Experimental Study On Desulfurization And Nitrification In Spray Scrubber

Optimization of Spray scrubber, which is one of the essential equipment of the The limestone/gypsum wet flue gas desulfurization(WFGD) process in thermal power plants, seized great concern of the researchers in the past decades. Among all the methods of optimization, installing a sieve tray in the spray scrubber is of the most economical and promising. In order to find out the characteristic of the sieve tray in the scrubber, a spray scrubber test stand with diameter of 148mm for limestone/gypsum wet flue-gas desulfurization with sieve tray was established.An experiment was performed to study the contacting mechanism in the vapor-liquid two-phase flow on the sieve tray, which is far from the same as the conventional spray scrubber. Air-water system had been used to study the nature of the two-phase mixture produced on the sieve tray with diameters from 6mm to 30mm and the free area from 16% to 48%. The Influence of the superficial velocities, liquid rates, hole sizes, free area, the locations and thickness of the tray on the dry pressure drop, spray pressure drop, liquid hold-up, froth height was discussed. The principles of the bubbling start-point under different hole sizes and free area were also showed in this article.Next, the desulfurization performance test was performed on the same scrubber. The major parameters which would influence the desulfurization efficiency were discussed, as the pH value, L/G ratio, superficial velocity, hole sizes, free area, the location and thickness of the tray. It was found that only when the vapor-liquid two-phase flow is in the vibration and thick froath regime, in which the two-phase flow is contacting sufficiently, the SO₂ removal efficiency will be high, otherwise in the regime that the foath is low or the flooding point appeared. Also it was found that when the free area of the tray is 36%, with great hole sizes, comes high desulfurization efficiency. And when the hole diameter is 12mm, the highest desulfurization efficiency comes when the free area is about 36%. In the test, the desulfurization efficiencies in the scrubber with sieve tray and the one without tray were compared. Commonly, the scrubber with sieve tray has a higher of 2 to 6 percent desulfurization efficiency (absolute values), when under the higher speed, the predominance would be 15 percent. As a consequence, the tray could bring high desulfurization efficiency in the scrubber.Third, the study used NaClO₂/CaCO₃ as the additive/absorbent to determine the extent of NO removal in a wet scrubber with dual sieve tray. The operating variables included pH value, NO and SO₂ concentrations, L/G ratio and NaClO₂/(NO+SO₂) molar ratio. The results indicated that, in the individual denitrification experiment the maimum NO removal efficiency is only 6%, The results of the simutaneous desulfurizatoin and denitrification experiments show that the maximum NO removal efficiencies ranged from 40.8～60.5% and the SO₂ removal efficiency were 97.5～100%.