Method for recovering fly ash

Abstract

Provided is a method for recovering fly ash, the method comprising a firing step for firing fly ash raw powder containing unburned carbon, and thereby burning and removing the unburned carbon. The method further comprises a step for measuring the content of unburned carbon in the fly ash raw powder, and a sieve classification step for sieve-classifying the fly ash raw powder to thereby obtain a fly ash fine powder which is the undersize fraction having a reduced content of unburned carbon, wherein the sieve mesh size used in the sieve classification step is set according to the content of unburned carbon in the fly ash raw powder, a sieve having a small mesh size is used when the content of unburned carbon is high, a sieve having a large mesh size is used when the content of unburned carbon is low, and the undersized fly ash fine powder is recovered through the firing step.

Description

technical field [0001] The present invention relates to a method for recovering fly ash, and more specifically, relates to a method for efficiently recovering modified fly ash with reduced unburned carbon content. Background technique [0002] When using fly ash as a cement admixture or concrete admixture (hereinafter collectively referred to as "admixture"), it is generally preferable that the fly ash contains less unburned carbon. [0003] However, the current situation is that the unburned carbon content of the fly ash generally produced by coal-fired thermal power plants is uneven, with many reaching 15% by mass, and only a part of them are preferable as a mixed material. [0004] In order to obtain fly ash with little unburned carbon, for example, there is a method of burning fly ash as shown in Patent Documents 1 to 3 to remove unburned carbon. [0005] However, in the method of roasting fly ash to remove unburned carbon, there is a problem that operating conditions m...

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Problems solved by technology

On the other hand, it is economically uneconomical to heat fly ash with a low unburned carbon content under the same conditions as those with a large amount of unburned carbon.

Therefore, it is difficult to treat all raw materials under the same conditions, and in the case of processing raw materials with variable unburned carbon content, the operating conditions have to be changed many times

[0007]However, even if the operating conditions are changed, the heating temperature for burning and removing unburned carbon will be a very high temperature (for example, above 700°C), which will not change not easy

For example, when the raw material is replaced, the heat balance in the furnace is easily broken, and the temperature often rises or falls too much. In addition, the oxygen supply is temporarily insufficient, resulting in insufficient reduction of unburned carbon.

In addition, when the frequency of raw material replacement is high, there is a possibility that the control cannot keep up with the replacement of raw materials, and as a result, it is almost impossible to obtain products that are preferred as mixed materials

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