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 fabricated to the machine's dimensions.
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 fabricated to your machine's width and circumference, 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 We do not publish typical figures for them; they go on the confirmation list below instead.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 the ones observed in phosphate and fertilizer service; the evidence level is stated as we found it, not upgraded.
| OEM family | Industries observed | Evidence level | Next step |
|---|---|---|---|
| ANDRITZ Delkor | Mining, fertilizer | OBSERVED | Send brand + model |
| FLSmidth EIMCO Extractor | FGD, minerals | OBSERVED (trade press) | Send brand + model |
| TAKRAF DELKOR HBF | Phosphate, iron, coal | OBSERVED (unit counts are company-reported) | Send brand + model |
| HASLER Filtres Philippe | Fertilizer, hydrometallurgy | OBSERVED | Send brand + model |
| EKCP EIMCO-KCP | FGD and phosphate (India) | OBSERVED | 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 factory specification package has not been confirmed in writing yet, so every parameter reads UNKNOWN. Each one 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 | UNKNOWN | — | Confirmed against slurry chemistry |
| Weave / construction | UNKNOWN | — | Confirmed against duty and machine |
| Air permeability | UNKNOWN | L/dm²/min | Measured per lot; test method and pressure stated on the report |
| Fabric weight | UNKNOWN | g/m² | Reported per lot |
| Seam type | UNKNOWN | — | Confirmed against machine and seam photo |
| Edge treatment | UNKNOWN | — | Confirmed against machine edge seal |
| Max fabricated width | UNKNOWN | mm | Confirmed against loom and machine width |
| Continuous temperature limit | UNKNOWN | °C | Confirmed per polymer and finish |
| Chemical limit (acid / fluoride) | UNKNOWN | — | 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 on the UNKNOWN list above until the factory confirms it.
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.
Poor cake release
Cloth surface and discharge geometry together; rarely one or the other alone.
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
This list is the engineering RFQ in plain form — what you gather here is exactly what the form asks for. 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. |
Question we get asked
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.
Every belt is fabricated to your machine dimensions — we quote per RFQ. No online checkout.
Samples available — freight terms 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 Compatibility
OEM families, what we can fit, and what we need from each machine.