Quench system for metallurgical gases

The present invention relates to a quench system for cooling and possibly cleaning in particular metallurgical gases, which are guided cocurrently with an acid-containing liquid, in particular sulfuric acid, comprising a gas inlet through which the gases are supplied from the top, an annular channel extending around the inner circumference of an upper Venturi portion, over whose inner overflow wall the acid-containing liquid flows over into the Venturi portion, and comprising lateral nozzles provided below the annular channel, through which additional acid-containing liquid is introduced.

Quench systems are used for instance for cooling and in part also for cleaning gases containing SO₂, as they are obtained in metallurgical processes during the smelting of metals, When the gases containing SO₂ are subsequently used for producing sulfuric acid, they must be liberated from solids and impurities before entering the contact region of the sulfuric acid plant. Upon largely separating the dust content, for instance in dust separators, electrostatic precipitators and the like, gas washing is effected in a quench system, for instance in radial-flow scrubbers. In the quench system, the gases are cooled to such an extent that they are suitable for the succeeding equipment, and are in part cleaned. Remaining impurities are partly absorbed in sulfuric acid and separated from the gas stream.

Quenching and simultaneous scrubbing of hot gases is e. g. known from US 6 019 818, in which the hot gases, such as sulphur dioxide, are passed through a packed column, which comprises an entry for quencher/scrubber liquid and an entry for wall irrigation liquid. The wall irrigation liquid is supplied above the entry of the flue gas by tangentially injecting the liquid onto a circular, horizontal shelf. From said shelf the liquid overflows and provides for a uniform irrigation of the wall with a continuous flow of liquid formed by spilling over the edge of the shelf.

US 4 469 493 discloses a method and apparatus for the purification of gases which contain solid and gaseous impurities, wherein the gas is introduced through a pipe into a Venturi, where it is contacted with scrubbing liquid introduced through a main nozzle. Additional tangentially directioned water nozzles rinse the upper cone and the entire inner surface of the Venturi, thereby forming a thin film of water from top to bottom and keeping the inner mantle surface clean. This rinsing water flows into a shelf and then onto the Venturi.

In a conventional quench system 1, as it is shown in Fig. 1, the lid 2 of the tower includes nozzles 3 through which e.g. 25% sulfuric acid is introduced. The hot, SO₂-containing gas to be cleaned is introduced through a gas inlet 4 and guided countercurrently to the sulfuric acid. To be able to resist the waste acid, the quench tower has an acid-resistant lining 5. The material of this lining is chosen corresponding to the respective exposure, and there are materials which are each particularly suitable for exposure to dry/hot or wet/cold conditions. What is always critical here is the transition between the wall portions exposed only to hot, dry gas or only to wet, relatively cold sulfuric acid. In the embodiment shown in Fig. 1, the marked area X at the gas inlet 4 repeatedly includes portions which at times are only exposed to the hot gas and then are exposed to dry/hot conditions or at times are wetted with sulfuric acid and then are exposed to wet/cold conditions. This alternating exposure leads to an increased wear of the lining, so that the same must be replaced.

In alternative embodiments of the quench tower, the SO₂-containing gas is guided cocurrently with the sulfuric acid used for cooling and cleaning. In the embodiment of a Venturi-type quench tower 10 as shown in Fig. 2, the sulfuric acid is injected via lateral nozzles 11 into the gas supplied from the top. Above the nozzles 11, an annular tube 12 is provided, through which additional acid is sprayed against the wall of the Venturi portion, in order to wet the same. This should ensure a clear separation between hot/dry and wet/cold regions. However, corrosion problems lead to a non-uniform wetting of the wall of the Venturi portion and hence undefined regions with wall portions exposed to both dry/hot and wet/cold conditions.

In the Venturi-type quench tower 20 as shown in Fig. 3, the wetting of the wall portions above the lateral nozzles 21 is effected via a circumferential annular duct 22, to which sulfuric acid is supplied. The sulfuric acid flows from the annular duct 22 via an overflow wall 23 into the Venturi portion of the quench tower 20 and is wetting the walls. Due to deposits in the annular duct 22 and due to turbulences caused by the gas stream containing solids, a non-uniform overflow can occur here as well, which can lead to lining zones alternately exposed to dry/hot and wet/cold conditions.

It is the object of the present invention to achieve a uniform liquid film on the wall of the Venturi and a clear separation between dry/hot and wet/cold zones in the Venturi portion to thereby improve the durability of quench towers.

According to the present invention there is provided a quench system comprising the features of claim 1.

Preferred embodiments are evident from the dependent claims.

By means of the invention, the gas flowing from the top through the gas inlet does not impair the overflow of the acid-containing liquid, in particular sulfuric acid, from the annular channel, so that the peripheral wall of the Venturi portion can be uniformly wetted with sulfuric acid. This ensures a clear separation between regions of the wall lining in the vicinity of the gas inlet which are only exposed to dry and hot conditions and regions proceeding from the annular channel which are only exposed to wet and cold conditions. By a corresponding selection of the materials for lining the quench tower the service life thereof can be increased substantially, so that the service intervals can be prolonged.

The known Venturi-type quench towers as shown in Figures 2 and 3, however, have in common that the gas inlet and the Venturi portion before the Venturi throat have the same diameter. The countercurrently operated quench tower 1 of the embodiment as shown in Fig. 1 also has a constant inside diameter.

In accordance with a preferred aspect of the invention, the inside diameter of the upper Venturi portion is greater than the inside diameter of the gas inlet by 5 - 15%, preferably by 7 -10%. This ensures that the sulfuric acid from the annular channel can flow over the overflow wall undisturbed and can uniformly wet the wall of the Venturi portion. With a diameter of the gas inlet of e.g. 2,800 mm, an increase of the inside diameter of the Venturi portion by 100 - 500 mm, preferably by about 300 mm, turned out to be expedient.

In accordance with the present invention, the annular channel is flared towards the top. This provides for a high flow rate at the bottom of the annular channel, which prevents the solids contained in the sulfuric acid from being deposited in the duct. On the other hand, the expansion of the annular channel in the upper portion thereof ensures a low overflow velocity of the sulfuric acid, so that a uniform liquid film is formed on the wall of the Venturi portion.

In accordance with one aspect of this invention, the annular channel is conically flared towards the top, the expansion of the annular channel preferably being achieved by bevelling the outer surface of the overflow wall facing the annular channel on one side. The outer wall of the quench tower then can be provided with a uniform insulation.

It turned out to be expedient to increase the width of the annular channel from its lower portion to its upper portion by 100 - 200%, preferably by about 150%.

To improve the uniform wetting of the peripheral wall of the Venturi portion, the upper edge of the overflow wall preferably is inclined by 20 to 70 °, preferably by 30 to 60 ° and normally about 45° in flow direction of the acid-containing liquid.

In accordance with one aspect of the invention, the annular channel is supplied with sulfuric acid via several, in particular six inlet openings. To achieve a uniform flow, the inlet openings preferably are uniformly distributed about the circumference of the Venturi portion and tangentially open into the annular channel.

In adaptation to the occurring exposure, the walls of the Venturi portion in the vicinity of the gas inlet, the Venturi ceiling and the annular channel are lined with different brick qualities in accordance with the invention. It turned out to be expedient to line the region of the gas inlet with temperature-resistant brick, in particular . nitride-bound silicon carbide brick, which has particularly good properties of resistance to an exposure to hot and dry conditions. On the other hand, the region of the annular channel preferably is lined with carbon/graphite brick, which can easily withstand an exposure to wet and cold conditions. Graphite brick has a good thermal-shock and acid resistance, so that this slightly more expensive material preferably is used in the vicinity of the Venturi ceiling and/or the transition from the gas inlet to the Venturi ceiling as well as possibly at the top of the overflow wall.

As the cements or mortars used for walling up the lining bricks also can easily withstand an exposure to either dry/hot or wet/cold conditions, the bricks for lining the walls of the gas inlet, the Venturi ceiling and the annular channel are laid by using different cement or mortar qualities adapted to the respective exposure profiles, in accordance with one embodiment of the invention.

The invention will subsequently be explained in detail with reference to an embodiment and the drawing. All features described and/or illustrated per se or in any combination form the subject-matter of the invention, independent of their inclusion in the claims or their back-reference.

Fig. 1

shows a schematic representation of a conventional quench tower which is operated countercurrently.

Fig.2

shows a schematic representation of a conventional Venturi-type quench tower which is operated cocurrently.

Fig. 3

shows a schematic representation of another conventional Venturi- type quench tower which is operated cocurrently.

Fig. 4

shows a schematic representation of the quench system in accor- dance with the present invention.

Fig. 5 -

shows an enlarged partial section through the quench system as shown in Fig. 4 in the vicinity of the annular channel.

Fig. 6

shows a section along line VI-VI of Fig. 4, and

Fig. 7

schematically shows the retrofitting of a conventional quench tower with the present invention.

Figures 4 to 6 schematically show a Venturi-type quench system in accordance with the present invention.

At its upper end, the venturi 50 comprises a gas inlet 51, an adjoining upper Venturi portion 52 and the succeeding Venturi throat 53. In the illustrated embodiment, the inside diameter D1 of the upper Venturi portion 52 is greater than the inside diameter D2 of the gas inlet 51 by about 7.5%. The dimensioning of the flared portion depends on the total size of the plant. The transition between the different diameters is referred to as Venturi ceiling 54.

Below the Venturi ceiling 54, a groove-like annular channel 55 extending around the Venturi portion 52 is provided. The annular channel 55 is defined by the outer wall 56 of the venturi 50 and an overflow wall 57. Below the annular channel 55, at the end of the upper Venturi portion 52, several, e.g. eight lateral nozzles 58 uniformly distributed about the circumference of the venturi 50 are provided for injecting sulfuric acid. The nozzles 58 preferably are 60° nozzles, which inject and atomize the sulfuric acid with a pressure loss of about 1-2 bar.

As can be taken in particular from Fig. 6, several, in particular six inlet openings 59 uniformly distributed about the circumference of the venturi 50 tangentially open into the annular channel 55 for supplying sulfuric acid.

As is shown best in Fig. 5, the lower portion of the annular channel 55, into which open the inlet openings 59, has a relatively small width of e.g. 80 mm, which approximately corresponds to the opening cross-section of the inlet openings 59. Towards the top, the annular channel 55 is flared uniformly due to the bevelling of the outer surface 60 of the overflow wall 57, until it has a width of e.g. 200 mm at its upper end; which corresponds to an expansion of the annular channel 55 by 150 %. The upper edge 61 of the overflow wall 57, which leads to the upper Venturi portion 52, is inclined downwards by about 45°.

The venturi 50 is walled up in several layers with linings adapted to the respective exposure to the introduced gas or sulfuric acid, which are shown in Fig. 5. In the vicinity of the gas inlet 51, there is provided from the outside to the inside first a simple insulating brick or foam glass 62, then a refractory insulating brick (lightweight firebrick) 63 and finally a temperature-resistant nitride-bound silicon carbide brick 64. In the vicinity of the Venturi ceiling 54, and in particular in the transitional region between the gas inlet 51 and the Venturi ceiling 54, a graphite brick 65, e.g. - as a shaped graphite ceiling brick, is provided instead of the silicon carbide brick. In Fig. 5, the graphite brick 65 merely is provided in the transitional region between the gas inlet 51 and the Venturi ceiling 54, but it can also extend over that part of the Venturi ceiling 54 which is arranged above the annular channel 55. In the vicinity of the annular channel 55 and of the upper Venturi portion 52, there is first provided a layer of acid-resistant standard bricks 66 on the outside, which is adjoined by a layer of carbon bricks 67. The overflow wall 57 also consists of carbon bricks 67, e.g. in the form of a carbon wedge brick. If necessary, the top of the overflow wall 57, which gets in contact with the gas stream, can also be made of graphite brick. Corresponding to the exposure, the linings are walled up with different kinds of cement or mortar.

The venturi 50 of the quench system of the present invention substantially is designed as described above. Its operation will be explained below.

Hot gas containing SO₂, which originates from a metallurgical plant, is supplied to the venturi 50 from the top through the gas inlet 51. Cooling and cleaning the gas stream is effected by means of sulfuric acid, which primarily is injected via the lateral nozzles 58 and cools the gas stream, so that the same can be supplied to the further equipment and then to a sulfuric acid contact plant. At the same time, impurities are absorbed and dust particles are bound.

Sulfuric acid likewise is supplied to the circumferential annular channel 55 arranged above the lateral nozzles 58, which sulfuric acid flows over the overflow wall 57 and wets the wall of the upper Venturi portion 52. Due to the flaring cross-section of the annular channel 55, the sulfuric acid in the lower portion of the annular channel 55 flows with a relatively high flow rate, so that solids contained in the sulfuric acid are kept in suspension and cannot settle. Due to the flaring cross-section of the annular channel 55, the flow rate is decreasing towards the top and in the upper region only is about 30 - 40% of the feed rate through the inlet openings 59, so that the sulfuric acid can slowly flow over the overflow wall 57 and uniformly wet the wall of the upper Venturi portion 52. This ensures that a uniform liquid film is formed at the upper Venturi portion 52, so that the lining 67 is exclusively exposed to wet and cold conditions in this region. In the vicinity of the gas inlet 51, however, only the hot and dry gas gets in contact with the lining 64.

The increased diameter D1 of the upper Venturi portion 52 ensures that the gas stream does not impair and rip up the liquid film on the wall of the upper Venturi portion 52. In this way, a clear separation is achieved between wall regions exposed exclusively to hot and dry conditions and exclusively to wet and cold conditions. This prolongs the service life of the lining and hence the service intervals.

Fig. 7 shows how a conventional quench tower 1, which previously was operated for instance according to the embodiment as shown in Fig. 1, can be retrofitted with the invention. The venturi 50 in accordance with the present invention is provided upstream of the gas inlet 3 as shown in Fig. 1 and mounted laterally on the inlet opening of the quench tower 1. The gas guided cocurrently with sulfuric acid flows through the venturi 50 and then enters the existing quench tower 1, which the gas leaves through the upper outlet opening, in order to be supplied for instance to a succeeding gas cleaning. The sulfuric acid is withdrawn from the sump 6 of the quench tower 1 and discharged via conduit 7. The nozzles 3, which in the previous quench tower 1 are provided in the ceiling 2 of the quench tower, are for instance only operated for 50%. In addition, emergency water nozzles for the further cooling of the gas stream are provided in the ceiling of the quench tower, in case said gas stream still is too hot to be supplied to the succeeding plastic elements. Since the existing quench tower is retrofitted with the venturi of the invention, a lining suited for a corresponding exposure can also be used in the problematic zone X at the transition from the gas inlet into the quench tower, which lining is not damaged by an alternating exposure.

In a quench tower in accordance with the invention, the inside diameter D1 of the upper Venturi portion 52 is about 3000 mm and is greater than the inside diameter D2 in the vicinity of the gas inlet 51 by about 200 mm.

Via the gas inlet 51, about 200,000 Nm³/h of gas containing SO₂ with a temperature of about 350°C are introduced. For cooling and cleaning the gas, a total of about 450 m³/h of maximally 25% sulfuric acid with a temperature of 60-70°C are supplied, and for instance 370-390 m³/h are supplied via the nozzles 58 and correspondingly 60-80 m³/h via the annular channel. In the nozzles 58, the sulfuric acid is atomized with a pressure loss of 1-2 bar. The sulfuric acid is introduced into the annular channel 55 with a flow rate of about 1-2 m/s, so that the solids contained in the sulfuric acid (not more than 10 g/l) are kept in suspension in the lower portion of the annular channel 55 and cannot settle. In the lower portion, the width of the annular channel is about 80 mm and is flared towards the top to about 200 mm. This reduces the flow rate of the sulfuric acid in the upper portion of the annular channel when flowing over into the upper Venturi portion 52 to about 40% of the feed rate. This provides for a uniform wetting of the upper Venturi portion 52.

1

quench tower

2

lid

3

nozzle

4

gas inlet

5

acid-resistant lining

6

sump

7

conduit

10

quench tower

11

nozzle

12

annular tube

20

quench tower

21

nozzle

22

annular channel

23

overflow wall

50

venturi

51

gas inlet

52

upper Venturi portion

53

Venturi throat

54

Venturi ceiling

55

annular channel

56

outer wall

57

overflow wall

58

nozzle

59

inlet opening

60

outer surface

61

upper edge

62

foam glass

63

refractory insulating brick

64

silicon carbide brick

65

graphite brick

66

acid-resistant brick

67

carbon brick

D1

inside diameter of the upper Venturi portion 52

D2

inside diameter of the gas inlet 51