Ammonia tank heating unit device and control method thereof

Abstract

The present invention relates to the field of storage tank heating technology, and discloses an ammonia tank heating unit device and a control method thereof. The control method includes the following steps: S1: The controller presets a conventional heat medium target temperature T2, a liquid ammonia target temperature T0, a high liquid level, a low liquid level, and detects the liquid ammonia level height in the ammonia tank body; S2: According to the detected liquid ammonia level height in the ammonia tank body, the controller determines the heating working mode, including a high-power heating module, a low-power heating module, and a variable temperature heating module. The heat medium target temperature is adapted to different heating modules, and PID dynamic compensation is used. The present invention is based on the actual process of the liquid ammonia level drop. When the liquid level drops, the heat exchange area is reduced. Therefore, a control method for increasing the heat exchange temperature difference of ethylene glycol is innovatively proposed, and the shutdown temperature of ethylene glycol is increased. The heat exchange can be ensured throughout the process and the vaporization heat of the residual material can be met, and energy saving and consumption reduction can be achieved, which has a broad application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of storage tank heating, and in particular to an ammonia tank heating unit device and a control method thereof. Background Art

[0002] At present, when ammonia tanks are used on the market, the tanks are full of liquid ammonia. The heating pipes in the heating unit heat the ethylene glycol in the pipeline, and the water pump circulates the ethylene glycol to heat the liquid ammonia in the tank. The liquid ammonia is heated and vaporized and supplied to the end. In this process, the operation of the heating pipe is controlled by controlling the temperature of the ethylene glycol and the temperature of the liquid ammonia in the tank.

[0003] As liquid ammonia continues to vaporize, the liquid level in the tank continues to drop. When it is below the middle liquid level, the actual heated area of ​​the liquid ammonia continues to decrease, and the later vaporization rate will decrease. When it is close to the bottom of the liquid level, the heating rate is extremely slow, and the end user will face the serious defect of insufficient gas. The current solution is to extend the heating time and wait until the gas pressure in the tank rises before using it. However, this will seriously affect the continuous processing and production of the production line. Therefore, it is urgent to provide an effective control method for the ammonia tank heating unit to ensure that the ammonia tank is continuously and effectively supplied with gas throughout the process to meet the normal use of end customers. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an ammonia tank heating unit device and a control method thereof, which can ensure the heat exchange capacity throughout the whole process and meet the gasification heat of the residual material, thereby meeting the normal use of the terminal.

[0005] The technical solution of the present invention is: an ammonia tank heating unit device, comprising:

[0006] A heating unit located at the top of the ammonia tank body, a liquid ammonia temperature sensor at the bottom of the ammonia tank body, a tank body heat exchange coil arranged outside the ammonia tank body, a liquid level sensor and a controller arranged at the top of the ammonia tank body. The heating unit includes a high-power heating module, a low-power heating module and a variable temperature heating module.

[0007] Furthermore, the heating unit comprises:

[0008] The water tank heater, circulation pump, heat medium heater, heat medium temperature sensor and flow switch located on the top of the heat medium heater are connected in sequence; the high-power heating module allows the heat medium heater and the water tank heater to work simultaneously, the low-power heating module allows the heat medium heater to work alone, and the variable temperature heating module allows the heat medium heater and the water tank heater to work simultaneously after increasing the heat medium target temperature.

[0009] Furthermore, the tank heat exchange coil comprises:

[0010] A plurality of coils are welded to the lower middle part of the ammonia tank body, and the coils are filled with a circulating ethylene glycol aqueous solution medium. The plurality of coils can be arranged horizontally and in parallel along the outer wall of the ammonia tank body.

[0011] The present invention also discloses a control method for an ammonia tank heating unit device, comprising the following steps:

[0012] S1: The controller presets the conventional heat medium target temperature T 2 、Liquid ammonia target temperature T 0 , high liquid level, low liquid level, and detect the liquid ammonia level height in the ammonia tank;

[0013] S2: According to the detected liquid ammonia level in the ammonia tank, the controller determines the heating working mode;

[0014] When the detected liquid ammonia level is higher than the preset high level, the controller controls the heating unit to start the high-power heating module, and the heat medium heater and the water tank heater work at the same time until the liquid ammonia temperature in the ammonia tank reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the heat medium heater and the water tank heater stop heating, as the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank is lower than the liquid ammonia target temperature and the heat medium temperature is lower than the normal temperature heat medium target temperature T 2 When the heat medium heater and water tank heater are heated again, the cycle is repeated;

[0015] When the detected liquid ammonia level is between the preset high and low levels, the controller controls the heating unit to start the low-power heating module, and the heat medium heater works alone until the liquid ammonia temperature in the ammonia tank reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the temperature of liquid ammonia in the ammonia tank is lower than the target temperature T, the heating is stopped. As the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank is lower than the target temperature T 0 And the heat medium temperature is lower than the normal heat medium target temperature T 2 When the heat medium heater heats again, the cycle repeats;

[0016] When the detected liquid ammonia level is lower than the preset low level, the controller controls the heating unit to turn on the variable temperature heating module, and the controller sets the variable temperature heat medium target temperature T 3 , the heat medium heater and the water tank heater work simultaneously until the liquid ammonia temperature in the tank reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the target temperature T of the variable temperature heat medium 3 When the temperature of liquid ammonia in the ammonia tank is lower than the target temperature T, the heating is stopped. As the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank is lower than the target temperature T 0 And the heat medium temperature is lower than the variable temperature heat medium target temperature T 3When the controller dynamically adjusts the target temperature T of the variable temperature heat medium according to the liquid ammonia level 3 , the heat medium heater heats again and the cycle is repeated.

[0017] Furthermore, the target temperature of liquid ammonia is T 0 The target temperature of conventional heat medium is 35℃. 2 12°C higher than the liquid ammonia target temperature.

[0018] Furthermore, the high liquid level and the low liquid level are preset in step S1, including the following steps:

[0019] S11, read the liquid ammonia level: use the liquid level sensor to detect the liquid ammonia level in the ammonia tank, read the value of the liquid level sensor through the 4-20mA current analog quantity, and feed it back to the controller;

[0020] S12, calibrating the liquid level: the liquid level of the entire tank of liquid ammonia is divided into 20 levels, and a low-power heating module is used at different liquid levels to measure the time required to heat the liquid ammonia to the target liquid ammonia temperature and reach a predetermined outlet pressure value, and obtain a control curve of the liquid ammonia level and the heating time;

[0021] S13, determine the high liquid level and low liquid level values.

[0022] Furthermore, the high liquid level is selected as 70% liquid level, and the low liquid level is selected as 30% liquid level.

[0023] Furthermore, step S2 includes:

[0024] If the detected liquid ammonia level is at the preset high level, high-end heating is turned on and the conventional heat medium target temperature T 2 To set the heat medium temperature, when the liquid ammonia reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 The heating will be stopped after a delay of 5-30s. When the heat medium temperature is lower than the normal heat medium target temperature T 2 And the liquid ammonia is lower than the target temperature T 0 The heating will be turned on again after a delay of 5-30s;

[0025] If the detected liquid ammonia level is between the preset high level and low level, low-speed heating is turned on, and the conventional heat medium target temperature T 2 To set the heat medium temperature, when the liquid ammonia reaches the liquid ammonia target temperature or the heat medium reaches the conventional heat medium target temperature T 2 The heating is stopped after a delay of 5-30s. When the heat medium temperature is lower than the heat medium target temperature T 2 When the liquid ammonia temperature is lower than the target temperature, T 0 Delay 5-30s and turn on heating again;

[0026] If the current liquid level is lower than the low level, the variable temperature heating module is entered: high-end heating is turned on, and the variable temperature heat medium target temperature T 3 To set the heat medium temperature, the target temperature of the variable temperature heat medium is T 3 is the target temperature of conventional heat medium T 2 +Heat medium temperature deviation value T 1 , when the liquid ammonia reaches the target temperature T 0 Or the heat medium temperature reaches the target temperature T of the variable temperature heat medium 3 The heating is stopped after a delay of 5-30s. When the heat medium temperature is lower than the heat medium target temperature T 3 And the liquid ammonia is lower than the target temperature T 0 Heating will be turned on again after a delay of 5-30s.

[0027] Furthermore, the heat medium temperature deviation value T 1 The maximum value is 10℃, the heat medium temperature deviation value T 1 The minimum value is 0℃.

[0028] Furthermore, the target temperature of liquid ammonia is T 0 =35℃, conventional heat medium target temperature T under high power and low power heating modules 2 = Liquid ammonia target temperature T 0 +12℃;

[0029] Under the variable temperature heating module, when the current temperature of liquid ammonia is T C When the temperature is less than 30℃, the variable temperature heat medium setting temperature T under the variable temperature heating module 3 = Conventional heat medium target temperature T 2 +Heat medium temperature deviation value T 1 Maximum value, when the current temperature of liquid ammonia is T C ≥35℃, variable temperature heat medium set temperature T 3 = Conventional heat medium target temperature T 2 +Heat medium temperature deviation value T 1 Minimum value;

[0030] When the current temperature of liquid ammonia is 30℃≤T C When the temperature is less than 35℃, the heat medium temperature deviation value T 1 Dynamically adjust between 0-10.

[0031] The beneficial technical effects of the present invention are:

[0032] The present invention discloses an ammonia tank heating unit device and a control method thereof. Through different heating methods in high-power, low-power and variable temperature heating modes, based on the actual situation of liquid ammonia level drop in the actual process, when the liquid level drops, the heat exchange area is reduced. Therefore, an innovative control method for increasing the heat exchange temperature difference of ethylene glycol is proposed, and the shutdown temperature of ethylene glycol is increased. The heat exchange can be ensured throughout the process and the vaporization heat of the residual material can be met, and energy saving and consumption reduction can be achieved. The invention has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The overall structure of the ammonia tank heating unit of the present invention is shown in FIG. Figure 1 ;

[0034] Figure 2 The overall structure of the ammonia tank heating unit of the present invention is shown in FIG. Figure 2 ;

[0035] Figure 3 It is the liquid level heating time curve diagram of the present invention;

[0036] Figure 4 It is a schematic flow chart of the control method of the ammonia tank heating unit of the present invention;

[0037] In the figure,

[0038] 1. Heating unit; 2. Liquid ammonia temperature sensor; 3. Ammonia tank body; 4. Tank body heat exchange coil; 5. Liquid level sensor; 101. Circulation pump; 102. Expansion water tank; 103. Heat medium heater; 104. Heat medium temperature sensor; 105. Water tank heater; 106. Flow switch. DETAILED DESCRIPTION

[0039] In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0040] See also Figure 1-4 This specific embodiment discloses an ammonia tank heating unit device, including: a heating unit 1 located at the top of the ammonia tank body 3, a liquid ammonia temperature sensor 2 at the bottom of the ammonia tank body 3, a tank body heat exchange coil 4 arranged outside the ammonia tank body 3, a liquid level sensor 5 arranged at the top of the ammonia tank body 3, and a controller (not shown in the figure), the heating unit 1 includes a high-power heating module, a low-power heating module and a variable temperature heating module. Among them, the liquid ammonia temperature sensor 2 is used to detect the liquid ammonia temperature, and the liquid level sensor 5 is used to detect the liquid ammonia level in the tank.

[0041] The heating unit 1 comprises: a water tank heater 105 located in an expansion water tank 102, a circulation pump 101, a heat medium heater 103, a heat medium temperature sensor 104 arranged on the top of the heat medium heater 103, and a flow switch 106 which are connected in sequence; in this specific embodiment, the high-power heating module is for the heat medium heater 103 and the water tank heater 105 to work simultaneously, the low-power heating module is for the heat medium heater 103 to work alone, and the variable temperature heating module is for the heat medium heater 103 and the water tank heater 105 to work simultaneously after increasing the target temperature of the heat medium;

[0042] More specifically, the tank heat exchange coil 4 disposed outside the ammonia tank body 3 includes: a plurality of coils welded to the middle and lower part of the ammonia tank body 3, and the coils are filled with a circulating ethylene glycol aqueous solution medium. In this specific embodiment, the plurality of coils can be arranged horizontally and parallel to the outer wall of the ammonia tank body 3.

[0043] This specific embodiment also discloses a control method for an ammonia tank heating unit device, comprising the following steps:

[0044] S1: The controller presets the conventional heat medium target temperature T 2 、Liquid ammonia target temperature T 0 , high liquid level, low liquid level, and detect the liquid ammonia level height in the ammonia tank body 3;

[0045] S2: According to the detected liquid ammonia level in the ammonia tank body 3, the controller determines the heating working mode;

[0046] When the detected liquid ammonia level is higher than the preset high level, there is more liquid ammonia in the tank. The controller controls the heating unit 1 to turn on the high-power heating module, and the heat medium heater 103 and the water tank heater 105 work at the same time until the liquid ammonia temperature in the ammonia tank body 3 reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the heat medium heater 103 and the water tank heater 105 stop heating, as the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank body 3 is lower than the liquid ammonia target temperature T 0 And the heat medium temperature is lower than the conventional heat medium target temperature T 2 When the heat medium heater 103 and the water tank heater 105 heat again, the cycle is repeated;

[0047] When the detected liquid ammonia level is between the preset high level and low level, the liquid ammonia in the tank decreases, the controller controls the heating unit 1 to turn on the low-power heating module, and the heat medium heater 103 works alone until the liquid ammonia temperature of the ammonia tank body 3 reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the heating is stopped, as the liquid ammonia continues to gasify, when the liquid ammonia temperature in the ammonia tank body 3 is lower than the liquid ammonia target temperature T 0And the heat medium temperature is lower than the conventional heat medium target temperature T 2 When the heat medium heater 103 heats again, the cycle is repeated;

[0048] When the detected liquid ammonia level is lower than the preset low level, the contact area between the tank heat exchange coil and the liquid ammonia is reduced, and the controller controls the heating unit 1 to turn on the variable temperature heating module. The controller presets the variable temperature heat medium target temperature T 3 The heat medium heater 103 and the water tank heater 105 work simultaneously until the liquid ammonia temperature in the tank reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the target temperature T of the variable temperature heat medium 3 When the heating is stopped, as the liquid ammonia continues to gasify, when the liquid ammonia temperature in the ammonia tank body 3 is lower than the liquid ammonia target temperature T 0 And the heat medium temperature is lower than the variable temperature heat medium target temperature T 3 When the controller dynamically adjusts the target temperature T of the variable temperature heat medium according to the liquid ammonia level 3 , the heat medium heater 103 heats again, and the cycle is repeated.

[0049] In this specific embodiment, the target temperature of liquid ammonia is T 0 The target temperature of conventional heat medium is 35℃. 2 12°C higher than the liquid ammonia target temperature.

[0050] More specifically, the high liquid level and the low liquid level are preset in step S1, including the following steps:

[0051] S11, read the liquid ammonia level: use the liquid level sensor 5 to detect the liquid ammonia level in the ammonia tank body 3, read the value of the liquid level sensor 5 through the 4-20mA current analog quantity, and feed it back to the controller;

[0052] S12, calibrating the liquid level: the liquid level of the entire tank of liquid ammonia is divided into 20 levels, and a low-power heating module is used at different liquid levels to measure the time required to heat the liquid ammonia to the target liquid ammonia temperature and reach a predetermined outlet pressure value, and obtain a control curve of the liquid ammonia level and the heating time;

[0053] S13, determine the high liquid level and low liquid level values.

[0054] like Figure 3 As shown, the tank heat exchange coil 4 outside the ammonia tank body 3 is in the lower half. In the 100%-50% liquid level range, the heating area remains unchanged, and the heating time decreases as the liquid level decreases. In the 50%-0% range, the heating area continues to decrease, and the heating time increases as the liquid level decreases. Through the control curve, it can be obtained that the 70% liquid level is selected as the high liquid level and the 30% liquid level is selected as the low liquid level.

[0055] More specifically, in step S2, when the detected liquid ammonia level is at a preset high level, the controller controls the heating unit 1 to turn on the high-power heating module, and the heat medium heater 103 and the water tank heater 105 work simultaneously until the liquid ammonia temperature in the ammonia tank body 3 reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the heat medium heater 103 and the water tank heater 105 stop heating, as the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank body 3 is lower than the liquid ammonia target temperature T 0 , the heat medium heater 103 and the water tank heater 105 heat again, and the cycle is repeated, including:

[0056] If the detected liquid ammonia level is at the preset high level, high-end heating is turned on and the conventional heat medium target temperature T 2 To set the heat medium temperature, when the heat medium reaches the conventional heat medium target temperature T 2 Or when the liquid ammonia reaches the target temperature of liquid ammonia, the heating is stopped after a delay of 5-30 seconds. When the heat medium temperature is lower than the heat medium target temperature and the liquid ammonia is lower than the target temperature of liquid ammonia, the heating is started again after a delay of 5-30 seconds. In this specific implementation, it is preferred that when the heat medium reaches the conventional heat medium target temperature T 2 Or liquid ammonia reaches the target liquid ammonia temperature T 0 The heating is stopped after a delay of 10 seconds. When the heat medium temperature is lower than the normal heat medium target temperature T 2 And the liquid ammonia is lower than the target temperature T 0 Heating is turned on again after a delay of 10s, and the dead time setting ensures the stability of heating.

[0057] More specifically, in step S2, when the detected liquid ammonia level is between the preset high level and the low level, the liquid ammonia in the tank is reduced, and the controller controls the heating unit 1 to turn on the low-power heating module, and the heat medium heater 103 works alone until the liquid ammonia temperature of the ammonia tank body 3 reaches the liquid ammonia target temperature T 0 Or the heat medium reaches the conventional heat medium target temperature T 2 When the heating is stopped, as the liquid ammonia continues to gasify, when the liquid ammonia temperature in the ammonia tank body 3 is lower than the liquid ammonia target temperature T 0 And the heat medium is lower than the conventional heat medium target temperature T 2 When the heat medium heater 103 heats again, the cycle is repeated, including:

[0058] If the detected liquid ammonia level is between the preset high level and low level, low-speed heating is turned on, and the conventional heat medium target temperature T 2 To set the heat medium temperature, when the heat medium reaches the conventional heat medium target temperature T 2 Or liquid ammonia reaches the target liquid ammonia temperature T 0 The heating is stopped after a delay of 5-30s (preferably 10s). When the heat medium temperature is lower than the conventional heat medium target temperature T2 And the liquid ammonia is lower than the target temperature T 0 After a delay of 5-30s (preferably 10s), heating is turned on again.

[0059] More specifically, in step S2, when the detected liquid ammonia level is lower than the preset low level, the contact area between the tank heat exchange coil and the liquid ammonia is reduced, and the controller controls the heating unit 1 to turn on the variable temperature heating module. The controller presets the variable temperature heat medium target temperature T 3 The heat medium heater 103 and the water tank heater 105 work simultaneously until the temperature of the liquid ammonia in the tank reaches the target temperature of the liquid ammonia or the heat medium reaches the target temperature of the variable temperature heat medium. When the liquid ammonia temperature in the ammonia tank body 3 is lower than the target temperature of the liquid ammonia and the heat medium is lower than the target temperature of the variable temperature heat medium, the controller dynamically adjusts the target temperature of the variable temperature heat medium according to the liquid ammonia liquid level. 3 , the heat medium heater 103 heats again, and the cycle is repeated, including:

[0060] If the current liquid level is lower than the low level, the variable temperature heating module is entered: high-end heating is turned on, and the variable temperature heat medium target temperature T 3 To set the heat medium temperature, the target temperature of the variable temperature heat medium is T 3 is the target temperature of conventional heat medium T 2 +Heat medium temperature deviation value T 1 , when the heat medium reaches the heat medium target temperature T 3 Or when the liquid ammonia reaches the target temperature of liquid ammonia, the heating is stopped after a delay of 5-30s (preferably 10s). When the heat medium temperature is lower than the heat medium target temperature T 3 When the liquid ammonia temperature is lower than the target liquid ammonia temperature, the heating is turned on again after a delay of 5-30s (preferably 10s).

[0061] In this specific embodiment, in the PID control, the target temperature of liquid ammonia is used as the set value, the current temperature of liquid ammonia is used as the measured value, and the output value is the deviation value adjustment ratio. The maximum output of the deviation value adjustment ratio is 100% and the minimum is 0%. The heat medium temperature deviation value T 1 =deviation value adjustment ratio×10, that is, the maximum value of the heat medium temperature deviation is 10℃, and the minimum value of the heat medium temperature deviation is 0℃.

[0062] In this specific embodiment, in the variable temperature heating mode, the PID temperature controller is used to calculate the heat medium temperature deviation value T 1 , if the target temperature of liquid ammonia is T 0 The current temperature of liquid ammonia T C When the deviation is large, the heat medium temperature will be set to increase to a limited extent to provide faster heating efficiency. 0 The current temperature of liquid ammonia T C When the deviation is small, the original set heat medium temperature is maintained to achieve energy saving.

[0063] In this specific embodiment, the target temperature of liquid ammonia is T 0 =35℃, conventional heat medium target temperature T under high power and low power heating modules 2 = Liquid ammonia target temperature T 0 +12℃. Under the variable temperature heating module, when the current temperature of liquid ammonia is T C When the temperature is less than 30℃, the variable temperature heat medium setting temperature T under the variable temperature heating module 3 = Conventional heat medium target temperature T 2 +Heat medium temperature deviation value T 1 The maximum value is 10, when the current temperature of liquid ammonia is T C ≥35℃, variable temperature heat medium set temperature T 3 = Conventional heat medium target temperature T 2 +Heat medium temperature deviation value T 1 The minimum value is 0. When the current temperature of liquid ammonia is 30℃≤T C When the temperature is less than 35℃, the heat medium temperature deviation value T 1 Dynamically adjust between 0-10.

[0064] The basic principle of PID control is:

[0065] is a given value, is the actual output, is the output control quantity; is the difference between the given value and the output value:

[0066]

[0067] After obtaining the deviation, the control quantity is obtained by linearly combining the deviation through the output values ​​of the three links.

[0068]

[0069] In the formula, , , are the proportional coefficient, integral time and differential time of the controller respectively. = , = , = , T is the time constant of the controlled object, and τ is the pure lag time of the controlled object.

[0070] This specific embodiment uses different heating methods under high power, low power and variable temperature heating modes, and based on the actual situation of liquid ammonia level drop in the actual process, innovatively proposes a control method for increasing the heat exchange temperature difference of ethylene glycol, thereby increasing the shutdown temperature of ethylene glycol, which can effectively meet the continuous gas demand of end users and save energy and reduce consumption, and has broad application prospects.

Claims

1. A control method for an ammonia tank heating unit, characterized in that: The following steps are involved: S1: The controller presets the conventional heat medium target temperature T2, the liquid ammonia target temperature T0, the high liquid level, the low liquid level, and detects the liquid ammonia level in the ammonia tank (3), wherein the liquid ammonia target temperature T0 is 35°C; S2: The controller determines the heating working mode according to the height of the liquid ammonia level in the ammonia tank body (3); When the detected liquid ammonia level is higher than the preset high liquid level, the controller controls the heating unit (1) to start the high-power heating module, and the heat medium heater (103) and the water tank heater (105) work simultaneously until the liquid ammonia temperature in the ammonia tank body (3) reaches the liquid ammonia target temperature T0 or the heat medium reaches the conventional heat medium target temperature T2, and then the heat medium heater (103) and the water tank heater (105) stop heating. As the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank body (3) is lower than the liquid ammonia target temperature T0 and the heat medium temperature is lower than the conventional heat medium target temperature T2, the heat medium heater (103) and the water tank heater (105) heat again, and the cycle is repeated, wherein the conventional heat medium target temperature T2 is higher than the liquid ammonia target temperature T0 by 12°C. When the detected liquid ammonia level is between the preset high liquid level and the preset low liquid level, the controller controls the heating unit (1) to start the low-power heating module, and the heat medium heater (103) works alone until the liquid ammonia temperature in the ammonia tank body (3) reaches the liquid ammonia target temperature T0 or the heat medium reaches the conventional heat medium target temperature T2, and then stops heating. As the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank body (3) is lower than the liquid ammonia target temperature T0 and the heat medium temperature is lower than the conventional heat medium target temperature T2, the heat medium heater (103) heats again, and the cycle is repeated. When the detected liquid ammonia level is lower than the preset low level, the controller controls the heating unit (1) to start the variable temperature heating module, the controller sets the variable temperature heat medium target temperature T3, the heat medium heater (103) and the water tank heater (105) work simultaneously until the liquid ammonia temperature in the tank reaches the liquid ammonia target temperature T0 or the heat medium reaches the variable temperature heat medium target temperature T3 and stops heating. As the liquid ammonia continues to vaporize, when the liquid ammonia temperature in the ammonia tank body (3) is lower than the liquid ammonia target temperature T0 and the heat medium temperature is lower than the variable temperature heat medium target temperature T3, the controller dynamically adjusts the variable temperature heat medium target temperature T3 according to the liquid ammonia level, and the heat medium heater (103) heats again, repeating the cycle. Wherein, the high liquid level and the low liquid level are preset in step S1, and the following steps are also included: S11, reading the liquid ammonia level: using the liquid level sensor (5) to detect the liquid ammonia level in the ammonia tank body (3), reading the value of the liquid level sensor (5) through a 4-20mA current analog quantity, and feeding it back to the controller; S12, calibrating the liquid level: the liquid level of the entire tank of liquid ammonia is divided into 20 levels, and a low-power heating module is used at different liquid levels to measure the time required to heat the liquid ammonia to the target liquid ammonia temperature and reach a predetermined outlet pressure value, and obtain a control curve of the liquid ammonia level and the heating time; S13, determining high liquid level and low liquid level values; The ammonia tank heating unit device used in the control method of the ammonia tank heating unit device includes: A heating unit (1) located at the top of the ammonia tank body (3), a liquid ammonia temperature sensor (2) at the bottom of the ammonia tank body (3), a tank body heat exchange coil (4) arranged outside the ammonia tank body (3), a liquid level sensor (5) installed at the top of the ammonia tank body (3), and a controller; The heating unit (1) comprises a high-power heating module, a low-power heating module and a variable temperature heating module; a water tank heater (105) located in an expansion water tank (102), a circulation pump (101), a heat medium heater (103), a heat medium temperature sensor (104) and a flow switch (106) which are connected in sequence; the high-power heating module enables the heat medium heater (103) and the water tank heater (105) to work simultaneously, the low-power heating module enables the heat medium heater (103) to work alone, and the variable temperature heating module enables the heat medium heater (103) and the water tank heater (105) to work simultaneously after increasing the target temperature of the heat medium.

2. The control method of an ammonia tank heating unit device according to claim 1, characterized in that: The tank heat exchange coil (4) comprises: A plurality of coils are welded to the middle and lower part of the ammonia tank body (3), and the coils are filled with a circulating ethylene glycol aqueous solution medium. The plurality of coils can be arranged horizontally and in parallel along the outer wall of the ammonia tank body (3).

3. The control method of an ammonia tank heating unit device according to claim 2 is characterized in that Furthermore, the high liquid level is selected as 70% liquid level, and the low liquid level is selected as 30% liquid level.

4. The control method of an ammonia tank heating unit device according to claim 3 is characterized in that Step S2 includes: If the detected liquid ammonia level is at the preset high level, high-end heating is turned on, and the conventional heat medium target temperature T2 is the set heat medium temperature. When the liquid ammonia reaches the liquid ammonia target temperature T0 or the heat medium reaches the conventional heat medium target temperature T2, the heating is stopped after a delay of 5-30 seconds. When the heat medium temperature is lower than the conventional heat medium target temperature T2 and the liquid ammonia is lower than the liquid ammonia target temperature T0, the heating is turned on again after a delay of 5-30 seconds. If the detected liquid ammonia level is between the preset high and low levels, low-speed heating is turned on, and the conventional heat medium target temperature T2 is the set heat medium temperature. When the liquid ammonia reaches the liquid ammonia target temperature T0 or the heat medium reaches the conventional heat medium target temperature T2, heating is stopped after a delay of 5-30s. When the heat medium temperature is lower than the heat medium target temperature T2 and the liquid ammonia is lower than the liquid ammonia target temperature T0, heating is turned on again after a delay of 5-30s. If the current liquid level collected is lower than the low liquid level, the variable temperature heating module is entered: high-end heating is turned on, and the variable temperature heat medium target temperature T3 is the set heat medium temperature. The variable temperature heat medium target temperature T3 is the conventional heat medium target temperature T2 + heat medium temperature deviation value T1. When the liquid ammonia reaches the liquid ammonia target temperature T0 or the heat medium reaches the variable temperature heat medium target temperature T3, the heating is stopped after a delay of 5-30s. When the heat medium temperature is lower than the heat medium target temperature T3 and the liquid ammonia is lower than the liquid ammonia target temperature T0, the heating is started again after a delay of 5-30s.

5. The control method of an ammonia tank heating unit device according to claim 4, characterized in that: The maximum value of the heat medium temperature deviation value T1 is 10°C, and the minimum value of the heat medium temperature deviation value T1 is 0°C.

6. The control method of an ammonia tank heating unit device according to claim 5, characterized in that: Liquid ammonia target temperature T0 = 35°C, conventional heat medium target temperature T2 under high power and low power heating modules = liquid ammonia target temperature T0 + 12°C; Under the variable temperature heating module, when the current temperature of liquid ammonia is T C When the temperature is less than 30℃, the variable temperature heat medium setting temperature T3 under the variable temperature heating module = the conventional heat medium target temperature T2 + the maximum value of the heat medium temperature deviation value T1. C When ≥35℃, the variable temperature heat medium set temperature T3 = conventional heat medium target temperature T2 + heat medium temperature deviation value T1 minimum value; When the current temperature of liquid ammonia is 30℃≤T C When the temperature is less than 35℃, the heat medium temperature deviation value T1 is dynamically adjusted between 0-10 under the influence of the PID controller.

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