1. Field of Invention
The present invention relates to a field of chemical or biological purification of waste gas by gas-liquid contact, and in particular, relates to a system and a process for capture and absorption of sulfur dioxide and carbon dioxide by an ammonia method at normal pressure.
2. Description of Related Arts
At present, the emission reduction of sulfur dioxide and carbon dioxide is in general performed separately, that is, first perform desulfurization and then perform decarbonization. The flue gas desulfurization techniques mainly include limestone-gypsum wet method, rotary spraying semi-dry method, in-furnace limestone injection and tail-section humidifying activation, seawater desulfurization, electron beam desulfurization, circulating fluidized bed flue gas desulfurization, and the like. Among which, the wet-type limestone method is at present the most widely used tail-section flue gas desulfurization technique around the world. In this technique lime slurry or lime is used to absorb sulfur dioxide in the flue gas in an absorption tower, resulting in the products of calcium sulfite and calcium sulfate, with the desulfurization efficiency of 75%-95%. The main problems of this method are the low dissolubility and utilization efficiency of absorption agent (lime or limestone), and large amounts of ash produced, causing the desulfurization equipment and pipeline prone to scaling and plugging, and it also produces secondary pollution caused by the process products. In the dry and the semi-dry desulfurization methods, due to the short contact time between the absorption agent and the flue gas, the desulfurization efficiency is generally in the range of 50%-75%, a low desulfurization efficiency, and there is also secondary pollution of solid pollutants. The recovery methods mainly include Wellman-Lord method, activated carbon method, ammonia method, and the like. In the Wellman-Lord method, sodium sulfite is used as the absorption agent, and the desulfurization efficiency can reach 95%, but the investment and operation costs are relatively high. In the activated carbon method, although the desulfurization efficiency can reach 98%, the process is complex, along with great technical difficulty and high consumption of activated carbon. In the ammonia method, the desulfurization efficiency is generally in the range of 95%-99%, the desulfurization product can be directly used as fertilizer, and no waste water or other wastes are produced. The ammonia method has incomparable advantages over other techniques, but this method often has the problem of relatively high loss of ammonia in the tail gas, which may directly lower the desulfurization efficiency. The carbon reduction techniques both at home and abroad mainly include absorption method, adsorption method, membrane separation method, storage method, and the like, but there are certain shortcomings for each of these methods.