liquid pressure and the saturated vapor pressure at the temperature is too low, and the LNG pump.

The second temperature sensor 320 may be implemented by a conventional temperature sensor, the differential pressure calculator 321 may be implemented by a circuit having a calculation function, and the sixth controller 322 may be implemented by a device having a control function, such as a PLC or a microprocessor.

The utility model provides a pressure control part among the control system includes liquid pressure control part and gaseous pressure control part. Wherein,

the liquid-phase pressure control section includes: a subcooled LNG transfer line regulating valve 314 on the subcooled LNG transfer line; the sub-cooled LNG transfer pipe damper valve 314 is connected to the fourth controller 313, and increases its opening degree according to the control of the fourth controller 313 when the fourth controller 313 determines that the final mixture fluid pressure is lower than the final mixture fluid pressure set value.

Further, as shown in fig. 3, the recondenser may further include a sub-cooled LNG transfer branch connected in parallel with the sub-cooled LNG transfer pipe, and thus, the above-mentioned liquid phase pressure control part may further include: a subcooled LNG transfer leg regulating valve 315 located on the subcooled LNG transfer leg; the sub-cooled LNG transfer branch regulating valve 315 is connected to the fourth controller 313, and increases its opening degree according to the control of the fourth controller 313 when the fourth controller 313 determines that the sub-cooled LNG transfer pipe regulating valve 314 has reached the maximum opening degree and the final mixed liquid pressure is lower than the final mixed liquid pressure set value.

Here, the sub-cooled LNG carrier pipe is connected in parallel to the sub-cooled LNG carrier pipes, and each pipe has a regulating valve, wherein the sub-cooled LNG carrier pipe regulating valve 314 on the sub-cooled LNG carrier pipe may be a normally open regulating valve with a small diameter, and the sub-cooled LNG carrier pipe regulating valve 315 on the sub-cooled LNG carrier pipe may be a large regulating valve with a large diameter, and the open and close states of the sub-cooled LNG carrier pipe regulating valve 314 and the final mixture pressure are determined according to the opening degree of the sub-cooled LNG carrier pipe regulating valve 314 and the final. The utility model discloses a judge whether the pressure of final mixed liquid is less than final mixed liquid pressure setting value and adjust two governing valves on supercooling LNG conveyer pipe and the supercooling LNG transport branch pipe to guarantee that final mixed liquid pressure keeps for mixed liquid pressure setting value, this is favorable to the safety of total output tube 305 and low reaches equipment (like the LNG pump in fig. 3).

The subcooled LNG transfer line regulating valve 314 and the subcooled LNG transfer branch regulating valve 315 may be electric or pneumatic regulating valves.

As shown in fig. 3, the recondenser further includes a gas output pipe communicating with the top of the enclosure 301, and the gas phase pressure control section includes: a gas output regulating valve 318 on the gas output pipe; a third pressure sensor 316 connected to the gas output pipe to detect the gas pressure inside the casing 301; and a fifth controller 317 connected to the third pressure sensor 316 and the gas output adjustment valve 318, respectively, for controlling the gas output adjustment valve 318 to be opened when the pressure in the casing 301 from the third pressure sensor 316 is judged to be greater than the first set value of the pressure in the casing 301.

In addition, in order to cope with a further increase in the gas pressure in the enclosure 301 and prevent damage to the recondensor device due to the gas pressure being too high, the gas phase pressure control portion may further include: a gas pressure relief valve 319 located on the gas outlet conduit that opens in the event that the gas pressure within the housing 301 is above a second set value for the gas pressure within the housing 301.

The utility model discloses can make comprehensive use of foretell two kinds of gaseous phase pressure control parts, as shown in fig. 3, this recondenser can set up two gas output pipelines that connect in parallel, set up gas output governing valve 318 on one of them, another sets up atmospheric pressure relief valve 319 on the way, and set up that the first setting value of the internal gas pressure of shell 301 is less than the second setting value of the internal gas pressure of shell 301 (for example, the first setting value of the internal gas pressure of shell 301 is 0.8MPa, the second setting value of the internal gas pressure of shell 301 is 1.0MPa), then when the internal gas pressure of shell 301 reaches or surpasses the first setting value of the internal gas pressure of shell 301, gas output governing valve 318 opens, the gas output pipeline at its place switches on, like this, the gas in the shell 301 just can be exported through this gas output pipeline, in order. If the pressure in the housing 301 rises too quickly, causing the pressure to rise further to the second set point, the pressure relief valve 319 opens to open the gas output line in which it is located, so that the gas in the housing 301 is further output through the second gas output line, thereby reducing the pressure more quickly and ensuring the safety of the recondenser.

The gas output regulator valve 318 may be a conventional electrically or pneumatically actuated valve and the gas pressure relief valve 319 may be a conventional relief valve. The third pressure sensor 316 may be a conventional pressure sensor, and the fifth controller 317 may be a PLC, a microprocessor, or other devices having a control function.

As shown in FIG. 3, the ends of the gas outlet pipes described in the above two gas phase pressure control sections may be connected to a BOG recovery header or flare system to recover the BOG in time or to burn it off to prevent environmental pollution and safety problems.

The subcooled LNG output flow control part in the control system comprises: a subcooled LNG flow meter 327 on the subcooled LNG transfer line to detect the flow of subcooled LNG therein; a seventh controller 323 connected to the supercooled LNG flow meter 327 and the first controller 211, respectively, determining whether the supercooled LNG flow input from the supercooled LNG flow meter 327 is smaller than a supercooled LNG flow set value, and transmitting the determination result to the first controller 211; the first controller 211 controls to decrease the flow of the BOG output from the BOG compressor when the determination result indicates that the flow of the supercooled LNG is smaller than the supercooled LNG flow set value.

Here, the supercooled LNG flow meter 327 may be implemented by a flow sensor, and the seventh controller 323 may be implemented by a device having a control function, such as a PLC or a microprocessor.

Because the subcooling LNG conveyer pipe governing valve 314 on the subcooling LNG conveyer pipe in fig. 3 is normally open state, has the subcooling LNG to flow through all the time in this subcooling LNG conveyer pipe, therefore the utility model discloses set up subcooling LNG flowmeter 327 on this subcooling LNG conveyer pipe, utilize the flow of the subcooling LNG that its detected to judge whether the flow of subcooling LNG is low excessively (being less than subcooling LNG flow setting value), if low excessively, then probably cause the saturation degree of the final mixed liquid in total output tube 305 to improve and pressure undersize, therefore need reduce the flow of BOG compression, reduce the input of BOG.

The supercooled LNG flow meter 327 may be implemented by a flow sensor, and the seventh controller 323 may be implemented by a device having a control function, such as a PLC or a microprocessor.

In the recondenser provided by the present invention, the packing in the packing bed 304 may be raschig rings or pall rings.

It can be seen from the five parts of the control system shown in fig. 2 and 3 that the first controller 211 controls and reduces the BOG output flow of the BOG compressor when receiving the three information of the liquid level sent by the second controller 209 being lower than the lowest liquid level value, the comparison result of the pressure difference being smaller than the pressure difference set value sent by the sixth controller 322, and the judgment result of the subcooling LNG flow being smaller than the LNG flow set value sent by the seventh controller 323, because the three information are sent in real time, there is a possibility that two or even three information are sent to the first controller 211 at the same time, and each information carries the information of the target flow value required for reducing the flow of the BOG compressor to the required flow value, therefore, the first controller 211 can be a low selector, that is, the first controller 211 selects the lowest target flow from the information of all the information of the target flow required for reducing the BOG compressor received by itself And taking the value as the target flow of the BOG compressor. This ensures the safety of the recondenser, downstream equipment, and lines.

Because the utility model provides a recondensor's control system has these five major parts of liquid level control part, LNG input flow control part, pressure differential control part, pressure control part and subcooling LNG output flow control part, for the control technique that only keeps the interior liquid level of shell invariable of current, the utility model discloses improve recondensor and downstream equipment's safety in utilization greatly, protected the environment, also taken precautions against the emergence of accidents such as explosion, conflagration simultaneously.

Therefore, the utility model has the advantages of it is following:

(1) in the utility model, because the liquid level in the shell that level sensor detected is less than under the condition of the minimum value of liquid level, it is higher to explain the air pressure in the shell, at this moment, the second controller will send the liquid level to the first controller and be less than the minimum value of liquid level information, make its BOG compressor that control links to each other reduce the flow of output BOG, thereby reduce the flow that BOG input shell, like this, BOG in the shell will be along with the lapse of time and the LNG condensation that is input gradually becomes mixed liquid, thereby make the proportion of LNG and BOG's volume reach coordination ratio gradually, the air pressure in the shell reduces gradually, and the liquid level rises gradually; under the condition that the liquid level height is higher than the liquid level maximum value in the shell that level sensor detected, it is lower to explain atmospheric pressure in the shell, and at this moment, the second controller will direct control open continuous NG ooff valve, and like this, NG will follow in the NG input tube gets into the shell to improve the atmospheric pressure in the shell, reduce liquid level height gradually. Therefore, the utility model discloses can keep atmospheric pressure and the liquid level in the recondensor shell all to stabilize at certain extent. And the stability of the air pressure in the shell also ensures that the pressure of the mixed liquid in the mixed liquid output pipeline (comprising the mixed liquid output pipe and the total output pipe) and downstream equipment (such as an LNG pump in figure 2) is not too small, thereby ensuring the safety of the mixed liquid output pipeline and the total output pipe. In addition, the mixed liquid output pipe and the supercooled LNG conveying pipe for conveying the supercooled LNG are combined into the total output pipe, so that the final mixed liquid obtained by mixing in the total output pipe is necessarily unsaturated mixed liquid, downstream equipment can be fully prevented from being damaged by cavitation, and the safety of the downstream equipment is guaranteed.

(2) The utility model discloses in, the top of subcooling LNG conveyer pipe and LNG input tube all can be continuous with the output tube of the LNG low pressure delivery pump of export LNG, and the LNG that the two was carried is the partly of the LNG that LNG low pressure delivery pump exported promptly, like this, under the condition of the LNG low pressure delivery pump that uses the same power, the utility model provides a capacity of recondenser shell will be less than prior art, therefore its volume, weight also are less than prior art. And the reduction of volume and weight means that compared with the prior art that needs to consume a large amount of manpower and material resources to place the heavy recondenser shell at a position higher than the LNG pump and design a complicated pipeline to adapt to the position relationship of the two, the utility model discloses the manpower and material resources spent in setting up the position relationship of recondenser and LNG pump and designing the pipeline are much less, and the cost is also much lower.

(3) Because the utility model provides a recondensor's control system has these five major parts of liquid level control part, LNG input flow control part, pressure differential control part, pressure control part and subcooling LNG output flow control part, for the control technique that only keeps the interior liquid level of shell invariable of current, the utility model discloses improve recondensor and downstream equipment's safety in utilization greatly, protected the environment, also taken precautions against the emergence of accidents such as explosion, conflagration simultaneously.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A recondenser control system, said recondenser comprising a shell, a Boil Off Gas (BOG) inlet communicating with a top of said shell, a Liquefied Natural Gas (LNG) inlet communicating with an upper portion of said shell and partially entering an interior of said shell, an inlet communicating with an end of said LNG inlet located within said shell, a liquid distributor located within said shell below said inlet for uniform distribution of LNG, a packed bed of packed material located within said shell below said liquid distributor, a mixed liquor outlet communicating with a bottom of said shell, a vortex breaker located at a bottom of said shell and located at an inlet of said mixed liquor outlet, a subcooled LNG transfer line for transferring subcooled LNG; the tail end of the mixed liquid output pipe and the supercooled LNG conveying pipe are converged into a total output pipe; the initial end of the BOG input pipe is connected with the output pipe of the BOG compressor and receives the BOG output by the BOG input pipe; the starting end of the LNG input pipe is connected with an output pipe of the LNG low-pressure delivery pump and receives the output LNG; at the filler bed layer, mixing and condensing the LNG input into the shell and the BOG input into the shell into a mixed liquid, and further mixing the mixed liquid with the supercooled LNG in the supercooled LNG conveying pipe in the total output pipe through the mixed liquid output pipe to obtain a final mixed liquid; characterized in that the control system comprises: the liquid level sensor is respectively connected with the top and the bottom of the shell through two pipelines to detect the liquid level of the mixed liquid in the shell, the natural gas NG input pipe is converged with the natural gas NG input pipe in the middle of the BOG input pipe, the NG switch valve is positioned on the NG input pipe, the second controller is connected with the liquid level sensor to receive the liquid level output by the liquid level sensor, and the first controller is respectively connected with the second controller and the BOG compressor to control and reduce the flow of BOG output by the BOG compressor when the liquid level output by the second controller is lower than the liquid level minimum value information;

2. The control system of claim 1, further comprising: the BOG flow meter, the first temperature sensor and the second pressure sensor are respectively connected with the BOG input pipe to respectively detect BOG flow, BOG temperature and BOG pressure in the BOG input pipe; the standard volume flow calculator is respectively connected with the BOG flowmeter, the first temperature sensor and the second pressure sensor so as to calculate and obtain BOG standard volume flow according to the BOG flow, the BOG temperature and the BOG pressure which are respectively input by the three; a first pressure sensor connected to the main output pipe to detect a final mixture pressure therein; a fourth controller connected to the first pressure sensor to receive the final mixture pressure as input thereto; the first calculator is respectively connected with the standard volume flow calculator and the fourth controller to calculate a set value of LNG input flow according to the BOG standard volume flow and the final mixed liquid pressure which are respectively input by the standard volume flow calculator and the fourth controller; an LNG flow meter connected to the LNG input pipe to detect an LNG input flow rate therein; the LNG input adjusting valve is positioned on the LNG input pipe; and the third controller is respectively connected with the first calculator, the LNG flowmeter and the LNG input regulating valve so as to compare the LNG input flow set value and the LNG input flow which are respectively input by the first calculator and the LNG flowmeter, thereby controlling and regulating the opening degree of the LNG input regulating valve.

3. The control system of claim 2, further comprising: a second temperature sensor connected with the total output pipe for detecting the temperature of the final mixed liquid therein; a pressure difference calculator which is respectively connected with the second temperature sensor and the fourth controller, calculates the saturation vapor pressure corresponding to the final mixed liquid temperature according to the final mixed liquid temperature input by the second temperature sensor, and subtracts the saturation vapor pressure from the final mixed liquid pressure input by the fourth controller to obtain a pressure difference; a sixth controller connected to the differential pressure calculator and the first controller, respectively, comparing a differential pressure set value with the differential pressure input from the differential pressure calculator, and transmitting a comparison result to the first controller; and the first controller controls to reduce the BOG compressor output BOG flow under the condition that the comparison result shows that the pressure difference is smaller than the pressure difference set value.

4. The control system of claim 2, further comprising a subcooled LNG transfer line regulating valve located on the subcooled LNG transfer line; and the supercooling LNG conveying pipe regulating valve is connected with the fourth controller, and the opening degree of the supercooling LNG conveying pipe regulating valve is increased under the control of the fourth controller under the condition that the fourth controller judges that the final mixed liquid pressure is lower than the final mixed liquid pressure set value.

5. The control system of claim 3, wherein the recondenser further comprises a subcooled LNG transfer leg in parallel with the subcooled LNG transfer tube; the control system further comprises a subcooled LNG transfer branch regulating valve positioned on the subcooled LNG transfer branch; and the supercooling LNG conveying branch pipe regulating valve is connected with the fourth controller, and under the condition that the fourth controller judges that the supercooling LNG conveying pipe regulating valve reaches the maximum opening and the pressure of the final mixed liquid is lower than the pressure set value of the final mixed liquid, the opening of the supercooling LNG conveying branch pipe regulating valve is increased according to the control of the fourth controller.

6. The control system according to claim 3 or 4, characterized by further comprising: a subcooled LNG flow meter on the subcooled LNG transfer line to detect a flow rate of subcooled LNG therein; a seventh controller which is connected to the subcooled LNG flow meter and the first controller, determines whether the subcooled LNG flow input from the subcooled LNG flow meter is less than a subcooled LNG flow set value, and transmits a determination result to the first controller; and the first controller controls to reduce the BOG compressor output BOG flow under the condition that the judgment result shows that the subcooled LNG flow is smaller than the subcooled LNG flow set value.

7. The control system of claim 1, wherein the recondenser further comprises a gas output tube in communication with a top of the enclosure; the control system further comprises: the gas output regulating valve is positioned on the gas output pipe; a third pressure sensor connected to the gas output tube for detecting a gas pressure within the housing; and the fifth controller is respectively connected with the third pressure sensor and the gas output regulating valve and controls the opening of the gas output regulating valve under the condition that the air pressure in the shell sent by the third pressure sensor is judged to be larger than a first set value of the air pressure in the shell.

8. The control system of claim 1, wherein the recondenser further comprises a gas output tube in communication with a top of the enclosure; the control system further comprises: and the air pressure safety valve is positioned on the gas output pipe and is opened under the condition that the air pressure in the shell is higher than a second set value of the air pressure in the shell.

9. The control system of claim 7 or 8, wherein the end of the gas output pipe is connected to a BOG recovery header or flare system.

10. The control system of any one of claims 1-5, 7, and 8, wherein the packing is Raschig rings or pall rings.