P84 Bag Filter (Polyimide)
Trilobal Fibre, Acid-Alkali Resistance and 240 °C Continuous Operation
The P84 bag filter is a needle-punched felt dust filter that holds fine dust at the surface with its trilobal polyimide fibre structure, operates continuously up to 240 °C and resists acids and alkalis.
500 g/m²
2.55 mm
240 °C
260 °C
What Is a Polyimide (P84) Bag Filter?
P84 is a high-performance yellow polyimide fibre synthesised from biphthalic anhydride and p-phenylenediamine and recognised by its trilobal (three-lobed) fibre cross-section. Thanks to the distinctive geometry of the fibre cross-section, P84 bag filters, made by the needle-punched felt method, create far more surface area than round-section fibres of the same weight. This structure holds fine dust particles at the filter surface; it works on the surface filtration principle rather than depth filtration.
P84’s most important advantages over glass fibre are its superior flex abrasion resistance and acid-alkali chemical compatibility (pH 2–12). P84 is the preferred choice in processes with high mechanical vibration, lime kilns and waste incineration plants, where glass fibre falls short because of its low flex resistance. However, its hydrolysis resistance is moderate; this should be taken into account in processes with high humidity and water vapour.
Product Identity and Technical Summary
Key Technical and Structural Features
- Fibre Type
- Polyimide (P84) — Trilobal Needle-Punched Felt
- Fabric Structure
- Needle-Punched Felt
- Weight
- 500 g/m²
- Thickness
- 2.55 mm
- Air Permeability
- 190 L/dm²·min @ 200 Pa
- Continuous Operating Temperature
- 240 °C (Dry)
- Peak (Surge) Temperature
- 260 °C (Dry)
- Chemical Resistance
- Compatible with acids and alkalis (pH 2–12); PTFE is recommended for strong alkalis at pH > 12; moderate hydrolysis resistance
- Surface Treatment Options
- Singeing & Calendering
- PTFE Coating
- ePTFE Membrane Lamination
- Antistatic Treatment
- Emission Performance
- ≤ 5 mg/Nm³ with ePTFE membrane
- Cleaning System Compatibility
- Pulse-Jet
- Reverse Air
- Shaker
- Service Life
- > 4,000 hours
Filtration Architecture and Working Principle
P84 bag filters pass dirty flue gas or dust-laden industrial air from the inside of the bag to the outside in a two-stage treatment process. The large surface area provided by the trilobal fibre structure makes surface retention easier and increases the effectiveness of the cleaning cycle.
Filtration takes place inside-out. Dust-laden gas fills the bag; particles are retained on the surface of the trilobal fibres and in the felt structure, and the cleaned gas passes out through the fibre structure and leaves the system. P84’s trilobal fibre cross-section creates far more micro-pores than smooth round-section fibres, holding dust particles at the surface; the dust cake does not penetrate into the depth and separates easily during the cleaning cycle.
Particle Capture at High Temperature
Thanks to up to 80% additional surface area, retention efficiency for fine particles increases and the risk of media blinding is minimised.
Low Differential Pressure and Stable Airflow
The smooth inner surface of the ePTFE membrane makes it easier for the dust cake to separate; differential pressure stays low and stable, reducing energy consumption and the risk of early bag replacement.
Advantages of the Polyimide (P84) Bag Filter
- Trilobal Fibre Structure
- The three-lobed fibre cross-section creates up to 80% more surface area than round fibres of the same weight, increasing retention efficiency for fine particles.
- High Temperature Resistance
- Withstands 240 °C continuously and 260 °C peaks; works reliably in high-temperature processes where organic polymers are limited.
- Superior Flex Abrasion Resistance
- Unlike the brittle structure of glass fibre, P84 felt shows high flex resistance through repeated pulse-jet cleaning cycles.
- Acid and Alkali Resistance
- Compatible with acids and alkalis in the pH 2–12 range; for strong alkalis at pH > 12, PTFE bags should be chosen.
- Low Differential Pressure
- Low ΔP profile thanks to the large surface area and surface retention; energy consumption and fan load are reduced.
- Fire Resistance
- P84 fibre is inherently non-flammable and does not melt; it provides safe filtration in processes with a risk of sparks or flames.
- ePTFE Membrane Compatible
- Emission values of ≤ 5 mg/Nm³ with an ePTFE membrane surface treatment; fine particles including PM2.5 are retained effectively.
- Long Service Life
- Low risk of media blinding thanks to high flex resistance and surface dust retention; service life of more than 4,000 hours.
- Sub-Micron and Fly Ash Capture
- Thanks to its trilobal fibre density, it captures sub-micron fly ash and heavy metal particles at PM2.5 level with high efficiency.
P84 Bag Filter Surface Treatment Options
| Surface Finish | Property | Recommended Application |
|---|---|---|
| Calendering | Smooths the surface, improves dust release and ensures compatibility with pulse-jet cleaning systems. | General industrial applications and cement plants |
| Singeing | Smooths the surface by singeing the surface fibres; reduces dust re-entraining from the filter surface into the flow. | Processes with a high dust load, lime and gypsum plants |
| Water and Oil Repellent | Reduces particle adhesion in flue gases containing moisture and oil, helping the filter surface clean more easily. | Waste incineration and chemical process applications |
| ePTFE Membrane | Provides surface filtration, ≤ 5 mg/Nm³ emission performance and high dust release performance. | All applications requiring strict emission limits |
Engineer's Note
- Senior Process Engineer
- 15+ Years of Field Experience
- Field-Test Approved
The most common problem we see in the field with polyimide P84 bag filters is hydrolysis and acid condensation caused by the flue gas temperature falling below the acid dew point. Although P84 fibre delivers exceptional dust retention efficiency with its unique trilobal (three-lobed) cross-section, fibre strength weakens quickly and there is a risk of tearing when moisture and SOx compounds in the gas stream condense.
When should it be chosen?
In cement rotary kilns, lime kilns, waste incineration plants and asphalt plants operating in the 190 °C to 240 °C continuous temperature range, it delivers top performance in capturing fine, volatile, hard-to-retain micronised dust thanks to its high surface area advantage.
When should it not be chosen?
On corrosive lines with high humidity where the temperature frequently drops below the dew point (hydrolysis hazard) and in strong alkaline environments at pH > 12, PTFE bags should be chosen; at peak temperatures above 260 °C, glass fibre bags with an ePTFE membrane should be chosen.
Application and Selection Criteria
- Bag and Cage Fit
- The bag diameter and length must match the cage dimensions exactly; a loose bag rubs against the cage and wears during pulse-jet pulses, and a tight bag will not fit the cage.
- Dew Point Control
- Keep the flue gas temperature above the acid dew point with a safe margin; condensation increases the risk of hydrolysis and blinding in P84 felt.
- Chemical and Thermal Resistance
- The 240 °C continuous and 260 °C peak temperature limits must not be exceeded; for gases containing HF or strong alkalis at pH > 12, consider the PTFE alternative.
Collar Types
In dust filters, a safe, leak-tight connection of the bag to the system starts with choosing the right collar. Four collar types (snap band, snap ring, flange top and plain top) can be selected according to the tube sheet design of your filter housing and the cleaning system. If you are not sure which collar type fits your filter housing, send us a sample or photo and we will make an exact replica.
Snap Ring (Steel Ring)
Galvanised or stainless steel ring. Seats the bag firmly and leak-tight in the tube sheet.
Flange Top (Flanged Collar)
The felt flanged collar is compressed between the tube sheet and the cage to provide a seal.
Plain Top
Has no ring; suitable for systems with clamps or special clamping devices.
Snap Band
The flexible steel band clicks into its seat. Allows fast change-outs.
Performance Parameters
The field performance of P84 (polyimide) bag filters is assessed on the large filtration surface area offered by the trilobal fibre geometry, high dust-holding capacity at low differential pressure and superior flex abrasion resistance under intensive pulse-jet cleaning cycles.
- Emission Value
- Standard P84 felt media provide high dust retention efficiency. With an ePTFE membrane surface treatment, emission values of ≤ 5 mg/Nm³ are achieved for fine particles including PM2.5, meeting the requirements of strict environmental legislation.
- Service Life
- High flex abrasion resistance and surface dust retention keep the risk of media blinding low. With the right surface treatment and controlled operating conditions, a service life of more than 4,000 hours is expected. Service life may be shorter in high-humidity environments with a risk of hydrolysis.
- Differential Pressure
- The large surface area and surface dust retention provided by the trilobal fibre structure stop the dust cake from penetrating into the depth of the felt. After the cleaning cycle, differential pressure returns close to its initial value, so system fan load and energy consumption stay stable.
Industry Applications
Bag filters suited to different process needs are used across a wide range of industrial applications to protect product quality and production continuity.
01
Vegetable Oil
Clarity, purity and shelf life in vegetable oil and refining.
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02
Pipe and Profile
Cooling water filtration in pipe and profile extrusion.
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03
Paint Industry
Surface quality and pigment filtration in the paint industry.
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04
Glass Industry
Furnace and process filtration in the glass industry.
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05
Dialysis Centers
Water preparation and process filtration in dialysis centers.
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06
Foundry Industry
Equipment protection and dust filtration in foundries.
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07
Industrial Oil
Filtration in industrial oil production and recovery.
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08
Energy and Biogas
Maximum efficiency and turbine protection in energy and biogas.
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09
Recycling
Filtration for efficiency and environmental compliance in recycling.
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10
Food and Beverage
Hygienic filtration in food and beverage.
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11
Pharmaceuticals and Biotechnology
GMP-compliant sterile filtration in pharmaceuticals and biotechnology.
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12
Paper and Packaging
Process water filtration in paper and packaging.
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13
Chemical Industry
Corrosion-resistant, safe filtration in the chemical industry.
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14
Cosmetics
Microbiological safety and precision filtration in cosmetics.
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15
Machinery
Precision and technical filtration in the machinery industry.
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16
Printing and Ink
Flawless color and print quality in printing and ink.
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17
Metal and Surface Treatment
Flawless surfaces and bath stability in metal and surface treatment.
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18
Forest Products
Resin and glue filtration in forest products and furniture.
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19
Automotive
Precision process filtration for zero defects in automotive manufacturing.
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20
Oil and Petrochemicals
Equipment protection and process safety in oil and petrochemicals.
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21
Plastic Packaging
Precision process filtration and raw material purity in plastic packaging.
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22
Plastic Injection Molding
Cooling and hydraulic filtration in plastic injection molding.
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23
Water and Environment
Recovery filtration in water and environmental technologies.
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24
Shipyards and Marine
Operational safety and efficiency in shipyards and marine.
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Filter Selection Technical Checklist
The wrong filter choice means early blinding, punctured bags and unplanned downtime. Choosing the most suitable P84 bag filter for your plant requires eight critical parameters to be considered together, from flue gas temperature to chemical composition and from moisture risk to emission limits. The checklist below is designed to help you make a fast, reliable choice on site and in technical discussions.
- Gas Temperature
- Ideal for 240 °C continuous; for temperatures above 260 °C, glass fibre bag filters (with ePTFE membrane) should be considered.
- Chemical Environment
- Compatible with acids and alkalis in the pH 2–12 range; for strong alkalis at pH > 12, PTFE bags should be chosen. Not suitable for gases containing HF.
- Humidity / Water Vapour
- Moderate moisture tolerance; with continuous high humidity and a risk of condensation, PPS or PTFE should be chosen.
- Mechanical Vibration
- Outperforms glass fibre in intensive pulse-jet cleaning systems thanks to its high flex abrasion resistance.
- Emission Limit
- ≤ 5 mg/Nm³ with an ePTFE membrane; fine particles including PM2.5 are retained effectively.
- Cleaning System
- It is compatible with pulse-jet, reverse-air and shaker systems.
- Alkaline Environment
- Works reliably up to pH 12 with alkaline flue gas components (lime, calcium) where glass fibre falls short; for strong alkalis at pH > 12, PTFE bags should be chosen.
- Fire Risk
- P84 is non-combustible; a safe choice for processes with a risk of flames.
Points to Watch During Use
- Operating Temperature Limit
- Flue gas temperature must not exceed the 240 °C continuous and 260 °C peak limits; temperature monitoring is mandatory.
- Hydrolysis Risk Assessment
- In processes with high humidity and water vapour, assess the risk of hydrolysis before commissioning and, if necessary, choose a water- and oil-repellent surface treatment.
- Initial Conditioning
- Use moisture-proof packaging in storage; condition bags that have absorbed moisture with dry, hot air before putting them into service.
- Pulse-Jet Cleaning Pressure
- Keep the pulse-jet cleaning pressure within the recommended range; excessive pressure can damage the felt structure.
- Mechanical Protection & Installation
- Protect bags from sharp bends and impact damage during installation.
- Chemical Compatibility & HF Warning
- P84 must not be used in applications containing hydrofluoric acid (HF).
- Gradual Start-Up
- At first start-up, raise the flue gas temperature gradually and avoid sudden thermal shock.
- Cage and Support Check
- Check the filter cage when changing bags; a deformed or rusted cage can cause early failure of the new bag.
Alternative media for the same application
Polyimide P84 Bag Filter
Your Questions Answered
Frequently Asked Questions
At Prosestim, we are committed to answering your questions and providing technical support for our filtration solutions.
What is a P84 bag filter?
P84 is a high-performance polyimide filtration medium made with a trilobal fibre cross-section. With its needle-punched felt structure, it withstands a continuous operating temperature of 240 °C, and its large surface area holds fine dust particles at the surface for high efficiency at low differential pressure.
Why choose P84 instead of glass fibre?
P84 has two main advantages over glass fibre: superior flex abrasion resistance and wide chemical compatibility (pH 2–12). In processes with high mechanical vibration where the brittle structure of glass fibre falls short, and in flue gases containing alkaline components, P84 offers a clear service life advantage.
What is the operating temperature limit?
P84 bag filters withstand 240 °C continuously and 260 °C peaks. For temperatures above 260 °C, glass fibre bag filters (with ePTFE membrane) should be considered.
Can it be used in high-humidity processes?
Care is needed. P84’s hydrolysis resistance is moderate; in processes with continuous high humidity and a risk of condensation, PPS or PTFE fibre media should be chosen.
What does trilobal fibre structure mean?
The cross-section of P84 fibre has a three-lobed (trilobal) geometry. This structure creates up to 80% more surface area than round-section fibres of the same weight and linear density, increasing retention efficiency for fine dust particles.
Can it be used with gases containing HF?
No. P84 is not resistant to hydrofluoric acid (HF); PTFE fibre media should be chosen for these applications.
What emission value is achieved with an ePTFE membrane?
With an ePTFE membrane surface treatment, emission values of ≤ 5 mg/Nm³ are achieved for fine particles including PM2.5.
What is the main difference between P84 and PPS?
P84 offers higher temperature resistance (240 °C vs 190 °C) and wider chemical compatibility, but its hydrolysis resistance is lower than that of PPS. PPS is preferred in processes with high humidity and water vapour, while P84 stands out in dry, hot applications above 200 °C.
Do you manufacture custom sizes?
Yes, custom production is available in non-standard diameter, length and surface treatment combinations.
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