DE2623735A1 - METHOD OF CONTACTING A GAS AND A LIQUID - Google Patents

Description

BERLIN 33 8 MUNICH 80

Augu.te-V.ktoria-StraBe 65 _n DIICPUliC Jl DAPTMFD Pienzenauerstraße 2

Pat. Dr. In ₈ . Ruschke Ur. KUbUMKt Ct ^ AKIINtK Pat.-Anw. Dipl.-Ing.

Pat. D.pl.-lng. P ATF N TA N WA LTE ^Ha " ^SE ' ^Ruechke

Olaf Ruschke Γ Λ I C IN I Λ IM ΪΙί Λ LI C 98 03 24

T _e lephone: 030 / | "" 5 "BERLIN - Munich ^Phone * ^088/987 268

Telegram address: Telegram address:

Quadrature Berlin Quadrature Munich TELEX: 183786 TELEX: 522767

Munich, May 26, 1976

A 1569

Alfa - Laval AB, Postfack, S-147 oo Tumba (Sweden)

Method for bringing a gas and a liquid into contact

The present invention relates to a method for bringing a gas and a liquid into contact, in which the Gas is caused to flow through a channel and pass through a perforated element which covers the flow cross-section of the channel, whereby the liquid, which is also flowed through the channel, is caused to form a foam layer with the gas, the layer through the perforated element is supported.

Processes of this type have been known for a long time. In some cases it may be necessary "to add a surfactant coat to achieve" us "eizis enough © foam ,, Liz ärzeuguiig a Sciia ^ üivss & as a gas and a Flüsa>;:" ince causes one sefcl · large contact surface between these two Media ^ what Ie context rs.it physika «

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Chemical and chemical effects between a gas and a liquid is desirable.

The perforated element must be provided with relatively narrow holes, but it must be the upward flowing gas with the Let the downward flowing liquid form foam which is supported by the perforated element. The pressure gradient of the gas will therefore be relatively large. To avoid this disadvantage, a method has been developed in the case of the foam from the liquid which is to be brought into contact with a gas, with a gas outside the contact channel is formed, in which the foam is then given into the contact channel and in which finally the first gas is flowed through the foam supported by the perforated element. This procedure, which is described in the British patent 1 231 5o5 and Swedish patent 354 194 makes it possible to use perforated To use elements that are provided with relatively large openings. A very suitable perforated one Element is described in Swedish Patent 356; this creates a slight pressure gradient, a even distribution of the gas in the foam, a strong turbulence just above the perforated element and an efficient drainage of the downflowing liquid.

The process for generating iron foam outside the contact channel and for. Introducing the foam into the contact channel

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does not represent a general substitute for the method mentioned at the beginning; in particular not in the case in which the liquid flow is very large compared to the gas flow. In addition, this just mentioned procedure has another disadvantage. To ensure good contact between the liquid in the form of foam and the flowing gas generate, the height of the foam layer must be controlled. The foam level can be sensed by known sensors. In those cases in which an acidic gas is to be brought into contact with an alkaline liquid for neutralization it is impossible to simultaneously and independently both the height of the foam layer in an optimal way as well as the Control the supply of alkaline foam to keep the acidity and alkalinity balanced.

It is therefore the object on which the present invention is based, a method of the generic type mentioned at the outset To provide a way that creates a small pressure gradient that a large liquid flow compared to the gas flow allows and allows independent control of the height of the foam layer and the liquid supply.

This object is achieved according to the invention in that a foam is added to the channel during start-up and, if necessary, during normal operation to obtain the desired height of the foam layer, the foam is formed from a liquid and a gas and, if necessary, with the addition of a surfactant.

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This method can be used both for separating suspended particles from a gas and for reacting with a gas a liquid or a combination of the two.

The invention is illustrated by the following examples with reference to the accompanying drawings described. The drawing shows an example of a device for carrying out the method according to the invention. A tube 1 encloses a channel 2 in which a perforated element 3 is arranged, which in this case is the Has the shape described in the above-mentioned Swedish patent 356 69o. Below the perforated element 3 a gas inlet 4 is provided in the pipe wall and in the upper part of the channel 2 there is an inlet 5 for supplying the liquid to be brought into contact with the gas. The inlet 5 is with a nozzle 6 which is directed downwards in order to spray the liquid downwards into the channel and it over the whole Distribute cross-section of the channel. At the lower part of the tube 1 is an outlet 7 for the downward flowing liquid This outlet 7 is connected to a pump 8, with the aid of which the liquid is returned to the inlet 5 and can be returned to the nozzle 6. Liquid can also be drained through the drain 9 and liquid can be supplied through the inlet 5 via an inlet 1o, the latter being arranged on the pressure side of the pump 8 is. Below the inlet 5 is an inlet pipe 11 for

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Foam provided, which has been produced in a (not shown) foam generator outside the channel 2. That Inlet pipe 11 is provided with a shut-off valve 12. Two sensors 13 and 14 are at different height levels in the Pipe wall 1 arranged between the inlet pipe 11 and the perforated element 3 to the height of the foam level to feel. They are connected to a transmitter 15, which can receive signals from sensors 13 and 14, to close or open the valve 12 depending on the type of signals received. This valve 12 can also be done by hand opened and closed or controlled by a timer.

The device works in the following way:

The one in the foam generator from a gas and a liquid, preferably with the addition of a surfactant produced foam is fed into the channel 2 to be carried by the perforated element 3. If the When the desired foam height has been reached, the foam feed is switched off. The gas that contains suspended particles can and which is to be brought into contact with said liquid is then flowed in through the gas inlet 4 and the liquid is introduced through inlet 1o and then through inlet 5 and nozzle 6. The liquid, which flows downwards from the perforated element 3 and the separated particles or reaction products out the reaction between the gas and the liquid, or both

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can then be completely discharged through the outlet 7 and the drain 9. On the other hand, a Part of the liquid can be returned by the pump 8 to the inlet 5 and to the nozzle 6. Such a return some of the surfactant is recovered if such a material contributes to foam formation the preparatory step mentioned above was used, so that in this way the formation of fresh foam occurs the contact between the gas and the liquid at the perforated element 3 is facilitated. If the foam level should fall after a certain period of operation, a certain amount of foam can be manually controlled by the foam generator through the inlet pipe 11 to restore the desired foam level. On the other hand, the sensors 13 and 14 can signal the foam feed steer. As already mentioned, the foam can be fed into channel 2 periodically by the foam generator.

example 1

From a factory for the production of NPK fertilizers (NPK = nitrogen, phosphorus, potassium) an exhaust gas is obtained which contains about 400 mg / Nm ³ NPK particles and about 500 mg / Wm ⁵ NH ₃ . From an environmental point of view, it is undesirable to release this exhaust gas into the atmosphere without purifying it, especially since it would also mean that valuable material would be wasted. In order to significantly reduce air pollution

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ring, the gas is according to the method according to the invention cleaned in a device shown in the accompanying drawing.

The beginning of the cleaning process

In the foam generator, foam is formed from 225 liters of water with the addition of 0.1 % of a surface-active agent which contains a mixture of anionic and nonionic surfactants and air. The foam is fed into the channel to be carried through the perforated element. The foam number, ie the ratio between the gas volume and the liquid volume of the foam, is about 10.

The ongoing cleaning process

8000 Nm / h of the exhaust gas are cooled from an original temperature of about 80 ° C. to about 48 ° C. and then the gas inlet is led into the device and up through the foam. At the same time, 65 l / h of 20 % ENT are fed in through the nozzle and sprayed over the foam. This creates fresh foam through contact between the rising gas and the downward flowing liquid. In order to maintain the desired foam level, foam, which would be generated in the foam generator as described above, is introduced into the channel in an amount corresponding to 6 l of water every 10 minutes, ie 36 l / h. During operation, the foam number is around 5-7.

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About 360 l / h of the liquid is returned to the circuit. 100 l / h of the liquid are discharged through the drain, this liquid being about 20 % salt, which originates from the reaction between the HNO and the NH _; and contains solid particles.

result

Approximately 90 % of the NH and 99 % of the NPK particles are removed.

Example 2

In tankers it is necessary to fill the free space above the liquid level in the oil tank with an inert gas keep filled to avoid the risk of explosion. The exhaust gases from the oil burners or the diesel engines of the tankers are often used for this purpose, but this one Exhaust gases must be cleaned of SO2 and the solid soot particles before they are used as an inert gas can. The exhaust gas can be purified in a device similar to that shown in the drawing. In this case, however, there is no recirculation of the liquid. In this case the gases contain about 0.5% by volume and 250 mg / Nnr of soot particles.

The start of cleaning operations

In the foam generator, foam is made from 30 liters of salt water

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Addition of 0.1 % of a surfactant similar to that used in Example 1 is produced. The foam is fed into the channel. The foam number is about 10.

Continuous cleaning operation

3000 Nm / h of the exhaust gas are cooled from 350 ° C to around 30 ° C in a simple cooler and fed into the duct. 380 l / h of a NaOH water solution are fed in through the nozzle and sprayed over the foam. Every 10 minutes it will Foam introduced from the foam generator in an amount corresponding to 6 liters of salt water. During operation If the foam number is around 5 to 7. The liquid is not put back into circulation, i.e. the entire downwards flowing liquid is drained away.

result

About 90 % of the SO ₂ and 95 % of the soot particles are removed.

Example 3

In the production of aluminum by the electrolysis of molten aluminum oxides, including fluorides, using carbon electrodes, large amounts of heat and A; nsen free. The exhaust gas contains HF in gaseous form and solid particles. The gas must therefore for environmental reasons

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Protection can be effectively cleaned. A device similar to that shown in the drawing can in principle be used for this purpose will. However, no liquid is drained off in the process. HF is absorbed in the water and the acid solution is then treated with lime to precipitate CaF and this mechanically together with the separated solid particles from the system. This means that a precipitation tank must be provided into which the downward flowing Liquid is introduced for precipitation, after which the liquid is returned to the circuit by a pump will.

Start of cleaning operations

Foam is formed from 900 l of water with the addition of 0.3 % of a surface-active agent which has a mixture of anionic, amphoteric and nonionic surfactants and air; the foam is then fed into the channel. The foam number is about 10.

Continuous cleaning operation

75,000 Nm / h of an exhaust gas at 30 ° C ₁ containing about 0.8 mg / Nm of HF and 8 mg / Nm of solid particles is introduced into the device. 280 l / h of water are fed through the pipes to the nozzle. Another 900 l / h of liquid is delivered to the nozzle through recirculation. Through evaporation, 400 l / h of the liquid with the outward flowing

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~ 11 -

send gas derived. The HF is intermittently separated in the precipitation tank in the form of CaF. Every 10 minutes foam from the foam generator is fed into the channel in an amount corresponding to 20 l of water. The height the foam layer is about 600 mm during operation and the foam number is 5 to 7.

result

85 % of the HF and 75 % of the solid particles are removed.

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Claims (1)

Claim A method of contacting a gas and a liquid in which the gas is caused to flow through a channel and pass through a perforated element which covers the flow area of the channel, thereby causing the liquid to also flow through the channel to form a foam layer with the gas, the layer being supported by the perforated element, characterized in that a foam is added to the channel during start-up and, if necessary, during normal operation, to the desired height of the foam layer wherein the foam is formed from a liquid and a gas and, if necessary, with the addition of a surfactant. 609851/0977