A crude oil heating system and method using solar energy graded heat collection

Abstract

The crude oil heating system using graded solar thermal collection of the present invention comprises a solar collector, a three-phase separator, a first heat exchanger, a second-stage separator, a heat collection circulation pump, and a heat dissipation circulation pump. It is characterized in that: n energy storage tanks are provided between the solar collector and the first heat exchanger, and the n energy storage tanks are respectively primary, secondary, ..., n-stage energy storage tanks, where n ≥ 2; the volumes of the primary to n-stage energy storage tanks increase in sequence; an electrically controlled valve ki is provided on the heat collection medium inlet pipeline of the i-stage energy storage tank, and an electrically controlled valve ji is provided on the heat collection bypass pipeline of the i-stage energy storage tank. The control method of the present invention includes a heat collection control process and a heat dissipation control process. The crude oil heating system and method using graded solar thermal collection of the present invention collects heat from the energy storage tanks in order of volume from small to large, and utilizes heat energy by prioritizing the use of heat stored in the larger-volume energy storage tanks, effectively reducing energy loss.

Description

Technical Field

[0001] The present invention relates to a crude oil heating system and method, and more particularly to a crude oil heating system and method using solar energy graded heat collection. Background Art

[0002] The crude oil and associated natural gas collected from each well are transported to the combined station. This mixture, with a water content of approximately 90%, is first separated into oil, gas, and water in a three-phase separator within the combined station. This crude oil is then heated (at a temperature of 65-80°C) and then passed through a secondary separator for further separation, ultimately achieving a water content that meets the required crude oil requirements. This crude oil is then stored in crude oil storage tanks. Because the associated natural gas discharged from the three-phase separator contains sulfur-containing aromatic hydrocarbons, direct use of this associated natural gas as fuel is now prohibited due to environmental regulations. Instead, it must be transported to a natural gas processing facility for standardized treatment.

[0003] Before the water-containing crude oil enters the secondary separator, it must be heated to a temperature between 65 and 80°C to ensure effective secondary separation. The temperature to which the water-containing crude oil must be heated is related to its viscosity; higher viscosity requires higher temperatures to ensure proper operation of the secondary separator. Currently, heating the water-containing crude oil is one of the most energy-intensive processes for oil production companies. Companies generally use water-jacketed heaters to heat the water-containing crude oil prior to secondary separation, fueled by natural gas. Since direct combustion of associated natural gas in oil fields is no longer permitted, oil production companies must purchase natural gas to maintain the operation of the water-jacketed heaters, which is detrimental to energy conservation and consumption reduction.

[0004] To reduce energy consumption during the heating of water-containing crude oil, the waste heat from the secondary separator, which is at a temperature of 60-70°C, can be reused, and energy collected by a solar thermal system can be used to heat the crude oil. However, since solar energy is available during the day but absent at night, and is more abundant in summer than in winter, using a large-capacity energy storage tank to collect solar energy can easily result in the solar energy not being able to heat the bulk medium in the tank to the required temperature (above 65-80°C) in winter. This results in the solar thermal energy being unusable. Furthermore, due to the large surface area of ​​the large-capacity energy storage tank, the heat loss is also high. This heat loss throughout the day and night further lowers the temperature of the medium in the tank, rendering the existing solar heating system inoperable during winter or rainy summer months. Summary of the Invention

[0005] In order to overcome the disadvantages of the above technical problems, the present invention provides a crude oil heating system and method using solar energy graded heat collection.

[0006] The crude oil heating system using solar energy graded heat collection of the present invention comprises a solar collector, a three-phase separator, a first heat exchanger, a secondary separator, a heat collection circulation pump and a heat dissipation circulation pump. The solar collector is used to heat a heat collection medium. The liquid inlet of the three-phase separator is connected to a well drainage liquid pipeline. The sewage outlet of the three-phase separator is connected to a sewage treatment system. The first heat exchanger is used to heat the water-containing crude oil output by the three-phase separator. The secondary separator is used to further separate the water-containing crude oil heated by the first heat exchanger. The crude oil output by the secondary separator is stored in a crude oil storage tank. The system is characterized in that: n energy storage tanks are provided between the solar collector and the first heat exchanger, the energy storage tanks storing energy storage medium, and the energy storage tanks are provided with a heat collection medium inlet and outlet and a heat dissipation medium inlet and outlet. The n energy storage tanks are respectively a first-stage energy storage tank, a second-stage energy storage tank, a third-stage energy storage tank, ..., an n-stage energy storage tank, where n ≥ 2; and the volumes of the first-stage energy storage tank to the n-stage energy storage tank increase in sequence.

[0007] The heat collecting medium outlet of the solar thermal collector is connected to the inlet of the heat collecting circulation pump via a pipeline, the outlet of the heat collecting circulation pump is connected to the heat collecting medium inlet of the first-level energy storage tank via a pipeline, the heat collecting medium outlet of the n-level energy storage tank is connected to the heat collecting medium inlet of the solar thermal collector; the heat collecting medium outlet of the i-level energy storage tank is connected to the heat collecting medium inlet of the i+1-level energy storage tank via a pipeline, and the heat collecting medium inlet of each energy storage tank is connected to its heat collecting medium outlet via an external heat collecting bypass pipeline; the heat collecting medium inlet pipeline of the i-level energy storage tank is provided with an electric control valve ki, and the heat collecting bypass pipeline of the i-level energy storage tank is provided with an electric control valve ji, 1≤i≤n-1;

[0008] The first heat exchanger is provided with a heat dissipation medium inlet and outlet and a medium to be heated inlet and outlet. The heat dissipation medium outlet of the first heat exchanger is connected to the inlet of a heat dissipation circulation pump via a pipeline. The outlet of the heat dissipation circulation pump is connected to the heat dissipation medium inlet of the n-level energy storage tank via a pipeline. The heat dissipation medium outlet of the first energy storage tank is connected to the heat dissipation medium inlet of the first heat exchanger; the heat dissipation medium inlet of the i-level energy storage tank is connected to the heat dissipation medium outlet of the i+1-level energy storage tank. The heat dissipation medium inlet of each energy storage tank is connected to its heat dissipation medium outlet via an external heat dissipation bypass pipeline; the heat dissipation medium inlet pipeline of the i-level energy storage tank is provided with an electric control valve vi, and the heat dissipation bypass pipeline of the i-level energy storage tank is provided with an electric control valve w1;

[0009] The heat collection circulation pump drives the heat collection medium to circulate, and stores the heat energy converted by the solar thermal collector in the first-level energy storage tank to the n-level energy storage tank in sequence; the heat dissipation circulation pump drives the heat dissipation medium to circulate, and utilizes the energy stored in the n-level energy storage tank to the first-level energy storage tank.

[0010] In the crude oil heating system using solar energy graded heat collection of the present invention, a second heat exchanger is provided between the three-phase separator and the first heat exchanger, and an inlet and outlet for the medium to be heated and an inlet and outlet for the high-temperature medium are provided on the second heat exchanger. The outlet of the water-containing crude oil of the three-phase separator is connected to the inlet of the medium to be heated of the second heat exchanger, the outlet of the medium to be heated of the second heat exchanger is connected to the inlet of the medium to be heated of the first heat exchanger, and the outlet of the medium to be heated of the first heat exchanger is connected to the liquid inlet of the secondary separator; the sewage outlet of the secondary separator is connected to the high-temperature medium inlet of the second heat exchanger, and the sewage discharged from the high-temperature medium outlet of the second heat exchanger is connected to the sewage treatment system.

[0011] In the crude oil heating system using solar graded heat collection of the present invention, an electric heating energy storage tank is provided between the primary energy storage tank and the first heat exchanger. The electric heating energy storage tank stores energy storage medium. The electric heating energy storage tank is provided with an electric heater for heating the energy storage medium. The electric heating is connected to an AC 220V or AC 280 power supply via an electronically controlled switch. The heat dissipation medium inlet of the electric heating energy storage tank is connected to the heat dissipation medium outlet of the primary energy storage tank via a pipeline. The heat dissipation medium outlet of the electric heating energy storage tank is connected to the heat dissipation medium inlet of the first heat exchanger. The heat dissipation medium inlet of the electric heating energy storage tank is connected to its heat dissipation medium outlet via an external electric heating bypass pipeline. An electric control valve w0 is provided on the electric heating bypass pipeline. An electric control valve v0 is provided on the pipeline of the heat dissipation medium inlet of the electric heating energy storage tank.

[0012] In the crude oil heating system using solar tiered heat collection of the present invention, the first-level energy storage tank, the second-level energy storage tank, the third-level energy storage tank, ..., the n-level energy storage tank are respectively provided with temperature sensors T1, T2, T3, ..., Tn for detecting the temperature of the energy storage medium; the electric heating energy storage tank is provided with a temperature sensor T0 for detecting the temperature of the energy storage medium; the inlet pipeline of the heat collection circulation pump is provided with a temperature sensor t0; and the outlet pipeline of the medium to be heated of the first heat exchanger is provided with a temperature sensor t1.

[0013] The crude oil heating system of the present invention using solar graded heat collection includes a control cabinet and a frequency converter, wherein the control end of the frequency converter is connected to the control cabinet; the temperature sensors t0, t1, and T0-Tn are connected to the control cabinet via signal lines; the control cabinet is connected to the electric control valves k1-kn, j1-jn, w1-wn, and v1-vn via control lines; and the output end of the frequency converter is connected to a heat collection circulation pump and a heat dissipation circulation pump.

[0014] The control method of the crude oil heating system using solar stratified heat collection of the present invention is characterized by including a heat collection control process and a heat dissipation control process. The heat collection control process is implemented by the following steps:

[0015] a) Setting the temperature value: According to the upper limit of the heating temperature allowed by the energy storage medium in the energy storage tank, the upper limit of the heating temperature of the energy storage medium is given as temp1; according to the viscosity of the water-containing crude oil to be heated, the temperature value temp2 to which the first heat exchanger needs to heat it is given; executing step b);

[0016] b) Determine the illumination conditions by closing the electrically controlled valves k1 to kn on the heat collecting medium inlet pipes of all energy storage tanks and opening the electrically controlled valves j1 to jn on the heat collecting bypass pipes of all energy storage tanks. Periodically detect the heat collecting medium temperature at the outlet of the solar collector through the temperature sensor t0 for a continuous period of time. If the collected heat collecting medium temperature does not change, it indicates that the current lighting conditions are poor, day or night or cloudy and rainy, and step g) is executed; if the collected heat collecting medium temperature increases, it indicates that the lighting conditions are good, and step c) is executed;

[0017] c) Temperature signal acquisition: the control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank, the first energy storage tank to the n-level energy storage tank through the temperature sensors T0~Tn, respectively, and records them as T0~Tn; execute step d);

[0018] d) Determine the energy storage tanks to be heated. The temperature of the energy storage medium in each energy storage tank is determined in order of priority: first-level energy storage tank, second-level energy storage tank, third-level energy storage tank, ..., n-level energy storage tank. If a tank is found to have an energy storage medium temperature lower than (temp1-△T1), where △T1 = 2°C to 5°C, then execute step e). If the temperature of the energy storage medium in all tanks is not lower than (temp1-△T1), then jump to step b).

[0019] e) Heat collection of energy storage tanks: Assuming that the energy storage tank whose energy storage medium temperature is lower than (temp1-△T1) as determined in step c) is the i-level energy storage tank, then open the electrically controlled valve ki on the heat collection medium inlet pipeline of the i-level energy storage tank and close the electrically controlled valve ji on its heat collection bypass pipeline. Simultaneously, close the electrically controlled valves on the heat collection medium inlet pipelines of the remaining energy storage tanks and open the electrically controlled valves on the heat collection bypass pipelines of the remaining energy storage tanks. Circulate the heat collection medium via the heat collection circulation pump to heat the energy storage medium in the i-level energy storage tank; proceed to step f);

[0020] f) Heating temperature determination, step e) using the solar heat collecting medium to heat the energy storage medium in the i-level energy storage tank, periodically determine whether the temperature of the energy storage medium in the i-level energy storage tank has reached temp1, if not reached, continue heating until the energy storage medium in the i-level energy storage tank reaches temp1; execute step d);

[0021] g) Determine the status of the primary energy storage tank by obtaining the temperature value T1 of the energy storage medium in the primary energy storage tank through the temperature sensor T1 and determining whether the temperature value T1 of the energy storage medium in the primary energy storage tank is higher than (temp1-△T1). If it is not higher, indicating that the energy stored in the energy storage medium by the solar thermal collector is about to be exhausted, the electric control switch is turned on to heat the energy storage medium in the electrically heated energy storage tank using a 220V or 380V AC power supply until the temperature of the energy storage medium in the electrically heated energy storage tank is heated to temp1, and then execute step b). If it is higher, execute step b) directly.

[0022] The control method of the crude oil heating system using solar stratified heat collection of the present invention is implemented by the following steps:

[0023] 1) Temperature information collection: The control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank and the first-level energy storage tank to the n-level energy storage tank through temperature sensors T0 to Tn, respectively, and collects the temperature of the water-containing crude oil discharged from the outlet of the heated medium of the first heat exchanger through temperature sensor t1, recorded as t1; then execute step 2);

[0024] 2) Select the energy storage tank to be heated and determine the temperature of the energy storage medium in each tank in the order of priority: n-level energy storage tank, n-1-level energy storage tank, ..., and first-level energy storage tank. If a tank with a temperature higher than (temp1-△T1) is found, and △T1 is 2°C to 5°C, the current tank is used for heating and step 3 is executed. If the temperature of the energy storage medium in all tanks is not higher than (temp1-△T1), step 7 is executed.

[0025] 3) Energy storage tank heating: Assuming the energy storage tank whose energy storage medium temperature, as determined in step 2), is higher than (temp1-△T1), is the i-th energy storage tank, the electrically controlled valve vi on the heat dissipation medium inlet pipe of the i-th energy storage tank is opened, and the electrically controlled valve wi on its heat dissipation bypass pipe is closed. Simultaneously, the electrically controlled valves on the heat dissipation medium inlet pipes of the remaining energy storage tanks are closed, and the electrically controlled valves on the heat dissipation bypass pipes of the remaining energy storage tanks are opened. The heat dissipation medium is driven to circulate via the heat dissipation circulation pump, thereby heating the water-containing crude oil in the first heat exchanger.

[0026] 4) Determine the temperature of the water-containing crude oil, determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, collected by the temperature sensor t1, is equal to or higher than temp2. ​​If the judgment result is yes, proceed to step 5); if the judgment result is no, proceed to step 6);

[0027] 5) Determine the temperature of the heating energy storage tank. Periodically collect the temperature of the energy storage medium in the currently heating i-level energy storage tank through the temperature sensor Ti, and determine whether the temperature value in the i-level energy storage tank is greater than temp2. ​​If the judgment result is yes, execute step 4); if the judgment result is no, execute step 2);

[0028] 6) Increase the flow rate of the heat dissipation medium. The control cabinet controls the flow rate of the heat dissipation circulation pump via the inverter to increase the heat transfer of the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 4);

[0029] 7) Using the electrically heated energy storage tank for heating, close the electrically controlled valves v1 to vn on the heat dissipation medium inlet pipes of all energy storage tanks, open the electrically controlled valves w1 to wn on the heat dissipation bypass pipes of all energy storage tanks, simultaneously open the electrically controlled valve v0 on the heat dissipation medium inlet pipe of the electrically heated energy storage tank, close the electrically controlled valve w0 on the heat dissipation bypass pipe of the electrically heated energy storage tank, and turn on the electric heater in the electrically heated energy storage tank; using the stored heat in the electrically heated energy storage tank driven by the heat dissipation circulation pump to heat the water-containing crude oil flowing through the first heat exchanger; proceed to step 8);

[0030] 8) Determining the temperature of the water-containing crude oil: determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, as measured by temperature sensor t1, is equal to or higher than temp2. ​​If so, after a delay of a set time period ST, executing step 2) while heating the water-containing crude oil using the electric heating energy storage tank; if not, executing step 9);

[0031] 9). Increase the flow rate, increase the flow rate of the heat dissipation circulation pump to increase the heat transferred from the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 8).

[0032] The beneficial effects of the present invention are:

[0033] (1) The crude oil heating system and method using solar energy graded heat collection of the present invention is characterized by arranging n energy storage tanks with increasing volumes from level one to level n between the solar collector and the first heat exchanger. In the process of solar energy collection, the energy storage tanks are sequentially collected in order from small to large volumes, thereby realizing rapid heating of the small-volume energy storage tanks to a usable temperature range. Compared with the existing large-volume energy storage tank, the system and method have the advantages of fast heating and low heat loss. In the process of heating the water-containing crude oil flowing through the first heat exchanger using the heat stored in the energy storage tanks, the heat energy stored in the large-volume energy storage tanks is used first. Since the energy storage tanks with large volumes and relatively high heat loss are used first, energy loss is further reduced.

[0034] (2) By setting up an electric heating energy storage tank powered by 220V or 380V AC mains electricity, when the heat stored in the energy storage tank by the solar collector is insufficient due to daytime or nighttime or daytime with poor lighting conditions, the AC mains electricity is used to heat the energy storage medium in the electric heating energy storage tank to ensure that the water-containing crude oil flowing through the first heat exchanger is always heated to the required temperature.

[0035] (3) By setting a second heat exchanger between the three-phase separator and the first heat exchanger, the wastewater discharged from the secondary separator with a temperature range of 60~70℃ is first used to heat the water-containing crude oil (45~48℃) discharged from the three-phase separator in the second heat exchanger, and then the water-containing crude oil heated by the wastewater discharged from the secondary separator is heated in the first heat exchanger, thereby realizing the reuse of the waste heat of the high-temperature wastewater discharged from the secondary separator and further reducing the energy consumption of crude oil heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of a crude oil heating system using graded solar heat collection according to the present invention;

[0037] Figure 2 Flowchart of the heat collection control process in the present invention;

[0038] Figure 3 Flowchart of the heat dissipation control process in the present invention.

[0039] In the figure: 1 solar collector, 2 primary energy storage tank, 3 secondary energy storage tank, 4 tertiary energy storage tank, 5 n-stage energy storage tank, 6 three-phase separator, 7 first heat exchanger, 8 secondary separator, 9 heat collection circulation pump, 10 heat dissipation circulation pump, 11 control cabinet, 12 frequency converter, 13 electric heating energy storage tank, 14 electric control switch, 15 second heat exchanger; k1~kn, j1~jn, w1~wn, v1~vn are all electric control valves, t0, t1, T0~Tn are all temperature sensors. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] like Figure 1 As shown, a schematic diagram of a crude oil heating system using solar graded heat collection according to the present invention is given, which consists of a solar collector 1, a first heat exchanger 7, a second heat exchanger 15, a secondary separator 8, a heat collection circulation pump 9, a heat dissipation circulation pump 10, a control cabinet 11, an electric heating energy storage tank 13 and n energy storage tanks, wherein the n energy storage tanks are a primary energy storage tank 2, a secondary energy storage tank 3, a tertiary energy storage tank 4, ..., an n-stage energy storage tank 5, where n ≥ 2; the solar collector 1 is used to convert solar energy into internal energy stored in a heat collection medium, and store the energy in the energy storage tank under the circulation driving action of the heat collection circulation pump 9 on the heat collection medium.

[0042] The three-phase separator 6 shown is used to separate the oil, gas, and water phases of the well drainage fluid. The liquid inlet of the three-phase separator 6 is connected to the well drainage pipeline of the oil well. After the well drainage fluid is separated into three phases of oil, gas, and water in the three-phase separator 6, the discharged wastewater is connected to the sewage treatment system. The discharged water-containing crude oil is passed to the heated medium inlet of the second heat exchanger 15. The heated medium outlet of the second heat exchanger 15 is connected to the heated medium inlet of the first heat exchanger 7, so that the crude oil heated in the second heat exchanger 15 can be passed to the first heat exchanger 7 for further heating. The heated medium outlet of the first heat exchanger 7 is connected to the liquid inlet of the secondary separator 8, so that the water-containing crude oil can be passed to the secondary separator for further oil-water separation. The wastewater outlet of the secondary separator 8 is connected to the high-temperature medium inlet of the second heat exchanger 15. The crude oil discharged from the secondary separator 8 is stored in a crude oil storage tank, and the wastewater discharged from the second heat exchanger 15 is connected to the sewage treatment system.

[0043] Because the wastewater discharged from the secondary separator 8 has a relatively high temperature, between 60 and 70°C, and contains a significant amount of waste heat, it is passed through the second heat exchanger 15, heating the water-containing crude oil, which has a temperature range of 45 to 48°C, discharged from the three-phase separator 6. This heats the water-containing crude oil to a temperature range of 50 to 60°C, effectively reusing the wastewater heat from the secondary separator 8 and reducing energy consumption during the crude oil heating process. The water-containing crude oil is heated to a temperature range of 65 to 80°C in the first heat exchanger 7, allowing for oil-water separation in the secondary separator 8. The temperature of the water-containing crude oil after being heated in the first heat exchanger 7 is related to its viscosity: the higher the viscosity, the higher the temperature required.

[0044] The volumes of the first-stage energy storage tank 2, second-stage energy storage tank 3, third-stage energy storage tank 4, ..., and n-stage energy storage tank 5 shown in FIG are successively increased. Each energy storage tank contains an energy storage medium, which can be water, thermal oil, or molten salt. The storage temperature of thermal oil can reach 400-600°C, while the storage temperature of molten salt is even higher, reaching over 1000°C. Currently, large-volume energy storage tanks are commonly used to collect solar energy. This has the following disadvantages: first, it takes a long time to heat the energy storage medium in a large-volume energy storage tank to the required temperature; second, the large surface area of ​​a large-volume energy storage tank results in significant heat loss when the energy storage medium within the tank is heated to the required temperature. Therefore, the present invention proposes the principle of preferentially using small-volume energy storage tanks to store solar energy, addressing the problems of slow heating and high heat loss in existing energy storage tanks.

[0045] The pipeline labeled A is the heat collection pipeline (or pipeline), which circulates a heat-collecting medium. Each energy storage tank is provided with a heat collection medium inlet and outlet and a heat dissipation medium inlet and outlet. The heat collection medium outlet of solar thermal collector 1 is connected to the inlet of heat collection circulation pump 9. The outlet of heat collection circulation pump 9 is connected to the heat collection medium inlet of the first-stage energy storage tank 2 via a pipeline. The heat collection medium outlet of the n-stage energy storage tank 5 is connected to the heat collection medium inlet of solar thermal collector 1 via a pipeline.

[0046] The heat collecting medium inlet pipeline of the first-level energy storage tank 2 is provided with an electric control valve k1, and the heat collecting medium inlet of the first-level energy storage tank 2 and its heat collecting medium outlet are connected through an external heat collecting bypass pipeline. The heat collecting bypass pipeline of the first-level energy storage tank 2 is provided with an electric control valve j1 for controlling its on-off state, and the heat collecting medium outlet of the first-level energy storage tank 2 is connected to the heat collecting medium inlet of the second-level energy storage tank 3; the heat collecting medium inlet pipeline of the second-level energy storage tank 3 is provided with an electric control valve k2, and the heat collecting medium inlet of the second-level energy storage tank 3 and its heat collecting medium outlet are connected through an external heat collecting bypass pipeline. The heat collection bypass pipeline of the energy storage tank 3 is provided with an electric control valve j2 for controlling its on-off state, and the heat collection medium outlet of the secondary energy storage tank 3 is connected to the heat collection medium inlet of the tertiary energy storage tank 4; and so on, that is, the heat collection medium inlet pipeline of the i-level energy storage tank is provided with an electric control valve ki, and the heat collection medium inlet of the i-level energy storage tank is connected to its heat collection medium outlet via the external heat collection bypass pipeline. The heat collection bypass pipeline of the i-level energy storage tank is provided with an electric control valve ji for controlling its on-off state, and the heat collection medium outlet of the i-level energy storage tank is connected to the heat collection medium inlet of the i+1-level energy storage tank.

[0047] Driven by the heat collection circulation pump 9, the heat collection medium preferentially conducts heat to the smaller energy storage tanks, raising their temperature so that the solar heat is first stored in these smaller tanks. For example, if the solar thermal collector is currently collecting heat from the i-th energy storage tank, the electrically controlled valve ki at the heat collection medium inlet of the i-th energy storage tank is opened, and the electrically controlled valve ji on the heat collection bypass line of the i-th energy storage tank is closed. Simultaneously, the electrically controlled valves at the heat collection medium inlets of the remaining energy storage tanks are closed, and the electrically controlled valves on the heat collection bypass lines of the remaining energy storage tanks are opened. In this way, while the heat collection circulation pump 9 drives the heat collection medium to circulate, the internal energy converted by the solar thermal collector 1 can be stored in the i-th energy storage tank.

[0048] In rainy weather, or during winter months with shorter daylight hours, an electrically heated energy storage tank 13 is installed to ensure that the first heat exchanger 7 can still heat the water-containing crude oil to the set temperature. This tank contains an energy storage medium and an electric heater for heating the energy storage medium. The heat dissipation medium inlet of the electrically heated energy storage tank 13 is connected to the heat dissipation medium outlet via an external heat dissipation bypass pipeline, which is also equipped with an electrically controlled valve w0. The electric heater is connected to 220V or 380V AC mains electricity via an electrically controlled switch 14, utilizing electrical energy to heat the energy storage medium in the tank 13.

[0049] Figure 1 The pipeline labeled B in the figure is the heat dissipation pipeline, which contains a heat dissipation medium. The high-temperature medium inlet of the first heat exchanger 7 is connected to the heat dissipation medium outlet of the electrically heated energy storage tank 13 via a pipeline. The high-temperature medium outlet of the first heat exchanger 7 is connected to the inlet of the heat dissipation circulation pump 10, and the outlet of the heat dissipation circulation pump 10 is connected to the heat dissipation medium inlet of the n-stage energy storage tank via a pipeline. Driven by the heat dissipation circulation pump 10, the water-containing crude oil flowing through the first heat exchanger 7 is heated based on the principle of preferentially utilizing the energy in the larger energy storage tank.

[0050] As shown, the heat dissipation medium outlet of the first-level energy storage tank 2 is connected to the heat dissipation medium inlet of the electrically heated energy storage tank 13, the heat dissipation medium inlet of the first-level energy storage tank 2 is connected to the heat dissipation medium outlet of the second-level energy storage tank 3, the heat dissipation medium inlet of the first-level energy storage tank 2 and its heat dissipation medium outlet are connected via an external heat dissipation bypass pipeline, and the heat dissipation bypass pipeline of the first-level energy storage tank 2 is provided with an electric-controlled valve w1, and the heat dissipation medium inlet of the first-level energy storage tank 2 is provided with an electric-controlled valve v1; and so on, the heat dissipation medium outlet of the i-level energy storage tank is connected to the heat dissipation medium inlet of the i-1-level energy storage tank, the heat dissipation medium inlet of the i-level energy storage tank and its heat dissipation medium outlet are connected via an external heat dissipation bypass pipeline, and the heat dissipation bypass pipeline of the i-level energy storage tank is provided with an electric-controlled valve wi, and the heat dissipation medium inlet of the i-level energy storage tank is provided with an electric-controlled valve vi.

[0051] In this way, when the energy stored in the i-stage energy storage tank is needed to heat the water-containing crude oil flowing through the first heat exchanger 7, the electrically controlled valve vi on the heat dissipation medium inlet of the i-stage energy storage tank is opened, and the electrically controlled valve wi on the heat dissipation bypass line of the i-stage energy storage tank is closed. At the same time, the electrically controlled valves on the heat dissipation medium inlets of the remaining energy storage tanks are closed, and the electrically controlled valves on the heat dissipation bypass lines of the remaining energy storage tanks are opened. Under the circulation drive of the heat dissipation circulation pump 10, the energy stored in the i-stage energy storage tank can be used to heat the water-containing crude oil flowing through the first heat exchanger 7.

[0052] To monitor the temperature of the energy storage medium in the energy storage tanks, the primary energy storage tank 2, secondary energy storage tank 3, ..., and nth energy storage tanks are each equipped with temperature sensors T1 through Tn. A temperature sensor t0 is installed on the inlet pipeline of the heat collection circulation pump 9. The electrically heated energy storage tank 13 is equipped with a temperature sensor T0 to monitor the temperature of the energy storage medium within it. A temperature sensor t1 is installed at the outlet of the heated medium of the first heat exchanger 7 to monitor the temperature of the water-containing crude oil after heating by the first heat exchanger 7. Temperature sensors 0, t1, and T0 through Tn are connected to a control cabinet 11 via signal cables to collect temperature signals. The control cabinet 11 is connected to the electrically controlled valves k1 through kn, j1 through jn, w1 through wn, and v1 through vn via control cables to control their on / off states. The control cabinet 11 controls the heat collection circulation pump 9 and the heat dissipation circulation pump 10 via a frequency converter 12, thereby controlling their flow rates.

[0053] The control method of the crude oil heating system using solar energy graded heat collection of the present invention includes a heat collection control process and a heat dissipation control process, such as Figure 2 As shown, a flow chart of the heat collection control process in the present invention is given, which is implemented through the following steps:

[0054] a) Setting the temperature value: According to the upper limit of the heating temperature allowed by the energy storage medium in the energy storage tank, the upper limit of the heating temperature of the energy storage medium is given as temp1; according to the viscosity of the water-containing crude oil to be heated, the temperature value temp2 to which the first heat exchanger needs to heat it is given; executing step b);

[0055] b) Determine the illumination conditions by closing the electrically controlled valves k1 to kn on the heat collecting medium inlet pipes of all energy storage tanks and opening the electrically controlled valves j1 to jn on the heat collecting bypass pipes of all energy storage tanks. Periodically detect the heat collecting medium temperature at the outlet of the solar collector through the temperature sensor t0 for a continuous period of time. If the collected heat collecting medium temperature does not change, it indicates that the current lighting conditions are poor, day or night or cloudy and rainy, and step g) is executed; if the collected heat collecting medium temperature increases, it indicates that the lighting conditions are good, and step c) is executed;

[0056] c) Temperature signal acquisition: the control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank, the first energy storage tank to the n-level energy storage tank through the temperature sensors T0~Tn, respectively, and records them as T0~Tn; execute step d);

[0057] d) Determine the energy storage tanks to be heated. The temperature of the energy storage medium in each energy storage tank is determined in order of priority: first-level energy storage tank, second-level energy storage tank, third-level energy storage tank, ..., n-level energy storage tank. If a tank is found to have an energy storage medium temperature lower than (temp1-△T1), where △T1 = 2°C to 5°C, then execute step e). If the temperature of the energy storage medium in all tanks is not lower than (temp1-△T1), then jump to step b).

[0058] e) Heat collection of energy storage tanks: Assuming that the energy storage tank whose energy storage medium temperature is lower than (temp1-△T1) as determined in step c) is the i-level energy storage tank, then open the electrically controlled valve ki on the heat collection medium inlet pipeline of the i-level energy storage tank and close the electrically controlled valve ji on its heat collection bypass pipeline. Simultaneously, close the electrically controlled valves on the heat collection medium inlet pipelines of the remaining energy storage tanks and open the electrically controlled valves on the heat collection bypass pipelines of the remaining energy storage tanks. Circulate the heat collection medium via the heat collection circulation pump to heat the energy storage medium in the i-level energy storage tank; proceed to step f);

[0059] f) Heating temperature determination, step e) using the solar heat collecting medium to heat the energy storage medium in the i-level energy storage tank, periodically determine whether the temperature of the energy storage medium in the i-level energy storage tank has reached temp1, if not reached, continue heating until the energy storage medium in the i-level energy storage tank reaches temp1; execute step d);

[0060] g) Determine the status of the primary energy storage tank by obtaining the temperature value T1 of the energy storage medium in the primary energy storage tank through the temperature sensor T1 and determining whether the temperature value T1 of the energy storage medium in the primary energy storage tank is higher than (temp1-△T1). If it is not higher, indicating that the energy stored in the energy storage medium by the solar thermal collector is about to be exhausted, the electric control switch is turned on to heat the energy storage medium in the electrically heated energy storage tank using a 220V or 380V AC power supply until the temperature of the energy storage medium in the electrically heated energy storage tank is heated to temp1, and then execute step b). If it is higher, execute step b) directly.

[0061] like Figure 3 As shown, a flow chart of the heat dissipation control process in the present invention is provided, which is implemented by the following steps:

[0062] 1) Temperature information collection: The control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank and the first-level energy storage tank to the n-level energy storage tank through temperature sensors T0 to Tn, respectively, and collects the temperature of the water-containing crude oil discharged from the outlet of the heated medium of the first heat exchanger through temperature sensor t1, recorded as t1; then execute step 2);

[0063] 2) Select the energy storage tank to be heated and determine the temperature of the energy storage medium in each tank in the order of priority: n-level energy storage tank, n-1-level energy storage tank, ..., and first-level energy storage tank. If a tank with a temperature higher than (temp1-△T1) is found, and △T1 is 2°C to 5°C, the current tank is used for heating and step 3 is executed. If the temperature of the energy storage medium in all tanks is not higher than (temp1-△T1), step 7 is executed.

[0064] 3) Energy storage tank heating: Assuming the energy storage tank whose energy storage medium temperature, as determined in step 2), is higher than (temp1-△T1), is the i-th energy storage tank, the electrically controlled valve vi on the heat dissipation medium inlet pipe of the i-th energy storage tank is opened, and the electrically controlled valve wi on its heat dissipation bypass pipe is closed. Simultaneously, the electrically controlled valves on the heat dissipation medium inlet pipes of the remaining energy storage tanks are closed, and the electrically controlled valves on the heat dissipation bypass pipes of the remaining energy storage tanks are opened. The heat dissipation medium is driven to circulate via the heat dissipation circulation pump, thereby heating the water-containing crude oil in the first heat exchanger.

[0065] 4) Determine the temperature of the water-containing crude oil, determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, collected by the temperature sensor t1, is equal to or higher than temp2. ​​If the judgment result is yes, proceed to step 5); if the judgment result is no, proceed to step 6);

[0066] 5) Determine the temperature of the heating energy storage tank. Periodically collect the temperature of the energy storage medium in the currently heating i-level energy storage tank through the temperature sensor Ti, and determine whether the temperature value in the i-level energy storage tank is greater than temp2. ​​If the judgment result is yes, execute step 4); if the judgment result is no, execute step 2);

[0067] 6) Increase the flow rate of the heat dissipation medium. The control cabinet controls the flow rate of the heat dissipation circulation pump via the inverter to increase the heat transfer of the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 4);

[0068] 7) Using the electrically heated energy storage tank for heating, close the electrically controlled valves v1 to vn on the heat dissipation medium inlet pipes of all energy storage tanks, open the electrically controlled valves w1 to wn on the heat dissipation bypass pipes of all energy storage tanks, simultaneously open the electrically controlled valve v0 on the heat dissipation medium inlet pipe of the electrically heated energy storage tank, close the electrically controlled valve w0 on the heat dissipation bypass pipe of the electrically heated energy storage tank, and turn on the electric heater in the electrically heated energy storage tank; using the stored heat in the electrically heated energy storage tank driven by the heat dissipation circulation pump to heat the water-containing crude oil flowing through the first heat exchanger; proceed to step 8);

[0069] 8) Determining the temperature of the water-containing crude oil: determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, as measured by temperature sensor t1, is equal to or higher than temp2. ​​If so, after a delay of a set time period ST, executing step 2) while heating the water-containing crude oil using the electric heating energy storage tank; if not, executing step 9);

[0070] 9). Increase the flow rate, increase the flow rate of the heat dissipation circulation pump to increase the heat transferred from the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 8).

Claims

1. A control method for a crude oil heating system using solar thermal grading collection, the crude oil heating system using solar thermal grading collection comprising a solar thermal collector (1), a three-phase separator (6), a first heat exchanger (7), a secondary separator (8), a heat collection circulation pump (9) and a heat dissipation circulation pump (10), the solar thermal collector being used to heat the heat collection medium, the liquid inlet of the three-phase separator being connected to a well discharge liquid pipeline, the sewage outlet of the three-phase separator being connected to a sewage treatment system, the first heat exchanger being used to heat the water-containing crude oil outputted from the three-phase separator, the secondary separator being used to heat the water-containing crude oil outputted from the three-phase separator, and the secondary separator being used to heat the water-containing crude oil outputted from the three-phase separator. The device is used to achieve further oil-water separation of the water-containing crude oil heated by the first heat exchanger, and the crude oil output by the secondary separator is stored in the crude oil storage tank; n energy storage tanks are arranged between the solar collector (1) and the first heat exchanger (7), the energy storage tanks store energy storage medium, and the energy storage tanks are provided with a heat collection medium inlet and outlet and a heat dissipation medium inlet and outlet; the n energy storage tanks are respectively a first-level energy storage tank (2), a second-level energy storage tank (3), a third-level energy storage tank (4), ..., an n-level energy storage tank (5), n ≥ 2; the volumes of the first-level energy storage tank to the n-level energy storage tank increase in sequence; The heat collecting medium outlet of the solar thermal collector is connected to the inlet of the heat collecting circulation pump (9) via a pipeline, the outlet of the heat collecting circulation pump is connected to the heat collecting medium inlet of the first energy storage tank via a pipeline, the heat collecting medium outlet of the n-level energy storage tank is connected to the heat collecting medium inlet of the solar thermal collector; the heat collecting medium outlet of the i-level energy storage tank is connected to the heat collecting medium inlet of the i+1-level energy storage tank via a pipeline, and the heat collecting medium inlet of each energy storage tank is connected to its heat collecting medium outlet via an external heat collecting bypass pipeline; the heat collecting medium inlet pipeline of the i-level energy storage tank is provided with an electric control valve ki, and the heat collecting bypass pipeline of the i-level energy storage tank is provided with an electric control valve ji, 1≤i≤n-1; The first heat exchanger is provided with a heat dissipation medium inlet and outlet and a medium to be heated inlet and outlet. The heat dissipation medium outlet of the first heat exchanger is connected to the inlet of a heat dissipation circulation pump (10) via a pipeline. The outlet of the heat dissipation circulation pump is connected to the heat dissipation medium inlet of the n-level energy storage tank via a pipeline. The heat dissipation medium outlet of the first energy storage tank is connected to the heat dissipation medium inlet of the first heat exchanger. The heat dissipation medium inlet of the i-level energy storage tank is connected to the heat dissipation medium outlet of the i+1-level energy storage tank. The heat dissipation medium inlet of each energy storage tank is connected to its heat dissipation medium outlet via an external heat dissipation bypass pipeline. An electric control valve vi is provided on the heat dissipation medium inlet pipeline of the i-level energy storage tank, and an electric control valve w1 is provided on the heat dissipation bypass pipeline of the i-level energy storage tank. The heat collection circulation pump drives the heat collection medium to circulate, and stores the heat energy converted by the solar thermal collector in the first energy storage tank to the n-level energy storage tank in sequence; the heat dissipation circulation pump drives the heat dissipation medium to circulate, and utilizes the energy stored in the n-level energy storage tank to the first energy storage tank; An electric heating energy storage tank (13) is provided between the first-level energy storage tank (2) and the first heat exchanger (7), wherein an energy storage medium is stored in the electric heating energy storage tank, and an electric heater for heating the energy storage medium is provided in the electric heating energy storage tank, and the electric heating is connected to an AC 220V or AC 280 power supply via an electric control switch (14); the heat dissipation medium inlet of the electric heating energy storage tank is connected to the heat dissipation medium outlet of the first-level energy storage tank via a pipeline, the heat dissipation medium outlet of the electric heating energy storage tank is connected to the heat dissipation medium inlet of the first heat exchanger, the heat dissipation medium inlet of the electric heating energy storage tank is connected to its heat dissipation medium outlet via an external electric heating bypass pipeline, an electric control valve w0 is provided on the electric heating bypass pipeline, and an electric control valve v0 is provided on the heat dissipation medium inlet pipeline of the electric heating energy storage tank; The first-stage energy storage tank (2), the second-stage energy storage tank (3), the third-stage energy storage tank (4), ..., the n-stage energy storage tank (5) are respectively provided with temperature sensors T1, T2, T3, ... Tn for detecting the temperature of the energy storage medium; the electric heating energy storage tank is provided with a temperature sensor T0 for detecting the temperature of the energy storage medium; the inlet pipe of the heat collection circulation pump (9) is provided with a temperature sensor t0; and the outlet pipe of the medium to be heated of the first heat exchanger (7) is provided with a temperature sensor t1; It comprises a control cabinet (11) and a frequency converter (12), wherein the control end of the frequency converter is connected to the control cabinet; the temperature sensors t0, t1, T0-Tn are connected to the control cabinet via signal lines, the control cabinet is connected to the electric control valves k1-kn, j1-jn, w1-wn, and v1-vn via control lines, and the output end of the frequency converter is connected to the heat collection circulation pump (9) and the heat dissipation circulation pump (10); It is characterized by: The control method of the crude oil heating system using solar graded heat collection includes a heat collection control process and a heat dissipation control process. The heat collection control process is implemented by the following steps: a) Setting the temperature value: According to the upper limit of the heating temperature allowed by the energy storage medium in the energy storage tank, the upper limit of the heating temperature of the energy storage medium is given as temp1; according to the viscosity of the water-containing crude oil to be heated, the temperature value temp2 to which the first heat exchanger needs to heat it is given; executing step b); b) Determine the illumination conditions by closing the electrically controlled valves k1 to kn on the heat collecting medium inlet pipes of all energy storage tanks and opening the electrically controlled valves j1 to jn on the heat collecting bypass pipes of all energy storage tanks. Periodically detect the heat collecting medium temperature at the outlet of the solar collector through the temperature sensor t0 for a continuous period of time. If the collected heat collecting medium temperature does not change, it indicates that the current lighting conditions are poor, day or night or cloudy and rainy, and step g) is executed; if the collected heat collecting medium temperature increases, it indicates that the lighting conditions are good, and step c) is executed; c) Temperature signal acquisition: the control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank, the first energy storage tank to the n-level energy storage tank through the temperature sensors T0~Tn, respectively, and records them as T0~Tn; execute step d); d) Determine the energy storage tanks to be heated. The temperature of the energy storage medium in each energy storage tank is determined in order of priority: first-level energy storage tank, second-level energy storage tank, third-level energy storage tank, ..., n-level energy storage tank. If a tank is found to have an energy storage medium temperature lower than (temp1-△T1), where △T1 = 2°C to 5°C, then execute step e). If the temperature of the energy storage medium in all tanks is not lower than (temp1-△T1), then jump to step b). e) Heat collection of energy storage tanks: Assuming that the energy storage tank whose energy storage medium temperature is lower than (temp1-△T1) as determined in step c) is the i-level energy storage tank, then open the electrically controlled valve ki on the heat collection medium inlet pipeline of the i-level energy storage tank and close the electrically controlled valve ji on its heat collection bypass pipeline. Simultaneously, close the electrically controlled valves on the heat collection medium inlet pipelines of the remaining energy storage tanks and open the electrically controlled valves on the heat collection bypass pipelines of the remaining energy storage tanks. Circulate the heat collection medium via the heat collection circulation pump to heat the energy storage medium in the i-level energy storage tank; proceed to step f); f) Heating temperature determination, step e) using the solar heat collecting medium to heat the energy storage medium in the i-level energy storage tank, periodically determine whether the temperature of the energy storage medium in the i-level energy storage tank has reached temp1, if not reached, continue heating until the energy storage medium in the i-level energy storage tank reaches temp1; execute step d); g) Determine the status of the primary energy storage tank by obtaining the temperature value T1 of the energy storage medium in the primary energy storage tank through the temperature sensor T1 and determining whether the temperature value T1 of the energy storage medium in the primary energy storage tank is higher than (temp1-△T1). If it is not higher, indicating that the energy stored in the energy storage medium by the solar thermal collector is about to be exhausted, the electric control switch is turned on to heat the energy storage medium in the electrically heated energy storage tank using a 220V or 380V AC power supply until the temperature of the energy storage medium in the electrically heated energy storage tank is heated to temp1, and then execute step b). If it is higher, execute step b) directly.

2. The control method of the crude oil heating system using solar graded heat collection according to claim 1 is characterized in that: The thermal control process is achieved through the following steps: 1) Temperature information collection: The control cabinet collects the temperature of the energy storage medium in the electric heating energy storage tank and the first-level energy storage tank to the n-level energy storage tank through temperature sensors T0 to Tn, respectively, and collects the temperature of the water-containing crude oil discharged from the outlet of the heated medium of the first heat exchanger through temperature sensor t1, recorded as t1; then execute step 2); 2) Select the energy storage tank to be heated and determine the temperature of the energy storage medium in each tank in the order of priority: n-level energy storage tank, n-1-level energy storage tank, ..., and first-level energy storage tank. If a tank with a temperature higher than (temp1-△T1) is found, and △T1 is 2°C to 5°C, the current tank is used for heating and step 3 is executed. If the temperature of the energy storage medium in all tanks is not higher than (temp1-△T1), step 7 is executed. 3) Energy storage tank heating: Assuming the energy storage tank whose energy storage medium temperature, as determined in step 2), is higher than (temp1-△T1), is the i-th energy storage tank, the electrically controlled valve vi on the heat dissipation medium inlet pipe of the i-th energy storage tank is opened, and the electrically controlled valve wi on its heat dissipation bypass pipe is closed. Simultaneously, the electrically controlled valves on the heat dissipation medium inlet pipes of the remaining energy storage tanks are closed, and the electrically controlled valves on the heat dissipation bypass pipes of the remaining energy storage tanks are opened. The heat dissipation medium is driven to circulate via the heat dissipation circulation pump, thereby heating the water-containing crude oil in the first heat exchanger. 4) Determine the temperature of the water-containing crude oil, determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, collected by the temperature sensor t1, is equal to or higher than temp2. ​​If the judgment result is yes, proceed to step 5); if the judgment result is no, proceed to step 6); 5) Determine the temperature of the heating energy storage tank. Periodically collect the temperature of the energy storage medium in the current heating i-level energy storage tank through the temperature sensor Ti, and determine whether the temperature value in the i-level energy storage tank is greater than temp2. ​​If the judgment result is yes, execute step 4); If the judgment result is no, go to step 2); 6) Increase the flow rate of the heat dissipation medium. The control cabinet controls the flow rate of the heat dissipation circulation pump via the inverter to increase the heat transfer of the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 4); 7) Using the electrically heated energy storage tank for heating, close the electrically controlled valves v1 to vn on the heat dissipation medium inlet pipes of all energy storage tanks, open the electrically controlled valves w1 to wn on the heat dissipation bypass pipes of all energy storage tanks, simultaneously open the electrically controlled valve v0 on the heat dissipation medium inlet pipe of the electrically heated energy storage tank, close the electrically controlled valve w0 on the heat dissipation bypass pipe of the electrically heated energy storage tank, and turn on the electric heater in the electrically heated energy storage tank; using the stored heat in the electrically heated energy storage tank driven by the heat dissipation circulation pump to heat the water-containing crude oil flowing through the first heat exchanger; proceed to step 8); 8) Determining the temperature of the water-containing crude oil: determining whether the temperature value t1 of the water-containing crude oil after being heated by the first heat exchanger, as measured by temperature sensor t1, is equal to or higher than temp2. ​​If so, after a delay of a set time period ST, step 2 is executed while the water-containing crude oil is being heated by the electric heating energy storage tank. If the judgment result is no, go to step 9); 9). Increase the flow rate, increase the flow rate of the heat dissipation circulation pump to increase the heat transferred from the heat dissipation medium to the water-containing crude oil in the first heat exchanger per unit time, and execute step 8).

3. The control method of the crude oil heating system using solar graded heat collection according to claim 1, characterized in that: A second heat exchanger (15) is provided between the three-phase separator (6) and the first heat exchanger (7). The second heat exchanger is provided with an inlet and outlet for a medium to be heated and an inlet and outlet for a high-temperature medium. The outlet of the water-containing crude oil of the three-phase separator is connected to the inlet of the medium to be heated of the second heat exchanger. The outlet of the medium to be heated of the second heat exchanger is connected to the inlet of the medium to be heated of the first heat exchanger. The outlet of the medium to be heated of the first heat exchanger is connected to the liquid inlet of the secondary separator (8). The sewage outlet of the secondary separator is connected to the inlet of the high-temperature medium of the second heat exchanger. The sewage discharged from the outlet of the high-temperature medium of the second heat exchanger is connected to the sewage treatment system.

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