Research On Intensified Desulphurization Technology Of Circulating Fluidized Bed Boiler

CFB combustion technology has gotten comprehensive industry application because of its good furnace desulphurization performance and the ability to burn wide variety of fuels efficiently. Because of the inherent disadvantage of furnace desulphurization, the efficiency of sulfur absorbent utilization is relatively low (20%～45%), so excess half of the absorbent is wasted. Research on improving the efficiency of calcium utilization will benefit to both the economic operation and the environment protecting. This thesis, basing on The Science and Technique Program during the 10th Five-year Plan Period—Research on improving desulphurization efficiency in full-scale CFB boiler burning high sulfur content coal, put forward the intensified desulphurization technology which combined with furnace desulphurization by adding calcium agent in CFB boiler and circulation-suspension semi-dry FGD technology, in order to get cost-effective desulphurization performance for full-scale CFB boiler.Firstly, taking limestone as the sulfur absorbent, thermobalance was used to study the furnace high temperature desulfurization behavior and the low temperature desulfurization ability of partially sulfated calcium-based absorbent by humidification activation. The experimental result proved that the partially sulfated calcium-based absorbent has the ability of desulfurization at low temperature again, lower hydration temperature is benefit to low temperature desulfurization, and the more insufficiency of the furnace desulfurization, the better desulfurization abilty of the partially sulfated absorbent can be got.Then, the study on hydration mechanism of fly ash from a 310t/h CFB combustor was carried out at different water hydration condition. The result show that the hydration reaction of free CaO and gelatification reaction of Ca(OH)₂ occur at the same time. The change of the content of Ca(OH)₂ show the rule of rapid rising, slow rising and slow falling. When hydration temperature is rising or the amount of hydration water is increasing, the reaction rate of both hydration and gelatification increase. Under a given hydration time, the hydration temperature has a optimum value. After hydration, the particle pore volume and BET surface area become larger, the proportion of large pore increases, so the pore structure of absorbent become better.On the base of hydration experiment, study the desulfurization behavior of partially sulfated absorbent at low temperature by humidification activation. The humidifying process was carried out in a humidifying activator, then, the hydrated absorbents were put into a small-scale fluidized-bed reactor for desulfurization, moving at a mode of suspension. The result show that the hydrated fly ash of CFB boiler has good ability of desulfurization, the efficiency of un-reacted CaO utilization can achieve to 33%. When the H₂O/Ca ratio increases from 1 to 10, the efficiency of calcium utilization is becoming higher. The optimum temperature for desulfurization reaction is in the scale of 60℃～80℃.Using the direct atomization spraying of water humidification method to hydrate the CFB desulphurization ash, the hydrated ash particles carry low temperature desulphurization reaction through the capture of fine water-drops. Compares to the humidification activator humidification way, the desulphurization velocity is faster and the desulphurization ability is better in the way of directly atomized spraying of water. The results show that the intensified desulphurization technology which combined with furnace desulphurization and fly ash low temperature desulphurization by humidification activation can enhance the efficiency of calcium utilization to 70%, as a result, the Ca/S ratio can be reduced below 1.5, greatly saved the CFB boiler limestone consumption quantity. The particle humidification effect and the reaction temperature is the primary factor to affect the desulphurization ability. The spray-water position, atomization water-drop size and spray-water method influence the humidification effect remarkably, when spray-water position is in the suspension section and the atomization water-drop size closes to 50μm, the ability of capture water-drop is strongest, and the humidification effect is best. The optimum temperature for desulfurization reaction is about 80℃. The SO₂ concentration is not remarkable to the low temperature desulphurization.Finally, based on the experimental study result, the low temperature desulphurization mechanism of the humidified desulphurization ash has been expatiated. On the base of double-film theory and shrink-core reaction model, considered the special product layer structure of desulphurization ash, an single-particle reaction model was built, which can be used to describe the low temperature desulphurization process of the humidified CFB desulphurization ash The model calculated result showed that the product layer diffusion resistance is the main reaction resistance, the model calculated result agreed with the experimental result well.