Design Of New Nozzles And Improvement Of Primary Air System In Circulating Fluidized Bed Boiler

The primary air supply system and nozzles are the key components of a Circulating Fluidized Bed(CFB)boiler.The degree of mixing of the bed material in the combustion chamber with the air can directly affect the combustion of the circulating fluidized bed boiler,which has a great relationship with the structure of the nozzles.The uniformity of air flow through the primary air supply system is important for highly efficient operation of the CFB boiler.Non-uniform air flow distribution within the primary air supply system can affect the boiler's combustion adversely,resulting in higher energy consumptions.In this paper,a technical improvement scheme is proposed for the two major problems in the above circulating fluidized bed boiler.A new type of nozzles is designed to help the fluidized bed material,and the problems of nozzles wear and slag leakage can be prevented,and the life of the nozzles can be further improved.An effective measure to solve this problem is to install an air flow modifier in the primary air supply system.Thus,extensive numerical investigations have been carried out to design a suitable air flow modifier in order to improve operational efficiency of the CFB boiler.It has been shown that inhomogeneity in the air flow velocity,at a control cross-section of the wind-box,reduces from 81% to 24% when flow modifier is used.In order to validate the numerical results,visual and velocity distribution uniformity experiments have been conducted under five different test conditions.At the same time,the similarity principle of the small-scale boiler model is verified.For this purpose,a small-scale model of a 220t/hr CFB boiler has been used.The experimental results substantiate the numerical predictions.Moreover,the same methodology has been implemented to a full-scale 220t/hr CFB boiler.The hot test results depict that the thermal efficiency of the boiler has increased from 85.71% to 88.34% when tested with an air flow modifier in place,which is equivalent to a saving of 5,000 tons of coal per year.The economic benefits of this energy-saving technology have been shown to be very significant,clearly demonstrating the effectiveness of the air flow modifier.