Ceramic Fiber Filter Applications

Flue Gas Filtration Scenarios

A complete exhaust gas filtration system for hot industrial duty has three jobs — dust, acid gas and, where the permit requires it, NOx. This section walks through how a ceramic flue gas purification stage handles each scenario: boilers, kilns and furnaces, combined dust-plus-DeNOx duty, and the comparison with electrostatic precipitators. For the underlying mechanisms, see the hot gas filtration principle. For the full technology overview, start with our flue gas filtration guide.

Boiler Flue Gas Filter Duty

Industrial and biomass boilers produce flue gas at 300–600°C with high alkali and chlorine loading — conditions beyond any fabric media. A ceramic fiber boiler flue gas filter stage sits directly after the economizer and removes dust at >99.9% efficiency without pre-cooling, so the heat stays in the gas for downstream recovery instead of being dumped in a quench tower.

Why fabric fails here first. Coal and biomass flue gas carries alkali salts (K, Na) and chlorine that condense into sticky, corrosive ash. Fabric bags blind as this ash works into the felt, and they burn when spark loads or temperature excursions exceed the 260°C fabric ceiling. The operator then pays twice: once for replacement bags every one to three years, and again for the dilution air or quench that keeps the bags alive — gas volume the ID fan must move and the downstream process must reheat.

What the ceramic stage changes. A rigid ceramic fiber filter tube operates continuously at 600°C with peaks to 1,000°C, so the cooling stage and its fan power disappear from the flowsheet. Because the ceramic body itself is the filtration barrier — not a dust cake on fabric — collection efficiency holds above 99.9% regardless of the cleaning cycle, and outlet dust stays below 5 mg/Nm³. Pulse-jet cleaning at 0.4–0.7 MPa releases the alkali ash as intact sheets; the rigid wall does not flex, so there is no secondary dust plume after each pulse.

Biomass and RDF boilers need one extra discipline: sticky ash management. Keep surface filtration velocity in the 2–5 cm/s band, hold pulse pressure stable, and apply a lime pre-coating at every cold start so the first sticky fraction never touches the ceramic pores. With that discipline we have supplied biomass and waste-to-energy boilers across 7 countries with tube life exceeding 5 years.

Where NOx control is also required, the catalytic grade turns the same vessel into a reactor: dust is captured on the tube surface while NOx is reduced inside the catalytic wall in the 170–300°C window — one vessel instead of a filter plus a separate SCR tower.

→ Sizing starts from your gas volume and temperature profile: see the filter element selection guide, or send us your boiler data for an element count and pressure-drop budget.

Kiln and Furnace Off-Gas Filtration

Cement kiln and glass furnace off-gas is the duty ceramic media was built for: continuous 600°C operation with peak tolerance to 1,000°C, abrasive mineral dust, and spark loads that would burn through fabric in a single campaign. No cyclone and no dilution air are needed ahead of the filter.

The conventional off-gas train — cyclone, cooling, drying, bag filter — exists to protect the fabric, not to clean the gas. Each stage adds pressure drop, footprint and failure modes, and the cooling stage throws away heat that a ceramic system delivers directly to waste heat recovery. In the ceramic train, hot off-gas enters the filter vessel at process temperature, dust is captured on the outside of the rigid tubes at >99.9% efficiency, and clean hot gas leaves for heat recovery with outlet dust below 5 mg/Nm³.

Two reference points from our installed base. On a 2,500 t/d cement clinker line in Shandong, retrofitted in 2019, 120 ceramic tubes replaced failing glass fiber bags and have held particulate emissions below 3 mg/Nm³ for over four years at 850°C continuous operation, with repeated thermal cycling between 400°C and 850°C during kiln start-ups. At the other end of the scale, a 120,000 m³/h float glass furnace line runs 1,500 catalytic elements with combined dedusting and DeNOx in one vessel.

The design variables that decide success in kiln and furnace duty are the same four everywhere: the temperature profile including upset peaks, dust loading in g/Nm³, gas chemistry (especially HF and alkali), and moisture relative to the acid dew point. Thermal shock — not steady temperature — is the real constraint: keep heating and cooling rates below 200°C per minute and the alumina-silicate fiber structure tolerates years of cycling.

→ See how the filtration principle handles the dust cake cycle, or browse measured performance data from operating kilns and furnaces.

Combined Dust and DeNOx in One Vessel

With the catalytic grade, the flue gas filtration system becomes a reactor as well: dust is captured on the tube surface while NOx is reduced inside the catalytic wall, in a 170–300°C window. That removes a separate SCR vessel, its casing and its reheat duty from the flowsheet — one vessel instead of two. Details on the catalyst window, chemistry and poisoning resistance are on the catalytic ceramic fiber filter page.

Ceramic Filtration vs Electrostatic Precipitator

An electrostatic precipitator (ESP) handles high gas temperature, but it struggles with high-resistivity dust, achieves no gas-phase pollutant removal, and demands skilled maintenance of high-voltage internals. Ceramic fiber filtration holds >99.9% collection efficiency regardless of dust resistivity and — in catalytic form — adds DeNOx and dioxin destruction that an ESP cannot offer.

Resistivity is the deciding variable more often than temperature. Dusts with high electrical resistivity — typical of high-alumina ash, cement raw mix and many metallurgical fumes — collect poorly in an ESP because the accumulated layer resists charge dissipation and back-corona forms. A ceramic filter does not care about resistivity at all: capture is mechanical, on the tube surface, at the same efficiency on day one and after every pulse.

Where an ESP already exists, the practical question is usually not replacement but sequence. In conventional trains the ESP sits upstream of SCR and a wet or semi-dry desulfurization stage; an integrated ceramic system collapses that chain into one vessel with dry sorbent injection upstream — no sewage, no SCR catalyst poisoning from dust, and roughly one third of the footprint.

For new lines and retrofits above 260°C, ceramic is usually the smaller, simpler answer. Below that threshold with easy dust and an existing ESP in good condition, keeping the ESP is often the honest recommendation — send us your gas data and we will tell you which side of the line your plant sits on.

→ Compare element-level economics in our ceramic filter vs bag filter analysis, or request a retrofit review for your existing precipitator.