Selection guide

Choosing filter media by dust type: a one-page decision path

Most buyers start with the dust name — “cement dust”, “fly ash”, “wood dust” — and look for the matching bag. That is the wrong end of the problem. The material name tells you what the dust is made of; it does not tell you what will destroy the felt.

Work through these four questions in order. Each one eliminates options, and by the fourth you usually have one or two candidates left.

Step 1: What is the continuous temperature?

Continuous, not peak, and measured at the baghouse inlet rather than at the process. Add 20 °C if your process has frequent excursions you do not log. Media above their continuous rating do not fail gradually; they shrink, embrittle and tear.

Step 2: Is the gas wet, and is it acidic?

This is where most money is lost. Water alone is manageable; water plus acid attacks the fibre and the scrim. Two things to establish: the moisture content, and whether the baghouse inlet temperature sits above the acid dew point.

• Dry and neutral → polyester or aramid, chosen on temperature and abrasion
• Wet, mildly acidic → acrylic, or PPS above 130 °C
• Wet and strongly acidic, or HCl present → PTFE felt, or PPS with PTFE membrane if temperature allows
• Alkaline (cement, lime) → polyester is fine; avoid acrylic

If the inlet is below the acid dew point, no media choice will save you. Raise the gas temperature or insulate the duct — that is a thermal fix, not a filtration one.

Step 3: How abrasive is the dust?

Silica, cement clinker, alumina and metal oxides abrade. So do badly aligned cages and over-tight installations. Abrasion resistance ranking, best first: polyester, aramid, PPS, fibreglass, P84, PTFE. If the dust is aggressive, do not put PTFE at the top of your list regardless of chemistry — fix the cage and consider a heavier felt.

Step 4: Is there an explosion or static risk?

Fine organic dust, coal, grain and some metal powders require conductive media and a grounded cage. Specify anti-static felt with a conductive fibre grid, and confirm the grounding path through the cage and tube sheet. This is a safety requirement, not a performance upgrade.

Dust type to media, as a starting point

Then choose the finish

• Singed — burns off surface fibre, improves dust release, cheap and usually worthwhile
• Calendered — smooth surface, but lower initial collection efficiency than singed
• PTFE membrane — surface filtration from day one; best value on fine ash below 10 µm
• PTFE impregnation — improves acid and moisture resistance without a membrane
• Water and oil repellent — for oily or humid dust that blinds the felt
• Anti-static — mandatory where explosive dust is present

A note on air-to-cloth ratio

Two plants can fit identical media and get completely different life because one runs at 1.4 m/min and the other at 0.8. If your collector was sized for coarse dust and now handles fine ash, velocity is the problem, not the fabric. Lower velocity means a larger collector — or the same collector with more bags, which is sometimes possible.

The cheapest bag is the one you buy once. Compare media on cost per year of service at your real conditions, not on price per piece.