Experimental and CFD Simulation Studies on Bell-Type Air Nozzles of CFB Boilers

Abstract

In this paper, a new bell-type air nozzle, which overcomes the structural defects of traditional bell-type air nozzles, is proposed and validated by cold test and numerical simulation. The pressure drop characteristic of the new bell-type air nozzle is measured. Furthermore, the causes of cover outlet abrasion and blockage, inner tube fracture, and irregular resistance change in traditional bell-type air nozzles applied in circulating fluidized bed (CFB) boilers are analyzed. Then, the performance of the new bell-type air nozzle is evaluated in a real CFB boiler, which is operated under regular working conditions. The results show that the new bell-type air nozzle has stronger anti-wear ability, excellent resistance characteristics, longer service life, and easier maintenance.

Characteristics of the Blockage from Air Nozzle Guide Duct in Circulating the Fluidized-Bed Coal Gasifier and Its Formation Mechanism

“…The lower side wall of the nozzle cover has a row of oval-shaped holes as the final outlet of the gasification agent. The gasification agent enters the air nozzle from the guide duct, sprays out through the round holes of the core tube, and finally enters the bottom of the gasifier through the oval-shaped holes …”

“…The gasification agent enters the air nozzle from the guide duct, sprays out through the round holes of the core tube, and finally enters the bottom of the gasifier through the oval-shaped holes. 7 The blocked part of the guide duct is shown in Figure 3a, and its cross section is shown in Figure 3b. As can be seen from Figure 3b, the blockage is roughly divided into two parts, one for the wall-layer blockage (WLB) and the other for the center-layer blockage (CLB), corresponding to I and II areas in Figure 3b respectively.…”

Modern design solutions in the design of boiler units, ovens and fireboxes burning solid fuel in a fluidified bed

“…In order to meet these requirements, many different caps and nozzles have been developed, which can be divided into several types, shown in Table 1 Although cap grilles offer the best performance compared to other air distributor designs, they are not without their drawbacks. Operating experience has revealed a number of problems, such as wear, clogging and separation of bell-type caps [25] or bottom ash leakage in arrow-shaped caps [26]. Work to solve these problems is currently underway.…”

Designing a new bell-type primary air nozzle for large-scale circulating fluidized bed boilers

“…Hence, they provided an 18.9% improving in pressure drop compared to a conventional bell-type nozzle and making 66% upgrading in flow uniformity, and also preventing bed material back-flow by designing the orifices 30° downwards. Huang et al [22] improved the design of the bell-type nozzle used in the air distributor of a 480 t/h CFB boiler through CFD analysis. Within the scope of the design, the risk of clogging was reduced by giving a special shape to the nozzle orifice outlet and thus the service life was extended.…”