A flue gas damper gate consists of a frame, blades, sealing strips, main shaft, bearings, shaft seals, crank linkage, actuator and the gate body. The shaft journals use a purpose-made sealing structure and a purpose-made bearing: the sealing structure gives good sealing performance, no external leakage and high temperature resistance, while the bearing has self-aligning and self-compensating functions so that it absorbs any misalignment between the front and rear shaft. The result is a gate that closes with low resistance, does not jam and turns freely.
The process requirements
- Every part of the gate is designed to withstand a flue gas temperature swing from 80 °C to 200 °C without damage, sticking, warping or leakage. Above 170 °C the FGD plant is bypassed; the high temperature excursion at 180 °C lasts no more than 30 minutes, and the gate must work normally throughout that period.
- Each gate and its drive is designed to resist corrosion by the ambient medium under the operating conditions at its own location.
- The gate uses a double blade. At a pressure difference of 5,000 Pa and without sealing air, leakage does not exceed 1.0 %. Blade operation is free, reliable and convenient to service.
- The clean gas outlet gate uses an electric double blade. Because the FGD outlet runs at only about 50 °C, corrosion protection and material selection are given full consideration.
- The gate operates against a very large pressure difference and closes tightly without bending or jamming. The blade matches the locking device in both the fully open and fully closed positions, and the blade design and position inside the duct keep ash accumulation on the blade surface to a minimum.
- The electric actuator is fitted with limit switches at both ends, rotation switches in both directions, an emergency hand wheel and a mechanical interlock for maintenance.
- The gate has an open/close function. Actuator speed meets the requirements of the unit and the induced draught fan; the electric actuator takes 75 seconds to travel from fully open to fully closed.
- The double-blade gate is supplied as a complete set: frame, double blades, electric actuator and all necessary sealing and control components of the sealing system.
- The frame is connected by flange, positioned with bolts and welded tightly to the duct.
- The gate is arranged with a horizontal main shaft. The shaft is made of suitable steel, and particular attention is paid to the design of the frame, shaft and supports to prevent dust ingress and deformation or degradation caused by high temperature.
Each of these points finds its way into the general arrangement drawing, and they are the items we check on the test bed before a gate is released.