A device for absorbing toxic gases that Shandong Changyi Petrochemical Co developed was recently recognized for a utility model patent. This gas-washing tower, is an auxiliary protective device for acid water storage tanks and can prevent damage that acid water storage facilities suffer at ultra-high pressures, and can effectively prevent the discharge of toxic gases into the atmosphere.
Acid water is a byproduct of heavy-oil catalytic and cracking, delayed coking, catalytic reforming, and hydrogen refining and usually contains a certain amount of toxic gases, such as hydrogen sulphide, ammonia and light hydrocarbon. For safety concerns, acid water storage facilities are designed to use nitrogen for insulation and to maintain micro positive pressure inside. There is a water insulation tank at the top of the storage facilities to prevent the escape of toxic gases into the air and to prevent air from entering the facilities. If the hydrogen sulphide and light hydrocarbon in the facility come in direct contact with oxygen, it can cause an explosion.
The nitrogen insulation can prevent the accumulation of explosive compounds inside the facilities and the spontaneous combustion of ferrous sulfide. When the facility went into operation, the water insulation tank’s designed pressure was 2.2 kPa. But, as the volume of materials in the facility grew, the acid water level would rise and gases from the acid water would be under increased pressure. When the pressure reaches the design level of the tank, the toxic gas will be released into the air. This process could protect the facilities, but it would naturally lead to the discharge of toxic gases and air pollution. And, since the gravity of such gases is greater than the air, they would be toxic to people on the ground.
The acid water facilities at Changyi Petrochemical went into use in May 2007 and this has been a headache for the company and its employees. To solve this problem, Changyi Petrochemical got the technical personnel to do an on-the-spot check and make suggestions. The company also did some renovations to the facilities, but the results were not satisfactory. So, in 2008, the company decided to deal with the problem in a fundamental way, and established a research group to contact experts and professions and take samples of the leaked gases through a special method and analyze the samples and look for a reagent to absorb or neutralize them. Through a painstaking effort, they finally came up with a solution to the toxic gases — the ammonia was first dissolved through the water washing process and hydrogen sulphide was absorbed with monoethanolamine.
After more than a year of research and experimenting, Changyi Petrochemical was able to design its own gas-washing, or deodorization, tower. This is directly connected to the gas discharge outlet at the top of the storage facilities and has upper and lower parts. The toxic gases from the acid water storage facilities first go to the lower part of the tower, which is the water-washing part, containing Pall rings. Desalting water is used to absorb the nitrogen to prevent jamming by ammonium salt crystallization, and the desalting water, after dissolving the nitrogen, flows back to the materials tank, while the remaining gases go to the upper part of the tower. The upper part is the deodorization part, with Pall rings. Monoethanolamine is poured down from the top and mixes with and absorbs hydrogen sulphide in the Pall ring section, and rich amine liquid, with hydrogen sulphide absorbed, then flows into the recycling device to dissolve into lean amine liquid for recycled use.
The gas washing tower has been proved effective in practice and has been approved by experts as up to the requirements. It has been granted a utility model patent for absorbing toxic gases, and could be widely used in the petrochemical industry.