CZ20001094A3 - Process for removing water from brown coal - Google Patents

Abstract

The invention relates to a process for dewatering raw brown coal used as a power plant fuel for producing electric current. According to the invention, the process consists in heating the raw brown coal by introducing hot water and/or steam at a working temperature ranging from 60 to 200 degC and feeding it as coal slurry into a solid wall centrifuge (2), the working chamber of which is under a pressure corresponding to the steam pressure at the working temperature wherein water bound in the raw coal is then separated by centrifuging and discharged from the solid wall centrifuge (2) working chamber as excess to be further on used in direct or indirect pre-heating of raw coal to be dewatered.

Description

Method of removing water from brown coal

Technical field

The invention relates to a process for removing water from brown coal.

Crude lignite contains a considerable amount of water, which is physically and chemically bound in capillaries and pores. The bound water content may be up to 65% by weight. The combustion of undried brown coal from which water is not removed results in considerable heat loss due to evaporation of the water contained in the fuel. A significant increase in the calorific value and a reduction in the electricity production costs of lignite power plants can be achieved by substantially reducing the water content of the raw lignite.

BACKGROUND OF THE INVENTION

In the process known from WO 96/10064, the raw brown coal from which water is to be removed is conveyed to a filter press and heated by means of the supplied steam. During steam heating, the fuel in the pressure chamber of the filter press is subjected to a pressure that is less than the pressure of the saturated steam supplied. When an operating temperature sufficient to break the physical / chemical bonding of the water in the fuel is reached, the pressing pressure is increased to values above 20 bar and the water is separated by filtration. In known measures, batch plate filters can be used, or a continuous filter press which operates in continuous operation and which is modeled on a double belt belt press can be used. Especially in a continuous flow filter press, sealing the heated area with respect to the exiting heating steam is very problematic. Further, pressure filtration has the disadvantage.

That the holes in the sieve plates are clogged and the filter current fades over time.

It is also disadvantageous that the extruded water contains a considerable amount of fine solids, which requires expensive waste water treatment.

Other methods of drying brown coal are known from Austrian patents 366 090, 369 423 and 366 405. The brown coal from which water is to be removed is further dried in an autoclave at temperatures above 200 ° C and at high temperatures. preferably at a temperature of about 250 ° C. The corresponding saturated steam pressure generated in the autoclave is approximately 40 bar. The substantially dried product is further fed to a centrifuge in which a final treatment is carried out at the same pressure and temperature. The energy consumption for drying, in which the water contained in the coal turns into steam, is high. Thus, drying in the autoclave is very costly in terms of the necessary machinery.

From Austrian patent no. 380,268 discloses a method for drying of peat, whereby the material to be zbaven'Wdy;'j ^r e after mechanical' pre-drying is brought into a filter centrifuge whose working space has an atmosphere of saturated steam. During the action of saturated steam, the material is mechanically dewatered by centrifugation, whereby the turf of the peat is compressed or compressed, thereby expelling the water contained in the peat. Furthermore, sedimentation centrifuges, known from German Patent Specification No. 28 50 825, are used to pre-dry very wet peat. water from coal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process which allows efficient mechanical-thermal drying of brown coal of high and constant output.

SUMMARY OF THE INVENTION The object of the present invention is to provide a process for drying raw lignite in which raw lignite is heated to a working temperature of between 60 and 200 ° C and supplied as a sludge to a full-scale centrifuge in hot water and / or steam. the pressure of which corresponds to the water vapor pressure at the working temperature. The water bound in the raw lignite is separated by centrifugation and discharged as a surplus from the working space of a full-thickness centrifuge.

Mechanical drying in a solid centrifuge follows a decanting process and is limited to the sedimentation of solids in the centrifuged area. Solid centrifuges, also called decanting centrifuges, are used in known measures to separate liquid, insoluble phases, to clarify a suspension, to thicken sludge, and to wetly separate the dispersed fine-grained components. It is surprising that, in combination with heat treatment, sedimentation in the spin region can also be effectively used to dry raw brown coal, which contains a high proportion of bound water. By clarifying the aqueous residue in a full-walled centrifuge, water is produced which is completely free of solids. This simplifies wastewater treatment. Thus, the process of the invention does not contaminate with fine particulate solids.

The raw lignite to be dewatered is fed to a solid centrifuge with a fixed feed / feed stream. The filling of the centrifuge working space with raw brown coal, which is subjected to steam pressure, can be easily carried out by means of a conveying pump, for example a screw pump. In addition to direct heating, the working space of the full-thickness centrifuge can also be heated indirectly.

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The water discharged from the full-thickness centrifuge has a temperature between 60 ° C and 60 ° C

200 ° C. The waste water energy can be used to directly or indirectly preheat the feed material.

According to a further embodiment of the invention, water is used to heat the fuel and / or the working space of the full-scale centrifuge coming from the steam jet driving the turbine of the power plant. In a brown coal power plant with a combined water vapor circulation, the water vapor required for mechanical-thermal drying of the fuel is preferably removed downstream of the high-pressure turbine and before intermediate stage preheating.

In accordance with the invention, the solid-walled centrifuge can be operated in a batch mode. In this process, the material is fed continuously during a one-cycle cycle and the water generated in the dewatering process is discharged as waste. Following the charge, the solid is collected by a discharge device. For example, a screw may be used as the discharge device. According to the invention, however, a fully continuous mode of operation can also be applied. In this method, the solid-walled centrifuge operates with continuous solids discharge, and is therefore equipped with an independent drive discharge screw for this purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further elucidated on the basis of an exemplary embodiment shown in the drawing. Here means:

Giant. 1 is a diagram of a device for removing water from raw coal.

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DETAILED DESCRIPTION OF THE INVENTION

The raw lignite to be dehydrated is fed to a solid centrifuge 2 via a screw conveyor 1. Prior to this, the raw lignite is heated to a working temperature between 60 ° C and 200 ° C by supplying water vapor 3 via a water vapor line 3. At this working temperature, which also prevails in the working space of the solid centrifuge 2, the water bound in the fuel is separated by centrifugation, which is drained from the working space of the solid centrifuge 2 via an overflow. or by means of a discharge screw 6 rotating at a different speed, is continuously discharged.

Furthermore, the working space of the solid centrifuge 2 can be indirectly heated. Indirect heating is also effected by means of the steam supplied via line 3. Condensate 7 is discharged through the underside.

Water at a temperature between 60 ° C and 200 ° C is drained at the overflow point 4 of the centrifuge 2. Part of the water stream is admixed by the return line 8 to brown coal to be dewatered, which is thus preheated. The water vapor stream for heating the fuel may be withdrawn from the water vapor circulation in the lignite power plant, preferably downstream of the turbine.

Claims (6)

Method for removing water from raw lignite, characterized in that the raw lignite is heated to a working temperature between 60 ° and 200 ° C by supplying hot water and / or water vapor and fed as a coal sludge to a full centrifuge (2), the working space of which is under a pressure corresponding to the water vapor pressure at the working temperature, the centrifugation separating the water bound in the raw lignite and pumped out of the working space of the full-thickness centrifuge (2) as excess. Method according to claim 1, characterized in that the working space of the full-thickness centrifuge (2) is indirectly heated. Method according to claim 1 or 2, characterized in that the raw lignite to be dehydrated is directly or indirectly preheated by hot water, which is discharged as an excess from the full-scale centrifuge (2). Method according to one of Claims 1 to 3, characterized in that water steam, which comes from the steam stream driving the turbine of the power plant, is used to heat the raw lignite and / or the working space of the solid centrifuge (2). Method according to one of Claims 1 to 4, characterized in that the solid-state centrifuge (2) operates in a batch-like manner, during which a material is fed during one working cycle and the water resulting from dewatering is discharged as waste, the substance (5) is collected by a discharge device. • · • · Method according to one of Claims 1 to 4, characterized in that the solid-walled centrifuge (2) operates in such a way that the solid (5) is discharged continuously.