TL;DR: A filter press for FGD gypsum dewatering is the standard technology coal-fired power plants use to convert flue gas desulfurization (FGD) scrubber slurry into a stackable cake. It reduces a roughly 90-95% water slurry to a 10-18% moisture solid cake in a 20-40 minute cycle, cutting landfill and transport volume by more than 70% and making the byproduct saleable to cement and wallboard plants.
Wet limestone FGD scrubbers produce a calcium sulfate slurry that cannot be landfilled or sold as-is. Plants first pass it through hydrocyclones to reject fines, then feed the underflow to an automatic filter press. Chamber (recessed-plate) presses are the default choice because FGD gypsum crystals are relatively coarse and free-draining; membrane presses are added when plants need cake moisture below 12% for wallboard-grade gypsum. Plate sizes from 800 mm to 2000 mm cover units from a 50 MW captive power plant up to a 1000 MW utility station, with cycle times of 20-40 minutes and full PLC automation for unattended operation.
What type of filter press is used for FGD gypsum dewatering?
Most FGD systems use a fully automatic recessed-chamber filter press with polypropylene plates, because raw FGD gypsum (largely calcium sulfate dihydrate crystals, 20-60 microns) filters quickly and forms a stable, low-resistance cake. Membrane (diaphragm) filter presses are specified instead when the offtake buyer — typically a wallboard or cement plant — requires cake moisture consistently under 12%, since the membrane’s post-filtration squeeze removes an extra 3-6 percentage points of water that a chamber press alone cannot reach.
How much moisture can a filter press remove from FGD gypsum?
A well-sized chamber filter press typically brings FGD gypsum cake to 15-18% moisture. Adding membrane squeeze (6-10 bar) after the initial chamber fill lowers that to 10-13%, which is the range most gypsum wallboard specifications call for. Inlet slurry to the press is usually 30-45% solids by weight after hydrocyclone thickening; without a filter press, FGD gypsum would remain a pumpable slurry unsuitable for truck transport or direct landfilling.
What plate size and chamber volume does a coal power plant need?
Sizing is driven by plant capacity (MW), sulfur content of the coal, and limestone utilization rate, which together determine daily gypsum output in dry tons. As a working rule, a 300 MW subcritical unit burning 1-2% sulfur coal generates roughly 15-25 dry tons of gypsum per hour at full load, requiring a press with 1200-1500 mm plates and 60-100 chambers to hold a full batch. Larger 600-1000 MW units commonly step up to 1500-2000 mm plates or run two presses in parallel for redundancy during outages.
| Plant Size | Approx. Gypsum Output | Recommended Plate Size | Typical Chamber Count | Cycle Time |
|---|---|---|---|---|
| 50-150 MW (captive/industrial) | 3-8 dry t/h | 800-1000 mm | 30-50 | 20-30 min |
| 150-350 MW | 8-25 dry t/h | 1200-1500 mm | 60-100 | 25-35 min |
| 350-600 MW | 25-45 dry t/h | 1500-1800 mm | 80-120 | 30-40 min |
| 600-1000 MW | 45-80 dry t/h | 1800-2000 mm (or 2 presses) | 100-150 | 35-40 min |
Membrane vs chamber filter press for FGD gypsum — which is better?
Choose a chamber filter press when the gypsum only needs to reach landfill-safe moisture (15-20%) and capital budget is the priority — it costs roughly 15-25% less than an equivalent membrane press. Choose a membrane filter press when the offtake contract requires wallboard- or cement-grade gypsum below 12% moisture, since the extra hydraulic squeeze stage pays for itself through the price premium gypsum boards command over landfilled waste. Many utilities in Southeast Asia and South Asia now specify membrane presses by default because selling gypsum to wallboard manufacturers offsets a meaningful share of FGD operating cost.
How much does an FGD gypsum filter press system cost?
A complete automatic filter press system for FGD gypsum — press, feed pumps, PLC control, plate-shifting mechanism, and cloth washing — generally falls in the range of USD 150,000-600,000 depending on plate size, chamber count, and whether membrane plates are included; larger 1800-2000 mm units for 600 MW+ plants can exceed this range. Request a quotation based on your plant’s actual dry-ton-per-hour output and target cake moisture, since underspecifying plate area is the most common — and most expensive — mistake in FGD dewatering projects.
Senjie supplies automatic chamber and membrane filter presses engineered for FGD gypsum duty, including corrosion-resistant PP plates and slurry-grade feed pumps for high-chloride scrubber liquor. Explore the chamber filter press range for landfill-moisture applications, or the membrane filter press line when wallboard-grade cake is required. For general dewatering equipment selection guidance, see our filter press buyer’s guide.
Frequently Asked Questions
Can a filter press handle the high chloride content in FGD wastewater?
Yes, provided the press uses polypropylene plates, chloride-resistant filter cloth, and stainless or FRP-lined feed pumps. Standard carbon-steel components will corrode quickly in high-chloride scrubber blowdown, so the material specification matters more than the press model itself.
How often does the filter cloth need replacing on an FGD gypsum press?
Under continuous FGD duty, polypropylene filter cloth typically lasts 4-8 months before blinding reduces cycle throughput enough to warrant replacement, though this varies with gypsum crystal size and cloth micron rating. Automatic cloth-washing systems extend service life by flushing gypsum scale after every cycle.
Can the same filter press dewater both FGD gypsum and coal ash slurry?
Not efficiently on the same plate set. FGD gypsum and fly/bottom ash have different particle size distributions and filtration rates, so plants running both typically use separate presses or at minimum separate filter cloth specifications to avoid cross-contamination and inconsistent cake quality.
What cake moisture is required to sell FGD gypsum to a wallboard manufacturer?
Most wallboard plants specify under 10-12% surface moisture on delivery, which usually requires a membrane filter press rather than a chamber-only press, plus consistent crystal purity above roughly 90% calcium sulfate dihydrate.
Is a filter press better than a centrifuge for FGD gypsum dewatering?
Filter presses generally achieve lower final cake moisture (10-18% vs. 15-25% for decanter centrifuges) and produce a more consistent particle-free effluent, which is why most large coal plants specify filter presses despite the higher capital cost and larger footprint compared to centrifuges.
By Senjie Engineering Team. Last updated: July 31, 2026.
External references: U.S. Environmental Protection Agency on flue gas desulfurization byproduct management; USGS National Minerals Information Center — Gypsum Statistics and Information.