EP2891771A1 - Method for refining crude lignite - Google Patents

Abstract

The invention relates to a method for refining crude lignite coal comprising pre-comminution (1) of the lignite-based lignite coal and pre-comminution (1) immediately downstream grinding and drying to dry lignite, wherein from a coupled power plant process with at least one steam generator (3) steam is removed and at least Partially used for drying the pit-wet raw lignite, wherein a fine crushing and drying (2) is carried out in one process step, wherein the still pit-dried pre-broken lignite coal is comminuted as ground material by means of at least one steam jet from steam production and dried, the steam jet in a with steam fluidized Mahlgutbett is initiated.

Description

The invention relates to a process for refining crude lignite coal comprising pre-crushing the lignite-like lignite coal and a pre-crushing immediately downstream grinding and drying to dry lignite, wherein extracted from a coupled power plant process with at least one steam generator and at least partially used to dry the lignite coal wet lignite.

Under refining of brown coal in the sense of the present invention, at least the drying and grinding of the brown coal for the purpose of producing a marketable product usable outside the power plant process is to be understood. Finishing may include at least the production of a dried, powdery or granular end product, which is supplied to a thermal utilization in a power plant or a further refinement for the enrichment of carbon in the final product. As a further finishing step, for example, the production of hearth furnace coke, liquefaction, gasification or the production of fuel pellets can be provided.

Cryogenic wet lignite in the context of the present invention is to be understood as meaning the lignite mined and not treated, which may have a moisture content of between 40% and 60% by weight, depending on the conditions of the deposit or storage time prior to refining.

In the brown coal power generation, the raw lignite is usually supplied to a flue gas inerted with flue gas. The raw lignite is crushed in the racket mill. The flue gas is used to dry the wet coal and transported as a carrier gas produced lignite dust through a separator to the burner of the boiler. In that regard, a treatment of the raw lignite to dry lignite is not required.

The refining of lignite, in contrast, requires an optionally multi-stage grinding and separate drying of the raw lignite in a separate drying unit. The drying units used are tube dryers, fluidized bed dryers or roller mills. When using tube dryers and fluidized bed dryers as drying units usually a multi-stage pre-crushing and / or grinding of the raw lignite is provided. In particular, fluidized bed dryers can only be operated with a relatively narrow feed grain belt, otherwise the fluidized bed would collapse. The operation of tube dryers is energetically complex. These are usually operated with steam from a coupled power plant process. The specific volume of steam required to operate a tube dryer is about 1.35 kg of steam per kilogram of raw coal. The situation is similar with the operation of a fluidized bed dryer, whose steam consumption based on the raw coal used is about 1.2 kg of steam per kilogram of raw coal. Finally, in particular the multistage grinding and classification of the fluidized bed dryer supplied raw coal is expensive in terms of apparatus.

In principle, a drying and grinding of the pit-wet raw lignite coal can be carried out in inverted with flue gas roller mills, but the investment costs for vertical roller mills are considerable.

The invention is therefore based on the object to provide a method for refining raw lignite coal comprising crushing and drying the lignite coal to dry lignite, which requires an energetically favorable drying with relatively little equipment expense.

The object is achieved with the features of claim 1. Advantageous embodiments of the invention will become apparent from the dependent claims.

A method according to the invention comprises a preliminary comminution of the pit-moist raw lignite coal and a pre-comminution preferably immediately downstream drying to dry lignite, wherein from a coupled power plant process with at least one steam generator steam is taken and this steam is at least partially used for drying the pit-wet raw lignite, the method comprises grinding and drying in a single process step, preferably a fine grinding and drying in a single process step, wherein the still pit-dried pre-broken raw lignite as regrind by means of at least one steam jet from the steam generation, which is introduced into a fluidized bed with fluidized bed, is crushed and broken.

According to the invention, a fine grinding and drying is thereby combined in one process step, which results in a considerable energetic optimization of the finishing process. According to the invention, it is provided to use the raw lignite even within a suitably designed aggregate as a grinding body. In the Mahlgutbett, comprising the pre-crushed or pre-shredded raw lignite as regrind, entering steam jet interacts with the surrounding fluidized bed such that a momentum exchange between the steam jet and the ground material takes place, resulting in the comminution of the ground material and at the same time to its drying in the Steam atmosphere leads. It is particularly advantageous when the steam jet is accelerated into the fluidized millbase bed together with a part of the millbase and, if this is so, that particle collisions occur within the millbase bed. The individual lignite particles are exposed to an impact stress, which leads to a crushing without the use of grinding media or baffle installations within the unit in question. In this case, a plurality of steam jets can be introduced in opposite directions in the Mahlgutbett, for example so that steam jets meet.

The comminution and drying can be carried out in at least one, preferably in several parallel hydraulic jet mills, preferably in fluidized bed counter-jet mills. In a fluidized bed counter-jet mill, at least two or more steam jets, each loaded with regrind, are directed against each other to achieve particle collisions to the maximum extent possible.

Such comminution is particularly advantageous when the refining process is coupled to a power plant process, in which case suitably conditioned steam from the power plant process or steam generation process is available.

In the method according to the invention it can be provided that a subset of the dry lignite is thermally utilized in the power plant process, wherein the power plant process is otherwise preferably operated with raw lignite as fuel.

The steam, for example, at a temperature of between 180 ° C and 330 ° C, preferably at a temperature between 200 ° C and 300 ° C and a vapor pressure between 4 bar and 6 bar, preferably introduced with a vapor pressure of 5 bar in the Mahlgutbett become.

In a particularly preferred variant of the method according to the invention, both water and volatile components of the raw lignite, such as methane, are expelled as fuel gas from the lignite coal during drying, wherein the fuel gas is stored and / or thermally recycled separately. For the purposes of the present invention, the so-called volatile constituents or volatile gaseous constituents are to be understood as meaning exclusively hydrocarbons, but not the roughly capillary-bound water of the raw lignite coal.

A further process variant according to the invention provides that the grinding and drying takes place in two stages, wherein in one stage the grinding and drying by means of at least one jet of steam at a first low temperature and in a second stage by means of at least one jet of steam at a second higher temperature. For example, the low temperature may be on the order of 200 ° C, whereas the higher temperature may be on the order of 300 ° C.

With an introduction of a steam jet with a temperature of about 200 ° C and a pressure of about 5 bar, only a fine comminution and Drying of the ground material, wherein preferably the dried ground material can then have a residual water content of about 2 wt .-% to 4 wt .-%. The product obtained in this case still comprises appreciable amounts of volatile gaseous constituents.

In a second stage of grinding and drying, for example, steam at a temperature of about 300 ° C can be supplied, which has an expulsion of the volatile gaseous components from the raw lignite result. These volatile constituents may for example be stored separately and / or supplied for thermal utilization.

It is particularly advantageous if the second stage of the fine grinding and drying is operated as a function of the load of the steam generator. Thus, for example, be provided for low load periods of the power grid to supply the steam generator, a subset of dry lignite, from which the volatile components have been expelled. The volatiles can be compressed in this case as a fuel gas and fed to a natural gas network or a natural gas storage. In this case, to drive off the volatiles in a second stage of fine grinding and drying, steam of relatively high energy content is needed, which is no longer available at the turbine power plant for power generation.

At peak load times, only a single stage of grinding and drying with steam of a first lower temperature can be operated so that the higher energy content steam is available to a turbine and ultimately to a downstream generator for power generation.

The partial stream of dry brown coal not supplied for thermal recycling can be coked into hearth furnace coke, for example in a further finishing step, if and insofar as this dry brown coal still contains gaseous volatile constituents. If the volatiles are already completely expelled in the second stage of fine grinding, the finished dried product is already present in the form of a high-quality coke. Preferably, vapor is provided as steam from a turbine of the coupled power plant process. For example, for this purpose, the steam between low-pressure part and medium-pressure part of a three-stage turbine be tapped.

The invention will be explained below with reference to an embodiment shown in the drawings.

Figur 1:

ein Verfahrensfließbild einer ersten Variante des erfindungsgemäßen Verfahrens und

Figur 2:

ein Verfahrensfließbild einer zweiten Variante des Veredelungsverfahrens gemäß der Erfindung.

Show it:

FIG. 1:

a process flow diagram of a first variant of the method according to the invention and

FIG. 2:

a process flow diagram of a second variant of the refining process according to the invention.

It is first referred to the FIG. 1 ,

In FIG. 1 a lignite processing coupled with a power plant process is shown, wherein the refinement comprises a pre-comminution 1 and a fine comminution with drying 2.

In the simplest case, the pre-crushing 1 for lignite-wet raw lignite can only include the breaking up of mined lignite coal obtained by mining using conventional crusher / pre-shredding systems. The raw lignite may for example have been pre-crushed to a particle size of ≥ 0 mm and ≤ 10 mm in the pre-crushing process. The pre-crushed raw lignite may, for example, have a moisture content of 54% by weight. The moisture content is given here only as an example, of course, the moisture content of the raw lignite can vary depending on storage conditions and reservoir conditions.

As fine comminution and drying 2, for example, an arrangement of parallel-connected fluidized bed counter-jet mills is provided, in which the insert grain from 0 mm to 10 mm to a target grain of ≤ 1 mm with simultaneous drying to a moisture content of about 2 wt .-% to 3 wt .-% is obtained.

A suitable for carrying out the method hydraulic jet mill may, for example, include a Mahlgutraum, dip in the multiple jet pipes. About the jet pipes both a steam injection and possibly the introduction of ground material, which was previously deducted from the Mahlgutbett or a Mahlguteinleinlauf. A Mahlgutaustrag can be done for example via a arranged within the Mahlgutraums classifier.

A partial stream A of the comminuted material stream discharged from the fine comminution and drying 2 in the form of dry brown coal is fed to a steam generator 3, which is designed, for example, as a boiler essentially fired with crude lignite coal. It can be provided, for example, that the steam generator 3 is fired to 75% with lignite and 25% with dry lignite. The hot steam generated in the steam generator 3 drives a turbine 4, which in turn drives a generator 5, which feeds into a power grid 6. A further partial stream B of dry lignite is fed to a second finishing stage 7, the aim of which is the production of a high-quality, marketable fuel. For example, a coking, gasification or liquefaction of lignite may be provided as a second upgrading stage 7.

For operating the fine comminution and drying 2, a partial stream of steam C is withdrawn from the turbine 4. This partial stream of steam C is introduced according to the invention as a jet of steam in the drying units provided there. In addition, this partial stream of steam C is used for fluidizing the Mahlgutbetts provided within the drying units. The steam is withdrawn between the low-pressure part and the medium-pressure part of the turbine 4 at a pressure of about 5 bar at a temperature of about 200 ° C, wherein about 0.95 kg of steam are required per kilogram used as regrind raw lignite. The deducted from the fine crushing and drying 2 vapor stream D, in the course of drying the raw lignite to Dry lignite is obtained, is condensed in a vapor condenser 8, wherein the heat of condensation occurring is used for example for boiler feed water preheating of the steam generator 3 or in a separate ORC process (Organic Rankine Cycle).

A variant of this method is in FIG. 2 represented where the same components and the same mass flows are provided with the same names there.

In the FIG. 2 illustrated variant of the method according to the invention differs essentially from the in FIG. 1 illustrated variant that the fine crushing and drying 2 one or more stages, but with a partial flow steam C, is operated, which has a higher energy content or has a higher temperature, namely about 300 ° C at a pressure of about 5 bar. When operating a hydraulic jet mill with steam at a temperature of about 300 ° C at about 5 bar pressure, both water and the gaseous volatiles of the lignite coal are expelled from this during comminution in such a way that almost 100% of that contained in the lignite coal Moisture is removed. When 100% lignite is used, about 54% by weight of water and 23.5% by weight of methane are produced. As a finished product from the fine crushing and drying 2 falls to a coke-like product with an increased carbon content, of which a partial flow A in the steam generator 3 is thermally recoverable, whereas a further partial flow B is obtained as finished finished product. The vapor D from the fine comminution and drying 2 can be condensed in the vapor condenser 8 for the purpose of waste heat utilization, as in the method variant described above.

The resulting methane E is first cleaned in a filter 9 and then fed via a compressor 10 in a natural gas network 11.

The fine comminution and drying 2 may comprise two grinding and drying stages, wherein in a first stage a fine comminution and drying or grinding and drying with steam of lower energy content may be provided. This can be done, for example, during heavy load periods of the power grid, since in this case the maximum amount of steam on the turbine 4 must be available. At low load periods, a second grinding and drying stage may be provided, which is operated with higher energy content steam, in which case, for example, steam at a temperature of about 300 ° C at the turbine 4 can be tapped. Only in this load case would methane E be expelled from the raw lignite and fed to a separate utilization as fuel gas.

LIST OF REFERENCE NUMBERS

1

precomminution

2

Fine comminution and drying

3

steam generator

4

turbine

5

generator

6

power grid

7

second refining step

8th

vapor condenser

9

filter

10

compressor

11

natural gas network

A

Dry lignite

B

Dry lignite

C

steam

D

vapors

e

methane

Claims (10)

Process for upgrading of gruel wet raw lignite coal comprising a pre - crushing (1) the lignite coal wet coal and a pre - crushing (1) immediately downstream grinding and drying to dry brown coal, taken from a coupled power plant process with at least one steam generator (3) steam and at least partially for drying the Crude lignite is used, characterized in that the grinding and drying is carried out in one process step, wherein the still pit-dried pre-broken raw lignite coal is introduced as ground material in a fluidized Mahlgutbett and finely comminuted within the Mahlgutbettes by means of at least one jet of steam and dried. A method according to claim 1, characterized in that the raw lignite is comminuted within the Mahlgutbettes by means of a plurality of oppositely directed steam jets, wherein at least parts of the raw lignite are introduced with the steam jets in the millbase. A method according to claim 1 or 2, characterized in that the fine comminution and drying in at least one, preferably in several parallel hydraulic jet mills, preferably in fluidized bed counter-jet mills is performed. Method according to one of claims 1 to 3, characterized in that the at least one steam jet at a temperature between 180 ° C and 330 ° C and a vapor pressure between 4 bar and 6 bar is introduced into the Mahlgutbett. Method according to one of claims 1 to 4, characterized in that in the drying water and volatile gaseous components such as methane are expelled as fuel gas from the raw lignite, wherein the fuel gas is stored and / or separately thermally utilized. Method according to one of claims 1 to 5, characterized in that a subset of the dry lignite is thermally utilized in the power plant process, which is otherwise preferably operated with raw lignite as fuel. Method according to one of claims 5 or 6, characterized in that the fine comminution and drying takes place in two stages, wherein in a first stage, the fine comminution and drying (2) by means of at least one jet of steam at a first lower temperature and in a second stage by means of at least one steam jet takes place at a second higher temperature. A method according to claim 7, characterized in that the second stage of fine comminution and drying (2) takes place as a function of the load of the steam generator (3). Method according to one of claims 1 to 8, characterized in that the waste heat from the fine comminution and drying (2) of the raw lignite is used in the steam generation. Method according to one of claims 1 to 9, characterized in that as steam bleed steam from a turbine (4) of the coupled power plant process is provided.

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