RU2543833C2 - Method of producing ash cement - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method of producing ash cement, which includes grinding brown coal to dust consistency - more than 95% of a fraction smaller than 0.09 mm while adding a correction additive, burning in a thermal power plant furnace to achieve combustion ratio of coal substances in the burners of up to 95-98% and removing flue ash - said end product - from electrofilters of exhaust flue gases; the brown coal is initially ground in an alkaline aqueous medium in the extraction chamber of a deposit during hydraulic borehole mining thereof to solid consistency in a pulp of up to 80% of a fraction smaller than 25 mm; grinding the brown coal for the second time in an alkaline aqueous medium in solid state in the pulp through hydraulic grinding to consistency of the coarsely dispersed phase of up to 75% of a fraction smaller than 0.145 mm; then separating a first intermediate coal product from a first useful by-product - humates, obtained by extracting humic acids with the alkaline medium during hydraulic grinding of the brown coal; subjecting the first intermediate coal product to hydraulic grinding for the third time in an acidic medium to particle size of 0.075 mm; feeding the obtained water-coal suspension into a bubbling tank, where warm filtered flue gases from the thermal power plant furnace are bubbled to increase concentration of acids in the dispersed phase of the suspension and extracting heavy rare metals into the solution; separating a second intermediate coal product from a second useful by-product - bulk concentrate of heavy rare metals and jointly homogenising the coal product with the correcting additive to obtain liquid coal fuel, which is fed for burning. The invention is developed in subclaims.EFFECT: improved properties, obtaining valuable by-products.3 cl, 1 tbl

Description

The invention relates to the field of production of building materials and to the power system, where it can be used in the production of binders and cements from furnace waste.

The interest in the use of fuel wastes from TPPs / CHPPs in cement production arose among specialists for a long time and the specialized institution of the USSR Ministry of Construction Materials - NIIcement in 1977, based on the experience gained, was structured in three areas:

- the use of ash as a raw material component;

- the use of ash as a hydraulic additive;

- the use of ash for the production of special cements, recognized as the most effective (Kishko BS, Kravchenko IV. The wider use of ashes of thermal power plants in cement production. - Cement, 1977. - No. 6. - p.1-2).

In the same period of time (1976-1980), the USSR Ministry of Energy carried out the construction of 23 plants for the selection of 6.1 thousand tons of dry ash with the commissioning of capacities in the amount of 370 thousand tons at Omsk TPP-4, 250 thousand tons at Krasnoyarsk TPP -1, 204 thousand tons at the Libyan state district power station, etc.

The existing ash and ash removal at TPPs / TPPs and the absence of electrostatic precipitators that capture dry fly ash in flue gases did not contribute to the practical use of ash in various types of binder and special cement production.

The emergence of the possibility of using high-quality raw materials - dry ash of TPPs / TPPs - has stimulated the emergence of a significant number of technical solutions for its use in the composition of the raw mix and binder.

For example, a proposal is known for obtaining a raw material mixture from industrial wastes, including cogeneration plant ash, Portland cement, aluminum powder and other components (AS USSR No. 1377269).

Known technical solution for the production of binder containing, wt.%: Portland cement 8.5-18.5; bauxite sludge 57.0-60.5; fly ash 6.5-9.0; water - the rest (SU 1766866).

It is known to use dry ash from Omsk TPP-4 to obtain a binder. A cement-cement binder (zolzit) is obtained by co-grinding to a specific surface of 4500-5500 cm ² / g of a mixture of ingredients, wt.%: Acid fly ash 30-40; bauxite or nepheline sludge 20-30; complex additive 3-5, Portland cement - the rest (RU 2452703).

Common disadvantages of the mentioned analogues are the use in the process of obtaining the target product of components that are not related to the activities of TPPs / TPPs, the sufficient complexity of obtaining the target product and its relative high cost.

The closest in technical essence to the proposed invention analogue (prototype) is the method proposed by prof., Doctor of Technical Sciences Moscow State University for Petrosov A.A. (Production of cement from the ash of thermal power plants. - Mining Journal, 2007, - No. 11. - p. 50-51).

According to the prototype method, the technology for burning coal in the furnaces of thermal power plants / thermal power plants should be changed and, along with heat and electricity, instead of ash and slag waste, ash cement should be obtained. For this, the coal is crushed to a dust consistency (up to ≥95% of the fraction - 0.09 mm); burned in the furnaces of TPPs / CHPPs, bringing the degree of burning in the nozzles of carbonaceous substances, especially brown coal, to 95-98%; removal of fly ash from electrostatic precipitators; loading of cement in cement silos; packaging of ash cement and its delivery to consumers.

As the disadvantages of the prototype method, there can be noted the restriction on underburning in the composition of the target product - content 3

limited residues in ash cement should not exceed 7% due to the action of humic acids, which impair the cementitious properties of cement; restriction on the presence of harmful elements in the composition of ash cement, preventing their use in housing construction; difficulties in organizing efficient flaring of coal dust lined with a certain amount of finely divided dolomite (limestone) dust and fine clay.

The task is to propose a method for producing from brown coals an ash cement that does not contain humic acids, harmful elements, with adjustable astringent properties.

The problem is solved by burning liquid coal fuel with humic acids and heavy rare metals removed from its composition and with additives introduced into its composition, if necessary, correcting the astringent properties of ash cement. In this case, brown coal is subjected to three times grinding, each time with an increase in its dispersion - in the process of hydraulic mining, in the process of extraction of humic acids, in the process of extraction of heavy rare metals with subsequent joint homogenization with corrective additives in the process of preparing liquid coal fuel that is homogeneous in composition and properties. The withdrawal from the composition of the feedstock - brown coal - of ingredients harmful to ash cement in the form of humic acids and heavy rare metals is carried out by imparting a water-dispersed suspension to the liquid dispersed medium, alternately, alkali properties and acid properties using the reagent resource of the furnace process. Entering into the composition of ash cement, if necessary, binders enhancers are carried out during the preparation of liquid coal fuel by adding limestone / dolomite dust to the solid dispersed phase or by preparing a liquid dispersed medium of a suspension in the form of limestone milk. However, brown coals are often found, the ash of which meets the requirements for the astringent properties of ash cements.

A method for producing ash cement can be described in more detail using a specific example of its possible use in the energy-chemical limit of brown coal from the Talovskoye deposit in the Tomsk Region of the Russian Federation.

Talovskoye brown coal deposit contains several packs of seams lying close to the day surface at depths of up to 90 m and deep at depths of 120-180 m, which significantly increases the cost of open-pit coal mining.

Therefore, the Tomsk mining company experts proposed to develop deep-seated Talov coal seams by the method of borehole hydraulic production with subsequent integrated use of the extracted raw materials by means of energy-chemical redistribution in order to reduce the development costs of the deposit (Technological solution of the Tomsk mining company for the development and integrated use of brown coal from the Talovskoye field / Otv. V.I. Lunev. - Tomsk: TomGDK, 2001 - 146 p.).

According to modern data (as of 2013), in the chemical processing of 1 ton of dehydrated Talovskiy brown coal, up to 300 kg of humic acids soluble in aqueous solutions can be extracted from their organic part, and up to 1 kg of collective from the mineral part rare metal concentrate, including up to 4 g of uranium and thorium.

Based on the acquired positive experience of borehole hydraulic mining of large-volume (1700 t) technological samples of Bakchar iron ore in the Tomsk region from the depths of the iron ore layer of 167-214 m, it is possible to extrapolate the obtained technological parameters of hydraulic production to a similar geological object - a deep-lying layer of Talov brown coal, namely: a coal seam of the Kuskovo Formation of the central section with an average thickness of 5.2 m, occurring at depths of 120-180 m from the day surface.

According to the "Report on the experimental work on the topic" Evaluation of the Bakcharsky iron ore manifestation for development by the SRS method "- State contract dated 04.04.2006 No. TV-04-04-2006. / Ans. Spanish: V.I. Lunev. - Tomsk: TomGDKruda, 2008 "Talov lignite can be mined from a mining chamber with a volume of 750 to 1,500 m ³ in the pulp composition with a solid to liquid ratio T: L = 1: 10 and a solid capacity of" 20 t / h (500 t / day; 15 thousand tons / month) with a content of up to 80% of the fraction - 25 mm (extrapolation data).

The working fluid of the hydraulic production process - water - can be in contact with coal for a period of 30-120 minutes, depending on where the pulp is taken from the extraction chamber to the surface: to the alluvium map or immediately to the technological conversion, but in any case most of the water is returned to the circulating water supply scheme of hydraulic production.

By alkalizing the circulating water with some cheap alkaline agent, selected, for example, from hydrates of oxides, sodium and potassium carbonates and bicarbonates, and ammonia water, it is possible to obtain up to 2 thousand m ^{3 of} liquid humates during the working time of the extraction chamber (several days).

When brown coal is sent to the thickened pulp (at T: G from 1: 5 to 1: 1), the alkalized water will only have time to “soften” humic substances due to the short contact time, which, however, will increase the efficiency and productivity of extraction of humic acids into sodium humates / potassium when lignite is milled, for example, in a jet mill in a 1% NaOH / KOH alkali solution to obtain a coarse coal phase with a content of up to 75% fraction - 0.145 mm with the release of humates up to 300 kg / t, followed by their separation, by for example centrifugation in entrifugah precipitation type.

Thus, the target product - ash cement - is freed from humic acids that impair the cementitious properties.

To use ash cement in housing, it must be free from heavy rare metals, including U, Th, REE, which are contained in Talov brown coals as a part of the monazite mineral, and from which they can be extracted by alkaline or acid leaching during the third coal grinding to fineness 0.075 mm, for example, in a hydraulic / cavitation mill. In the case of acid leaching, the chemical potential of the flue gases of TPPs / TPPs containing carbon, nitrogen, sulfur oxides can be used, which, when reacted with water, can produce the corresponding acids, for example, Н ₂ СО ₃ , HNO ₃ , H ₂ SO ₄ , etc. To do this, the water-coal suspension after the third hydraulic grinding in acidified water is poured into a bubbler tank, in which bubbled warm filtered flue gases are bubbled to obtain a more concentrated amount of acid dispersed leaching medium yazhelye rare metals in the form of bulk concentrate with a yield of up to 1 kg / ton, including the release of uranium and thorium to 4.1 g / t.

Thus obtained collective concentrate of heavy rare elements can be divided into fractions by hydrometallurgy in which this or that element predominates, and the technologies for processing individual fractions in order to obtain individual metals of high purity are known and well developed. After the extraction of humic acids and heavy rare metals, the brown coal product is sent for homogenization with a liquid dispersed medium and additives, if their presence is desired, to obtain liquid coal fuel, homogeneous in composition and properties with parameters close to the parameters of a typical water-coal fuel (VUT): content coal 60-65%; viscosity less than 1200 MPa / s; calorific value lower 4000-4700 kcal / kg; ash content of 6-10%; sulfur content 0.25-0.80%; the content of particles of a fraction of less than 0.075 mm more than 75%; degree of burning of carbonaceous substances up to 98%. The burning of liquid fuel prepared from the processed product of Talovsk brown coal can be carried out on the flames of the nozzles of the furnaces of Tomsk TPP-3, located on board the Talovsk brown coal deposit, designed to burn coal from KATEC (Berezovsky open pit), and currently burning Tomsk natural gas.

The chemical composition of Talovsky ash cement and the main characteristics of the binder in comparison with analogue coal ashes and cements are shown in Table 1. The coal composition of the analogs includes section coal: Tunguisky OJSC Vostsibugol; Borodinsky OJSC Krasnoyarskugol; Berezovsky, OJSC Krasnoyarskugol; "Nazarovsky" OJSC "Krasnoyarskugol"; Pereyaslavsky OJSC of Krasnoyarskugol; Irbeyskiy OJSC Krasnoyarskugol and ash from electrostatic precipitators of Espenheim TPP (formerly GDR); the composition of cements includes: sulfated cement 225; slag Portland cement 225; Portland cement 225 and Portland cement 350 (according to A.A. Petrosov, 2007).

Here the main characteristics of the binder are calculated by the formula:

where β is the content of the component in%.

, что в 1,5 раза больше среднего значения для цементов и в 2 раза больше среднего значения для зол углей-аналогов. Модуль щелочности таловского золоцемента равен $$M_0^{т}=0,16$$

, что в 1,5 раза меньше нижнего значения для цементов, но находится в вилке значений для зол углей-аналогов 0,07-2,04. Известковый стандарт таловского золоцемента равен $$K_{cт}^{т}=\text{5,49}$$

, что в 6,6 раза меньше нижнего значения для цементов, но находится в вилке значений для зол углей-аналогов 2,03-81,4.From the above comparative data of binders, it can be seen that the activity indicator of Talovsky ash cement is of the highest value $$P_{\mathrm{but}}^t=0,\mathrm{fifty}$$

that is 1.5 times more than the average value for cements and 2 times more than the average value for ashes of analog coal. The alkalinity modulus of Talovo ash cement is $$M_0^t=0,16$$

, which is 1.5 times less than the lower value for cements, but is in the plug values for the ashes of analog coal 0.07-2.04. The lime standard of Talovsky ash cement is $$K_{ct}^t=\text{5.49}$$

, which is 6.6 times less than the lower value for cements, but it is in the plug of values for analogue coal ashes 2.03-81.4.

Table 1 Comparison of data of binders Binder Performance Chemical composition of materials Binder Characteristics Type of binder SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ Cao MgO SO ₃ Activity indicator, Pa Alkalinity Module, Mo Lime standard, Kst Cement 20.7-28.3 6.6-10.5 1.5-2.9 38.7-62.7 2.0-9.2 2,3-7,7 0.28-0.37 0.24-1.8 36.1-93.5 Coal ash 15.0-66.5 5.3-22.8 6.0-14.1 3.9-49.0 1.4-6.0 1.4-10.0 0.08-0.44 0.07-2.04 2.03-81.4 Talovsky ash cement 49.5 25,2 8.8 10.1 1,6 0.32 0.50 0.16 5.49

Thus, Talov ash cement obtained without corrective additives will have the following characteristic properties of ash cement as a binder:

- with a high content of Al ₂ O ₃ and low CaO, the mixtures on ash cement with the addition of water are prone to rapid setting at the beginning of the process, accompanied by intensive heating of the mixture;

- the high content of SiO ₂ provides a high final strength of the hardening mixture;

- "fly ash" - the main component of the ash cement - has good resistance to aggressive water.

и $${К}_{ст}^{т}$$

к значениям, свойственным портландцементам, для целевой коррекции вяжущих свойств угольную пыль перед сжиганием можно шихтовать с некоторым количеством тонкоизмельченной доломитовой (известняковой) пыли и мелкодисперсной глины. В случае если требуемый объем корректирующих добавок будет негативно влиять на процесс сжигания угольной пыли (в случае ВУТ, например, минеральная часть не должна превышать 10% мас. в составе топлива), золоцемент можно получить путем смещения золы-уноса с порошком обожженного доломитового/известнякового продукта без участия потерь после прокаливания (ППП). При этом соотношение между корректирующей добавкой и золой-уносом в весовых частях «X» в шихте может быть рассчитано по известной формуле:In order to approximate indicators $$M_0^t$$

and $${\mathrm{TO}}_{\mathrm{from}t}^t$$

to the values inherent in Portland cement, for targeted correction of astringent properties, coal dust can be burnt before burning with a certain amount of finely ground dolomite (limestone) dust and fine clay. If the required amount of corrective additives will adversely affect the process of burning coal dust (in the case of HLF, for example, the mineral part should not exceed 10% by weight in the fuel composition), ash cement can be obtained by displacing fly ash with calcined dolomite / limestone powder product without loss after calcination (RFP). Moreover, the ratio between the corrective additive and fly ash in the weight parts “X” in the charge can be calculated by the well-known formula:

where KN = 0.9 - saturation coefficient; S ₁ , A ₁ , F ₁ , C ₁ - content in% wt. respectively, SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO in limestone and S ₂ , A ₂ , F ₂ , C ₂ - the content of the same oxides in fly ash.

In the case of our example, marl limestones of the Komlev site of the Kamen-Kamenskoye deposit, located nearby, can be used as a corrective additive to the Talovsk cement;

from Talovskoye brown coal deposits having the following chemical composition,% wt: PPP - 42.88; SiO ₂ -3.70; Al ₂ O ₃ -0.89; Fe ₂ O ₃ -0.21; CaO-51.88; MgO-1.02; SO ₃ - no.

Then, after calculating, we get that Talovsky ash cement with a corrective additive of finely divided calcined Kamensk marl limestone will consist of 78% wt. from fly ash and 22% wt. from the material of the corrective additive with the values of the main characteristics of the binder equal to P _and ^td = 0.48; M ₀ ^td = 1.30; K _st ^td = 14.44.

In addition, it should be noted that another fly ash can be used as a corrective additive, for example, ash from coals of the Berezovsky open pit mine, which has the highest calcareous standard of 81.4.

Thus, the alkalinity modulus was increased by almost an order of magnitude and approached the maximum value for cements, equal to 1.8, and the lime standard rose by more than 2.5 times. Such properties of ash cement are close to the properties of slag Portland cement - 225 and sulfated cement - 225, surpassing the latter in quick setting and in higher final strength of the hardening mixture.

The technical result from the application of the invention consists in obtaining the target product - ash cement and two associated valuable products - humates and collective concentrate of heavy rare metals while producing heat and electricity under conditions of reducing environmental load on the environment. The attainability of the technical result is confirmed by the experimental work of the Tomsk mining company - the owner of licenses for the subsoil use of the Talovskoye brown coal deposits and laboratory studies of mineral raw materials of the Tomsk Polytechnic University in the period 1999-2014.

Claims (3)

1. A method of producing ash cement, including grinding brown coal to a dust consistency - more than 95% of the fraction less than 0.09 mm with the introduction of a corrective additive, burning it in the furnace of a thermal power plant to bring the degree of combustion in the nozzles of carbonaceous substances to 95-98% and removing ash - entrainment - the specified target product from the exhaust gas electrostatic precipitators, characterized in that the first time the brown coal is milled in an alkaline aqueous medium in the extraction chamber of the reservoir during its downhole hydraulic production to the consistency of solid in bullets f, comprising up to 80% of the fraction less than 25 mm, the second time grinding of brown coal in an alkaline aqueous medium is carried out as a solid in the pulp by means of a hydraulic mill to the consistency of a coarsely dispersed phase, comprising up to 75% of the fraction of less than 0.145 mm, then the first intermediate carbon product is separated from the first associated beneficial product - humates obtained by extraction of humic acids with an alkaline medium during brown coal hydrofishing, after which the first intermediate carbon product is subjected for the third time to hydraulic grinding in an acidic aqueous medium to tonin s 0.075 mm, after which the resulting water-carbon suspension is sent to a bubbler tank, where they carry out bubbling of warm filtered flue gases leaving the furnace of the power plant with an increase in the concentration of the sum of acids of the dispersed medium of the suspension and extraction of heavy rare metals into the solution, then the second intermediate carbon product is separated from the second associated useful product - collective concentrate of heavy rare metals and jointly homogenize this coal product with a corrective additive with radiation of liquid coal fuel supplied to the specified combustion. 2. The method according to p. 1, characterized in that finely ground dolomite or limestone dust is used as a corrective additive. 3. The method according to p. 1, characterized in that as a corrective additive use finely ground brown coal, providing a higher coefficient of lime standard fly ash.