Study On The Techniques Of Removal SO₂ And NO_X From The Flue Gas

Wet limestone-gypsum FGD(flue gas desulfurization)technology is the maturest and most largely applied currently. In the foreseeable future, the typical limestone-gypsum way will be still dominant. With the raise of"The Exhausting Standard of the Air Contamination in the Power Plant"and the execution of"the Managing Ordinance of How to collecting and Using the draining Fee", the control of NO_x will be more important. Therefore, it will be the main research to remove DeNox in the FGD process. It is also the main research point of the essay to add the additive to FGD process to remove DeNox. It is new both abroad and at home. It is largely invested by the China Guodian Group.The research has been developed in the following aspects:1. Collecting, digesting and mastering the latest DeNox technology around the world; researching the most advantaged DeNox technology in China; finding out the research highlight of the proper DeNox technology for the power plants in China according to the current situation.2. Comparing the effect of the different additives in DeNox process, Carbamide was proved to be most effective. Besides, it's cheap and easily got. Optimizing the pH value during the absorbing reaction, liquid gas contact time, temperature, oxidizability of NO_x and the add-on of additive, finding out the best condition for the next test.3. The equipment in the next test is that for simple wet desulfurization and DeNox process with the capacity of 10000Nm3/h. The simulated flue gas comprises air, liquefacient SO₂ and NO. The gas enters the absorber ofÏ€type from the inlet duct,then goes down to the downstream reacting area and then goes up to the upstream reacting area. After being washing, it goes to the ME of two layers (the first layer on the upper reacting area while the second on the outlet duct). The clean stimulated gas is discharged through the ID fan. In the research, the effect, characteristic, reacting velocity, reacting principle of the carbamide in wet flue gas desulfurization process and the different effect of the various process conditions to the carbamide. It turns out that adding carbamide to the limestone slurry in simple limestone-gypsum FGD process could deprive NO_x. Under the best working condition with carbamide as the additive, the removal efficiency of SO₂ is higher than 90% and that of the NO_x is higher than 50%.The above mentioned research that carbamide is added to the limestone slurry as additive is the innovative way in the world.4.After confirming that carbamide could help remove NO_x, I have analyzed its feasibility according to thermodynamics theory and calculated its limitation. The conclusion is such absorbing reaction is feasible with very high DeNox efficiency.5. By analyzing the reaction product, I have found that there will be large quantity of sulfite in the reacted slurry without oxidizing forcedly the dense absorbing slurry. Then the byproduct of gypsum could not be used. Yet over 90% of SO₃^2- could be transformed to sulfite by being aerated. After dewatering separation, the content of calcium sulfitc in the gypsum is very small, which doesn't effect the normal use of the gypsum. It's also concluded that the effect of carbamide to the process system and byproduct could be neglected.6. Through analyzing from economy and technology, there will be low investment, low operation cost and no bad effect to the original WFGD system with carbamide as the additive for desulfurization and DeNox at the same time. Then it will be largely applied in...