Method and Plant for Thermal Conversion of Solid Fuels

Abstract

The invention relates to thermal conversion of solid fuels with a low organic content and can be used in the fuel-processing industry. Conversion of oil shale or high-ash solid fuels comprises flue-gas drying of feedstock, recovering the solid phase as a heat-carrying agent, feedstock pyrolysis in a reactor, separating a gas-vapour mixture from the coke-ash residue in a dust-settling chamber, discharging ash, cooling flue gases, and combustion of the coke-ash residue. An inert material having an ambient temperature is supplied to the outlet of the coke-ash residue ignition chamber. The plant comprises, arranged in series, a reactor, a dust-settling chamber, a flash-process furnace, a heat-carrier cyclone, an ash cyclone, a waste-heat recovery system, an ash-discharge system and a bin for inert material connected to the outlet of the coke-ash residue ignition chamber. The invention allows for a more complete use of the oil shale energy potential and for obtaining ash with a reduced negative effect on the environment, which makes it possible to use the ash for recultivation of quarries resulting from oil shale mining.

Claims

1. A method for converting oil shale or high-ash solid fuels comprising: flue-gas drying of feedstock; recovering a solid phase as a heat-carrying agent; performing feedstock pyrolysis in a reactor; separating a gas-vapor mixture from a coke-ash residue in a dust-settling chamber; discharging ash, cooling flue gases, and combusting the coke-ash residue; and controlling temperature in a flash-process furnace by supplying an inert material having an ambient temperature to an outlet of a coke-ash residue ignition chamber.

2. The method according to claim 1, wherein the inert material is ash from a discharge system, the ash having a temperature of 10 to 200 C.

3. A device for converting oil shale or high-ash solid fuels comprising: arranged in series a reactor, a dust-settling chamber, a flash-process furnace, a heat-carrier cyclone, an ash cyclone, a waste-heat recovery system, an ash-discharge system, wherein a bin for inert material is connected to an outlet of a coke-ash residue combustion chamber for temperature control in an ignition chamber of the flash-process furnace.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 shows a schematic illustration of a device for converting oil shale or high-ash solid fuels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The method for conversion of oil shale or high-ash solid fuels comprises flue-gas drying of feedstock, recovering the solid phase as a heat-carrying agent, feedstock pyrolysis in a reactor, separating a gas-vapour mixture from the coke-ash residue in a dust-settling chamber, discharging ash, cooling flue gases, and combustion of the coke-ash residue. Here, an inert material having an ambient temperature is supplied to the outlet of the coke-ash residue ignition chamber for temperature control in the flash-process furnace, and ash from the ash discharge system with a temperature of 10 to 200 C. is used as an inert material.

[0017] The plant for implementation of this method comprises, arranged in series, flash-process drier 1, waste drying agent separator 2, pyrolysis reactor 3, its inlet connected to fuel discharge branch pipe of the waste drying agent separator, flash-process furnace 5, solid drying agent separator 6, its gas exhaust branch pipe 7 connected to the drier inlet, ash-and-smoke mixture cooler 8 and ash separator, its gas exhaust branch pipe connected to the smoke exhauster and further to the flash-process drier. The plant operates as follows.

[0018] The shale ground to 0-25 mm is fed with an auger to flash-process drier 1, where the shale is dried with exhaust flue gases. Next, the gas suspension of shale and the flue gases is fed to the dry shale cyclone for separation of the solid phase. Upon being mixed with the circulating ash heat-carrying agent, the dry shale is fed to reactor 3, where pyrolysis of the organic part of the shale occurs at temperatures 450-550 C. The pyrolysis products in the vapour phase and the mixture of the circulating heat-carrying agent with the mineral part of the shale are fed to dust-settling chamber 4. The vapours of pyrolysis products are fed to condensation (not shown in the diagram), where purification, fractionation, and cooling take place, and the target products are released (shale oil and pyrolysis gas).

[0019] The mixture of the circulating heat-carrying agent with the mineral part of the shale (coke-ash residue) from dust-settling chamber 4 is fed with an auger to flash-process furnace 5. Air is fed to the lower part of the flash-process furnace to ensure burning of organic matter in the coke-ash residue and to enable the flash drying process.

[0020] The gas suspension of combustion products, nitrogen and the solid phase is fed from the upper part of the flash-process furnace to the heat-carrying agent separator, wherefrom a part of the solid phase is returned to reactor 3. Further on, the gas suspension from the separator comes into ash cyclone 6, where it is separated into ash and flue gas. The flue gas is fed to heat recovery (recovery boilers) and into flash-process drier 1, where it gives heat to the shale drying process and further, after cyclone 2, is discharged through a filtration system into the atmosphere.

[0021] The ash from cyclone 6 is cooled down in an ash heat exchanger to the temperature of 80-120 C., and is then fed to humidification and further on to recovery. As distinct from the prototype, a part of the ash, prior to its humidification, is fed at the temperature 80-120 C. with an auger to the flash-process furnace to the outlet from the accelerating section of the furnace. Here, the coke-ash residue from the dust-settling chamber has been ignited, and delivering the ash enables to regulate the temperature in the furnace. Feeding cold ash at the temperature of 80-250 C. makes possible to increase the air flow to ensure the fluid dynamics of the spouted bed and to increase the air/combustibles ratio above 1, which ensures more thorough combustion of fuel in the coke-ash residue.

[0022] Therefore, the invention allows for a more complete use of the oil shale energy potential and for obtaining ash with a reduced negative effect on the environment, which makes it possible to use the ash for recultivation of quarries resulting from oil shale mining.