GB2092729A

GB2092729A - Regenerative Dryer

Info

Publication number: GB2092729A
Application number: GB8200002A
Authority: GB
Original assignee: TECHNOSCRIPT AB
Current assignee: TECHNOSCRIPT AB
Priority date: 1981-01-07
Filing date: 1982-01-04
Publication date: 1982-08-18
Also published as: GB2092729B; SE8100042L

Abstract

Surplus heat is extracted from the air circuit of a regenerative drier (which may be a tumble drier) and applied to external purposes. Air enters drier 1 by conduit 2 and leaves by conduit 3 and is recirculated or, alternatively, replaced by fresh air. Heat exchanger 6 uses the exhaust heat to heat the inlet flow of air, and provides a surplus by way of offtake heat exchanger 10. <IMAGE>

Description

SPECIFICATION Method and Apparatus for Drying Material in a Dryer Background of the Invention The present invention relates to a method and an apparatus for drying material in a dryer, for instance drying washing in tumble dryers or drying cabinets, drying textiles in textile industry, grain drying in silo plants, timber drying, drying of chemicals, drying or painted products, etc.

DE-OS 2 630 853 discloses an apparatus for drying material in a dryer and in particular a dryer comprising a housing that encloses the drying part of a paper machine. An inlet conduit for the supply of hot air for the drying and an outlet conduit for the discharge of moist air are coupled to the dryer. The evaporator of a heat pump is coupled to the outlet conduit and the condensor of the heat pump is coupled to the inlet conduit for transmitting heat from the air discharged through the outler conduit to the air incoming through the inlet conduit and, as usual, there are in the flow direction in the heat pump circuit a compressor between the evaporator and the condensor and an expansion vessel between the condensor and the evaporator.Moreover, a further cooling device including a heat pump is in this known apparatus coupled to the outlet conduit after the evaporator of the first mentioned heat pump. In this cooling device, the air is first flowing through a heat exchanger for heat exchange with a heat transport medium flowing in a connected circuit and thereafter through the condensor of the heat pump, and said connected conduit passes after the heat exchanger through the evaporator of the heat pump. This cooling device is arranged for further cooling of the air in the outlet conduit after the first mentioned heat pump and for transmitting heat to said heat transport medium, said transmission of heat taking place in the heat exchanger directly and in the heat pump indirectly.Thus, in this known apparatus further heat is extracted from the discharged air after that the air has passed the evaporator of the first mentioned heat pump by allowing it to pass said cooling device, involving for this heat extraction a comparatively complicated and expensive equipment coupled to the outlet conduit.

Summary of the Invention The present invention includes like the apparatus according to DE-OS 2 630 853 inlet and outlet conduits to a dryer, said conduits being in a corresponding way coupled to a heat pump for transmitting heat from the air discharged from the dryer to the air supplied to the dryer.

In accordance with the present invention and as distinguished from prior art, for instance as disclosed in DE-OS 2 630 853, excess heat above the heat required for the exchange of heat in the condensor to the air supplied to the dryer and existing after the compressor in the heat pump circuit is extracted out of the heat pump by heat exchange. In this way, said excess heat can, in a simple and particularly from energy point of view economic way be obtained at a high temperature and can be used for a variety of applications, such as space heating, water heating, process heat, etc.

Preferred Embodiments In order to explain the invention with its characteristics and advantages more in detail, some embodiments of the invention are in the following described with reference to the accompanying drawings, in which: Fig. 1 shows schematically simplified a principal design of a drying apparatus according to the invention.

Figs. 2 and 3 show also schematically simplified and in a similar way as in Fig. 1 two other embodiments of a drying apparatus according to the invention.

In the embodiments shown on the drawings corresponding details in the various apparatuses have been designated with the same reference numerals.

In all embodiments heated air is supplied to a dryer 1 through an inlet conduit 2 and humid air is discharged from the dryer through an outlet conduit 3. The air is blown by a fan 4 to the dryer.

The inlet conduit 2 passes through the condensor 5 of a heat pump, commonly designated by the reference numeral 6, and the outlet conduit passes through the evaporator 7 of the heat pump. A compressor 8 and an expansion vessel 9 are arranged in the heat pump circuit.

In Figs. 1 and 2 the air circuit is shown closed, while it in Fig. 3 is shown open.

According to the present invention the excess heat produced in the heat pump cycle is utilized.

This takes place by allowing the medium in the heat pump circuit to pass after the compressor 8 a heat exchanger 10. Existing excess heat above the heat required for raising the air temperature in the inlet conduit 2 to the dryer for obtaining correct value for the drying is in the heat exchanger 10 controllably (not shown) extracted from the heat pump circuit. In other words, the heat amount to be transmitted to the incoming air via the consensor 5 is governing for the amount of excess heat that is extracted from the heat pump circuit by the heat exchanger 10. This excess heat is obtained at a high temperature and can be utilized for various purposes, such as space heating, water heating, process heat, etc.

In the apparatus shown in Fig. 1, all the heat that is recovered from the air leaving the dryer 1 must be transmitted by the heat pump 6. The temperature difference between the air before and after the evaporator 7 is, however, considerable and therefore a portion of the heat recovery could take place by heat exchange in the air circuit after the dryer. Such an apparatus is shown in Fig. 2. The air flows from the dryer 1 through a heat exchanger arranged ahead of the evaporator 7. The cold air leaving the evaporator 7 flows through the heat exchanger 11 in which it absorbs a portion of the heat from the air exhausting from the dryer, while the remaining heat in this air is extracted in the evaporator 7.

The amount of heat handled by the heat pump circuit and thereby the effect of the heat pump will in such an apparatus be reduced considerably compared with the apparatus according to Fig. 1.

Particularly in the case that the material being dried emits undesired substances, an apparatus according to Fig. 3 could be used. This apparatus is principally the same as the apparatus of Fig. 2.

The air circuit is, however, now open but the heat recovery is still complete.

An apparatus according to the invention and particularly an apparatus according to Fig. 2 could be economically advantageous to use also in private homes, but particularly such an apparatus is an economically advantageous solution for washing machines and tumble dryers in large blocks of flats where such machines are used in a larger extent. The apparatus shown in Fig. 2 should be of still more economic advantage in laundries and self-service launderettes, where washing machines and tumble dryers are used very intensively. Textile industries is another advantageous application field. Since the process heat demand in this industry is high, the heat pump could be driven by a diesel engine. The utilization of the heat from the jacket cooling water and the exhaust gases, together with the benefits offered by the heat pump, should have a substantial effect on the overall energy demand.

The apparatus according to Fig. 3, possibly also combined with a diesel motor, can be beneficial to grain silo plants, where the drying air is explosive on leaving the silo. On the other hand, the "scrubbing" action of the heat exchanger 11 and the evaporator 7 can in the apparatus according to Fig. 2 be so effective that also this apparatus is possible to use in this field. It is as an alternative conceivable to use the apparatus according to claim 2 together with an inert gas.

An apparatus according to Fig. 2 or Fig. 3 can also be used for timber drying, drying of chemicals, drying of painted products, etc.

If the substances liberated in connection with drying are commercially usable or can be reused in the manufacture process, these substances can be recovered either by their condensation on the evaporator 7 or by recovery from the water condensed out on the evaporator.

The invention is not limited to the embodiments described above and shown on the drawings but can be varied in several ways within the frame of the following claims. For instance, the heat exchanger 10 must not be arranged ahead of the condensor as shown, but it can be positioned on the other side of the condensor or in parallel with the condensor.

Claims

1. A method for extracting heat out of a circuit coupled to a dryer for drying material therein, wherein air flowing in an air circuit before and after the dryer passes respectively a condensor and an evaporator of a heat pump for transmitting heat from the air after the dryer to the air before the dryer, and wherein the medium flowing in the heat pump circuit in its flow direction is compressed between the evaporator and the condensor and is expanded between the condensor and the evaporator, characterized in that the medium flowing in the heat pump circuit is in its compressed state heat exchanged for extracting out of the heat pump circuit excess heat above the heat required for the transmission of heat in the condensor to the air supplied to the dryer.

2. A method according to claim 1, characterized in that the heat amount required for said transmission of heat in the condensor governs the amount of extracted excess heat.

3. A method according to claim 1 or 2, characterized in that the heat exchange for the extraction of excess heat takes place in the flow direction before the condensor.

4. An apparatus for extracting heat out of a circuit coupled to a dryer (1) for drying material therein, including an air circuit with an air conduit (2) incoming to the dryer and an air conduit (3) outgoing from the dryer, a heat pump (6), the condensor (5) of which is coupled to the incoming air conduit (2) and evaporator (7) is coupled to the outgoing air conduit (3) for transmitting heat from the air in the outgoing air conduit to the air in the incoming air conduit, a compressor (8) arranged in the heat pump circuit in the flow direction between the evaporator (7) and the condensor (8), and expansion means (9) arranged in the heat pump circuit in the flow direction between the condensor (18) and the evaporator (7), characterized in a heat exchanger (10) arranged in the heat pump circuit after the compressor (8) for extracting out of the heat pump excess heat above the heat required for the transmission of heat in the condensor (5) to the air in the incoming air conduit (2).

5. An apparatus according to claim 4, characterized in control means for governing extracted amount excess heat in the heat exchanger (10) in response to the required transmission of heat in the condensor (5).

6. An apparatus according to claim 4 or 5, characterized in that the heat exchanger (10) is arranged between the compressor (8) and the condensor (5).