RU2185421C2 - Powdered coal fuel and method for production thereof - Google Patents

Abstract

FIELD: solid fuels. SUBSTANCE: invention relates to solid fuel production technology for burning fuel in combustion apparatus in metallurgy, in silica, keramzite, lime, cement, and brick production, operated on mazut, water-coal and mazut-coal suspensions, and dust-like coal. Fuel contains coal disintegrated to fineness 0-1 mm, hydrocarbons, and water steam at weight ratio between 0.74: 0.11:0.15 and 0.84:0.15:0.01 and 5.4% of coal fraction 0-74 mcm. Fuel is prepared by simultaneously grinding and mixing fine coal fractions with hydrocarbons in presence of steam, content of fraction 0-74 mcm during the grinding is 70%. EFFECT: enabled production of freely flowing and non-dusting solid fuels. 3 cl, 1 dwg, 2 tbl

Description

The invention relates to a technology for producing solid fuel before burning it, in particular to producing fuel powders for burning in furnace devices, in metallurgical processes, for example, in the production of alumina, expanded clay, lime, cement, brick, working with fuel oil, water-coal, fuel oil suspensions or pulverized coal
A known method of producing powdered coal fuel SU 684251, C 10 L 9/00, 09/05/1979 [1], which consists in the simultaneous grinding and mixing of the finely ground coal fraction with liquid combustible substances. In this case, combustible substances used may contain up to 20% water. The disadvantage of this method is the explosiveness of the process, since the use of water-combusted up to 20% liquid fuel when grinding together with coal does not exclude the formation of explosive fine fractions of coal.

It is also known to obtain brown coal dust at Nazarovskaya TPP (V. Filipov, "Technology for Coal Drying and Thermo-Aeroclassification", Moscow, Nedra, 1987, 284 pp.) [2]. Crude coal of the Nazarovsky open pit is crushed to sizes less than 20 mm with R10 = 5%. Coal with an initial moisture content of 36-39% is dried to a residual moisture content of 14-16% in tube dryers heated by steam with a pressure of 0.36-0.80 MPa at 140-170 ^o C. The dryer is sent through pneumatic presses closer to the boilers, where it is milled in hammer mills equipped with a ventilation system. The grinding ventilation circuit is closed in a chain mill-separator-cyclone-mill fan-mill. Dust is trapped in cyclones. About 20% of the agent in each cycle is sucked off by a special fan to a separate group of cyclones, then a wet dust collector passes and is discharged into the atmosphere. Dust enters the intermediate hopper at the boiler. From it through the dust pipe to the burner devices. Dust is transported by autonomous compressed air with an overpressure of 0.05 MPa.

 The disadvantages of the ongoing method of producing coal dust include: the complexity of the technological chain, the dustiness of the workplaces, explosiveness, arched formation of dust in the bunker, large production areas for installation of equipment, and high initial capital investments.

 A known method of producing powdered coal fuel (K. Kegel. "Briquetting of brown coal". - M .: "Ugletekhizdat", 1957) [3], including the processing of fine fractions of coal with spray steam to ensure explosion-proof processes. In this embodiment, the effect of steam as an inert substance that reduces the percentage of oxygen in the working area of coal processing is considered, but the effect of the combined action of steam and hydrocarbons has not been studied. The process uses one steam without hydrocarbons.

 The closest to the proposed in essence and the achieved result is a powder-coal fuel obtained according to patent DE 210598 I, 06.24.76, C 10 L 5/16, 5/22 [4]. Powder fuel composition includes coal dust, hydrocarbons and water vapor. The amount of hydrocarbons is 5-10 wt. % calculated on coal dust, and the amount of steam 1-3 tons per 1 ton of dust. The disadvantage of the proposed fuel of this composition is that in the preparation of powdered coal fuel according to the known patent [4] dusty fuel is obtained. This arises as a result of the fact that with a decrease in the consumption of hydrocarbons below 11%, the process of complete coagulation of finely dispersed dusting particles of coal and their binding to larger non-dusting particles is disrupted. The resulting fuel continues to dust, and an increase in steam consumption leads to technologically unjustified, excessive watering of the fuel and a decrease in its calorific value, which increases the cost of operating costs for the consumer.

 The objective of the present invention is to obtain non-dusting solid coal fuel in the form of powders: powdered water-oil-coal fuel (PVMUT), which does not form arches during storage, is free-flowing and is easily transported through pneumatic tubes to nozzles for atomization and mixing with air.

 This is achieved by obtaining from coal fuel products of a specific material and particle size distribution. The specific surface area of coal decreases due to the absence of finely dispersed particles (micronics) and their enlargement into larger fractions. It should be noted that this contributes to a decrease in the chemical activity of the coal surface during interaction with oxygen and to an increase in the duration of storage of the powder until spontaneous combustion. The surface of the coal is passivated by antioxidants. Apolar (petroleum) coagulants, for example, hydrocarbon oils with water, are used as antioxidants. The resulting fuel product and the composition of PVMUT includes natural transition states of coal as a result of exposure to coagulants - antioxidants.

 The implementation of the invention can be illustrated by the drawing, which presents a histogram of oil-gas-coal fuel in various states. The positions in the drawing indicate: 1 - transitional states, 2 - PVMUT, 3 - natural state.

 As can be seen, the state of the coal powder moistened with a film of heavy hydrocarbons and water (in our case, steam), which loses pyrophoricity, is an object of special attention.

As a result of mixing coal dust with a coagulant - antioxidant, a dispersed system is formed in the form of non-dusting coal powder (see drawing, histogram area 2), which under industrial conditions has a number of advantages:
- cheaper due to the involvement of coal;
- high calorific value of fuel;
- fire and explosion safety by reducing the specific surface area and passivation of coal (coagulation of submicron particles);
- reduction of dusting during grinding of coal and pneumatic conveying of powder;
- flowability necessary for transporting fuel through pipes and spraying in a burning torch.

 The advantage of the proposed method lies in the simplicity of the technological organization of the production of a fuel product that does not require the installation of additional dust removal and cleaning systems. During the coagulation process, explosive fine particles of coal (micronics) are not present in the environment, as can be seen from the comparative particle size distribution of coal powders obtained by the present method and the basic version (table. 1).

 As a result, the coal powder does not dust; it is easily atomized through nozzle devices under the influence of the air flow supplied to burn fuel. The powder is stable during storage - it does not cake in the hopper and does not turn into paste or into a briquette at the bottom of the hopper. The powder burns well with maximum use of the calorific value of coal. Due to its higher thermal conductivity than that of air, the water present in the powder stabilizes combustion as well as when burning suspensions. Microexplosions of the water contained in the powder increase the completeness of combustion of coal and fuel oil due to their more complete atomization in a medium of sufficiently heated secondary air; a torch more extended along the length of the furnace than when burning fuel oil or dry dusty fuel helps to improve the cement clinker firing process, expanded clay powder or alumina cake.

 Modes of sintering and firing become softer, stretched over time. Especially favorable is the proposed powder during sintering of alumina. The risk of melting the charge at the boundary of the maximum productivity of the furnace is reduced.

Fuel powder is prepared as follows. Coal is used, for example, in the Kansk-Achinsk basin with a specific heat of combustion of 3740-3800 kcal / kg (15.69-15.90 MJ / kg) or berthinate, which are crushed to a particle size of 5-6 mm. Crushed coal is fed, for example, to a ball mill and crushed to a particle size of 0-1 mm (fraction content of 0-74 μm is not less than 70-80%). At the same time, steam is fed into the mill at 135-170 ^° C and 0.3-0.8 MPa and an antioxidant at the same pressure and 70-90 ^° C, which contributes to fine atomization.

 Steam supply ensures the explosion safety of the process and with the introduction of an antioxidant - microcoagulation of explosive thin, dusty particles of coal - linking them into a dispersed powder. Steam is supplied in an amount of at least 15-20% by weight of the antioxidant. Hydrocarbon oils, for example, fuel oil, are used as an antioxidant. According to the table. 2 select the weight ratio of the input components: coal: fuel oil: steam.

 As can be seen from the above data, when the ratios in the oil-gas-coal fuel are equal to coal: fuel oil: steam = 0.74: 0.11: 0.15-0.84: 0.15: 0.01, a free-flowing powder-coal fuel is obtained.

EXAMPLE. Coal, crushed to a particle size of 5-6 mm, is loaded into a ball mill at the rate of 10 t / h, where, at 70 ^o C, fuel oil is fed at a flow rate of 1807 kg / h, sprayed with steam at a pressure of 0.4-0.5 MPa with a temperature of 135 -155 ^o C. the Consumption of steam is 240 kg / h As a result of grinding, powders with a mass fraction of components according to the table are obtained. 2.

Sources of information
1. Copyright certificate SU 684251, C 10 L 9/00. 09/05/1979.

 2. Filippov V.A. "Technology of drying and thermal aeroclassification of coal." - M.: Nedra, 1987, 284 p.

 3. K. Kegel. "Brown coal briquetting". - M .: "Ugletekhizdat", 1957, p. 526.

 4. Patent DE 210598 I, 06.24.76. C 10 L 5/16, 5/22 (prototype).

Claims (3)

 1. Powder-coal fuel, including coal, crushed to a particle size of 0-1 mm, hydrocarbons and water vapor, characterized in that it contains components in the following mass ratio: coal: hydrocarbons: steam = 0.74: 0.11: 0 , 15-0.84: 0.15: 0.01, with the content of the coal fraction 0-74 microns equal to 5.4%.  2. A method of producing powdered coal fuel, including the simultaneous grinding and mixing of finely divided fractions of coal with hydrocarbons, characterized in that the process is carried out in the presence of water vapor in the following mass ratio: coal: hydrocarbons: steam = 0.74: 0.11: 0 , 15-0.84: 0.15: 0.01 and the content when grinding the coal fraction 0-74 μm is not less than 70%.  3. The method according to p. 2, characterized in that the hydrocarbons use fuel oil, oil, process fuel, diesel fuel, gas oil, coal processing resin.

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