JPH03247503A - Production of sulfuric acid - Google Patents

Abstract

PURPOSE:To reduce an air pressure drop and to prevent the damage to catalyst in the catalytic production of sulfuric acid by using a converter in which a granular or annular catalyst is arranged in the preceding stage and a grid- shaped or honeycomb parallel gas flow-type catalyst in the succeeding stage. CONSTITUTION:A granular or annular catalyst is packed on the preceding tray of a converter 1 to form a catalyst bed (a). A grid-shaped or honeycomb parallel gas flow-type catalyst is packed on the succeeding trays to form catalyst beds (b), (c) and (d). The raw gas contg. SO2 and O2 is refined, then introduced into the converter 1 from a line 2 and passed successively through the beds (a), (b), (c) and (d) to convert So2 to SO3, and the SO3 is absorbed in aq. sulfuric acid to produce sulfuric acid. Since the dust in the raw gas is collected by the bed (a), the inflow of dust to the beds (b), (c) and (d) is reduced, hence the gas passage hole is not clogged, and the product sulfuric acid is not deteriorated.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in the method for producing sulfuric acid.

[Conventional technology]

The conventional sulfuric acid production method uses sulfur dioxide (hereinafter abbreviated as SO2).
A heat recovery process in which heat is recovered from high-temperature gas containing oxygen and oxygen (abbreviated as 0□ below) using a waste heat boiler, a gas purification process in which dust and impurities such as arsenic and mercury are removed, and a vanadium-based catalyst is used in multiple stages. It consists of a conversion step in which SO□ is oxidized to sulfur dioxide (hereinafter abbreviated as S03) in a packed converter, and an absorption step in which SO8 is absorbed into an aqueous sulfuric acid solution to produce product sulfuric acid. As a gas source containing SO□, copper,
Various refined gases such as zinc, lead, and nickel, or combustion gas obtained by burning pure sulfur in a sulfur combustion furnace are used. The former gas contains dust mainly composed of oxides of silica, aluminum, iron, etc., and sulfates of sodium, magnesium, calcium, etc., so cyclones,
These are removed in a gas purification process that includes electrostatic precipitators, scrubbers, etc. The gas may also contain components such as arsenic that poison the catalyst in the oxidation process, and these are also removed in the purification process. However, the removal efficiency in the purification process is not 100%, and a considerable amount of dust is entrained in the converter at the later stage. On the other hand, when pure sulfur is burned, a gas purification process is not required because the dust content in the gas is usually small. However, even in the case of pure sulfur combustion, dust is generated from the small amount of ash present in the raw sulfur and is entrained in the subsequent converter.

Initially, converters were filled with granular catalysts, but recently they are mainly filled with ring-shaped or petal-shaped catalysts. Various catalyst shapes have been explored in order to reduce the initial pressure drop in the catalyst layer and, as mentioned above, to prevent clogging due to dust entrained in the raw material gas.

The catalyst bed is made up of 3 to 5 layers, and the gas after the reaction is extracted from the converter through the outlet of the catalyst bed in the first stage, and after temperature adjustment by a heat exchanger, it is returned to the catalyst bed in the second stage. .

This is a measure to avoid an excessive rise in gas temperature due to heat generation during S03 generation and to obtain a high conversion rate. In addition, the mainstream method is the double contact method, in which 803 in the reaction gas is removed by an absorption tower in the middle of the converter, and the gas is returned to the converter again. There is one.

Finally, in the absorption step 803 for producing sulfuric acid, the hot reaction gas is brought into contact with an aqueous sulfuric acid solution to obtain product sulfuric acid of a predetermined concentration.

[Problems to be Solved by the Invention] As described above, a considerable amount of dust entrained in the raw material gas enters the converter. Since most of this dust adheres to the catalyst layer, the ventilation pressure loss increases with the passage of operating time. Therefore, it is necessary to install a blower corresponding to the ventilation pressure loss, and the disadvantage is that the operating power cost of the blower increases. If the ventilation pressure drop increases significantly, it becomes difficult to operate at the rated gas flow rate, so conventionally it was necessary to periodically extract the catalyst from the converter and separate and remove the dust by sieving. This had the disadvantage of reducing operating rates due to the suspension of operations. Therefore, various attempts have been made to reduce the initial ventilation pressure loss in the catalyst layer, such as changing the shape of the catalyst from granular to ring-shaped or petal-shaped, as well as to prevent clogging by dust and reduce the rate of increase in ventilation pressure loss over time. Although improvements have been made to some extent, no fundamental solution has been reached, and the current situation is that the above-mentioned drawbacks remain.

[Means to solve the problem]

In view of the above-mentioned state of the art, the present inventors have made extensive studies on a method for producing sulfuric acid that does not have the problems of conventional methods, and as a result, we have developed a method for producing sulfuric acid using a gas parallel flow type that has a lattice-like or honeycomb-like structure with low ventilation pressure loss. We proposed a method for producing a catalyst, as well as an apparatus and method for producing sulfuric acid using this catalyst.

(Patent application 1986-028951.Patent application 1983-07821
2. Patent application No. 63-08415. Patent application 1986-28254
9) The present invention has further developed the previous proposal, and in order to further stabilize the function of a gas parallel flow type catalyst having a lattice-like or honeycomb-like structure, a conventional pellet-like or ring-like structure having a catalytic effect is added to the front stage of this catalyst. It uses a converter filled with catalyst.

That is, in the catalytic sulfuric acid production method, the present invention disposes a granular or ring-shaped catalyst in the first stage, and a single-layer or multi-layer packing of a gas parallel flow type catalyst having a lattice-like or honeycomb-like structure in the rear stage of the catalyst. This is a method for producing sulfuric acid, which is characterized by using a converter.

[Effect]

The present invention provides the following advantages by filling the front stage catalyst layer in the converter with a pellet-shaped or ring-shaped conventional catalyst.

One of these is the quality of the product sulfuric acid due to the clogging of gas through holes and dust contamination during the S03 absorption process, as the dust entrained in the raw material gas is collected in this catalyst layer and can be prevented from flowing into the lattice catalyst in the subsequent stage. No more decline.

Further, although the catalyst layer is composed of three to five layers, the oxidation reaction of SO7 proceeds by 60 to 70% in the first catalyst layer. Since this reaction is exothermic, the temperature of the catalyst layer is between 550 and 600.
The temperature rises to near ℃. As described above, extremely severe temperature conditions are imposed on the first layer. In particular, when there are fluctuations in the composition and amount of raw material gas introduced into the converter, the conditions become even more severe, but in the present invention, a conventional catalyst is used in this first layer, and the conditions are relaxed to a certain extent. Since a lattice-shaped catalyst is used in the process, performance can be maintained for a long period of time without damaging the lattice-shaped catalyst due to temperature changes.

In addition, the initial pressure drop is considerably lower than that of a conventional converter that uses conventional catalysts in all layers, as only the first layer uses a conventional catalyst and the latter stage uses a lattice catalyst with low pressure drop. Become.

In the present invention, dust accumulates on the pellet-shaped or ring-shaped catalyst in the front stage, which increases the ventilation pressure loss during operation.In this case, catalyst layers filled with the conventional catalyst in the front stage are installed in parallel, and If the arrangement is such that switching is possible, dust can be separated and removed without stopping operation.

In a gas parallel flow type catalyst having lattice-like through holes filled in the latter stage, SO7 can be converted with low pressure drop and high efficiency by selecting the equivalent diameter and porosity.

That is, the equivalent diameter of the through hole is preferably 3 mm or more.
If the porosity is preferably 40% or more and 70% or less, it provides a converter having a catalyst layer that has a conversion efficiency equal to or higher than that of conventional pellet-shaped or ring-shaped catalysts and has a low ventilation pressure loss. can.

If the equivalent diameter of the through hole is less than 3 mm, the ventilation pressure loss will be large, and blockage will occur due to a small amount of inflowing dust or foreign matter flying from the heat exchanger, piping, etc., and the drawbacks of the conventional method cannot be solved.

On the other hand, if the equivalent diameter of the through-hole exceeds 15 mm, the surface area of the catalyst per unit volume becomes small, requiring a large capacity catalyst, which is not a practical idea.

Furthermore, if the porosity of the through-holes of the lattice catalyst is less than 40%, the pressure loss will be large, and the end faces will likely be clogged with dust, resulting in a large increase in the ventilation pressure loss over time. On the other hand, the porosity is 70%
If it exceeds this value, the partition walls of the lattice-shaped catalyst will become thinner and the necessary strength will not be obtained, which is undesirable from a practical standpoint.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

This embodiment is an example in which a conventional ring-shaped catalyst is packed in the first layer (front stage) catalyst shelf of the solid converter, and three layers of lattice-shaped gas parallel flow type catalysts are packed in the latter stage catalyst shelf. In FIG. 1, S02 and 0.02 are passed through a sulfur combustion furnace and a waste heat boiler (not shown). The gas containing the gas is sequentially supplied from the first catalyst layer a filled in the converter 1 through the line 2 to the fourth catalyst layer d. Catalyst layer a is filled with a ring-shaped catalyst as shown in FIG. 3, and catalyst layer b-d is filled with a lattice-shaped gas parallel flow type catalyst consisting of a plurality of pieces, the cross section of which is shown in FIG. Filled.

The gas leaving the catalyst layer passes through the ducts 3, 5, or 7 and enters a heat exchanger (not shown), where it is cooled and then passed through the duct)4.6. or 8, it is returned to the converter 1, and introduced into the catalyst bed on the downstream side. Also, when passing through the catalyst layer, SO2 in the gas becomes SO,
Finally, it is sent to the S03 absorption process via line 9.

As shown in detail in FIG. 2, one lattice-like parallel flow type catalyst is a sulfuric acid catalyst 20 of a lattice-like gas parallel flow type having a plurality of rectangular through holes 22 partitioned by partition walls 21. The equivalent diameter of the hole 22 is selected to be 3 or more and 15IllIIl or less, the pore size is 40% or more and 70% or less, and the overall thickness is 300 mm square to 75 mm due to manufacturing method constraints.
mm square is used.

In this example, since the ring-shaped catalyst is filled in the front stage, the pressure drop is slightly lower than when using 100% (all layers) of a gas parallel flow type catalyst, which has a low initial pressure drop and is less likely to be clogged with dust. Although the size of the lattice-shaped catalyst packed in the latter stage is small, since less dust enters the catalyst and the reaction conditions are gentle, the catalyst itself suffers less damage and can maintain stable performance for a long time.

[Experiment example]

In a sulfur-burning sulfuric acid production plant, gas at a flow rate of 150 Nm'/h was supplied from the converter inlet to a 200 x 200 mm square converter, and the ventilation pressure loss and oxidation rate were measured before and after the converter, and the results in Table 1 were obtained. Obtained.

The first layer of catalyst shelves in the converter is equipped with a conventional ring-shaped catalyst (outer diameter 10φm [I+×inner diameter 4φ×11L mm)
was packed to a height of 1 mm, and the latter catalyst shelf was filled with three layers of 1 m each of grid-shaped catalysts each having an equivalent diameter of 4.2 mm and a porosity of 64%. The gas temperature at the inlet of each layer was controlled by a heat exchanger. The lattice catalyst was prepared using v205 as the main catalyst material and K as a co-catalyst.

[Comparative example]

A conventional ring-shaped catalyst was filled in the entire layer (total catalyst layer height: 4 m) in the same converter as in the experimental example, and the ventilation pressure drop and oxidation rate were measured in the same manner as in the experimental example. The artificial gas conditions and the catalyst layer artificial temperature were controlled in the same manner as in the experimental example. The results obtained are shown in Table 2.

〔Effect of the invention〕

Comparing the experimental example and the comparative example, it was found that although the conversion rates of both were almost the same, the use of a converter like the one in the present invention was effective in reducing the ventilation pressure loss to about 173.

Furthermore, after several months of continuous operation, we examined the adhesion of dust to the lattice-shaped catalyst, and found that there was hardly any dust attached, and there was no damage to the catalyst.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention. Second
The figure is a cross-sectional view of a lattice-shaped catalyst. FIG. 3 is an explanatory diagram of a conventional ring-shaped catalyst.

Claims (1)

[Claims] In the catalytic sulfuric acid production method, a converter is used in which a granular or ring-shaped catalyst is placed in the first stage and a single layer or multiple layers of gas parallel flow type catalyst having a lattice-like or honeycomb-like structure are packed in the rear stage of the catalyst. A method for producing sulfuric acid, characterized by: