EP0801262A1 - Apparatus with an ammonia pressure vessel - Google Patents

Abstract

The device has a pressure tank (1) for holding the ammonia at above atmospheric pressure, enclosed by an outer casing (2), with the space (3) between the pressure vessel and the outer casing having inlet and outlet openings (19,20) for circulation of a rinsing stream (10). The exit air stream from the inter-space (3) is fed to an ammonia leakage detector (5), with a catalyser (7), a heater (11), a temperature detector (16) and a control (14), responding to detection of a given ammonia concentration by a sensor (13) for heating the exit air stream to a given temperature for catalytic oxidation. This converts the ammonia into oxygen and nitrogen which is then released into the atmosphere.

Description

The invention relates to a device with an ammonia pressure container which has a filling pressure above atmospheric pressure and which is surrounded by a further shell, the space between the shell and the ammonia container having an inlet opening and an outlet opening so that it can be used to discharge ammonia leaks by a fan with a flushing flow is flushable from normal outside air.

The operators of ammonia systems - be it as a pressure tank for chemical uses or as refrigeration systems or heat pumps operated with ammonia - have so far managed to dilute ammonia leaks as much as possible in order to bring them to a concentration below the odor limit, i.e. around 5 ppm Surrender environment. Another option is to surround the ammonia system with a second shell and to flush the resulting space with fresh air. Especially if the space in between has to be accessible, this is a possibility of a planned dilution of the ammonia leaks. If larger ammonia leaks occur briefly in the flushing flow, which are, for example, above a MAK value of 50 ppm or a tolerability limit of 500 ppm, you can use the Guide the flushing stream through a washing system with water and first dissolve most of the ammonia in the water. If the ammonia is dissolved in water, there are different ways of disposing of the ammonia spirit that arises. Either the ammonia is expelled again in a controlled manner, which means that the immission of the ammonia is only stretched over a longer period of time. The real problem remains. As a second disposal method, the water-ammonia solution can be neutralized with acid. Discharge into normal wastewater is only possible if the ammonium concentration is not too high (over-fertilization of the water). Otherwise, the water-ammonia mixture must be disposed of as special waste.

As an alternative to a system with water, an absorption device with dilute sulfuric acid can be used. The ammonia is not dissolved in such a safety device, but is bound. The reaction product is ammonium sulfate (artificial fertilizer) in dissolved form. This solution must then be disposed of in a flat manner.

Ammonia does not form any chemical bond with water, so it is not firmly bound in water, but only dissolved. In principle, a very large amount of ammonia can be taken up in water. However, note the high vapor pressure of the ammonia, i.e. the strong desire to steam out of the water again.

The mixture of liquid ammonia and water creates highly concentrated water-ammonia mixtures (ammonia spirit). When stored in a closed container, the leakage of ammonia must be prevented by gas-tight sealing of the container.

However, if gaseous ammonia components are to be washed out of the room air, a large contact area between air and water must be available. This can be done, for example, using a bubble column (bubble bath) or a spray system (gas scrubber). Due to the inevitably large contact area, the concentration in the exhaust air is always directly related to the concentration of ammonia in the water. If operation is unsuccessful, ammonia can also be discharged again, i.e. the concentration at the outlet of the absorption system can be higher than at the inlet. Dissolving ammonia in water can therefore not be a permanent safety device.

The object of the invention is to provide a device which prevents the disadvantages listed above. This is achieved in accordance with independent claim 1 in that for the disposal of ammonia leakage, an apparatus is connected downstream of an escaping flushing stream, which apparatus has a large-area, for example metallic catalyst, a heating device, at least one temperature sensor, at least one sensor for ammonia in the intermediate space and a controller and which heats the rinsing stream when a given ammonia concentration K ₁ is exceeded to given temperatures for a catalytic oxidation in order to catalytically decompose ammonia leaks into nitrogen and water from the rinsing stream with the help of oxygen taken from the rinsing stream and to discharge the latter to the environment outside the envelope.

The advantage of such a device is that, knowing the amount of air passed through in the flushing flow, the operator can determine from which concentration K ₁ the ammonia, which corresponds to an absolute amount, is determined by a wants to decompose catalytic oxidation into water and nitrogen, the nitrogen mixed with the flushing stream reaching the atmosphere, while the precipitated water can be fed to an industrial sewage treatment plant. Advantageous developments of the invention are listed in the dependent claims 2 to 10. So it is advantageous, after the process has been ignited by the heating device upstream of the catalytic converter, to recover the heat escaping with the purge flow, which is done by a control flap which redirects the purge flow entering the apparatus via a heat exchanger at the outlet. According to the recovered amount of heat, the heating power can be regulated back by the temperature detected between the heating device and the catalytic converter, so that no unnecessary amounts of nitrogen oxides are generated by exceeding a predetermined temperature and so that the material is not overheated by the catalytic converter. As soon as the heating power of the heating device has been reduced to zero, a reversing device, which is designed, for example, as a control flap, takes over the temperature control by only passing a partial flow through the heat exchanger, to which a non-preheated residual current is mixed before the catalytic converter. This has the advantage that even large amounts of ammonia leakage can be broken down for as long as the oxygen content in the purge stream is sufficient. A further possibility in order to be able to reduce large leaks of ammonia that occur at short notice without overdimensioning the apparatus is to pre-purge the purge flow in such a case, which is detected, for example, as an impermissible concentration K ₂ via an ammonia sensor at the outlet of the apparatus to change the entry into the apparatus through a control flap via a washing system. At its outlet, this washing system is always connected to the inlet to the catalytic converter and can Therefore, slowly release the briefly dissolved ammonia as a buffer to a later flushing stream that is not diverted by the control valve. A further passive safety is obtained if the inlet opening to the intermediate space has a non-return flap which, even in the event of a fan failure, forces an additional volume flow through the apparatus caused by leakage and a possibly upstream washing system. Even if it is no longer possible to enter the space due to excessive ammonia concentrations, a redundant replacement fan can be put into operation without large amounts of ammonia getting into the environment.

Platinum and platinum alloys are suitable as catalyst material at temperatures between 150 ° C and 250 ° C in order to keep the proportion of nitrogen oxides low. In general, the material can be processed into a large reaction surface in the form of fine-meshed wire nets processed into a package or in the form of layers which are applied to a large-area substrate, such as an open-pore ceramic body. Mixed oxide catalysts can also be used.

It is also conceivable to use the electrical resistance of the material in such a way that the energy for igniting the reaction is supplied to the catalyst itself. The energy control of the heating device or the flap control for the energy consumption of the partial flow can also be controlled in accordance with the deviation from a predetermined outlet temperature from the catalyst in order to prevent overheating and formation of nitrogen oxides.

Fig. 1

Schematisch einen Schnitt durch eine Vorrichtung mit einer Kälteanlage, die von einer Hülle umgeben ist, um eventuelle Ammoniakleckagen abzufangen und einem Apparat zur katalytischen Zerlegung in Wasser und Stickstoff zuzuführen;

Fig. 2

schematisch eine Vorrichtung nach Fig. 1, bei der zwischen der Hülle und dem Teil für die katalytische Zerlegung eine Waschanlage für Ammoniak als Puffer zuschaltbar ist und

Fig. 3

schematisch eine Vorrichtung analog zu Fig. 2, bei der ein zusätzlicher Ventilator ammoniakhaltige Luft durch ein Wasserbad presst.

The invention is described below using exemplary embodiments. Show it:

Fig. 1

Schematic of a section through a device with a refrigeration system, which is surrounded by a casing to catch any ammonia leaks and to feed an apparatus for catalytic decomposition into water and nitrogen;

Fig. 2

schematically shows a device according to FIG. 1, in which a washing system for ammonia as a buffer can be connected between the shell and the part for the catalytic decomposition and

Fig. 3

schematically a device analogous to Fig. 2, in which an additional fan presses ammonia-containing air through a water bath.

The figures show a device for ammonia plants 1 which have an internal pressure greater than atmospheric pressure and which are surrounded by a further shell 2 which has an inlet and an outlet opening 19, 20 for purging the intermediate space 3 with a purging stream 10 of outside air. By connecting an apparatus 5, an ammonia leakage which is inadvertently mixed with the flushing stream 10 can be catalytically oxidized with oxygen from the flushing stream and broken down into nitrogen and water, the apparatus comprising a large-area catalyst 7, a heating device 11, at least one temperature sensor 16, at least one sensor 13 for Ammonia in the space 3 and a controller 14 to carry out the catalytic oxidation at a predetermined temperature.

1 shows an ammonia pressure container 1 in the form of a closed refrigeration circuit 9 of a closed shell 2, for example in the form of a walk-in one Machine hall surrounded. Across the shell 2, a fan 6 promotes a flushing stream 10 emerging from the shell 2, which is composed of a flushing stream 4 of ambient air 8 entering through an inlet opening 19 and any leaks within the shell 2. The position of the fan 6 at the outlet from the casing 2 has the advantage that a negative pressure is created in the casing 2 via the flow resistance of the inlet opening, which prevents loss of ammonia due to unwanted leaks in the casing. The inlet opening is provided with a non-return flap in order to generate a flow in the direction of the outlet from the casing even if the fan fails with a volume increase due to ammonia leakage in the casing 2.

The fan 6 could also be attached to an outlet opening 20 of the apparatus 5 in order to prevent leakage to the outside in the event of leaks in the apparatus 5. The fan drives the rinsing flow 10 against the flow resistance of the subsequent components, the rinsing flow 10 being divided according to the resistances by a heat exchanger 12 connected in parallel with a flap 21 into a partial flow 10a and a remaining rinsing flow 10b, which subsequently mix. A temperature sensor 16 monitors the mixing temperature and reports it to the controller 14. The mixed stream flows through a heating device 11, for example an electric heater with a limited surface temperature, which, if necessary, supplies the mixed stream with heat in order to maintain a predetermined temperature, which is reported back via a temperature sensor 17, in the controller 14 with a heating control when entering a catalytic converter 7. A catalytic reaction takes place in the catalytic converter, in which, with the help of the oxygen present in the purge stream, a decomposition of Ammonia in nitrogen and water is made partly in vapor form. At the same time, heat is released.

4 NH ₃ + 3 O ₂ arise 6 H ₂ O + 2 N ₂ when the catalyst permits low temperatures so that the formation is largely suppressed by nitrogen oxides. Platinum and platinum alloys have proven themselves as catalysts in a temperature range between 150 ° C and 250 ° C. These are processed, for example, in multi-layer, fine wire meshes in order to produce a sufficiently large and evenly distributed reaction area. Such wire nets are manufactured, for example, by Heraeus, Heraeusstrasse 12-14, D-63450 Hanau, and are used in apparatus to reduce odor emissions in fattening farms. Other embodiments consist of open-pore ceramic parts which are coated with a layer of the catalyst or of mixed oxides.

Since heat is released with the decomposition and oxidation in the catalytic converter, depending on the dimensioning of the purge stream 10 and catalytic converter area, the sub-stream 10a must be regulated back by an overarching regulation as a function of an impermissibly increased outlet temperature 18 at the outlet of the catalyst 7.

At the outlet of the catalyst, a first portion of condensed water 23 is already formed, which is precipitated from the flushing stream, while a further portion is formed in the downstream heat exchanger 12 and is likewise collected in a sump 30. The sump 30 releases its water via a siphon from a water outlet 24.

The nitrogen released in the catalytic converter reaches the flushing stream via an outlet opening 20 The atmosphere. An ammonia sensor 15 is mounted in the outlet opening, which measures the remaining ammonia content and, if necessary, triggers an alarm via the control. Another ammonia sensor 13 measures the ammonia portion in the intermediate space 3. When a predetermined limit value at the sensor 13 is exceeded, the ignition of the process is initiated by heating the flushing stream 10 to a predetermined value dependent on the catalyst material. The flap 21 is practically closed and the entire purge stream 10 passes through the heat exchanger 12. When the process starts, additional heat is released in the catalytic converter, which is partially released in the heat exchanger 12 to the purge stream 10. The heating output must now be reduced in accordance with the specified permissible temperatures 16, 17, 18. If the heating power of the heating device has to be reduced to zero, the flap 21 takes over the temperature control in that the partial flow 10a through the heat exchanger is reduced accordingly and the remaining purge flow 10b through the flap 21 is increased. In order to keep the heat losses in the apparatus 5 small, the components which are exposed to high temperatures are provided with thermal insulation 25.

The actual "ignition" of the system, in which the flushing stream 10 is brought to the predetermined temperature by the heating device 11, takes place via the control 14 by the ammonia sensor 13 in the intermediate space 3. The response value for ignition can, for example, be lower than the MAK Value (50 ppm) can be set when the space is accessible and a second, lower value can be specified in order to prevent the supply of heat in the heating device 11 and thus the process. When dimensioning the system, the size of the flushing flow 10 therefore determines the maximum installed heating power by the predetermined one To reach ignition temperature in the catalytic converter. For example, to break down and oxidize 50 kg of ammonia according to the above equation, the oxygen of 140 m ^{3 of} normal air is necessary. A large flushing stream 10 allows the volume in the intermediate space to be converted relatively often and more leakage to be removed with the same outlet concentration, but it also costs correspondingly more heating energy in order to keep the larger flushing stream at the ignition temperature. For this reason, it is possible, starting from a minimum purge flow 10, to design the controller 14 in such a way that, in combination with a multi-stage fan 6, the purge flow 10 is increased and additional heating registers are switched on if the concentration measured with the ammonia sensor 13 in the interspace is not returns within a reasonable period. In this way, a multi-stage fan can be used to achieve a flushing flow that is tailored to the needs and disposal. When the second, lower concentration value is reached, it is possible to switch from a higher flushing current to a lower flushing current in order to save heating power.

It is customary to dimension systems which relate to the security area to an assumed worst case, which in the present arrangement would correspond to a maximum ammonia leakage over a certain time. FIG. 2 shows how, by interposing a washing system, a buffer 27 of ammonia dissolved in water is created, which enables a later slow degradation if the solution equilibrium is disturbed by a reduced ammonia concentration above the liquid level.

In the event of a sudden increase in the ammonia concentration in the space above the sensor 13 is detected or which can be detected by the sensor 15 in the outlet opening 20, the flushing flow 10 is reversed via a flap 26a and brought in counterflow to a spray device 26c via a pipe 28. At the same time as the flap 26a, the spray device 26c is activated by drawing water out of a water basin below the spray device 26c with a pump 26b and supplying it to the spray device 26c. The ammonia is delivered to spray drops in the spray device, which collect in the water basin and form a buffer 27 with dissolved ammonia there. The flushing stream 10d thus reduced in its ammonia content is further treated as described in relation to FIG. 1. In the example of FIG. 3, which otherwise corresponds to that of FIG. 2, a reversing flap 26a was dispensed with and instead a second fan 6a was installed which leads directly to a pipe 28 and the characteristics of which can be adapted to the additional resistance in the washing system. It should be noted that when passing through pipe 28 and by blowing holes 29 into the water bath, an additional resistance arises, which should be able to be compensated for by the delivery characteristics of fan 6a. The fan 6 conveys a flow 10, while the second fan 6a generates an additional flow 10e, which - reduced in the ammonia concentration - combines as a flow 10d with that of the fan 6 in order to be fed to the catalyst 7. In the normal case, only the fan 6 would be in operation in order to ventilate the intermediate space 3 and to dispose of smaller ammonia leaks via the decomposition in the catalyst 7. A backflow through the fan 6a is not possible as long as a water column corresponding to the internal pressure can be backed up in the pipe 28. In the event of a sudden increase in the ammonia concentration in the intermediate space 3, measured with the ammonia sensor 13, the controller 14 can switch the second Switch on the fan 6a and thus ensure a substantially greater air throughput and briefly reduce the concentration in the combined flow of the fans 6, 6a with the buffer 27. An additional non-return valve 31 in the flow 10 ensures that the system is effective even if the fan 6 fails.

Claims (10)

Device with an ammonia pressure container (1) which has a filling pressure above atmospheric pressure and which is surrounded by a further shell (2), the space (3) between the shell (2) and the ammonia container (1) having an inlet opening (19) and an outlet opening ( 20), so that it can be flushed through a fan (6) with a flushing stream (4) of normal outside air (8) for discharging ammonia leaks, characterized in that an apparatus (5) for an escaping flushing stream (10) for the disposal of ammonia leaks. is connected downstream, which apparatus has a large-area catalyst (7), a heating device (11), at least one temperature sensor (16), at least one sensor (13) for ammonia in the intermediate space (3) and a controller (14) and which has the flushing stream ( 10) when a predetermined ammonia concentration in the intermediate space (3) is exceeded to predetermined temperatures for a catalytic oxidation to catalyze ammonia leaks With the help of the purge stream (10), the oxygen taken out into nitrogen and water and to discharge the latter to the environment outside the envelope (2). Device according to claim 1, characterized in that the apparatus (5) has a heat exchanger (12) downstream of the catalytic converter (7) and has a control flap (21) in front of the catalytic converter (7), at least one partial flow (10a ) of the flushing stream (10) before entry in the catalyst (7) by redirection through the heat exchanger (12) can be heated. Apparatus according to claim 1 or 2, characterized in that the apparatus (5) as a pre-switchable preliminary stage for the rinsing flow (10) from the intermediate space (3) has a washing system (22) through which the rinsing flow (10) via a reversing element (26 ) can be reversed when a predetermined measured value K ₂ for the ammonia concentration at the outlet opening (20) is exceeded in order to form a buffer (27) of ammonia dissolved in the water for its subsequent decomposition and oxidation in the catalyst (7). Device according to one of claims 1 to 3, characterized in that the ammonia tank (1) consists of a heat pump or refrigeration system operated with ammonia in a closed circuit (9). Device according to one of claims 1 to 4, characterized in that the catalyst (7) has a metallic surface, for example made of platinum or a platinum alloy or consists of a mixed oxide catalyst. Device according to one of claims 1 to 5, characterized in that the catalytically active material is formed by wires or by layers applied to ceramic. Device according to one of claims 1 to 4, characterized in that the catalytically active material is electrically heated via its electrical resistance. Device according to one of claims 1 to 7, characterized in that the controller (14) ignites the catalytic reaction by heating the flushing stream in a temperature range between 150 ° C to 250 ° C and on a when a first ammonia concentration K _{1 is} exceeded regulates the specified temperature in this area. Device according to Claim 8 in connection with one of Claims 2 to 7, characterized in that the control, when ignited, first redirects the complete flushing stream (10) via the heat exchanger (12) in order to correspond to the heat absorbed in the heat exchanger and between the heating device (11 ) and the catalytic converter (7) measured temperature (17) to regulate the heating power of the heating device (11), so that the control regulates the partial flow (10a) through the heat exchanger (12) as far back when the heating power is reduced to zero heating power by opening the flap (21) that the intended temperature for catalytic decomposition is maintained. Device according to one of claims 1 to 9, characterized in that the inlet opening (19) in the intermediate space (3) has a non-return flap in order to prevent at least part of the atmospheric oxygen in the intermediate space (3) for a failure of the fan (6) Use water and nitrogen decomposition.

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