Evaporation dryer and method for operating same

Abstract

The invention relates to an evaporation dryer (1) for drying particles, having—a process chamber (10) with at least one product inlet (11) for supplying the particles to be dried into the process chamber (10) and a product outlet (12) for discharging dried particles from the process chamber (10), —a heat exchanger (20) arranged within the process chamber (10), —having at least one inlet (21, 211) into the heat exchanger (20) for pressurized steam as process steam and at least one condensate outlet (22, 222) from the heat exchanger (20), wherein—the at least one condensate outlet (22, 222) is connected to an expansion tank (30), wherein at least one pump (40) is connected to the expansion tank (30), and the expanding steam is pumped out of the expansion tank (30) and supplied to the process steam.

Claims

1. An evaporation dryer for the drying of particles, comprising: a process chamber having at least one product inlet for feeding of particles to be dried into a process chamber space and having a product outlet for evacuation of dried particles from the process chamber; a heat exchanger arranged within the process chamber, the heat exchanger comprising at least one inlet for highly pressurized steam as heating steam and at least one condensate outlet connected to an expansion tank, wherein the expansion tank is connected to at least one pump which pumps off flash steam from the expansion tank and supplies the flash steam to the heating steam, wherein the heat exchanger is of multi-stage construction having at least a first stage and a second stage, wherein to the first stage comprises a mixed steam of the heating steam and the flash steam, and wherein the second stage is configured such that the heating steam is fed to the heat exchanger.

2. The evaporation dryer as claimed in claim 1, wherein the first and second stages are assigned separate condensate tanks which are coupled to the expansion tank.

3. The evaporation dryer as claimed in claim 2, wherein the separate condensate tanks are coupled to the expansion tank via a control valve.

4. The evaporation dryer as claimed in claim 2, wherein the separate condensate tanks each have a pressure level equating to or below a pressure of the heating steam.

5. The evaporation dryer as claimed in claim 2 further comprising a connecting line from the expansion tank leads to a mixing point arranged downstream of a steam generating device, wherein the heating steam is mixed with condensate from the expansion tank and/or the separate condensate tanks in the mixing point.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) An illustrative embodiment of the invention is explained in greater detail below with reference to the single FIGURE.

(2) The FIGURE is a schematic representation of an evaporation dryer plant with a fluidized-bed evaporation dryer.

DETAILED DESCRIPTION

(3) In the FIGURE, an evaporation dryer 1 in the form of a fluidized-bed evaporation dryer is represented. The evaporation dryer 1 has a process chamber 10 having a product inlet 11 for the feeding of particles to be dried, for instance wood chips, chips, pellets or other fluidizable particles having a moisture content which is to be reduced. Upstream of the product inlet 11 can be arranged devices for feeding the particles out of a store 13, in the represented illustrative embodiment these are a star feeder and a worm conveyor, which are both operated by motorized means. At the product outlet 12, a motor-driven worm conveyor and a star feeder, which convey the ready dried product into an expansion cyclone 14, are arranged in reverse order. The structure of the fluidized-bed evaporation dryer 1 provides a substantially cylindrical housing 15 having a heat exchanger 20 which is arranged centrally therein and which can be formed of a multiplicity of heat exchanger elements. As an alternative to a substantially cylindrical housing 15, this can also be of conically tapered configuration or be formed of a combination of cylindrical and conical portions. The heat exchanger 20 forms together with the cylindrical housing 15 the ring-like process chamber 10. Insofar as the heat exchanger 20 too has a round outer contour, the process chamber 10 is annular, while, in principle, also polygonal inner and outer contours of the process chamber 10 are possible. Outside the evaporation dryer 10, a control valve 57 for the dryer pressure is arranged. By way of a conveying device 16, a fluidizing agent in the form of vapor or steam is passed from below through a sieve tray on the underside of the process chamber 10. Within the process chamber 10 are arranged vertical walls, or walls inclined in the direction of conveyance, so that the annular process chamber 10 is divided into individual cells. The walls can reach right up to the sieve tray and enable at their upper ends, and, where appropriate, at further openings (not represented), a transfer to adjacent cells, so that the fluidized product or the fluidized particles are transported from the product inlet 11 to the product outlet 12 through the whole of the process chamber 10. It is advantageous if the inlet cell lies directly next to the outlet cell, so that the product must move once around the heat exchanger 20 through the process chamber 10. As soon as the discharge cell is reached, the dried product can there be transported away by the appropriate conveying devices. This structure is fundamentally known, for instance from EP 1 956 326 A1.

(4) In the represented illustrative embodiment, the heat exchanger 20 is of two-stage configuration and has two inlets 21, 211, via which heating steam is passed from a steam generating device 2, for instance a boiler house, which provides highly pressurized heating steam on the one hand for operating a turbine for the generation of electrical energy and on the other hand for providing steam for the drying of the particles, into the heat exchanger 20. The respective inlet 21, 211 is arranged in the upper part of the respective heat exchanger stage or superheater stage. On the respective underside of the vertically oriented heat exchanger stages 23, 25 are arranged the corresponding condensate outlets 22, 222. The condensate outlets 22, 222 lead to separate condensate tanks 33, 35, in which the condensate coming from the respective heat exchanger stage 23, 25, which condensate is under the operating pressure of the heat exchanger, is collected. On the outlet side, to each condensate tank 33, 35 is assigned a control valve 53, 55, via which the condensate to be evacuated is regulated in terms of the fill level in the condensate tank 33, 35. From the condensate tanks 33, 35, lines lead to a common expansion tank 30, in which the condensate from both heat exchanger stages 23, 25 and, where appropriate, from heating surfaces (not described in detail) is collected. In the expansion tank 30, a pressure which is lower than the operating pressure of the heat exchanger 20 prevails. The condensate collected therein has a substantially lower temperature than the condensate in the condensate tanks 33, 35, and a likewise lower temperature in comparison to the heating steam. The temperature difference dictates the formation of flash steam.

(5) In the process chamber 10 are additionally arranged internal heating surfaces 28 or heating plates, in which condensate can likewise form, which condensate is conducted via a condensate line, having a built-in condensate drain 37, to the expansion tank 30. As an alternative to a direct supply line, condensate from the heating surfaces 28 can also be conducted via the condensate tanks 33, 35 for the heat exchanger stages 23, 25 to the expansion tank 30.

(6) From the expansion tank 30, a flash steam line 34 leads to a suction pump 40, which in the represented illustrative embodiment is configured as a steam jet pump. At the steam jet pump 40, heating steam from the steam generating device 2 is present at a motive steam port 41, so that the heating steam is supplied as motive steam to the steam jet pump 40. Upstream of the steam jet pump 40 is connected a control valve 54, in order to be able to control the operating pressure of the motive steam. Within the steam jet pump 40, the heating steam is mixed with the flash steam from the expansion tank 30, so that the condensate, which due to the suction process by the steam jet pump 40 has turned back into steam, mixes as flash steam with the heating steam. The quantity of steam fed to the first heat exchanger stage 23 is thereby increased.

(7) Before the control valve 54, the heating steam line branches off from the steam providing device 2. Via an upper line branch, a partial flow is conducted via a control valve for driving an ejector 17 within the process chamber 10. A substantially greater steam quantity is conducted into the second heat exchanger stage 25, which is arranged beneath the first, upper heat exchanger stage 23. At the second heat exchanger stage 25, a higher steam pressure obtains than in the first heat exchanger stage 23. By way of the quantity of the admixed flash steam from the expansion tank 30, it is possible to set different pressures for the first heat exchanger stage 23, so that an adaptation to the respectively different heat requirement is possible and the dryer performance, in particular in a partial load operation, is easily adjustable. For an elevation of the dryer performance, the fed quantity of flash steam is reduced, so that, in extremis, both heat exchanger stages 23, 25 are able to be operated with the unmixed heating steam.

(8) From the expansion tank 30, or alternatively, in a variant (not represented), from other condensate tanks, a condensate line 42 leads to a mixing point 3, in which condensate is admixed to the original heating steam from the steam providing device 2 after the heating steam has passed through a control valve 52. It is thereby possible to adjust, according to requirement, the quality of the steam fed to the evaporation dryer 1, in particular to lower the pressure and the temperature and to increase the total steam quantity.

(9) Downstream of the expansion tank 30 is connected a further tank 36 for receiving condensate at a lower temperature and a lower pressure, which condensate can continue to be used.

REFERENCE SYMBOL LIST

(10) 1 evaporation dryer 2 steam generating device 3 mixing point 10 process chamber 11 product inlet 12 product outlet 13 store 14 expansion cyclone 15 cylindrical housing 16 conveying device 17 ejector 20 heat exchanger 21 heating steam inlet, upper heat exchanger 22 condensate outlet, upper heat exchanger 23 upper heat exchanger 25 lower heat exchanger 28 internal heating surfaces 30 expansion tank 33 condensate tank, upper heat exchanger 34 flash steam line 35 condensate tank, lower heat exchanger 36 condensate tank 40 pump 41 motive steam port 42 condensate line to the mixing point 53 control valve, upper heat exchanger 54 control valve for motive steam 55 control valve, lower heat exchanger 57 control valve for dryer pressure 211 heating steam inlet, lower heat exchanger 222 condensate outlet, lower heat exchanger