RU2551330C2 - Vertical fluidised-bed furnace - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: invention relates to designs of furnaces with fluidised bed for treatment of loose materials in inert, reducing or oxidising media. A furnace includes a heating chamber opening through 180 degrees in a vertical plane for quick cooling, a removable quartz reactor with a grate, a loading device in the form of a plastic pipe with a sealing and cleaning gasket and an unloading device operating as per a vacuum venting principle. With that, the grate of the reactor is made from quartz glass in the form of a flattened cone with holes on side walls and on the vertex of the flattened cone.

EFFECT: invention allows prevention of formation of stagnant zones and obtaining a high-purity product.

3 cl, 3 dwg

Description

The invention relates to designs of fluidized bed furnaces for processing bulk materials in an inert, reducing or oxidizing environment. The patented furnace is designed to operate up to 1000 ° C for the production of silicon dioxide powder with a purity of at least 99.95% from rice husk.

The technical requirements for equipment for the production of high-purity powders (with a base material content of at least 99.95%) are high in relation to the purity of the materials from which the parts that come into contact with the powders are made, as well as to design features that minimize the number of moving parts in order to exclude their abrasion and contaminants in the produced materials.

The requirements for equipment for high-temperature roasting of husk of rice in order to obtain a high-purity silicon dioxide powder are as follows: the apparatus parts in contact with the obtained powder (reactor, loading, unloading and liquefying gas nozzles, finished product receiving hopper) must be made of non-oxidizing, solid, wear-resistant abrasive high temperature gas streams of material; lack of rotating, rubbing parts; providing husk mixing to accelerate the process of oxidation and smoke removal; the temperature of the feed zone (the lower part of the vertical reactor) at the time of loading should not be higher than 100 ° C; external heating of the reactor (prevention of combustible gases and products of its combustion inside the working space of the furnace); adjustable speed of temperature rise; rapid cooling of the reactor and furnace heater.

The best materials for such conditions for the reactor and pipes are quartz glass and silicon carbide.

There is no specialized equipment for the high-temperature processing of rice husks with the above design. The use of existing equipment for heat treatment of bulk materials is inefficient in productivity and does not ensure the purity of the final product.

Known designs of single and multi-chamber furnaces with a fluidized bed with continuous loading and unloading, consisting of a vertical column with 1-5 horizontal gratings and flows, with a supply pipe for the starting material in the upper part of the column, with a supply of fluidizing gas in the lower end of the column, with the supply pipe of gaseous fuel in the middle or lower part of the column, with an exhaust pipe of exhaust gas in the upper end part of the column. The inner part of the column is made of ceramics (See K.E.Makhorin, A.T. Tishchenko “High-Temperature Fluidized Bed Plants.” Kiev. “Technique”, 1966. Fig. 1, Fig. 15).

The disadvantage of these structures when used for processing rice husks is that the horizontal lattice causes the formation of stagnant zones and the formation of a vault of particles of the resulting powder.

To eliminate the arch and stagnant zones, it is required to create a pulsation of the fluidizing gas; however, at the moment of maximum increase in the pressure of the fluidizing gas in the pulse and increase in the flow rate of the fluidizing gas, the lightest and most floating part of the powder particles rises to a high height and is carried away into the exhaust pipe with a gas flow - a large loss of product occurs.

The second disadvantage is the device flows. Getting into the flows of precisely those particles that have passed this stage of heat treatment is a difficultly regulated process; fresh particles that have not passed the required heat treatment stage also get into the flows, as a result, the purity of the final product decreases.

The third drawback is the introduction of fuel inside the column, which is unacceptable in view of the decrease in the purity of the final product.

A known apparatus with continuous loading and unloading (see AS No. 4884792/06 of 11/21/90), a distinctive feature of which is the ability to change the productivity of the process by changing the cross section of the discharge pipe and due to the ejection effect.

It is not possible to make a device of this design from ceramics or quartz glass, in addition, the design of the device does not provide for the possibility of changing the duration of the heat treatment process.

A device is known (see A.S. No. 4725390 of 07.27.89) for heat treatment of granular material in a fluidized bed, comprising a housing divided by partitions into a firing chamber and a cooling chamber with partitions between them, in which, in order to control the duration of the heat treatment process installed turning in the horizontal and vertical planes of the partition.

This device cannot be made of quartz glass or ceramics, since breakages of the turning partitions are inevitable, and inevitable leaks in the systems of turning partitions will lead to the loss of fine fractions of silicon dioxide powder.

The simplest way to comply with the requirements for creating conditions for obtaining high purity of the final product is possible in batch apparatuses.

Known vertical apparatus of the fluidized bed of periodic action (see K.E.Makhorin, A.T. Tishchenko "High-temperature installations with a fluidized bed". Kiev. "Technique". 1966. Fig. 35) with loading from above and unloading from below.

The disadvantages of this design is that it does not provide for cleaning the channel of the reactor before the unloading process; heating is carried out by supplying hot gas to the inside of the reactor; accelerated cooling of the furnace heater and reactor is not provided.

The closest in technical essence is a vertical fluidized bed apparatus with external heating, with loading and unloading through the lower part of the reactor by means of a screw feeder, with a conical inlet for liquefied gas without a grate (see Fig. 70 in the book by K.E.Makhorin / A.T. Tishchenko “High-temperature installations with a fluidized bed.” Kiev. “Technique.” 1966.).

The disadvantages of this apparatus are: 1) the reactor cooling process is long, since it is carried out together with the heating chamber, and this reduces the productivity of the apparatus; 2) cleaning of the discharge nozzle before the unloading process is not provided, which leads to contamination of the product with unprocessed particles adhering to the upper low-temperature part of the apparatus; 3) the presence of rotating parts in contact with the powder; 4) lack of a grate.

The aim of this invention is the creation of a furnace with a fluidized bed of a vertical design without moving parts, with external heating and rapid cooling of the heaters and the reactor to 30-100 ° C, with a grate, which prevents the formation of stagnant zones from the processed powder, with a loading pipe that cleans the wall reactor from the original and unfinished powders.

The problem is achieved in that the vertical heating chamber with electric heaters is made of two equal parts, opening 180 degrees in a vertical plane; the reactor in the form of a pipe narrowed below, with a cone-shaped grate and two air dividers (all made of quartz glass) is fixed motionless on a common holder with a heating chamber; the grate is made in the form of a truncated cone with periodically arranged holes on the lateral surface and on a truncated apex with a diameter of 0.2-0.3 mm, 6 pieces per 1 cm ² : the reactor is equipped with a loading device made in the form of a plastic pipe with beads, between which fixed non-dusting elastic material that acts as a seal and cleaner; the unloading device is made in the form of a vacuum suction with a collecting tank; manual unloading is possible by removing the quartz reactor after cooling. To speed up the cooling process, air blowing is provided from a common compressed air network or from a separate fan.

A variant of the reactor is possible, with expansion in the upper part in the form of a bell with chippers of powder particles. The extension is designed to reduce the upward velocity of the fluidizing gas and prevent the entrainment of light particles (the bell and chippers are made of heat-resistant steel). The use of the bell allows you to reduce the length of the quartz reactor.

Opening the furnace after the end of the process, the reactor and the heating chamber with heaters are cooled using a stream of cold air to the temperature of the beginning of the next heat treatment cycle (up to 30-100 ° C), and the larger the diameter of the quartz reactor, the greater the power of the heaters, the greater the insulation layer, the greater the gain in cooling time compared to a non-opening furnace of the same diameter.

The cone-shaped grate prevents the formation of stagnant zones and the arch of the processed substance above the holes, since the radial flows of the fluidizing gas from the side holes destroy the resulting accumulations of powder. Auto-pulsation of gas occurs in the radial direction due to unregulated, but periodic overlapping of the side openings by falling particles.

The loading device, at the time of introduction into the reactor, cleans the walls of the reactor, dropping down adhering particles, and protects the side surface of the reactor (middle and upper parts) from contamination by particles of the loaded powder during the loading process. After loading a portion of the powder, the loading device is removed and the walls of the reactor remain clean.

Before unloading the reactor, the walls of its upper and middle parts are cleaned of adhering powder particles (possibly not having passed the high-temperature processing stage) so as not to contaminate the product. Cleaning is performed by a special bath.

In the second embodiment of the furnace, the cleaning process is easier to perform, since the bell - the upper metal part of the reactor - is removed before unloading.

Unloading can be carried out in two ways: 1) after cooling the reactor and the heating chamber, the reactor is removed manually and the powder is poured through the upper part of the reactor; 2) using vacuum suction. A vacuum suction unloading device allows you to quickly unload cold or hot powder.

Figure 1 shows the layout of the furnace, consisting of the following main components: 1 - furnace; 2 - boot device; 3 - vacuum discharge pipe; 4 - cylinder with fluidizing gas (air compressor option is possible); 5 - collector tank; 6 - vacuum pump; 7 - vacuum suction valve; 8 - vacuum tap, suction powder; 9 - unloading gateway; 10 - control panel; 11 - power source.

Figure 2 shows a diagram of a furnace, consisting of: 1 - furnace body; 12 - reactor; 13 - lower reactor holder; 14 - heaters; 15 - thermal insulation; 16 - holder of the chamber and reactor.

Figure 3 shows the options for the reactor: a) a single-piece quartz reactor; b) prefabricated quartz-metal reactor; 12 - reactor vessel; 17 - grate; 18, 19 - dividers flow fluidizing gas; 20 - pipe supply fluidizing gas; 21 - bell; 22 - powder chipper; c) collapsible quartz reactor; 23 - removable part of the reactor.

The principle of operation of the furnace is as follows: when the heating chamber is open, a purified reactor is inserted; close the heating chamber; install a boot device; supplying a half-pressure liquefying gas; pour a portion of the powder; increase the flow of fluidizing gas to normal; turn on heating and raise the temperature according to a given program; after the process is completed, the heating is turned off; open the heating chamber and cool with a stream of air; upon reaching a temperature of 30-50 ° C in the reactor: a) in the first embodiment, the middle and upper parts of the reactor are cleaned with a special bannic; set the pipe suction; close the crane 8 and the gateway 9; include a vacuum pump - create a vacuum in the receiver tank; close the valve 7 and open the valve 8 (there is a suction of powder); or manually remove the reactor and pour the powder into the hopper; b) in the second variant remove the bell 20; purify it; manually or using vacuum suction unload the reactor.

This device can be used for heat treatment of various powders (metal, ceramic, organic) in a neutral / reducing or in oxidizing environments.

Claims (3)

1. A vertical fluidized bed furnace containing a heating chamber, a quartz reactor in the form of a pipe with a grate and a fluidizing gas supply pipe, a holder for the heating chamber and reactor, a loading and unloading device, characterized in that the heating chamber is made of two equal parts, opening onto 180 degrees in the vertical plane, the holder of the heating chamber and reactor is made in the form of a vertical axis, the loading device is made in the form of a plastic pipe with a sealant-cleaner In particular, the unloading device consists of a vacuum pump, a collector hopper and a suction pipe, and the grate of the reactor is made of quartz glass in the form of a truncated cone with holes on its side walls and apex. 2. The furnace according to claim 1, characterized in that the quartz reactor is made detachable at the level of the grate. 3. The furnace according to claim 1, characterized in that the quartz reactor is made detachable with expansion in the upper metal part in the form of a bell, the diameter of which is larger than the pipe of the quartz reactor.

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