AU610374B2 - Apparatus for manufacturing sulfuric acid by contact process - Google Patents

Description

1 Z~kXMAnS0doN~N1K)rI(1:a2V 01' [jj-25 111111.4 PATENTS ACT 1952 COMPLETE

SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: 610-"37 Application Number: Lodged: Class Int. Class Complete Specification Lodged: Accepted: Published: tiod en ca t i l 49 411d is collev)Ct for Priority: Reiihted Art: Name of Applicant(s);- MITSUBISHI JUKOGYO KABTJSHIKI KAISHA Address of Applicant(s); 5-1, Marunouchi 2-Chome, Chiyoda-ku, Tokyo

JAPAN

Actual Inventor(s): Address for Service: NACHIKO UKAWA and TSUMORU NAKAMURA Kelvin Lord Co., 4 Douro '?lace, WKEST PERIA, Western Auistralia 6005.

Complete Specification for the invention entitled: "APPARATUS FOR MANUFACTURING SULFURIC ACID BY CONTACT PROCESS11 The following statement is a full description of this invention, Including the best method oftperformning It knoNwn to me/ us BY tneir Patent Attorneys KELVIN LORD AND COMPANY This form must be accompanied by either a provisional specification (Form 9 and true copy) or by a complete specification (FonrT 10 and true copy).

These sections are to be completed only where applicable..

C. J.THoMsoN. Common illh Govcmment Printe I II I I II I I I I .1

SPECIFICATION

1. TITLE OF THE INVENTION: APP'ARATUS FOR MANUFACTURING SULFURIC ACID BY CONTACT

PROCESS

2. FILED OF THE INVENTION AND RELATED ART STATEMENT: The present invention relates to an improvement of the apparatus for manufacturing sulfuric acid by the contact process.

The conventional process for manufacturing sulfuric acid includes the heat recovery step in which heat is ecovered by a waste-heat boiler from the hot gas «e containing sulfur dioxide (abbreviated as SO, hereinafter) 9 00 0 ,of and oxygen (abbreviated as 02 hereinafter), the gas purifi- 1 cation step in which the gas is purified from dust and impurities such as arsenic and mercury, the conversion step in which SO is oxidized into sulfur trio.cide (abbreviated as S03 hereinafter) by a converter filled with a vanadium catalyst in multiple tiers, and the absorption step in which SO 3 is absorbed by an aqueous solution of sulfuric acid to yield sulfuric acid as the product.

The sources of S0 2 -containing gas include smelter gases evolved by the smelting of copper, zinc, lead, nickel, etc. and combustion gases evol-ed by the combustion of pure suifu;r or H2S gas in a combustion furnace.

la- t t completing i this part DECLARED at Tokyo, Japan this 6th day of April, 1989 KAISHA, 5-1, Marunouchi MITSUBISHI JUKOGYO KABUSHIKI KAISHA 2-chome, Chiyoda-ku, Tok Ja The smelter gas has its dust and impurities removed by a cyclone, electric dust collector, scrubber, etc. in the gas purification step. The dust is composed mainly of silica, oxides of alumina and iron, and sulfates of sodium, magnesium, and calcium, and the impurities include arsenic, fluorine, etc. which are catalyst poisons in the conversion step. Since the efficiency in the gas purification step is not 100%, a considerable amount of dust is accompanied by tht gas entering the subsequent converter.

On the other hand, the gas purification step is not used for the combustion gas of pure sulfur because of its low dust content. The combustion gas, however, does contain dust originating from a small amount of ash in sulfur, and the dust is accompanied by the gas entering the subsequent converter.

The converter used to be filled with a granular catalyst; but recently it is filled with a ring-shaped catalyst 30 as shown in Fig. 4 or a petaloid catalyst.

Researches have been made on the shape of catalyst in order to reduce the initial pressure loss in the catalyst layer and to prevent the clogging with dust accompanied by the feed gas and with dust of iron oxide and iron sulfate formed by the oxidation of the steel wall.

-i *1L PAT NIT 0 FF IC E'A-,CT'.

~-li -rm~Y-i- The converter usually has three to five catalyst layers. However, it does not allow the gas to pass through all the layers straight. The gas which has passed through the previous catalyst layer is discharged from the converter and then returned to the inlet for the subsequent catalyst layer after temperature adjustment by a heat exchanger. This is intended to avoid the excessive temperature rise by the heat which is evolved at the time of SO3 formation, thereby increasing the conversion efficiency. In addition, the reaction gas is discharged from the intermediate stage of the converter and introduced i into the absorbing tower in which SO 3 is removed and then i* returned again to the converter, in the case where the double-contact process is employed. (This process has been developed to increase the conversion efficiency and is now predominant in the industry.) The hot reaction gas discharged from the converter is finally introduced into the absorbing step in which S03 is ''i brought into contact with an aqueous solution of sulfuric acid to make sulfuric acid of desired concentration.

3. OBJECT AND SUMMARY OF THE INVENTION: There are some drawbacks in the conventional apparatus for manufacturing sulfuric acid by the contact process. One of them originates in the fact that a considerable amount of dust accompanied by the feed gas -3- *i .i Si J; r i, s i 1 l

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enters the converter as mentioned above. A large portion of the dust sticks to the catalyst layer, increasing the pressure loss with the lapse of operating time. The increase in pressure loss necessitates the installation of a blower to compensate the loss. This leads to an increase in power cost.

In addition, the increase in pressure loss prevents the operation at the rated gas flow rate. To avoid this situation, it is necessary to remove the catalyst from the converter and clear the catalyst of dust by sieving at Scertain intervals. This cleaning work needs the suspen- 4 4 O sion of operation and hence lowers the rate of operation.

0044 0o o To eliminate this disadvantage there was proposed a ring- 4 04 t 0 shaped catalyst or petaloid catalyst in place of the conventional granular one. The new catalyst was expected to lower the initial pressure loss in the catalyst layer o0 d* and alleviate the increase in pressure loss by the clog- S ging with dust which takes place with the lapse of time.

These attempts made improvements to a certain extent but did not eliminate the drawbacks completely.

Another drawback originates in the fact that the conventional converter is of vertical type. This type of converter is pro'rided with a plurality of trays holding the granular, ring-shaped, or petaloid catalyst through which the feed gas passes. A disadvantage of this 4

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converter is that it needs intricately arranged ducts between it and heat exchangers on the ground, because the reaction gas which has passed through one catalyst layer is discharged and returned to the subsequent catalyst layer after temperature control by a heat exchanger to increase the conversion efficiency as mentioned above.

This disadvantage leads to the increased installation cost.

Moreover, the conventional process has another disadvantage that the converter itself has to be replaced by a larger one when it is necessary to increase the capacity of the existing sulfuric acid plant. Thus there has been a need for the method of increasing the amount of catalyst.

il Io in a simple manner.

The present invention was completed to solve the above-mentioned problems.

The gist of the present invention resides in an apparatus for manufacturing sulfuric acid by the contact process, said apparatus comprising a duct through which the feed gas containing sulfur dioxide and oxygen is passed, said duct being filled with the catalyst of parallel gas flow type for sulfuric acid in a single layer or multiple layers, said catalyst having a plurality of S- 6 -6through holes in the lattice or honeycomb form, said through holes having an equivalent diameter of 3.0 mm to 15 mm and an opening ratio of 40% to According to the present invention, the gas feed duct is provided with the catalyst of the gas flow type. A catalyst of this type has a structure in which the feed gas flows parallel to the catalytic surface. Such a catalyst may have, for example, a number of through holes in which the feed gas flows the gas flow is parallel to the inner surface of the catalyst. The catalyst of the present invention having through holes of-a lattice or honeycomb form.

The catalyst used in the present invention has an advantage over the conventional one as shown in Figure 4. That is, it 14 15 permits the feed gas to flow regularly along the pa',rition walls forming the individual through holes. Therefore, it keeps the pressure loss low until the gas flow rate becomes comparatively high, and it can be installed in the duct. It has an additional advantage that it can be placed horizontally without being broken and hence it obviates the i trays to support the conventional granular catalyst in the converter.

.Tn addition, the present inventors found that the catalyst of the present invention can convert SO 2 efficiently without becoming clogged With dust if the equivalent diameter and opening ratio of the through holes are properly selected.

The equivalent diameter of the through holes also called the T o qydraulic diameter, may be defined as: 6a equivalent diameter =4A/U where A is the cross sectional area of a flow passage in which the feed gas flows, and U is the peripheral length of the passage. For example, for a square passage an inner side of which has length 1, the equivalent diameter is 4A/U 4 x 1 x 1/41 1.

The opening ratio refers to the ratio of the gas passage area to the cross sectional area as measured in a direction perpendicular to the flow passage.

i! 4 a 25 1 4 t r t

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S' 1r In other words, the catalyst of the present invention should have the through holes whose equivalent diameter is .3 mm to 15 mm and the opening ratio of 40% to 70%. It was found that the catalyst meeting these requirements has a conversion efficiency comparable to or better than that of the conventional catalyst and yet has a low initial pressure loss and little possibility of becoming clogged with dust, keeping low the increase in pressure loss that -takes place with the lapse of time. It was also f ound that the catalyst can be installed in the duct.

With the equivalent diameter of through holes smaller than 3 mm, the i.atalyst is liable to increase the pressure :41: loss and become clogged with dust. Such a catalyst has no.

improvements over the conventional one. Conversely, with the equivalent diameter of through holes larger than mm, the catalyst has a small surface area per unit volume a.nd hence a large volume of catalyst is required for the necessary surface area. This is of no practical use.

Witti the opening ratio smaller than 40%, the catalyst has a high pressure loss, permits the pressure loss to increase more with the lapse of time, and is liable to become clogged with dust. Conversely, with the opening ratio smaller than 70%, the catalyst has thin partition walls, which leads to a low str'4,ngth. This is not dlesirable for practical use.

7.

For reasons mentioned above, the present invention requires that the catalyst should have the through holes whose equivalent diameter is 3 mm to 15 mm and the opening rat 'o of 40% to 70%. The catalyst n.seting these requirements has a conversion efficiency comparable to or better than that of the conventional one and yet has a low initial pressure loss and little possibility of becoming clogged with dust, keeping low the increase in pressure loss that takes place with the lapse of time. Owing to this catalyst, the present invention provides an improved apparatus for manufacturing sulfuric acid by the contact process.

4. BRIEF DESCRIPTION OF THE DRAWINGS: ,Fig. 1 is a schematic sectional view showing one embodiment of the present invention.

Figs. 2 and 3 are sectional views showing the catalysts of parallel flow type in the lattice and honeycomb S forms used in an embodiment of the present invention.

Fig. 4 is a perspective view showing the conventional ring-shaped catalyst.

5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: An embodiment of the present invention will be described with reference to Figs. 1 to 3.

8 There are shown a horizontal duct 1 and catalysts of parallel flow type in the lattice form which are arranged in four tiers in the .luct. The left-hand arrow indicates the flow of the feed gas containing SO 2 and 02 which has been supplied from the sulfur combustion furnace through the waste-heat boiler (not shown). The feed gas flows through the horizontal duct 1 and passes through the first to fourth catalyst layers a to d consecutively. The catalyst layer consists of sulfuric acid catalyst 10 of parallel flow type in the lattice form which has a plurality of square through holes 11 separated by partition walls 12, as shown in section in Fig. 2. This cata- 4t1 lyst layer may be replaced by the one which consists of 1 1i sulfuric acid catalyst 20 of parallel flow type in the honeycomb form which has a plurality of hexagonal through

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I, holes 21 separated by partition wda.ls 22, as shown in section in Fig, 3.

There are also shown ducts 2, 3, 4, 5, 6, and 7 which are connected to the duct 1. These ducts are intended to discharge the reaction gas, introducing it to a heat exchanger (not shown), and return the cooled reaction gas to the duct 1, thereby controlling the temperature of the reaction gas. The catalysts 10 and 20 have the through holes 11 and 21 whose equivalent diameter is 3 mm to 15 mm and have the opening ratio of 40% to 9-

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The gas entering the catalyst 10 or 20 is distributed to the throug, holes 11 or 21, and the gas flows through the through iholes along the partition wals 12 or 22, during which SO 2 in the gas is converted into SO 3 The gas leaving the catalyst enters a heat exchanger for cooling via the duct 2e 4, (r 6 and returns to the horizontal duct 1 via the duct 3, 5, or 7, entering the catalyst placed downstream.

In this embodiment, the catalysts 1,0 of parallel flow type in the lattice form or the catalysts 20 of parallel flow type in the honeycomb form are arranged in multiple Q 44 tiers in the horizontal duct, This construction leads to an advantage of obviating the trays to hold the catalyst and eliminating the possibility of the catalyst disintegrating.

The catalyst in this embodiment has a low initial pressure loss and does not become clogged with dust because it has the through holes whose equivalent diameter is 8 mm to 15 mm and also has the opening patio of 40% to 20 70F. In addition, it achieves the aonlrersion efficiency 0:44 for SOa which is comparable to or higher than that of the conventional granular or ring-shaped catalyst. Moreover, its ability to be arranged in the horizontal duct i obviates the installation of the converter. This leads to the reduction of the installation cost.

This embodiment has an additional advantage over the conventional vertical converter. That is, it permits heat exchangers to be installed in the close vicinity of the duct 1. because the catalysts are arranged in the duct 1.

This obviates the ducts arranged high for the connection to the heat exchangers and also reduces the duct length.

This leads to the reduction of the installation cost.

So far, there has been demonstrated an embodiment which achieves a desired conversion efficiency and hence obviates the conventional converter. However, it is not intended to restrict the scope of the present invention.

4 S it is possible to arrange the catalysts of parallel flow tc 0« type in the duct connected upstream ana/or downstream the S conventional converter, thereby increasing the amount of SO2 conversion.

Arranging the catalyst in the duct connected upstream 04 and/or downstream the converter needs no ground space; therefore, it iss useful for the expansion of the existing 0 4 9 plant with a limited site, Experiment Example A square duct, 80 mm by 80 mmt for experiment was connected to the inlet of a converter in a sulfur-burning sulfuric acid plant, The duct was filled with the catalyst in the lattice form as shown in Fig. 2. The duct 11

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allowed the gas to flow at a rate of 30 Nm3/h. The catalyst was tested for pressure loss (measured before and after the catalyst) and conversion efficiency. The results are shown in Table 1. The conversion efficiency was calculated by determining the concentrations of SO 2 in the incoming and outgoing gases. The catalysts were arranged in four tiers. The gas temperature at the inlet of each catalyst layer was controlled by means of a heat exchanger. The catalyst has through holes in the lattice form having an equivalent diameter of 8.3 mm and also has an opening ratio of 64%, The catalyst has an overall S length of 4 m. The lattice-shaped catalyst is composed of

VQ

5 as the major catalyst component and K and Na as cocatalysts.

Table 1

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4 4 44 '4 4f 4U *4 *t 41 441

I

C

O/SO, ratio (by vo!) at duct inhit 1.05

SO

2 concentratlon at duct inlet 10,2 SO, conversion efficiency 96,6 Gas temperature 420 (at duct Inlet) Gas temperature 455 (at duct outlet) Pressure loss (mmHaO) 92 Comparative Example The same procedure as in Experiment Example was repeated except that the catalyst was replaced by the conventional ring-shaped one. The catalyst layer is as 12 The following statement is a full description of this invention, including the best method of performing it known to me/u US long as that in Experiment Example. The pressure loss and conversion efficiency were measured under the same con,--.itions as in ExperimEnt Example. The results are shown in Table 2.

t Table 2 9 *4 44 4 4 ~4 4 44 0 2 S0 2 ratio (,by vol) at duct inlet 1,05 S0 2 concentration at duct inlet 10.2

SQ

2 conversion efficiency 97.0 Gas temperature ()42 (at duct inlei) Gas temperature (0C) 450 (at duct outlet) Prescure loss (mmH2O) 2100 49 9 4,44 4, 4 4 44 0 '4 4 4 It is noted from Tables I and 2 that there is almost no difference in S0 2 conversion between Experiment Example and Comparative Example but there is a great difference in pressure loss between them.

The apparatus was operated continuously for several months to test the catalysts for increase in pressure loss. In Experiment Example, the pressure loss increased to 1.1 times the initial value; in Comparative Example, the pressure loss increased to 1.5 times the initial value, These results indicate that the catalyst in the lattice form hardly becomes clogged with dust and increases only a little in pressure loss with the lapse of time.

-2.3lai 4 As mentioned above, the present invention produces the following effects.

According to the invention, the sulfuric acid catalyst of parallel flow type in the lattice form or honeycomb form is arranged in a single tier or multiple tiers. The catalyst layer needs no tray to hold it and does not disintegrate.

According to the invention, the catalyst layer is arranged in the duct. This obviates the converter and permits the heat exchangers to be installed in the close vicinity of the duct. This leads to the reduction of the installation cost.

According to the invention, the catalyst of parallel .flow type in the lattice form or honeycomb form has the through holes whose equivalent diameter is 3 mm to 15 mm and also has.the opening ratio of 40% to Therefore, it has a low initial pressure loss and increases only a little in pressure loss with the lapse of time. In addition, it ach eves the S02 conversion comparable to or higher t.'n that of the conventional catalyst.

The apparatus of the present invention can be added to the converter to expand the capacity of the existing plant without requiring any ground space.

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Claims (3)

1. An apparatus for manufacturing sulfuric acid by the contact process, said apparatus comprising a duct through which the feed gas containing sulfur dioxide and oxygen is passed, said duct being filled with the catalyst of parallel gas flow type for sulfuric acid in a single layer or multiple layers, said catalyst having a plurality of through holes in thel attice or honey comb said through holes having an equivalent diameter of 3.0 mm to mm and an opening ratio of 40,% to S2. An apparatus according to Claim 1, wherein the catalyst of parallel flow type is arranged in multiple t c layers in the duct and the duct is provided with branching. ducts which are intended to discharge the gas which has passed through the previous catalyst layer, introducing it to a heat exchanger, and return the cooled gas to the duct, introducing it to the subsequent catalyst layer. 4 it

3. An apparatus for manufacturing sulfuric acid by the contact process substantially as hereinbefore described in any one of Figures 1 to 3 of the accompanying drawings. DATED APRIL 4 1989 MITSUBISHI JUKOGYO KABUSHIKI KAISHA By their Patent Attorneys KELVIN LORD AND COMPANY PERTH, WESTERN AUSTRALIA

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