Project Brief
A waste-management company in Southeast Asia enquired about fabric filter bag systems for incinerator gas cleaning at 48 m³/min (2,880 m³/h) continuous duty, with a gas temperature of 900 °C. The enquiry noted the gas could be cooled if the filter required it, and asked us to advise on filter media.
That single line — "can be cooled based on filter limitation" — is the whole project. No filter medium in commercial production survives 900 °C. The engineering question is not which bag to buy; it is how the gas gets from 900 °C to a filterable temperature, and what that cooling method does to the size and cost of everything downstream.
| Parameter | Value |
|---|---|
| Application | Incinerator flue gas cleaning |
| Blower flow rate | 48 m³/min = 2,880 m³/h (at gas conditions) |
| Gas temperature | 900 °C |
| Operation | Continuous |
| Duty | Particulate removal from incinerator gases |
Source: client-supplied design basis.
Why 900 °C Cannot Reach the Bags
Continuous service limits for the media used in this duty:
| Filter medium | Continuous limit | Notes |
|---|---|---|
| PTFE-membrane glass fibre | ≈ 260 °C | Best acid resistance for incineration duty |
| P84 (polyimide) | ≈ 240 °C | Good filtration efficiency, sensitive to hydrolysis |
| PPS (polyphenylene sulphide) | ≈ 190 °C | Degrades under high O₂ with acid gases |
| Polyester | ≈ 150 °C | Not applicable to this duty |
The gap between 900 °C and 260 °C is not a safety margin question. It is a design requirement for a dedicated cooling stage.
Source: standard published continuous-service limits for these media. Confirm against the selected manufacturer's datasheet before purchase.
Choosing the Cooling Method — This Decides the Project Cost
Option A — Dilution with ambient air (usually the wrong answer)
Mixing in cool ambient air is the simplest method and the most expensive one to live with. A heat balance from 900 °C to 180 °C with ambient air at 30 °C requires roughly 13,800 m³/h of dilution air — bringing total volume to about 16,700 m³/h.
Because the baghouse is sized on volumetric flow, that inflates the filter roughly six-fold against the cooled-gas alternative, and inflates the fan, ducting and building along with it. Dilution suits small intermittent sources, not continuous incineration duty.
Option B — Evaporative quench (selected)
Water sprayed into a quench chamber absorbs heat as it evaporates. Volume still rises, but far less than with dilution because the cooling comes from latent heat rather than mass dilution. For a continuous 2,880 m³/h incinerator stream this is the conventional choice.
Option C — Heat exchanger / waste-heat recovery
Technically the most efficient, and it returns useful energy. It carries the highest capital cost and needs a use for the recovered heat. At this flow rate the payback rarely justifies it unless a heat sink already exists on site.
Two Temperature Limits That Bracket the Design
Upper bracket — dioxin re-formation
Chlorinated organics re-form in the 200–400 °C window through de novo synthesis as flue gas cools. The design intent is therefore to pass through that band quickly. A slow cooling profile — an oversized duct run, an undersized quench — increases residence time in exactly the temperature range you least want it.
Lower bracket — acid dew point
Incinerator gas carries HCl and SOₓ, which raise the acid dew point well above the water dew point. Operate below it and condensing acid attacks the bags, the casing and the hopper, while wet dust blinds the fabric. Operating temperature must sit a clear margin above the acid dew point.
These two limits leave a working window, and 180 °C sits inside it: below dioxin re-formation, comfortably above acid dew point, and inside the continuous rating of PTFE-membrane glass fibre.
Source: standard incineration flue-gas treatment engineering practice. Actual acid dew point depends on measured HCl/SO₃ and moisture content and should be established from a gas analysis.
Sizing the Baghouse at 180 °C
| Step | Calculation | Result |
|---|---|---|
| Gas volume at 900 °C | Client basis | 2,880 m³/h |
| Volume after cooling to 180 °C | 2,880 × (453 K ÷ 1,173 K) | ≈ 1,110 m³/h |
| Plus quench water vapour | + ~20% | ≈ 1,330 m³/h |
| Air-to-cloth ratio (pulse-jet, incineration duty) | Conservative 0.8 m/min | — |
| Filter area required | (1,330 ÷ 60) ÷ 0.8 | ≈ 28 m² |
Note what cooling did: the gas contracts to roughly 40% of its 900 °C volume simply by cooling, before any other consideration. Sizing a baghouse on uncooled volume — or on dilution-cooled volume — produces a filter several times larger than the duty needs.
Source: HydroPure design calculation. Air-to-cloth ratio is deliberately conservative for incineration duty; vapour addition depends on the final quench design.
Media Recommendation
PTFE-membrane glass fibre for this duty. Glass fibre carries the temperature, and the PTFE membrane provides surface filtration — dust releases from the membrane rather than embedding in the fabric, which matters when the dust is sticky and acidic. The membrane also holds emission performance stable over the bag's life instead of relying on a dust cake that repeatedly builds and is cleaned away.
Equipment
- ZSDM Pulse-Jet Bag Dust Collector — the filtration stage.
- Flue Gas Desulfurization Scrubber — where measured HCl/SOₓ requires acid-gas removal ahead of or after the filter.
The choice between fabric filtration and electrostatic precipitation for this class of duty is examined in our baghouse vs electrostatic precipitator comparison, and pulse-jet cleaning optimisation in our pulse-jet dust collector guide.
Frequently Asked Questions
Can any filter bag handle 900 °C flue gas?
No. The highest continuous rating among media used in this duty is around 260 °C (PTFE-membrane glass fibre). Gas at 900 °C must be cooled before filtration — the cooling stage is part of the system, not an optional extra.
Should I cool incinerator gas with dilution air or a quench?
For continuous duty, a quench. Dilution to 180 °C at this flow rate would add roughly 13,800 m³/h of air and inflate the baghouse, fan and ducting several-fold, because filter size follows volumetric flow. Dilution suits small intermittent sources only.
What temperature should an incinerator baghouse operate at?
In the window between the acid dew point (below which condensing acid corrodes and blinds the bags) and the 200–400 °C dioxin re-formation band. Around 180 °C typically satisfies both, but the actual acid dew point depends on measured HCl, SO₃ and moisture and should be confirmed by gas analysis.
How much filter area does 48 m³/min of incinerator gas need?
Approximately 28 m² — but only after cooling. At 900 °C the stream is 2,880 m³/h; cooled to 180 °C it contracts to roughly 1,110 m³/h, about 1,330 m³/h with quench vapour. At a conservative 0.8 m/min air-to-cloth ratio that gives ~28 m². Sizing on the uncooled volume would oversize the filter by more than double.
Why PTFE membrane rather than plain fabric?
Surface filtration. Dust releases from the membrane instead of embedding in the fabric, which matters with sticky, acidic incinerator dust, and emission performance stays stable over the bag's life rather than depending on a dust cake that is repeatedly built and cleaned off.
