Ashes processing

        1. Initial data for the assessment

                           1.1.      Initial raw materials

        2. The advisable flowsheet for the ashes processing

                           2.1.    The main chart of the process

                           2.2.    The level of development of component parts of the suggested technology

                                      2.2.1. Unit of the ashes break

                                      2.2.2.  Water leaching of fusion cakes

                                      2.2.3.  The alumina production

                                      2.2.4.  The production of concentrates of less-common metals

        3. The evaluation of the economic performance of the production

        4. Summary

 

Here are results of the technical and economic assessment of the technology for a deep processing of ashes in heat-electric generating plants with the emission of valuable components as marketable products.

The basis of technological solutions is comprised of results of researches done by members of the Institute "Hydrotsvetmet" and by YOUR initiative.

1. Initial data for the assessment

        1.1. Initial raw materials

As the raw material for the technical and economic assessment there was used a sample of the current ash of the Novokemerovsk Heat-electric Generating Plant, the chemistry of which is given in the table 1.1.

Table 1.1.

The chemistry of the ash sample of the Novokemerovsk Heat-electric  Generating Plant 

 

Component	Content, %	Component	Content, gram per ton
Si02	58.0	ZrO3	730
Аl2Оз	20.3	La2Оз	92
Fе20з	6.1	Се2Оз	117
Р2О5	0.27	Y2Оз	76
CaО	2.5	Sc203	77
MgO	1.6
Na2O	0.63
К20	2.3
ВаО	0.21
МnО	0.11
TiO2	0.81
WO3	0.02

 

As seen from the data shown in the table 1.1 the following components in the given chemistry are of commercial interest: silica, aluminium and less-common metals (Zr и rare earth elements). The mineralogical analysis of the given ash sample showed that aluminium in general is represented by mullite and silicon - by mullite and cristobalite. The given mineralogical composition of the product under processing suggest the usage of rigid techniques for its breaking, for example, baking or alloying with  reagents which destroy the structure of mullite. Such reagents can be soda or nutrium sulphate in the presence of a reducing agent (carbon in the form of chark or charcoal) 

2. The advisable flowsheet for the ashes processing

        2.1. The main chart of the process

    The flow chart of the advisable technology for the processing of ashes of the Novokemerovsk Heat-electric Generating Plant, is represented on the figure. The break of ashes has the putting of its components in the soluble state as its aim. The method of breaking is the alloying of ash with soda in electric furnaces. The cooled fusion cake is put through the process of water leaching of sodium silicate and potassium. The water leaching solution is later used in the repartition of the production of silicon comounds. In the economic part of the present "Data note" as the marketable product of the repartition of the production of silicon comounds there is taken "carbon white".

 

 

Annual production                                       Table 3.3.

Production	Quantity, tonns	Cost, $/ton	Total, in thousands $
"Carbon white"	13860	500	6930
Alumina	6171	115	710
Zirconium concentrate (50%)	26.4	1500*	40
Concentrate of rare earth elements (10%)	75.9	60000*	4524
Marketable products			12204

 

* prices are calculated according to Ministry of External Economic Links of the Russian Federation

Annual profit (calculated) is 12204 - 5934 = $ 6270000 . The annual income tax (calculated ) is 6270*0.35 = $ 2194.5 thousand. The annual after-tax profit is 6270 - 2194.5 = $ 4075.5 thousand. The calculated profitableness of the production of the ashes processing is (4075.5/5934) * 100 = 68.6%. The calculated pay-back period is 4255/4075.5 = 1.04 year.

The production of alumina from cake leaching is done according to the classical "bayer" technology. Cakes of the "bayer limit' are directed to the acid leaching.

The acid leaching of the cake is done with the help of sulphuric acid solution. Cakes of the acid leaching are dropped into a dump pit, and the sulfuric solution - for the revision of the production of less-common metals concentrates.

        2.2. The level of development of component parts of the suggested process flowsheet 

         2.2.1. Unit of the ashes breaking.

    As a technique for the ashes breaking here is suggested the alloying of ashes with soda. This allows to convert a considerable part of silica to water-soluble silicates (sodium and potassium silicates)[4].

    The suggested technique has been tasted in the laboratory environment by memebers of the institute "Hydrotsvetmet" (Novosibirsk) and the joint-stock company VAMI (Saint-Petersburg).

    The alloying with soda by the water leaching of the fusion cake allows to convert 70% of silica to a solution. Alloying conditions need a detailed development work and optimization. It is advisable to alloy the ashes with sodium sulfate and coal, that reduces the consumption of reagents at the expense of sodium sulfate which is produced in the technological cycle.

        2.2.2. Water leaching of fusion cakes

    Rates of the water leaching of fusion cakes are worked through by members of the institute "Hydrotsvetmet" and need to be refined and optimized.

The seimentation rate of the silicate has also been worked through while developing this project and need an optimization.

        2.2.3. The production of alumina

    Rates of the aluminium leaching have been worked over in details by memebers of the joint-stock company VAMI. While the development work of the scheme there might need the refinement of operating practices with reference to the specific raw material and the optimization of material and energy runs as applied to the whole process flowsheet.

        2.2.4. The production of concentrates of less-common metals

The technology and conditions of the production of less-common metals have been worked over by members of the institute "Hydrotsvetmet" in the context of the performance of the contract N  of     . Conditions have been worked through in thelaboratory environment and tested on a laboratory scale.

3. The evaluation of the economica performance of the production

    The evaluation of the economic perfomance of the production of deep processing of ashes on a heat-electric generating plant includes:

•the evaluation of capital outlays for the production establishing (table 3.1);

•the calculation of the planned prime cost of the processing (table 3.2);

•the evaluation of the volume of marketable production in product and cost terms (table 3.3.);

•the evaluation of profitableness of the production and of the pay-back period.

4. Summary.

    The preliminary technical and economic assessment of the plant of the ashes processing on Novokemerovsk Heat-electric Generating Plant allows to conclude that the suggested production is economically effective.

Thus the pay-back period of the plant for the processing of ashes (output - 100 tonn per day) is less than a year. Discharges are reduced in 5 times and still they can be used for the production of portland cement.

Though there are some unsolved problems. First, there are needed serious marketing research, which will allow to determine the economically expedient volume of thr ashes processing and the needed range of products.