CS251301B1 - Equipment for energy-saving heating and drying with heat pumps - Google Patents

Abstract

The device solves the problem of utilizing all the thermal energy of gases exiting the heating or drying space. Its essence lies in at least a two-stage system consisting of heat pumps, heating spaces or dryers, compressors and heat exchangers connected to them. To drive at least one of these compressors, these multi-stage systems have a built-in motor or expansion machine, for example a turbine, for converting the energy of the compressed gaseous medium into mechanical work.

Description

The invention relates to a device for energy-saving heating and drying of substrates of various types using heat pumps.

Heating and drying as technological operations are used in almost all sectors of the national economy. Their purpose is either to bring the substrate - products, semi-finished products, materials - or even the atmosphere in a certain closed space to the required temperature - then it is heating - or to reduce the proportion of water and other volatile components or remove them altogether from the substrates subjected to this operation - and then it is drying. Both operations are usually quite energy-intensive, which is especially true for drying, since the largest share of the energy consumed here is for the evaporation of the liquid phase, regardless of the fact that thermal energy must be spent on heating the mass of the dried substrate and that it is necessary to take into account the energy that must be spent on covering heat losses. Drying mainly involves low-level heat, but even this is produced in the vast majority of cases using highly noble types of energy and fuels. The energy intensity of the drying process stands out especially when we consider the huge amounts of various substrates dried in industry and agriculture.

The previously known drying technologies, consisting of direct or indirect heating of the dried substrates and the transfer of the resulting vapors from the drying room to the atmosphere, have been gradually improved with the aim of reducing energy losses resulting from the aforementioned escape of vapors without use. However, losses due to heat dissipation by flue gases, radiation, etc. must also be taken into account, so the overall energy balance - especially for large-capacity dryers - shows that these devices operate with a low efficiency coefficient.

One direction of the mentioned improvements follows the utilization of heat escaping from dryers in the described manner, namely by the gaseous phase of heat transfer substances being fed into heat pumps similarly to the usual application of these thermodynamic devices when utilizing low-potential heat from the atmosphere, from river flows and natural water reservoirs or from underground spaces at a certain depth below the surface.

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The compression of this gas phase, which occurs in the heat pump, requires the expenditure of some mechanical energy, for example from an electric or gas engine, but it allows the use of the previously lost waste heat brought to a higher level for both re-drying and heating or other heating. During the drying process, the moist air exiting the dryer after filtration and the aforementioned compression is recirculated through a heat exchanger, where it transfers part of its heat to the expander or expansion turbine, where the resulting expansion both supplies part of the power needed to drive the compressor and cools the gas below the saturation temperature, thereby condensing the water vapor into water, which is then removed from the circuit to the separator. The dried air or gas is heated in the heat exchanger of the heat pump to a higher temperature for re-entry into the dryer.

Although this system represents a significant cost-effectiveness of the thermal drying process compared to the previous state, it does not allow the use of all the thermal energy of the gas phase emerging from the drying space, including the condensation heat of components capable of condensation under heat exchange conditions, for example water vapor. Also, in the case where it is expedient to divide the drying or heating process into several branches or stages depending on whether drying or heating is required at different temperatures or under other different conditions, for example humidity levels, the previously known systems cannot achieve the aforementioned higher and more demanding effects of the application of heat pumps.

According to the invention, these systems are improved by arranging at least two-stage systems in heat pump devices consisting of heating spaces or dryers with at least two compressors and heat exchangers connected to them, whereby both motors and expansion machines, for example turbines, are built in to drive these compressors for converting the energy of the compressed gaseous medium into mechanical work. Compressors are built into the devices for compressing atmospheric air or air or gases exiting the dryers, to which discharge pipes leading either to the heating space or dryer or to a heat exchanger are connected. Similarly, i.e. at the outlet from the heating spaces or dryers, suction and discharge pipes are arranged for compressors in further stages, whereby heat exchangers are located inside the dryers or heat exchangers located outside the dryers are connected to

- 3,251,301 radiators located inside drying rooms or heating rooms.

When compared with previously known drying systems using heat pumps for heating, operating with their own heat transfer ^medium , which circulates in a closed loop between the expander and the condenser, the advantage of the device according to the invention is that it is possible to use as a heat transfer medium the gaseous phase directly emerging from the dryer, i.e. air, moist air, water vapor and therefore operating in a circuit that is not closed; this allows for a simplified design of the device and a reduction in investment costs and heat losses in the drying process. In addition, in the device according to the invention, it is possible to act on the dried substrates even under increased air pressure or another gaseous medium, blown directly into the drying or heating space through the discharge pipe of the compressor. It is also possible to carry out drying in a vacuum.

The higher effects achieved by the device according to the invention /B/ compared to the previously known single-stage solution /A/ are evident from the energy balances in these cases of direct and indirect heating, which were carried out at the Gottwald workplace of the Faculty of Technology of the Brno University of Technology.

251 301

Direct heating of the substrate with a hot gaseous medium, such as air, superheated steam or other gases:

' SS° ^3t '« ^Te P ^iota Pressure -,- Energy |/type, quantity/ I 1 1 ; delivered /+/

drained /-/ 1. Input values 1 kg of air 0°C 0.1013 MPa 2. Compression + 134 KJ /mechanical/ 3. New values a/ after compression b/ heat extraction c/ after heat extraction 133°C 40°C 0.4053 MPa 0.4053 MPa - 94 KJ /thermal/ 4. Expansion to the original /outer atmosphere/ pressure 0.1013 MPa - 103 KJ /mechanical to drive the compressor/ 5. Output values 1 kg of air -62°C 0.1013 MPa Energy balance: 1 η λ τζτ

/thermal energy/ + 134 - 103 KJ with +31 KJ /mechanical energy/ so the total ratio is 94 : 3.1 « 3.03

Conclusion: For every 31 KJ of mechanical energy expended, 94 KJ of thermal energy was obtained, so an input of 1 KJ of mechanical energy yielded 3.03 KJ of thermal energy.

251 301

B/

Indirect heating of the substrate by sharing heat through the walls of the device, through radiators, etc.:

a. at the inlet ^of a medium with a pressure equal to the external atmosphere:

Mass, substance Temperature Pressure Energy /type, quantity/ delivered /+/ withdrawn /-/ 1. Input values 1 kg of water vapor 110° C 0.1013 MPa 2. First compression + 170 KJ /mechanical/ 3. New values and/or after the first compression 200° C _ 0.24 MPa b/ heat extraction - 124 KJ /thermal/ c/ after heat extraction 140° C 0.24 MPa 4. Second compression + 105 KJ /mechanical/ 5. New values a/ after the second compression 195° C 0.4 MPa b/ heat extraction - 2256 KJ /thermal/ c/ after heat extraction /output values/ 1 kg of water 140° c 0.4 MPa Energy balance: - /124 + 2256/ KJ /thermal energy/ = 2380 KJ

170 + 105 KJ /mechanical energy/ = 275 KJ so the total ratio is 2380 : 275 «8.65

Conclusion: For 275 KJ of mechanical energy expended, 2380 KJ of thermal energy was obtained, so the input of 1 KJ of mechanical energy brought 8.65 KJ of thermal energy /regardless of the possibility of further use of the output pressure of 0.4 MPa, e.g. to drive a compressor/.

AND

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b. when the medium enters from a vacuum dryer with a pressure of 0.04 MPa:

Weight, substance

Temperature

Pressure

Energy /type, quantity/ delivered /+/ drawn off /-/

Input values kg water vapor

80°C

0.04 MPa

2. First compression + 498 KJ /mechanical/

3. New values a/ after first compression b/ heat extraction c/ after heat extraction

337°C

140°C

0.4 MPa

0.4 MPa

- 2510 KJ /thermal/

Second compression + 208 KJ /mechanical/

5. New values a/ after the second compression b/ heat extraction c/ after heat extraction /output values/

248°C

0.4 MPa kg of water

140°C

0.4 MPa

- 2370 KJ /thermal/

Energy balance: - /2510 + 2370/ KJ /thermal energy/ = 4880 KJ

498 + 208 KJ /mechanical energy/ «=. 706 KJ so the total ratio is 4880 : 706 « 6.9

Conclusion: For 706 KJ of mechanical energy expended, 4880 KJ of thermal energy was obtained, so the input of 1 KJ of mechanical energy brought 6.9 KJ of thermal energy /regardless of the possibility of further use of the output pressure of 0.4 MPa, e.g. to drive a compressor/.

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The drawing shows 3 examples of embodiments of the invention in schematic sections, with Fig. 1 showing a two-stage device with a combination of direct heating in the first dryer with indirect heating in the second dryer, Fig. 2 also showing a two-stage device with a single dryer with two built-in radiators, and Fig. 3 showing a three-stage device again with one dryer, but with three built-in radiators.

Fig. 1. The first suction pipe 1 for supplying atmospheric air opens into the first compressor 2^, to which is connected the first discharge pipe _3 leading the heated compressed air to the dryer _4, in which the materials 4a intended for drying are distributed. From the space above these masses 4a, a suction pipe 5a emerges for supplying air depleted of heat given off to the masses 4a and enriched with water and volatile components evaporated from the masses 4a to the second compressor 5. From there, a second discharge pipe 2 is led, opening inside the heating space 8_, which is provided with an opening 8b for the escape of volatile components, to the heat exchanger 9./ ^and continuing via a coupling 7a to the turbine 10, arranged on a shaft 11 together with the first compressor _2 and the second compressor 5. The same shaft 11 is connected by a gear 12 to a motor 13, while the turbine 10 is connected by a discharge pipe 14a to a separator 14 for removing water condensed from the gaseous medium during cooling and condensation.

In the dryer 4^ the decomposed materials 4a are heated by air blown in from the first compressor 2, in which it is compressed and the temperature increases. This also causes the evaporation of water and volatile components from the materials 4a decomposed in the dryer _4, which are gradually dried at the same time. The air discharged through the suction pipe 5a is further compressed in the second compressor _5 and its temperature is increased at the same time, so that through the second discharge pipe 7_ the increased temperature is transferred to the second heat exchanger 9b, which causes indirect heating of the materials 8a surrounding this heat exchanger 9. If there is still water or other volatile components in them, they evaporate and escape through the opening 8b in the shell of the heating space £5. In the heat exchanger 2, the temperature of the air ^is reduced, which expands in the turbine 10 to a pressure close to the external atmosphere; this expansion will supply part of the power required to drive both compressors 2, 5j? the rest of the power will be supplied by the motor 13. At the same time, the expansion will cool the air below the saturation value, which will cause the water removed from the masses 4a decomposed in the dryer 4 to condense and be removed from the circuit

- 8 tubes 14a into separators 14. 2Sí 301

The heating space £ can be arranged similarly to the dryer £, if it is necessary to replace mere heating with drying, and conversely the dryer £ can be similarly modified to be adapted for mere heating. As needed, direct heating can then be combined in various ways by replacing the heat exchanger 2 by forcing warm gas or air under pressure directly into the dryer space or by drawing atmospheric air under vacuum into the dryer space, after which the compressor is only in operation.

Fig. 2 shows another solution of a two-stage drying or heating process, however, both stages are adapted to function in one drying or heating space. A supply £ of gaseous medium flows into the dryer £, for the discharge of which a first suction pipe £ is arranged, flowing into the first compressor 2, to which a first discharge pipe 2a leading to the first heat exchanger 9a inside the dryer £ is connected. From there, a second suction pipe 5a is arranged to the second compressor £, to which a second discharge pipe T_ leading to the second heat exchanger 9b also located inside the dryer £ is connected. Here too - similarly to the case according to Fig. 1 - a coupling 7a is arranged for the supply of gaseous medium from the second heat exchanger 9b to the turbine 10 and everything else is the same as in the first described solution.

Fig. 3 shows an example of a three-stage drying or heating process. A gaseous medium feed £ flows into the dryer £, for the removal of which a first suction pipe £ is arranged, flowing into the first compressor _2, to which a first discharge pipe 2a is connected, leading to the first heat exchanger 9a located outside the dryer £ and connected to a radiator 9d, located inside the dryer £. From the first heat exchanger 9a, a second suction pipe 5a leads to the second compressor £, to which a second discharge pipe ]_ follows, leading to a second heat exchanger 9b also located outside the dryer £ and connected to a radiator 9e, located inside the dryer £. From the second heat exchanger 9b, a third suction pipe 6a leads to the third compressor £, which is connected to a third discharge pipe 7fe leading to the third heat exchanger 9c, also located outside the dryer £. Also in this embodiment of the invention - similarly to the two previous examples - a coupling 7a is provided for the supply of the gaseous medium from the third heat exchanger 9c to the turbine 10 and everything else is the same as in the first described solution.

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It should be added to the general design of the device that it is not decisive whether the dried substrates are placed on conveyors, in containers or stored loose or otherwise placed. Heating is carried out in the dryers or heated spaces by radiators or by the walls of the dryers of the heating device, which here perform the function of radiators. A multi-stage arrangement then allows various combinations of direct and indirect heating according to the purpose of heating or according to the types and properties of the materials being dried.

SUBJECT OF THE INVENTION

Claims (3)

SUBJECT OF THE INVENTION 251 301 An apparatus for energy-efficient heating and drying by means of heat pumps connected to waste, atmospheric and / or other unused heat sources, characterized in that they consist of at least one heating space (8) and / or a drying oven (4) forming together with at least two compressors (2, 5, 6) and heat exchangers connected thereto (9, 9a, 9b, 9c) of at least a two-stage system, which are built-in to drive at least one of these compressors (2, 5, 6) in these multistage systems a motor (13) and / or an expansion machine, for example a turbine (10) for converting the energy of the compressed gaseous medium into mechanical work. Device according to claim 1, characterized in that the first suction line (1) for supplying atmospheric air or heat transfer gas flows into a first compressor (2) to which the first discharge line (3, 2a) is connected. leading directly to the heating chamber or dryer (4) or to a heat exchanger (9, 9a) placed there or to a heat exchanger (9a) located outside the heating chamber or dryer (4) but connected to a radiator (9d) there located by means of a forced-circulation piping of the heat transfer medium, while the second suction line (5a) runs either from the heating space or drying chamber (4) or from the first heat exchanger (9a) to the second compressor (5) from which the second discharge line (7) either directly to the drier (4) or to the heat exchanger (9b) within the heating space (8), from where the coupling (7a) leads to the expansion of the compressed heat m A medium for a turbine (10) in which a shaft (11) is provided for transmitting rotational movement from both the turbine (10) and the engine (13) to the compressors (2,5). Device according to Claims 1 and 2 ₍ characterized in that a third suction pipe (6a) is arranged between the heat exchanger (9b) into which the second discharge pipe (7) opens and the coupling (7a) leading to the turbine (10). with a third compressor (6) from which a third discharge line (Tni) extends 11 251 301 to a heat exchanger (9c) located outside or inside the drying chamber (4), while the shaft (11) is adapted to transmit rotational movement from both the turbine (10) and the engine (13) to the third one. of the compressor (6), wherein outside the heat exchangers (9b, 9c). driers or heating space (4) are beverages with radiators (9e, 9f) by means of forced circulation piping