Phosphogypsum Filter Cloth for Horizontal Vacuum Belt Filters
Phosphogypsum is the by-product gypsum of wet-process phosphoric acid (WPPA) plants. On modern acid plants it is typically dewatered on rubber-belt horizontal vacuum belt filters, and the filter cloth is a consumable endless belt.
HVBFcloth accepts inquiries for replacement horizontal vacuum belt filter cloth.
What phosphogypsum is, and where the cloth sits
Phosphogypsum is the calcium sulphate by-product of wet-process phosphoric acid production: phosphate rock is attacked with sulphuric acid, and gypsum drops out of the reaction while the acid goes forward. Gypsum is the bulk by-product of the route, not a side stream, so the filter is not a polishing step at the end of the plant — it is in the main production line, and when the belt stops the acid plant slows down with it.
The filter has two jobs at once. It has to separate the gypsum from the acid, and it has to wash the soluble P2O5 out of the cake so the product yield is not thrown onto the stack. Those two jobs pull the cloth specification in different directions, which is why the wash stage matters as much as the filtration stage when a belt is selected.
The cloth itself is a consumable. It is an endless belt running on the grooved rubber transporter, and it is replaced on a cycle set by your duty rather than by a catalogue.
Different origin — an acid plant rather than a scrubber — and different chemistry: fluoride-bearing on this side, chloride-bearing on the FGD side. They are separate duties and, in practice, separate belts.
Phosphogypsum vs FGD gypsum →Process flow across the belt
- 01 Slurry Feed Gypsum slurry from the acid reactor / filtration circuit is distributed onto the moving cloth.
- 02 Filtration Vacuum pulls mother liquor through the cloth; the gypsum cake builds on the surface.
- 03 Washing Counter-current wash stages recover soluble P2O5 from the cake.
- 04 Dewatering A final dry-vacuum zone pulls residual moisture out of the washed cake.
- 05 Cake Discharge Cake releases at the discharge roller; the cloth is washed and returns to the feed end.
Operating values for each stage — slurry temperature, pH, particle size, solids, cake moisture — are plant-specific. We do not publish typical figures for them; they go on the confirmation list below instead.
What makes this duty hard on a belt
The chemistry is acidic and fluoride-bearing because the gypsum comes out of an acid process. Polymer and finish have to be chosen against that, and the temperature and chemical window is confirmed in writing for your duty rather than published as a general figure.
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Blinding and poor wash
Free area closes progressively as fines and scale lodge in the fabric; wash water starts to channel instead of displacing liquor.
Cloth implication: Weave geometry and surface finish decide how fast the fabric closes and how much of it washes back.
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Tracking and wrinkling
The belt wanders on the grooved rubber transporter, touches the edge guides, and the vacuum seal starts leaking.
Cloth implication: Fabricated length, seam squareness and edge treatment all feed into whether a belt tracks.
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Seam and joint leakage
A clipper or PAD joint opens up, vacuum drops as the joint passes the box, and the cake wets back.
Cloth implication: Seam type is a specification to be decided, not a detail to be left to the shop.
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Short life at the edges
The cloth fails at the edge or frays out while the body of the belt is still serviceable.
Cloth implication: Edge treatment and the condition of the machine edge seal have to be assessed together.
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Cake sticking at discharge
Cake does not release cleanly at the discharge roller and carry-over builds up on the return run.
Cloth implication: Surface finish and calendering change release behaviour.
These are the difficulties common to horizontal vacuum belt duty. How severe each one is on your machine depends on numbers we do not have yet — which is what the confirmation list is for.
The machines this duty actually runs on
Rubber-belt horizontal vacuum belt filters are the dominant route on modern acid plants. The families below are machine families you can enquire about for phosphate and fertilizer service.
| OEM family | Industries listed | Next step |
|---|---|---|
| ANDRITZ Delkor | Mining, fertilizer | Send brand + model |
| FLSmidth EIMCO Extractor | FGD, minerals | Send brand + model |
| TAKRAF DELKOR HBF | Phosphate, iron, coal | Send brand + model |
| HASLER Filtres Philippe | Fertilizer, hydrometallurgy | Send brand + model |
| EKCP EIMCO-KCP | FGD and phosphate (India) | Send brand + model |
Some acid plants still run pan or tilting-pan filters. If your plant uses a pan filter, this belt page does not apply to you — tell us your machine and we will say honestly whether we can help.
OEM names above are used only to identify the machine a cloth has to fit.
How the cloth is specified for this duty
Selection runs backwards from the slurry. The chemistry and temperature of the liquor narrow the polymer; the particle size distribution and the wash requirement narrow the weave and the surface finish; the machine narrows the fabricated dimensions, the seam and the edge treatment. The candidate polymers for horizontal vacuum belt duty are PET monofilament, PET mono/multifilament combinations, polypropylene, double- and multi-layer weave constructions, and hydrolysis- or alkali-resistant specialities.
We are not going to tell you on a web page which of those your phosphogypsum belt should be. That decision belongs to your liquor chemistry, your wash configuration and your machine — and getting it from a published table instead of from your data is how plants end up with a belt that filters well and washes badly.
Specification status
Our own values are not yet confirmed in writing. Each parameter is fixed against your machine and slurry during the engineering review, and it is stated in the quotation — not inferred from this page.
| Parameter | Value | Unit | How it is fixed |
|---|---|---|---|
| Polymer | Confirmed per enquiry | — | Confirmed against slurry chemistry |
| Weave / construction | Confirmed per enquiry | — | Confirmed against duty and machine |
| Air permeability | Confirmed per enquiry | L/dm²/min | Test method and test pressure will be stated with the value, once the mill confirms them in writing |
| Fabric weight | Confirmed per enquiry | g/m² | Reported with the value, once confirmed in writing |
| Seam type | Confirmed per enquiry | — | Confirmed against machine and seam photo |
| Edge treatment | Confirmed per enquiry | — | Confirmed against machine edge seal |
| Max fabricated width | Confirmed per enquiry | mm | Confirmed against loom and machine width |
| Continuous temperature limit | Confirmed per enquiry | °C | Confirmed per polymer and finish |
| Chemical limit (acid / fluoride) | Confirmed per enquiry | — | Confirmed per polymer and finish |
Industry reference — not our specification
| Parameter | Industry reference | Unit | Source |
|---|---|---|---|
| Belt width range seen on this machine family | up to 4500–4800 | mm | Equipment-family observation, third-party machines |
This row describes the machine population, not what we can weave. Our own width limit is not yet confirmed in writing.
What we can build for this duty
Our own values are not yet confirmed in writing, and we will not fill them in with industry averages. This section sets out the options this cloth is built from, what each one changes, and which piece of your data decides it. Nothing below is a specification — it is the shape of the decision.
Cloth form An endless belt running on the grooved rubber transporter.
Recommended material direction
The liquor is acidic and fluoride-bearing because the gypsum leaves an acid process. That points the polymer decision at acid resistance and at what the cleaning cycle does — not at the alkaline hydrolysis problem that governs the caustic duties elsewhere on this site.
This narrows the field; it does not pick. Which polymer goes on your machine is settled against your measured numbers and not on a web page — the same position the selection section above takes. What follows is the reasoning behind that position, not a departure from it.
- Polyester (PET) PET
Continuous reference up to ~150 °C — a published property of the polymer, not a value of ours
- Acid Good
- Alkali Limited
- Hydrolysis Limited
- Abrasion Excellent
Acid is not polyester's weak side, and it carries the abrasion resistance and the dimensional stability under tension that make it the reference polymer for belt duties. Its published weakness — alkaline hydrolysis — is a question about your cleaning chemistry here, not about the process liquor.
- Polypropylene PP
Continuous reference up to ~90 °C — a published property of the polymer, not a value of ours
- Acid Excellent
- Alkali Excellent
- Hydrolysis Excellent
- Abrasion Good
Comfortable at both ends of the pH scale, so the acid itself is not the constraint. Temperature is. It also creeps under sustained load, which is a real consideration on a long tensioned belt.
- Polyvinylidene fluoride (PVDF) PVDF
Continuous reference ~120°C continuous / short excursions to ~140°C — a published property of the polymer, not a value of ours
- Acid Excellent
- Alkali Moderate
- Hydrolysis Excellent
- Abrasion Good
A direction rather than a default. Halogen-bearing and strongly oxidising liquors are where a fluoropolymer earns its cost step over PET and PP, and a fluoride-bearing acid is the kind of duty that raises the question.
- PA Acid attacks polyamide. Its abrasion resistance is excellent and that does not help it here.
What actually decides it Your operating pH and your cleaning pH — they are often different, and the cleaning one is frequently the one that decides the polymer. Then the normal and peak liquor temperature, read against the polypropylene ceiling above.
Everything in this block is reasoning from published polymer behaviour applied to the chemistry described further up this page. It is a direction, not a selection — and the selection is made against your measured numbers during the engineering review, then written into the quotation. The full polymer envelope is on the materials page.
Weave options
Two jobs pull in different directions on this duty. The belt has to separate the gypsum from the acid, and it has to wash soluble P2O5 out of the cake. Filtration wants retention; washing wants a structure that displaces liquor instead of channelling through it.
- Double layer / multi-layer Two or more interlaced fabric layers woven as one. A fine filtering face carried on a coarse structural back — high strength with fine retention, and drainage channels inside the fabric. Watch: Thicker and heavier; more expensive to weave. The usual answer on heavy belt duties.
- Twill The crossing point steps sideways each pick, giving a diagonal rib. More flexible and more permeable than plain at the same yarn count, with better cake release. Watch: Slightly less dimensionally stable than plain.
- Plain One over, one under. The most stable and the most rigid. Tight, uniform pores; lower permeability for a given yarn. Watch: Least forgiving of dimensional movement; can blind faster on fine solids.
A fine filtering face carried on a coarse structural back is the usual answer on heavy belt duties, because it delivers retention and strength without closing the drainage path inside the fabric.
Yarn form. Monofilament releases cake and washes back best; multifilament retains finer solids but holds more of them inside the yarn bundle. Mono-and-multi combinations are common on belt filters carrying a wide particle distribution.
Yarn form, weave and surface finish are settled as one decision. Standard woven options are monofilament, multifilament and mono+multi combination; staple / spun yarn is evaluated under engineering review.
Permeability considerations
Air permeability is the figure everyone compares and the easiest one to quote meaninglessly. It is measured per ISO 9237 at a stated pressure drop — often 200 Pa — or per ASTM D737 (Frazier). A value with no stated pressure and no stated unit is not comparable to anything, including ours. The same applies to a pore or retention rating: on a woven cloth that is a nominal figure and not an absolute cut-off, because woven media do not have a single pore size and the cake quickly becomes the real filter.
On this duty the as-new figure is only the starting point. What decides the belt is how much of it comes back after the wash, and that is a weave and surface-finish question before it is a number.
How each property is measured, and what to ask any supplier for alongside the number, is set out on the testing and inspection page. Naming the method is a fact about a public standard, not an assertion of completed mill testing.
Joint options
- Clipper (metal hook) Interlocking metal hooks crimped onto both cloth ends, joined by a pintle wire. Fitted and replaced on the machine without dismantling it. The fastest change-out. Watch: The joint is a discontinuity: it leaks vacuum as it passes the box, and it is where most belt failures start. Hook material has to suit the liquor.
- PAD / welded overlap The two ends are overlapped and thermally fused. A smoother, quieter joint that seals better than a clipper and carries load more evenly. Watch: Made off the machine or with a portable press; a change-out takes longer.
- Spiral Spiral coils on each end interlaced and pinned. Flexible, drains through the joint, distributes load along the full width. Watch: Adds an open line across the belt — not appropriate where the joint must seal.
The machine usually dictates which construction it is set up for, so this decision starts with a close-up photograph of the joint you run now, both faces. In an acid, fluoride-bearing liquor the hook material of a clipper joint is a chemical decision as much as a mechanical one.
The four constructions drawn in cross-section: how joints fail and what each one costs you.
Edge treatment
- Cut and sealed The cut edge is thermally sealed against fraying. The baseline. Adequate where the machine edge seal is in good condition.
- Folded / hemmed The selvedge is folded back and secured. Adds thickness and stiffness at the edge where the seal rubs.
- Reinforced edge band A separate band is bonded along the selvedge. For machines that chew edges — the usual answer when a belt keeps failing at the edge while its body is sound.
- Coated / sealed band A polymer band is applied to the edge. Seals the edge against vacuum bypass as well as protecting it mechanically.
- Guide strip / tracking profile A profile bonded to the underside to run in the machine guide. Only where the machine is built for it. Fitting one to a machine that is not is a common and expensive mistake.
A belt that fails at the edge while its body is still sound is an edge-treatment question, not a fabric question. Which of these applies is settled from photographs of both edges of the old cloth and of the machine edge seal.
Edge constructions drawn in cross-section: how vacuum belt edges wear and what each treatment addresses.
Relevant equipment
A filter belt is decided at the loom before it is decided anywhere else: what a weaving platform can hold — pick density, tension, width — sets what the finished cloth can be asked to do.
On a belt this wide the pick density has to hold right across the web. An out-of-square or unevenly tensioned belt is a tracking fault before it is anything else.
The eleven process stations from yarn to crate and the nine laboratory checks: manufacturing.
Factory capability for this duty
The rows below are the part of our capability envelope that this duty touches. The last group is the one that makes the rest of it worth reading — a supplier who can do everything has told you nothing.
Machine families
- Rubber-belt horizontal vacuum belt filter Confirmed per enquiry
Core family. Endless belt with clipper, PAD or spiral joint and a finished edge.
What decides it Brand and model, measured width and developed length, a photograph of the joint.
- Indexing / tray vacuum filters Not offered
Different cloth mechanics. We will tell you so rather than sell you a belt that does not fit.
Fabrication
- Clipper, PAD / welded and spiral joints Confirmed per enquiry
Matched to the construction your machine is already set up for.
What decides it A close-up photograph of the existing joint, both faces.
- Edge: cut and sealed, hemmed, reinforced band, coated band Confirmed per enquiry
The usual answer when a belt keeps failing at the edge while its body is still sound.
What decides it Photographs of both edges and of the machine edge seal.
What we do not do
- OEM spare parts Not offered
Independent replacement cloth — not an OEM spare part. Dimensions and construction are confirmed per enquiry.
The full envelope, including the machine families and services we decline: what we build to order and what we will not take on. Fifteen pages on how a specification like this is built and read: the filter cloth specification guide.
How phosphogypsum belts come off the machine
A failed belt is usually three-way: something in the cloth, something in the machine, and something in the process. Diagnosing it as purely a cloth problem is the fastest way to buy the same failure twice.
Belt tracking and wrinkling
Often machine-side (roller alignment, edge guides) before it is cloth-side.
Diagnose this →Seam / joint failure
Cloth-side and fabrication-side: seam type, squareness, and how the joint was closed on site.
Diagnose this →Cloth blinding
Process-side (fines, scaling, wash balance) interacting with weave choice.
Diagnose this →Poor cake release
Cloth surface and discharge geometry together; rarely one or the other alone.
Diagnose this →Cloth life on a horizontal vacuum belt filter is duty-specific. Published third-party cases run from weeks to months depending on slurry and machine condition, and we do not quote a life figure before seeing your duty. Anyone who promises you a number of months without asking what you filter is selling, not engineering.
Measuring the old belt and photographing where it failed is the first step in telling the three causes apart. How to measure your old belt →
What we need from you to quote
Gather this before you fill in the engineering RFQ form; anything the form has no field for goes in the Message box. Nothing on it is optional because we like paperwork; each item removes a guess from the specification.
| What to confirm | How to get it |
|---|---|
| Machine brand and model | Copy it off the machine nameplate. “Unknown” is an acceptable answer. |
| Belt width | Measure the old cloth across the web, not the rubber transporter. |
| Belt length (circumference) | Measure the endless loop, or give us the machine centre distances. |
| Seam type in use now | Photograph the joint close up — clipper, PAD, or spiral. |
| Photos of the old cloth | Face and back, plus wherever it failed. This is the single most useful thing you can send. |
| What failed | Life, blinding, tracking, seam leak, or cake release. Compare against the failure modes above. |
| Slurry temperature and pH | From the process sheet or a recent lab analysis. |
| Duty context | Throughput, number of wash stages, and whether the machine has been rebuilt. |
Before you enquire
What information do you need to quote a phosphogypsum belt filter cloth?
Machine brand and model, belt width and length, the seam type you run now, photographs of the old cloth and its joint, what failed, and the slurry temperature and pH. If you have all of that, a quotation is straightforward. If you have only some of it, send what you have — we will tell you which missing item actually blocks the quote and which one we can work around.
Get an engineering quote for phosphogypsum duty
Three steps after you submit: an engineer checks what you sent against the machine, we come back for anything missing, and you get a quotation or a sample plan.
We quote per RFQ. No online checkout.
Sample availability, size, freight and lead time are confirmed per request.
Where to go next
HVBF Filter Cloth
The cloth family this duty uses: weave, polymer, seam, edge and width options.
FGD Gypsum Dewatering
A different duty, not a variant of this one — scrubber origin, chloride chemistry.
Phosphogypsum vs FGD Gypsum
The two duties side by side, and why one belt does not cover both.
HVBF Machine List
OEM families you can enquire about, and what we need from each machine.