Ammonia vapor removal equipment

Abstract

To provide an ammonia vapor gas removal device capable of recovering ammonia vapor gas during emergency or maintenance without requiring an excessively large facility.SOLUTION: An ammonia vapor gas removal device 27 according to the present invention is provided in a facility having a liquefied ammonia vaporizer 15 or an ammonia vapor gas reliquefaction device 22, and is configured to prevent ammonia vapor gas from the liquefied ammonia vaporizer 15 or the ammonia vapor gas reliquefaction device 22 from leaking to the outside during inspection or emergency. The ammonia vapor gas removal device comprises an adsorption device 31 that adsorbs the ammonia vapor gas. The adsorption device 31 comprises: an adsorption container 37 that contains an adsorbent that adsorbs the ammonia vapor gas; a coolant 39 that is disposed in the adsorption container 37, and keeps the adsorbent cooled to a predetermined temperature or lower; and a cooling medium circulation mechanism 41 that circulates a cooling medium that cools the coolant 39 to cool and keep the coolant 39 below its melting point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ammonia evaporation gas detoxification device that is installed in a facility having a liquefied ammonia vaporizer or an ammonia evaporation gas reliquefaction device, and that prevents ammonia evaporation gas from the liquefied ammonia vaporizer or the ammonia evaporation gas reliquefaction device from leaking to the outside during inspection or in an emergency. [Background technology]

[0002] Ammonia, which does not emit CO2 when burned, is expected to be a carbon-free fuel, and is used, for example, by co-firing it with coal as boiler fuel in large-scale coal-fired power plants. Large amounts of ammonia are required for co-firing in large-scale coal-fired power plants, and for this reason ammonia is stored in huge storage tanks as liquefied ammonia.

[0003] These huge storage tanks are often low-temperature, atmospheric pressure liquefied storage tanks, and external heat input causes the constant generation of evaporated ammonia gas inside the storage tank, which, if left unattended, could cause the internal pressure of the tank to rise and damage it.For this reason, in normal times, the evaporated gas is supplied to a boiler for combustion, or re-liquefied in an ammonia evaporated gas re-liquefaction device and returned to the storage tank.

[0004] However, in the event of an accident at the power plant, an emergency shutdown, or maintenance, the above measures become impossible, and ammonia is a flammable, toxic gas that cannot be released directly into the atmosphere and requires detoxification treatment. Furthermore, synthesizing ammonia using renewable energy sources is expensive, and there is a need to use ammonia as efficiently as possible.

[0005] As such a treatment method, for example, Patent Document 1 proposes detoxifying ammonia by burning it. Furthermore, Patent Document 2 proposes dissolving ammonia in water or an aqueous solution and releasing it by stripping. Furthermore, Patent Document 3 proposes recovering evaporated gas (also referred to as BOG: Boil Off Gas) from a storage tank for liquefied fuel using an adsorption tower packed with an adsorbent. Furthermore, Patent Document 4 proposes recovering ammonia gas while cooling the adsorbent by circulating a heat medium. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 51-53636 [Patent Document 2] Japanese Patent Application Publication No. 54-51251 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-308844 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-317246 Summary of the Invention [Problem to be solved by the invention]

[0007] In a system that detoxifies ammonia by burning it, such as that disclosed in Patent Document 1, the ammonia cannot be reused. Furthermore, because ammonia burns slowly, petroleum gas or other fuels are added to aid combustion, but this generates CO2 and NOx, which have a negative impact on the environment.

[0008] Furthermore, the method of dissolving ammonia in water or an aqueous solution as in Patent Document 2 is the simplest abatement facility, but in cases where a large amount of evaporated gas is generated, such as in large-scale coal-fired power plants, the pressure of the ammonia evaporated gas is low, at almost atmospheric pressure, making it difficult to inject the ammonia into water to a depth sufficient for sufficient dissolution. Even if it were possible, a large water tank would be required, which would increase the installation area. Furthermore, the large amount of ammonia water produced is basically discarded, which increases costs, and there are problems in that regeneration in a stripping device requires high equipment and power costs.

[0009] Furthermore, when recovery is performed using an adsorption tower packed with an adsorbent as in Patent Document 3, the adsorption capacity of the adsorbent decreases exponentially as the temperature of the adsorbent increases. Therefore, when a large amount of 100% ammonia gas is adsorbed, the temperature rises due to the heat of adsorption, which poses a problem of a significant decrease in the adsorption capacity.

[0010] In this regard, Patent Document 4 recovers ammonia gas while cooling the adsorbent by circulating a heat medium, but requires a large heat exchanger capable of exchanging the same amount of heat as the heat of adsorption per unit time and a large circulation flow rate. This is an effective method for small-scale applications requiring continuous treatment of exhaust gases from the semiconductor industry, etc., but is difficult to apply to evaporated gases generated in large facilities, as the adsorption tower and circulation equipment become large.

[0011] The present invention has been made to solve such problems, and aims to provide an ammonia evaporated gas detoxification device that can recover ammonia evaporated gas in emergencies or during maintenance without requiring excessively large equipment. [Means for solving the problem]

[0012] (1) The ammonia evaporation gas detoxification device according to the present invention is installed in a facility having a liquefied ammonia vaporizer or an ammonia evaporation gas reliquefaction device, and is intended to prevent ammonia evaporation gas from the liquefied ammonia vaporizer or the ammonia evaporation gas reliquefaction device from leaking to the outside during inspection or in an emergency, an adsorption device that adsorbs the ammonia evaporated gas, The adsorption device is characterized by comprising an adsorption vessel containing an adsorbent that adsorbs the ammonia evaporated gas, a cooling agent disposed within the adsorption vessel for maintaining the adsorbent cooled to a predetermined temperature or below, and a cooling medium circulation mechanism for circulating a cooling medium that cools the cooling agent in order to cool and maintain the cooling agent below its melting point.

[0013] (2) In addition, in the above (1), the melting temperature of the ice pack is in the range of -30°C to 30°C.

[0014] (3) In the above (1) or (2), the cooling medium circulation mechanism circulates ammonia evaporated gas or liquefied ammonia.

[0015] (4) Furthermore, in the device according to any one of (1) to (3) above, it is characterized in that it has a decompression means for reducing the pressure inside the adsorption vessel. [Effects of the Invention]

[0016] The ammonia evaporative gas detoxification apparatus of the present invention comprises an adsorption device that adsorbs ammonia evaporative gas, and the adsorption device comprises an adsorption vessel that contains an adsorbent that adsorbs the ammonia evaporative gas, a cold pack that is disposed within the adsorption vessel and that keeps the adsorbent cooled to a predetermined temperature or below, and a cooling medium circulation mechanism that circulates a cooling medium that cools the cold pack to keep the cold pack below its melting point.As a result, it is possible to provide an ammonia evaporative gas detoxification apparatus that requires a small amount of adsorbent and a small adsorption tower size, and also requires a small cooling medium circulation mechanism. This effect is due to the heat capacity (heat of fusion) of the ice pack, which suppresses the temperature rise caused by heat generation during adsorption by the adsorbent, and allows the adsorbent to be kept at a low temperature at which its high adsorption performance can be maintained. Furthermore, the ammonia evaporated gas can be recovered using an adsorbent and released to a recycling facility after desorption, so no ammonia is released to the outside and 100% recycling is possible. Furthermore, unlike a water tank, the adsorption vessel can be placed upright, which allows for a significantly smaller installation space compared to a water absorption system. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of an ammonia evaporative gas detoxification device when applied to an ammonia storage facility. [Figure 2] 1 is a graph illustrating general characteristics of an adsorbent. [Figure 3]3 is a graph showing the measured values ​​of the NH3 adsorption amount and the ultimate temperature for each pre-cooling temperature of the adsorbent having the characteristics shown in FIG. 2. [Figure 4] FIG. 2 is an explanatory diagram illustrating the state inside the adsorption vessel during adsorption and desorption of the ammonia evaporated gas detoxification device. [Figure 5] 4A and 4B are diagrams showing the open and closed states of the first on-off valve, the second on-off valve, the first safety valve, and the second safety valve during adsorption and desorption. DETAILED DESCRIPTION OF THE INVENTION

[0018] The ammonia vapor gas detoxification device according to this embodiment will be described by taking as an example a case where it is applied to an ammonia storage facility when ammonia is used for co-firing in a coal-fired boiler of a thermal power plant.

[0019] FIG. 1 is a diagram showing the equipment configuration of an ammonia storage facility 1. The ammonia storage facility 1 includes a storage tank 3 for storing liquefied ammonia 2, a discharge line 5 for discharging the liquefied ammonia 2 from the storage tank 3 toward a coal-fired boiler 4, a re-liquefaction line 7 for re-liquefying ammonia evaporated gas (sometimes referred to as BOG) generated in the storage tank 3 and returning the gas to the storage tank 3, an ammonia evaporated gas discharge line 9 for supplying the ammonia evaporated gas generated in the storage tank 3 to the discharge line, and an abatement line 11 for adsorbing and detoxifying the ammonia evaporated gas generated in the storage tank 3. In this example, an ammonia gas recovery line 12 is provided which connects the downstream side of the discharge line 5 with the abatement line 11.

[0020] The discharge line 5 is provided with a transfer pump 13, a vaporizer 15, and a first on-off valve 17. The reliquefaction line 7 is provided with a first BOG compressor 19 and a reliquefaction unit 21, which together constitute an ammonia evaporated gas reliquefaction device 22. Furthermore, the ammonia evaporated gas discharge line 9 is provided with a second BOG compressor 23. Furthermore, the ammonia evaporated gas detoxification line 11 is provided with a first safety valve 25 and an ammonia evaporated gas detoxification device 27, and the ammonia gas recovery line 12 is provided with a second safety valve 29. The first on-off valve 17, the first safety valve 25, the second safety valve 29, and the second on-off valve 33 (described later) are shown in white when in an open state and in black when in a closed state.

[0021] In the ammonia storage facility 1 configured as described above, under normal circumstances, the first on-off valve 17 is open, and the first safety valve 25, the second safety valve 29, and the second on-off valve 33 are closed. The liquefied ammonia 2 stored in the storage tank 3 is discharged to the discharge line 5 by the transfer pump 13, vaporized by the vaporizer 15, and supplied to the coal-fired boiler 4. In addition, the ammonia evaporated gas generated in the storage tank 3 is compressed by the first BOG compressor 19, liquefied in the reliquefaction unit 21, and returned to the storage tank 3, or compressed by the second BOG compressor 23 and supplied to the discharge line 5 and then to the coal-fired boiler 4.

[0022] In the event of an emergency or unexpected power outage or during maintenance, the ammonia evaporated gas re-liquefaction device 22 cannot operate, and during maintenance, the ammonia evaporated gas cannot be discharged to the coal-fired boiler 4, and the discharge line 5 may be closed in an emergency. Even in such a case, ammonia evaporation gas continues to be generated in the storage tank 3, and a large amount of ammonia evaporation gas is generated from the vaporizer until the discharge line is stopped, so the ammonia evaporation gas detoxification device 27 of this embodiment is the equipment for recovering this gas.

[0023] 1, the ammonia evaporated gas detoxification device 27 includes an adsorption device 31 that adsorbs the ammonia evaporated gas. In this embodiment, a second on-off valve 33 and a vacuum pump 35 are provided at the outlet of the adsorption vessel 37 as devices for desorbing the adsorbed ammonia gas. The ammonia evaporated gas detoxification device 27 is an effective device when the storage tank 3 is large and the pressure resistance of the storage tank 3 or the pressure of the vaporized ammonia evaporated gas (atmospheric pressure level to 110 kPaA) is low.

[0024] The adsorption device 31 includes an adsorption vessel 37 containing an adsorbent that adsorbs ammonia evaporated gas, a cooling agent 39 disposed in the adsorption vessel 37 for maintaining the adsorbent cooled to a predetermined temperature or below, and a cooling medium circulation mechanism 41 for circulating a cooling medium that cools the cooling agent 39 to cool and maintain the cooling agent 39 at a temperature below its melting point.

[0025] The adsorbent may be an adsorbent having excellent ammonia adsorption and desorption performance, such as activated carbon, zeolite, metal organic frameworks (MOF), silica gel, activated alumina, ion exchange resin, clay mineral, etc. The adsorption vessel 37 filled with such an adsorbent is cooled to a low temperature (above the melting point of ammonia and below atmospheric temperature: −30 to 30° C.) and kept on standby in a vacuum. Examples of ice packs include ordinary water (ice), gel materials in which water is absorbed into a highly absorbent polymer, and water with ethylene glycol added (antifreeze).Other examples include latent heat storage materials with a melting (freezing) temperature in the range of -30 to 30°C, such as paraffin or decane-based ice packs, and hydrate-based materials such as calcium chloride, sodium sulfate, and tetrabutylammonium bromide (TBAB).

[0026] Generally, the lower the temperature, the higher the adsorption performance of an adsorbent, and the higher the temperature, the lower the adsorption performance. This point will be explained based on Figure 2. In Figure 2, the horizontal axis represents the adsorbent temperature, and the vertical axis represents the adsorption amount. In an actual process, as shown in Figure 2, when adsorption is started from a state in which the adsorbent is cooled (pre-cooled) to, for example, -30°C, the adsorption performance is high and the adsorption amount is large at the start of adsorption because the temperature is low, but the adsorbent temperature gradually rises due to the heat of adsorption, and the adsorption performance decreases. The final temperature achieved varies depending on the flow rate, heat dissipation, and cooling conditions, but as shown by the black circles in Figure 2, it may be 40°C or may rise to 100°C.

[0027] FIG. 3 is a graph showing the amount of ammonia gas (NH3) adsorbed and the temperature reached by the adsorbent having the characteristics shown in FIG. The flow rate of the ammonia gas to be adsorbed is constant, and the adsorption rate is defined as the flow rate per hour divided by the volume of the adsorbent. -1 , 120h -1 , 1200h -1 The three conditions were as follows: the pre-cooling temperature was -30°C, -15°C, and 10°C, as plotted on the left side of the horizontal axis.

[0028] The operating conditions for this process are to recover ammonia in an emergency purged adsorption vessel 37 at a pressure of approximately 1 atmosphere at a predetermined flow rate and time (for example, flow rate 20 to 100 ton / h x time 60 to 10 min). Measurements were carried out with different adsorption rates, and the recovery time was 72 hours. -1 is the rate under the 1-hour adsorption conditions. The inflow of ammonia gas was stopped the moment the internal pressure of the adsorption vessel 37 reached 1 atmosphere. As shown in FIG. 3, the lower the pre-cooling temperature and the smaller the flow rate, the greater the amount of ammonia adsorbed.

[0029] The ice pack 39 is used to make effective use of the large heat of fusion, which is latent heat, and therefore needs to be kept below the melting temperature. When a cooling method using liquefied ammonia or the like is used as the cooling method, it is possible to cool to -30°C, which is close to the ammonia liquefaction temperature of -33.4°C. Furthermore, when using seawater or circulating water cooling using outside air, the upper limit of the temperature that can be cooled is 30°C. Therefore, it is preferable that the melting temperature be in the range of -30°C to 30°C. Such ice pack 39 is filled into the adsorption vessel 37 so as not to mix with the adsorbent. The amount of ice pack 39 filled is preferably set so that the total heat of ammonia adsorption is approximately equal to the total heat of fusion of ice pack 39 . In other words, it is preferable that the heat of adsorption generated when the adsorbent adsorbs the ammonia evaporative gas can be offset by the heat of fusion of the ice pack 39, and that the heat of solidification of the ice pack 39 can be offset by the heat of desorption generated when the ammonia evaporative gas is desorbed from the adsorbent.

[0030] This reduces the equipment and capacity of the cooling medium circulation mechanism 41 and the amount of adsorbent, keeping the temperature of the adsorbent at the refrigerant melting temperature level, suppressing the temperature rise of the adsorbent due to the heat of adsorption, and ensuring the amount of adsorption. Furthermore, it can also be used in cases where the cooling medium circulation mechanism 41 stops functioning and detoxification is not possible due to an emergency or unexpected power loss (for example, Patent Document 4).

[0031] It is preferable to pre-cool the adsorbent and ice pack 39 to a low temperature below the melting temperature, since this allows the amount of ice pack 39 to be reduced by an amount equivalent to the specific heat capacity, utilizing the sensible heat of the adsorbent and ice pack 39. Furthermore, by setting the temperature reached during adsorption to a high temperature above the melting temperature, the same amount can be reduced by utilizing the sensible heat of the adsorbent and ice pack 39. However, the temperature reached during adsorption should be such that the adsorption performance of the adsorbent used is not significantly reduced.

[0032] The cooling medium circulating mechanism 41 prevents the ice pack 39 from melting due to external heat input, and circulates a cooling medium that cools the ice pack 39 to keep the ice pack 39 at or below its melting point. In order to further reduce the external heat input, it is preferable to insulate the adsorption vessel 37 with a heat insulating material, etc. This allows the cooling medium circulating mechanism 41 to be made even more compact. The cooling medium is not particularly limited, but liquefied ammonia or ammonia vapor can be used. Generally, a liquefied ammonia facility has liquefied ammonia 2 and a low-temperature gas circulation system (cold circulation system) for cooling, which can be used to pre-cool the adsorption vessel 37 and to maintain the low temperature of the ice pack 39. In this way, by using the liquefied ammonia before vaporization and the low-temperature gas circulation system that are abundantly present within the factory to cool the adsorbent, cooling can be achieved with almost no power costs. The cooling medium circulation mechanism 41 can also be used for the initial cooling of the adsorbent and the refrigerant. However, since there is no time limit for this initial cooling and slow cooling is sufficient, a cooling medium circulation mechanism 41 with reduced equipment and capacity can be used.

[0033] In this embodiment, a vacuum pump 35 (pressure reducing means) for reducing the pressure inside the adsorption vessel 37 is provided as a means for desorbing the ammonia gas adsorbed by the adsorbent. As described above, the adsorption device 31 is not operated constantly but only in emergencies or during maintenance, and there is almost no time limit for desorption of the adsorbed ammonia gas, so desorption can be carried out over time. Therefore, the capacity of the vacuum pump can be small, and the equipment cost and installation space can be reduced. Furthermore, by simply continuing to suction the inside of the adsorption vessel 37 with a low-output vacuum pump 35, the adsorbent and ice pack can be cooled by the desorption heat generated by desorption under reduced pressure. By solidifying the ice pack, it is possible to prevent the adsorbent from being overcooled by the desorption heat, and desorption can be carried out more easily.

[0034] The method of detachment is not limited to the pressure reducing means, and various other methods can be used. For example, it is also possible to stop the refrigerant circulation of the cooling medium circulation mechanism 41, raise the temperature inside the adsorption vessel 37 by external heat input (natural or forced), increase the internal pressure, and then vent the gas. For example, seawater, water, or vaporized ammonia can be used as the forced external heat input.

[0035] The operation of the ammonia evaporated gas detoxification device 27 of this embodiment configured as above will be described with reference to FIGS. 4(a) is a schematic diagram showing the state inside the adsorption vessel 37. Also, FIG. 4(b) is a graph showing the relationship between the time during operation (adsorption and desorption) of the ammonia evaporated gas detoxification device 27 and the pressure (i), temperature (ii), and adsorption amount (iii) inside the adsorption vessel 37. In the example shown in FIG. 4, the adsorption vessel 37 is evacuated to desorb ammonia, the internal pressure is 1 kPa, and the adsorbent is on standby in a state pre-cooled to −20° C. with liquefied ammonia 2.

[0036] In the event of an unexpected power outage or maintenance, the ammonia evaporative gas detoxification device 27 will be activated, and at this time, as shown in Figure 5(a), the first on-off valve 17 will be closed or the first BOG compressor 19 will be stopped, so the second safety valve 29 or the first safety valve 25 will be opened. Also, the second on-off valve 33 will be kept closed.

[0037] The ammonia evaporated gas is supplied to the adsorption vessel 37 via the ammonia gas recovery line 12 or the abatement line 11 and adsorbed onto the adsorbent. As shown in Figure 4(b), ammonia at atmospheric pressure to 100 kPa flows into the adsorption vessel 37 at a predetermined (constant) flow rate and is adsorbed onto the adsorbent. The adsorption heat increases the temperature of the adsorbent (see Figure 4(b)(ii)). Because the condition is for total adsorption at a constant flow rate, the amount of adsorption increases linearly (see Figure 4(b)(iii)). The pressure in the adsorption vessel 37 gradually increases, and sufficient adsorbent is contained so that the generation of ammonia gas ends before the pressure reaches 100 kPa, and adsorption is completed at a pressure below 100 kPa.

[0038] There is no particular time limit for desorption, and so it can be performed, for example, as shown in Fig. 5(b) when an emergency situation or maintenance has ended and the ammonia storage facility 1 is operating normally. At this time, the first on-off valve 17 and the second on-off valve 33 are in an open state, and the first safety valve 25 and the second safety valve 29 are in a closed state.

[0039] Desorption is performed by slowly drawing with the vacuum pump 35 (there is no time limit), and when the standby pressure reaches 1 kPa, it stops, closes, and goes into standby. The desorbed ammonia gas can be reused.

[0040] During desorption, the pressure gradually decreases (see Figure 4(b)(i)), and the temperature also gradually decreases due to the heat of desorption (see Figure 4(b)(ii)). The temperature of the adsorbent decreases due to the heat removed by desorption, and this desorption heat can be effectively used to cool and re-solidify the adsorbent and refrigerant. The adsorbed ammonia gas is desorbed, and the amount of adsorption becomes almost zero (see FIG. 4(b)(iii)). The adsorbent temperature at the start of adsorption, including the pre-cooling temperature, is in the range of -30 to 30°C, and the adsorption end temperature also varies depending on the flow rate and thermal conditions, but in this example, the start temperature is -20°C and the end temperature is 0°C.

[0041] As described above, the ammonia evaporated gas detoxification device 27 according to this embodiment recovers ammonia using the adsorbent and releases it through desorption, so no ammonia is released to the outside and 100% of the ammonia can be reused. Furthermore, unlike a water tank, the adsorption vessel 37 can be placed upright, so the installation space can be significantly reduced compared to a water absorption system. Furthermore, by pre-cooling, the amount of adsorbent can be reduced, so the adsorption vessel itself can be made smaller, and the refrigerant circulation device for cooling can also be made smaller. Furthermore, since it does not require a power source, it can also cope with power outages in emergencies. [Explanation of symbols]

[0042] 1. Ammonia storage facility 2. Liquefied ammonia 3. Storage tanks 4. Coal-fired boiler 5. Payment Line 7 Reliquefaction Line 9. Ammonia evaporation gas discharge line 11 Abatement Line 12 Ammonia gas recovery line 13 Transfer pump 15. Vaporizer 17 First shut-off valve 19 No. 1 BOG compressor 21 Reliquefier 22 Ammonia evaporation gas re-liquefaction device 23 No. 2 BOG compressor 25 First safety valve 27 Ammonia evaporation gas removal device 29 Second safety valve 31 Adsorption device 33 Second shut-off valve 35 Vacuum Pump 37 Adsorption container 39 Ice packs 41 Cooling medium circulation mechanism

Claims

1. An ammonia evaporation gas detoxification device that is provided in a facility having a liquefied ammonia vaporizer or an ammonia evaporation gas re-liquefaction device, and that prevents ammonia evaporation gas from the liquefied ammonia vaporizer or the ammonia evaporation gas re-liquefaction device from leaking to the outside during inspection or emergency, an adsorption device that adsorbs the ammonia evaporated gas, The adsorption device is an ammonia evaporative gas detoxification device characterized by comprising an adsorption vessel containing an adsorbent that adsorbs the ammonia evaporative gas, an ice pack disposed in the adsorption vessel for keeping the adsorbent cooled to a predetermined temperature or below, and a cooling medium circulation mechanism for circulating a cooling medium that cools the ice pack in order to cool and maintain the ice pack below its melting point.

2. 2. The ammonia vapor detoxification device according to claim 1, wherein the melting temperature of the ice pack is in the range of -30°C to 30°C.

3. 3. The ammonia evaporated gas detoxification device according to claim 1, wherein the cooling / heating medium circulating mechanism circulates ammonia evaporated gas or liquefied ammonia.

4. 3. The ammonia vapor detoxification device according to claim 1, further comprising a pressure reducing means for reducing the pressure inside the adsorption vessel.

5. 4. The ammonia vapor detoxification device according to claim 3, further comprising a pressure reducing means for reducing the pressure inside the adsorption vessel.

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