Energy & Fuels, Vol.32, No.11, 11710-11717, 2018
Experimental Study of Alkali Salt Adsorption in a Circulating Fluidized Bed Boiler
Spraying the concentrated wastewater into a circulating fluidized bed (CFB) boiler furnace is an economical way to process the saline wastewater generated in coal gasification. However, if the wastewater is overdosed and the alkali salt mass fraction exceeds the capability of the bed material, the excess alkali components in the flue gas may raise not only boiler fouling and corrosion problems but also environmental problems. Therefore, the alkali salt adsorption capability of the bed material is a crucial parameter for the overall feasibility and security of this process. Experiments were conducted under laboratory conditions using analytical devices and a pilot-scale 3.3 MWth hot CFB test rig to understand the NaCl (determined through component analysis of the wastewater) adsorption characteristics and mechanism. The lab-scale experimental results showed that the NaCl adsorption capacity of the bed material for a blending ratio (BR, the ratio of the NaCl weight to the bed material weight) of 8% is higher than that for BRs lower than 8%. The pilot-scale experimental results showed that the Na mass fraction could reach 1.55% in the bed material and 1.24% in the fly ash. Component analysis results indicated that the NaCl adsorption process, which was highly related to the calcination temperature and BR, was boht physical and chemical in the lab-scale experiments but only chemical in the pilot-scale experiments. The NaCl adsorption capacity of the bed material was lower in the pilot-scale CFB boiler than in a muffle furnace at the same BR.