JPS6153102B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for purifying gas containing impurities. In particular, it relates to a method for purifying gas containing impurities such as hydrogen sulfide and hydrogen cyanide. Taking carbonized coal gas as an example, impurities in the gas include hydrogen sulfide, hydrogen cyanide, ammonia, and tar, which must be purified and removed. As a method for removing these impurities, according to Patent No. 827210 (Special Publication No. 47-47561), rhodanide is generated by effectively reacting hydrogen sulfide and hydrogen cyanide, which are harmful components in the gas. Harmful components are rendered harmless. At this time, it is known that a catalyst such as picric acid contributes to the regeneration reaction after desulfurization and is involved in the isolation of sulfur and the subsequent progression of the rhodanization reaction. However, when using picric acid as a catalyst, because picric acid is extremely poorly soluble in cold water,
There was a problem in the process that it had to be dissolved in small quantities. This is because the solubility of picric acid in water is only about 1.2g/100g. An example of a coal carbonization gas purification system is shown in FIG. 1. Tar in the crude gas carbonized from a coke oven 1 is first collected in a decanter 2 together with the gas liquid. The gas is then cooled in an indirect condenser 3, and the cooled tar is collected in a tar pit 4. Thereafter, the gas passes through a tar remover 5 and a discharger 6, and then undergoes desulfurization and decyanization in a desulfurization tower 7 and a desulfurization tower 8. Further, excess ammonia is removed by an ammonia washing tower 10, passed through a naphthalene washing tower 11, and then transferred to a benzol absorption tower 12.
Benzol is absorbed and separated, and the gas then passes through a final scrubber 13 and is treated by a dry desulfurizer 14, completing gas purification. Note that 9 is a regeneration tower, and the cleaning liquid from the desyanation tower 7 and the desulfurization tower 8 is sent to the regeneration tower via a waste liquid tank 15. A part of the liquid from the sewage tank is circulated to the sewage tank 15 after separating sulfur in a centrifuge 17, but picric acid is dissolved in water in a picric acid dissolving tank 16.
The waste liquid tank 15 is replenished. The problem was the dissolution of picric acid in the picric acid dissolution tank 16. Figure 2 shows the treatment process for coal tar that has been cooled and separated using an indirect condenser or the like. coal tar is 1
8 and enters the pressure dehydrator 21 via heat exchangers 19 and 20. After being dehydrated in a pressure dehydrator 21, it is supplied to an evaporation column 22, and the distillate from the top is separated into tar gas oil and water in an oil-water separator 23. The bottom oil of the evaporation tower 22 is heated in the heating furnace 24 and supplied to the atmospheric rectification tower 25, and the distilled oil from the top is cooled in 19, and then separated into tar gas oil and water in the oil-water separator 27. separated. A part of the bottom oil of the atmospheric rectification column 25 is combined with the oil from the pressure dehydrator 21, and
A portion is sent to the heating furnace 24. After being heated in the heating furnace 24, it enters a vacuum rectification column 26, the top of which is connected to a vacuum pump and subjected to reduced pressure, while the middle pitcher is taken out from the bottom of the column via a heat exchanger 20. By the way, the separated waste water from ports 23 and 27 contains a lot of cyanide, and cannot be discharged as is. Therefore, processes such as oil/water separation, activated sludge treatment, coagulation sedimentation, and chemical oxidation treatment had to be carried out, which required considerable expense in terms of equipment costs and running costs. Typical components of the wastewater are shown in Table 1.

[Table] On the one hand, the inventor was forced to solve the problem that picric acid, which is required for gas purification, is not easy to dissolve and requires a long time and a great deal of effort. We faced the challenge of requiring a large amount of equipment for treatment, and after much deliberation, we finally discovered an excellent method that could solve both of these problems at once. First, as shown in Table 2, when a certain amount of picric acid was added under the same conditions to a certain amount of industrial water and tar distillation wastewater, and the time required for it to completely dissolve was measured and compared, there was a noticeable difference. I found out that there is. In addition, we compared the absorption liquid using industrial water with 0.3% picric acid added and the absorption liquid using tar distillation wastewater, which were regenerated by blowing air after flowing crude coal carbonization gas under the same conditions.

[Table] As shown in Table 3, it was found that there was a clear difference in the desulfurization effect based on the average of 10 comparison tests. The sulfur content in the absorbent is higher when using tar distillation wastewater, and less ammonium thiosulfate is produced when the activity of picric acid is insufficient. Furthermore, distillation wastewater has better absorption efficiency of hydrogen cyanide, and the rhodanization reaction is also progressing. In other words, it has been confirmed that better results can be obtained in both desulfurization and decyanization by using tar distillation wastewater instead of the commonly used absorption liquid using industrial water.

[Table] As a method of implementing the present invention, for example, evaporation tower 2
Oil-water separators 23 and 27 are installed in the distillate line from 2 or the atmospheric rectification column 25, and the waste water from the aqueous layer is stored in a cushion tank via a strainer. Acid dissolution tank 16
If the liquid is sent out by a transfer pump through a line led to the tank, the waste water generated by tar distillation will not be discharged to the outside and will be used entirely for dissolving the picric acid. Thereafter, the picric acid solution is sent to the regeneration tower 9 via the waste liquid tank 15, and after the liquid is regenerated, it is used in the gas purification process. Since tar distillation wastewater is ammonia alkaline, it is extremely advantageous for dissolving picric acid, and the cyanide contained in tar distillation wastewater is fixed in rhodanide. Furthermore, when ammonia, which exists as a harmful component in gas, is used, it can be fixed as rhodan ammonium, and the waste liquid containing these fixed impurities is recycled as sulfuric acid or sulfate through combustion treatment after concentration. (Japanese Patent Publication No. 52-3404) Therefore, the present invention has an excellent synergistic effect in streamlining the desulfurization and decyanization steps and in making tar distillation wastewater harmless.

[Brief explanation of the drawing]

FIG. 1 is a system diagram illustrating the entire purification process for gas containing impurities, and FIG. 2 is a system diagram illustrating tar distillation equipment. 1...Coke oven, 2...Decanter, 3...
Condenser, 4... Tar pit, 7... Desulfurization tower, 8... Desulfurization tower, 9... Regeneration tower, 12... Benzol absorption tower, 15... Sewage tank, 16... Picric acid dissolution tank, 22...Evaporation column, 25...Normal pressure rectification column, 23, 27...Oil-water separator.

Claims (1)

[Claims] 1. In the process of cleaning and purifying gas containing impurities such as hydrogen sulfide and hydrogen cyanide with an aqueous solution using picric acid as a catalyst, other impurities in the gas, such as tar, are cooled and separated and then distilled. A method for purifying gas containing impurities, in which the distilled waste water produced during the process is used as cleaning water for dissolving picric acid and cleaning the gas.