Phosphoric acid production (wet-acid process) involves grinding phosphate rock, digestion with sulfuric acid, and filtration of gypsum. Pumps handle highly corrosive phosphoric acid, abrasive gypsum/rock slurry, and scaling. This guide covers pump selection for phosphoric acid fertilizer production.
Phosphoric Acid Pump Services
| Service | Fluid | Solids | Key Characteristic | Pump Type |
|---|---|---|---|---|
| Phosphate rock slurry feed | Ground phosphate rock + water (slurry) | 50–70% solids | Very abrasive (rock), viscous, large flow, continuous, settling | Horizontal slurry pump (rubber-lined, large passage, recessed impeller) or screw pump (gentle, large passage) |
| Digester feed / recirculation | Phosphate rock + H2SO4 + H3PO4 (reaction slurry) | 30–50% solids (gypsum + unreacted rock) | Very corrosive (H3PO4 + H2SO4), very abrasive (gypsum + rock), hot (80–100°C), scaling (gypsum), large flow, critical | Horizontal slurry pump (rubber-lined or high-chrome, large passage) — standard for digester |
| Filter feed (to vacuum filter) | Phosphoric acid + gypsum (slurry) | 30–40% solids (gypsum) | Corrosive (28–32% P2O5 acid), abrasive (gypsum), hot (80–100°C), large flow, continuous, critical | Horizontal slurry pump (rubber-lined, large passage) or vertical sump slurry (sump service) |
| Filter acid (product, weak acid) | Filter-grade phosphoric acid (28–32% P2O5, with fine gypsum) | 1–5% solids (fine gypsum) | Corrosive (H3PO4), slightly abrasive (fine solids), hot (80°C), large flow, valuable (product), scaling | 316SS/duplex centrifugal or fluoroplastic (corrosion, large flow) — with flush seal |
| Clarifier / settler feed | Weak phosphoric acid + fine solids | 1–5% solids | Corrosive, slightly abrasive, large flow, continuous, settling | 316SS centrifugal or slurry pump (if higher solids) |
| Evaporator feed (concentration) | Phosphoric acid (30% → 54% P2O5) | 0.5–2% solids | Very corrosive (concentrating H3PO4), hot (80–120°C, vacuum), scaling, viscous (concentrated), valuable, large flow | 316SS/duplex centrifugal or fluoroplastic (corrosion, high temp) — low-NPSH for vacuum |
| Concentrated acid transfer (54% P2O5) | Merchant-grade phosphoric acid (52–54% P2O5) | ＜0.5% solids | Very corrosive (concentrated H3PO4), viscous (50–200 cP), hot (60–80°C), valuable, precise (custody transfer), scaling | 316SS/duplex centrifugal or screw pump (viscous, precise, corrosion-resistant) |
| Gypsum disposal (stack feed) | Gypsum slurry (phosphogypsum, waste) | 40–60% solids | Very abrasive (gypsum), corrosive (residual acid), large flow, continuous, environmental, long pipeline | Horizontal slurry pump (high-chrome, large passage, high pressure for pipeline) — multiple stages for long distance |
| Sulfuric acid feed (to digester) | Sulfuric acid (93–98%) | 0% | Very corrosive (concentrated H2SO4), dense (SG 1.84), precise (stoichiometric), large flow, hazardous, exothermic dilution | Fluoroplastic pump or 316SS centrifugal (concentrated H2SO4 — carbon steel OK for 93%+ ambient, but 316SS safer) — zero leakage |
| Scrubber liquor (acid plant) | Dilute H2SO4 + water (scrubbing SO3/SO2) | 0–1% solids | Corrosive (dilute acid — more corrosive than concentrated), hot, large flow, continuous, environmental | Fluoroplastic pump or 316SS centrifugal (dilute acid corrosion) |
| Cooling water (acid coolers) | Cooling water (for acid coolers) | 0% | Large flow, low head, continuous, scale (hard water) | Horizontal split case or 316SS centrifugal (large flow, low head) |
| Wastewater (acid plant) | Acidic wastewater (dilute H3PO4 + H2SO4 + fluoride) | 0–2% solids | Corrosive (acid + fluoride), toxic (fluoride), environmental, large flow | Fluoroplastic pump or 316SS centrifugal (corrosion, zero leakage) |
| Fluoride handling (byproduct) | Fluosilicic acid (H2SiF6) or HF | 0% | Very corrosive (fluoride attacks glass/metals), toxic, fuming, small flow, safety-critical | Fluoroplastic pump (PTFE/PFA — only for HF/H2SiF6) or PTFE metering (zero leakage) |
| Flocculant dosing | Polyacrylamide (flocculant solution) | 0% | Viscous (0.1–0.5% solution), shear-sensitive (degrades), precise (dosing), small flow | Screw pump or peristaltic (low shear, precise, viscous) |
| CIP / flush | Water + dilute acid (flush gypsum/scale) | 0% | Intermittent, large flow, scale removal, corrosive | Slurry pump or 316SS centrifugal (large flow, flush) |
Critical: Corrosive + Abrasive + Scaling (The Triple Challenge)
Phosphoric acid is uniquely difficult because it combines corrosion, abrasion, and scaling:
- Corrosion: Phosphoric acid (H3PO4) is corrosive — more aggressive at higher concentration and temperature. 30% acid at 80°C = moderate; 54% acid at 100°C = severe. Plus fluoride (from phosphate rock) attacks most metals. Use 316SS (for dilute/low temp), duplex/super duplex (for concentrated/hot), or PTFE-lined (for severe corrosion + fluoride). Carbon steel = NOT for phosphoric acid (rapid corrosion). Hastelloy C for extreme. Our corrosion-resistant range handles phosphoric acid.
- Abrasion: Gypsum (CaSO4·2H2O) and phosphate rock are highly abrasive. Use rubber-lined slurry pump (natural rubber or synthetic rubber — excellent abrasion resistance) or high-chrome iron (28% Cr) for high temp where rubber fails. Tungsten carbide seal faces. Large passage. Recessed impeller (reduces wear). For high solids (＞30%): horizontal slurry pump is standard. Our slurry pump range handles gypsum/rock abrasion.
- Scaling: Gypsum and fluorosilicates scale on pump internals — reduces flow, increases vibration. Use large passage, smooth surfaces (rubber lining resists scale adhesion), continuous flow (avoid stagnation), acid flush (periodic), mechanical cleaning (rotors easy to remove). Rubber-lined pumps are preferred (scale doesn't adhere well to rubber). Our slurry design resists scaling.
Critical: Digester Slurry (Most Severe Service)
- Digester conditions: 80–100°C, 30–50% solids (gypsum + rock), H3PO4 + H2SO4 + fluoride. This is the worst pump service in fertilizer production. Use horizontal slurry pump with: rubber-lined casing/impeller (abrasion + corrosion), large passage, recessed impeller, external flush (seal plan 32 — clean water/acid flush to seal), heavy-duty bearing frame. Pump life: 3–12 months (depending on conditions). Standby pump (critical service). Our heavy-duty slurry range handles digester service.
- Seal flush: Mechanical seal in digester slurry fails rapidly without flush. Use external flush (plan 32 — clean water or weak acid injected into seal chamber, dilutes slurry at seal faces). Tungsten carbide vs tungsten carbide seal faces. Quench (plan 62) for safety. Our sealed slurry pumps include flush provisions.
Critical: Evaporator Feed (Concentrating Acid + Vacuum)
- Concentrating acid: 30% → 54% P2O5 under vacuum (80–120°C). Corrosion increases with concentration. Use 316SS/duplex centrifugal or fluoroplastic (PTFE-lined for severe corrosion). Low-NPSH impeller (vacuum evaporator — NPSH critical). Flooded suction. Jacketed (maintain temp, prevent crystallization). Our low-NPSH corrosion-resistant range handles evaporator feed.
- Crystallization: Concentrated phosphoric acid can crystallize (below ~21°C for 54% acid). Use jacketed pump (maintain ＞30°C), heat tracing, insulation. Pre-heat before startup. Flush with water before shutdown (don't let concentrated acid sit and crystallize). Our jacketed range prevents crystallization.
Critical: Sulfuric Acid + Fluoride
- Sulfuric acid: 93–98% H2SO4 feed to digester. Concentrated H2SO4 is less corrosive than dilute (passivates steel). Carbon steel is OK for 93%+ at ambient, but 316SS or PTFE-lined is safer (especially for variable concentration/temp). Zero leakage (H2SO4 is hazardous, exothermic with water). EPDM/PTFE seals (NOT NBR for concentrated H2SO4 — NBR degrades). Our corrosion-resistant range handles sulfuric acid.
- Fluoride (HF/H2SiF6): Phosphate rock contains fluoride — released as HF/H2SiF6. Fluoride attacks glass, 316SS (pitting), and most metals. Use PTFE/PFA-lined pump (only reliable material for HF). Zero leakage (HF is toxic, penetrates skin). PPE (calcium gluconate gel for HF burns). Our PTFE-lined range handles fluoride.
Material Compatibility
| Material | 30% H3PO4 (80°C, corrosive) | 54% H3PO4 (100°C, severe) | Digester slurry (90°C, gypsum + acid) | 98% H2SO4 (ambient) | HF/H2SiF6 (ambient, fluoride) |
|---|---|---|---|---|---|
| Carbon steel | NOT (H3PO4 corrosion) | NOT | NOT | Good (93%+ ambient, passivated) | NOT |
| 316SS | Good (dilute, ＜80°C) | Fair (concentrated, pitting risk) | Fair (abrasion + corrosion) | Good | NOT (fluoride pitting) |
| Duplex SS | Excellent | Good (concentrated) | Good (abrasion + corrosion) | Good | Fair (fluoride risk) |
| Super duplex | Excellent | Excellent | Excellent | Good | Fair (fluoride risk) |
| Hastelloy C | Excellent | Excellent | Good (abrasion) | Excellent | Good (fluoride) |
| High-chrome iron (28% Cr) | Good | Fair | Excellent (abrasion, high temp) | Good | Fair |
| Rubber-lined (natural rubber) | Good (dilute acid) | NOT (high temp ＞80°C) | Excellent (abrasion + dilute acid) | NOT (concentrated H2SO4 attacks rubber) | Good (dilute HF) |
| Rubber-lined (synthetic, butyl/EPDM) | Good | Fair (temp ＜100°C) | Excellent (abrasion + acid) | NOT | Good |
| PTFE/PFA lined | Excellent | Excellent | Fair (abrasion — not for high solids) | Excellent | Excellent (ONLY for HF) |
| Tungsten carbide (seal) | Good | Good | Excellent (abrasion) | Good | Good |
| Silicon carbide (seal) | Excellent | Excellent | Good (abrasion, brittle) | Excellent | Excellent |
| EPDM seals | Good (acid) | Good (up to 100°C) | Good | NOT (concentrated H2SO4) | Good (dilute HF) |
| PTFE/FFKM seals | Excellent | Excellent | Excellent | Excellent | Excellent |
| NBR seals | Fair | NOT (high temp) | Fair | NOT (concentrated H2SO4 degrades NBR) | Fair |
Critical: Dilute H3PO4 (＜40%, ＜80°C) = 316SS/duplex + EPDM/PTFE. Concentrated H3PO4 (＞40%, ＞80°C) = duplex/super duplex/Hastelloy + PTFE/FFKM. Digester slurry (gypsum + acid) = rubber-lined slurry pump (natural/synthetic rubber) + tungsten carbide + seal flush. High temp (＞80°C) = high-chrome iron (rubber fails). Sulfuric acid = carbon steel (93%+ ambient) or 316SS/PTFE + EPDM/PTFE (NOT NBR). Fluoride = PTFE/PFA lined ONLY. All = zero leakage + standby (critical) + flush/scale prevention.
Common Problems and Solutions
Problem 1: Digester pump wears out in 3 months. Gypsum + rock + acid = extreme abrasion/corrosion. Solution: use rubber-lined horizontal slurry pump (large passage, recessed impeller). Tungsten carbide seal + plan 32 flush. High-chrome for ＞80°C. Standby pump. Our heavy-duty slurry range extends life.
Problem 2: Concentrated acid pump corrodes. 54% H3PO4 at 100°C corrodes 316SS. Solution: upgrade to duplex/super duplex or Hastelloy centrifugal or PTFE-lined. PTFE/FFKM seals. Jacketed. Our corrosion-resistant range handles concentrated H3PO4.
Problem 3: Pump scales up (gypsum). Gypsum deposits in pump — flow drops. Solution: rubber-lined pump (scale doesn't adhere). Large passage. Acid flush (periodic). Continuous flow. Mechanical cleaning. Our slurry design resists scaling.
Problem 4: Evaporator pump cavitates (vacuum). Vacuum evaporator — low NPSH. Solution: use low-NPSH 316SS/duplex centrifugal (large eye, inducer). Flooded suction. Jacketed. Our low-NPSH range handles vacuum evaporator.
Problem 5: Fluoride pump fails (metal corrosion). HF attacks 316SS. Solution: use PTFE/PFA-lined pump (only for HF). Zero leakage. PPE. Our PTFE-lined range handles fluoride.
Selection Summary
- Rock slurry: Horizontal slurry pump (rubber-lined, 50–70% solids, large passage) or screw
- Digester: Horizontal slurry pump (rubber-lined/high-chrome, 30–50% solids, 80–100°C, acid + gypsum, seal flush, standby)
- Filter feed: Horizontal slurry pump or vertical sump slurry (30–40% gypsum, acid, 80–100°C)
- Filter acid (weak): 316SS/duplex centrifugal or fluoroplastic (28–32% P2O5, 1–5% solids, 80°C, large flow)
- Evaporator feed: 316SS/duplex centrifugal or fluoroplastic (concentrating, 80–120°C, vacuum, low-NPSH, jacketed)
- Concentrated acid (54%): 316SS/duplex centrifugal or screw (50–200 cP, 60–80°C, custody transfer, jacketed)
- Gypsum disposal: Horizontal slurry pump (high-chrome, 40–60% solids, long pipeline, multistage)
- Sulfuric acid: Fluoroplastic or 316SS (93–98%, zero leakage, EPDM/PTFE, NOT NBR)
- Scrubber liquor: Fluoroplastic or 316SS (dilute acid, more corrosive, large flow)
- Fluoride (HF/H2SiF6): Fluoroplastic pump (PTFE/PFA, ONLY, zero leakage, toxic)
- Flocculant: Screw pump or peristaltic (low shear, viscous, precise)
- Critical: phosphoric acid = corrosion + abrasion + scaling (triple challenge), dilute = 316SS/duplex, concentrated = duplex/Hastelloy/PTFE, slurry = rubber-lined slurry pump + tungsten carbide + seal flush, high temp ＞80°C = high-chrome (rubber fails), sulfuric = carbon steel (93%+ ambient) or 316SS/PTFE + EPDM (NOT NBR), fluoride = PTFE/PFA ONLY, all = zero leakage + standby (critical) + flush/scale prevention + crystallization prevention (jacketed for concentrated acid)
- Our horizontal slurry and vertical slurry cover rock/gypsum/digester; 316SS/duplex centrifugal and fluoroplastic cover acid; screw covers viscous/concentrated acid. For phosphoric acid pump selection, talk to our chemical engineers with your acid concentration, solids content, temperature, and fluoride level.