EP0784660B1 - Method and device for reducing the water content of water-containing brown coal - Google Patents

Description

The invention relates to a method and an apparatus for Reduction of the water content of hydrated, granular lignite under the influence of thermal energy and pressure on the bed distributed material.

Process to reduce the water content of fossil fuels under So far, mechanical pressure and thermal energy have been used only known for peat. Peat is the youngest natural geologically Fuel, it is due to a high water content of 85-95% excellent. Unlike lignite, peat still contains parts of cellulose, so that the water only with little force on the Solid substance is bound and therefore largely by simple Squeezing can be removed. Such a method is known from the DE-PS 3 59 440 known. This patent describes a method for Dewatering of peat and the like is described, in which the dewatering material with a piston press in layers of less Pre-pressed starch after releasing the pressure of the effect of exposed to high tension steam and then a final pressing is subjected. The is of particular importance Process step in which the material is exposed to the steam, wherein the space containing the material, delimited by a plunger by its withdrawal is expanded so that the material in this space can expand, thereby loosening the press cake is made possible by the action of the steam. Because of this The press cake can be loosened in the concerned Process step supplied, high-tension steam easily paths through the Spread the press cake and push the loosened material away, see above that channels can form due to the large amounts of steam flow through with practically no effect on the material. Through the Prepressing, which takes place when the material is cold, becomes this cold pressed water withdrawn, which in peat mostly as Surface water is contained in significant quantities. However, it is make sure that this pre-pressing with no too high pressure takes place, otherwise a solid press cake is formed, in which the steam does not more can easily penetrate.

If it is about the drainage of brown coal, it is assume that this material does not contain free water. In brown coal rather, water is molecularly bound and cannot be squeezed out cold will.

Lignite has a water content of up to 65% by weight. At The combustion of these brown coal in power plants must be considerable Share of the brown coal used either directly or the adequate Amount of heat from the combustion gases to evaporate the water be used. This proportion can be up to depending on the water content 22%. This energy loss can be reduced if the Water content of raw lignite in one before combustion efficient drying or dewatering processes is reduced. In addition, the upstream drying step reduces the Size of the boilers installed in the power plant and the downstream ones Plant components. For the generation of electricity from brown coal with high humidity can the overall efficiency of the power plant process through Upstream of an energetically favorable process for removing the Improve water significantly.

There are procedures for reducing the water content of lignite and devices known in the articles "Brown Coal 39 (1987) Issue 3, pp. 46/57 "and" Braunkohle 39 (1987) Issue 4, pp. 78/87 "and in the patents cited therein as the source. Thermal drying by evaporation is used here as a method and thermal drainage by introducing superheated steam into the brown coal contained in an autoclave in a pressurized atmosphere 3.0 MPa (Fleissner method). The warmed up by this After emptying the autoclave, brown coal is in one Dry coal bunker transferred to where the thermally dewatered brown coal brought to cooling by post-ventilation and then dried becomes.

Difficulties in using the known reduction methods the water content of brown coal in large power plants consists of that due to the high lignite throughput required, the apparatus Effort and / or energy consumption is very large. Both Procedures for thermal drainage have been made despite less specific energy consumption compared to thermal drying so far no commercial success. The disadvantage of thermal Drainage in particular is that for continuous Implementation of pressure locks or rotary valves and High pressure pumps used for the entry and exit of the brown coal Need to become. Furthermore, in the known thermal Drainage process the saturated steam temperature to heat the Lignite needed steam the high pressure required Correspond to the pressure atmosphere.

The invention is based on the object in the known Disadvantages arising from energy saving and Avoid reducing technical effort. The features of claim 1 serve to solve this problem.

With this thermal / mechanical drainage process it is possible to Lignite with little thermal and mechanical effort Energy both continuously and discontinuously to a high degree to drain. The warming of under the initial surface pressure standing lignite beds causes physical and chemical processes by binding in the coal contained water molecules is loosened. The water can in liquid form from the capillaries and pores of the coal and thus be easily squeezed out. This is compared to the thermal drying process the energy to evaporate the Water saved.

An essential advantage of the method according to the invention over the known method for thermal dewatering is that no pressure locks, valves or high pressure pumps are necessary for the continuous introduction or discharge of the brown coal and the dewatered brown coal. This eliminates the elements that can be a source of interference and that make continuous drainage difficult. The saturated steam temperature of the supplied water vapor can be below the saturated steam temperature corresponding to the maximum surface pressure due to the inventive design of the method. Furthermore, because of the filter effect of the lignite bed and the low saturated steam temperature, the solids content of the water squeezed out and the ratio of the COD value to the BOD ₅ value are lower than the values given in the literature for the known processes.

The general requirements for a large-scale Drainage process such as low investment costs, small space requirements, high throughput, possible continuous operation, high operational and plant safety, environmental compatibility, lower Handling effort and the lowest possible energy consumption fulfilled by the inventive method.

In the operating phase before the surface pressure increases, there is one particularly even heating of the material, since that under the Material at the initial surface pressure forms a kind of filter cake that offers an even resistance to the introduced steam and therefore it passes through the material evenly. It can the pressure of water vapor in the order of magnitude of each mechanical pressure load, e.g. at 0.4 MPa.

During the pressing process, the surface pressure can be applied to the Change lignite, especially raise the process to the to be able to cheaply adapt the respective conditions of the material. Here has proven to be useful for the maximum surface pressure Value of at least about 2 MPa.

Advantageously, the water vapor is overheated to ensure an immediate Condensation of the water vapor at its point of entry into the material to avoid. This overheating is at least about 10 ° C. Because of this overheating there is also the advantage that in Area of supply of water vapor via supply pipes and the like does not occur in advance of condensation.

Around the water vapor a good possibility to act on the material to give this will be advantageous before its flat distribution on one Grain size of at most about 20 mm broken. By preheating of the material you can meet the energy requirements for carrying out the Continue to lessen the procedure. To do this, use appropriately Waste heat or as a waste heat source also in the process from the Material squeezed out water.

To with regard to the action of the supplied water vapor and the Possibility of intensive squeezing to favorable conditions create, you give the bed-like distribution of the material a medium Height, which is in a pressing height resulting from the pressure load of at least approx. 0.2 m results. In the case of using the Process on lignite this means that the average height of the bed-like distribution before the pressure load in about one area is between 0.4 m and 1 m. It has proven favorable that the the resulting press height after the pressure load is at most approx. 0.6 m is.

Designed to be able to carry out the process as quickly as possible one expediently so that the surface pressure steadily on the material acts.

Due to the bed-like spread of the granular brown coal on one Press pad and under the impression of an initial surface pressure is created an almost homogeneous pack that is supplied to the heating Water vapor a sufficiently even over the bed area Flow resistance opposed.

The water vapor is supplied in a favorable manner such that the heating of the brown coal to process temperature in one Condensation zone of the water vapor takes place in a Bed surface is almost parallel to the plane and perpendicular to it Plane propagated into the bed. The steam supply can be designed in this way that if the condensation zone is the outer boundary surface reached, the entire bedding material is heated. That way a steam escape avoided without expensive shut-off devices become necessary; it is rather sufficient that the bedding material through the walls to support that the material does not flow outwards.

To achieve an optimal rate of progress of the condensation zone inside the coal bed you can see the flow resistance increase with the distance from the bed surface in that the maximum Grain size of the coal bed within approx. One tenth of the Layer thickness of the coal bed is limited to about 2 mm.

To achieve a distance from the bed surface changing flow resistance becomes part of the amount of coal, that of a layer of approximately one tenth of the maximum height of the Beetes corresponds, pre-pressed with a surface pressure of approx. 1 MPa.

By consistently taking advantage of the benefits that flowed from the flow properties a bed with a grain size-specific layering and result in a pre-compression for the implementation of the method, manages to optimize the drainage of brown coal Different provenance required adjustment with regard to process temperature and heating rate. This will be useful thereby achieved that the flow resistance of the deck and / or Bottom layer of the coal bed is changed in that this layer is either formed from coal with low grain size, or, in particular when performing the method with the plate press according to claim 20, is pre-compressed accordingly.

The process can be carried out continuously with location-dependent pressure in a continuous press as well as discontinuously with a time-dependent Carry out pressure loading in a plate press.

An apparatus for performing the continuous process in one Continuous press is conveniently done using a double belt press a lower and an upper conveyor belt and an infeed area for a bed-like, distributed image of the material and its increasing compression as well as a multitude of steam supply lances in the inlet area, from the bed of the material are enclosed. Double belt presses with one lower and one upper conveyor belt, for example, in connection with the continuous production of chipboard used. Such Double belt press is e.g. disclosed in DE OS 40 10308.

In order to give the squeezed water a favorable outlet is at least the lower conveyor belt of one Double belt press with passages for the extraction of the pressed Water. The upper conveyor belt can be adjusted in height arranged and provided with pressing elements, the pressing force is adjustable. In this way, the double belt press can be used on different Adjust operating conditions.

The conveyor belts are expediently heated in order to also pass through the Conveyor belts also add heat to the solid material can.

For carrying out the process in batch operation expediently use a plate press with press ram and Press pad that receives the bed-like material, wherein at least the press pad with openings for the supply of Steam and provided with outlets for the squeezed water is.

Even if a plate press is used, it is advisable to Press ram and press pad to heat this way add heat to the material.

It should also be pointed out that the method according to the invention and the device in question also for draining peat and Sewage sludge.

Fig. 1 eine als kontinuierlich arbeitende Durchlaufpresse verwendete Doppelbandpresse,

Fig. 2 eine Plattenpresse für den diskontinuierlichen Betrieb vor dem Beginn der Auspressung,

Fig. 3 die gleiche Plattenpresse von der Betriebslage des Auspressens.

The invention is explained below using exemplary embodiments. Show it

1 is a double belt press used as a continuously operating continuous press,

2 a plate press for discontinuous operation before the start of the pressing,

Fig. 3 shows the same plate press from the operating position of the pressing.

Fig. 1 shows the brown coal bunker 1, which on a certain Particle size contains pre-broken brown coal. In the coal bunker 1 steam or hot water supply lines or Heat exchanger surfaces are installed, which preheat the Enable coal. The pre-broken lignite is extracted from the Coal bunker 1 bed-like on the lower dashed line Conveyor belt 2, through which the coal is transported in the direction of the arrow, distributed. Above the conveyor belt 2 of the double belt press shown an upper conveyor belt 3, also shown in dashed lines, moves (Printing tape) in the direction of the arrow, the speed of which corresponds to that of the Conveyor belt 2 almost matches. The distance between conveyor belt 2 and conveyor belt 3 becomes smaller in the running direction in the inlet area 8 and thus enables the pressure increase on the coal bed 4. The Conveyor belt 3 is depending on the throughput and water content Lignite throughout its course via power transmission Press elements 5 adjustable in height. Between conveyor belt 2 and conveyor belt 3 are a variety of dotted in the moving drawn coal bed 4 projecting steam supply lances 6 arranged, whose steam outlet openings end at a point in the inlet area 8, in which the pressure on the coal below the maximum surface pressure in Course of the conveyor belts 2 and 3 is. The one from the steam supply lances 6 escaping water vapor gives off its heat to the coal and condenses. Due to the multitude of different in length and feed lances 6 of different heights become one ensures relatively even heating of the coal bed 4.

This heat effect while increasing pressure in the inlet area 8 has the following chemical and physical Processes in which the colloidal structure of the Lignite and water properties change:

• gleichmäßige Durchwärmung des Kohlekorns,
• Zusammenbruch der Kapillarstruktur gekoppelt mit:
• Volumenschwund der in den plastischen Zustand versetzten Braunkohle,

• Verfestigung des Kohlegefüges,
• Auspressen des Wassers aus den Kapillaren in flüssiger Form begünstigt durch:
  • Expansion des Kohlewassers bei gleichzeitiger Herabsetzung der Viskosität,
  • Anderung der Oberflächeneigenschaften (hydrophil - hydrophob) als Folge der ablaufenden chemischen Vorgänge,
  • Auswaschen der Ascheanteile, insbesondere von Alkalisalzen

Physical processes:

• uniform heating of the coal grain,
• Collapse of the capillary structure coupled with:
• Loss of volume of the lignite which has been plasticized,

• Consolidation of the coal structure,
• Squeezing the water out of the capillaries in liquid form favored by:
  • Expansion of the coal water while lowering the viscosity,
  • Change in surface properties (hydrophilic - hydrophobic) as a result of the ongoing chemical processes,
  • Washing out the ash parts, especially alkali salts

• Abbau von sauerstoffhaltigen funktionellen Gruppen unter Freisetzung von CO₂,
• Einsetzen des thermischen Abbaus der Braunkohle unter Freisetzung von CH₄ und höheren Kohlenwasserstoffen.

Chemical processes:

• Degradation of oxygen-containing functional groups with the release of CO ₂ ,
• Onset of lignite thermal degradation releasing CH ₄ and higher hydrocarbons.

• Durchsatzmenge bzw. Schichthöhe,
• Korngröße der Braunkohle,
• Wassergehalt der Braunkohle,
• Druck,
• Temperatur,
• Verweilzeit.

The drainage of lignite is essentially determined by the following factors:

• Throughput or layer height,
• Grain size of lignite,
• Water content of lignite,
• Pressure,
• Temperature,
• Dwell time.

Depending on the throughput, grain size and water content of the brown coal the parameters pressure and temperature can be adjusted via the height adjustable Conveyor belt 3 and the water vapor pressure or the temperature of the supplied heating steam can be set. In the course of the first Process section (inlet area 8) is the coal bed 4 from above on the conveyor belt 3 by means of continuously increasing, mechanically impressed Forces under pressure. After reaching a maximum to be determined The solidified coal bed 4 enters the following area Process section in which the from the upper conveyor belt 3rd applied pressure is kept constant or is only slightly varied. The Pressure in connection with the increased temperature Consequence that free and released water from the coal bed 4 pressed out and through passages 7 on the conveyor belt 2 and optionally additionally deducted on the conveyor belt 3 in one or more stages can be. The hot water emerging from the passages 7 or a partial flow of this water can be used to preheat the brown coal be used.

The one emerging at the end of the double belt press up to a certain one Dehydrated coal can be dewatered with the help of a facility Pieces of a given size divided and on a continuation Conveyor belt transported to mills over a certain distance in which the coal is used for combustion or gasification required grain size is crushed.

Fig. 2 shows a plate press with the press pad 9 and Press die 10. The press base 9 rests here only in principle illustrated supports 11 and 12. The ram 10 depends on the Tappet 13, which is opened by a press mechanism, not shown here. and is deported. Acting in the design of this plate press it is basically state of the art.

The press pad 9 is trough-shaped here, so that in it Solid material 14 are applied in a bed-like, flat distribution can. Press pad 9 and press ram 10 are with water outlets 15 and 16 and steam supply ports 21 and 22 are provided, whereby in the case of the closed plate press shown in FIG Solid material 14 water vapor supplied and escaping water can be dissipated. The water outlets 15 and 16 and the Steam supply openings 21 and 22 are via channels 17 and 18 and 23 and 24 with the bottom of the press pad 9 and the front of the Press ram 10 connected so that squeezed water and drain Water vapor can flow into the solid material 14.

On the bottom of the press pad 9 and on the front of the Press ram 10 is placed on a close-meshed sieve 19 or 20, the Permits the passage of water or steam, but the entry of Solid material in channels 17 and 18 or 23 and 24 prevented, so that they cannot be clogged.

Fig. 3 shows the plate press according to FIG. 2 in the closed position, in the the ram 10 is lowered against the press base 9 and that Solid material 14 compresses. When doing so first on the Solid material 14 acting compared to the maximum pressure lowered Pressure becomes water vapor via the steam supply openings 21 and 22 introduced in the solid material 14, whereby this is heated. Then the pressure caused by the ram 10 on the Solid material 14 increased to the maximum pressure, so that now water contained in the solid material 14 is squeezed out and over the outlets 15 and 16 can emerge. Regarding yourself processes and results are explained in the explanations for Fig. 1 referenced.

This is suitable due to the relatively low system expenditure described method especially for use in lignite fired large power plants. Furthermore, through an application the process at the site of lignite mining depending on the ratio the moisture content of the dry cabbage to the raw brown coal of the mass-related calorific value increased and thus a more economical Lignite can be transported.

Claims (20)

1. Process for reducing the water content of water-containing granular brown coal involving the action of thermal energy and pressure on the material distributed as a flat bed, characterized in that

   a) the brown coal is subjected to a mechanically applied initial surface pressure which is below the maximum surface pressure occurring in the process and at which thermal energy is supplied to the brown coal by steam which heats the brown coal, with condensation,

   b) and then, without further steam feed, the surface pressure is increased to at least 2.0 MPa to the extent that the water present in the heated brown coal is expressed.
2. Process according to Claim 1, characterized in that the specific mechanical pressure load is in the order of magnitude of the respective steam pressure.
3. Process according to one of Claims 1-2, characterized in that the steam is superheated.
4. Process according to Claim 3, characterized in that the superheating is at least about 10°C.
5. Process according to one of Claims 1-4, characterized in that the brown coal (4, 14), prior to its flat distribution, is crushed to a particle size of at most about 20 mm.
6. Process according to one of Claims 1-5, characterized in that the brown coal (4, 14), prior to the distribution as a bed, is preheated by waste heat.
7. Process according to Claim 6, characterized in that the waste-heat source used is the water expressed from the brown coal (4, 14) in the process.
8. Process according to one of Claims 1-7, characterized in that the brown coal (4, 14) is distributed as a bed in a height of from 0.4 m to 1 m which results in the press height produced after the pressure load being at least approximately 0.2 m.
9. Process according to Claim 8, characterized in that the press height is at most approximately 0.6 m.
10. Process according to one of Claims 1-9, characterized in that the surface pressure acts continuously on the solid material.
11. Process according to one of Claims 1-10, characterized in that the initial surface pressure is chosen (at least 0.2 MPa) in such a manner that the brown coal forms a packing having a uniform resistance to flow over the bed surface against the flowing steam.
12. Process according to one of Claims 1-11, characterized in that the steam is fed in such a manner that the heating of the brown coal takes place in a planar condensation zone virtually parallel to the bed surface, which condensation zone advances into the coal bed perpendicularly to the bed surface.
13. Process according to one of Claims 1-12, characterized in that, to achieve an optimum rate of advance of the condensation zone within the coal bed, the resistance to flow is increased with the distance from the bed surface by the maximum particle size of the coal bed being restricted to approximately 2 mm within approximately one tenth of the layer thickness of the coal bed.
14. Process according to one of Claims 1-13, characterized in that, to achieve a resistance to flow which alters with the distance from the bed surface, a portion of the coal volume which corresponds to a layer of approximately one tenth the maximum bed height is prepressed at a surface pressure of approximately 1 MPa.
15. Process according to one of Claims 1-14, characterized by

    a) a double-belt press having a lower and an upper conveyor belt (2, 3) and an intake region (8) for receiving the brown coal (4) distributed as a flat bed and its increasing compression,

    b) a multiplicity of steam feed lances (6) in the intake region (8) which are surrounded by the bed (4) (Fig. 1).
16. Device according to Claim 15, characterized in that at least the lower conveyor belt (2) is provided with through-holes (7) for withdrawal of the expressed water.
17. Device according to Claim 15, characterized in that the upper conveyor belt (3) is arranged to be adjustable in height and is provided with press elements (5) whose pressing force is adjustable.
18. Device according to one of Claims 15-17, characterized in that the conveyor belts (2, 3) are heatable.
19. Device for carrying out the process according to one of Claims 1-14, characterized by a platen press having press ram (10) and press base (9) which receives the brown coal (14) distributed as a flat bed, at least the press ram (10) being provided with orifices (21, 22) for feeding the steam and at least the press base (9) being provided with outlets (15, 16) for the withdrawal of the water expressed from the brown coal (14) (Figs. 2, 3).
20. Device according to Claim 19, characterized in that press ram (10) and/or press base (9) are heated.

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