DE2926524C2 - Process for drying pre-crushed salty brown coal with simultaneous extraction of steam - Google Patents

Description

- In a combustion chamber cooled by means of heat exchange surfaces dte flue gases, their Oxygen content is adjusted to a maximum of 13% by burning a salty fuel are produced,

- the flue gas temperature over the heat exchange surfaces to that for the following The required drying level is set,

- the heat transferred to the heat exchange surfaces to generate steam for process, Drive and / or heating purposes is used in integrated systems

- and the flue gas without the interposition of a separator for unburned Residue and fly ash is introduced into the dryer.

2. The method according to claim 1, characterized in that the production of the hot flue gas takes place in a multiple subdivided combustion chamber, in a first uncooled or weak cooled part the flame is maintained and in one or more following parts through suitable heat exchange surfaces, preferably radiant heating surfaces, the hot flue gas in normal operation cooled at least approximately to the temperature required for the drying process will.

3. The method according to claim 2, characterized in that a controllable partial flow of the flue gas from the first uncooled or weakly cooled part of the combustion chamber in whole or in part excluded from contact with the heat exchange surfaces of the or the following parts of the combustion chamber and again with the rest of the flue gas after it has left the combustion chamber is united.

4. The method according to claim 1 or 2, characterized in that corrections of the temperature of the flue gas flow at the outlet from the combustion chamber as well as a regulation within certain limits of the ratio of dry coal production and steam production take place in that a part or a variable in size part of the heating surface installed in the combustion chamber from Contact with the hot flue gas of the combustion chamber is excluded.

5. The method according to any one of claims t to 4, characterized in that the control of the process, in particular a regulation of the ratio of dry coal production and steam production

by changing the air ratio number A for the operation of the combustion chamber.

6. The method according to any one of claims 1 to 5, characterized in that the salt-containing fuel, which reaches the combustion chamber for combustion is salty raw lignite

7. The method according to any one of claims 1 to 5, characterized in that the salt-containing fuel, that reaches the combustion chamber for combustion, part of that coming from the dryer Is dry coal

8. The method according to claim 7, characterized in that the coming to the combustion salty Fuel is separated from the dry coal by a suitable separation process, for the weitero Ennobling unwanted fractions consists.

9. The method according to any one of claims 1 to 5, characterized in that the for combustion Salt-containing fuel that arrives is partly from combustible fuels that occur in the integrated system Residues

The invention relates to a method for drying pre-crushed salty brown coal according to the im Generic term of the main claim specified genus.

Soft lignite is characterized by its low calorific value, high water content and in the production state low dimensional stability It is therefore usually necessary to use this soft brown coal in a utility energy carrier to convert with high utility value for the end user of the energy. Case in point for Such a refinement of the lignite is the conversion into gas for the public supply or as an intermediate product for chemical syntheses (synthesis gas) according to the following scheme:

Pre-shredding
Drying

possibly shaping or further comminution or classification
gasification

Gas cleaning and recovery of by-products, such as. B. Tar; Release of the cleaned gas as town gas or synthesis gas.

For some of these process steps (drying, gasification, gas cleaning) as well as for additional process steps There is a need for steam to provide auxiliary media and to work up waste products different pressure levels. This steam requirement is - if not covered by waste heat recovery - Generated in a coal-fired counter-pressure power plant, which is usually processed with the rest of the refining. Supply and ancillary systems form an integrated economic unit.

There are known occurrences of soft lignite due to the very high content of sodium chloride and other alkali compounds in the raw coal are marked, so-called salt coals. It is common as a "Saline raw brown coals" to designate such coals, their anhydrous state Sodium content, calculated as NajO, greater than 0.5% is. A typical value is, for example, 2.5% NajO, based on the anhydrous state, with the bond

The sodium in the coal is given in the form of humates and chlorides The high content of alkali compounds in the coal leads to considerable difficulties during combustion in steam generators mineral deposits on the heating surfaces. It is characteristic that these approaches, which are partly due to the sublimation of alkali salts, which evaporate during combustion are partly attributed to the sticking of fly ash by means of eutectic partial melts, occur predominantly in the area of the secondary heating surfaces.

Despite intensive development work, it has not yet been possible to achieve a technically and economically satisfactory one To find a solution to use salty raw lignite in coal dust-fired steam generators to be able to. The level achieved so far is limited despite the use of special constructions and restrictions in terms of efficiency and travel times of the maximum permissible alcohol content Raw coal with coal dust-fired steam generators to 0.1 to 0.3% Na2O, based on anhydrous substance.

Higher salt contents, e.g. B. up to 2.5% Na ₂ O, based on the anhydrous state, have so far only been mastered in grate-fired steam generators for a maximum steam generation of up to 60 t / h.

For gas generation from lignite, a prior drying of the coal of z. B. 55% water content in the delivery state to (depending on the gasification technology used) water content of 8 to 20% necessary.

The usual way in lignite technology is to use steam for drying. In addition there is steam used with a pressure of 0.3-0.5 MPa, which is taken from a back pressure power plant. This The path that is advantageous in terms of the energy economy is not feasible for salty raw lignite because it is suitable and sufficient powerful steam generators for the use of brine, as shown, are not available.

For a lignite refining combine economically and economically optimal size on the basis the use of saline raw lignite means this state that for the operation of the necessary Counterpressure power plant either completely or at least to a substantial extent salt-free coal of others Provenance must be used or that the power plant part with a large number of smaller grate boilers equipped with the disadvantages of low labor productivity and high investment requirements will. Both alternatives are unsatisfactory.

It is known to dry lignite by means of hot flue gases, for example convection drum dryers (so-called fire gas drum dryer) or flight dryer, in which the coal to be dried in the flue gas is suspended through a pipe, find use. Thereby these Flue gases often generated by burning lignite. The incineration runs in refractory lined Combustion chambers, with grate firing, but also dust firing use. The regulation

J Τ »· λλΙ» »* Α ·· Γϊη (ι · ΐ» Ιι · «Ληι> · ΛΒη4 · ι ·· -» •• ff .- »! *» * ^ J ..— _n L. Γ » ί1—1-

uv · ■ ι is *. ■% ■ ti.1 uiiui lllJlVIIip \, l UtUI V.1 IVSIg I UUI VlI IXUVfV- conduction of comparatively cold flue gas / vapor mixtures from the end of the dryer or by adding air. (See, for example, BE Rammler, HJ v. Alberti: Technologie und Chemie der Braunohlenverwertung; VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1962. pp. 155/156.) Experience has shown that both the recirculation of exhaust gases and the addition of air increase, above all in the case of an - and shutting down the system, there is a risk of fire. In terms of safety, it is also critical - especially in the case of high-performance dryers - the relatively large amount of heat stored in fireproof masonry in the combustion chamber, and the special measures ζ. B. the construction of an emergency chimney, in order to quickly drive the dryer cold and to be able to take it out of operation in the event of malfunctions.
In power plant technology it is known to be hot

ίο Part of large steam generators with against pollution to equip relatively insensitive radiant and bulkhead heating surfaces and with these heating surfaces the flue gases on z. B. 700 ° C to cool.

For the dimensioning of such radiant and bulkhead heating surfaces, z. B. to K. Schröder, Große Dampfkraftwerke, Third Volume, Springer-Verlag Berlin, Heidelberg, New York, 1966, pages 144-146, can be referred to.
After investigation by Hanel, Freiberger Forschungshefte, Heft A 257, 1963, pages 79-92, explosions of lignite dust can be avoided if the oxygen content in the dust-laden atmosphere z. B. a dryer remains below 13%
The invention is based on the object of specifying a method of the type according to the application, which is intended for the use of salty raw lignite, does not require counterpressure steam to be obtained from outside, overcomes the above-described, in particular safety-related disadvantages of conventional lignite drying with hot flue gases, at the same time steam for other uses allowed, which works with satisfactory travel time, without the need to supply salt-free or low-salt lignite, and which allows economic standard services for large-scale plants

This object is achieved with the means specified in the characterizing part of the main claim
According to the invention, the heat output of the cooled combustion chamber is matched to the heat demand of the drying process. In order to ensure favorable ignition and burnout conditions in the combustion chamber, according to the invention it can be subdivided two or more times, with the first part of the combustion chamber viewed in the direction of flow not being cooled or being cooled to a limited extent. This can e.g. B. can be achieved by refractory lining instead of steam generator heating surfaces or on the side facing the flame of such heating surfaces. In this case, the steam generation takes place wholly or for the most part in the following parts of the combustion chamber which are equipped with suitable heating surfaces, preferably radiant heating surfaces.
According to the invention, the heating surfaces and the geometry of the said combustion chamber are designed in a known manner so that, under normal conditions, the temperature of the flue gas emerging from the combustion chamber corresponds to the temperature required for the dryer.

For the correction of deviating operating conditions, for the on-site and outdoor work as well as for the control According to the invention, the temperature of the flue gas after it emerges from partial load states the combustion chamber and before entering the dryer can thus be set to the desired value, that a controllable partial flow of the flue gas from the first uncooled or slightly cooled part of the Combustion chamber in whole or in part from a contact

with the heat exchange surfaces of the following Parts of the combustion chamber is excluded and with the rest of the flue gas after its exit from the Combustion chamber is reunited.

To achieve the same purpose, it is also possible according to the invention to use the entire hot flue gas flow the combustion chamber with suitable technical possibilities from contact with a possibly in his Exclude a variable part of the installed heating surface.

In an embodiment of the invention that is advantageous in many cases, the process is controlled, in particular the adaptation of steam generation and dry coal generation, by changing the air-fuel ratio, that is to say the air ratio λ is for operating the combustion chamber. This can be done both by regulating the coal supply and by changing the amount of combustion air. An increasing value of λ lowers the specific steam generation per kg of dry coal produced. However, for safety reasons, the oxygen content in the flue gas should not exceed an upper limit of 13%.

The carbon dioxide content can be used in a known manner as a measure of the air ratio, possibly as an impulse for a control system or the oxygen content of the flue gas as it exits the combustion chamber can be used.

The water content of the dry coal can be changed in a known manner under otherwise identical conditions the ratio of flue gas to the amount of raw coal used in the dryer can be corrected.

According to the invention it is also possible as fuel to use part of the dry coal produced in the dryer for said combustion chamber. Likewise there is the possibility of unneeded or unusable quantities in the further refinement process on dry coal or dry coal dust to heat the combustion chamber. Not like that usable proportions are z. B. coarse-grained fractions that occur in downstream processes in the Airborne cloud would interfere or dust-like fractions, which are undesirable in fluidized bed processes.

Finally, the heating of the combustion chamber can be wholly or partially carried out at other points throughout the whole Flammable waste products or residues occurring during the refining process. Is the subsequent one Refining process is a gasification process, this applies in particular to separated from the raw gas, carbonaceous fly ash.

The fly ash produced during the combustion of coal in the combustion chamber is made according to the invention transferred from the flue gas to the dryer, so that on the otherwise usual ash separation from the flue gases is waived. The ashes are from the to be dried Coal included. She will in the event of a subsequent Gasification incorporated into the ash or slag produced during gasification. For elimination of the ash remaining in the combustion chamber (combustion chamber residue) become the known ones technical facilities used.

The inventive method is for drying crushed salty brown coal with simultaneous Extraction of steam for use in integrated systems for generating gas from saline Raw lignite determines Its use is not limited to the use of brine, but rather can be used in all cases where, in addition to a need for dried raw lignite,

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Embodiment

The invention is to be explained in more detail using the following exemplary embodiment with reference to FIGS. 1 to 3 will:

In a plant, synthesis gas is obtained from salty raw lignite. The raw coal has a water content of 54% and a calorific value of 2500 kcal / kg. The process scheme of the plant is based on FIG. 1 explains The main amount of the supplied salty raw lignite is comminuted in a processing plant 1 to a grain size of 0-6 mm and fed to the fuel gas dryer 4. A further partial stream of the raw coal is comminuted in a mill 2 to dust fineness (<1 mm) and as fuel for the fitted with heating surfaces of the combustion chamber 3 is used with the installed in the combustion chamber heating surfaces, steam having state quantities of 81 kp / cm ² (abs.) and 460 ⁰ C, the flue gas cools to temperatures of 700-800 ° C. At this temperature, the flue gas enters the fire gas dryer 4, in which, using the heat content of the flue gases, the main crushed amount of raw coal is dried to a water content of 10%. The flue gases and the vapors produced during the drying process leave the dryer at a temperature of 120 ^° C. and, after dedusting in the filter 5, enter the atmosphere. The amount of dust deposited in the filter is added to the dry coal from dryer 4. The dry coal is fed to generator 6 ("angle generator"), which works on the principle of gasification in the fluidized bed, and gasified with a mixture of oxygen and steam at approx. 900 ° C After separating off carbon-containing fly ash in separator 7, raw gas passes through the usual waste heat recovery systems 8, some of which, not shown in the diagram, are used to preheat the feed water, cooling and condensation 9 and desulphurisation 10 and then used for further processing and use.

The high pressure steam generated in the combustion chamber 3 is used as drive energy, as shown in FIG. 1 shown, for example for the steam-powered turbo compressor of the oxygen system 11 and for other conventional ones Uses used while the process steam demand of the generator 6 by the advent is covered by waste heat steam from the waste heat recovery plant 8 of the gasification process.

The C-containing flue dust accumulating in the separator 7 has a calorific value of approx. 3500 kcal / kg and is the Fuel for the combustion chamber 3 is added with a corresponding reduction in the need for raw coal.

Based on an input quantity of 100 t / h dry lignite for the gasification, the following specific information results, valid for a flue gas inlet temperature of the flue gases in the dryer of 750 ^D C. an air ratio / 2 = 1.20, a dryer exhaust gas temperature of 120 ° C and a Feed water temperature when entering the heating surface of the combustion chamber of

Quantities, t / h 29 Yes 230 26 524 7th Raw coal total of that Airborne dust recirculation 195 for drying no 35 for combustion chamber 20th 5 Airborne dust recirculation 258 100 Dry coal for ver gassing 195 104 Steam generation in 63 Combustion chamber - 10 Quantities / m ³ i. N7h 28,000 Oxygen demand 138,000 Synthesis gas production 15th

In condensation mode, the amount of steam generated corresponds to a drive power of 25 MW, the compared to the demand for oxygen generation approx. 14 MW. The surplus is used for other consumers of drive energy used in the factory.

The process is controlled, in particular the change in the ratio of steam generation to dry coal generation, is carried out by adapting the combustion air ratio of the combustion chamber; 2 sets the relationship between air ratio number A and steam generation per kg of dry lignite or fire coal demand per kg of dry lignite. The relationship between the air ratio number A and the easily measurable Cb content in the flue gas when it emerges from the combustion chamber is shown in FIG. 3 shown. In Fig. 2, a possible return of fly ash from the gasification process as additional fuel for the combustion chamber is not taken into account, but the influence on the steam generation is negligible.

For this purpose 3 sheets of drawings

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Claims (1)

Patent claims: 1. Process for drying pre-crushed salty brown coal with simultaneous extraction of steam for process, drive and / or heating purposes, with flue gases having a temperature introduced from 500 to 1000 ° C in a dryer charged with raw coal and the coal up a final water content required for further processing is dried, for use in integrated systems for gas generation from salty lignite, characterized by a combination of process steps known per se, wherein