Problems and countermeasures of wet tail gas desulfurization

Wet tail gas desulfurization usually has problems such as difficulty in handling rich liquid, precipitation, scaling and clogging, corrosion and wear, etc. If these problems are not well solved, it will cause secondary pollution, low operation efficiency or operation failure.

1. Rich liquid treatment

The chemical absorption operation of tail gas desulfurization must not only meet the desulfurization requirements and the requirements of national and regional environmental protection regulations, but also reasonably handle the washed SO2 rich liquid (including flue gas, sulfate, sulfite and other waste liquids) to avoid wasting resources or cause secondary pollution. Reasonable treatment of waste liquid is often one of the key factors for the success or failure of wet tail gas desulfurization technology. Therefore, the absorption of SO2 and the rational treatment of the rich liquid need to be considered in the design of the absorption tail gas desulfurization process.

The so-called reasonable treatment of rich liquid refers to the waste liquid of sulfate and sulfite formed by lye absorbing SO2 in flue gas, which cannot be discharged without treatment, otherwise it will cause secondary pollution. The reasonable treatment process is to recycle the sulfate in the rich liquid and recycle the waste water.

2. Flue gas pretreatment

Flue gas containing SO2 generally contains a certain amount of soot. Before absorbing SO2, high-efficiency dust collectors, such as electrostatic precipitators, wet dust collectors, etc., can be specially set up to remove smoke and dust. However, this may lead to complex processes, high equipment investment and operating costs, and is not economical. When SO2 is absorbed, it is economical and ideal to consider both dedusting and dedusting in the process of purifying SO2, that is, a dedusting and desulfurizing machine is multi-purpose, or is an integrated dedusting and desulfurizing.

Part of the pre-wash tower and absorption tower are integrated, the lower part is the pre-wash section, and the upper part is the absorption section. For tail gas desulfurization technology, spray drying method is more scientific. The soot in the sulfur-containing flue gas has no effect on the spray drying tower. Sulfate dry powder and fumes collected with baghouses are not economical.

3. Flue gas pre-cooling

The temperature of most sulfur-containing flue gas is 120~185℃ or higher, while the absorption operation requires lower temperature (about 60℃). Low temperature is favorable for adsorption, and high temperature is favorable for desorption. Therefore, the flue gas should be pre-cooled before absorption. At present, the wet tail gas desulfurization technology developed in my country, especially the tail gas desulfurization technology of coal-fired industrial boilers and kilns, directly absorbs high-temperature flue gas without humidification and cooling. The higher absorption operating temperature reduces the SO2 absorption efficiency, which It is one of the main reasons for the low efficiency of wet tail gas desulfurization of coal-fired industrial boilers in my country.

4. Scaling and clogging

In wet tail gas desulfurization, equipment is often fouled and blocked. Fouling and blockage of equipment has become a key issue for the long-term normal operation of some absorption equipment. Common methods to prevent fouling and clogging are: in the process operation, control the evaporation rate and evaporation amount of water in the absorption liquid; control the pH value of the solution; control the easy crystallization substances in the solution to be too saturated; Dust removal, control the amount of smoke and dust that the flue gas enters the absorption system. The structure of the equipment should be specially designed, or the absorption equipment that is not easy to scale and block should be selected. For example, moving bed scrubbers are less prone to fouling and clogging than fixed packing scrubbers; materials with smooth surfaces that are not easily corroded are used to make absorption equipment.