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Ammonia desulphurization: Large units have more advantages

From: Nov. 30, 2014 China Chemical Industry News

  Ammonia desulphurization technology uses ammonia as absorbent to remove sulfur dioxide in the coal-fired flue gas and produces  ammonium sulfate fertilizer as by-product. As a green and environmental desulfurization technology in line with the requirements of circular economy, ammonia desulphurization technology attracts more and more industrial attention. Afterpromotion and application in recent years, ammonia desulphurization technology obtained significant development in Chinese desulfurization industry; its advantages of high desulfurization efficiency, no waste water or solid discharge and recycled sulfur resources also obtained general recognition in the industry.

  So far, dozens of domestic ammonia desulphurization devices have been successfully put into operation, of which the largest scale is 2 × 135 mw unit ammonia desulphurization device of Guangxi Tiandong Power Plant, contracted by Jiangnan Environmental Protection Company. This device adopts a configuration of two boilers corresponding to two absorbers andflue gas capacity for each tower reaches 1.1 million Nm/h. But at present, there is no operation performance of ammonia desulphurization technology in 600 mw unit; There rises the concern from who has limited understanding on ammonia desulphurization technology: Is ammonia desulphurization technology only applicable to small and medium units, and cannot apply to large units? The following analysis can get a clear conclusion.

  System configuration of ammonia desulphurization device is similar to limestone/gypsum method and their key equipments are almost identical. Technical problems need to be solved of the two technologies are basically the same, mainly including corrosion, abrasion, clogging; the solutions are identical, and the only difference is the by-product output systems. Ammonia desulphurization device uses flue gas heat or additional steam heat to evaporate and concentrate ammonium sulfate solution to crystallize; and then it will be further refined through dehydration by a centrifuge and drying by a dryer. It is a mature process in the caprolactam and coke industries. The basic factor influencing reliability of ammonia desulphurization is the same as wet limestone/gypsum method. The reliability of two devices is at the same level. Even in some parts, ammonia process has more advantages, for example, ammonium sulfate is soluble in water, so the possibility of clog is relatively low, even if there is partial clog, flushing with water can solve it. As a result, it can be concluded that with similar configuration, reliability level of ammonia desulphurization device is not lower than wet limestone/gypsum method; if applied to large units; it can also ensure long-term and reliable operation.

  In addition, aerosol problem of ammonia desulphurization has been resolved, and ammonia slipslip is under effective control. Ammonia slip has two main ways: One is that free ammonia slipslips into atmosphere with flue gas; the other is that ammonium salt slips with flue gas in the form of aerosol, and forms obvious smog. The latter is the main form of ammonia slip. Ammonia slip caused by aerosol and secondary pollution have been industry problems since ammonia desulphurization technology emerges, which haven't been solved effectively for a long time. Ammonia slip amount of early ammonia desulphurization technology could reached more than 20%; Recovery rate of ammonia was less than 80%; However current ammonia process technique has successfully solved this problem.

  In 2009, ammonia desulphurization devices of Yangzi Petrochemical Thermal Power Plant and Guangxi Tiandong Power Plant, contracted by Jiangnan Environmental Protection Company, passed performance test of Xi'an Thermal Institute, and the test report shows: Ammonia slip amount in flue gas of the two sets of ammonia desulphurization device in Yangzi Petrochemical Thermal Power Plant, are 7.52 mg/m³ and 3.47 mg/m³, respectively, and its ammonia recovery rate can reach 97.5% Ammonia slip amount in ammonia desulphurization device of Guangxi Tiandong Power Plant is 7 mg/m3. This ammonia recovery rate can reach 97.83%. At present; Ministry of Environmental Protection has prepared drafting of the ammonia desulphurization technology specification, which requires ammonia slip amount to be no more than 10 mg/m³ and ammonia recovery rate to be no less than 96.5%. Therefore, current ammonia desulphurization technology represented by Jiangnan Environmental Protection has successfully solved aerosol and ammonia slip problems which impedes development of ammonia desulphurization technology in the long term.

 
 
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