GB2067732A

GB2067732A - Drying organic solid materials

Info

Publication number: GB2067732A
Application number: GB8038791A
Authority: GB
Original assignee: Voestalpine AG
Current assignee: Voestalpine AG
Priority date: 1980-01-21
Filing date: 1980-12-03
Publication date: 1981-07-30
Also published as: JPS56104996A; DE3045762C2; YU41759B; DD157017A1; AU6605481A; PL229299A1; IN152919B; DE3045762A1; AT366090B; PL131417B1; AU522318B2; CA1153200A; GB2067732B; ATA31180A; YU12781A

Abstract

For the purpose of drying organic solid materials, particularly brown coals, the preheated solid materials are continuously passed through at least one drying stage (2) and subjected to the action of saturated steam at super-atmospheric pressure and at elevated temperature. Condensed water and water expelled from the solid materials is at least partially removed, and the solid materials are transferred into a steam atmosphere (4) which is at a temperature of at least 200 DEG C and is supplied with superheated steam. The solid materials are centrifuged within this steam atmosphere, the steam of this steam atmosphere being passed along a closed circle 5 ... 7 through at least one heat exchanger (6) for obtaining and/or maintaining the temperature of at least 200 DEG C. Excess steam is tapped off at 10 and supplied to stage (2). Finally, the solid materials are, after having been centrifuged, removed from the steam atmosphere 4 and pressure-released at 9, whereupon the solid materials are, if desired, immediately transferred to a hot briquetting plant (13). <IMAGE>

Description

SPECIFICATION Process for drying and modifying organic solid materials, particularly brown coals and use thereof The present invention refers to a process for drying and modifying organic solid materials, particularly brown coals, by means of steam as well as to a preferred type of use of brown coals having been dried and modified according to this process. When drying brown coal it has been recognized that the frequently considerable humidity content of brown coal has its origin in water absorbed within the capillaries but also in chemically bound water which can be removed only with great energy consumption when drying the coal by immediately heating the coal. It is already known that this water can be expelled by steam or also by hot water. There are also known processes which make it possible to perform the drying process in a semi-continuous manner.Such known processes have made in most cases an essentially better use of the energy supplied than the original Fleissner-process, but the problem of water removal was with this known processes only solved in an unsatisfying manner. With all these processes, the solid materials are, after having been dried under the action of saturated steam or hot water, subjected to a further drying operation and, respectively, a final drying operation by aeration. The obtained dried solid materials still show a water content which, however, is low.

The present invention particularly refers to a process for drying of organic solid materials, particularly brown coals, in which the preheated solid materials are continuously passed through a drying stage operated with saturated steam and are in this drying stage subjected to the action of saturated steam under superatmospheric pressure and elevated temperature.It is an object of the present invention to improve the dryirig effect achieved by such a process and to improve the economy of such a process and the invention essentially consists in that the solid materials are subsequently further dried in a steam atmosphere at a temperature of the steam atmosphere of at least 2000C thereby supplying superheated steam and centrifuging the solid materials, in that the steam of the steam atmosphere is passed along a closed circuit through at least one heat exchanger for obtaining and, respectively, for maintaining the temperature of the steam atmosphere, in that the excessive portion of the steam to be supplied to the heat exchanger is tapped off and introduced into the drying stage operated with saturated steam and in that the solid materials are, after having been centrifuged, discharged from the steam atmosphere and pressure-released.In view of supplying superheated steam into the steamatmosphere, the solid materials are treated within this steam-atmosphere under high temperatures so that the final water content of the solid materials is still further reduced. In view of centrifuging the solid materials, water removal from the solid materials is mechanically enhanced by the centrifugal force thus increasing the drying efficiency. By this measure, the solid materials are energetically activated so that, as has been found, the drying effect is substantially increased. When treating brown coals, centrifuging and the energetic activation of the brown coal associated therewith has an effect that bitumen contained in the brown coal is accumulated at the surface of the coal lumps or grains, so that the inflammability of the brown coal is improved.According to a preferred embodiment of the invention, the brown coals treated according to this process are finegrain brown coal having a particle-size of 1 Mm to 5 mm.

According to a further preferred embodiment of the invention, the steam passed along a closed circuit is passed within the steam atmosphere where the solid materials are centrifuged in countercurrent to the solid materials. The steam is entering the steam atmosphere where the solid materials are centrifuged as superheated steam and is there cooled by contact with the solid materials. This cooled steam, which flows out of the steam atmosphere and a portion of which is introduced into the drying stage operated with saturated steam, becomes, by contact with the solid materials releasing water, saturated steam at any rate. According to the invention the steam is, within the steam circuit, tapped from the steam atmosphere in form of saturated steam and supplied to the steam atmosphere in form of superheated steam.

The steam passed along a closed circuit can, according to the invention, be heated by external heat, for example by the flue gases of a boiler plant used for generating the steam required for the drying stage operated with saturated steam. In this manner, heat energy at disposal from the process itself is made use of, thus increasing the economy of the process.

According to the invention the steam atmosphere is conveniently maintained under a pressure of approximately 40 bar and has a temperature of 350 to 5500 C. The steam passed along a closed circuit can, in this case, be tapped off the steam atmosphere with a temperature of approximately 2500C and be heated to a temperature of approximately 5500C prior to being recycled into the steam atmosphere.

Saturated steam produced in a boiler-plant can be supplied to the drying stage operated with saturated steam. According to a preferred embodiment of the invention, more than the excessive portion of the steam to be supplied into the heat exchanger is, however, tapped off and introduced into the drying-stage operated with saturated steam, fresh steam, particularly fresh saturated steam, being supplied to the steam circuit at a position between the tap-off position and the heat exchanger. In this case it is possible to tap off from the steam circuit, however, the total amount of steam required for the drying stage operated with saturated steam.This provides the advantage that to the drying stage operated with saturated steam, the steam is supplied with a higher temperature than the temperature of the steam coming from the boiler plant, because the steam passed along a closed circuit and being replenished by the steam coming from the boiler plant is again reheated within the heat exchanger and is introduced into the steam atmosphere.

In practice, the process according to the invention can be performed such, that fresh steam is supplied to the steam circuit in an amount corresponding to approximately 20% of the amount of steam recycled into the steam atmosphere, the amount of steam tapped off the steam circuit and introduced into the drying stage operated with saturated steam approximately corresponding to 50% of the amount of steam recycled into the steam-atmosphere and the amount of steam tapped off the steamatmosphere approximately corresponding to 130% of the amount of steam recycled into the steam atmosphere.

A preferred use of brown coals dried and modified according to the process of the invention is, when using such coals for producing briquettes or for gas-production, is characterized in that the brown coals are, after having been pressurereleased, used for gasification or briquetting in a still hot condition. On centrifuging, bitumen is accumulated on the surface of the coal grains.

Such accumulation of bitumen on the surface of the coal grains provides a substantial advantage during subsequent briquetting, because the individual coal grains can better mutually be bounded on briquetting. When briquetting coals it is, of course, advantageous to add bitumen, but this measure can be omitted when working according to the process according to the invention. Benefication of the brown coal can, however, also be effected by gasification of the brown coals and also in this case the accumulation of bitumen on the surface of the coal grains results in essential advantages. In view of further water being removed from the solid materials within the steam atmosphere, the amount of steam is increased and at least the portion of steam resulting therefrom must be tapped off the steam circuit.In view of this tapped-off portion of steam being introduced into the drying-stage operated with saturated steam, this saturated steam can be used in the drying stage operated with saturated steam thus increasing the economy of the process. This is possible without further because the solid materials are pressure released only after having been centrifuged and, respectively, after having been discharged from the steam atmosphere.

The invention is further illustrated with reference to the figure of the drawing schematically illustrating drying of brown coal in a flow-chart.

The preheated brown coal is supplied into the drying stage 2 operated with saturated steam at 1 and is dehumidified there to a great extent by contact with saturated steam at a pressure of approximately 40 bar. After separation of the water foamed, the brown coal enters at 3 an atmosphere 4 of hot steam and is centrifuged within this atmosphere 4 under a pressure of approximately 40 bar which is maintained within this atmosphere. Steam is extracted from or tapped off this atmosphere at 5, fed through a heat exchanger 6 and recycled into the steam atmosphere 4 at 7, thereby closing the steam circuit. The solid materials are discharged at 8 and pressure released to atmospheric pressure within a pressure release stage 9.Steam is flowing out at 5 from the atmosphere 4 of hot steam with a temperature of approximately 2500C, is then heated within the heat exchanger 6 and is at 7 recycled into the atmosphere 4 of hot steam with a temperature of approximately 5500C. The location 5, where steam is tapped off the steam atmosphere 4, is located adjacent the supply end 3 and the location 7, where steam is recycled into the steam atmosphere 4, is located adjacent the discharge end 8. Therefore the steam is flowing within the steam atmosphere 4 in countercurrent to the brown coal At the location 10, a portion of the steam is tapped off for being supplied into the drying stage 2 operated with saturated steam.

This portion of steam corresponds to the whole amount of saturated steam required in the drying stage 2 operated with saturated steam. The amount of steam tapped off is greater than the amount for which the amount of steam is increased by the water expelled from the brown coal within the steam atmosphere 4. Therefore, saturated steam coming from a boiler plant 11 is introduced at the location 12 into the steam circuit, thus compensating the amount of steam tapped off at the location 10, which amount is exceeding the amount of steam expelled from the brown coal within the steam atmosphere.

The brown coal is supplied at the location 1 in form of fine grains having a particle size of 1 ym to 5 mm. The dried brown coal coming from the pressure-release station 9 is briquetted in a hot briquetting plant 1 3.

Claims

1. Process for drying and modifying of organic solid material in which the preheated solid materials are continuously passed through at least one drying stage operated with saturated steam and are in this drying stage subjected to the action of saturated steam under superatmospheric pressure and elevated temperature, the condensed water and the waste water expelled from the solid materials being at least partially discharged, characterized in that the solid materials are subsequently further dried in a steam atmosphere at a temperature of the steam atmosphere of at least 2000C thereby supplying superheated steam and centrifuging (4) the solid materials, in that the steam of the steam atmosphere is passed along a closed circuit through at least one heat exchanger (6) for obtaining and, respectively, for maintaining the temperature of the steam atmosphere, in that the excessive portion of the steam to be supplied to the heat exchanger (6) is tapped off and introduced into the drying stage (2) operated with saturated steam, and in that the solid materials are, after having been centrifuged (4), discharged from the steam atmosphere and pressurereleased.

2. Process as claimed in claim 1, characterized in that the said organic material is a brown coal in the brown coals to be treated are used in form of fine grains having a particle size of 1 Mm to 5 mm.

3. Process as claimed in claim 1 or 2 characterized in that the steam passed along a closed circuit is passed within the steam atmosphere where the solid materials are centrifuged in countercurrent to the solid materials.

4. Process as claimed in any of claims 1, 2 or 3 characterized in that the steam is, within the steam circuit, tapped from the steam atmosphere in form of saturated steam and supplied to the steam atmosphere in form of superheated steam.

5. Process as claimed in any of claims 1 to 4, characterized in that the steam passed along a closed circuit is heated by external heat, for example by the flue gases of a boiler plant (11) used for generating the steam required for the drying stage (2) operated with saturated steam.

6. Process as claimed in any of claims 1 to 5, characterized in that the steam atmosphere is maintained under a pressure of approximately 40 bar and has a temperature of 350 to 5500 C.

7. Process as claimed in any of claims 1 to 6, characterized in that the steam passed along a closed circuit is tapped off the steam atmosphere with a temperature of approximately 2500C and is heated to a temperature of approximately 5500C prior to being recycled into the steam atmosphere.

8. Process as claimed in any of claims 1 to 7, characterized in that more than the excessive portion of the steam to be supplied into the heat exchanger (6) is tapped off and introduced into the drying stage (2) operated with saturated steam, fresh steam, particularly fresh saturated steam, being supplied to the steam circuit at a position between the tap-off position (10) and the heat exchanger (6).

9. Process as claimed in any of claims 1 to 8, characterized in that the total amount of steam required for the drying stage (2) operated with saturated steam is tapped off from the steam circuit.

10. Process as claimed in claim 8 or 9, characterized in that fresh steam is supplied to the steam circuit in an amount corresponding to approximately 20% of the amount of steam recycled into the steam atmosphere, the amount of steam tapped off the steam circuit and introduced into the drying stage operated with saturated steam approximately corresponding to 50% of the amount of steam recycled into the steam atmosphere and the amount of steam tapped off the steam atmosphere approximately corresponding to 130% of the amount of steam recycled into the steam atmosphere.

11. Process for drying and modifying organic solid materials as claimed in claim 1, substantially as hereinbefore described with particular reference to the accompanying drawing.

12. Use of brown coals dried and modified according to the process according to any of claims 1 to 11 for producing briquettes or for gas production, characterized in that the brown coals are, after having been pressure-released (9), used for briquetting (13) or gasification in a still hot condition.