IE55322B1 - Plant for drying animal or vegetable material - Google Patents

Description

2 The present invention relates to a method and plant for drying animal or vegetable material, using two or more heat treatment apparatuses for successive heat treatment of the material.

It is well known within various branches of industry to employ waste heat from a first heat treatment apparatus - in the form of recompressed exhaust steam in a subsequent heat treatment apparatus. In known process techniques the waste heat is usually employed in the form of impure exhaust gas or impure process exhaust steam, and such known, secondary heat medium as a consequence of the impurities in the exhaust steam or exhaust gas from the first heat treatment apparatus place special material technical demands on -compressor(s) and on remaining process apparatus for the said subsequent heat treatment apparatus. These special demands involve complicated and expensive apparatus.

The main object of the present invention is to obtain a possibility for employing compressors and other apparatus which is simple and inexpensive in procurement as well as in use.

The invention provides a plant for drying animal or vegetable material, comprising at least two heat treatment apparatuses connected in series relative to a flow of the material therethrough: a conduit extending from one of the heat treatment apparatuses for exhausting waste gas: a first closed circuit for circulating a flow of water, including a circulating pump and a tank; a heat exchanger between the said conduit and the first closed circuit for transferring heat from waste gas flowing in the said conduit to water flowing in the 3 first closed circuit, the heat exchanger being upstream of the tank of the first closed circuit so that the tank receives a flow of heated water; a second closed circuit connected to the tank of the first closed circuit and with the other or another of the heat treatment apparatuses to receive and convey a flow of water vapour from the tank through the said other heat treatment apparatus in heat exchange relation with the material flowing therethrough, the second closed circuit including a compressor or compressors for compressing the flow of water vapour upstream of the said other heat treatment apparatus.

The invention also provides a method of drying a flow of animal or vegetable material, comprising passing the flow of material sequentially through at least two heat treatment apparatuses; exhausting hot waste gas from one of the heat treatment apparatuses;· passing the hot waste gas in heat exchange relation with a flow of water circulating in a first closed circuit to heat the water; separating a flow of water vapour from the heated water in the closed circuit; passing the flow of water vapour in a second closed circuit through the other or another of the heat treatment apparatuses to heat the flow of material therein and thereafter return the flow of vapour to the first closed circuit; and compressing the flow of water vapour in the second closed circuit upstream of the said other heat treatment apparatus.

By employing a secondary heat medium circuit, based on uncontaminated water which is circulated in a closed circuit, the problems with the impurities in the exhaust steam or the exhaust gas from the first heat treatment apparatus are avoided, and equipment of conventional d construction materials, such as mild steel, can thereby be employed in the second apparatus. In other words, corrosion of the material can be avoided at the surfaces which are only exposed to uncontaminated water and 5 uncontaminated water vapour, respectively. In addition, process-associated disturbances are avoided which are due to entrained particles, entrained impure fluid drops, scum formations, and the like.

Even if the plant requires extra energy for 10 operating pump and compressor in the closed circuits, there are obtained operatively economic favourable results as a consequence of the advantages of using uncontaminated water and water vapour in the closed circuits.

The invention will be further described in the following description having regard to the accompanying drawing, which illustrates a process diagram of a plant for drying a flow of animal or vegetable material.

The plant illustrated in the accompanying drawing 20 comprises two heat treatment apparatuses 1 and 2. By broken lines there is shown, respectively, a feed conduit 3 for the material which is to be treated in the apparatus 1. a transfer conduit 4 for the material between the apparatus 1 and the apparatus Z. and a 25 discharge conduit 5 for the material from the apparatus 2. If desired, there can be present in series with the apparatus Z or in series with the apparatus 1 one or more additional apparatuses (not shown further). The apparatus 2 and possible further apparatuses effect 50 heating of the material or portions of the latter by means of waste heat from the apparatus 1.

In the illustrated embodiment there is a conduit 6 for exhaust gas or exhaust steam or a mixture of exhaust gas and exhaust steam from the apparatus 1. The conduit 55 6 leads the gas/steam via a primary duct 7 in a heat exchanger 8 to a discharge conduit 9 to a collection location (not shown).

The heat exchanger 8 has a secondary duct 10 which is included in a separate, closed circuit for uncontaminated water to which heat is supplied in the heat exchanger 8 from the gas/steam waste heat duct of 5 the primary side. From the secondary duct 10 in the heat exchanger 8 extends a conduit ll, in which a regulating valve 12 is inserted and by which water heated in the heat exchanger is supplied to the upper portion of a flash tank 13. From the bottom of the 10 flash tank 13 a return conduit 14 extends via a pump 15 back to the secondary duct 10 in the heat exchanger 8, so that by repeated circulation of water from the tank 13 to the heat exchanger duct 10 the temperature of the circulating water can be increased.

From the top of the flash tank 13 water vapour is drawn outwardly via a conduit 16 to a compressor 17 which brings the pressure of the water vapour upwards from a pressure of below 1.5 bar (absolute pressure) to process steam pressure.

In the conduit 6 between the heat treatment apparatus 1 and the heat exchanger 8 one operates with an exhaust gas temperature of between 80 and ΙΟΟ'Ό at a pressure of 0.8 to 1.5 bar (dependent upon what medium one dried in the heat treatment apparatus l). In the 25 conduit 16 between the flash tank 13 and the compressor 17 one operates correspondingly with a temperature of between 60 and 100°C and at a pressure of 0.2 to 1 bar. In a conduit 18 between the compressor 17 and the second heat treatment apparatus 2 one operates at a pressure of 30 between 1.0 and 4.0 bar, depending upon the type and number of compressors.

Hater vapour at process steam pressure is thus led from the compressor 17 via the conduit 18 to the heat treatment apparatus 2 and - still in a closed circuit -35 through the apparatus 2 and outwardly from the latter in the form of exhaust steam and condensate via a conduit 6 19 back..to the tank 13. By means .of the closed heat medium circuits, in which uncontaminated water and water vapour circulate respectively, conduits 11, 14, 16, 18, 19 together with valve 12, tank 13, pump 15. and 5 compressor 17 can be made of conventional construction materials (for example mild steel). The metal in or the contact surfaces in the heat exchanger 8 and in the apparatus 2, respectively, can on the other hand be of special construction with respect to the contacts with 10 the medium in the primary duct 7 and the contact with the material which is to be heat treated in the apparatus 2, respectively. λ ventilation conduit 20 with an associated ventilation valve 21 is used for venting the secondary heat medium circuit of the plant.

Claims (8)

1. 7 1. Ά plant for drying animal or vegetable material, comprising at least two heat treatment apparatuses connected in series relative to a flow of the material therethrough: a conduit extending from one of the heat treatment apparatuses for exhausting waste gas: a first closed circuit for circulating a flow of water, including a circulating pump and a tank: a heat exchanger between the said conduit and the first closed circuit for transferring heat from waste gas flowing in the said conduit to water flowing in the first closed circuit, the heat exchanger being upstream of the tank of the first closed circuit so that the tank receives a flow of heated water; a second closed circuit connected to the tank of the first closed circuit and with the other or another of the heat treatment apparatuses to receive and convey a flow of water vapour from the tank through the said other heat treatment apparatus in heat exchange relation with the material flowing therethrough, the second closed circuit including a compressor or compressors for compressing the flow of water vapour upstream of the said other heat treatment apparatus.

2. A method of drying a flow of animal or vegetable material, comprising passing the flow of material sequentially through at least two heat treatment apparatuses; exhausting hot waste gas from one of the heat treatment apparatuses; passing the hot waste gas in heat exchange relation with a flow of water circulating in a first closed circuit to heat the water; separating a flow of water vapour from the heated water in the closed circuit: 8 passing the flow of water vapour in a second closed circuit through the other or another of the heat treatment apparatuses to heat the flow of material therein and thereafter return the flow of vapour to the first closed circuit; and compressing the flow of water vapour in the second closed circuit upstream of the said other heat treatment apparatus.

3. A method as claimed in claim 2. in which the flow of water vapour in the second closed circuit is compressed to a pressure between 1.0 and 4.0 bar.

4. A method as claimed in claim 2 or 3, in which the flow of water vapour from the first closed circuit is at a temperature between 60eC and l00eC.

5. A method as claimed in any of claims 2 to 4. in which the flow of hot waste gas from the said one heat treatment apparatus is at a temperature between 80°C and 100°C and a pressure of 0.8 to 1.5 bar.

6. A plant as claimed in claim 1 for drying animal or vegetable material, substantially as described, with refer-ence to, and as shown in, the accompanying drawing.

7. A method as claimed in claim 2 of drying animal or vegetable material, substantially as described with reference to the accompanying drawing.

8. Animal or vegetable material whenever dried by a method claimed in a preceding claim. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.