FI128128B - Method for refining coal ash of coal power plants and/or carbonaceous ashes produced in other combustion plants by separating carbonaceous product for further processing - Google Patents

Abstract

A process for the industrial processing of coal-fired ash and / or carbonaceous ash produced by other combustion plants, separating both the carbonaceous product and the substantially carbon-free silicate ash products from each of these ash types for further processing, the process comprising separating the properties of foamed silicate containing almost carbon-free ash fractions. The carbonaceous ash separated in the flotation is passed or later transferred to a carbon activation process to produce activated carbon therefrom.

Description

METHOD FOR THE PROCESSING OF COAL ASH ASP FROM COAL POWER PLANTS AND / OR OTHER FUELS, BY SEPARATING THE COAL-PRODUCED PRODUCT FOR PROCESSING

The present invention relates to a process for the industrial processing of coal-fired ash and / or carbonaceous ash produced by other combustion plants by separating both the carbonaceous product and the substantially carbon-free silicate ash products from both these the properties of foaming silicate-containing, almost carbon-free ash fractions more easily.

The enrichment of coal-containing slags from ash from coal-fired power plants is known in the prior art from FI121299. According to the present invention, the enriched carbon fraction is recycled to fuel.

Further, the enrichment of carbonaceous ash slags in other combustion processes, such as gasification plants for the industrial processing of forged ash, is disclosed in FI-125598. In this case, the coal is recovered from the ash for recovery and recovered in the process to recover substantially carbon free ash.

The carbon segregated according to the methods disclosed in the publications cited above is recycled to combustion, whereby this carbon is also converted to carbon dioxide and thus increases the amount of carbon dioxide in the atmosphere.

In the present invention, the carbon separated from the ash is not burned but is converted into useful activated carbon and thus remains carbon. The present invention is characterized in that the carbonaceous ash separated during foaming is passed or subsequently transferred to a carbon activation process to produce activated carbon therefrom.

An advantage of the invention is that the carbon fraction generated in the ash from the combustion of coal and other similar fuels is separated and is no longer recycled, thereby reducing the total formation of carbon dioxide. However, the recovered carbon is usefully utilized when it is converted into activated carbon.

Activated charcoal is currently produced, for example, from coal, peat, animal tissue, etc. The principle is that at least the hydrocarbons must be removed from the raw material. The raw material is heated while allowing partial combustion which is controlled by limiting oxygen supply. By heating the raw material at 800-1000 degrees, the carbon is porous and its surface, especially inside the granules or particles, becomes very large.

At the same time, coal-fired ash from power plants contains flammable carbon in varying amounts from 1% up to 20%. The ash material of coal ash is predominantly in the form of spherical particles which are vitrified silicate minerals. The particulate form is inexpensive and allows coal ash to be utilized in many applications as long as its carbon content is sufficiently low and stable. Coal ash can be used as such in concrete products and other construction related dry products and in concrete work applications.

The large-scale utilization of coal ash is hampered by the large variation in the amount of unburned coal in the ash. High carbon content reduces the workability of fresh concrete, makes it difficult to use some additives and loose concrete. The use of coal ash is defined in the standards where its use is controlled according to the carbon content of the coal ash. In addition, the coal ash has a very broad grain distribution of 0.1 µm to 1000 µm.

Experimentally, it has been found that coal ash can be economically removed by pneumatic grading up to 50% by weight of the fine fraction having a particle size less than 50 µm. Depending on the combustion process, unburnt coal is enriched in various products or fractions. In certain cases, the carbon content of the fine product or fraction is significantly higher than the average carbon content. By returning such a product or fraction back to the power plant's boiler plant, non-combustible coal can be burned and the energy of the coal utilized in the combustion process. The present invention avoids the re-combustion of such unburnt carbon when the carbon is converted to activated carbon.

Pneumatic grading based on particle size allows the desired fraction to be reduced from the coal ash, enabling the water-based flotation technique to operate selectively and accurately and economically separating the carbon from the actual silicate-based ash.

In the following, the invention will be explained in more detail with reference to the accompanying drawings in which

Figure 1 schematically shows a coal ash refining process.

Figure 2 schematically shows the distribution of a batch of coal ash in the various stages of the process as a percentage by weight.

Figure 3 shows experimentally achieved mass distributions and concentrations.

Figure 1 shows a coal ash 1 feed tank 8 from which coal ash is dispensed to a process such as a pneumatic conveying pipeline 17 which transfers said ash to pneumatic classifiers 2 ... 4, of which the coarse fraction 5 continues to the silo 18. The finest fractions are recovered in tanks 9 and 10.

From the silo 18, the coarse fraction 5 is metered into a frothing device to a frother apparatus coach 11, from where the frothed material is fed to the frothing cells 6a, 6b and further from the ash fraction through filter 7a to drying and through classifiers 14, 15 to product filters 12 and 13.

Preferably, the feed tank 8 is provided with a measurement of the carbon content of coal ash 1 by means of a device 16 which, based on on-line analysis or continuous analysis, directs the material stream from the grading apparatuses to 2 ... 4 and, if necessary, directing the fluff-free fraction to the first grading steps 2 ... 4. Foaming uses chemical chemicals added to water to enhance foaming.

For silicate end products, it is preferred that the carbon-free silicate ash products obtained from the product silos 12 and 13 are micronized or micronized using various fine grinding methods, such as counter-jet grinding and recycling, so that their index of activity becomes higher than that of cement.

Figure 2 shows a batch of coal ash of 10 units initially in a tank 1. The batch has a conventional carbon content of 10% by weight. The unit numbers at each stage of the process are shown as numbers within brackets.

The batch of coal ash leaving tank 1 is classified in classifiers 2 ... 4 and in the example the number of units 10 is distributed such that 7.5 fraction coarser fraction is continued into tank 18 and the finer fraction is recovered 1.5 + 1 = 2.5 units into tanks 9 and 10.

The 7.5 units introduced into the tank 18 are distributed by the flotation apparatus 6a such that 1.5 units of carbon, about 60% by weight of carbon is passed to further processing and a finer fraction of 6 units containing less than 1% of carbon is passed through the classifiers 14.15 product silos 12 and 13, in Example 3 units for each silo, where the carbon content is less than 1% and these become silicate products.

From the container 12, according to an exemplary embodiment, a fine classified fraction having a C content of less than 1% by weight is derived, for example, into containers 9 and 10 for mixing with the fractions therein having a total unit number of 2.5 + 3 = 5.5 and a carbon content of less than 5 wt%.

If a high carbon fine product is separated from classifiers 2 and 4 into tanks 9 and 10, in one embodiment, this fine product may be combined with the filtered carbon concentrate 7b and the mixture thereof used as a raw material for the production of activated carbon.

The quality of the ash to be processed depends on the coal and the construction of the boiler. If the ash contains a large amount of finely divided carbon, it is treated in a pneumatic classifier, wherein the embodiment of the invention is according to claim 2. If the ash fines do not contain significantly foaming carbon, such as size <10 µm, the ash can be directly introduced into the flotation process, wherein the embodiment of the invention is according to claim 1.

Figure 3 shows the separation of carbon intended as a feedstock for the preparation of activated carbon. Carbon is almost completely separated from coal ash to coal concentrate, and Figure 3 further shows that the water used for the purification medium operates in a closed circuit, which requires only the addition of moisture from the product.

The ash to be processed contains carbon, soot and silicate particles. The carbon may be adhered to the surface of the silicate particles. The pneumatic treatment of the ash removes carbon from the silicate particles and by classifying the ash stream prior to flotation, the carbon content of the carbon fraction can be increased.

In making the ash fraction activated carbon, the carbon contained in the ash is already partially activated in the combustion. However, the carbon fraction according to the invention must be activated by chemical or physical activation known per se in order for the carbon to become porous and large-area.

Claims (2)

1. Process for ash from coal-fired power plants and / or from other combustion plants 5 for the industrial processing of carbonaceous ash, separating both the carbonaceous product and the substantially carbon-free silicate ash products from said ash types, both for their own further processing, the process comprising separating the improves by first classifying the coal ash or ash products in a series of pneumatic classifiers (2 ... 4) such that the ash as a medium is classified in the fine and coarse fraction according to the particle size and, where necessary, the classifications are repeated so that the coarse fraction has 10 µm, whereby the coarse fraction is introduced into the flotation process and the carbon content separated in the flotation is The ash is passed or later transferred to a carbon activation process to produce activated carbon therefrom. Process according to claim 1, characterized in that the activation process utilizes chemical or physical activation known per se.