EP0579214B2 - Process for milling crude lignite - Google Patents

Description

The invention relates to a method for grinding from raw lignite to fine coal.

For grinding of usually moist raw lignite So far, raw lignite has been turned into fine coal passed through dryer in which for example indirect steam heating Coal is carried out and in this way the coal the moisture is largely removed. The raw lignite usually leaves this dryer with a temperature of 70 - 85 ° C.

Since this relatively high temperature of 70 - 85 ° C in With regard to ignition or explosion Coal dust mixture viewed as extremely problematic must be used for lignite dust as permissible temperature is set to 60 ° C to be able to exclude the aforementioned dangerous moments.

Because of this starting temperature after The raw lignite is dried at 70 - 85 ° C dried raw lignite to a temperature range cooled down from about 40 ° C. This happens e.g. in air-cooled trough chain conveyors.

The raw lignite that has been dried and cooled in this way has so far been comminuted and ground in pure continuous mills with grinding media, which are designed in particular as rods or balls. In these continuous mills designed, for example, as vibratory mills or agitator ball mills, the raw lignite is mainly comminuted between the grinding media and the grinding chamber wall.
In these continuous mills, the friction between the grinding media with one another and between the grinding media and the wall of the grinding chamber generates heat, which can result in a sharp temperature increase of, for example, 20 ° C. with dried raw lignite. The previously cooled raw lignite therefore again reaches the permissible temperature limit of around 60 ° C.

In this previously practiced process, it has been found to be particularly disadvantageous that the continuous mills used had a capacity limit of approximately 10 t / h in raw lignite throughput.
In order to achieve a throughput of raw lignite of around 60 t / h, six to ten such continuous mills had to be used, depending on the fineness of the product.

It was therefore shown that the higher throughput capacity a variety of such units with accordingly higher number of drives, inlets and Removal equipment, foundations, buildings with Sound insulation and a higher surveillance and Regular effort required.

It was for this previously practiced process however, the temperature of raw lignite is required in front of the mills to a maximum of 40 ° C what only with additional cooling units high investment, space requirements and continue associated transport, regulation and maintenance expenses was connected.

From DE 37 34 359 A1 a method is known in which pre-dried lignite in a roller mill with constant supply of pre-dried and about Flue gas heated to 60 ° C is ground to lignite dust becomes. To avoid oxygen or air, this is Inert gas introduced with overpressure and in a certain Share constantly replaced. Analogous to the inert gas atmosphere of the Roller mill is also used to store lignite dust in silos in an inert atmosphere. This grinding process in a bowl mill and required in an inert gas atmosphere of about 60 ° C an additional facility for generating Flue gas as well as blower equipment and a heat exchanger in a separate circuit of the flue gas. In order to a corresponding apparatus and control technology is connected Expenditure.

From the article "Use of brown coal using the example of a dust-fired 80 MW boilers in the sugar industry ", Yearbook of steam generation technology, Vol. 2, 5th edition 1985/86, pages 1287 to 1297, is a production of Lignite dust known for direct injection. It will Baunkohlegranulat, which in briquette production as Waste product accumulates and a water content of 18% as well has a grain size of 0 to 15 or 20 mm, in Delivered silo vehicles and a coal silo of an airflow roller mill given up. Grinding in the airflow roller mill takes place at approx. 40 ° C with feed of air, which also has a temperature of 40 ° C having. As a protective measure against mill fires, that at a classifier temperature> 80 C for inerting Saturated steam is blown in. Starting from the delivery of lignite granules across the street and Silo storage can be assumed that the lignite granules with about 30 ° C to a maximum of 40 ° C Airflow roller mill is fed.

In the company brochure "Wälzmühlen-Roller Grinding Mills" from LOESCHE GmbH, 2/84, are grinding and drying systems with LOE-SCHE coal mills described and plant diagrams shown. Coal dust production can be done in inert mode or Air operation take place, always starting from raw coal which is the airflow roller mill from a raw coal bunker is abandoned. There is a milling drying of the Raw coal with the help of the hot gas supplied, the in the water contained in the raw coal through intimate contact evaporated spontaneously with the hot gas, so that already in the grinding chamber the desired mill outlet temperature from 70 to 130 ° C arises. The lignite dust can be one Burners are supplied, or after separation from the hot gas temporarily stored in a filter in a dust bunker.

Disadvantages of the known coal dust generation are Transport and storage costs of the lignite granulate to be delivered, which also before being transported to a permissible temperature must be cooled. Inertbetriebene Grinding and drying plants are control and investment technology due to the generation of hot gas or hot air also relatively complex.

The invention is based on the object of developing a method for grinding lignite which, while maintaining the required operational reliability, is particularly favorable in terms of investment and enables efficient and qualitatively particularly good grinding and screening.

This object is achieved by the Features of claim 1 solved.

An essential core idea of the invention is to combine the grinding process with the cooling process below the critical limit temperature of 60 ° C., an airflow roller mill being particularly suitable for this.
Such an airflow roller mill, for example of the LOE-SCHE type, has a rotating grinding table or a grinding bowl and thereon friction rollers driven by the material to be ground or provided with its own drive. A circumferential blade ring is arranged around the edge of the grinding bowl, through which the air flow is sucked or blown into the grinding chamber at high speed and with a swirl component. The material which is thrown and also comminuted by the grinding bowl is in this case caught in the approximately hollow cylindrical outer annular space by the air flow and guided in a rotating fluidized bed to the classifier arranged above the grinding chamber.

The invention now goes the way Cold air or ambient air over which Vacuum or blow in the blade ring into the grinding chamber and by an intimate washing of the e.g. raw lignite particles at a temperature of about 80 ° C, a cooling of these particles during the rotation of the fluidized bed of the dust-air mixture to reach up to the sifter. in this connection can flow rate and throughput the cold air also depending on the task the raw lignite to be ground are regulated that the critical limit temperature of 60 ° C at which the airflow roller mill and the classifier raw lignite particles or is undercut.

The preferred airflow mill type for this Process points between the grinding media, ie the grinding bowl and the grinding rollers a minimum distance on so that a direct metallic contact, which leads to high frictional heat is avoided.

The subsequent sighting of the ascending rotating fluidized bed fed to the classifier Raw lignite particles are therefore guaranteed independently of part load or full load operation a high consistency of the Feinkorn-Bandes, including a visible material with largely unchangeable grain distribution characteristic understand is.

In addition, however, can flow in through the Cold air at the same time as a pumping medium to forward the ground and spotted good in intermediate silos or to consumers be used optimally.

The procedural integration of an airflow roller mill for the grinding of raw lignite as well as other raw coal enables particularly high throughput rates, since these airflow roller mills can be built in larger units and can, for example, replace six to ten vibratory mills of a known type.
In addition, with these roller mills, the frictional heat is avoided by the direct contact between the grinding parts. This can be achieved, for example, by mechanical spacers for the grinding rollers in relation to the grinding bowl.

Since the cold air flow in such an air flow roller mill be sucked in from the atmosphere can, there is no need to cool down the dried Raw lignite from the temperature range of 70 - 85 ° C to areas around 40 ° C, making significant investments cooling units can be saved.

In addition, the total expenditure on equipment when using an airflow roller mill instead of six to ten vibrating mills and the corresponding one Follow-up effort can be significantly reduced.

Another advantage arises in that the Airflow roller mill operated in negative pressure mode is what the cooling processes and the pneumatic Funding within the roller mill more efficiently and are more energy efficient. For that preferred selected vacuum mode, which is also called suction mode can be designated, the corresponding Fans behind the airflow roller mill and in particular behind the dust collectors that the sifter are provided downstream. Because of this suction the fans avoid any temperature increase inside the airflow roller mill, which creates the cooling effect in the roller mill is maintained.

The predestined field of application of the method is the grinding of raw lignite. Other types of raw coal can also be found in extremely above by means of the method grind economically.

Fig. 1

eine schematische Darstellung des Verfahrens mit den wesentlichen Aggregaten und

Fig. 2

eine vergrößerte Darstellung eines Ausschnittes durch den Mahlbereich der Luftstrom-Wälzmühle nach Fig. 1 mit den wesentlichen Strömungsverhältnissen.

The invention is further explained below using an example. Show it:

Fig. 1

a schematic representation of the process with the essential units and

Fig. 2

an enlarged view of a section through the grinding area of the airflow roller mill of FIG. 1 with the essential flow conditions.

An airflow roller mill 1 is shown in FIG. This roller mill 1 has a driven, rotating Grinding bowl 2 and on this frictionally rolling or separately driven grinding rollers 3. A classifier 4 is integrated above the grinding chamber 5 provided in the housing of the airflow roller mill 1.

The usually moist raw lignite is in the The process initially takes place via dryer 11, which e.g. tube dryer can be with indirect steam heating, led and dried in it. The raw lignite reaches a temperature of around 70 - 85 ° C these dryers 11 on a conveyor 12 and then on a weighing belt 13 for the metered task the dried raw lignite. Via a rotary valve 14 and a feed 7 will Raw lignite is introduced into the airflow roller mill 1.

The roller mill 1 becomes a cold gas in the lower region 18, especially cold air from the atmosphere, fed, which then via a shovel ring 17 flows into the grinding chamber 5.

2 is a larger, schematic partial view the grinding chamber 5 of the roller mill 1 is shown. The cold air 18 is in the edge region of the grinding bowl 2, which is rotated via a drive 16 is, via a blade ring 17 with a The upward swirl movement is blown into the grinding chamber 5. In an outer, hollow cylindrical annular space 22 takes place here between the cold air 18 and the ground Raw carbon particles 21 an intimate washing. The Formation of a rotating and rising fluidized bed 24 of cold air 18 and ground raw coal particles 21 leads to a cooling of the Raw lignite particles below the critical limit of 60 ° C.

The raw lignite 23 is approximately in the middle of the rotating Grinding bowl 2 abandoned and passes through Centrifugal force radially outward where it is under pressure the grinding rollers 3 is crushed and ground. The Carbon particles thrown off in the direction of arrow 25 21 are then in the rotating fluidized bed 24 effectively cooled by contact with the cold air 18. This cooling process can be done by the flow rate the cold air and its temperature become.

The rotating fluidized bed rising in the direction of arrow 20 24 between the housing 15 and the Edge of the grinding table 2 is created by the blade inclination of the blade ring 17 and the thereby creates a swirl offset vortex flow 19.

In this fluidized bed they give off cold air everywhere carbon particles flowed around their heat to the cold air from until at the outlet 9 of the coal dust from the in the Rolling mill 1 integrated classifier 4 a temperature is reached below 60 ° C (Fig. 1).

The classifier 4 also enables that independently of part-load or full-load operation that the classifier 4 Fine material leaving via outlet 9 to a high level Constancy of a desired dust grain band set can be.

The cold air 18 used can advantageously at the same time for the pneumatic conveying of the Fine goods to intermediate silos or to consumers to be used.

Claims (9)

1. Process for crushing raw lignite to fine coal, in which previously the raw lignite is dried and subsequently the dried raw lignite is crushed in an air-swept roller mill (1),
   characterized in that the raw lignite (23) from the drying with an exit temperature of approximately 70 to 85°C is supplied to the air-swept roller mill (1) and is crushed therein,
   that the air-swept roller mill (1) is passed through by cold air and/or ambient air, and
   that hereby at least the crushed lignite particles (21) in exchange with the cold air and/or ambient air (18), are cooled to a temperature below 60°C.
2. Process according to claim 1,
   characterized in that in an outer annulus (22) of the air-swept roller mill (1), which comprises a crushing pan (2), crushing rollers (3) and a blade ring (17), is formed a rotary fluidized bed (19) of cold air and/or ambient air (18) and lignite particles (21) for cooling the lignite particles (21) to below 60°C.
3. Process according to one of the claims 1 or 2,
   characterized in that the crushing of the raw lignite (23) is carried out whilst maintaining a minimum spacing between the crushing pan (2) and crushing rollers (3).
4. Process according to anyone of the claims 1 to 3,
   characterized in that the cold air and/or ambient air (18) and the lignite particles (21) form a gas-dust mixture, which is supplied to a classification process, particularly in an classifier (4) integrated with the air-swept roller mill (1).
5. Process according to one of the claims 1 to 4,
   characterized in that the fluidized bed (19) is formed by blowing a spiral flow of cold air and/or ambient air (18) through the blade ring (17) surrounding the crushing pan (2).
6. Process according to one of the claims 1 to 5,
   characterized in that the cooling of the lignite particles (21) is regulated by the inflow speed, particularly in the range 40 to 80 m/s, and/or by the temperature of the cold air and/or ambient air (18)
7. Process according to one of the claims 1 to 6,
   characterized in that there is a pneumatic conveying of the crushed and cooled lignite particles.
8. Process according to one of the claims 1 to 7,
   characterized in that independently of the full or partial load operation, the classification of the lignite particles is set to a desired constancy of a particle band.
9. Process according to one of the claims 1 to 8,
   characterized in that the air-swept roller mill (1) is operated in the vacuum range.

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