Experiences of a Fibrous Ceramic Candle Filter for Hot Gas Cleaning in Pressurized Fluidized Bed Combustion

Abstract

A fibrous, layered Al₂O₃/SiO₂-based ceramic candle filter has been tested for pressurized fluidized bed combustion (PFBC) hot gas cleaning at the Otaniemi PFBC test rig. The fuels used have been bituminous coal and peat. The exhaust gas from a pressurized fluidized bed reactor was passed through two cyclones before entering the ceramic filter unit, which was operated at a temperature range from 853 to 1013 K (580 to 740 °C) and at a pressure range from 0.6 to 1.0 MPa. Total exposure time of the two candle filter elements was about 340 hours.

This paper presents measured data and operating experiences of the ceramic filter. The inlet particle loading was in the range of 1–20 g/m³n depending on operating conditions and the properties of the fuels and sorbents. The mass median diameter of particles entering the filter unit was 6–8 µm. The outlet particle concentration was always lower than 5 mg/m³n. The collection efficiency of the studied filters was very high, typically higher than 99.9%. These results indicate clearly that they will meet particle removal requirements of most gas turbines and environmental emission limits.

The permeance of the filter behaved as expected: it first dropped quickly and then seemed to stabilize to a constant level or about 15% of the original permeance of the clean element. The effect of pulse pressure on cleaning of the candles, strength of the filter material and dust penetration into the filter element have also been investigated.