IL106543A - Arrangement for separating impurities from a gas stream - Google Patents

Description

AN ARRANGEMENT FOR SEPARATING IMPURITIES FROM A GAS STREAM O'TJ D'-ιτηη n^iOD 'ηηιπ rmgn"? rmyn The present invention relates to an arrangement for separating impurities from a gas stream.

More particularly, the invention is concerned with providing an arrangement wherein a gas stream containing impurities, such as that produced by a fossil fuel-burning furnace, is first sprayed repeatedly with a cleaning fluid and subsequently the sprayed gas is immersed in a pool of washing liquid, for the efficient removal of solid, liquid and even some gaseous impurities from said gas stream.

Power generating installations, cement manufacturing plants, and other locations wherein the combustion of large quantities of fossil fuels occurs are equipped with smokestacks to exhaust large volumes of hot gases into the atmosphere. For legal, health and environmental reasons, it is essential to greatly reduce, before discharge, the quantity of pollutants contained in the exhaust gases. The magnitude of the problem can be appreciated by considering a 1 million kilowatt power station which burns Mid-Western bit coal: 60,000 kilograms of various solids are emitted per hour. The problem of air pollution is too well-known to require further elaboration. Most civilized countries have laws mandating limits for industrial emissions. It is usually considered satisfactory to collect more than 99% of the emitted solids, and to produce a smoke plume which is invisible to the unaided eye.

Furnaces burning large quantities of fossil fuels, whether for power generation, manufacturing, or incineration of wastes, are usually provided with high, and consequently expensive, smokestacks. These serve to distribute the pollutants over a wide area, and prevent the settlement of a high concentration of pollutants in the immediate vicinity of the smokestack. A true pollution-reduction benefit is obtained only insofar as these smokestacks distribute the pollutants out to sea or over uninhabited areas. The remaining benefit of the high smokestack, unconnected to the problem of air pollution, lies in the field of producing a substantial upward draft, due to the cool air surrounding the stack, said draft improving fuel combustion in the furnace.

Various apparatus for the removal of impurities from a gas stream are known and are in use. Such devices include gravity-settling tanks, cyclone separators, impingement separators and electrostatic devices. These devices are primarily intended to remove particulate matter, but also have limited application for the removal of liquids. When it is required to remove solids, liquids and also, to some extent, gases, it is usual to bring the gas stream into contact with a liquid. Devices of this type are known as scrubbers, and the present invention refers to this type of separator .

Scrubbers are commonly used for the removal of particles in the 1 to 10 micron size range. Types of scrubbers known include cyclone, impingement, dynamic, fog, pebble bed, multi-dynamic, venturi, submerged nozzle and jet types .

Scrubbers using spray heads to divide a liquid stream into droplets and to direct such droplets at the gas stream are also well-known. Examples of such devices are described in Israel Patents 33657 (Rachel); 37247 (Bateman); 39650 (Swiss Aluminium); 47635 (Weigand Karlsruhe); 43532 (Lone Star) and 60964 (Rhone-Poulenc) , and in U.S. Patent No. 4,529,421 (Parma). These devices offer the advantage of posing close to zero obstruction to the flow of gas.

In a further type of scrubber, the gas stream to be cleaned is caused to pass through at least one liquid curtain, at the cost of some pressure loss to the gas stream. A simple device of this type is described in U.S. Patent No. 3,460,819 (Pike). A more complex device, wherein the gas stream is successively caused to pass through four liquid curtains, is described in Italian Patent 575,293 (Andriolo, et al.).

Also known are scrubbers which direct the gas flow towards the surface of a liquid reservoir. The gas to be purified enters the liquid under the gas nozzle, and exits from the liquid elsewhere. Examples of such scrubbers are described in Israel Patents 39903 and 43005 (both to Bateman). Such a process entails high pumping costs to achieve the needed gas flow and pressure.

Tests have been carried out by the present inventor wherein an apparatus was arranged to insert the gas stream directly into the liquid, some distance below the surface of a liquid reservoir. These tests resulted in the surprising conclusion that direct immersion in water of a hot, dry gas stream does not provide an effective separation process. This single-stage process has been found to be particularly ineffective in cases where it is required to remove malodors caused by particles in the 1 micron to molecular range. However, when the gas stream was previously exposed to spraying with a liquid, it was found that the subsequent immersion process proved to be highly effective.

It is therefore one of the objects of the present invention to obviate the disadvantages of the prior art scrubbers and to provide a novel gas purification arrangement, suitable for processing large volumes of hot gases emanating from a combustion process. - Λ - It is a further object of the present invention to provide a high flow scrubber suitable for the absorption of C02 and S02 gases.

It is yet a further object of the present invention to provide a high-flow gas scrubber, suitable for the absorption of malodors .

The present invention achieves the above objectives by providing an arrangement for separating impurities from gases by means of a washing liquid, comprising a smokestack having an elbowed, substantially horizontal segment extending therefrom and terminating in an end which is immersed in a reservoir of washing liquid. This segment is provided with impeller means, arranged to propel the gases in a stream under increased pressure therethrough.

A plurality of spray heads is arranged to impinge droplets of a cleaning fluid onto the gas stream while it is within the substantially horizontal segment. The spray heads are arranged with their nozzles substantially at the center of the gas stream, to produce a plurality of hollow cone sprays, the axes of the cones being substantially parallel to the axis of the substantially horizontal segment. The largest diameter of the spray from the cones faces the oncoming gas stream, and extends over the entire inner cross-section of the substantially horizontal segment .

Thus, gases passing through the segment and exiting into the reservoir pass through a plurality of cones of sprayed cleaning fluid, whereby impurities, including particles of carbonaceous substances produced during the imperfect combustion of fossil fuel, are entrained in the sprayed droplets of cleaning fluid. The gases then enter the reservoir of washing liquid at a depth below the surface thereof, and when said gases bubble to the surface of said reservoir, they are substantially free of impurities.

In a further, preferred embodiment of the present invention, there is provided a second arrangement for separating impurities from gases, which is provided with filtering means for separation of solid impurities from the reservoir, and with pumping means whereby filtered washing liquid from the reservoir is supplied to the spray heads. Re-use of the washing liquid makes feasible the use of an alkali solution at a concentration suitable for the absorption of C02 and S02 gases.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures, so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a diagrammatic view of a preferred embodiment of the apparatus according to the invention; Fig. 2 is a diagrammatic view of an apparatus provided with filtering and pumping means for recycling the fluid; and Fig. 3 is a diagrammatic view of a modification of the embodiment of Fig. 1, provided with a sloping segment.

There is seen in Fig. 1 an arrangement 10 for separating impurities from gases 12, such as those emitted by a fossil fuel-burning furnace 14. A smokestack 15 connected to furnace 14 is provided with an elbowed, substantially horizontal segment 16 extending therefrom. Segment 16 is provided with impeller means 18, arranged to propel gases 12 in a stream under increased pressure through segment 16.

Suitable impeller means 18 comprise an electrically-driven turboblower 20, arranged to achieve a gas pressure in the range of 3 to 5 atmospheres. Such pressure is needed to charge the gases 12 into a washing reservoir, as will be described further below.

A plurality of spray heads 22 are arranged in a spaced-apart formation along segment 16. Good results have been obtained with heads 22 spaced at a pitch of 50 cm. Heads 22 are arranged to impinge droplets of cleaning fluid 24 onto the gas stream within segment 16. In the arrangement 10 wherein the cleaning fluid is used only once, fluid 24 can suitably be water.

Spray heads 22 are arranged with their nozzles 26 substantially at the center of the gas stream, each nozzle producing a hollow cone spray 28, the axes of the cones being substantially parallel to the axis of segment 16. The largest diameter of cone spray 28 faces the oncoming gas stream, and extends over the entire inner cross-section of segment 16. The opposing directions of the spray and the gas stream cause high velocity collisions between the spray droplets and the impurities carried in the gas stream, thus improving the probability that impurities, including particles of carbonaceous substances produced during the imperfect combustion of fossil fuel, are entrained in the droplets of the spray.

Segment 16 terminates in an open end 30, which is immersed in reservoir 32 of washing liquid 34. In the present embodiment, the gas stream is redirected into a substantially downward direction, to enter reservoir 32 through its upper surface 36. Preferably, open end 30 is positioned so that the gas stream contacts the washing fluid 34 at a depth of between 5 to 20 cm below the surface 36 thereof .

Washing liquid 34 may be water; in coastal locations, it will be convenient to use seawater. In using seawater, accumulating impurities 37 in reservoir 32 are disposed of by the removal and replacement of the seawater entraining the impurities. Such an arrangement not only saves the cost of fresh water, but additionally provides a low-cost method of removing the impurities 37 from the reservoir 32.

The gases 38 bubbling to the surface of reservoir 32 are substantially clean, and may then be collected by hood 40 and vented to the atmosphere by a vertical-axis conduit 42, of moderate height.

Fig. 2 shows a further arrangement 44 for separating impurities 37 from gases 12.

Arrangement 44 is provided with filtering means 46 for separation of solid impurities 37 from washing liquid 34, and also with pumping means 48, whereby filtered washing liquid 50 from reservoir 32 is supplied to spray heads 22.

Arrangement 44 thus provides for recycling of the washing fluid 50, none of which is discharged to the environment. Consequently, a washing liquid other than water may be used. It is therefore feasible to use as washing liquid an alkali solution at a concentration suitable for the absorption of C02 and S02 gases, the former being a major cause of the "greenhouse" effect, while the latter is a prime cause of "acid rain".

When particle size is large enough to settle in the liquid and sufficient space is available, a gravity sedimentation basin (not shown) may be used, obviating the familiar problems of filter clogging and replacement or cleaning of the filter elements.

In large-scale installations, the solid particles 37 may be utilized, for example, for the manufacture of road and pavement surfacing materials.

There is seen in Fig. 3 a third preferred arrangement 52, for separating impurities 37 from gases 12 by means of washing liquid 34. This arrangement is similar to that illustrated in Fig. 1, and like numerals have been used to indicate like parts. A substantially horizontal segment 54 is similar to segment 16, but slopes downward at a small angle, to cause any sprayed fluid 24 not entrained in the gas stream to be drained into reservoir 32.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (10)

WHAT IS CLAIMED IS:

1. An arrangement for separating impurities from gases by means of a washing liquid, comprising: a smokestack having an elbowed, substantially horizontal segment extending therefrom terminating in an end which is immersed in a reservoir of washing liquid, said segment being provided with impeller means arranged to propel said gases in a stream under increased pressure through said segment; and a plurality of spray heads arranged to impinge droplets of a cleaning fluid onto said gas stream while said gas stream is within said substantially horizontal segment, said spray heads being arranged with their nozzles substantially at the center of said gas stream to produce a plurality of hollow cone sprays, the axes of the cones being substantially parallel to the axis of said substantially horizontal segment, the largest diameter of said spray facing the oncoming gas stream and extending over the entire inner cross-section of said substantially horizontal segment ; whereby gases passing through said segment and exiting into said reservoir pass through a plurality of cones of sprayed cleaning fluid, impurities including particles of carbonaceous substances produced during the imperfect combustion of fossil fuel being entrained in the droplets of said sprayed fluid, said gases then entering said reservoir at a depth below the surface of said washing liquid, the gases then bubbling to the surface of said liquid being substantially free of impurities.

2. The arrangement for separating impurities from gases as claimed in claim lr wherein said washing liquid is water.

3. The arrangement for separating impurities from gases as claimed in claim 1, wherein said washing liquid is an alkali solution at a concentration suitable for the absorption of C02 and S02 gases.

4. The arrangement for separating impurities from gases as claimed in claim 1, wherein said substantially horizontal segment slopes downwards at a small angle, to cause any sprayed fluid not entrained in said gas stream to be drained into said reservoir.

5. The arrangement for separating impurities from gases as claimed in claim 1, wherein said impeller means comprises an electrically-driven turboblower, arranged to achieve a gas pressure in the range of 3 to 5 atmospheres.

6. The arrangement for separating impurities from gases as claimed in claim 1, wherein said gas stream is redirected in a substantially downward direction, to enter said reservoir through its upper surface.

7. The arrangement for separating impurities from gases as claimed in claim 1, wherein said gas stream enters said reservoir at a depth below the surface of between 5 to 20 cm.

8. The arrangement for separting impurities from gases as claimed in claim 1, further provided with filtering means for separation of solid impurities from said reservoir, and provided with pumping means whereby filtered washing liquid from the reservoir is supplied to said spray heads.

9. The arrangement for separating impurities from gases as claimed in claim 1, wherein said washing liquid is said reservoir is seawater, and accumulating impurities in said reservoir are disposed of by the removal and replacement of said seawater.

10. An arrangement for separating impurities from gases by means of a washing liquid, substantially as hereinbefore described and with reference to the accompanying drawings. for the Applicant: WOLFF, BREGMAN AND GOLLER