FGD slurry pumps circulate limestone absorbent in wet flue gas desulfurization systems, removing SO2 from coal plant emissions. This article covers slurry pump selection, abrasion resistance, materials, and reliability for scrubber systems.
FGD (Flue Gas Desulfurization) slurry pumps handle limestone slurry, gypsum slurry, and recirculation slurry in coal-fired power plant scrubbers. These are the most abrasive and corrosive slurry applications in power generation, requiring specialized wear-resistant pumps. This guide covers FGD slurry pump selection, materials, system design, and common problems.
FGD System Overview
| Component | Function | Typical Spec |
|---|
| Absorber tower | SO2 absorption (limestone slurry contacts flue gas) | Spray towers, 10–30 m height, 95–99% SO2 removal |
| Recirculation pump | Recirculate limestone slurry from absorber sump to spray headers | Horizontal slurry pump (vertical cantilever also used). Large flow 5000–20000 m³/h, 15–30 m head, 300–1500 kW. 3–6 pumps per absorber. |
| Limestone slurry preparation | Grind limestone + mix water → slurry | Ball mill, slurry tank, slurry pump to absorber. 20–30% solids. |
| Limestone feed pump | Feed fresh limestone slurry to absorber | Horizontal slurry pump or peristaltic. 20–30% solids, moderate flow. |
| Gypsum bleed / dewatering | Remove gypsum slurry → dewater (vacuum belt filter) | Horizontal slurry pump or peristaltic. 10–20% solids gypsum. |
| Gypsum dewatering | Vacuum belt filter → gypsum cake (90%+ dry) | Vacuum pump, filter feed pump. Gypsum byproduct (wallboard, cement) |
| Wastewater treatment | Treat FGD wastewater (heavy metals, chloride) | Peristaltic or slurry pump. Precipitation, filtration. |
| Oxidation air | Blow air → oxidize sulfite to sulfate (gypsum) | Blower/compressor (not pump) |
Critical: FGD Slurry Properties
| Property | Limestone Slurry | Gypsum Slurry | Pump Implication |
|---|
| Solids concentration | 20–30% by weight | 10–20% by weight | High solids = high SG (1.15–1.3), high wear |
| Particle size | Limestone: 90% ＜44 μm (325 mesh) | Gypsum: 20–100 μm crystals | Fine particles = rubber-lined suitable; limestone harder than gypsum |
| Specific gravity (solids) | 2.6–2.7 (limestone CaCO3) | 2.3 (gypsum CaSO4·2H2O) | Slurry SG 1.15–1.3 → power = SG × water power |
| pH | 5.5–6.5 (absorber, controlled) | 5.5–6.5 | Mildly acidic + chloride = corrosion. Rubber-lined or duplex. |
| Chloride | 10,000–50,000 ppm (high!) | 10,000–50,000 ppm | High chloride = pitting corrosion. 316SS insufficient → duplex/superduplex or rubber-lined. |
| Temperature | 45–60°C (absorber) | 45–60°C | Modest temp. EPDM rubber OK (＜80°C). High-chrome OK. |
| Abrasiveness | Very high (hard limestone, angular) | High (gypsum crystals, softer) | Rubber-lined (fine particles) or high-chrome (coarse). Recirculation = highest wear. |
| Corrosiveness | High (acidic + high chloride) | High | Rubber-lined (corrosion + abrasion) or duplex/CD4MCu. NOT 316SS (chloride pitting). |
| Scaling | Gypsum scaling on surfaces | Same | Smooth surfaces, flush, proper velocity. Avoid dead zones. |
Critical: FGD Recirculation Pump (Largest, Most Critical)
- Function: Recirculates absorber sump slurry (limestone + gypsum + water) to spray headers at top of absorber. This is the heart of FGD — 3–6 pumps per absorber, each serving a spray level. Largest pumps in FGD (5000–20000 m³/h, 300–1500 kW).
- Pump type: (1) Horizontal slurry pump (most common, rubber-lined or high-chrome, heavy-duty), (2) vertical cantilever slurry pump (no shaft seal, sump-mounted — common in FGD, no seal issues, but shorter shaft life). Horizontal preferred for large flow/maintenance. Our heavy-duty slurry pumps handle FGD recirculation.
- Material: (1) Rubber-lined (natural rubber or EPDM, 5–10mm thick) — BEST for FGD fine slurry (abrasion + corrosion, low cost, but ＜80°C, no coarse particles ＞5mm), (2) high-chrome A05/A49 — for coarser slurry or high temp, (3) duplex/superduplex stainless — for high chloride corrosion (but less abrasion than rubber/high-chrome). Rubber-lined is standard for FGD recirculation (fine limestone/gypsum, 45–60°C). Our rubber-lined slurry pumps are ideal for FGD.
- Impeller: Large passage, open or semi-open (no clog), rubber-lined or high-chrome. Low tip speed (wear ∝ speed³) — use gear reducer or large pump. Our FGD pumps optimize for low speed.
- Sealing: (1) Gland packing with water flush (most common for slurry — cheap, but leaks), (2) mechanical seal with Plan 32 flush (clean water, zero leakage, but expensive, can clog), (3) expeller seal (centrifugal seal, no flush, dry-running). Vertical cantilever = no seal (best). Our slurry pumps offer all seal options.
Critical: Material Selection for FGD (High Chloride + Abrasion)
| Material | Abrasion | Corrosion (high Cl-) | Temp Limit | FGD Use |
|---|
| Natural rubber-lined | Excellent (fine particles) | Excellent (acid + chloride) | ＜70°C | Recirculation, feed (standard FGD) |
| EPDM rubber-lined | Good (fine) | Excellent (acid + chloride) | ＜120°C | Higher temp FGD, chemical resistance |
| Polyurethane (PU) lined | Excellent (fine/medium) | Good | ＜60°C | Fine slurry, low temp |
| High-chrome A05 (28% Cr) | Excellent (coarse/angular) | Fair (chloride pitting) | Any | Coarse slurry, high temp, where rubber fails |
| High-chrome A49 (15% Cr) | Very good (tougher) | Fair | Any | Large particles, impact |
| Duplex stainless (2205) | Fair | Excellent (high chloride) | Any | High chloride corrosion, low abrasion |
| Superduplex (2507) | Fair | Outstanding (very high Cl-) | Any | Extreme chloride (＞50,000 ppm) |
| CD4MCu (alloys 20) | Fair | Very good (chloride) | Any | Cast duplex alternative, FGD specific |
| 316SS | Poor | Poor (pitting ＞1000 ppm Cl-) | Any | NOT for FGD slurry (chloride too high) |
| Cast iron | Poor | Poor | Any | NOT for FGD slurry |
Critical: FGD slurry = high chloride (10,000–50,000 ppm) + fine abrasive particles + mild acid (pH 5.5–6.5) + 45–60°C. Standard solution: rubber-lined (natural rubber or EPDM) slurry pump — handles both abrasion (fine particles) and corrosion (acid+chloride), cost-effective, ＜80°C. For coarser/higher temp: high-chrome A05. For extreme chloride: duplex/superduplex. NEVER 316SS or cast iron for FGD slurry. Our rubber-lined slurry pumps are the FGD standard.
Critical: FGD System Design
- Redundancy: Recirculation pumps critical (SO2 removal). 3–6 pumps per absorber (N+1 or N+2 redundancy). One pump out = reduced removal, not trip. Feed pumps 100% backup. Our systems include redundant pumps.
- Piping: Rubber-lined steel or FRP (fiberglass) — corrosion + abrasion. FRP common for FGD (lightweight, corrosion-resistant, but lower pressure). Proper velocity 2–3 m/s (prevent settling, minimize wear).
- Seal water: Gland seal flush requires clean water (filtered, ＜100 ppm solids) at pressure ＞ pump discharge. Critical to prevent slurry entering seal/bearing. Our systems include seal water.
- Gypsum scaling: Gypsum scales on pump/piping. Mitigate: smooth rubber lining, proper velocity, periodic flush, pH control, organic additives (anti-scalant). Our designs minimize scaling.
- Wear monitoring: Recirculation pumps wear (rubber lining 2–5 years, high-chrome 1–3 years). Monitor: vibration, performance (head/flow drop), thickness (ultrasonic). Planned overhaul. Our pumps have wear indicators.
- Environmental: FGD wastewater (heavy metals, chloride, selenium) treated before discharge. Zero liquid discharge (ZLD) increasingly required. Gypsum byproduct sold (wallboard). Our pumps support FGD environmental compliance.
Critical: Common Problems
- Problem 1: Recirculation pump wears (abrasion + corrosion). Fine limestone/gypsum + high chloride wears rubber lining. Solution: rubber-lined slurry pump (thick 5–10mm), low tip speed, proper material,定期 inspection, replaceable liners. Our rubber-lined pumps maximize wear life.
- Problem 2: Seal failure (slurry ingress). Abrasive slurry enters seal/bearing → failure. Solution: gland water flush (Plan 32, clean water ＞discharge pressure), mechanical seal with flush, or vertical cantilever (no seal). Our slurry pumps include proper flush systems.
- Problem 3: Gypsum scaling (flow reduction). Gypsum deposits reduce flow/head. Solution: smooth rubber lining, velocity 2–3 m/s, flush after shutdown, anti-scalant, pH control. Our designs minimize scaling.
- Problem 4: Chloride corrosion (wrong material). 316SS/cast iron pits in high chloride FGD slurry. Solution: rubber-lined or duplex/superduplex, NEVER 316SS/cast iron. Our FGD pumps use correct materials.
- Problem 5: Pump clogs (large particles). Oversized limestone or scale chunks jam impeller. Solution: open large-passage impeller, inlet strainer, proper grinding (limestone 90%＜44μm). Our large-passage pumps avoid clogging.
- Problem 6: Cavitation (NPSH). Hot slurry (45–60°C) + low sump → cavitation. Solution: adequate submergence, low-NPSH impeller, sump level control, vertical cantilever (no NPSH issue). Our pumps handle FGD NPSH.
Selection Summary
- FGD recirculation (largest): Horizontal slurry pump rubber-lined (natural rubber/EPDM, 5000–20000 m³/h, 15–30m, 300–1500 kW, low tip speed, large passage, gland flush) or vertical cantilever (no seal)
- Limestone feed: Horizontal slurry pump rubber-lined (20–30% solids, moderate flow) or peristaltic (small flow, no seal, EPDM hose)
- Gypsum bleed/dewatering: Horizontal slurry pump rubber-lined (10–20% gypsum) or peristaltic (small, precise)
- Wastewater: Peristaltic or slurry pump (heavy metals, chloride, rubber-lined/EPDM)
- High temp/coarse: Horizontal slurry pump high-chrome A05/A49 (when rubber ＜80°C limit exceeded or coarse particles)
- Extreme chloride: Duplex/superduplex stainless pump (＞50,000 ppm Cl-, corrosion-focused)
- Critical: FGD slurry = ABRASIVE (fine limestone/gypsum) + CORROSIVE (pH5.5–6.5 + 10,000–50,000 ppm chloride) + 45–60°C → rubber-lined slurry pump (standard, handles both abrasion+corrosion, ＜80°C), NEVER 316SS/cast iron (chloride pitting), recirculation = largest most critical (3–6 pumps, redundant, low tip speed, gland flush), materials = rubber (fine) / high-chrome (coarse/hot) / duplex (extreme chloride), all = SO2 removal reliability + environmental compliance + wear management
- Our horizontal slurry pumps (rubber-lined and high-chrome options), vertical slurry pumps, peristaltic hose pumps, and mortar pumps cover FGD slurry systems. For FGD pump selection, talk to our power generation engineers with your slurry concentration, particle size, chloride level, flow, head, and temperature.