Ammonia gas supply equipment

Abstract

It enables power supply and shutdown in response to load fluctuations without placing an excessive burden on some equipment. [Solution] In an ammonia gas supply system 11 that supplies ammonia gas obtained by introducing liquid ammonia from a low-temperature storage tank 13 into a vaporizer 14 to an ammonia consuming device 12 via an ammonia gas supply line 15, a return line 21 is provided in the liquid ammonia supply line 17 connecting the low-temperature storage tank 13 and the vaporizer 14 to return the liquid ammonia to the low-temperature storage tank 13. A control valve 22 for adjusting the opening and closing of the return line 21 is provided, and a pressure control device 41 is provided in the vaporizer 14 to measure the pressure and operate the control valve 22 based on the measured pressure. The pressure control device 41 is configured to open the control valve to an opening degree corresponding to the height when the pressure is higher than a predetermined pressure set in advance.

Description

Technical Field

[0001] This invention relates to a facility for supplying ammonia gas to ammonia-consuming equipment that uses ammonia gas, such as industrial furnaces, power generation, and denitrification.

Background Art

[0002] An ammonia storage and supply base for supplying ammonia gas to a combustor of a thermal power plant is disclosed in Patent Document 1 below.

[0003] The ammonia storage and supply base has a configuration including a low-temperature storage tank for storing liquid ammonia, a vaporizer for vaporizing the liquid ammonia discharged from the low-temperature storage tank, and a combustor of a thermal power plant for burning the gaseous ammonia vaporized by the vaporizer. Among them, the low-temperature storage tank and the vaporizer are connected by a liquid ammonia supply line, and the vaporizer and the combustor are connected by a gaseous ammonia supply line.

[0004] In such a facility, even when the demand side of ammonia gas is in an unsteady operation, it is required to reduce the waste of ammonia as fuel and to ensure safe and stable operation on the fuel supply system side.

[0005] Therefore, in Patent Document 1, a recycle line is provided, and surplus gas exceeding the consumption amount of the combustor among the gaseous ammonia supplied to the combustor, that is, surplus gas generated from the vaporizer according to load fluctuations, is sent to a boil-off gas treatment facility connected to the low-temperature storage tank. The boil-off gas treatment facility is a device that liquefies the boil-off gas and returns it to the low-temperature storage tank. That is, the recycle line connects the gaseous ammonia supply line downstream of the vaporizer and the BOG discharge line of the boil-off gas treatment facility, and passes the surplus gas through the off-gas treatment facility to make effective use of the boil-off gas treatment facility.

[0006] Control valves are installed in the recycling line and the liquid ammonia supply line, and when excess gas is generated, the following actions are taken: the control valve in the liquid ammonia supply line is throttled to reduce the amount of liquid ammonia supplied to the vaporizer, and the control valve in the recycling line is opened to return the excess gaseous ammonia to the BOG treatment facility.

[0007] This configuration offers the following advantages: Even if the thermal power plant on the demand side is in a non-steady-state operation, the waste of ammonia, the fuel, can be reduced. There is no need to enlarge the pollution control equipment. The entire system can be optimized while stably satisfying the overall operating range of the thermal power plant on the demand side. Because flow control devices and pressure control devices are installed to reduce the amount of gaseous ammonia recycled, the pipe diameter of the recycling line is small, and the initial cost is minimal.

[0008] However, in the configuration of Patent Document 1, the gaseous ammonia after vaporization in the vaporizer is sent to a boil-off gas treatment facility to be recovered by being converted back into liquid ammonia. In other words, instead of simply returning it, the excess gaseous ammonia is passed through a recycling line to be regenerated into liquid ammonia.

[0009] If the volume of gas flowing through the recycling line is not large, the desired effect can be expected. However, in non-steady-state operations such as emergency shutdowns, the desired effect may not be obtained. An emergency shutdown immediately stops the supply of ammonia gas to ammonia-consuming equipment, resulting in a more rapid change than fluctuations when demand falls below the supply of gaseous ammonia. To ensure safe and stable operation, such emergencies must be anticipated.

[0010] Even if the control valve of the liquid ammonia supply line is closed and the pump that discharges the liquid ammonia is stopped instantly in the event of an emergency shutdown, the pressure inside the vaporizer will rise sharply due to the heat input in the vaporizer. This will cause a large amount of ammonia gas to flow into the recycling line, placing an excessive load on the boil-off gas treatment equipment. However, this would be the least of our worries. If the ammonia gas does not flow quickly and sufficiently into the recycling line, the safety valve in the vaporizer will activate. As mentioned earlier, it is said that the diameter of the recycling line piping can be reduced, so the possibility of the safety valve activating cannot be said to be low. Once the safety valve activates, maintenance work on the safety valve will be required, and in some cases, the plant may need to be temporarily shut down, resulting in a burdensome workload, so we want to avoid the activation of the safety valve as much as possible.

[0011] Ultimately, considering the potential for large volumes of ammonia gas to flow, the pipe diameter of the recycling line needs to be large enough. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2023-105853 [Overview of the project] [Problems that the invention aims to solve]

[0013] The main objective of this invention is to enable the supply of ammonia gas in response to changes in demand without placing an excessive burden on some equipment. [Means for solving the problem]

[0014] Therefore, this invention provides the following ammonia gas supply equipment.

[0015] In other words, in an ammonia gas supply system that supplies ammonia gas obtained by introducing liquid ammonia from a low-temperature storage tank into a vaporizer to ammonia consuming equipment via an ammonia gas supply line, a return line is provided in the liquid ammonia supply line connecting the low-temperature storage tank and the vaporizer to return the liquid ammonia to the low-temperature storage tank. The return line is equipped with a control valve for opening and closing adjustment, and the vaporizer is equipped with a pressure control device that measures the pressure and operates the control valve based on the measured pressure. The pressure control device is configured to open the control valve to an opening degree corresponding to the height when the pressure is higher than a predetermined set pressure.

[0016] In this configuration, when ammonia gas is supplied from the ammonia gas supply line under certain set conditions, non-steady-state operation, including emergency shutdowns, may occur, causing the pressure in the vaporizer leading to the ammonia-consuming equipment to exceed the predetermined pressure. When this happens, the pressure control device activates, opening the control valve in the return line according to the pressure level, and the liquid ammonia before vaporization is returned to the low-temperature storage tank. Because the liquid ammonia returning through the return line is a liquid, it moves quickly through the small-diameter piping. [Effects of the Invention]

[0017] This invention employs a configuration that returns liquid ammonia to a low-temperature storage tank before vaporization based on the pressure of the vaporizer. This allows for rapid control of the supply of liquid ammonia to the vaporizer, preventing excessive vaporization. Therefore, even in the event of an emergency shutdown, a quicker and more appropriate response can be taken. Moreover, since the liquid ammonia is returned to the low-temperature storage tank, regeneration is unnecessary, reducing energy waste compared to recycling. Furthermore, the piping constituting the return line can have a smaller required diameter compared to piping through which gas is carried, while still maintaining sufficient functionality. Thus, even in the event of non-steady-state operation, especially emergency shutdowns, appropriate control of the ammonia gas supply is possible, ensuring safety.

[0018] Furthermore, since it is configured to switch to the return line according to the pressure of the vaporizer, the operation target to be controlled can be made single, and the configuration can be simplified.

Brief Description of the Drawings

[0019] [Figure 1] Schematic configuration diagram of ammonia gas supply equipment. [Figure 2] Schematic configuration diagram of ammonia gas supply equipment. [Figure 3] Schematic configuration diagram of ammonia gas supply equipment.

Embodiments for Carrying Out the Invention

[0020] One embodiment for carrying out this invention will be described below with reference to the drawings.

[0021] As shown in FIG. 1, the ammonia gas supply equipment 11 supplies ammonia gas obtained by vaporizing liquid ammonia to an ammonia-consuming device 12 which is a supply destination. That is, it includes a low-temperature storage tank 13 for storing liquid ammonia, a vaporizer 14 for introducing and vaporizing the liquid ammonia in the low-temperature storage tank 13, and an ammonia gas supply line 15 for supplying the ammonia gas vaporized by the vaporizer 14 to the ammonia-consuming device 12. The ammonia-consuming device 12 is exemplified by a boiler of an industrial furnace.

[0022] The low-temperature storage tank 13 is a large-capacity tank that stores the liquid ammonia received from ships, lorries, etc. at a constant temperature of about -34°C and is generally composed of a common double-shell structure. An off-gas liquefier 16 is connected to the low-temperature storage tank 13 to take in the boil-off gas generated in the tank due to natural heat ingress, etc., liquefy it, and then return it to the low-temperature storage tank 13. In the off-gas liquefier 16, although not shown in the figure, it has a compressor for boosting the pressure of the boil-off gas and a condenser for liquefying the pressurized ammonia gas. In the figure, 16a is an off-gas line for sending the boil-off gas from the low-temperature storage tank 13 to the off-gas liquefier 16, and 16b is a return line for cooling the liquid ammonia liquefied in the off-gas liquefier 16 and returning it to the low-temperature storage tank 13.

[0023] A pump 18 for transferring the liquid ammonia to the vaporizer 14 is provided in the liquid ammonia supply line 17 connecting the low-temperature storage tank 13 and the vaporizer 14. Although not shown in the figure, between the pump 18 and the low-temperature storage tank 13, a minimum flow line for preventing shutdown operation and a reverse line for returning the ammonia gas slightly evaporated due to the rotational heat of the pump 18 to the low-temperature storage tank 13 are provided.

[0024] A return line 21 for returning the liquid ammonia to the low-temperature storage tank 13 is provided downstream of the pump 18 in the liquid ammonia supply line 17. When an in-tank type pump 18 is used, the return line 21 is formed from an appropriate position of the liquid ammonia supply line 17. The tip of the return line 21 is directly connected to the low-temperature storage tank 13. In this case, the return line 21 may be provided with a cooler (not shown) composed of a heat exchanger, etc. to cool the returned liquid ammonia.

[0025] The return line 21 is a flow path for reducing the amount of liquid ammonia supplied to the vaporizer 14, and is equipped with a control valve 22 that automatically controls the flow rate of liquid ammonia by adjusting the opening and closing of the flow path. Since liquid and not gas flows through the return line 21, the diameter of the piping that makes up the return line 21 can be significantly smaller than that of piping that carries gas.

[0026] The opening and closing of the control valve 22 of the return line 21 is controlled based on input from a pressure control device 41 installed in the vaporizer 14. Specifically, the pressure control device 41 is equipped with a pressure gauge (not shown) that measures the pressure of the vaporizer 14, and operates the control valve 22 based on the pressure measured by the pressure gauge. The operation is such that when the pressure is higher than a predetermined set pressure, the control valve 22 is opened to an opening degree corresponding to that height.

[0027] The vaporizer 14 is a known device that vaporizes liquid ammonia using hot water heat, steam heat, an electric heater, etc., and is equipped with a safety valve (not shown) that automatically releases pressure when the pressure inside the vaporizer 14 rises abnormally.

[0028] Therefore, the output signal from the pressure control device 41 to the control valve 22 is set to be output considering the pressure at which the safety valve of the vaporizer 14 operates. In other words, when the pressure control device 41 measures a predetermined pressure lower than the pressure at which the safety valve of the vaporizer 14 operates, or more precisely, a predetermined pressure at which the safety valve of the vaporizer 14 will not operate even in the event of an emergency stop, it outputs a valve opening control signal to the control valve 22 that opens the closed control valve 22. The opening degree of the control valve 22 at that time is set to be larger as the pressure increases, depending on conditions such as the pipe diameter of the return line 21.

[0029] The ammonia gas supply line 15 connecting the vaporizer 14 and the ammonia consuming equipment 12 is equipped with, in order from the upstream side, a control valve 51 that automatically controls the flow rate of ammonia gas by adjusting the opening and closing of the flow path, a buffer tank 52, and an emergency shut-off valve 53. The buffer tank 52 is a tank that temporarily stores ammonia gas and has the function of suppressing the effects of load fluctuations on the ammonia gas supply line 15, vaporizer 14, pump 18, etc. The size of the buffer tank 52 is set to obtain the necessary tolerance for fluctuations. The emergency shut-off valve 53 closes the ammonia gas supply line 15, that is, cuts off the supply of ammonia gas, in the event of an earthquake, gas leak, abnormal operating parameters (flow rate, temperature, pressure, etc.), pressing the emergency stop button, or other abnormal situations. When the emergency shut-off valve 53 is activated, the pump 18 of the liquid ammonia supply line 17 is controlled to stop.

[0030] A pressure control device 54 is provided in the buffer tank 52, and a flow rate control device 55 is provided between the buffer tank 52 and the emergency shut-off valve 53. The pressure control device 54 of the buffer tank 52 is equipped with a pressure gauge (not shown) for measuring the internal pressure and operates the control valve 51 based on the pressure measured by the pressure gauge. The flow rate control device 55 is equipped with a flow meter (not shown) for measuring the ammonia gas flow rate and operates the control valve 51 based on the flow rate measured by the flow meter. Through cascade control of these pressure control device 54 and flow rate control device 55, the flow rate and pressure of the ammonia gas supplied to the ammonia consumption equipment 12 are adjusted to predetermined values.

[0031] Some of the above components can also be configured as follows.

[0032] Figure 2 shows an example in which the end of the return line 21 is connected to the low-temperature storage tank 13 via the off-gas liquefaction unit 16. In other words, in the configuration of Figure 2, liquid ammonia passing through the return line 21 returns to the low-temperature storage tank 13 via the off-gas liquefaction unit 16.

[0033] Specifically, a gas-liquid separator 25 is provided on the low-temperature storage tank 13 side of the return line 21, and the liquid discharge line 25a of the gas-liquid separator 25 is connected to the return line 16b to the low-temperature storage tank 13 in the off-gas liquefaction treatment unit 16. The gas discharge line 25b of the gas-liquid separator 25 is connected to the off-gas line 16a that sends boil-off gas from the low-temperature storage tank 13 to the off-gas liquefaction treatment unit 16.

[0034] The gas-liquid separator 25 may be omitted, and the return line 21 may be connected to the return line 16b of the off-gas liquefaction treatment unit 16.

[0035] Figure 3 shows an example in which the vaporizer 14 is divided into multiple stages with different amounts of heat supplied to each stage. Specifically, the vaporizer 14 consists of a heater 45 that heats the ammonia with a fluid at or below room temperature, above the boiling point of ammonia, and an evaporator 46 that completely vaporizes the ammonia with a fluid at a higher temperature than the fluid used in the heater 45. For example, seawater can be used as the heat source for the heater 45, and steam or hot water can be used as the heat source for the evaporator 46. The pressure control device 41 is installed in the connecting line 47 that connects the heater 45 and the evaporator 46.

[0036] In Figures 2 and 3, parts identical to those described earlier are denoted by the same reference numerals, and their detailed explanations are omitted.

[0037] In the ammonia gas supply equipment 11 configured as described above, when the pump 18 is driven, the pressure control device 54 and the flow rate control device 55 control the control valve 51 to flow ammonia gas through the ammonia gas supply line 15 in a predetermined state. In other words, steady-state operation is performed by supplying ammonia gas to the ammonia consuming equipment 12.

[0038] If there are fluctuations in the ammonia consuming equipment 12 during non-steady-state operation, i.e., load fluctuations, the pressure control device 54 and flow rate control device 55 adjust the opening of the control valve 51 to maintain a steady-state operation. At this time, the buffer tank 52 suppresses pressure fluctuations and flow rate fluctuations so that the effects of load fluctuations do not extend to the ammonia gas supply line 15 or the liquid ammonia supply line 17.

[0039] If the pressure in the vaporizer 14 rises above a preset value, the pressure control device 41 of the vaporizer 14 outputs a valve opening control signal to the control valve 22 of the return line 21, causing liquid ammonia to flow into the return line 21. This reduces the amount of liquid ammonia supplied to the vaporizer 14.

[0040] In the event of an emergency shutdown, which is the largest load fluctuation, the emergency shutoff valve 53 will close upon receiving a signal, and the pump 18 of the liquid ammonia supply line 17 will stop.

[0041] Then, between the pump 18 and the emergency shut-off valve 53, the ammonia evaporates due to the heat from the vaporizer 14, and the pressure gradually increases. When the pressure rise in the vaporizer 14 reaches a predetermined value, the pressure control device 41 measures it and outputs a valve opening control signal to the control valve 22 corresponding to the pressure, opening the control valve 22. This opens the return line 21, and liquid ammonia flows into the low-temperature storage tank 13. Since liquid ammonia is already at a low temperature and the low-temperature storage tank 13 has a large capacity, there is no problem in returning it, and it does not put a burden on the off-gas liquefaction treatment unit 16.

[0042] Thus, the ammonia gas supply equipment 11 has a rational return line 21 that returns liquid ammonia to the low-temperature storage tank 13 based on the pressure of the vaporizer 14, and quickly controls the supply of liquid ammonia to the vaporizer 14 to prevent it from vaporizing more than necessary. Therefore, even if a large load fluctuation occurs due to an emergency shutdown, appropriate measures can be taken to avoid affecting the ammonia gas supply line 15 and the liquid ammonia supply line 17. Consequently, proper supply of ammonia gas is possible even during non-steady-state operation, and in particular, in the event of an emergency shutdown, the supply can be stopped appropriately, ensuring safety.

[0043] Moreover, since the system returns liquid ammonia, it reduces energy waste compared to the case where ammonia gas is returned and recycled. It also reduces power consumption by not placing an excessive burden on the off-gas liquefaction unit 16. Furthermore, since the system can adequately accommodate the use of small-diameter pipes in the return line 21, it can reduce equipment construction costs, unlike when large-diameter pipes are used to pass gases.

[0044] Furthermore, since the system operates in accordance with the pressure of the vaporizer 14, the control target can be reduced to a single control valve 22 on the return line 21, making it easier to control and simplifying the configuration.

[0045] In addition, if the return line 21 is equipped with a gas-liquid separator 25 as shown in Figure 2, even if the ammonia returning through the return line 21 becomes a gas-liquid mixture, the liquid ammonia will return directly to the low-temperature storage tank 13. Meanwhile, the ammonia gas passes through the off-gas line 16a of the off-gas liquefaction treatment unit 16, is liquefied in the off-gas liquefaction treatment unit 16, and returns as liquid ammonia to the low-temperature storage tank 13 via the return line 16b. In this way, by equipping the gas-liquid separator 25 and connecting it to the off-gas liquefaction treatment unit 16, even if the supply of liquid ammonia is stopped and the ammonia in the return line 21 becomes a gas-liquid mixture, appropriate ammonia recovery can be performed without placing an excessive burden on the off-gas liquefaction treatment unit 16.

[0046] Furthermore, as shown in Figure 3, if the vaporizer 14 is configured in two stages and the pressure in the connecting line 47 from the heater 45 to the evaporator 46 is measured to control the control valve 22, the heater 45 and evaporator 46 that make up the vaporizer 14 can be miniaturized. When the vaporizer 14 is configured as a single device, it is necessary to have heating and evaporation functions in order to vaporize low-temperature liquid ammonia, so a large device was required. In particular, when a large amount of ammonia gas is consumed, a larger vaporizer 14 was required, but it is now possible to miniaturize it. Moreover, by miniaturizing the vaporizer 14 by dividing it into a heater 45 and an evaporator 46 in this way, the amount of ammonia that vaporizes after an emergency stop is reduced, which has the advantage of allowing for a quicker response.

[0047] The above configuration is one embodiment for carrying out this invention, and this invention is not limited to the above configuration; other configurations can also be adopted.

[0048] For example, multiple vaporizers 14 can be installed in series, in which case the pressure control device 41 should be installed on the outlet line of the vaporizer 14. [Explanation of Symbols]

[0049] 11…Ammonia gas supply equipment 12…Ammonia-consuming equipment 13…Cryogenic storage tanks 14…Vaporizer 15…Ammonia gas supply line 16… Off-gas liquefaction treatment unit 16a... Off-gas line 16b...Return line 17…Liquid ammonia supply line 21…Return line 22…Control valve 25…Gas-liquid separator 25a... Liquid discharge line 25b...Gas discharge line 45...warmer 46... Evaporator 52... Buffer Tank

Claims

1. An ammonia gas supply system comprising a low-temperature storage tank for storing liquid ammonia, a vaporizer that introduces and vaporizes the liquid ammonia in the low-temperature storage tank, and an ammonia gas supply line that supplies the ammonia gas vaporized by the vaporizer to ammonia consuming equipment, A return line is provided in the liquid ammonia supply line connecting the low-temperature storage tank and the vaporizer to return the liquid ammonia to the low-temperature storage tank. The return line is provided with a control valve for adjusting opening and closing, and the vaporizer is provided with a pressure control device that measures the pressure and operates the control valve based on the measured pressure. The pressure control device is configured to open the control valve with an opening degree corresponding to the pressure when the pressure is higher than a predetermined set pressure. Ammonia gas supply equipment.

2. The vaporizer comprises a heater that heats a fluid at a temperature above the boiling point of ammonia and at or below room temperature, and an evaporator that completely vaporizes the fluid using a fluid at a higher temperature than the fluid used in the heater. The ammonia gas supply equipment according to claim 1.

3. The ammonia gas supply line is equipped with a buffer tank. The ammonia gas supply equipment according to claim 1 or claim 2.

4. An off-gas liquefaction device is connected to the aforementioned low-temperature storage tank, which liquefies and returns the boil-off gas. The aforementioned return line is connected to the return line to the low-temperature storage tank in the off-gas liquefaction treatment unit. The ammonia gas supply equipment according to claim 1 or claim 2.

5. A gas-liquid separator is provided on the low-temperature storage tank side of the return line. The liquid discharge line of the gas-liquid separator is connected to the return line. The gas discharge line of the gas-liquid separator is connected to the off-gas line that sends boil-off gas from the low-temperature storage tank to the off-gas liquefaction treatment unit. The ammonia gas supply equipment according to claim 4.

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