JP3890458B2 - Sulfur trioxide absorption removal method in sulfur dioxide production - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to sulfur trioxide (SO ₃₎ absorption removal process in the sulfur dioxide (SO ₂₎ production.
[0002]
The present invention can be applied to, for example, production of purified SO ₂ gas (sulfurous acid gas) having a temperature of 45 ° C. or lower and an SO ₃ concentration of 30 mg / Nm ³ or lower, which is a secondary raw material in the caprolactam production process by a direct oxidation method from cyclohexane.
[0003]
[Prior art]
When producing purified SO ₂ gas, it is necessary to completely remove SO ₃ as an impurity and to cool to a temperature required in a subsequent process.
[0004]
In the prior art, as shown in FIG. 2, the mixed gas of high-temperature SO ₂ and SO ₃ generated in the sulfur combustion furnace (21) is used as a waste heat boiler (22), a steam superheater (30), and an economizer (23 ), And then enters a one-stage packed bed scrubber (24). In the scrubber (24), sulfuric acid in the sulfuric acid tank (27) is circulated through a cooler (29) by a circulation pump (28), and SO ₃ is absorbed and removed by this sulfuric acid. The remaining SO ₂ is cooled to a predetermined temperature by cooling air in a shell-and-tube type gas / gas heat exchanger (25) to be purified SO ₂ gas.
[0005]
In the SO ₂ manufacturing apparatus having this configuration, an air blower (26) for supplying cooling air to the gas / gas heat exchanger (25) is required, and an air blower (25) is connected to the heat exchanger (25). 26) extra ducts are required, as well as considerable power for the drive motor of the air blower (26). In addition, since extra equipment is required as described above, there is a problem that the management and maintenance costs are high in terms of operation and maintenance.
[0006]
[Problems to be solved by the invention]
An object of the present invention provides a three sulfur dioxide absorption method for removing the sulfur dioxide production can be achieved savings in management and maintenance costs in operation plane and maintenance plane by simple equipment reduces the number of devices There is.
[0007]
[Means for Solving the Problems]
The present invention includes a packed bed operating temperature for cooling the purified SO ₂ gas temperature to the temperature required to set the optimum filling layer operating conditions SO ₃ absorbed and removed within one column, the optimum condition SO ₃ absorber removed At the same time, the gas is cooled in the SO ₃ absorption removal tower.
[0008]
That is, in the method for absorbing and removing sulfur trioxide in the production of sulfur dioxide according to the present invention, a mixed gas of SO ₂ and SO ₃ coming from a sulfur combustion furnace is guided to a packed bed type scrubber and brought into contact with circulating sulfuric acid, and SO ₃ is Upon obtaining the sO ₂ is absorbed removal sulfate, the same scrubber, mainly the upper filling layer for the sO ₂ gas and cooling (4a), mainly composed of the lower packed bed for sO ₃ removal (4b) In the upper packed bed (4a) , low-temperature sulfuric acid is circulated at a temperature of 30 ° C. to 40 ° C., and in the lower packed bed (4b) , high-temperature sulfuric acid is circulated at a temperature of 70 ° C. to 90 ° C. The low-temperature sulfuric acid supplied to 4a) flows down the packed bed (4a), slightly rises in temperature by heat exchange with the SO ₂ gas, enters the lower packed bed (4b), and is supplied here. The lower packed bed ( b) flows down, mainly the lower packed bed in (4b), SO ₃ in the mixed gas by the sulfuric acid flowing down the same layer as the mixed gas contacts is absorbed removed from sulfuric acid, the sulfuric acid bottoms The temperature of sulfuric acid flowing out and flowing down the lower packed bed (4b) is relatively low in the upper part of the lower packed bed (4b) due to the combined mixing with the low-temperature sulfuric acid flowing down from the upper packed bed (4a), The temperature gradually rises due to heat exchange with the high-temperature mixed gas and SO ₃ absorption , and reaches a temperature suitable for SO ₃ absorption removal at the lower part of the lower packed bed (4b) , and then the SO ₂ remaining after SO ₃ absorption and removal Is cooled to the required temperature by contacting with low-temperature sulfuric acid in the upper packed bed (4a), and is made into purified SO ₂ gas .
[0009]
In SO ₃ absorbed removal method of the above-described configuration, cycled at a temperature of 70 ° C. to 90 ° C. The sulfuric acid in the lower packed bed is intended to circulate at a temperature of 30 ° C. to 40 ° C. The sulfuric acid in the upper packed bed. The sulfuric acid is preferably in a concentration of 98% to 98.5%.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described in detail with reference to FIG.
[0011]
The liquefied sulfur is burned in the combustion furnace (1) to generate 10% to 18% high concentration SO ₂ gas. This gas is a mixed gas of SO ₂ and SO ₃ at a high temperature of 1000 ° C. to 1400 ° C. corresponding to the concentration, and contains about 3% of SO ₃ by-produced by oxidation of SO ₂ . This mixed gas is heat-recovered by the waste heat boiler (2), the steam superheater (10), and the economizer (3), and then enters the two-stage packed bed scrubber (4) at a temperature of 160 ° C to 250 ° C.
[0012]
The two-stage packed bed type scrubber (4) is a vertical cylindrical packed tower, and is mainly an upper packed bed (4a) for cooling SO ₂ gas and a lower packed bed (4b) mainly for removing SO _3. It is composed of The material of the scrubber (4) is stainless steel, special alloy, acid-resistant brick lining or the like. In the upper packed bed (4a) of the scrubber (4), 98% to 98.5% sulfuric acid in the sulfuric acid tank (7) is cooled by the circulation pump (8) via the cooler (9), and then the low temperature that being circulated at 30 ° C. to 40 ° C., high temperature i.e. 70 ° C. to 90 without passing through the cooler (9) is in the lower packed bed (4b) is sulfuric acid in the sulfuric acid bath (7) by the circulation pump (8) Circulated at a temperature of ℃.
[0013]
The low-temperature sulfuric acid supplied to the upper packed bed (4a) flows down the packed bed (4a), slightly rises in temperature by heat exchange with the SO ₂ gas, and then enters the lower packed bed (4b). It joins with the hot sulfuric acid supplied here and flows down the lower packed bed (4b). Mainly in the lower packed bed (4b), the sulfuric acid flowing down the same layer and the mixed gas come into contact with each other, so that SO ₃ in the mixed gas is absorbed and removed by sulfuric acid. The sulfuric acid flows out from the liquid discharge nozzle at the bottom of the column and is returned to the sulfuric acid tank (7). The temperature of the sulfuric acid flowing down the lower packed bed (4b) is relatively low at the upper part of the lower packed bed (4b) due to merging and mixing with the low-temperature sulfuric acid flowing down from the upper packed bed (4a). The temperature gradually rises due to heat exchange with the gas and SO ₃ absorption, and at the lower part of the lower packed bed (4b), the temperature becomes suitable for SO ₃ absorption removal.
[0014]
Next, the SO ₂ remaining after SO ₃ absorption / removal is cooled to a temperature required by contacting with low-temperature sulfuric acid in the upper packed bed (4a) to be purified SO ₂ gas.
[0015]
Actual Operation Example The SO ₃ absorption and removal method in the SO ₂ production according to the present invention was actually carried out under the following design conditions, and it was confirmed that the performance sufficiently satisfied the requirements during the guaranteed operation period.
[0016]
(1) Inlet gas conditions Gas amount: 28121 (Nm ³ / hr)
Gas component
SO ₂ : 13.9 (%)
SO ₃ : 0.4 (%)
O ₂ : 6.5 (%)
N ₂ : 79.2 (%)
Gas temperature: 180 (° C)
Gas pressure: 0.36 (Kg / cm ² G)
(2) Outlet gas conditions Gas amount: 28000 (Nm ³ / hr)
Gas component
SO ₂ : 14.0 (%)
SO ₃ : 0 (%)
O ₂ : 6.5 (%)
N ₂ : 79.5 (%)
Gas temperature: 45 (℃)
Gas pressure: 0.28 (Kg / cm ² G)
(3) Two-stage packed bed type SO ₃ gas scrubber Tower diameter: 2600 (mm)
Tower height: 14600 (mm)
Upper stage filling height: 1100 (mm)
Lower filling height: 2900 (mm)
Demister: 6 candle type 【0017】
【The invention's effect】
According to the present invention, a filling layer operating temperature for cooling the purified SO ₂ gas temperature to the temperature required, and the optimum filling layer operating conditions SO ₃ absorbed and removed and set within one column, the SO ₃ absorber removed Since the gas is cooled in the SO ₃ absorption and removal tower at the same time as the optimum conditions, management costs and maintenance costs can be reduced in terms of operation and maintenance by reducing the number of equipment and making the equipment simple.
[0018]
That is, it is possible to reduce the overall equipment maintenance cost by reducing the cost for utility such as electric power. By reducing the operation and maintenance of equipment, the burden on operators and maintenance personnel can be reduced. Eliminates the need for an air blower for supplying cooling air to the gas and gas heat exchanger of the shell and tube and the gas and gas heat exchanger, and the gas duct connecting the equipment can be shortened, reducing the overall equipment cost. The electric power required for the air blower is not necessary, and the utility cost can be reduced. The site area for facilities is narrowed, and there is room for equipment placement throughout the plant.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the present invention.
FIG. 2 is a flow sheet showing a conventional technique.
[Explanation of symbols]
1: Combustion furnace 2: Waste heat boiler 3: Economizer 4: Two-stage packed bed type scrubber 4a: Upper packed bed 4b: Lower packed bed 7: Sulfuric acid tank 8: Circulation pump 9: Cooler 10: Steam superheater

Claims (1)

A mixed gas of SO ₂ and SO ₃ coming from the sulfur burner led to the packed bed type scrubber, circulating in contact with the sulfuric acid, the SO ₃ in obtaining the SO ₂ is absorbed removal sulfate, the same scrubber, the main Are composed of an upper packed bed (4a) for SO ₂ gas cooling and a lower packed bed (4b) mainly for SO ₃ removal, and the upper packed bed (4a) has a temperature of 30 ° C. to 40 ° C. in low temperature sulfuric acid, hot sulfuric acid at a temperature of 70 ° C. to 90 ° C. the lower packed bed (4b), is circulated respectively, sulfuric cold supplied to the upper filling layer (4a) is, the fill layer (4a) , And after a slight temperature increase due to heat exchange with SO ₂ gas, it enters the lower packed bed (4b), merges with the hot sulfuric acid supplied thereto, and flows down the lower packed bed (4b), Mainly mixed with sulfuric acid flowing down in the lower packed bed (4b) SO ₃ in the mixed gas by contacting the gas are absorbed and removed in sulfuric acid, in the sulfuric acid flows from the bottom, the lower packed bed temperature of the sulfuric acid flowing down the lower filling layer (4b) (4b) top Is relatively low due to the combined mixing with the low-temperature sulfuric acid flowing down from the upper packed bed (4a), but gradually rises due to heat exchange with the high-temperature mixed gas and SO ₃ absorption , and the lower packed bed (4b ) becomes a temperature suitable for the SO ₃ absorbed and removed in the lower part, then, SO ₂ remaining after SO ₃ absorbed and removed is cooled to a temperature required by contacting the upper packed bed (4a) and low-temperature sulfuric acid, A method for absorbing and removing sulfur trioxide in sulfur dioxide production, characterized in that the SO ₂ gas is purified .

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