AU616334B2

AU616334B2 - Process of decreasing the emission of sox in the exhaust gas from sintering plants

Info

Publication number: AU616334B2
Application number: AU47201/89A
Authority: AU
Inventors: Norbert Magedanz; Hermann Schmidt
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1988-12-24
Filing date: 1989-12-22
Publication date: 1991-10-24
Anticipated expiration: 2009-12-22
Also published as: DE3843929A1; SE466004B; SE9000832L; EP0378877B1; SE9000832D0; DE58904735D1; ATE90734T1; EP0378877A1; AU4720189A

Abstract

Iron oxide-containing materials and solid fuel are loaded onto a movable grid (1) and the mixture is ignited at the surface and is sintered by sucking through oxygen-containing gases. To reduce the SOx content in the waste gas, a bleed stream of the waste gas (19) having a high content of total SOx produced is taken off separately and is again passed (22) through the load in the final part of the movable grid. An SOx-binding material, for example CaO or Ca(OH)2, as a solution or powder, is added (23) to the load before or in the recycled zone of the bleed stream, which material reacts with the SOx compounds and thus removes them from the waste gas. <IMAGE>

Description

To: THE COMMISSIONER OF PATENTS.

WATERMARK PATENT TRADEMARK ATTORNEYS 4.

Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

6163fo Class Int. Class Application Number: Lodged: oo0 Complete Specification Lodged: o *Accepted: o 0 00 0 000 o o Priority: 0 00 Published: Related Art S*Name of ApplicantTALLGESELLSCHAFT AKTIENGESELLSCHAF Address of ApplicantIENGESELLSCA A s Reuterweg 14, D-6000 Frankfurt/Main, Federal Republic of Germany a as o0 0 0 'Actual Inventor NORBERT MAGEDANZ and HERMANN SCHMIDT Address for Service WATERMARK PATENT TRADEMARK ATTORNEYS.

O.

290 Burwood Road, Hawthorn, Victoria, Australia Complete Specification for the invention entitled: PROCESS OF DECREASING THE EMISSION OF SO IN THE EXHAUST GAS FROM SINTERING PLANTS The following statement is a full description of this invention, including the best method of performing it known to 1

I

r- L LA U\ dL iU..

tf 1st day of 19.89....

ge hMetaligeseilschaft s~igu. (Aktiengesellschaft To: THE COMMISSIONER OF PATENTS. -Cl] i(" (Wolfgang Schneider) (anel ese asteyer) Edd. Wtn So, Authorized Officers

I

-2- PROCESS OF DECREASING THE EMISSION OF SO x IN THE EXHAUST GAS FROM SINTERING PLANTS DESCRIPTION OF THE INVENTION This invention relates to a process of decreasing the emission of SO x in the exhaust gas from sintering plants in which a mixture of materials which contain iron oxide and solid fuel is charged onto a travelling grate and the mixture is ignited on its surface and is sintered in that I oxygen-containing gases are sucked through the mixture, wherein the SO content of the exhaust gas from the 10 x o travelling grate is decreased in that SO x binding substances S°ooe are delivered onto the travelling grate.

0 0 Sintering on a travelling grate is effected in that t o a mixture of materials which contain iron oxide, recycled o o 105o material, solid fuel and optional fluxes is charged onto the receiving end of the travelling grate. The charge bed is ignited on the surface and is sintered in that oxygen-containing gases are sucked through the charge bed.

Coke breeze or fine coal is used as a fuel. The sintered 0 coke is either discharged in a hot state or is cooled on the oO a 20 o*o travelling grate in a cooling zone, which succeeds the sintering zone, whereafter the sintered coke is discharged o in a cold state. The exhaust gas formed by the sintering has a certain content of SOx, which is mainly formed by the combustion of the solid carbonaceous material. The limiting o o 25 °o value for the SO x emission from sintering plants is presently about 500 mg SOx/sm 3 (sm 3 standard cubic meter).

O 04 Various processes are known by which the SO x compounds formed during sintering are chemically bound.

This may be effected, by a scrubbing process.

The scrubbing of gas has the disadvantage that it results in a sewage which is laden with pollutants and must be treated in an additional purifying stage.

SU Patent Specification 692,875 discloses the provision of an interlayer consisting of limestone having a particle size of 1 to 5 mm between the grate protecting layer provided on the grate and the layer to be sintered, L 11Y.N,.. -n r f 00909r f a 0 0000 0 0 0 0 00 S00 00 0 000 ooOO 0000 *o .oo 0 0 o a o 0 0 0 0 00 0 0 0 0 00 00 00 0 0 00 0 and serving to combine with the SO x compounds. German Patent Specification 30 164 96 describes a process in which lump-form burden materials which are suitable for use in a blast furnace and may consist, of pellets, lump ore, 5 LD slag, and sintered product are provided on the travelling grate instead of or in addition to the usual grate protecting layer to form a layer which is much thicker than the grate protecting layer, which is usually provided in a thickness of 2 to 3 cm on the grate bars of the sintering 10 conveyor. Before that grate protecting material is delivered to the travelling grate, the material is impregnated or sprayed with a basic slurry or liquid which is intended to combine with the SO x content.

Said processes have considerable disadvantages.

15 They are expensive because substantial masses or volumes must be charged onto the travelling grate in addition to the sinterable mixture. The provision of an interlayer of limestone is not economical because the SO x compounds are mainly bound on the surfdce of the lumps of limestone so that the limestone must be charged onto the travelling grate in a large surplus over the amount required in view of the formula for the chemical reaction.

It is an object of the invention to provide for decreasing the SOx emissions from sintering processes a 25 process in which the disadvantages described hereinbefore are not encountered and, in particular, the increase of the volume of the charge by the addition of the SO -binding substances is minimised.

That object is accomplished in accordance withthe invention in that a partial stream of the exhaus gas, which partial stream contains a large part of th nitre SO x which is formed, is withdrawn and is pas-sed again through the charge in the final portion the travelling grate, and oxides or hydroxides o carbonates of alkaline earth metals or alkali metal re delivered onto the charge before or in the zone rr receiving the recycled partial stream. The mbt-erials which contain iron oxide consist mainly of iron 3a 3a That object is accomplished in accordance with the invention in that a partial stream of the exhaust gas, which partial stream contains such a large proportion of the entire SO. which is formed, is withdrawn and is passed again through the charge in the final portion of the travelling grate, and oxides or hydroxides or carbonates of alkaline earth metals or alkali metals are delivered onto the charge before or in the final portion of the travelling grate. The materials which contain iron oxide consist mainly of iron e o o 0 N T -Is o i 3 5 -4ores. The SO, -binding substance may mainly consist of the stated compounds which containAlin such as CaH), CaO and CaCO 3 They may be delivered as a solution, suspension or powder onto the charge. The powder should have a particle size below 1 mm and preferably below 0.1 mm. The substances may be used individually or as a mixture. Waste materials which contain the above mentioned materials may be employed.

In general, air is used as an oxygen-containing gas which is sucked through the charge with the exception of the recycled 1 0 partial stream. If the oxygen content of the recycled l partial stream is not sufficient for effecting a sintering, ,0q 9oxygen may be added to the partial stream. On a travelling a0 0 S0 grate on which the sintering zone is not succeeded by a 0 cooling zone, the final portion of the travelling grate is 15 constituted by the last portion of the sintering zone.

Viewed in the direction of travel, the zone for receiving the recycled gas may extend as far as to the end of the last wind box or to a point over the last or last but one wind box. If the sintering zone on the travelling grate is s20 succeeded by a cooling zone, that cooling zone will constitute the final portion of the travelling grate.

0 Viewed in the direction of travel the zone for receiving the recycled gas is disposed in the first portion of the cooling zone. The rate at which SO x is formed will vary over the length of the sintering cori'eyor and will have maximum at a o certain point, which will depend on the operating condition and may empirically be determined. The partial stream of exhaust gas must be sucked off in such a manner that the position and length of the suction zone are so selected that 30 the largest possible amount of the SO formed by the me y h sintering will be sucked off and that the SO, will be I contained in an exhaust gas having such a volume rate that said exhaust gas can be passed through the charge again in the receiving zone provided in the final portion of the 35 travelling grate. The suction zone will generally be i!i disposed in the middle of the sintering zone and in most cases will slightly be offset from the middle toward the tijt ro i, ,i.l

B

r o 00 0 0 00 o 0o 0o o 0 0 00 0000 0«? 0000 o o o 00 0 0 00 oo 3 So D 0 00 0 00 0& 0 a a 0 0 0 0 0 OA a 0o 1.

i o o J discharge end. The partial stream of exhaust gas must contain a large part of the entire SO X which is formed.

This means that the SO, compounds must be sucked off at such a rate that the SO X values will be below the limits prescribed for the desulphurisation of the entire exhaust gas. Those wind boxes from which the partial stream of exhaust gas is sucked off are connected to a recycling line, which opens in a gas hood over the zone for receiving the recycled gas. The partial stream may be passed through the deduster. Some wind boxes before or behind that suction zsone are preferable so designed that they can be connected to the gas-collecting line and to the recycling line in case of need. In that case the position of the suction zone may be adapted to the point at which the SO, is formed at a maximum rate in the dependence on the current operating conditions. If the volume of the sucked off partial stream is to be changed too, the gas hood is designed to have such a length that the partial stream can be recycled through the gas hood at the highest possible rate. In a normal case, the portion of the gas hood will be supplied with air rather than with the recycled partial stream of exhaust gas. If the rate of the partial stream is increased, a corresponding portion of the gas hood, which portion is normally supplied with air, will be connected to the recycling line.

In accordance witd a preferred further feature of 25 the invention the partial stream of exhaust gas is withdrawn from the travelling grate in an area which occupies 15 to of the length of the active sintering area of the travelling grate in a range that is selected in dependence on the local formation of SO

X

The active sintering area of the travelling grate is constituted by that area on the upper course of the travelling grate which is disposed over wind boxes, into which oxygen-containing gases are sucked through the sinterable mixture. In that case a gas flowing at a relatively low rate can be used to entrain SO X at a relatively high rate and to recycle said SO X to the zone for receiving the recycled gas.

Y -6- In accordance with a further preferred feature of the invention the partial exhaust gas stream which is withdrawn contains at least 50% of the entire SO X which is formed. In that case a good purifying effect can be achieved in a relatively low gas volume.

A further feature of the invention resides in that a travelling grate is used on which the sintering zone is succeeded by a cooling zone and the zone for receiving the recycled partial stream of exhaust gas extends from a point within the cooling zone toward the charging point to such an extent that the gas is sucked off from the zone for I receiving the recycled gas at a rate which is at least as large as the rate at which the partial stream of exhaust gas Ooo is recycled to the zone for receiving the recycled gas. In 15 that case the zone for receiving the recycled gas will be o 15 arranged in the first portion of the cooling zone, which succeeds the sintering zone, so that a cooling in dependence on the temperature of the recycled partial stream will be effected. In the second portion of the cooling zone, cold 0 air is sucked through the sinter bed for a further cooling.

o Do 20 o~ This will ensure that the recycled gas can entirely be oo passed through the charge again and no recycled exhaust gas 0 0 can escape from the gas hood into the atmosphere. Besides, o the result of the sintering will not be influenced by the oO 25 oxygen content of the recycled partial stream.

o In accordance with a further feature the sintering Oo0 zone of the travelling grate is not succeeded by a cooling zone and that the zone for receiving the recycled partial stream of exhaust gas extends from the discharge end of the travelling grate toward the charging point to such an extent that the rate at which gas is sucked from the zone for receiving the recycled gas is at least as high as the rate at which the partial stream of exhaust gas is recycled to said receiving zone. This will ensure that the recycled gas can entirely be passed through the charge again and no recycled exhaust gas can escape from the gas hood into the atmosphere.

-7- In accordance with the further feature of the invention, lime-containing material is delivered as a solution or powder onto the charge. The term solution describes a slurry in an aqueous fluid. The term powder described a slurry in an aqueous fluid. The term powder describes powder particles having a particle size below 1 mm, preferably below 0.1 mm. This will result in a good distribution of the lime-containing material. As a result, a large proportion of the line-containing material will Sreact with the SO, compounds so that it will be sufficient to supply the lime-containing materials only in a small Ole* surplus over the stoichiometrically required amount in order S to remove SO, compounds at the required rates from the partial stream of exhaust gas.

the In accordance with the further preferred feature of S 15 the invention, CaO or a solution of Ca(OH)2 is used as lime-containing material. If solutions are employed which contain 10 to 25% Ca(OH) 2 the lime-containing material can effectively be conveyed and distributed and water will be required at a relatively low rate so that the sintering rate Co 20 will not substantially be influenced. CaO and Ca(OH) 2 have a high reactivity with SO, compounds and are inexpensive reactants, which may be used to control the basicity of the sinterable mixture. explarned The subject matterlof the invention will be p-ained4 Oo o 25 more in detail with reference to the drawings.

Figure 1 is a diagrammatic representation of a sintering conveyor having no cooling zone.

Figure 2 is a diagrammatic representation showing a sintering conveyor provided with a cooling zone.

On the sintering conveyor 1 diagrammatically shown in Figure 1 the sintering zone is not succeeded by a cooling zone. Wind boxes 5 to 14 are disposed under the lower course of the sintering conveyor. Details have been omitted for the sake of clearness. The rate at which SO, is locally formed is plotted over the upper course of the sintering ii conveyor as a curve 2 against the length of the sintering i.

conveyor and has a peak 3. All wind boxes are connected to ii -8a gas-collecting line 15, which opens into a deduster 16.

In a suction zone 4, which comprises the active sintering area over the wind boxes 9 amd 10, a partial stream of exhaust gas is sucked off. In accordance with the curve 2 said partial stream contains a large part of the SO 2 which 52 is formed. The shut-off valves 17b and 17c are so controlled that the partial stream of exhaust gas which has been sucked off in the zone 4 is conducted through lines 18b and 18c to a recycling line 19. The partial stream of -It 10 exhaust gas is dedusted in a deduster 20. The dedusted 10 partial stream is delivered by the fan 21 to the gas hood 22. The SO, -binding material is supplied by means of a sprayer 23, which is disposed over the wind box 12 aabove the sintering area. In the zone 24 for receiving the S1o 5 recycled gas the partial stream of exhaust gas is again 0, 15 0passed through the charge so that the Sox-binding material to form CaSO 4 which will be slagged in the blast furnace process which succeeds the sintering. The partial stream of 6oo exhaust gas then enters the gas-collecting line 15 through the wind boxes 13 and 14. By means of the shut-off valves o o 17a and 17d the wind boxes 8 and 11 may be connected via the lines 18a and 18d to the recycling line 19. As a result, the position of the suction zone 4 can be displaced. In 0 o this case the suction zone 4 includes a sintering area over two wind boxes. In dependdnce on the position of the peak 25 o 3, which depends on operating conditions, the suction zone S may alternatively include the wind boxes 8 and 9 or 10 and ii.

Figure 2 differs from Figure 1 in that Figure 2 shows a sintering conveyor 1 in which the sintering zone is succeeded by a cooling zone 25. The gas hood 22 is provided over the cooling zone.

The process in accordance with the invention will be explained more in detail with reference to the following example.

Example A sintering conveyor in which the sintering zone is not succeeded by a cooling zone was operated under the following cc'itions: jI -9- Sinter production 575,000 kg/h Exhaust gas rate 1,408,000 sm /h Velocity of travelling grate: 3.2 m/min Height of layer of sinterable mixture: 581 mm Length of sintering area: 100 m wind boxes were arranged under the lower course of the sintering conveyor. The rate at which SO x was sucked 10 through each wind box as a percentage of the rate at which exhaust gas was sucked through each wind box as a percentage of the total rate of exhaust gas were measured. The wind boxes are consecutively numbered from the beginning to the end of the sintering area.

1 Table 1 15 4 0 00 0 o o 0 00 0o 3 4 03 0 oo0000 20 o o 0 0 0 o 25 0 0 I Wind box 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18

SO

x rate through wind box in of total SOX rate 0.03 0.06 0.12 0.21 0.36 0.55 0.88 1 1.37 2.49 4.07 5.69 7.42 9.24 10.09 10.40 10.52 9.49 7.54 Exhaust gas rate through wind box in of total exhaust gas rate 3.38 3.80 4.22 4.33 4.33 4.28 4.27 4.27 4.23 4.22 4.22 4.16 4.04 3.92 3.62 3.44 3.27 3.15

-I

00 01

IPI

00 c' 0 Ot D0* 01 O 0400, Forts. Table 1

SO

x rate through Exhaust gas rate wind box in through wind box in Wind box of total SO x rate of total exhaust gas rate 519 5.08 3.21 4.50 3.38 21 3.95 3.68 22 2.55 3.92 23 1.82 4.39 24 1.09 4.87 0.48 5.40 The zone which was selected as the suction zone was op that portion fe-the active sintering area of the travelling grate which is disposed over the wind boxes, 13 to 18. It is apparent from Table 1 that 57.3% of the eni-tr- SO x which is formed are contained in the partial stream of exhaust gas which is sucked through that suction zone. But that sucked off partial stream constitutes only a small part of the entire exhaust gas which is formed by the sintering process.

It is apparent from Table 1 that the partial stream of exhaust gas amounts to only 21.4% of the entire exhaust gas.

The device for spraying the lime-containing material is disposed over that portion of the upper course which extends over the wind box 19. The selected lime-containing material 25 consists of a milk of lime Which consists of 15% Ca(OH) 2 and water. The partial stream of exhaust gas is recycled to a gas hood, which is disposed over a portion of the wind box 19 and over the wind boxes 20 to 24.

The following requirements were to be met by the desulphurisation: 1. The exhaust gas contains 800 mg SOx.sm.

2. The highest permissible SO, content in the exhaust gas is 400 mg SOx/sm 3 3. The desulphurisation has an efficiency of The partial strema of exhaust gas contains SO at a rate of 645.4 kg/h. The 15% milk of e- has an average density of 1090 mg/ 3 and is sprayed at a rate of 6.2 m 3 /h.

0 0 o o 0 o 09 00 0 a00 0 00 'i 1; .1 Sit -11- In view of the fact that the desulphurisation had an efficiency of 90%, Ca(OH), was stoichiometrically required.

The measured SO x content of the pure gas amounted to less than 400 mg/sm 3 The advantages afforded by the invention reside in that only the sinterable mixture is transported by and sintered on the travelling grate from the point at which the material to be sintered is charged to that point in the zone for receiving the recycled gas to which the SOx-binding material is delivered onto the charge. A partial stream of on"x 10 the exhaust gas can be sucked off and recycled with a low c e t o expenditure. Older plants can readily be provided with the equipment which is required. Only a small surplus of the coo SOX-binding material is required.

n 15 -Although only a small partial stream of the exhaust gas is treated and the structural expenditure is low, the content of SO x compounds in the exhaust gas from sintering plants can be decreased distinctly below the prescribed oo0 limits.

o a 4 4 *T

O

S-

Claims

6-- I I III .II I-.r i j l I i i ii_ k *1 12 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A process of decreasing the emission of SO x in the exhaust gas of sintering plants wherein a mixture of materials which contain iron oxide and solid fuel is charged onto a travelling grate and the mixture is ignited on its surface and is sintered by oxygen-containing gases being drawn through the mixture, and the SO x content of the exhaust gas from the travelling grate is decreased by SO x binding substances being delivered onto the travelling grate, characterised in that a partial stream of the exhaust gas is withdrawn which contains such a large proportion of the entire formed SO x that the remaining SO x values will be below prescribed limits for the desulphurisation of exhaust gas, said partial stream is passed again through the charge in the final portion of the travelling grate, and oxides or hydroxides or carbonates of alkaline earth metals or alkali metals are delivered as SO.-binding substances onto the charge before or in the final portion of the travelling ograte which receives the recycled partial stream. 0, 2. A process according to claim 1, characterised in that the partial stream of exhaust gas is withdrawn from the ao travelling grate in an area which occupies 15 to 30% of the 'ooo length of the active sintering area of the travelling grate in a range that is selected in dependence on the local formation of SO "0 3. A process according to claim 1 or 2, characterised in that the partial exhaust gas stream which is withdrawn S °ocontains at least 50% of the entire SO which is formed. .0 0 1 SW1. 13 4. A process according to any one of claims 1 to 3, V characterised in that a travelling grate is used on which the sintering zone is succeeded by a cooling zone and the final portion of the travelling grate for receiving the recycled partial stream of exhaust gas extends from a point within the cooling zone toward the charging point to such an extent that the gas is drawn from the final portion of the travelling grate at a rate which is at least as large as the (I rate at which the partial stream of exhaust gas is recycled j to the final portion of the travelling grate. A process according to any one of claims 1 to 3, characterised in that the sintering zone of the travelling grate is not succeeded by a cooling zone and that the final portion of the travelling grate extends from the discharge end of the travelling grate toward the charging point to such an extent that the rate at which gas is drawn from the final portion of the travelling grate is at least as high as the rate at which the partial stream of exhaust gas is recycled to said final portion of the travelling grate. o 6. A process according to any one of claims 1 to further characterised in that a lime-containing material is 0 0° delivered as a solution or powder onto the charge.
7. A process according to claim 6, characterised in that CaO or a solution of Ca(OH) 2 is employed as lime- o0:° containing material. j ft t t «'U rpmI 'B! l- I- r- 0' ir.ri.. i n~ni. 1 ii...r mi..11i 1 11 "ii iti i iff, 14
8. A process of decreasing the emission of SO x in the exhaust gas from sintering plants, substantially as hereinbefore described with reference to the accompanying drawings and/or the Example. DATED this 26th day of June, 1991. METALLGESELLSCHAFT AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS, 290 Burwood Road, HAWTHORN. VIC. 3122 AUSTRALIA se**o* 0 a a c o a a s o a 6 o n o o oo o o o oo o e~ o 0 o0 n o o o 0 o oo 0, SKP:AGB:JZ (13.21) 0r ii 9 4, Th -l I~LL IIL~--LI-_ J I ~i -1