Title of Invention

A METHOD FOR RECOVERY OF UNBURNED CARBON FROM FLY ASH

Abstract

This invention relates to a method for recovery of unburned carbon from flyash generated by a power plant using pulverized coals. The method comprising the steps of; preparing a slurry of flyash and water and providing it in a floation cell; mixing the pulp and conditioning it with a frother and a collector by starting the impeller and keeping the pulp in suspension; passing air into the slurry maintaining a predetermined flow rate; and removing the froth containing carbon rich ash particles after floatation.

Full Text

FIELD OF APPLICATION: The present invention relates generally to a method for recovery of unburned carbon from fly ash and particularly to a method of removing unburned carbon from fly ash generated by a pulverized coal power plant by froth flotation. BACKGROUND OF THE INVENTION; Fly ash is a solid fine grained material resulting from the combustion of pulverized coal in power station furnaces. Fly ash is composed chiefly of silica, alumina with little of N2O, K2O, CaO, TiO2, SO3, MgO and MnO. Fly ash can be used as an admixture or as a replacement of Portland cement in concentrate in a ratio upto 50%. The fly ash can be incorporated into Portland cement in one of three ways. It can be interground with Portland cement clinker in the factory to produce Portland cement, It can also be added as the concrete mix as a separately dry batched compound or mixed as a water slurry with Portland cement and aggregate during batching of concentrate. Fly ash reaching with Ca (OH)2 at the room temperature can act as pozzolanic material. But the pozzolanic activity is attributable to the presence of SiO2 and Al2O3 in amorphous form. Pozzolans are siliceous and aluminous material containing little or no cementatious value will react chemically with Ca(OH)2 in the presence of moisture at room temperature. The carbon content of fly ash determines the amount of water that has to be added to make a paste of normal consistency which is usually high when the carbon content is high. The carbon content in fly ash has a large porosity and a large specific surface and will absorb large quantities of water, water reducing agents, air entraining agents, set retarders etc. Hence the lower the carbon content better the fly ash. Fly ash carbon content is also related to the thawing and freezing resistance of concentrate. The higher the carbon content lesser the resistance. Fly ash generated from the pulverized coal power plant contains unburned carbon ranging from 5 to 15% based on the weight, in the form of fine particles. There is a need to remove this unburned carbon in order to overcome the harmful effect of the presence of carbon in the fly ash. Various methodsare known for the separation of carbon particles from the fly ash. The technology generally practiced relates to the classification followed by gravity separation. However, this technique can be employed only when there is a significant difference in the distribution of carbon in different size fractions. This technique cannot be practiced when the particles are very small in size i.e. 0.5 mm to 20 µ size. Therefore, the need exists to provide a process for the efficient separation of such particles. SUMMARY OF THE INVENTION; The main object of the present invention therefore is to provide an effective method for separating urnburned carbon from fly ash and producing high quality ash containing low carbon. This is achieved in the present invention by flotation technique. Froth flotation utilizes the differences in physico-chemical surface properties of particles of various minerals. The froth-floated cleaned fly ash can then be reused as an admixture in cement making. The present invention provides a method for recovery of unbumed carbon from fly ash generated by a power plant using pulverized coal, said method comprising the steps of preparing a slurry of fly ash and water and providing it in a flotation cell; mixing the pulp and conditioning it with a frother and a collector by starting the impellar and keeping the pulp in suspension; passing air into the slurry maintaining a predetermined flow rate; and removing the froth containing carbon rich ash particles after flotation. When the carbon percentage in the ash is less than 8%, the following technique could be followed. A slurry of ash and water of 10% pulp density is prepared and is put in the flotation cell. The impellar is started and the pulp kept in suspension. He sample is then conditioned with pine oil as the frother and diesel oil as the collector. The conditioning time maintained is 2-3 minutes. Air is then passed into the slurry. The air flow rate is maintained between 5-10 1pm. He dosages of the frother and the collector can vary from 0.5-0.7 kg/t and 0.5 to 1.5 kg/t. The froth is then removed at intervals of 1 minute. The samples are dried, weighed and sent for carbon and ash content analysis. While the carbon rich ash particles float, that which remains in the flotation cell is, after 3 minutes of flotation is devoid of carbon. Results of froth flotation of a fly ash sample with different carbon percentages are given in table 1. The unburnt carbon as can be seen from table 1 has reduced from 7% to 1.6% after froth flotation. The yield from flotation has been as high as 73% and the unburnt carbon percentage has reduced by 77%. This froth floated fly ash can then be used as an admixture in cement making. When the carbon percentage in the fly ash is above 10% the following process could be adopted. The required quantity of fly ash would be taken in a mixer provided with an impellar. Sufficient quantity of benzol would be added so as to immerse the particles. The suspension would then be mixed with impellar and then froth floated as in case 1. In table 2, where the % of unburnt carbon in feed is 19.24%, the percentage has reduced 13.4% with the carbon reduction being only 30.4%. Table 3 shows another instance where the fly ash has first been washed with benzol before being subjected to froth flotation. Here the unburnt carbon percentage has reduced to 8.3.% from a level of 22.5%, the reduction being as high as 63%. So froth flotation can be an effective way of reducing carbon from fly ash. In cases where the percentage of unburnt carbon is less than 8% froth flotation alone would suffice on the other hand when the carbon percentage is above 8% washing with benzol followed by froth flotation would reduce the carbon. TABLE 1: Froth flotation of fly ash Conditions: Pine Oil: 0.6 kf/t; Light Diesel Oil: 1 kg/t; Pulp Density : 10% WE CLAIM; 1. A method for recovery of unburned carbon from fly ash generated by a power plant using pulverized coal, said method comprising the steps of: -preparing a slurry of fly ash and water and providing it in a flotation cell; -mixing the pulp with a frother and a collector by starting the impeller and keeping the pulp in suspension; and -passing air into the slurry at a predetermined flow rate; and characterized in that the unburned carbon is removed by removing the froth containing carbon rich ash particles after flotation. 2. The method as claimed in claimed in claim 1, wherein in case of carbon content higher than 10%, said method comprises an additional step of adding a predetermined quantity of benzol to the pulp so as to immerse the particles before starting the step of mixing and conditioning the pulp. 3. The method as claimed in claims 1 or 2, wherein said frother is pine oil and said collector is diesel oil. 4. The method as claimed in the preceding claims, wherein the conditioning time is maintained at 2/3 minutes. 5. The method as claimed in the preceding claims, wherein the flow rate is maintained between 5-10 ipm. 6. The method as claimed in the preceding claims, wherein the dosage of the frother and the collector can respectively vary between 0.5 to 0.7 kg/t and 0.5 to 1.5kg/t. 7. The method as claimed in the preceding claims, wherein the froth containing carbon rich ash particles is removed at intervals of one minute. 8. The method as claimed in the preceding claims wherein the froth containing carbon rich ash particles and the remaining ash particles in the flotation cell are dried and weighed for analysing carbon and ash content. 9. The method of removing unburned carbon from fly ash generated by a power plant using pulverized coal, substantially as herein described. This invention relates to a method for recovery of unburned carbon from flyash generated by a power plant using pulverized coals. The method comprising the steps of; preparing a slurry of flyash and water and providing it in a floation cell; mixing the pulp and conditioning it with a frother and a collector by starting the impeller and keeping the pulp in suspension; passing air into the slurry maintaining a predetermined flow rate; and removing the froth containing carbon rich ash particles after floatation.

Documents:

466-kol-2004-abstract.pdf

466-KOL-2004-AMANDED PAGES OF SPECIFICATION.pdf

466-KOL-2004-AMANDEDCLAIMS.pdf

466-kol-2004-claims.pdf

466-KOL-2004-CORRESPONDENCE 1.1.pdf

466-kol-2004-correspondence.pdf

466-kol-2004-correspondence1.2.pdf

466-KOL-2004-DESCRIPTION (COMPLETE) 1.1.pdf

466-kol-2004-description (complete).pdf

466-kol-2004-description (provisional).pdf

466-KOL-2004-EXAMINATION REPORT REPLY RECIEVED.pdf

466-kol-2004-examination report.pdf

466-KOL-2004-FORM 1-1.1.pdf

466-kol-2004-form 1.pdf

466-kol-2004-form 13.pdf

466-kol-2004-form 18.1.pdf

466-kol-2004-form 18.pdf

466-KOL-2004-FORM 2-1.1.pdf

466-kol-2004-form 2.pdf

466-KOL-2004-FORM 3-1.1.pdf

466-kol-2004-form 3.1.pdf

466-kol-2004-form 3.pdf

466-KOL-2004-FORM 5-1.1.pdf

466-kol-2004-form 5.1.pdf

466-kol-2004-form 5.pdf

466-kol-2004-gpa.pdf

466-kol-2004-gpa1.1.pdf

466-kol-2004-granted-abstract.pdf

466-kol-2004-granted-claims.pdf

466-kol-2004-granted-description (complete).pdf

466-kol-2004-granted-form 1.pdf

466-kol-2004-granted-form 2.pdf

466-kol-2004-granted-specification.pdf

466-KOL-2004-OTHERS 1.1.pdf

466-kol-2004-reply to examination report.pdf

466-kol-2004-specification.pdf