RU2322641C2 - Method and device for processing condensed fuel - Google Patents

Abstract

FIELD: processing of condensed fuels.

SUBSTANCE: method comprises charging fuel into the cylindrical reactor, supplying the oxygen-containing gasifying agent to the reactor from the side of reactor where the solid products of processing are collected, setting the fuel charged in motion along the axis of the reactor, discharging solid products of processing from the reactor, discharging the drying products from the reactor, and pyrolysis and combustion of gas product so that the fuel is gasified in the heating and drying zone, pyrolysis zone, combustion (oxidation) zone, and cooling zone. The gas is filtered by flowing though the layer of the charged fuel, thus flowing through the cooling zone, combustion zone, pyrolysis zone, and zone of heating and drying in series. The burning is stabilized by means of rotation of the reactor around its axis inclined to horizon under an angle from 22 to 65°. The device for processing of condensed fuel is also presented.

EFFECT: enhanced efficiency.

12 cl, 1 dwg, 1 ex

Description

The present invention relates to methods for processing condensed fuels, including solid combustible waste, by pyrolysis and gasification of the combustible components of the fuel in a dense layer and obtaining products of pyrolysis and combustible gas and then with energy. Processing low-grade condensed fuels, including municipal solid waste (MSW), coal, oil sludge, biomass, is an urgent problem, since the existing methods for their destruction / processing are not quite economically and environmentally acceptable. Significant advantages are provided by condensed fuel gasification, which makes it possible to use advanced energy generation technologies and ensures the environmental cleanliness of gas emissions.

A number of methods are known for processing condensed fuels in a combustion mode to produce combustible gas based on sequential layer-by-layer gasification of solid organic fuels in countercurrent oxidizing gas in shaft-type furnaces. So, for example, in relation to the processing of oil shale, this scheme is described in patents US-A-2796390 (Elliot) and US-A-2798032 (Martin et al.).

The general scheme of gasification of solid organic fuels in countercurrent gasification agent can be presented in the following form. A gasifying agent containing oxygen and possibly water and / or carbon dioxide enters the combustion zone, in which oxygen interacts with the carbon of solid fuel in the form of coke or semi-coke at temperatures of about 900-1500 ° C. The gasification agent is fed into the reactor countercurrent to the fuel in such a way that the oxidizing gas is at least partially preliminarily passed through a layer of hot solid combustion products in which carbon is already absent. In this zone, solid combustion products are cooled and the gasification agent is heated before it enters the combustion zone. In the combustion zone, the free oxygen of the gasifying agent is completely consumed and hot gaseous products of combustion, including carbon dioxide and water vapor, enter the next layer of solid fuel, called the reduction zone, in which carbon dioxide and water vapor react chemically with the carbon fuel, forming combustible gases. The thermal energy of the gases heated in the combustion zone is partially consumed in these reduction reactions. The temperature of the gas stream decreases as the gas flows through the solid fuel and transfers its heat to the latter. The fuel heated in the absence of oxygen undergoes pyrolysis. Pyrolysis produces coke, pyrolysis resins and combustible gases. The product gas is passed through freshly loaded fuel so that the gas cools and the fuel warms up and dries. Finally, the product gas (containing hydrocarbon vapors, water vapor, and pyrolysis resins) is discharged for later use.

Known applications of such a scheme for the processing of used tires (patent RU 2062284, Manelis and others), municipal solid waste (RU 20799051, Manelis and others), oil sludge and similar oil wastes (RU 20799051, Manelis and others), in which together with the processed fuel into the reactor is loaded with solid lumpy inert material, which, in particular, ensures uniform gas permeability of the charge in the reactor.

At the same time, a significant problem remains unresolved - ensuring the stability of the flow of combustion during gasification of the processed charge. Since the processed materials often have uneven gas permeability and are prone to sticking together during pyrolysis, the front of the pyrolysis and gasification can also propagate unevenly over the reactor cross section. In the layer of the processed charge, “burnouts” can occur, through which the gas stream mainly flows, material collapses in the cavity formed during combustion, and at the same time practically gas-tight regions can form. As a result, the temperature distribution in the combustion zone is heterogeneous and poorly controlled.

To solve the problem of uniform distribution of the combustion zones along the loaded material, a gasification method is proposed, described in US-A-4732091 (Gould), for gasification of garbage. According to this method, solid fuel is loaded into the top of a vertical shaft furnace. Fuel is directed at a controlled speed through a sequence of chambers separated by horizontal movable gratings in which the fuel is pyrolyzed and burned in countercurrent gas-vaporizing agent. This method provides a method for loosening debris during processing and, thus, to ensure its uniform gas permeability and for uniform movement of the processed charge sequentially in the zone of drying, pyrolysis, gasification, cooling. It also gives a way to control the flow of fuel into the corresponding zones. The main disadvantage of this method is the presence of moving gratings in it. In high temperature zones, moving grilles will inevitably wear out quickly. In addition, dust and tar particles will be deposited on the moving structures of the reactor, disrupting its operation.

The objective of the present invention is to provide efficient processing of condensed fuels, including low-calorie, without the use of additional energy sources. To solve this problem, a method of gasification of condensed fuels is proposed.

The proposed method includes the following main steps.

Condensed fuel in a solid, liquid or pasty state, possibly containing solid non-combustible components and moisture (hereinafter referred to as “fuel”), is loaded into the reactor to sequentially dry the fuel and then pyrolyze / gasify the combustible fuel components. An oxygen-containing oxidizing gas (for example, air) is supplied to the reactor through that part where the solid residue of the processing is accumulated, so that the gas flow is substantially directed in countercurrent flow through a dense layer of fuel loaded into the reactor. The fuel in the reactor passes sequentially through a series of zones, as described below. First, through the drying zone, where the temperature of the fuel rises to 200 ° C due to heat exchange with the flow of product gas filtered through the fuel; in this zone, the fuel is dried, and the gas stream is cooled before the latter is removed from the reactor. The gaseous products of drying, pyrolysis and gasification are removed from the reactor after passing through this zone as product gas. Then the fuel enters the pyrolysis and coking zone, where due to heat exchange with the gas stream, the temperature gradually increases from 200 to 800 ° C and the combustible components of the fuel pyrolyze with the formation of coke. Then, the coked fuel enters the combustion and gasification zone, where the temperature of the solid phase is 700-1400 ° C. Here, coke reacts with a hot oxidizing gas to form fuel gas. The solid combustion residue enters the cooling zone, where it is cooled by the countercurrent of the gasifying agent from the combustion temperature to the discharge temperature. The counter flow of the oxidizing gas, in turn, filtered through a dense layer of solid residue of combustion, is heated to a temperature close to the temperature of combustion, before it enters the combustion zone.

The above classification of zones is somewhat arbitrary. These zones could be determined differently, for example, by the temperature of the gases, the composition of the reagents, etc. In particular, in US-A-4732091, the same zones are named differently. In any classification of zones, it is significant that due to the countercurrent of interpenetrating gas flows and solid loading, the oxidizing gas (gasifying agent) is preheated on the solid combustion residue, and subsequently, hot gaseous combustion products transfer their heat to the original fuel.

To solve this problem, it is necessary to ensure a uniform degree of fuel processing over the reactor cross section and its uniform movement to the corresponding zones. The problem at the current level of technology is solved only by using moving elements in the hot zone of a shaft furnace (US-A-4732091 (Gould)).

However, rotary kilns are a widely known device. They are widely used for firing cement, for burning waste. The rotation of the furnace provides uniform mixing of the processed material under the action of its own weight.

It is known to use a rotary kiln for carrying out a gasification process, for example, described in US Pat. No. 2,447,322 issued September 30, 1881. From patent application US-2005051066 there is known a method for gasifying solid fuels in a direct-flow gas / solid mode using a rotary kiln. US Pat. No. 3,9908,065 (Cybriwsky & Petersen) describes a gasification process carried out in a slightly inclined rotary kiln in which the feed inlet side is higher than the discharge side of the material. Solid carbonaceous material is continuously fed into a rotary kiln. Passing through the furnace, the material loaded at a temperature below 315 ° C passes through the preheating, volatile exit zones and gradually heats up to 871 ° C, and at this temperature it loses its tendency to agglomerate, and then enters the gasification zone, where it is fed under the mixed layer an oxidizing medium containing steam, resulting in the formation of combustible gases containing hydrocarbons that are discharged from the side of the furnace into which the fuel is loaded.

When the furnace rotates, the processed charge is effectively mixed under its own weight. However, in existing rotary kilns, the combustion process proceeds predominantly above the surface of the charge. None of the gasification processes carried out in such furnaces implements the conditions for effective interfacial heat transfer inherent in a dense porous layer. The present invention allows you to combine the advantages of a dense-layer process — efficient interfacial heat transfer and mixing of the processed material under its own weight during the rotation of the reactor, inherent in rotary kilns.

To solve the problem of efficiently conducting countercurrent gasification in a dense layer and stabilizing the combustion process in the reactor, condensed fuel is loaded into a cylindrical reactor, while a dense layer of fuel loading is created in the reactor, it is fed into the reactor, to that part where solid processed products are accumulated, oxygen-containing gasification agent, and the gasification of fuel is carried out in the reactor by its sequential stay in the zones of drying, pyrolysis, combustion and gasification, cooling gas stream, filtered through a dense fuel layer countercurrent to the fuel movement along the reactor axis; at the same time, in order to stabilize the combustion process in the reactor and ensure uniform stay of fuel in a dense layer in the above zones, the cylindrical reactor is arranged with its axis inclined at an angle to the horizontal and rotated so that the material is poured in the direction perpendicular to the axis reactor, and along the axis of the reactor and the filling of the voids formed during the burning of low-density materials. The gasifying agent is supplied from the side of the downstream end of the cylindrical reactor, and the product gas is taken from the opposite end.

The slope of the axis of the cylindrical reactor is selected in the range from 22 to 65 degrees to the horizon. When choosing an angle of inclination less than the specified lower limit does not form a dense layer of granular material in an inclined reactor. On the contrary, a solid fuel layer forms over which a gas stream is established. At the same time, the gas stream is not filtered through the fuel and the main advantage of gasification in the dense layer is not realized - the high efficiency of interfacial heat transfer, and the uniformity of the process along the reactor cross section is not ensured. When choosing an angle of inclination greater than the specified upper limit, proper mixing of the solid material is not ensured in the case of the formation of "burnouts".

The best combination of conditions for the movement of fuel along the axis of the reactor and the uniformity of the structure of the combustion zone is achieved by choosing the angle of inclination of the axis of the reactor to the horizon from 40 to 50 degrees.

Preferably, the rotation period of the reactor should be small enough to allow mixing of the material in the combustion zone. This allows you to implement the proposed process with a shorter reactor length. In order to achieve an effective effect of rotation on the entire volume of material located in the combustion zone, provided that the dimensions of the combustion zone along the axis of the reactor do not exceed an order of magnitude D - the diameter of the reactor cross section (m), it is necessary to ensure a sufficient rotation speed of the reactor. If the volumetric rate of discharge of the solid residue of the processing is V (m ³ / h), then the average residence time of the solid residue in the combustion zone will be approximately πD ³ / 4V (h). The rotation period of the reactor T should preferably be not more than approximately D ³ / 4V (h), in order to ensure at least three times the mixing of the material during the time that it is in the combustion zone.

Preferably, the reprocessing fuel should be solid lumpy material that is sufficiently permeable to the filtered gas stream. In case of insufficient permeability of the fuel, in particular during the processing of finely dispersed, liquid or pasty fuels, together with the fuel, lumpy solid non-combustible material is loaded into the reactor, which provides both uniform gas permeability of the fuel charge in the reactor and improves the mixing conditions of the material in the combustion zone in case of burnout formation . In the case of processing liquid or paste materials, it is not necessary to pre-mix them with solid lumpy material before loading into the reactor, since uniform mixing of the load is ensured during rotation of the reactor. To ensure the mixing conditions of the materials in the pyrolysis and combustion zones, preferably, the solid inert material added to the charge should differ in density from the processed fuel.

The process is carried out in a device for gasification of condensed solid fuel, including a loading device, a cylindrical reactor, a discharge device, a gasifying agent supply device, a product gas outlet, a reactor rotation drive, and seals providing gas tightness of the reactor during rotation, the cylindrical reactor being installed with an axis angle to the horizon in the range from 22 to 65 degrees, the loading device and the product gas outlet are located in the upper part of the reactor, and the unloading devices and gasifying agent feed device - the bottom of the reactor. Preferably, the angle of inclination of the rotating reactor to the horizon is from 40 to 50 degrees.

To ensure the propulsion of the fuel along the axis of the reactor during the rotation of the latter, it is necessary to remove solid combustion residue from the reactor in a controlled manner. Preferably, this is due to the natural precipitation of solid granular material from the holes in the side wall of the reactor during its rotation. The size of the holes and their number are chosen so that a portion of the solid material that pours out at each revolution is consistent with the required volume of material unloading. The number of holes should be at least two, and their linear size should be no more than half the inner diameter of the reactor to ensure uniform discharge of the solid combustion residue over the cross section of the reactor. The solid combustion residue is freely poured from the reactor into an unloading device, such as a lock or a water seal, which removes the solid residue while maintaining the gas density of the device.

Preferably, the openings on the side of the reactor are provided with devices that control the opening of the openings, for example, in the form of adjustable shutters.

Alternatively, the unloading of the reactor can be carried out through a cone provided with a hole along the axis of the reactor, mounted in the lower part of the latter, the diameter of the hole being less than half the inner diameter of the reactor.

In order to ensure a consistent stay of fuel in the zones of heating, pyrolysis, combustion and cooling, it is necessary to ensure a sufficient length of the cylindrical reactor. In order for the corresponding zones to be accommodated in the reactor, it is necessary to fulfill the following relationship between the geometric dimensions of the reactor: L · sinα> 3 · D, where L is the length of the rotating reactor, α is the angle of inclination of the axis of the reactor to the horizontal, and D is the inner diameter of the reactor.

Maintaining the upper level of loading in the reactor as fuel is consumed during pyrolysis, combustion and unloading can be carried out both by measuring the actual level (for example, using a radiation sensor) and issuing a command to load another portion of fuel, or using a loading device that includes a vertical a cylinder with a diameter less than the diameter of a rotating reactor, placed the lower end inside the upper part of the reactor. With such a loading device, the fuel loading level in the reactor is kept constant by spilling fuel from a vertical pipe as it is consumed in the reactor.

Further, the present invention is disclosed by the example of one of the possible embodiments of the process, schematically shown in the drawing.

Condensed fuel "F", if necessary pre-crushed and with the addition of solid non-combustible material, is loaded into the reactor 1 through a loading device 2, including a lock chamber 3. The fuel enters the reactor through a vertical cylinder 4. At the same time, the level of processed fuel in the reactor is kept constant, since when the reactor 1 rotates, fuel spills out of the cylinder 4, which replenishes the consumption of material during combustion and unloading of ash. The material in the reactor passes sequentially through the drying zone 5, the pyrolysis zone 6, the combustion zone 7 and the cooling zone 8. The solid combustion residue “R” is poured into the openings 9 with the shutters 10 as the reactor rotates, and then is continuously or portionwise discharged through the gas-tight discharge the device — in the example shown in the figure — a water trap 11. The ratio of the openings of holes 9, the rotation speed of the reactor, and the flow rate of the oxidizing agent supplied to the reactor ensures the discharge rate of the solid processing residue, at which ix combustion zone in the reactor remains constant - in the middle of the reactor. Air "A", if necessary, together with water vapor, is supplied by the compressor 12 to the lower part of the reactor. Product gas "G" is taken off at the top of the reactor and sent for further use, which may include cleaning and burning it in an energy device. The temperatures in the respective zones are continuously measured, and when the temperatures go beyond the prescribed optimal limits, the control parameters are adjusted, such as: the speed of the reactor, the speed of air supply to the reactor, the speed of steam supply. The presence of a sufficient amount of fuel in the loading device is measured by a level sensor and, as it is exhausted, fresh portions are loaded through the gateway 3. To coordinate the rate of discharge of the solid residue of the processing, the openings of holes 9 are adjusted, increasing the clearance when the discharge speed is more than desired, and decreasing in the opposite case .

Due to the rotation of the reactor at an angle to the horizon, the material is mixed primarily in the pyrolysis and combustion zones, where there is a significant decrease in fuel volume and voids are formed. When rotating at an angle to the horizon of the reactor, burnouts resulting from the burning of low-density materials are filled with portions of unburned material that collapse under the influence of gravity, which ensures stabilization of the combustion process in the reactor.

The invention is further illustrated by the following example.

In an experimental laboratory reactor made of quartz, gasification of a mixture of sawdust with a crumb of fireclay brick 2: 1 by weight was carried out. The angle of inclination of the axis of the reactor to the horizon ranged from 5 to 90 degrees. Direct observation shows that at an angle of inclination of the axis of less than 22 degrees, the gas stream is not filtered through a dense layer of fuel - a cavity forms along the upper generatrix of the reactor, in which the gas stream rushes above the surface of the fuel. With the vertical arrangement of the reactor after a short time of its operation, burnouts are formed in the fuel layer along the walls of the reactor and, as a result, one of them “sprouts” to the loading surface. In this case, the product gas begins to burn directly above the loading surface in the reactor. When the axis of the reactor deviates from the vertical, the collapse of burnt cavities in burnout gradually begins to appear during rotation of the reactor. When the angle of the axis to the horizontal is less than 65 degrees, it is possible to completely suppress the burnout output to the surface and to provide stabilization of the combustion zone in the middle part of the reactor. In the entire range of angles at which the combustion zone is stabilized, stable combustion of the product gas is observed in the flare, and unburned carbon is not found in the solid combustion residue. The best stabilization of the combustion front is achieved with an angle of inclination of the axis from 40 to 50 degrees, while the size of the combustion zone along the axis of the reactor does not exceed half the diameter of the reactor. To realize a stable front, it was necessary to carry out rotation at a speed exceeding some given for each angle of inclination. Evaluation shows that to stabilize the combustion zone, it is necessary to repeatedly mix the material during the passage of a distance along the axis of the reactor, approximately equal to the diameter of the latter.

Thus, the present invention, in contrast to known methods, provides an effective method of gasification of condensed fuels with a high yield of combustible gas and high energy efficiency.

The present invention has been described without limitation and is subject to further improvements in its general framework.

Claims (12)

1. A method of processing condensed fossil fuels by gasification, including loading fuel into a cylindrical reactor, feeding a gasifying agent containing oxygen to the reactor from the side of the reactor, where solid processing products are accumulated, loaded fuel is moved along the axis of the reactor, and solid processing products are removed from the reactor , the conclusion from the reactor of products of drying, pyrolysis and combustion in the form of a product gas in such a way that gasification is carried out by sequential stay fuel in the heating and drying zone, the pyrolysis zone, the combustion (oxidation) zone and the cooling zone, and the gas stream is filtered through a loaded fuel layer, passing successively the cooling zone, the combustion zone, the pyrolysis zone and the heating and drying zone, characterized in that the combustion process in a dense layer they stabilize by rotating the reactor around an axis inclined with respect to the horizon at an angle ranging from 22 to 65 °. 2. The method according to claim 1, characterized in that the angle of inclination of the reactor to the horizon is maintained in the range from 40 to 50 °. 3. The method according to claim 1, characterized in that the speed of rotation of the reactor around the axis is selected from the relation T <D ³ / 4V, where T is the rotation period (h), D is the diameter of the reactor cross section (m), V is the space velocity discharge from the reactor of solid combustion residue (m ³ / h). 4. The method according to claim 1, characterized in that, together with the processed fuel, solid lumpy non-combustible material is loaded into the reactor. 5. The method according to claim 4, characterized in that a solid lump of non-combustible material with a density different from the density of the processed fuel is loaded into the reactor. 6. A device for processing condensed fuel according to any one of claims 1 to 5, including a rotating cylindrical reactor installed at an angle to the horizon in the range from 22 to 65 °, a drive for rotating the reactor, a loading device and a product gas outlet in the upper part of the reactor, an unloading device and a gasifying agent supply device are located in the lower part of the reactor, and seals ensuring the gas tightness of the reactor during rotation. 7. The device according to claim 6, characterized in that the angle of inclination of the axis of the reactor to the horizon is from 40 to 50 °. 8. The device according to claim 6, characterized in that in the lower part of the cylindrical surface of the reactor there are two or more holes with a linear size of not more than half the inner diameter of the reactor. 9. The device according to claim 8, characterized in that the holes on the side surface of the reactor are equipped with devices that change the lumen of the holes, for example, in the form of adjustable dampers. 10. The device according to claim 6, characterized in that in the lower part of the cylindrical surface of the reactor there is a cone equipped with a hole located on the axis of the reactor, having a diameter of less than half the inner diameter of the reactor. 11. The device according to claim 6, characterized in that the length of the reactor satisfies the condition L · sinα> 3D, where L is the length of the reactor, α is the angle of inclination of the axis of the reactor to the horizontal, and D is the inner diameter of the reactor. 12. The device according to claim 6, characterized in that the loading device includes a vertical cylinder with a diameter less than the diameter of the reactor, placed the lower end inside the upper part of the reactor.