US3411864A - Method of removing suspended acidic or alkaline pulverulent particles from gases - Google Patents

Description

Nov. 19, 1968 J. PALLINGER 3,411,864

METHOD OF REMOVING SUSPENDED ACIDIC OR ALKALINE PULVERULENT PARTICLES FROM GASES Filed July 9, 1964 j f P ELF liar United States Patent METHOD OF REMOVING SUSPENDED ACIDIC 0R ALKALINE PULVERULENT PARTICLES FROM GASES Josef Pallinger, Vienna, Austria, assignor to Waagner- Biro Aktiengesellschaft, Vienna, Austria Filed July 9, 1964, Ser. No. 381,320 Claims priority, application Austria, July 10, 1963, A 5,538/63 11 Claims. (Cl. 23-2) ABSTRACT OF THE DISCLOSURE Acidic or alkaline purverulent particles suspended in a gas are washed out of the latter with a washing liquid so that the spent Washing liquid, not withstanding the acidic or alkaline nature of the pulverulent impurities will be substantially neutral, by introducing into the gaseous suspension of non-fluid and generally solid acidic or alkaline impurities a pul-verulent alkaline or acidic ma- The present invention relates to a gas washing method and device and, more particularly, is concerned with puritying gases, especially dust-containing gases, such as are formed in the operation of metallurgical furnaces and combustion devices.

It is an object of the present invention to provide a method and device for washing such gases and gaseous suspensions of finely subdivided particles so as to obtain a spent washing or scrubbing liquid which is substantially neutral irrespective of the acidity or alkalinity of the gas or suspension which is subjected to such scrubbing or washing.

It is a further object of the present invention to provide a method and device for cleaning waste gases and particularly solid particles containing waste gases by means of a washing liquid so that in a simple and economical manner a substantially neutral spent washing liquid is obtained.

It is a further object of the present invention to obtain in a gas washing process a substantially neutral spent washing liquid without having to adjust the pH of the washing liquid after the same has been in contact with the gas to be purified.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention is concerned with a method of washing a gaseous suspension containing acidic impurities, comprising the steps of introducing into the gaseous suspension an alkaline pulverulent neutralizing agent for the acidic impurities, and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid so as to form a purified gas and a spent washing liquid containing the impurities and being substantially neutral due to the introduction of the neutralizing agent.

More particularly, the present invention contemplates a method of washing a gaseous suspension containing acidic impurities, comprising the steps of introducing into the gaseous suspension calcium carbonate as a salt 3,411,864 Patented Nov. 19, 1968 adapted at an elevated temperature to be split into a basic oxide and a volatile acid residue, the basic oxide being adapted to neutralize the acidic impurities, subjecting the thus formed mixture to the elevated temperature so as to form the volatile acid and the basic oxide adapted to act as a neutralizing agent for the acidic impurities, and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid so as to form a purified gas and a spent washing liquid containing the impurities and being substantially neutral due to the introduction of the neutralizing agent.

The present invention also includes a gas purification device comprising, in combination, conduit means having inlet and outlet ends for passing therethrough a gaseous suspension of solid particles including constituents which with a washing liquid will give a reaction other than neutral, introduction means communicating with the conduit means at a point spaced from the inlet and outlet ends thereof for introducing into the same a pulverulent neutralizing agent for the gaseous suspension, gas washing means operatively connected to the outlet end of the conduit means for washing the neutralizing agentcontaining suspension with a Washing liquid to form a washed gas and a substantially neutral spent washing liquid, and separating means for separating the thus washed gas from the spent washing liquid.

According to one preferred embodiment, the present invention includes in a gas purification device, in combination, reactor means for forming a combustible gaseous suspension of solid particles including constituents which with a washing liquid will give a reaction other than neutral, combustion means for burning the combustible gaseous suspension and including injector means for injecting into the combustible suspension a pulverulent neutralizing agent suspended in combustion air so as to form in the combustion means a burnt gas having solid particles suspended therein, washing means for washing the suspension of solid particles in burnt gas with a washing liquid forming a washed gas and a spent washing liquid which is substantially neutral due to the injection of the neutralizing agent, conduit means for passing gaseous suspension from the reactor means to the combustion means and from the combustion means to the washing means, and separating means for separating washed gas and spent washing liquid from each other.

Thus, according to the present invention, a pulverulent neutralizing agent, for instance, a salt or an oxide is introduced into the gases which are released from the reactor, for instance, from a metallurgical furnace, and the thus formed mixture is then contacted with the washing liquid.

The washing liquid will thus contact a gas which contains, for instance, acidic components either in gaseous form or in the form of suspended solids, and which also contains pulverulent neutralizing agent. Either during the washing, or at least partly prior thereto, a reaction will take place between the acidic constituents and the neutralizing agent so as to neutralize the acidic constituents and thus the wash water will remain neutral and will not be acidified by the presence of acidic constituents in the gas or gaseous suspension of solids which is to be washed.

Generally, the gas or suspension will contain acidic constituents and the neutralizing agent will be a salt or oxide of alkaline reaction, however, it is of course also possible to utilize the present invention for neutralizing alkaline gases or suspensions with an acidic neutralizing agent.

While the present invention also could be applied to a gas of acidic or alkaline reaction which does not carry any suspended solids, it is primarily contemplated to be employed in connection with the removal of dust or suspended solids from gases which emanate from a variety of reaction devices, such as metallurgical furnaces, converters, or combustion devices.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which the figure is a schematic elevational view of a device according to the present invention for purifying gases emanating from a steel converter, combined with combusting such gases and utilizing the heat content of the same.

A converter 1 is shown from the opening 2 of which gases will be discharged upon refining of steel in the converter 1. These gases are caught or received by hood 3 while simultaneously air will flow into hood 3 through the annular opening 4 between converter 1 and hood 3. Through an opening 5, the gases pass into boiler 6, in contact with the water or steam tubes therein. Opening 5 can be closed by means of gate valve 7 and immediately behind gate valve 7 are nozzles 8 for blowing secondary air into the boiler. This secondary air serves for igniting the combustible gas which is introduced through hood 3 and for thorough mixing of the converter gases with the additional air introduced through opening 4. Turbulence is created and serves for an intimate mixing of the gases, combustion of which will be practically completed when the gases leave boiler 6 at its upper end portion. The gases, which contain suspended solids, flow then through conduits 9 and 10 whereby, as illustrated, a super-heater 11 and a preheater 12 are arranged in conduit 10. After the gases have passed in contact with preheater 12, they are introduced into the washer 13 in which, through nozzles 14, a washing liquid is passed in contact with the gases. The waste gases which have been purified by contact with the washing liquid, generally water, and from which solid suspended particles have been removed, pass then through flue 15 into a smoke stack (not shown).

The air which is blown into the boiler through nozzles 8 is ambient air which is introduced through conduit 16 into blower 17. The air is compressed in blower 17 and flows through a nozzle 18, for instance, into an ejector device 19 wherein a suction effect is created which will serve to carry along pulverulent materials, for instance, pulverulent neutralizing agents for acidic converter gases, such as calcium oxide, calcium carbonate or the like which have been ground to greater or lesser degree of fineness. This pulverulent neutralizing agent, for instance, calcium carbonate, is stored in hopper 20 and reaches ejector 19 through a dosing device 21 so that controlled quantities of the pulverulent neutralizing agent are sucked into the ejector and will then flow together with secondary air through conduit 22 to nozzles 8.

Thus, the secondary air which is introduced into the boiler for combustion of the converter gases, is charged with the solid neutralizing agent and the solid neutralizing agent together with the Waste gases and the converter dust container in the same will pass into washing device 13.

In washing device 13, the neutralizing agent as well as the converter dust will be washed out of the waste gases before the waste gases are released through flue 15-.

In this manner, it is possible to maintain the pH of the washing liquid at all times within the desired limit of between 6 and 8.

The spent washing liquid leaves Washer 13 at its outlet 23 and is passed by way of pump 24 into clarifier 25 in which sludge is separated from the liquid. The clear liquid flows then to storage tank 26 and is then recycled by means of pump 28 through conduit 27 to the nozzles 14 of Washer 13.

The desired water level is maintained in storage tank 26 by introducing into the same in conventional manner the amount of fresh water required for this purpose. The heavy sludge is discharged from converter 25.

Under certain operating conditions, it has been found advantageous to introduce the neutralizing agent, such as calcium carbonate or calcium oxide as relatively large particles, particularly when the neutralizing agent is introduced into an area of very high temperatures. Preferably, the lime dust or the like is injected into a zone where the waste gases are of very high temperature, either initially or due to combustion of the same, and quite obviously, the neutralization reaction will be facilitated by reduction of the particle size of the neutralizing agent. However, if the gases in the hot zone wherein the neutralizing agent is introduced, are sufliciently hot, then coarser lime dust, for instance, wil be split up by exposure to such high temperature and thus a desired small particle size will be obtained even though the initially introduced lime dust may have been of coarser grain size.

The invention is not limited to the illustrated device and the manner of operation of the same which has been described by way of example.

Thus, it is also possible to introduce the neutralizing agent, such as calcium carbonate, into the reactor, for instance, converter 1 under such operating conditions that the desired oxide and a volatile gaseous residue will be formed, for instance, calcium oxide as the basic oxide and carbon dioxide as the volatile acidic residue in the case of introducing calcium carbonate. The salt or oxide is then carried along by the gases flowing from the reactor, such as converter 1, due to the high speed of flow of such gases.

It is also possible to introduce the neutralizing agent into the boiler flue through a dust mill or sprinkler stoker whereby mixing of the converter or the like Waste gases and the pulverulent neutralizing agent will take place within the boiler fiue.

The present process and device has considerable advantages over prior art arrangements according to which in the case of acidic waste gases alkaline substances, such as calcium carbonate are added to the feed water of the washing device, for instance, to neutralize S0 or S0 in order to keep the wash water at a pH approximating 7.

For instance, in some cases, when the sulfur content of the waste gases is high, so much lime would have to be added to the scrubbing liquid that the limit of solubility of lime in water would be reached or even exceeded. This is one of the problems solved according to the present invention, which provides that the required amount of lime is introduced in pulverulent form into the gas stream for the purpose of keeping the wash water or scrubbing liquid neutral. In this manner, the amount of pulverulent lime or the like can be so proportioned that any amount of acidic constituents can be washed out and by the injection of the neutralizing agent in pulverulent form into the hot waste gases still neutralization of the scrubbing liquid is achieved.

Neutralization may take place in the gas flow, i.e. prior to contact with the washing liquid, as well as in the scrubber upon contact with the washing liquid (generally water).

Neutralization of the wash water could be achieved in the above described manner, for instance, in connection with the purification of converter gas carrying converter dust which contained 1.7% CaO, 0.3% MgO, 3.4% S03 and FB2(SO4)3H2SO4'2H20.

Basically, the present invention proposes introduction of the neutralizing agent in solid pulverulent form anywhere between the reaction vessel in which the gases which are to be cleaned are formed (or even in the reaction vessel) and the washing device. The optimum point of introduction of the pulverulent neutralizing agent will depend on temperature and flow conditions, as well as on the chemical compositions of the gas, the dust carried by the same and the neutralizing agent. Thus, there may also exist conditions under which it is advantageous to introduce the neutralizing agent at high temperature in the form of a very finely subdivided dust, or at somewhat lower temperature as coarser particles.

The addition of neutralizing agent should be controlled in such a manner that the waste wash Water will be substantially neutral without burdening the recycling wash water with excessive amounts of neutralizing agent. Thus, it should be possible to temporarily interrupt the addition of neutralizing agent when the concentration of the same in the recycling wash water exceeds a desired value.

It should also be possible, instead of completely interrupting the addition of neutralizing agent, to reduce the amount thereof which is introduced per unit of time. By controlling the addition of the neutralizing agent depending on the condition of the washing liquid, it is advantageous to measure the pH value of the washing liquid leaving the washer at outlet 23 and based thereon to control in an automatic manner known per se the amount of neutralizing agent which will be added. Thus, pH meter 31 may be located in the conduit leading from washing device 13 to pump 24 and may serve to actuate dosing device 32.

Particularly if the neutralizing agent is introduced into the gas near its point of origin and relatively distant from the washer, as has been illustrated in the drawing, and when, consequently, the neutralizing agent is introduced into hot gas, a neutralizing reaction will take place between the neutralizing agent and the hot gas and/or the dust carried by the same already long before the gas reaches washer 13.

Furthermore, the introduction of the neutralizing agent may also be carried out jointly with the introduction of a fuel into burner 6 or jointly with the introduction of primary combustion air into the same.

The term coarser dust or coarser particles is used herein to denote particles of a size of 200 microns or larger, while particles of a size smaller than 200 microns are referred to as very finely subdivided dust. When the pulverulent neutralizing agent, for instance calcium carbonate, is blown into gas having a temperature of at least 1000 C. i.e. at a relatively high elevated temperature, due to the temperature stress, the particles of the neutralizing agent will be broken up into smaller particles and thus will act more efiectively due to the larger surface area relative to the volume of the individual smaller particles.

However, if the pulverulent neutralizing agent is to be introduced into gas having a temperature of less than 1000" C., then it is preferred to use very finely subdivided dust, or particles of the neutralizing agent which have a size smaller than 200 microns since at such relatively low temperatures, i.e. a temperature of below l000 C., the heat stresses will not sufiice to cause further breakdown in the particle size.

By introducing for instance lime into a zone of higher temperature, for instance into converter or reaction vessel 1, the greatest degree of splitting of the particles can be achieved and thus the reducing agent will become available in most finely subdivided form and consequently will be of higher reactivity.

By way of example, it may be described that a conventional gas washing device 220 cubic meters per hour of water were used for purifying waste gases. The waste gases carried 100 kg. of sulfur per hour, the latter being chemically bound in various manners, for instance as S0 The wet washing device removed about 80 90% of the sulfur content of the waste gas and thus, theoretically, should have required about 300 kg. of calcium carbonate per hour for neutralizing the wash water.

However, it was found that even by introducing into the wash water twice the theoretically required amount of calcium carbonate, i.e. 600 kg. per hour, it was not possible to obtain a neutral spent washing liquid. In fact,

the pH of the washing liquid leaving the device was between 2 and 3.

However, by blowing 300 kg. per hour of calcium carbonate into the hot stream of gas and subsequently subjecting the gas to washing in the same manner as before, the runoff from the washing device was completely neutral, having a pH of 7.

This comparison will show greater effectiveness of blowing the required amount of lime or other neutralizing agent in pulverulent form into the hot gas stream. In the given case it was also found that the investment required for neutralizing the gas by blowing neutralizing agent into the same amounted to only about one-tenth of the investment required for neutralizing the washing liquid in accordance with the conventional process.

In the herein described case, calcium carbonate particles having a particle size greater than 200 microns were blown into acidic gas having a temperature of about 1300 C.

Substantially similar results are obtained in the case of neutralizing alkaline waste gases by introducing acidic neutralizing agents into the same.

Since sludge sedimentation in the clarifier is carried out in a more economical manner at neutral pH, acidic neutralizing agents were blown into a stream 'of hot alkaline waste gas. In this manner neutralization and sedimentation could be carried out much more economically than by introducing the acidic neutralizing agent into the wash water. As the acidic neutralizing agent, sulfur chemically bound in any suitable manner was introduced into the alkaline gas. In this manner, it was possible to use installations Which did not require any specific protection against acid corrosion.

As has been pointed out above, coarse particles having a particle size of 200 microns or more will disintegrate into smaller particles due to heat stresses when such coarse particles are introduced into a relatively hot stream of gas, having a temperature of 1000 C. or more. For instance, by introducing lime having a particle size of up to mm. into a reactor in which a temperature of about 1300 C. prevailed, the lime was subdivided into particles of the magnitude of 200 microns. This effect, i.e. the comminution of coarser particles by exposing the same to high temperatures will, with respect to acidic as well as alkaline neutralizing agents, eliminate the necessity for employing mechanical comminution devices.

In another installation, in order to burn CO, secondary air had to be introduced under high pressure and it was found advantageous to introduce the neutralizing agent dispersed in the secondary air so that the neutralizing agent was blown into the crude gas at high pressure together with the secondary air.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of waste gas purification devices differing from the types described above.

While the invention has been illustrated and described as embodied in a waste gas purifying device combined with a boiler arrangement, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any Way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of washing a gas containing solid, at least partially soluble impurities adapted to be washed out with,

and at least partially dissolved in, a washing liquid and which with said washing liquid will give a reaction other then neutral, comprising the steps of introducing into said gas a pulverulent neutralizing agent for said impurities which is at least partially soluble in said washing liquid; contacting the thus formed neutralizing agent-containing mixture with a washing liquid so as to wash out said impurities and said neutralizing agent and at least partially dissolve the same, thereby purifying said gas and forming a substantially neutral spent washing liquid; and separating the thus purified gas from said spent substantially neutral washing liquid.

2. A method of washing a gaseous suspension of finely subdivided non-fluid, acidic impurities, comprising the steps of introducing into said gaseous suspension an alkaline pulverulent neutralizing agent for said acidic impurities; and contacting the thus formed neutralizing agentcontaining suspension with an aqueous washing liquid in which said acidic impurities and said neutralizing agent are at least partially soluble so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

3. A method of washing a gaseous suspension of finely subdivided, non-fluid, acidic impurities, comprising the steps of introducing into said gaseous suspenson a salt adapted at an elevated temperature to be split into a basic oxide and a volatile acid residue, said basic oxide being adapted to neutralize said acidic impurities; subjecting the thus formed mixture to said elevated temperature so as to form said volatile acid and said basic oxide adapted to act as a neutralizing agent for said acidic impurities; and contacting the thus formed neutralizing agent-containing suspension With an aqueous washing liquid in which said acidic impurities and said basic oxide are at least partially soluble so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

4. A method of washing a combustible gaseous suspension including finely subdivided, non-fiuid, acidic impurities, comprising the steps of introducing into said gaseous suspension a suspension in air of an alkaline neutralizing agent for said acidic impurities; subjecting the thus formed mixture to combustion so as to form a neutralizing agent-containing gaseous suspension of solid particles; and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid in which the non-fluid constituents of said suspension are at least partially soluble so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

5. A method of washing a gaseous suspension including finely subdivided, non-fluid, acidic impurities, comprising the steps of introducing into said gaseous suspension a relatively coarse pulverulent alkaline neutralizing agent for said acidic impurities adapted to split at an elevated temperature into particles of smaller size; subjecting the thus formed mixture to said elevated temperature so as to reduce the particle size of said neutralizing agent; and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid in which the non-fluid constituents of said suspension are at least partially soluble so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

6. A method of washing a gaseous suspension including finely subdivided, non-fluid, acidic impurities, com- 8 acid residue, said basic oxide being adapted to neutralize said acidic impurities; subjecting the thus formed mixture to said elevated temperature so as to form said volatile acid and said basic oxide adapted to act as a neutralizing agent for said acidic impurities; and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid in which said impurities and said basic oxide are at least partially soluble, so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

7. A method of washing a gaseous suspension including finely subdivided, non-fluid, acidic impurities, comprising the steps of introducing into said gaseous suspension pulverulent calcium oxide as a neutralizing agent for said acidic impurities; and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid in which said acidic impurities and said calcium oxide are at least partially soluble, so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

8. A method of washing a gaseous suspension including finely subdivided, non-fluid, acidic impurities, comprising the steps of introducing into said gaseous suspension at a relatively low elevated temperature a finely subdivided pulverulent neutralizing agent for said acidic impurities; and contacting the thus formed neutralizing agent-containing suspension with an aqueous washing liquid in which said acidic impurities and said neutralizing agent are at least partially soluble, so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

9. A method of washing a gaseous suspension including finely subdivided, non-fluid, acidic impurities which suspension is formed in a reaction vessel, comprising the steps of introducing into said reaction vessel an alkaline pulverulent neutralizing agent for said acidic impurities so as to form a neutralizing agent-containing gaseous suspension; withdrawing the thus formed neutralizing agent-containing suspension from said reaction vessel; and contacting said withdrawn suspension wit-h an aqueous washing liquid in which said acidic impurities and said neutralizing agent are at least partially soluble, so as to form a purified gas and a spent washing liquid containing said impurities and being substantially neutral due to said introduction of said neutralizing agent.

10. In a method according to claim 2, the steps 0 determining the pH of said spent Washing liquid and adjusting the amount of alkaline pulverulent neutralizing agent being introduced into said gaseous suspension so as to maintain said pH within a predetermined substantially neutral range.

11. A method according to claim 2, wherein said gaseous suspension of finely subdivided, non-fluid, acidic impurities consists of the waste gases of a metal converter.

References Cited UNITED STATES PATENTS 1,221,505 4/1917 Bradley et al. 23-2 X 2,718,453 9/1955 Beckman 23-2 2,877,086 3/ 1959 Mackay 232 2,919,174 12/1959 Pring 23-2 3,310,365 3/ 1967 Dundas et al. 232

FOREIGN PATENTS 435,560 9/1935 Great Britain.

OSCAR R. VERTIZ, Primary Examiner.

EARL C. THOMAS, Assistant Examiner.

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