DE3628963C2 - - Google Patents

Description

The invention relates to a method in the preamble of claim 1 above.

Fly ash made from fossil fuels Furnaces such as B. from hard coal, lignite power plants and mill incinerators are often too high Carbon content for the further use of the fly ash on.

If the loss on ignition is over 5%, the ash is not more test mark capable, what according to DIN 1045 (Certification mark directive) a prerequisite for a direct Use of fly ash e.g. B. is as a concrete additive.

Furthermore, in large combustion plants, the combustion devices are converted to single or multiple-stage combustion with a view to reducing the NO _x formation as far as possible. An increase in the C content in the fly ash occurs up to 20-30%.

From DE-PS 8 90 032 it is known to fly ash through a Foam floating process (flotation), in a coal-rich  and a low carbon fraction with an ash fraction of disassemble up to 97%. The coal rich part in Form of an extraordinarily fine and light coal dust dries as fuel again after drying use.

It is the object of the present invention Specify the procedure of the type mentioned, in which the carbon-rich portion (foam product) without drying is to be reused.

This object is achieved in that the foam product the furnace is fed directly, and that the Fly ash with water and such a flotation aid medium is floated in a furnace can also be burned.

The C-rich foam product can be obtained from the operator of the Firing system thus ent in a simple manner be sure that he is the foam product of the furnace feeds the plant itself. The flotation can be on a multiple ways using the flotation aid used medium the fraction limit is set; the Flotation aids disrupt the operation of the furnace plant not.

Preferably, the foam product is possibly after a partial drainage to the firing system main fuel before or in a mill that leads to the grinding of the main solid fuel material is provided.  

As a flotation aid in the furnace can also be burned, z. B. heating oil or aliphatic hydrocarbons.

Starting from DE-PS 8 90 032, the present Invention as a further task, in addition to Burn the foam product another Specify application.

According to the invention it is provided that the foam product after drainage and drying as pouring and Covering powder is used for the continuous casting area.

The foam product is drained and dried preferably by means of a pre-dewater such. B. one Thickener or decanter, and one of these downstream drainage filter and a Drainage filter downstream with a hot gas charged dryer, which a dust collector is connected downstream.

Although hot gases also come from the furnace in the form of hot flue gases or after the air preheater to the combustion system of branched hot air it is advantageous if the hot gas is in a hot gas generator separate from the furnace is produced.

When drying in a power dryer, it is advisable if as fresh air only for the hot gas generator necessary amount of air is supplied, and as a mixed gas Flue gas is supplied, which after the electrostatic precipitator Firing system is removed. In this way the Heat economy of the process when heating the Current dryer with hot gas <1100 ° C, preferably 900 ° C improved.  

Finally, it is useful if the mechanical Drainage of the C-rich foam product by adding is supported by flocculants.

An embodiment of the method according to the invention is intended now using the block diagram are explained.

Of the multitude of components of a combustion system, only one mill ( 1 ), a boiler ( 2 ) and an electrostatic filter ( 3 ) downstream of this are shown in the figure. The mill is supplied with main fuel ( 4 ), which is burned in the boiler with the combustion air ( 5 ). The fly ash separated in the electrostatic filter ( 3 ) is fed via a line ( 6 ) to a conditioner ( 7 ), to which flotation aids ( 8 ) and fresh water ( 9 ) or circulating water ( 10 ) are also fed. The suspension is fed from the conditioner ( 7 ) to a flotation apparatus ( 12 ) via a line ( 11 ). The applicant claims no protection for the flotation itself and therefore does not go into a further description of the structure of the flotation apparatus.

Flotation machines are e.g. B. in "Ullmann's Encyclopedia der Technischen Geräte ", 4th ed., 1972, Vol. 2, Process engineering I, pp. 110-142 in a sufficient manner described.

The foam product of the flotation apparatus ( 12 ) is fed via line ( 13 ) to a partially dewatering filter ( 14 ) and from there is added to the main coal stream ( 4 ).

The waste product of the flotation apparatus is fed to a thickener ( 16 ) via a line ( 15 ), and the thickened product is fed to a filter ( 18 ) via line ( 17 ). A wide variety of filter types can be used as filters, e.g. B. band filter, vacuum filter, drum filter or the like. The return water from thickener ( 16 ) and filter ( 18 ) is fed as circulating water ( 10 ) to the conditioner ( 7 ). The filter cake is fed to a thermal dryer ( 19 ), which is preferably a current dryer. Instead of a current dryer, other convection dryers can be used, for example the two-stage convex dryer from BUSS. These have the advantage of also processing a C-poor fly ash fraction that has only been dewatered to a pasty state. Other drying processes, such as e.g. B. directly or indirectly heated rotary dryer or the like. Finally, the current dryer itself can be operated without dry material backmixing or with dry material backmixing, in the latter case a transfer of the feed material from pasty to a more easily pourable state is possible.

The current dryer ( 19 ) is supplied with hot gas by a hot gas generator ( 20 ). Combustion air ( 21 ) and a foreign fuel ( 22 ) in the form of oil and gas are fed to the hot gas generator.

The dotted line ( 13 ' ) in the figure shows that the C-rich fraction can also be directly entered as a so-called coal water slurry (CWS) via one or more additional lances directly into the combustion chamber of the boiler, ie not necessarily that Main coal stream must be supplied.

The line ( 21 ' ) shows that under certain circumstances it can be useful to remove flue gases behind the electrostatic filter ( 3 ) and to use it as mixed air for the current dryer ( 19 ).

The material dried in the current dryer ( 19 ) is fed via a line ( 23 ) to a dust separator ( 24 ), from which the dried C-poor fly ash fraction is drawn off via line ( 25 ). The exhaust air from the dust separator is mixed via a line ( 26 ) with the flue gases supplied from the boiler ( 2 ) to the electrostatic filter ( 3 ). Because of this vapor recirculation, the fly ash separation in the dust separator ( 24 ) does not have to be complete, ie multi-cyclones can be used, for example, as dust separators ( 24 ). However, it would also be the use of intensive filters, such as. B. jet filters as a dust collector ( 24 ) conceivable so that the exhaust air of the dust collector ( 24 ) can be derived directly into the atmosphere.

The dash-dotted line ( 26 ' ) indicates that the exhaust air can be mixed in whole or in part with the combustion air ( 5 ).

As already mentioned in the introduction to the description, it should also be convenient not only to the C-rich fraction to drain, but also to dry and not in the Combustion plant to burn, rather than high quality Sell product, e.g. B. as a casting and masking powder Operator of continuous casting plants.

example

In a 550 MW large boiler, one to be fractionated Fly ash flow of approx. 12 t / h with a C content of 10% at. This fly ash is made with aliphatic Float hydrocarbons as flotation aids and can be separated into 15% with a C content of 50% and 85% with a loss on ignition of 4%, whereby the C content or Loss of ignition on each of the dewatered and dried  Obtain fraction. The foam product is on one Moisture content of 20% dewatered and as the CWS Boiler supplied, which corresponds to a supply of 1 t / h C.

Claims (3)

1. Method for using fly ash of a combustion plant operated with solid fuels ( 2 ) with a downstream electrostatic filter ( 3 ) by flotation ( 12 ) as a function of the C content, in which the fly ash is a C-rich foam product ( 13 ) and Low-carbon waste product ( 15 ) is broken down, the flotation conditions being chosen so that the waste product ( 15 ) has a loss on ignition of at most 10% by weight, characterized in that the foam product ( 13 ) of the furnace ( 2 ) is direct is supplied, and that the fly ash ( 6 ) is floated with water ( 6, 10 ) and a flotation aid ( 8 ) which can be burned in the furnace ( 2 ). 2. The method according to claim 1, characterized in that the Schaumpro product ( 13 ) possibly after a partial drainage ( 14 ) to the main fuel flowing to the furnace ( 4 ) before or in a mill ( 1 ) is supplied for the grinding of the solid main fuel is provided. 3. Method for using fly ash of a combustion plant operated with solid fuels ( 2 ) with a downstream electrostatic filter ( 3 ) by flotation ( 12 ) depending on the C content, in which the fly ash is a C-rich foam product ( 13 ) and Low-carbon waste product ( 15 ) is broken down, characterized in that the foam product ( 13 ) is used after casting and drying as casting and covering powder for the strand casting area.