The influence of secondary air supply on the aerodynamics of a cyclone furnace reactor

Abstract

593Studies of the combustion of high ach coal in the prototype model of a four stage cyclone reactor have shown that flue gases emitted from it have a high con tent of ash particles [1]. The carryover of ash from the combustion chamber depends to a larger extent on the aerodynamics characterizing the motion of powdergas mixture in the reactor stages. In this connection, the authors of this paper measured and analyzed air velocity fields in a four stage cyclone reactor for dif ferent parameters and different locations at which sec ondary air is supplied to the third stage with due regard to the fact that the fourth stage is intended not only for afterburning solid fuel particles, but also and primarily for separating their ash residue on the wall and remov ing them to a dust receiving hopper.The first stage of the cyclone reactor has the shape of a truncated cone (D 1b = 120 mm, D 1t = 140 mm, and L 1 = 180 mm) and serves for initially swirling dust-gas flow and preheating fuel particles. It con tains four rectangular nozzles (60 × 12 mm) placed at the relative stage height ψ 1 = а/L 1 = 80/180 = 0.44 with the flow swirling parameter S 1 = 7.6. The tangen tial nozzles for supplying two phase mixture have the total relative cross section ϕ 1 = 21.7%. The swirling parameter and the total relative cross section of tan gential nozzles are determined from the formulaswhere β is the tangential nozzle setting angle in the reactor's first stage, f in is the nozzle cross section area, and F m1 is the first stage area in the middle section of nozzles.Fuel burns mainly in the cyclone reactor's second and third stages (D 2 = 180 mm, L 2 /D 2 = 1.39, D 3 = 250 mm, in m tg 1 2 [2]; 100% [3], 3 f S F = β ϕ = ∑and L 3 /D 3 = 1.12). Secondary air, which is required for combustion and additional flow swirling, is sup plied to the third stage through three rectangular tan gential nozzles (28 × 6.5 mm) with the parameters S 3 = 12.7 and ϕ 3 = 1.1%. Two positions of the second ary air tangential supply nozzles were studied: ψ 3 = а 1 /L 3 = 50/280 = 0.18 and ψ 3 = а 2 /L 3 = 0.71, where а 1 and а 2 are the distances from the air supply nozzles to the third stage shelf (Fig. 1), and L 3 is the third stage's height. In addition, with the swirling parameter S 3 maintained constant, the secondary air flow inclina Abstract-The aerodynamics of a four stage cyclone furnace reactor is experimentally studied for different methods of supplying secondary air to the third stage. The obtained experimental results make it possible to estimate the method of secondary air supply with which the minimal emission of ash particles is achieved dur ing the combustion of solid fuel.