Method and system for recovering ammonia from gas containing hydrocyanic acid

Abstract

A method and a system for recovering ammonia from mixed gas generated from hydrocyanic acid synthesis by Andrussow method. The method comprises steps of ammonia absorption, cyanide removal, ammonia desorption and ammonia water distillation. The method is characterized in that in the process of ammonia desorption, barren liquor at the bottom of a desorption tower (12) is sent into a reboiler (13) at the desorption tower bottom by a barren liquor circulating pump (14) at desorption tower bottom. The present method for recovering ammonia from mixed gas generated from hydrocyanic acid synthesis by Andrussow method skillfully utilizes the equipment companied with the suitable process conditions to realize high ammonia recovery efficiency, low operation cost, little loss of hydrocyanic acid, and hydrocyanic acid loss rate reduced from 1% in the existing technology to 0.4%, and is suitable for industrial recycling production.

Description

technical field [0001] The invention relates to a method and a system for recovering ammonia from a gas containing hydrocyanic acid, in particular to a method and a system for recovering ammonia from a reaction mixture of hydrogen cyanide synthesized by an Angler method. Background technique [0002] Hydrocyanic acid is a chemical raw material with a wide range of uses, widely used in medicine, food additives, feed additives, electroplating, metallurgy, polymers, photography, mining, rubber, cosmetics, pesticides, dyes, fertilizers and other fields. At present, there are mainly three methods of synthesis in industry: one is Angle's method, and its principle is to use methane in natural gas, ammonia, and oxygen in the air as raw materials to synthesize HCN by high-temperature oxidation in the presence of a platinum catalyst; the second method is Degussa The BMA method invented by the company is based on the principle of using methane and ammonia to synthesize HCN without addi...

AI Technical Summary

Problems solved by technology

[0007] The ammonium phosphate method is used to recover ammonia from coke oven gas and has been used in industrial production; but if this method is applied to reclaim ammonia in the mixed gas of Angler's synthesis of hydrocyanic acid, the composition of the mixed gas of Angler's synthesis of hydrogen cyanide is different from that of the mixed gas. Coke oven gas is different and has its particularity. The Fersum process used to recover ammonia in coke oven gas cannot simply be used for the post-reaction mixed gas of Angle's synthesis of hydrocyanic acid.

[0008] The content of hydrocyanic acid in the reaction mixture gas of Angle's method is about 8%, and the water content is about 25%. The temperature of the reaction mixture gas from the reaction process is about 230°C. On the one hand, acid polymers accumulate in the ammonium phosphate solution circulation system to increase the discharge of ammonium phosphate; on the other hand, polymers are the cause of the foaming of the entire system. For this reason, some patents propose to use activated carbon to filter the polymers, so The reaction mixture gas must be cooled to a lower temperature quickly, and the local temperature of the absorption liquid should not be too high. In the existing patent, the gas cooling and the absorption of ammonia are completed in the packing section, because the gas enters the packing section and the gas in the packing The area in contact with the liquid is not very large, and the gas temperature cannot be lowered rapidly, which inevitably makes the local temperature of the absorption liquid higher, and the time at high temperature is also longer. This problem has not been solved; During the process, direct steam stripping or decyanation tower is used, which will keep the rich liquid at high temperature for a long time, and the hydrocyanic acid contained in the rich liquid will polymerize and decompose, and release more ammonia; Most of the water in the ammonia recovery process is condensed down into the ammonium phosphate solution, which requires heat to be provided by a reboiler during the desorption process. In the existing patent, a thermosiphon reboiler is used, which is prone to phosphorus Ammonium scales in the reboiler and blocks pipes and equipment. In order to avoid crystallization, the ammonium phosphate solution is circulated at a lower concentration, which increases the operating cost accordingly.

To sum up, the existing systems and methods for recovering ammonia from mixed gas containing hydrocyanic acid are likely to cause the decomposition of hydrocyanic acid, resulting in a large loss of hydrocyanic acid, and the pipelines and equipment are easily blocked, which brings potential safety hazards. Problems with normal production

The commonly used system for recovering ammonia from hydrogen cyanide-containing gas is as disclosed in Chinese patent CN101264901A, an ammonia recovery system for mixed gas in hydrogen cyanide production, including an ammonia absorption part, a decyanation part, a desorption part and a rectification part , including phosphoric acid storage tanks, absorption towers, upper tower coolers, lower tower coolers, decyanation towers, lean-rich liquid heat exchangers, and desorption towers, etc. The ammonia in the recovery system recovers the mixed gas, and there are also problems such as large loss of hydrocyanic acid, easy blockage of pipelines and equipment, potential safety hazards, and high operating costs.

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