Abstract
The paper presents the most important flow characteristics of low-pressure drop primary air nozzles used in circulating fluidized bed boilers. The role of an air nozzle pressure drop, pressure fluctuation, as well as air jet penetration length, orifice outlet jet kinetic energy and aerodynamic drag force of the gas outlet jet have been discussed. For the purpose of cold model studies the Lagisza 966MWth supercritical CFB boiler operating at the company TAURON Wytwarzanie SA, Poland has been chosen as the reference facility. In the experimental tests, three types of primary air nozzles with comparable static pressure drop and varied aerodynamic drag force have been tested. The experiments clearly showed that the pressure drop cannot be the only parameter characterizing the operation of the primary air nozzle and the air jet penetration length is determined primarily by the orifice outlet jet kinetic energy and not by the outlet jet velocity.
Highlights
The paper presents the most important flow characteristics of low-pressure drop primary air nozzles used in circulating fluidized bed boilers
Flow characteristics of air nozzles working with circulating fluidized bed (CFB) boilers can be regarded as a set of parameters determining the ability of nozzles to ensure homogeneous and stable fluidization in the cross-section of the combustion chamber, as well as to supply the primary air in a way that prevents:
The flow characteristics of tuyere-type air nozzles working in CFB boilers determine a set of parameters allowing for long-term and failure-free operation of the air distributor, providing homogeneous and stable fluidization in the entire cross-section of the boiler's combustion chamber
Summary
Optimal nozzle design should ensure an easy horizontal flow of solids on the grid surface resulting from a transport a loose material moving in the internal (combustion chamber) and external (boiler return system) circulation loop. Providing homogeneous and stable fluidization in the whole cross-section of the combustion chamber is only possible when the resistance of the air distributor for the vertical (upward) and the horizontal gas flow is determined by the relationship ∆ ≥ 0.3∆ , while for the gas flowing downwardly by the relationship ∆ ≥ 0.1∆. In Polish CFB boilers, the ranges of pressure drops for minimum and maximum boiler loads are 5.1 kPa and 8.9 kPa respectively. In the case of low-pressure drop air nozzles, the static pressure fluctuations caused by the turbulent mixing of a loose material have a significant influence on the nozzle operation.
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