Performance improvement of a Circulating Fluidized Bed Boiler through flow modifications in Primary Air Supply System

The primary air supply system is a key component of a Circulating Fluidized Bed (CFB) boiler. 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. 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 65.79% to 21.25% 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. 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.