GB2065865A - Heat pumps in painting plant - Google Patents

Abstract

A painting unit comprises a painting booth (12), a pretreatment station (10) up-stream of the painting booth, and a paint drier (27) down- stream of the painting booth. A heat pump is driven by an internal combustion engine (23). The arrangement is such that waste heat obtained by cooling the engine (23) is predominantly used for supplying energy to the pretreatment station (10). Vaporised and compressed refrigerant is predominantly used for heating air flowing to the painting booth (12) and the waste heat contained in the exhaust gases from engine (23) is predominantly used for supplying energy to the drier station (27). <IMAGE>

Description

SPECIFICATION Painting unit This invention relates to painting units.

It is known that painting units, in particular those for workpieces having a large surface area, for example motor vehicle bodies, have a high energy demand. Moreover individual stations of the painting unit must be supplied with differing quantities of heat of widelyyarying temperatures.

A large part of the total energy demand in such a painting unit is required for heating up the air which flows through painting booths forming a part thereof and a substantial part of this heat cannot be re-used. However, this air needs to be heated merely to a comparatively low temperature of, for example, 240 C. For the pretreatment of workpieces, for example, in a degreasing and phosphating station, the energy demand as such is, as a rule, not so high as in the painting booths, but temperatures of, for example 600C are required. Finally, in a paint drier station or stations, temperatures of, for example, 1400 C-i 800C must be reached.

These energy requirements of a painting unit make very high demands on the energy supply equipment to be used.

German Specification No. 2 907 310 discloses the use of a heat pump for recovering a part of the energy expended in painting booths for heating the air. However, this heat pump does not work satisfactorily because paint agglutinations can occur on heat exchangers of the heat pump even after a short period in operation. Moreover, the process disclosed in German Specification No. 2 907 310 does not in any way take account of the overall energy requirement of a painting unit, which is highly differentiated with respect to energy quantity and temperature.

In view of the rapidly increasing shortages of the primary energy sources, in particular petroleum, available at present, heat pumps are indeed gaining increased importance generally.

These heat pumps extract heat from environmental heat sources which are available virtually everywhere -- for example the surrounding air, soil, rainwater, water from melting snow and domestic effluents -- and this heat is exploited for heating purposes.

Amonst the various heat pumps hitherto available, those which interact with a water store which, on the one hand, is in heat exchange with the surrounding heat sources via a vaporiser and, on the other hand, is in heat exchange with the refrigerant cycle of the heat pump, have already proved successful in the heating of buildings, mainly residential accommodation. Due to the extraction of heat from the water store into the refrigerant cycle, this water store is always at a comparatively low temperature level. Heat pumps of this type have been disclosed in German Specification Nos. 2 634 233 and 2 71 5 075.

The above mentioned heat pumps can - as disclosed in German Specification No. 2 744 615 - be substantially improved by driving the refrigerant compressor with primary energy and transferring the waste heat of the primary energy drive by heat exchange with a water store. According to the present state of the art, possible primary energy drives are internal combustion engines, in particular diesel engines.

Through heat exchange with the water store, and the cooling and condensation thus caused, their exhaust gases are not only largely detoxified, but they also transfer a part of their heat content to the water store. Additionally, a part of the heat of the exhaust gases and the water store is transferred directly into the heating cycle, and this heat need no longer be supplied by the heat pump.

The present invention seeks to supply energy by means of a heat pump to a painting unit in such a way that not only is the quantity of energy which is to be provided substantially reduced but, additionally, the specific energy demands of the individual stations of the painting unit are also fully taken into account.

According to the present invention there is provided a painting unit comprising: a painting station; a pretreatment station upstream of the painting station; at least one paint drier station down-stream of the painting station; a heat pump; and an internal combustion engine for driving the heat pump, the arrangement being such that not only circulating refrigerant but also waste heat from the internal combustion engine, including waste heat from the exhaust gases, can be utilised for the extraction of heat energy and waste heat obtained by cooling the internal combustion engine is predominantly used for supplying energy to the pretreatment station, vaporised and compressed refrigerant is predominantly used for heating air flowing through the painting station and waste heat contained in the exhaust gases from the internal combustion engine is predominantly used for supplying energy to the drier station or stations.

The present invention is based upon the discovery that, in a very specific type of heat pump, namely a heat pump driven by an internal combustion engine, the quantities of heat energy, which are obtained at three points and differ with respect to amount and temperature, can be matched in an almost ideal manner to the abovedescribed differentiated energy demand of a painting unit. Thus with respect to amount and temperature, the quantity of heat to be removed from the internal combustion engine by cooling water is eminently suitabie for supplying energy to the pretreatment station (for example a degreasing and phosphating station), where temperatures of, for example, 600C are required.

By contrast, the exhaust gases leaving the internal combustion engine at high temperatures are for heating up the paint drier station or stations, which must reach temperatures of, for example, 1 400C-1 800C. The major part of the total energy delivered by the heat pump naturally arises in the refrigerant cycle itself. This proportion of heat is to be used for heating up the air for the painting station, since the energy demand in the latter is as a rule very large, the temperature level at the same time being relatively low.

In a preferred embodiment of the heat pump has a water reservoir for heating the refrigerant, the reservoir being in heat exchange with the air flowing through the painting station. This leads to the very advantageous possibility of bringing the water store into heat exchange with the air flowing through the painting station.

The reservoir may be a water store for the heat pump.

It is entirely conceivable that, during a small part of the year, the outside temperature is so high that temporarily no heating, or only slight heating, of the air flowing through the paining station will be necessary. In this case, the painting unit may include means whereby, in operation, the refrigerant normally used for heating the air flowing through the painting station, or a part of the regrigerant, can be used for supplying additional energy to the pretreatment station and/or the drier station or stations. In this case, the internal combustion engine (for example disel engine) driving the heat pump needs to be run advantageously only under part load whereby primary energy can, in turn, be saved.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which Figure 1 shows schematically an embodiment of a painting unit according to the present invention in "normal" operation, that is to say over the whole year except merely those days on which the prevailing outside temperatures are above, for example, 240C; Figure 2 shows schematically another embodiment of a painting unit according to the present invention likewise in "normal" operation; Figure 3 shows the painting unit of Figure 1, with the heat pump switched to "summer" operation, that is to say at high outside temperatures; and Figure 4 shows the painting unit of Figure 2 with the heat pump switched to "summer" operation.

Throughout the drawings like parts have been designated by the same reference numerals.

Referring first to Figure 1 , there is shown one embodiment of a painting unit according to the present invention having a pretreatment station 10, for example, for degreasing and phosphating of workpieces which are to be painted. The workpieces may, for example, be metal parts having a large surface area, for example, motor vehicle bodies. Downstream of the pretreatment station 10, there is an electrophoretic painting station 11 which can be an electrophoretic dip coat (EDC) station or an electrophoretic powder coat (EPC) station, or a combination thereof.

In a painting booth 12, for example a spray booth, of the painting station, a final coat is applied to the workpiece. The painting booth 12 is supplied with air, as indicated by arrows 1 3, 14. If only for the benefit of the personnel working in the painting booth, the air should be heated to a constant temperature of, for example, 240C.

Heating takes place in a heat exchanger 1 5 of an air feed unit 1 6. Since the air fed to the painting booth 12 is enriched with paint mist due to the painting process taking place therein, subsequent purification of the air extracted from the painting booth is necessary. This is carried out in the customary manner by so-called wet-scrubbing of the painting booth, and this is indicated by reference numeral 1 7. The scrubbing water which is contaminated with paint particles etc. is then passed to a heat store or reservoir 1 9 via a line 18, where purification of the scrubbing water takes place by coagulation of the paint particles and contaminants contained therein. The purified scrubbing water can then be returned via a line 20 to the painting booth 12 where it is re-used for scrubbing the contaminated air.The air leaving the painting booth is then passed to atmosphere as indicated by an arrow 21, but before doing so the air has transferred a large part of its heat content to the circulating scrubbing water.

The reservoir 1 9 also serves at the same time as the heat store of a heat pump. The heat pump comprises a compressor 22 which is preferably a piston pump and is driven by an internal combustion engine 23, preferably a diesel engine, via a transmission 24.

Cooling water indicated by reference numeral 25 passing through the pretreatment station 10 is used for cooling the internal combustion engine 23. Heat exchange by means of a heat exchanger 26 takes place in the pretreatment station in such a way that the cooling water is cooled and, at the same time, the pretreatment station 10 is supplied with the required energy so that a temperature of, for example, 600C is reached.

After painting in the painting booth 12, the workpieces are passed to a drier station 27 which is downstream of the painting booth 12. For the drying process, the drier station should be brought to a temperature of, for example, between 1 400C and 1 800C. On starting up the painting unit, a supplementary heater 28 assists in bringing the drier station to the requisite operating temperature. At other times, however, the hot exhaust gases indicated by arrow 29 of the internal combustion engine 23 serve to supply energy to the drier station 27. These exhaust gases are passed into a heat exchanger 30, where they release a large part of their heat content to the drier station. The quantity of heat contained in the exhaust gases of the internal combustion engine 23 normally suffices to balance the heat loss of the drier station so that, in "normal" operation (i.e. when the prevailing outside temperature is less than 240 C) of the painting unit (Figures 1 and 2) the supplementary heater 28 can be switched off after the end of the start-up procedure.

As shown by an arrow 31, the exhaust gases are, after leaving the heat exchanger 30, passed to the reservoir 1 9. In the latter, a heat exchanger 33 is located below the water level indicated by reference numeral 32, this heat exchanger ensuring transfer of the residual heat from the exhaust gases to the water present in the reservoir 19. The simultaneous further cooling of the exhaust gases resulting from this advantageously effects condensation of the predominant part of the noxious substances contained in the exhaust gases and hence results in a very effective exhaust gas purification. Finally the exhaust gases, cooled and purified in this way, are passed to atmosphere as indicated by reference numeral 34.

As shown in Figure 1 refrigerant extracts heat from the water present in the reservoir 1 9 by means of a heat exchanger 40 and is thus vaporised, if the regrigerant has not already been vaporised beforehand in a separate vaporiser 41.

The vaporised regrigerant is then passed via a line 35 to the compressor 22, where it is compressed and its temperature is thus substantially increased. The vaporised and heated compressed refrigerant now passes via a line 36 into the heat exchanger 15 which is located within the air feed unit 1 6. In the latter, the heated refrigerant releases a predominant part of its heat content, including the latent heat of condensation, to the air fed in, the air being heated to the requisite temperature. At the same time, the refrigerant is thus correspondingly cooled and condensed.

Subsequently the cooled and condensed refrigerant passes via a line 37 to a valve 42 where pressure reduction takes place. Then the refrigerant is passed back, either directly via a line 38 or via the vaporiser 41 to the heat exchanger 40 within the reservoir 1 9.

Figure 2 shows another embodiment of a painting unit according to the present invention where the electrophoretic painting station 11 is also included in the refrigerant cycle of the heat pump. The heat pump here has the important task of removing the so-called Joule heat obtained in the electrophoretic painting station 11, that is to say cooling the electrophoretic painting station. At the same time, the electrophoretic painting station 11 here serves as an additional heat source for reheating the refrigerant. In other words by means of the heat pump, the Joule heat removed from the electrophoretic painting station 11 is beneficially re-employed at another station: in this embodiment for heating the air fed to the painting booth 12.

In detail, the refrigerant circulation in this case proceeds as follows: after the refrigerant has released most of its heat content to the air feed unit 1 6 and has thus been condensed, it passes via a line 43, including the valve 42 in which pressure reduction takes place, to a mixing valve 44 which can be regulated in dependence upon the temperature prevailing in the electrophoretic painting station 11. On the one hand, the two following extreme positions of the mixing valve 44 are possible: (a) The mixing valve 44 passes the total quantity of refrigerant through a vaporiser 45 which extracts heat from the surrounding air via a line 39 directly back to the heat exchanger 40 located in the reservoir 19, while by-passing the electrophoretic painting station 11.This extreme position of the mixing valve 44 is important only in the case where the temperature of the electrophoretic painting station 11 is below a predetermined temperature.

(b) The mixing valve 44 is set in such a way that the total quantity of refrigerant, by-passing the vaporiser 45, passes via a line 46 into the electrophoretic painting station 11. In the latter, the refrigerant absorbs heat by means of a heat exchanger 47, the refrigerant being partially or completely vaporised. At the same time, the electrophoretic painting station 11 is thus cooled down to the desired operating temperature.

Finally, the refrigerant passes via the line 39, the heat exchanger 40 and the line 35 to the suction side of the compressor 22.

In the normal case, however, the mixing valve 44 will assume an intermediate position in such a way that, in the valve, the quantity of condensed refrigerant coming from the air feed unit 16 is divided into two streams, one of which is directly fed to the reservoir 1 9 as described above under (a) and the second of which is fed to the reservoir 1 9 only after preceding heat exchange in the electrophoretic painting station 11, as described above under (b).

The painting units according to Figures 1 and 2 are intended for the "normal" operation, that is to say for all those days on which the outside air temperatures are below, for example, 240C and the air for the painting booth 12 must thus be heated up. Such conditions apply, at least in Northern and Central Europe, during by far the greater part of the year.

Figures 3 and 4 show how it is possible to supply the painting units of Figures 1 and 2 respectively with energy in an optimum manner, on those few days of the year the outside temperature is, for example, about 240 C: this is referred to as "summer" operation.

The essential common characteristic of the embodiments according to Figures 3 and 4 is the fact that, due to the high outside air temperature, heating of the air for the painting booth 1 2 is no longer necessary or desirable. In contrast to the painting units of Figures 1 and 2, parts 12 to 16 are here therefore not included in the refrigernnt cycle of the heat pump. In practice, the switchover from "normal" operation (according to Figures 1 or 2) to "summer" operation (according to Figures 3 or 4) respectively can be effected by a suitable valve control mechanism which is not shown in the drawings in order to avoid making the latter confusing.

The painting unit shown in Figure 3 (the painting unit according to Figure 1 when switched to "summer" operation) now operates as follows.

The vaporised heated refrigerant, compressed by the compressor 22, passes via a line 48 into a heat exchanger 51 within the pretreatment unit 10, where it releases a substantial part of its energy and thus supplies energy to the pretreatment station. At the same time, the refrigerant liquefies as it flows through the heat exchanger 51. Subsequently, the pressure of refrigerant is reduced and cooled as it flows through the valve 42 in line 49. The refrigerant then passes via line 52 into the heat exchanger 40 of the reservoir 1 9, where it absorbs heat from the water and is thus vaporised. The vaporised refrigerant finally flows via line 50 back to the compressor 22, where the process is repeated.

In other respects, energy is supplied to the pretreatment station 10 and the drier station 27 in the same way as described in relation to Figures 1 and 2. This means that the pretreatment station 10 is not only connected to the refrigerant cycle, as described, but is additionally also supplied with heating energy by the cooling water of the internal combustion engine 23. The drier station 27 obtains its energy from the hot exhaust gases of the internal combustion engine 23.

Of course, in the so-called "summer" operation the heat pump does not have to provide its full output as in "normal" operation. The internal combustion engine 23 will thus be regulated to a iower speed of rotation since, in this case, the heat from the exhaust gases might not be sufficient to supply the drier station 27 continuously with the required energy, the supplementary heater 28 will not only be in operation for starting up the painting unit but, to a certain extent, it will be required continuously. As necessary, it is also possible to use the refrigerant cycle of the heat pump, or part thereof, for supplying additional energy to the drier station or drier stations.

In the embodiment shown in Figure 4, energy is supplied to the pretreatment station 10 and the drier station 27 as described above with reference to Figure 3.

However, after leaving the pretreatment station 10 and subsequently flowing through the valve 42, the refrigerant does not return directly to the reservoir 19, but flows first through the heat exchanger 47 in the electrophoretic painting station 11. The electrophoretic painting station 11 thus functions as a vaporiser. The refrigerant whose pressure has been reduced in the valve 42 and brought to a lower temperature, absorbs heat within the electrophoretic painting station 11. At the same time, as indeed intended, the electrophoretic painting station 11 is cooled corresponding to the latent heat of vaporisation absorbed by the regrigerant. The refrigerant already vaporised in the electrophoretic painting station 11, can now be returned, by-passing the reservoir 19 - as indicated in Figure 4 by a bypass line 53 - directly to the compressor 22, where the process is repeated. However, it is also possible, for example if the heat absorbed by the refrigerant within the electrophoretic painting station 11 should not be sufficient, to let the refrigerant flow through the heat exchanger 40 in the reservoir 19, from where it passes back to the compressor 22. The residual heat still required for its vaporisation or reheating can be absorbed by the refrigerant in the reservoir 1 9.

Claims (6)

1. A painting unit comprising: a painting station; a pretreatment station upstream of the painting station; at least one paint drier station down-stream of the painting station; a heat pump: and an internal combustion engine for driving the heat pump, the arrangement being such that not only circulating refrigerant but also waste heat from the internal combustion engine, including waste heat from the exhaust gases, can be utilised for the extraction of heat energy and waste heat obtained by cooling the internal combustion engine is predominantly used for supplying energy to the pretreatment station, vaporised and compressed refrigerant is predominantly used for heating air flowing through the painting station and waste heat contained in the exhaust gases from the internal combustion engine is predominantly used for supplying energy to the drier station or stations.

2. A painting unit as claimed in claim 1 in which the heat pump has a water reservoir for heating the refrigerant, the reservoir being in heat exchange with the air flowing through the painting station.

3. A painting unit as claimed in claim 2 in which the reservoir is a water store for the heat pump.

4. A painting unit as claimed in any preceding claim including means whereby, in operation, the refrigerant normally used for heating the air flowing through the painting station, or a part of the refrigerant, can be used for supplying additional energy to the pretreatment station and/or the drier station or stations.

5. A painting unit as claimed in any preceding claim including an electrophoretic painting station downstream of the pretreatment station and upstream of the painting station, and means for removing the Joule heat from the electrophoretic painting station by means of the heat pump, the heat pump being arranged to supply heat to the pretreatment station, the painting station and the drier station or stations, and at the same time to cool the electrophoretic painting station, the heat extracted from the electrophoretic painting station being used, by way of the refrigerant of the heat pump, for heating the air flowing through the painting station and/or for heating the pretreatment station and/or for heating the drier station or stations.

6. A painting unit substantially as herein described with reference to and as shown in the accompanying drawings.