DE2410700A1 - PROCESS FOR THE SEPARATION OF SOLIDS FROM A GAS FLOW AND A SUITABLE DEVICE - Google Patents

Description

Bayer Aktiengesellschaft 2410700

Central area of patents, trademarks and licenses

Br-her 509 Leverkusen. Bayerwerk

March 5th 1974

Process for the separation of pesticides from a gas stream and suitable device

The use of cyclones with dense walls for separating solid particles from a gas stream is generally known. These cyclones have a tangential feed of the raw gas, a central outlet for the cleaned gas and a central discharge for the separated pesticides. Furthermore, these cyclones have tight walls made of metallic or non-metallic materials. Depending on the temperature of the gas and depending on the material, the walls of the cyclone can also with be provided with cooling.

Many research results are known which show the influence of various parameters on the deposition of pesticides describe in cyclones. In addition to the properties of the gases and solids, there is also the structural design of the cyclone had a major impact. In addition to the dimensions of the cyclone, mainly the flow conditions determine in the cyclone is, among other things, the formation of the inner walls of the facing the gas flow Cyclones of influence.

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A number of solids can only be separated in an unsatisfactory manner or not at all in cyclones of known design. For example, there are solids - which have a strong tendency to stick to walls and / or to stick to one another. This adhesion, promoted by the rotation of the gas-solid mixture inside the cyclone, can cause blockages inside the cyclone, in the solids discharge and / or in the gas outlet. This worsens the separation or the cyclone will run out after a short period of operation completely ineffective as a separator for such solids.

With other materials it is necessary to protect the walls from abrasion by abrasive solid particles in order to contamination of the separated solids by the removed wall material, as well as destruction to prevent the walls. It may also be necessary to protect the walls from corrosion by an aggressive gas protection.

A method for separating solids from a gas stream has now been found, which is characterized Is that in a cyclone-like separator the inner surfaces facing the gas-solids flow at least partially consisting of porous material and the porous walls are flowed through by gas from the outside to the interior, that a gas film forms on the inner surfaces.

The present invention also relates to a device for separating solids from gas mixtures consisting of a cyclone with a gas outlet and a feed pipe, the cyclone and the gas outlet nozzle are provided with a gas-tight outer wall and the inside have porous walls

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and wherein intermediate spaces with gas supply lines are arranged between the gas-tight outer wall and the porous inner wall.

With the help of this method and this device it is possible to separate pesticides, which lead to clogging or abrasion in cyclones, from gases. Such solids include, in particular, finely divided pigments, such as TiO ₂ from the so-called chloride process.

An example of the application is therefore the deposition of solid particles, as occurs in gas phase reactions between metal or metalloid halides, e.g. the chlorides of titanium, silicon, zirconium, iron, zinc, chromium or aluminum and oxygen-containing gases at temperatures of around 800 to 1500 ⁰ C arise, listed.

The reaction gases essentially consist of halogens, e.g. chlorine and a certain proportion of inert gases such as Nitrogen and / or carbon oxides and oxygen.

It is possible with the method of the invention, too at temperatures above 400 ° C a large proportion of the solid particles to be deposited, although these fine particles, some of which are used as pigments, are often directly after the reaction, for a reason not yet fully understood, a strong tendency to stick to walls or Have sticking.

The method according to the invention is illustrated using FIGS. 1 and 2 as well as suitable devices explained in more detail:

In Figures 1 and 2, 1, 2, 3 and 10 represent feeders or discharges for gases and / or solids, 4 and

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INSPECTED

are gas-tight walls, 6 and 7 are porous walls, and 8 and 9 are spaces.

According to FIG. 1, the raw gas containing pesticide particles is fed tangentially into the cyclone via a feed 1. The separated solid is discharged through the nozzle 2. The gas freed from most of the solids is fed through the nozzle 3 into the downstream separator. The cyclone has a gas-tight outer jacket 4. The gas outlet also has a gas-tight outer jacket 5 · on the Inside the cyclone and the gas outlet, porous walls 6 and 7 are used.

In the spaces 8 and 9 between the gas-tight jacket and A purging gas, such as chlorine, nitrogen, carbon dioxide or return gas from the reaction, is supplied to the porous wall via feed lines 10 fed. The porous walls are made gas-tight by methods such as gluing, cementing, welding, soldering or screwing Coat connected. These connection points should be essentially gas-tight, with a low gas permeability need not be disturbing.

The purge gas supplied via the supply lines 10 is through the porous walls pressed into the interior of the cyclone. As a result, it forms on the inside of the porous Wall is made of a gas film, This gas film causes the rotating solids, if the walls are sufficiently flushed with gas particles do not get on the walls or that prevents the build-up of solids on the rinsed walls will.

FIG. 2 shows another possible embodiment of a cyclone with porous walls. This cyclone is in the lower Part divided again. It is thus possible to use the porous

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Walls through suitable subdivisions to the different, already proven designs and internal dimensions more normal Adapt cyclones. The porous walls can be made of any material. Co-determining for the selection of the material for the porous walls are strength and corrosion problems. It can be metallic or non-metallic materials, e.g. ceramic materials or carbon or graphite are used, The porosity of the walls used can be produced by sintering; It is also possible to use porous walls Process like punching or drilling or by means of electrolytic processes. Also the use of seven or weaving is possible. The gas forced through the porous walls depends on the particular process. It is expedient to select the gas so that it is opposite to the solids-containing gas, compared to the solids and behaves like an inert gas towards the materials in the cyclone and in downstream equipment. With some procedures it is beneficial to have purified and cooled return gases from the respective reaction.

It is useful to relate the amount of flushing gas flowing through the porous walls to the porous surface. The so determined In the context of the present invention, value is called specific exposure and has the dimension

2 '

Liters of gas per hour per cm of porous wall surface. The specific Admission is largely on the dimensions of the cyclone, the amount of gas and the size and the Density of solid particles dependent. If the specific application is too low, the gas film on the is sufficient Do not wall out to prevent buildup and / or material removal. If the specific application is too high, solid particles are carried back into the gas flow, so that the separation efficiency is reduced. It

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it is advisable to adjust the amount of purging gas so that the specific application is a value in the range between 1 to 200, preferably in the range between 5 to 100 liters

per hour per cm of porous wall surface.

In some processes it is advantageous to have the pesticide separation in several cyclones with porous walls perform.

Furthermore, in the case of some solids, a change in the solids which is advantageous with regard to separation occurs. Through the Turbulence and the possible collision of particles can create active particle surfaces that tend to adhere become largely inactive and / or finely divided particles can form larger agglomerates, so that the separation no longer causes problems in normal, downstream cyclones or other separators.

It has further been found that by adding small quantities of water - about 0.05 to about 3 wt -.%, Based on the solids content, especially in vaporous state of aggregation in the crude gas prior to feeding into the cyclone or by adding water directly into the Cyclone in the vicinity of the longitudinal axis of the cyclone an increase in agglomeration and thus an improvement in separation can be achieved.

The particular advantages of this method according to the invention and the device suitable for it are:

a) By preventing deposits, a trouble-free, continuous deposition is more difficult to adhere inclined solids possible in continuous operation.

b) Deposition is also possible at high temperatures.

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c) Since the walls are prevented from being eroded, it is possible to separate solids for which contamination from the erosion of the wall material is undesirable.

d) The porous walls can largely be adapted to tried and tested types of cyclones.

The method according to the invention will now be explained in more detail using the following examples:

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Example 1:

60 l / h of liquid titanium tetrachloride (TiCIh) were evaporated, superheated and introduced into a reactor at a temperature of 450 C. At the same time became one in one Arc heated to approx. 1800 ° C gas mixture of oxygen and nitrogen perpendicular to the TiCl ^ stream in the reaction zone fed to the reactor. According to the equation

TiCl ^ + O ₂ - »TiO ₂ + 2 Cl ₂

Titanium dioxide (TiO ₂ ) and chlorine (Cl ₂ ) were formed. _{The TiO 2} -containing gas was passed into a separator according to FIG. 2 by adding nitrogen and chlorine and by indirect heat exchange. The walls of this separator were made of porous graphite on the side facing the hot gas flow. The gas-solid mixture had a temperature at the inlet of 4 ^ 5 ° C. The outer walls of the cyclone were provided with water cooling. The gas impermeable walls were made of stainless steel.

The inlet gas had a solids loading of approx. 90 g TiO ₂ per tc? Gas - based on a temperature of 435 ° C. The porous walls were filled with an amount of nitrogen of 10 liters

ρ
flushed per hour per cm of surface. The inner surface of the cyclone (5500 cm), which was equipped with porous walls, was used as the reference area. The duration of the experiment was 6 hours. During the test period 61 % of the TiO ₂ produced was deposited in the cyclone. After the attempt, the cyclone was opened. The cyclone was not clogged at any point.

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-4 ·

The product was of excellent quality. It was neither deposited in the titanium dioxide nor on the walls Graphite was found to be worn away. The cyclone was used in another 25 trials with a total trial time of over 200 hours without any changes in the product or on the walls.

Example 2:

The same experimental set-up and the same experimental procedure as in Example 1 were selected. The gas-solid Mixture was thus fed into the deposition under the same conditions as in Example 1. The cyclone with the porous walls were replaced by a water-cooled cyclone without porous walls. This cyclone whose walls are made of Aluminum, had essentially the same internal dimensions as the cyclone in Example 1.

After a test duration of about J> 0 minutes, the product discharge from the cyclone was completely blocked, so that separation of solids was no longer possible.

Example }:

The same arrangement and the same test procedure as in Example 1 were selected. Only after leaving the cyclone with the porous walls through which gas flows were introduced into the water-cooled cyclone of Example 2. The experiment was terminated after 8 hours. In the cyclone with the porous walls, 58 % _{t was} deposited in the subsequent cyclone without porous walls, 23 % of the TiOp produced.

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» 40.

In the downstream cyclone without porous walls, there were no disruptive deposits.

Example 4:

The same arrangement and the same experimental procedure as in Example 4 were chosen. Only 0.5 kg / h of water vapor were continuously fed into the hot gas stream before it entered the cyclone with porous walls. The experiment was terminated after 8 hours. The amount of TiOp deposited in both cyclones was 90.5 % of that produced

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Claims (7)

Patent claims: Ij) process for the separation of pesticides from a gas stream, characterized in that the gas-solid mixture is passed through a cyclone-type separator, in which the inner surfaces facing the gas / pesticide flow at least partially consist of porous material and the porous walls so flows through the porous walls from the outside to the interior of the gas that a gas film forms on the inner surfaces. 2) Method according to claim 1, characterized in that through the porous material an amount of gas between 1 and 2
200 1 is passed per hour per cm of porous wall surface. 3) Method according to one of claims 1 to 2, characterized in that that the deposited solids have pigment properties. 4) Method according to one of claims 1 to J>, characterized in that the deposited solids arise in gas phase reactions between metal or metalloid halides and oxygen-containing gases. 5) Method according to one of claims 1 to 4, characterized in that that the gas flowing through the porous walls is return gas from the gas phase reaction. 6) Method according to one of claims 1 to 5, characterized in that the deposited solid is TiO _p . 7) Device for separating solids from gas mixtures according to one of the methods 1 to 6, consisting of a cyclone, a gas outlet nozzle, a feed pipe the cyclone and the gas outlet nozzle Le A 15 457 - 11 - 509837/0489 are provided with a gas-tight outer wall, the inner side have porous walls (6, J) and intermediate spaces (8, 9) with gas feed lines (10) are arranged between the gas-tight outer wall and the porous inner wall. Le A 15 457 - 12 - 509837/0 4 89