DE3827005A1 - Compressed air dryer - Google Patents

Abstract

Compressed air dryer having a flow duct which is completely provided, at least in sections, with a porous component which can be flowed through. The articles can be joined to one another and to the boundary of the flow duct or of the heat exchanger wall by adhesion (bonding) or by sintering. The porous component, which can be flowed through, can act simultaneously as a filter. It is possible to connect downstream of the compressed air dryer a heat store (accumulator) which can be thermally discharged by the refrigerating (cooling, cold-producing) machine in the case of part-load operation on the compressed air side, and is provided with a heat exchanger surface to the compressed air, which corresponds to the recuperator output or leads to the desired escape temperatures of the compressed air. It is thereby possible to design the refrigerating machine for an output which corresponds to the non-recuperable output in the case of full-load operation.

Description

A particular problem of compressed air technology is that in the Compressed air contained moisture in the form of water vapor as well the oil residues that are carried away from the compressor. High water content in the compressed air leads to in the distribution network Corrosion problems or malfunctions, for example in Pneumatic motors. The oil escaping at the tapping points can to affect the health and well-being of the Lead people in the workplace as well as pollution Compressed air contact workpieces.

The ones sucked in through the compressor, mainly in the gas phase present water portions are therefore e.g. by con condensation heat exchanger separated from the air and by special le separation systems removed. To get the highest possible separation Achievement is achieved with this type of dryer in the heat rope with coolant temperatures far below the dew point temperature worked. Optimal results are achieved when the air outlet temperature is minimally above zero, so that the freezing of the defrost water is just avoided.

The compressed air / steam mixture is located behind the heat exchanger current through a separation system, for example by Deflecting lamella separates water and oil from the air. This A mechanical fine filter is usually used for the separator Separation of oil drops in the range of 10 µm downstream. The air exits the separator at a low temperature, residual moisture of 0.5 g / kg is common. Furthermore it is usual to pass this cold air into a recuperator to the Pre-cool air coming out of the compressor, causing after the state of the art saves about 50% of the cooling capacity that can.

Are used as heat exchangers in dryers of the type described all common systems such as counter-current tube bundles, coaxial tube in-pipe systems or plate heat exchangers applied. It's be knows that the heat transfer coefficient in the compressed air dryer with such smooth tube heat exchangers under non-return the condensation heat is around 140 W / m2k.

This means that especially with small temperature differences between the coolant and the compressed air to be cooled Metabolic surfaces are required. In this respect, the Verla of large power shares in the recuperator the price for against such a heat exchanger as that inevitably increasing pressure losses on the compressed air side.

In the case of the cooler, a large-scale design is unavoidable Lich, because of the risk of icing a heat exchanger surface temperature must not fall below 0 ° C, other on the other hand, the air outlet temperature to be as complete as possible condensation of the water vapor content as close as possible the zero point must be brought up. According to the state of the tech Outlet temperatures of 0.5-2.0 ° C are common, because of that already mentioned - residual moisture above 0.5 g / kg air undesirable are.  

This means that for cooling from 1 ° C to 0.5 ° C for example approx. 7.2 m2 heat exchanger surface of conventional construction are required if the compressed air mass flow is 1 kg / s wearing.

Even if the high costs of large heat exchanger surfaces are left aside, it should be noted that large heat exchanger surfaces lead to a high pressure drop, since a cooling task - to bring the mass flow to be cooled as close as possible to the coolant temperature - can only be achieved by extending the flow channels. In compressed air technology in particular, pressure losses are expensive, since with a constant mass flow, the power consumption of the compressor increases to the square of the pressure increase. Substantially, this application is about the application of heat exchangers, which enable much better heat transfer coefficients of the compressed air / water vapor mixed flow, with the aim of realizing larger recuperation efficiency and smaller heat exchanger surfaces and pressure losses.

The solution to the problems described above lies after Main claim 1 in the application of porous, flowable construction elements, preferably based on aluminum powder secondary components of the heat-exchanging surface.

Relative to the interfaces that the medium to be cooled and the cooling medium can be separated compared to smooth wall heat exchangers significantly better heat transfer coefficient achieve that depending on the configuration 5000 W / m2k and more be.

In addition to the use of heat rope disclosed in claim 1 shear, especially condensation separators with porous, flowable secondary components, preferably based of aluminum powder, some embodiments are shown which allow favorable litigation. That's a pro Blemstellung in that already cooled air up to the entrance in the recuperator if possible no longer with components in touch should come above the respective dew point temperature temperature, as this leads to evaporation and thus to unnecessarily high residual moisture content. Another, not yet The problem addressed is that in the condensation separators, So on the cooling side of the recuperator, and in the cooler occurring pollution.

The pollution occurs in the form of over the air compressor sucked in dust and cracked oil residues.

Conventionally, there is a risk of heat pollution Exchanger surfaces in such a way that heat accumulation is as smooth as possible shear surfaces are chosen so that the dirt particles find the lowest possible basis of detention.

If certain boundary parameters are adhered to, the otherwise expected contamination in porous heat exchangers the components.  

It is also shown that elsewhere by ge aimed adjustment and structure of the capillary size and structure Separation and filtering processes using metal filters are excellent let solve, the mechanical effect targeted by ther mixing treatment is optimized.

For the area of heat-exchanging surfaces are fiction according to recuperators and coolers used, at least in area carrying compressed air, the flow channels with porous, flowable elements based on sintered or ver glued particles are provided. This is an optimization the ratio of the heat transfer area to the thermal conductivity distance achieved. It is therefore a good heat-conducting starting material to give preference, e.g. Alumi powder or granules nium.

Furthermore, the heat transfer properties by kon vective cross-currents that result in constant mixing of the mass flow, improved.

Fig. 1 shows the basic structure of a heat exchanger system for compressed air treatment according to the 1st main claim.

Fig. 1 shows a recuperation heat exchanger ( 1 ) and a cooler ( 2 ). The compressed air delivered by the compressor ( 3 ) is fed to the upper heat exchanger space / distribution space ( 4 ) and is distributed there to the individual heat exchanger tubes ( 5 ). In the area of the heat exchanger (length A ), the pipes are provided with a porous, flowable component that is in good heat-conducting contact with the pipe or heat-exchanging wall. However, contact with the surrounding housing should be avoided, since the heat flow from the surroundings has a negative influence on the heat-exchanging process taking place. The pipelines are continued in the area of the cooler ( 2 ), a porous component connected to the pipe or heat exchanger wall also being used in the area of length B. The Rohrwan applications or heat exchange surfaces are also provided on the outside with a porous, flow-through component, which is flowed through by a cooling medium. The cooling medium is conditioned so that the outlet temperature of the compressed air is as close as possible to the zero point. The compressed air mass flow is multi-phase at this point. The cold compressed air as well as the condensed water and the oil present in drops are now led from the lower heat exchanger space / collecting space ( 6 ) to a separator ( 7 ) which separates the phases and drains the liquid phase ( 8 ). The cold air is passed into a storage chamber ( 9 ) and from there into a porous component (length A ) which closes the heat exchanger tubes ( 5 ). The cold air can thus absorb heat from the flow of compressed air, an individual heat exchanger tubes ( 5 ), the heat-exchanging section A should be designed in an ideal manner so that the outlet temperature of the dehumidified air ( 10 ) comes as close as possible to the inlet temperature of the compressed air .

The performance of the system compared to a Glatt tubular heat exchanger should be shown using the temperature curve diagrams in Fig. 2.

Design described in a shell and tube heat exchanger with a average heat exchanger area of 0.04523 m2 was 18 Nm3 / h Compressed air passed according to a mass flow of 6.13 g / s. The cooling medium was water with an inlet temperature of 0.7 ° C.

The compressed air inlet temperature was 28.1 ° C. The length ( B ) of the porous member 30 mm. The air outlet temperature was reduced to 1.4 ° C, the Delta T between the coolant outlet temperature of 0.84 ° C and the air outlet temperature was only 0.56 K.

The transmitted power (latent + sensitive) is 164.8 W. A Smooth tube heat exchangers would otherwise have the same geometry instead of 30 mm, 127 mm long or the middle one Heat exchanger area increased from 0.04523 m2 to 0.1273 m2 Need to become.

A measurable increase in differential pressure due to contamination of the bottom Cracked oil residues or dust could damage the ge chose diameter of the flow channels of 40 mm and one Length of 30 mm not found after 1000 hours of operation will.

The pressure difference of the heat exchanger was approximately 20 mbar.

Starting from a basic application according to Fig. 1, some embodiments according to subclaims 2 to 17 will now be explained in their function.

As with all other heat exchangers, the thermal conductivity plays material plays an important role.

According to claim 2, the use of aluminum powder, the by sintering to mechanically firm, flowable bodies pern was claimed as new. By in the Sinterpro zeß trained diffusion bridges are good heat conductive Bridges between the particles and the pipe walls, if these consist of a material that has similar sintering properties has the same properties as the aluminum powder or granulate.

According to claim 3, the availability of aluminum powder or - Granules also carried out in the form of an adhesive process will. Due to the presence between the particles Adhesion bridges deteriorate the heat transfer coefficient by 30-40%, but you get smooth particles surfaces as well as a corrosion-resistant surface protection.  

Combined heat is also conceivable according to both disposition techniques exchanger systems.

The performance share of the overall system to be realized in the air / air recuperator deserves special attention, since it is decisive for the operating costs. In conventional technology, because of the poor heat transfer coefficients, very large heat exchanger surfaces are inevitably used in order to achieve the current recuperation share of approx. 50% of the total output. Fig. 3 shows the temperature profiles over the distance of the flow channels in the recuperator according to the invention.

According to claim 4, the execution of the Reku Perators brought in as vulnerable to registration, because the before partial properties regardless of the other armament of the overall system.

A conventional cooler is connected downstream of the recuperator or a cooler according to claim 5 or 6, which the Temperaturdif reference between the desired final temperature of 0 ° C and the Outlet temperature of the recuperator must overcome. At a to simplify assumed full recovery of the The instal lated cooling capacity to an almost complete con density of the water vapor content necessary power limited will.

The temperature difference between the compressed air inlet temperature temperature (35 ° C) and the compressed air outlet temperature is le only 4 k. This means in comparison to the prior art a 30% increase in the recuperation share and thus ver improvement of economy without the additional Heat exchanger surfaces must be installed or higher Dif must be accepted.

With entry conditions of P = 8 bar, 35 ° C, 100% RFE ( x = 6.0 g / kg), which are common in compressed air technology, corresponding to an entry enthalpy of h = 50.4 kJ / kg, the proportion of sensible heat is ( 0 → 35 ° C; h = 37.8 kJ / kg) = 73.8%. Ideally, the cooling capacity to be installed is 36.2% of the total capacity plus the temperature difference between the inlet and outlet temperatures lost in the recuperator. In conventional systems, the outlet temperature is approx. 27 ° C (0 → 27 ° C; h = 29.4 kJ / kg), corresponding to a maximum coverage rate of 58.3% by the recuperator.

This means that the cooler downstream of the recuperator regardless of its construction of 41.7% of the respective total performance when installing the recuperator according to the invention can be reduced to approx. 27% of the total output.

The application of equipment of the compressed air side flow channels in the cooler, according to claim 1, leads to a further Ver reduction of the cooler interfaces compared to the conventional one len technology, as in the recuperator with small temperature differences limit very high heat outputs = 5000 W / m2k the. Claims 7 to 10 formulate different shapes tion possibilities of the heat exchanger for the described Functions are of minor importance.

The cooling capacity to be installed and thus also the consumption under full load conditions can by the previously described Kon figuration can be reduced by approx. 35%.

In terms of economy, it is worth noting that the heat exchanger according to the invention with unchanged flow cross-sections has a lower total pressure difference than conventional heat exchangers. Furthermore, given a Mass flow the inflow area can be increased almost arbitrarily, without the heat transfer coefficient not being a multiple of smooth tube heat exchanger surfaces.

Through the previously described reduction in installed cold performance, however, the problem arises that when starting as well as when changing loads to larger compressed air volumes desired state variables can only be achieved with a time delay nen.

On the other hand, the installed cooling capacity for compressed air side load operation too large. According to the invention Problem according to main claim 2 by the integration of a Wär mespeichers solved, that in the compressed air part load operation is thermally discharged by the chiller and with regard Lich output and heat capacity is designed so that he can temporarily take over the function of the recuperator.

This can be carried out according to claim 12 in such a way which is described below.

For a mass flow of 1 kg / s compressed air, the accumulator perform heat exchanger 37.2 kW, the storage capacity is 0.010 kWh. Because of the water separated from the air flow potentially suitable for heat storage and transmission Medium available. The following is intended to be simplistic be assumed that only shoot out behind the radiator whose water is to be used. Abge behind the radiator Different water volume is 1 g / kg. The heat of fusion of the what sers is 0.332 kJ / g. The minimum necessary storage mass the system delivers in approx. 110 s full load operation.  

Assuming that the heat exchange tubes according to the Main claim 1 of an ice storage mass in a very thin Layer are covered, the heat transfer coefficient of the In tube for dimensioning the heat exchanger to be installed area in the latent memory can be used.

This value is, for example, 5145 W / mK if the particle size aluminum powder with an equivalent pore diameter diameter of 200 microns and a flow velocity of 1.98 m / s is present.

The upstream cooler can pre-cool the incoming compressed air at the power distribution quoted above ( Δ h cooler = 13.2 kJ / kg) to approximately 27 ° C, so that air flow between the storage temperature (water / ice 0 ° C) and the pressure there is an average temperature difference of 13.5 K, the heat-exchanging interface must therefore be 1.86 m2.

The process described above can be carried out constructively in the manner shown in FIG. 4, which is claimed as claimed in claim 12.

Coming from the recuperator, the compressed air arrives via the line ( 1 ) into a deflection chamber ( 2 ), in the bottom area of which the accumulated condensation water is discharged via a siphon ( 3 ), which can be switched on or off via a level monitor (not shown).

The deflected compressed air is fed into the cooling pipes ( 4 ), which are acted upon on the outside by a cooling medium.

From there they reach the area of the storage heat exchanger. At the pipe outlet, the now two-phase compressed air flow enters a chamber ( 7 ), which is provided with a water separator ( 8 ), which conducts the condensation water to the chamber floor. From there, the water reaches the channels ( 9 ) enclosing the storage heat exchanger.

As soon as the compressed air side is operated in the partial load range, there is also excess power available on the refrigerator side. The excess power is now to be used in such a way that the refrigerant is guided into the outer region ( 10 ) of the channels ( 9 ), a temperature below 0 ° C. being set so that the water flowing through freezes.

Due to the volume in the channel gap ( 9 ), the storage capacity is set, the contact surface ice / heat exchanger ( 6 ) determines the transferable power. Power and volume are selected so that with recurring full-load operation, which leads to increased temperatures at the radiator outlet ( 4 ) due to a lack of recuperation, the lack of recuperation is temporarily provided by the memory. This power is applied by the heat of fusion of the water, which is conducted to the collecting trough ( 2 ) via the channel ( 10 ), which surrounds the inlet pipe ( 1 ) from the recuperator. Especially in the case of continuous, compressed air-side partial load operation, depending on the selected storage capacity, the chiller can be switched off when the minimum storage temperature is undershot.

Care can be taken to increase the storage capacity by using the rooms marked with ( 11 ). Both the collection of condensation water with temporary freezing and drainage of the ice water via channels 9 and 10 is conceivable as well as the filling of these rooms ( 11 ) with a latent storage medium.

Another embodiment as claimed in the invention is shown in an embodiment of a cooler in the form of a latent memory see according to claim 3.

In this case, the coolant chamber designated with (5) in Fig. 4 is filled with a suitable storage medium, for example water. The pipes designated with (4) are designed for an area sufficient for cooling and recuperation. The connected chiller is only controlled with regard to upper and lower temperature limit values, so that longer periods of idle time of the chiller result automatically from longer periods of time on the air-pressure side part-load operation, which can lead to considerable reductions in operating costs.

Another disadvantage of conventional systems is the übli Chen separation of the structural unit of the heat exchanger system and the Separation device in the form of a mechanical filter hen.

For a favorable process control it is recommended to print airflow after leaving the cooling side of the recuperator to contact more with areas that have temperatures above Have dew point, as this leads to the fact that already condensate water is returned to the vapor phase. To that extent is the distance from the cooler to the separator in this respect hung most critical point in conventional systems.

Fig. 5 shows an arrangement that fully integrates the separator into the heat exchanger system, furthermore has a ge cooled separator, which is realized in such a way that the separator in the form of a good heat-conducting filter consists of porous sintered or glued aluminum powder and this filter with the cooling circuit is contacted.

In addition to the advantages recognizable for the process, a such filter by washing or blowing out the dirt par particles are regenerated.

The mass flow coming from the compressed air compressor is introduced into the system via a storage chamber ( 1 ). Before being introduced into the recuperator cooling heat exchanger ( 2 ), the mass flow can be passed through a coarse deflection filter ( 3 ), which retains coarse dirt particles. The recuperator cooling pipes lead directly into the cooler ( 4 ) and into the storage tank ( 5 ). From there, the now two-phase mass flow reaches into a deflection chamber ( 6 ) which is limited by a liquid separator ( 7 ) to the Filterein.

From there, the compressed air, which is largely separated from the water, reaches the filter pre-chamber ( 8 ). The filter itself is designed as a closed cylinder made of preferably porous sintered aluminum. Pore diameter (filter fineness), particle structure and the flow velocity defined by the flow area are designed to retain oil mist drops. The filter effect is supported in such a way that this filter is cooled. Since the air at this point has only the smallest amount of water vapor, the cooling temperature can also be below 0 ° C.

Such a system is preferably cooled by a liquid cooler.

The coolant enters here in the area of the accumulator ( 5 ), which is in contact with the highly conductive filter. The use of a latent storage medium with a phase change temperature of 0 ° C reliably prevents the undesired subcooling of the compressed air heat exchanger in the storage.

From there, the coolant is led to the cooler ( 4 ), a drop below the coolant outlet temperature below 0 ° C. being selected as an indicator for switching off the refrigeration machine.

In such shutdown phases, the filter inevitably warms up on the temperature of the compressed air flow, so that Ice that is present on the filter surface can thaw.

Especially with compressed air dryers with larger volume flows provides the unused drainage of the condensed water represents an energetic loss re increase the recuperator output to the possible reduction the cooling capacity to be installed, based on a stationary full load operation.

In claims 16 and 17 are two processes according to the invention guides declared as according to the invention, the one approximately Allow full recuperation of the heat of condensation.

Fig. 6 shows a configuration that shows a use within the process management of compressed air treatment.

Prior to entering the air dryer (1) coming from the com pressor (2) of compressed air via a heat exchanger tet Gelei, the inside a porous device can be flowed through, according to which claim. 1 Such a porous component is also applied to the outside in order to obtain the largest possible evaporation area. This heat exchanger, which can be called a trickle cooler, is suctioned off by a jet pump ( 3 ) operated with compressed air.

With the valve ( 4 ) closed, which separates the condensation water tub of the dryer ( 1 ) and an intermediate container ( 5 ), condensation water can be drawn into the evaporative cooler via a line ( 6 ), which can be ventilated for the purpose of optimal evaporation. The enthalpy of evaporation is extracted from the air flow pressure. The mixture escaping the jet compressor can be blown off because it mainly consists of water vapor and air.

By opening the valve ( 4 ), the condensate-oil mixture that has been collected in the meantime is passed into the collection container. Via the valve ( 7 ), the oil floating on the surface can be concentrated and discharged into a designated container ( 8 ). During filling, the line ( 6 ) should be closed by a valve.

Fig. 7 shows a recuperation device according to claim 17, wherein the heat of condensation of the condensation water is used to reduce the condensation temperature of the refrigerator and thus to lower the primary energy output for the cooling work to be performed.

The oil mixture condensate collected from the compressed air dryer ( 1 ) is fed into an intermediate container ( 2 ) which is provided with a line for oil extraction described above. As soon as the chiller ( 3 ) goes into operation, the valve ( 4 ) is opened and water via the line ( 5 ) leads to the refrigeration condenser ( 6 ). The heat of evaporation is applied by the heat of condensation of the refrigerant. As a result, the condensation temperature can be reduced in comparison to the pure air cooling of the condenser and / or the amount of air with which the condenser is acted on can be reduced.

Claims (17)

1. Heat exchanger for dehumidifying compressed air, characterized in that the flow channel is at least partially completely filled with a porous, flowable component made of mechanically firmly connected particles with a particle size of 100-1500 microns and a mechanical bond between the particles and the pipe - or heat exchanger wall is present. 2. Heat exchanger according to claim 1, characterized net that the particles of aluminum powder or aluminum Minium granules exist that are mechanically strong Compound with each other and with the pipe or heat exchanger wall in the form of sintering processes have created diffusion bridges. 3. Heat exchanger according to claim 1 or 2, characterized ge indicates that the particles are made of aluminum powder or aluminum granules, which have a mecha nically tight connection with each other and with the pipe or heat exchanger wall in the form of in adhesive processes have created adhesion bridges. 4. Heat exchanger according to one of claims 1 to 3, there characterized in that the heat exchanger as Air / air recuperator is designed. 5. Heat exchanger according to one of claims 1 to 3, there characterized in that the heat exchanger as Air cooler is designed, one side of the heat A coolant can flow through the exchanger.   6. Heat exchanger according to claim 5, characterized net that on the side of the cooling medium to the on order of a porous, flowable component is waived. 7. Heat exchanger according to one of claims 1 to 6, there characterized in that the heat exchanger in the form a tube bundle is created, the inner and / or outer flow channel at least in part stretch provided with flowable components is. 8. Heat exchanger according to one of claims 1 to 6, there characterized in that the heat exchanger in the form a plate heat exchanger is created, the inner and / or outer flow channel at least in Ver sections with flowable components see is. 9. Heat exchanger according to one of claims 1 to 6, there characterized in that the heat exchanger in the form a flow-through lamella is created, the one contacted heat-exchanging pipe, the flow channel at least in sections with through flowable components is provided. 10. Heat exchanger according to claim 9, characterized net that the heat-exchanging pipe does not flow through bare component. 11. Storage device, characterized in that the A compressed air dryer system cooler on heat memory is connected downstream, that of compressed air partial load operation by the chiller ther is mix discharge and with a heat exchanger  surface is provided to the compressed air that the Reku perator output corresponds to or to the desired off temperature of the compressed air with which Aim to design the chiller for a performance to be able to use the non-recuperable power in Full load operation corresponds. 12. Storage device according to claim 12, characterized ge indicates that condensation is present in the Partial load range due to excess cooling capacity is freezable, the through the ice layer leading compressed air pipes on one of the Rekupera tion performance at least approximately corresponding Performance. 13. Storage device according to claim 11 or 12, there characterized in that the cooler as a latent memory is formed and by the Spei leading heat exchanger on one of the Cooling and recuperation performance corresponding Lei are designed. 14. Device, characterized in that a Wär Exchange system with a heat exchanger after a of claims 1 to 10 on the cooling circuit closed filter downstream of the cooler which is preferably from a good heat material exists. 15. Filter unit, characterized in that the fil sintered or glued aluminum powder consists. 16. Compressed air dryer system, characterized in that it is equipped with a heat recuperator that sensitive and the heat of condensation of the sweat  recovered in such a way that the collected Condensation water by means of a compressed air powered Jet compressor is extractable, and this water in a heat rope upstream of the recuperator is evaporable and the heat of evaporation Compressed air flow coming from the compressor is withdrawn becomes. 17. Recuperation device for a compressed air dryer nersystem, characterized in that the total melted condensation water to cool the cooling system Line capacitor can be used.