RU2569132C1 - Method for processing bottom ash waste from dump pits of hydraulic ash-transportation system at heat power plants in order to receive conditioned ash products - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: result is obtained by drying of initial bottom ash waste from treated section of HPP dump pit and additional grinding of dried material at the grinding system of impact and centrifugal type with built-in sorter, in result reactivation - reduction of active properties takes place and the material obtains the preset standard properties.

EFFECT: in result of the method usage conditioned ash products are obtained with guaranteed stable and reproducible properties, and the above products may be used in construction and industry construction materials in wide scope of applications - as mineral supplement during cement production, as additive and filling material at production of concrete grouts and mixes, in dry construction mixes, as mineral powder at production of asphalt mixes and in other sectors.

3 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of processing ash and slag waste (ASW) from the combustion of coal from thermal power plants.

In Russia and neighboring countries, the overwhelming majority of coal-fired thermal power plants are equipped with ash removal systems, through which the ash and slag mixture in the form of pulp is discharged into the ash and slag dumps of thermal power plants.

To date, according to experts, they have stored more than 1.5 billion tons of ash and slag, and the territory they occupy is approximately 28 thousand hectares.

Moreover, according to various estimates, the degree of utilization and processing of ASW in Russia is 10-12% of their current annual output, while in the most developed countries in this regard (USA, UK, Germany, Poland, India, China and others) this the value reaches 70-100%.

This leads to overfilling of ash dumps, which is currently one of the serious problems of the coal power industry and is already systemic in nature. The construction of new ash dumps in the current conditions is difficult for a number of reasons and seems to be inefficient by solving the problem of ash and slag waste from TPPs.

Therefore, one of the important tasks of the coal power industry at the present stage is a significant increase in the degree of utilization of ash and slag waste in order to relieve the existing overflowing ash dumps.

In terms of their physicochemical characteristics, the ash and slag materials are a valuable mineral raw material of technogenic origin, which in many cases can replace non-renewable natural resources in various fields of application, among which the main ones are construction, including road construction, and the building materials industry.

However, the main requirement of consumers for ash and slag materials is that they are a conditioned product and have guaranteed stable characteristics and quality, and are not just waste, which is now mainly offered by energy companies, including dry fly ash obtained at some thermal power plants in the few available dry systems ash removal.

Obtaining conditioned ash products is today the main direction of solving the problem of ash and slag waste. It is this principle that is the basis of the invention.

A known method of processing ash and slag waste from the dumps of the hydro-ash removal system of thermal power plants, including mechanically transporting waste from dumps, liquefying it, dividing the liquefied ash and slag mixture into fractions with at least two streams of ash and slag particles required for subsequent disposal, thickening each stream with separation of hollow microspheres and particles of unburned coal, as well as clarified water, and the supply of dehydrated mass of each fraction to the appropriate disposal [1] - analog.

The main disadvantage of the analogue [1] with respect to the claimed method is that the ash and slag materials obtained as a result of its use essentially remain raw materials and are not full-fledged conditioned products, requiring further processing by various technologies.

There is a method of processing ash and slag waste from dumps of the system of hydro-ash removal of coal-fired thermal power plants, including mechanical transportation of waste from the dump, liquefying it, dividing the liquefied ash and slag mixture into fractions with at least two streams of ash and slag particles required for subsequent disposal, thickening each flow with separation of hollow microspheres and particles of unburnt coal, as well as clarified water, and the supply of dehydrated mass of each fraction to appropriate disposal [2] - prototype.

The main disadvantage of the prototype [2] in relation to the claimed method in terms of obtaining a product similar to the claimed one — dried to a residual moisture of 5% ash — is that such a product is a semi-finished product, essentially the same raw material for further processing, as the authors themselves point out .

This significantly narrows the possibilities for its further use, since it requires additional material and financial costs for potential consumers to finalize such a product.

In addition, the use at the stage of drying the ash to a residual moisture content of 5% of a steam dryer in the current economic conditions, when steam is necessarily released to consumers at market prices, and not free of charge (even for the internal needs of the power plant itself), as at the time when this the dryer was developed, it is unlikely to be economically feasible, although it is an interesting technical solution.

The main achieved result of the invention is to obtain, as a result of its application, in contrast to the prototype, a truly conditioned ash product with guaranteed stable and reproducible characteristics and quality, which does not require further refinement and in this form can be used in a wide range of directions - as a mineral additive cement production, as an additive and filler in the production of mortars and concrete mixtures, in dry building mixtures, as a mineral Foot powder in the manufacture of asphalt mixes, and other areas.

By its properties, this product is an analogue of dry fly ash, which is already used in the above industries. However, unlike dry ash obtained at Russian stations, which is still the same by-product ash and slag waste from electricity production, since its properties and quality are not controlled in any way either by producers or sellers, this ash product is a full-fledged conditioned product and goods produced by strictly adhered technology based on technical specifications with guaranteed quality and stable performance.

In addition, during the processing of ash and slag treatment using this method, reactivation occurs - restoration of the active properties of the inert ash and slag mass stored in the spent and drained section of the ash dump of the TPP.

The indicated effects are achieved by drying and additional grinding to the required fineness of grinding the ash-slag mixture dried to a moisture content of less than 1% (mechanical activation) and adding, if necessary, organic additives in the resulting product, grinding (chemical activation).

This method of processing ash and slag waste includes, at the first stage, the harvesting of raw materials - ash and slag mixtures of natural humidity - from the worked out and dried sections of the ash dump of a TPP and its mechanical dehydration by digging in an open area.

The use of such dump ash and slag mixtures has certain advantages compared to the use of fly ash and ash and slag mixtures of the current yield.

According to some researchers, over time, while in the ash dump, there is some “averaging” and “improvement” of the ash characteristics.

So according to V.I. It is hot [3], as a result of aging in the ash dump, the hydraulic ash contains less sulfur compounds and alkaline oxides compared to dry ash, which are naturally washed out of ash particles.

According to O.B. Vysotsky and I.Yu. Danilovich [4], particles of unburned fuel in dump ash are characterized by less reactivity due to oxidation, as well as the possible washing out of humic acids, which significantly reduces their effect on the water demand of ash in concrete mix and the corrosion resistance of reinforcement in reinforced concrete structures.

That is, the content of technologically harmful impurities, which are standardized in GOST 25818-91 “Fly ash of thermal power plants for concrete. Technical conditions ”, a conditional product based on dump hydraulic ash is more preferable for use in the production of cement, as well as various types of concrete for concrete and reinforced concrete structures.

In addition, due to the use of ash and slag mixture "deposited" in the worked out and drained sections of the ash dump, an additional - ecological - effect on the final product is achieved - the final product is more environmentally friendly compared to similar products obtained from the ash or ash and slag mixture of the current TPP yield, in particular on the content of heavy metals, which was shown in [5].

Flouring the ash and slag mixture and keeping it in an open area (in an ash dump or in a raw materials warehouse) allows you to reduce the moisture content of the feedstock to 25-30% depending on the initial humidity, weather conditions, and aging time. While in the natural occurrence in the ash dump, the ash and slag humidity can reach 45-50%.

Mechanical dehydration can significantly reduce the cost of energy (gas) in the next stage of drying the material in the drying unit, which makes the process economically viable.

At the next stage, the raw material is dried to a moisture content of less than 1% with the separation of the dried ash and slag material into at least two fractions according to particle size distribution and dispersion — a finely divided fraction with a particle size of mainly less than 50 μm and the remaining larger fraction with a particle size of more than 50 μm.

This makes it possible, firstly, to obtain stable characteristics of the final product in terms of humidity (approximately 0.2-0.5%) and, secondly, to separate the dried material already at the drying stage into at least two different products in terms of particle size distribution and dispersion, the first of which is finely dispersed - can already be used as a fully finished product.

At the final stage, reactivation occurs - restoration of the active properties of the dried ash and slag material and giving it the desired conditioning properties. This is achieved by grinding the material to a predetermined fineness and, if necessary, adding organic additives at the grinding stage to impart special properties to the final product.

A distinctive feature is that for the reactivation of ash and slag material and giving it the specified properties, the shock activation method is used with the use of a crushing complex of shock-centrifugal type with an integrated classifier.

Using the shock activation method, due to the characteristic shape of the grain obtained as a result of the split of the crushed particles, characterized by jagged edges, to increase the specific surface area of the final product. In this case, the particle size spectrum of the particles remains in a relatively narrow range determined by the classifier parameter (given by the maximum particle size), that is, the particle spectrum is not overloaded with a finely divided fraction, characteristic, for example, of the erasure method, which is used, in particular, in ball mills.

This, in turn, will reduce the water demand of the mixture when using the resulting product, for example, as a mineral additive in cements, mortars, concrete.

Thus, setting the parameter of the classifier (maximum size of grinding particles) allows you to get certain values of the specific surface, a certain particle size distribution of the product and, as a result, a certain bulk density, that is, to give the resulting product certain conditioning properties.

Table 1 shows the characteristics of two different conditioned products of the processing of ash and slag from coal combustion of two different thermal power plants obtained by this method, in comparison with the analogue - dry fly ash of Ryazan state district power station.

In addition to the fact that this method allows you to get a truly conditional product with the specified parameters in terms of humidity, dispersion, particle size distribution, bulk density, the technology implemented in it allows you to level out differences in the particle size distribution, chemical and phase-mineralogical compositions of the initial ash and slag raw materials obtained from burning of various grades and types of coal at different thermal power plants.

Such an effect was noted during laboratory studies of the properties of samples of conditioned ash products obtained from ash and slag mixtures from burning the Kuznetsk coal (a branch of TPP-22 of Mosenergo OJSC) and brown suburban (Ryazanskaya GRES branch of OJSC OGK-2) coal when testing them in quality of mineral additives in cement and concrete in the Testing Center of the State Unitary Enterprise “NIIMosstroy”.

The obtained results on strength tests using different conditioned ash products (samples 3 and 5) turned out to be quite close, despite differences in the granulometric, chemical and phase-mineralogical compositions of the feedstock from which they were obtained.

It should be noted that the fineness of grinding sample 3 (grinding for mineral powder) differed from the same indicator for sample 5 (mineral additive), which can be seen and can explain the discrepancies and slightly lower strength indicators for sample 3.

The noted effect requires, however, a more detailed study.

The results are shown in table 2 and illustrated in Fig. 1, which shows the dependence of the compressive strength of a standard cement-sand mortar on the ash content for various additives.

One of the distinguishing features of this method is the use of a drying chamber with a special design of the rear chamber at the drying stage, which reduces the dust removal effect of fine particles of the ash and slag mixture and thus solves one of the technical problems that arise during the industrial implementation of this method - the dust removal problem.

Testing conducted in the testing center of the drying equipment manufacturer showed that with a maximum dust removal of up to 60% (depending on the particle size distribution of the feedstock and the dynamic drying mode), the majority of particles emitted into the aspiration system have a diameter of basically not more than 50 μm.

The value of the specific surface obtained in laboratory studies of this fraction by the method of laser granulometry reached a value of almost 640 m ² / kg

This means that this fraction can be used as a separate fine product or, if necessary, returned to the grinding system along with the main product for additional activation.

In fig. Figure 2 shows the particle spectrum of the fine fraction of the dried ash and slag mixture deposited in the aspiration system of the drying complex obtained by laser granulometry (the X axis is the particle size in microns, the Y1 axis is the integral yield in%, the Y2 axis is the fraction of particles in relative units).

The proposed method on an industrial scale can be implemented as follows.

Raw materials are delivered to the plant by dump trucks from the ash dump of the TPP and stored at the raw materials warehouse in the piles.

From the warehouse, the raw materials are picked up by a bucket forklift and put into the receiving hopper with a grate.

From the hopper, by means of a belt feeder, the material is transported to a drying drum equipped with a gas burner, where the raw materials are dried to a moisture content of 0.5%. After passing the drum, the dried material is discharged into the screw conveyor.

The coolant (a mixture of flue gases with air) used to dry the material, passing through the drum, carries small particles into the aspiration system, which consists of a high-performance bag filter. The rear chamber of the dryer drum is specially designed to reduce dust removal, as a result of which a finely dispersed fraction of the ash component of the initial mixture with a particle size of mainly less than 50 microns gets into the aspiration system. This material settles in a bag filter and is a separate finished product - a finely dispersed mineral additive.

This product is fed by a pneumatic conveying system to a finished product warehouse in a separate silo or, if necessary, can be supplied together with the main product to a grinding complex. Purified air is released into the atmosphere.

The material of their screw conveyor enters the bucket elevator and is transported to the distribution hopper. In the hopper, the material is dosed and fed into the grinding complex, consisting of a centrifugal mill, a classifier, cyclones and a bag filter, with a belt feeder.

This site is central from the point of view of implementing the proposed method and its distinguishing feature, since the product is reactivated here - its active properties are restored, and the conditioning properties of the final ash product are determined by setting the parameters and grinding mode.

Reactivation is carried out mechanically by the method of shock activation and chemically by adding organic additives to the product during grinding.

The final characteristics of the conditioned ash product are set by setting the parameters of the classifier and are determined by the fineness of grinding.

Material after the mill is deposited in cyclones. The air after the cyclones is further cleaned in a bag filter. The products of suction and grinding are combined with a screw.

The finished product is unloaded from the hopper located under the cyclones of the complex, and the pneumatic conveying system is fed to the silo warehouse, from where it is shipped to consumers.

As a result of the implementation of the claimed method according to this scheme, it is possible to obtain a conditioned ash product of guaranteed quality and with stable desired characteristics, which, depending on the parameters, can be used as a mineral additive, siliceous filler, mineral powder, concrete modifier in a wide range of areas in construction, including road, building materials industry, as well as related fields.

The introduction of this method for the processing of ash and slag waste from TPPs will not only help solve the problem of emptying ash dumps of coal power plants, but also is an example of resource-saving technologies, since it allows saving natural non-renewable materials used in the construction field (sand, limestone and others), using technogenic resources instead - substitutes.

Bibliography

1. The method and production line for the processing of ash and slag waste from the dumps of the system of hydraulic removal of thermal power plants. Patent RU 2363885 C1, priority of January 11, 2008 - analogue.

2. Kozlov I. M., Chernyshev E. V., Kochurov S. N., Ilyin V. A., Brovkin B. A. The use of new technologies in the processing of ash and slag waste at TPP-22 of Mosenergo OJSC. Power stations. 2005, No. 11 - prototype.

3. Zharko V.I. Resource base of mineral additives for cement production. International Building Forum “Cement. Concrete. Dry mixes". Moscow, Expocenter, November 27-29, 2012

4. Danilovich I.Yu., Vysotskaya O.B., Varsanova G.V. The use of ashes with a high content of unburned fuel in building materials and products. Collection of reports of the All-Union Scientific and Technical Conference "Concrete based on ash and slag of TPPs and their complex use in construction" / Edited by S.I. Pavlenko. September 1990, Novokuznetsk, USSR // Novokuznetsk, Gosstroy Publishing House of the USSR, 1990, volume 1, p. 80-97.

5. Ivanykina OV, Zhuravleva N.V. The study of toxicity of waste from enterprises of the fuel and energy complex of the Kemerovo region. 5th International Conference “Cooperation for Solving the Problem of Waste” April 2-3, 2008, Kharkov, Ukraine.

Claims (3)

1. A method of processing ash and slag waste from the dumps of the hydro-ash removal system of thermal power plants with the aim of obtaining conditioned ash products, including the harvesting of raw materials - ash and slag mixtures of natural humidity - from the spent and dried ash and slag section of TPPs, mechanical dewatering of raw materials by digging in the ash dump or at the storage site to moisture 25-30%, forced drying of the raw materials in the drying unit to a final moisture content of less than 1% with separation of the dried material during drying and at least two fractions, characterized in that they additionally carry out reactivation - restoration of the active properties of the dried ash and slag material and bring it to conditional properties - give certain guaranteed stable characteristics - by grinding the material to a predetermined grinding fineness, which is determined by the final destination obtained in as a result of grinding a conditioned ash product (mechanical activation) and, if necessary, adding chemically active additives at the grinding stage for I impart special properties to the final product conditionally ash (chemical activation). 2. The method according to p. 1, characterized in that to activate the dried ash and slag mixture and give conditioning properties to the final ash product, the shock activation method is used using a shock-centrifugal type grinding complex with an integrated classifier that allows you to adjust and control the main characteristics of the product, before total, such as particle size distribution, dispersion, bulk density, as well as set these characteristics in the production process, depending on requirements the final product. 3. The method according to p. 1, characterized in that at the stage of forced drying of the raw materials, a drum-type drying unit with a special design of the rear chamber is used to reduce the removal of the finely dispersed ash component of the initial ash and slag mixture from the drum and to isolate the fraction with a particle size of mainly not more than 50 microns , which is carried away by the exhaust flue gases from the drying unit and trapped in an aspiration system, and which, in turn, depending on the requirements for the final product can be used either as worthwhile product or, if necessary, be directed to an additional grinding and shredding activation complex.

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