METHOD FOR COAL CONVERSION AND APPARATUS FOR IMPLEMENTATION THEREOF

Abstract

The invention relates to coal conversion, and in particular, to the production of thermal power and high-calorific solid fuel (coke) out of coal for metallurgy, power production, and other industries. The method uses 0-35 mm coal particles as initial raw material, the coal conversion being performed in two steps of fluidized bed heat treatment. At the first step, the raw material is thermally oxidized at 650-800° C. with air supply, and at the second step the coke product is cooled by supply of water steam or chilled flue gases. The apparatus for embodying the method includes a boiler where a furnace comprises two fluidized-bed sections separated with a barrier, the first section being supplied with air, and the second section being supplied with water steam or chilled flue gases.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to power-engineering, more particularly to coal power conversion, and even more particularly to the production of thermal power and high-calorific solid fuel (coke) from coal for metallurgy, power industry, and other industries.

2. Description of Related Art

Numerous methods have been known for coal thermal treatment by means of fluidized bed technology intended for the production of high-calorific solid fuel (coke), preferably, from brown coal. A characteristic example thereof is a method of thermal contact fluidized-bed carbonization (, . -: , 1980) (Andryushchenko A. I., Popov A. I., The Foundations of Designing Power Engineering Installations for Power Plants, Moscow: Vysshaya shkola, 1980.). Coking of fine coal is performed in an apparatus with fluidized bed. The admission of heat to the fluidized bed is provided by an intermediate carrier, the role of which is performed by the coke produced in the process. For this purpose, a recycled portion of coke is heated in a coke heater at the combustion of pyrolysis gas formed in the course of the coal-to-coke conversion. The main product of this method is fine grained coke with the particle size of up to 3 mm. The vapor-gas products of the thermal decomposition of coal are condensed with the release of tar and pyrolysis gas.

The drawbacks of this method involve a multi-stage pattern of the coking process, the inherent complicacy of the applied technological flowchart and the design of the applied apparatuses, as well as environmental hazard of the technology stemming from the toxicity and carcinogenic activity of certain substances (phenols, polycyclic aromatic hydrocarbons, and others), contained in the products of the thermal decomposition of coal.

Also known is a method of the production of metallurgic medium-temperature coke (RU 2285715, Int. Cl. C10 B49/10, dated 29.07.2005). The method allows for the production of coke by fluid-bed thermal-oxidative treatment of coal at 800-900° C., the bed consisting of the coal particles in the range of 0-15 mm, and the air being supplied to the bed.

The drawbacks of this method are a narrow particle size distribution of the coal charged for the treatment (0-15 mm) that calls for increased power consumption for grinding of the feed coal, as well as high coke temperature at the outlet of the coking apparatus amounting to the temperature of the coal treatment (800-900° C.) that results in a cumbersome multistage system of cooling a solid product.

According to the Patent RU 2209901, Int. Cl. C10 B47/04, dated 27 Jul. 2005, an apparatus is known for processing solid fuel and including a layered shaft-type structure implemented in a combination of a top, a middle and a bottom levels. The top level consists of a charging door, a gas outlet manifold, a hydraulic lock, and an electrical thermal assembly. The middle level consists of a cylindrical shell and a water jacket, and the bottom level has the shape of a truncated cone and consists of a discharge assembly, a grate, an inlet unit for air or/and cooling gas supply and thermal electrical sensors.

Its drawbacks are a batch operation mode and a low specific throughput capacity due to extended residence of coal in the apparatus (several hours), that in combination results in high specific capital costs per unit product.

A power-generating boiler with fluidized bed for coal combustion (, 1995 195-197) (Baskakov A. P., Matsnev V. V. and Raspopov I. V., Boilers and Furnaces with Fluidized Bed, Moscow, Energoatomizdat, 1995, pp. 195-197) is believed to be the closest analog to the claimed one. However, this boiler assembly is intended only for the production of thermal power at the minimal mechanical underburning of solid fuel. Another drawback thereof is the necessity of ash and slag waste disposal resulting in the pollution of environment.

The object of the invention is to improve efficiency and to simplify a method of thermally processing coal, as well as to improve environmental safety.

An engineering result of the invention is the production of high-calorific solid fuel and thermal power from coal.

BRIEF SUMMARY OF THE INVENTION

The aforementioned result is achieved by using coal with particle size of 0-15 mm as feed stock and performing coal processing successively in two sections of the fluidized bed, thermal oxidative treatment being carried out in the first section at 650-800° C. in air flow, the resulting coke being cooled in the second section by feeding water steam or precooled flue gases. The apparatus for the implementation of the method includes a boiler with a furnace wherein the furnace consists of two fluidized bed sections separated by a barrier, the first section being fed with air flow, the second section being supplied with water steam or the precooled flue gases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is made to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 illustrates schematically an apparatus for implementing the method of coal conversion according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, the apparatus for coal conversion in accordance with the present invention comprises a boiler 1 with a furnace 1 a separated with a barrier 2 into two fluidized-bed sections 3 and 4. Subsections 5 are intended for air supply to the sect ion 3, and channels 6 are intended for supplying a cooling agent. Coal is fed to the section 3 via a feeder 7. The ultimate products are discharged through an outlet 8.

The method of coal conversion into high-calorific industrial solid fuel according to the present invention is performed as follows. Preliminary crushed coal with particle size of 0-35 mm is continuously fed by the feeder 7 to the first fluidized-bed section 3 where it is subjected to thermal-oxidative treatment. The temperature of the bed in the first section being from 650 up to 850° C., depending on the preset mode determined by the ratio of the air flow rate to the coal feeding rate. As this takes place, the coal particles are crushed as a result of thermal shock when entering the high-temperature fluidized bed. Coarser coal particles, heating up to the temperature of the fluidized bed and moving horizontally along the first section 3 of the fluidized bed, successively pass the stages of drying, pyrolysis, and partial gasification. Air to the first section 3 is supplied via independently adjusted subsections 5 along the fluidized bed. Further on, flowing over the barrier 2, separating the sections 3 and 4, the coke particles are transferred to the second section 4 of the fluidized bed, where water steam or flue gases cooled in the end surfaces of the boiler 1, supplied via the channels 6, are used for cooling down (quenching) the coke via the channels 6 to, for example, 150-250° C. As a rule, overall residence time of the coal particles in both sections at the conversion does not exceed 10 seconds, which stipulates high specific yield of the apparatus. The fine coal particles, vapor-gaseous products of the thermal decomposition of coal, as well as the products of coke gasification are partially burned in the first section 3 of the fluidized bed, providing its operational temperature, are transferred from the fluidized bed and burn down in the above-bed space due to supply of a secondary air flow. The resulting combustion products and emitting surface of the fluidized bed, as well as the heated gases from the second section 4 of the fluidized bed transfer heat to the heating surface of the boiler 1 for generating thermal power in the form of hot water or water steam.

The heat of the combustion products and of the emitting surface of the fluidized bed is transferred to the heating surface of the boiler 1 for generating thermal power—hot water or water steam with preset parameters.

An example, illustrating the method and apparatus according to the present invention, is based on the results of performance tests of a modified version of a KVTS-20 boiler, where a standard furnace was replaced with two fluidized-bed sections separated by a barrier, the first section being supplied with air for fluidizing coal, and the second section being supplied with flue gases chilled in the end surfaces of the boiler.

Table 1 summarizes operational properties of the modified KVTS-20 boiler; Tables 2 and 3 contain characteristics of the used coal, particle size range: 0-35 mm, Grade 2B, from the Kansk-Achinsk coal basin “Berezovsky-1” Open Pit Mine, and of the final product—high-calorific solid fuel, coke, formed therefrom, respectively.

TABLE 1
Operational properties of the modified KVTS-20 boiler
Overall coal consumption:
Coal consumption	14	t/hr
Temperature in the section of thermal oxidation	690-740°	C.
Heating value of the coal	51.8	Gcal/hr
Production of thermal power:
Hot water	20	Gcal/hr
Gross heating efficiency of the boiler	83%
Coal consumption for heat production	6.5	t/hr
Specific coal consumption, t/Gcal	0.325
Production of brown coal coke:
Heating value of the coke product	23	Gcal/hr
Coke yield	3.33	t/hr
Coke temperature at the outlet of cooling section	190-220°	C.
Coal consumption for semi-coke product (at 83%	7.5	t/hr
efficiency)
Specific coal consumption, t/t of coke	2.25
Total valuable products (100%)
including:
Hot water (46.7%)	20	Gcal/hr
Heating value of coke product (53.3%)	23	Gcal/hr
Power efficiency of the overall process	83%

TABLE 2
Technical and elemental analysis of the initial coal
Wtr	Ad	Vdaf	Cdaf	Odaf	Hdaf	Ndaf	Std	Qir
34.0%	7.0%	48.0%	70.0%	24.0%	5.0%	0.7%	0.3%	3700
								kcal/kg
								(15.5
								MJ/kg)

TABLE 3
Technical and elemental analysis of the coke product
Wtr	Ad	Vdaf	Cdaf	Odaf	Hdaf	Ndaf	Std	Qir
2.0%	14.7%	10.2%	92.2%	5.7%	1.6%	0.3%	0.2%	6900
								kcal/kg
								(28.9
								MJ/kg)
where Wtr is moisture content; Ad — ash content on a dry basis; Vdaf — volatile constituents on a dry ash free basis; Cdaf, Odaf, Hdaf, Ndaf — carbon, oxygen, hydrogen and nitrogen content, respectively, on a dry ash free basis; Std — sulphur content on a dry ash free basis; Qir — lower heating value

Therefore, the proposed method and the apparatus for implementing the method make it possible to convert coal with particle size of 0-35 mm into high-calorific solid fuel simultaneously producing thermal power.

Claims

1-2. (canceled)

3. A method of coal conversion in a fluidized-bed boiler made with a first and a second sections and a barrier separating said sections from each other, said method comprising the steps of: crushing coal to a fraction of 0-35 mm,continuously feeding said first section of said boiler with said crushed coalsupplying air to said first sectionsubjecting said crushed coal to thermal-oxidative treatment at 650-800° C. in said first section, whereby coke particles are produced,transferring said coke particles into said second section of said boiler,supplying water steam or precooled flue gases to said second section, andcooling said transferred coke particles with said water steam or flue gases,to thereby produce high-calorific solid fuel and heat.

4. A fluidized-bed apparatus for coal conversion according to a method as claimed in claim 1, including a boiler comprising a first and a second section separated from each other by a barrier, wherein said first section is connected to a source of coal crushed to a fraction of 0-35 mm and to a source of air supply, operating temperature inside said first section being maintained at 650-800° C., and wherein said second section is connected to a source of water steam or flue gases.