RU2335696C1 - Method of solid fuel burning at thermal power plants - Google Patents

Abstract

FIELD: technological processes; chemistry.

SUBSTANCE: method includes preparation of fuel for burning, its burning, dry catching of ashes, moistening of ashes, its granulation, hardening of granules and their dispatch for recycling or storage, in which fuel is dosed prior to burning, and mineral additive is introduced, crushing of which is carried out together with fuel or separately, and for moistening of ashes during its granulation water or water alkaline solution are used, for instance, sodium carbonate or sulfate, with content of alkaline compound of 5-10% from ashes mass.

EFFECT: application of invention allows to prepare multipurpose solid granulated product suitable for recycling and stockpiling.

3 cl

Description

The invention relates to technologies for burning solid fuel at TPPs, and relates primarily to objects burning solid fuel with an acidic composition of the mineral part, that is, with a low, less than 5% content of calcium and magnesium oxides in ash and slag formed during fuel combustion.

A known method of burning solid fuel at thermal power plants, including dry ash collection, in which the mineral part of the fuel in the form of an ash and slag mixture is taken from the recovery system, slag is shipped to consumers, and ash is transported to the storage site. Subsequently, it is humidified in a special device up to 14-16% and transported to the place of laying, where it is distributed in a layer of 20-30 cm and compacted with the help of road equipment into an array up to 10 m high with subsequent reclamation (Vishnya B.L. Ufimtsev V.M. Promising technologies for the removal, storage and use of ash and slag from TPPs, Ekaterinburg, Ural State University - UPI, 2006, p.10). Essentially, this technology is used for the disposal of fuel ashes and slag.

The disadvantage of this technology is the difficulties encountered in the selection of ash and slag for their use. In this case, a set of measures is necessary that corresponds to the organization of a quarry, as in the development of natural raw materials, since it is planned to develop anthropogenic massif after its restoration. This increases the costs associated with the disposal of coal combustion products. In addition, the increased humidity of the ash and slag mixture makes it difficult to select it in the winter and requires an increase in energy consumption for drying.

A known method of burning solid fuel in thermal power plants, including preparing fuel for burning, dry ash collection of its products, moistening the ash, its granulation, hardening of granules and shipping for disposal or storage (AS USSR 1043424 IPC 3 F23J 1/02 from 23.09. 1983).

Granulation of ash increases its consumer properties, expands the scope and volume of its consumption.

The disadvantages of this technology include the restriction on the minimum content of alkaline-earth oxides (CaO and MgO) in the composition of the ash, which should be at least 20%. With a lower content, the ash granules slowly harden and do not gain sufficient strength. Such granules are destroyed during storage and disposal, which reduces their consumer properties, especially when used as a large aggregate in lightweight concrete. In this case, it is necessary to add 10-15% of Portland cement to the ash, as is done when obtaining non-calcined ash gravel (Itskovich S.M., Chumakov L.D. Bazhenov Yu.M. Concrete aggregate technology. M: Higher school. , 1991.S. 224). The amount of cement added should be inversely proportional to the content of calcium and magnesium oxides contained in the ash. The latter significantly increases the cost of disposal of ash by granulation.

The technical problem solved in the invention is to obtain a high-quality granular product based on acid ash, in which the amount of CaO and MgO is less than 20%.

The problem is achieved in that in a method for burning solid fuel at a thermal power plant, including preparing fuel for burning, burning it, dry collecting ash, moistening the ash, granulating it, hardening the granules and shipping them for disposal or storage, the fuel is metered and injected mineral supplement. It is recommended to use carbonate-containing rocks as a mineral additive: chalk, limestone, dolomite, marl, which are crushed together with coal or separately from it. In the latter case, the milled mineral additive is dosed and fed to a coal mill.

To moisturize the ash during its granulation, water or an aqueous solution of 5-10% alkali, for example, sodium carbonate or sulfate, is used.

The granular product intended for shipment or storage is subjected to drying to a residual moisture content of 5-10% and subsequent wetting to 20-30%.

Experimental verification of the proposed method was carried out on a mixture simulating the introduction of Kuznetsk coal 4-5% mineral additives in the form of limestone, which corresponds to the following composition of the mixture: ash 83%, lime 8% and anhydrite 9%. The composition of the ash, wt.%: SiO ₂ ... 60,70; Al ₂ O ₃ ... 28.68; Fe ₂ O ₃ ... 4.55; CaO ... 1.77; MgO ... 0.45. Anhydrite is formed due to the binding of sulfur from coal, which reduces the emission of sulfur from the flue gases of thermal power plants. The above components were thoroughly mixed and subjected to granulation on a laboratory plate granulator. The obtained granules hardened in air-wet conditions at room temperature. Table 1 shows the change in the properties of the granules over time.

Table 1 Change in the properties of ash granules during air-wet storage The limit of compressive strength, N / granule Storage duration 1 hour 8 hour 16 hour 1 s 1.5 s 7 s 14 s 21 s 28 s Ash + 15% cement 6 8 fifteen 25 37 150 195 225 270 Ash + lime. + anhydride. four 9 19 38 43 191 263 460 488 . Ash + lime + anhydrite + drying * - 85 103 120 137 153 207 254 305 Ash + lime + anhydride. + drying + moisture ** - - - - 204 287 353 411 451 Ash + lime. + anhydride. + 5% Na ₂ SO ₄ 8 19 45 97 120 187 253 382 470 Note: * Dry for 2 hours at a temperature of 90 ° C. The moisture content of the granules decreased from 28 to 15%. ** The dried granules were moistened to 25% after 24 hours. from the moment of granulation.

From the presented it follows that the introduction of a mineral additive in the form of limestone provides a higher effect than the use of 15% cement additive. It is very important that the rate of curing of the granules by the end of 1 day is almost twice the strength of the granules on cement. Pellets with a compressive strength of 38 N (3.8 kgf) can be shipped to the consumer, especially in the summer, when they continue to harden intensively during transportation and during storage in the warehouse. However, for use in concrete technology or in road materials, the strength of 38 N is insufficient. Therefore, it is rational to accelerate the hardening of ash granules, which will speed up their shipment and reduce the area under the granular storage at thermal power plants.

To accelerate the shipment of granules obtained on a lime-anhydrite binder with an initial moisture content of 20-30%, it is recommended to dry them in a gentle mode, which excludes destruction from thermal shock, to a residual moisture content of 5-15%, drying. However, after drying, the "final" strength of the granules is significantly reduced (in the long term). In the “drying-moistening” mode, moistening of the dried granules to the level of 20-30% is provided. In this case, the final (monthly) strength of the granules increases.

An alternative to the “drying-wetting” method is to introduce an alkaline water-soluble additive into the ash by replacing the water used in the granulation with an alkaline aqueous solution, for example sodium sulfate or sodium carbonate, or a mixture thereof. In this case, the technological scheme of obtaining ash granular product is simplified. It is especially effective to use for this purpose cheap alkaline waste from chemical and metallurgical technologies: soda-alkali smelter or soda-sulfate waste from alumina production. The amount of alkaline additives in dry form should be from 5 to 10% by weight of dry ash.

Table 2 contains comparative results on the dynamics of the growth of strength of the granules using various modes of drying and wetting.

table 2 Change in the properties of ash granules during air-wet storage using drying and dampening The limit of compressive strength, N / granule Storage duration 1 hour 8 hour 16 hour 1 s 1.5 s 7 s 14 s 21 s 28 s Ash + lime. + anhydride. four 9 19 38 43 191 263 460 488 . Ash + lime + anhydride. + drying up to 10%, * 40 105 138 204 227 275 303 342 353 - “- drying up to 5% 43 74 96 103 105 98 111 115 123 - “-, drying up to 15% 25 85 103 120 137 153 207 254 305 Ash + lime + anhydride. + drying + ent. up to 20%, ** - - - 170 204 287 353 411 451 - " - up to 15% - - - 180 211 280 324 373 409 - "- up to 25% - - - 165 193 258 333 375 420 Note: * drying for 2 hours at a temperature of 90 C. The moisture content of the granules decreased from 28 to 15%. ** - The granules dried according to the regimen * were moistened to 25% after 24 hours from the moment of granulation

Table 3 compares the results of experiments on accelerating the hardening of ash granules by the introduction of an alkaline additive during granulation. As an alkaline additive used sodosulfate waste production of alumina containing 21% Na ₂ CO ₃ and 58% Na ₂ SO ₄ .

Table 3 Changing the properties of ash granules containing an alkaline additive during air-wet storage The limit of compressive strength, N / granule Storage duration 1 hour 8 hour 16 hour 1 s 1.5 s 7 s 14 s 21 s 28 s Ash + 15% cement 6 8 fifteen 25 37 150 195 225 270 Ash + lime. + ang-dith + 5% Na ₂ SO ₄ 8 19 45 97 120 187 253 382 470 - “- + 10% Na ₂ SO ₄ eleven 23 53 95 111 163 233 377 399 - “- + 8% Na ₂ SO ₄ eleven 25 60 112 143 178 250 419 495

Achievement of the claimed technical result, expressed in the manifestation of astringent properties when burning coals having an acidic composition of the mineral part, is ensured by the thermochemical interaction between the decomposition products of carbonates and the mineral part of coal. The result of this interaction is probably the formation of hydraulically active phases: lime, anhydrite (calcium sulfate), low-basic silicates, aluminates, calcium ferrites. The mixture of ash and these phases is well granulated, and the granules are capable of hardening.

In terms of hardening speed, such granules are significantly inferior to granules obtained from high-calcium ash, in which the amount of CaO + MgO exceeds 20%. In order to accelerate hardening, it is proposed to dry by heating to a residual moisture content of 5-15% by heating. Thanks to heating, chemical hardening reactions are accelerated, and the evaporation of part of the water leads to a densification of the granule structure due to the crystallization of dissolved salts. However, the residual moisture is not enough to complete the hydration of the phases that provide the hardening of the granules. Therefore, it is advisable to subject them to additional wetting up to 15-25%, which probably stimulates the completion of hydration of the astringent phases and increases the strength of the granules.

The drying of the granules and their subsequent moistening complicate the technology for producing an ash granular product, which can be avoided by introducing an alkaline additive, for example sodium sulfate or sodium carbonate, or a mixture thereof in an amount of 5-10%. The acceleration of the hardening of the granules in this case is apparently associated with an increase in the solubility of silicon oxide in water, which stimulates the formation of low-basic calcium silicates.

Using the proposed invention allows to obtain a convenient, for disposal and storage, durable, granular product. Ash granules, depending on their composition and properties, can be used as aggregate in lightweight concrete or as an active hydraulic additive in cement production, or in some other way. Storage of ash granules is not expensive and environmentally friendly. It can be expected that the application of the invention will provide a total economic effect from eliminating the cost of storing ash in a dry dump and its disposal of about 100-200 rubles. per 1 ton of granular product.

Claims (3)

1. A method of burning solid fuel in thermal power plants, including preparing fuel for burning, burning it, dry collecting ash, moistening the ash, granulating it, hardening the granules and shipping them for disposal or storage, characterized in that the fuel is metered and injected with mineral the additive, grinding of which is carried out together with the fuel or separately, and to moisten the ash during its granulation, use water or an aqueous alkaline solution, for example, carbonate or sodium sulfate, with an alkaline content 5-10% by weight of ash. 2. The method according to claim 1, characterized in that the carbonate rock, chalk, limestone or marl are used as a mineral additive. 3. The method according to claim 1, characterized in that the granular product intended for shipment or storage is subjected to drying to a residual moisture content of 5-10% and subsequent wetting up to 20-30%.