High Temperature Pump for Furnace and Foundry Applications

High-temperature pumps are critical in metallurgical furnace operations — circulating thermal oil, molten salt, hot water, and process fluids at temperatures up to 400°C. These pumps require special materials, sealing, and cooling systems to handle extreme temperatures reliably. This guide covers high-temperature pump selection, operation, and maintenance for metallurgical furnace applications.

High-Temperature Fluids in Metallurgy

High-Temperature Pump Types

Design Considerations for High-Temperature Pumps

Thermal Expansion

• Pump casings expand significantly at high temperature — must accommodate thermal growth
• Centerline support (pump supported at centerline, not feet) allows symmetrical expansion
• Use expansion joints in piping to absorb thermal growth
• Allow pipe movement — don't anchor pipes rigidly near pump
• Shaft and casing expand at different rates — maintain clearances
• Warm-up procedure: gradual temperature increase (50°C/hour) to prevent thermal shock
• Cool-down: gradual, avoid quenching hot pump with cold fluid

NPSH (Net Positive Suction Head)

• Hot fluids have high vapor pressure — NPSH available is reduced
• NPSH required increases with pump speed and flow
• Solutions:
  • Elevate suction tank (increase static head)
  • Use low-NPSH impeller (inducer, larger eye)
  • Lower pump speed
  • Use vertical pump (submerged impeller)
  • Pressurize suction tank
  • Insulate suction piping to prevent temperature loss (flashing)
• Maintain NPSH margin: 1.5-3m above required NPSH
• For thermal oil: NPSH available = tank pressure head + static head - vapor pressure - friction

Mechanical Seals for High Temperature

• Plan 23 (recirculation with cooler): Most common for hot pumps. Process fluid recirculated through cooler, back to seal chamber. Reduces seal temp to < 80°C.
• Plan 32 (external flush): Clean, cool fluid injected into seal chamber. Good for dirty/hot fluids, but consumes flush fluid.
• Plan 53B (double seal with barrier): For toxic/hazardous hot fluids. Barrier fluid cooled and pressurized.
• Metal bellows seal: Instead of spring — springs can clog or lose elasticity at high temp. Metal bellows handles high temp.
• Seal face materials: SiC/SiC (high temp capability), carbon/SiC (carbon limits to ~200°C)
• Elastomers: PTFE or Kalrez (EPDM limited to 150°C, Viton to 200°C)
• Seal cooling: Water-cooled seal chamber or jacket for extreme temps

Bearings and Lubrication

• High temperature conducts through shaft to bearings — must keep bearings < 80°C
• Bearing housing cooling: water jacket, fins, or fan
• Lubrication:
  • Oil: high-temperature oil (ISO VG 68-100), change more frequently
  • Grease: high-temperature grease (lithium complex or polyurea), don't over-grease
  • Forced lubrication: for very high power or temp
• Bearing type: deep groove ball (moderate), angular contact (thrust), cylindrical roller (high load)
• Install RTDs on bearings — alarm at 80°C, shutdown at 95°C
• Thermal barrier (heat dam) between pump casing and bearing housing

Material Selection

Jacketed Pumps

For fluids that solidify or crystallize at room temperature (sulfur, pitch, molten salt, some acids):

• Steam jacket: steam circulates around casing to maintain temperature
• Electric jacket: electric heating elements for precise control
• Hot oil jacket: thermal oil circulation
• Jacket covers: casing, seal chamber, suction/discharge flanges
• Never start jacketed pump cold — preheat to operating temp first
• Temperature sensors on jacket and casing
• Insulate jacket to reduce heat loss

Application-Specific Recommendations

Thermal Oil Circulation (Furnace Heating)

• Fluid: mineral or synthetic thermal oil, 150-350°C
• Pump: API 610 hot oil pump, centerline support, cast steel or 316SS
• Seal: Plan 23 (recirculation with cooler), SiC/SiC faces, metal bellows
• Bearings: oil lubrication, water-cooled housing
• NPSH: critical — thermal oil has high vapor pressure at operating temp
• Fire safety: thermal oil is flammable — leak detection, secondary containment, fire suppression
• Expansion tank: pressurized or atmospheric, maintains NPSH and accommodates expansion
• Typical: 50-500 m³/h, 20-100m head, 50-500 kW

Hot Acid Circulation (Pickling, Smelting)

• Fluid: H₂SO₄ or HCl, 50-90°C
• Pump: High-temperature chemical pump or high-temp sulfuric acid pump
• Material: PTFE/PFA lined (for acid), 316SS (for concentrated cold acid), high-silicon iron (for concentrated hot acid)
• Seal: magnetic drive (zero leakage) or double mechanical (Plan 53B)
• Cooling: Plan 23 or Plan 32 for seal cooling
• Jacketing: optional for acid that crystallizes (e.g., sulfuric acid at high concentration)
• Never use 304SS or 316SS for hot dilute sulfuric acid — rapid corrosion

Hot Caustic (Bayer Process, Alumina)

• Fluid: NaOH 15-20%, 100-280°C, 10-40 bar
• Pump: high-pressure multistage or barrel pump
• Material: duplex 2205 or super duplex (hot caustic + pressure)
• Seal: double mechanical (Plan 53B), high-temp design
• NPSH: critical — hot caustic has high vapor pressure
• Scaling: sodium aluminate precipitates — use open impeller, flush connections
• Jacketing: steam tracing to maintain temperature and prevent scaling

Boiler Feedwater

• Fluid: deaerated water, 100-180°C
• Pump: Multistage centrifugal (horizontal ring section or vertical inline)
• Material: carbon steel or 316SS (for high-purity water)
• Seal: Plan 23 (recirculation with cooler) or floating bushing
• NPSH: very critical — hot water near boiling. Use inducer, elevated deaerator, low speed
• Minimum flow: ARC valve or minimum flow line (prevents overheating)
• Typical: 10-500 m³/h, 100-2000m head, 4-10 stages

Molten Metal Transfer

• Fluid: molten aluminum (700-800°C), zinc (420-450°C), lead (330-400°C)
• Pump: special molten metal pump (not standard centrifugal)
• Construction: refractory-lined steel, ceramic or graphite impeller
• Immersion type: pump submerged in molten metal, no shaft seal
• Drive: electric motor above, long shaft or belt drive
• Material: cast iron or steel shell with refractory lining, graphite or ceramic impeller
• Preheat pump before immersion (prevent thermal shock, moisture explosion)
• Not covered in detail — specialized equipment

Installation Best Practices

1. Foundation: Heavy-duty, rigid. Allow for thermal expansion — don't anchor pump rigidly.
2. Piping: Use expansion joints, loops, or bends to absorb thermal growth. Support piping independently (not from pump).
3. Suction: Large diameter, short, minimum fittings. Insulate to prevent heat loss and flashing.
4. Discharge: Check valve, gate valve, pressure gauge. Expansion joint near pump.
5. Seal system: Plan 23 cooler, Plan 32 flush, or Plan 53B reservoir. Verify cooling water supply.
6. Bearing cooling: Water jacket or fan. Verify cooling water flow.
7. Jacketing: For crystallizing fluids — connect steam/electric, preheat before startup.
8. Instrumentation: Suction/discharge pressure, bearing RTDs, seal temp, vibration, flow.
9. Alignment: Cold alignment + hot alignment check after 24 hours (thermal growth changes alignment).
10. Warm-up: Gradual temperature increase (50°C/hour). Bypass line for warm-up circulation.
11. Insulation: Insulate pump and piping for personnel protection and heat retention.
12. Fire safety: For flammable hot fluids (thermal oil) — leak detection, containment, fire suppression.

Operation and Maintenance

Startup

1. Preheat pump gradually (if jacketed or high-temp) — 50°C/hour
2. Verify seal cooling water flow
3. Verify bearing cooling (if water-cooled)
4. Open suction valve, vent air
5. Start pump with discharge valve closed (or bypass open)
6. Allow pump to reach operating temperature
7. Slowly open discharge valve
8. Monitor bearing temp, seal temp, vibration, pressure
9. Check hot alignment after 24 hours

Shutdown

1. Close discharge valve (or open bypass)
2. Stop pump
3. Continue cooling water until pump cools to < 80°C
4. For jacketed pumps: maintain jacket heat if fluid will solidify
5. For thermal oil: keep system pressurized to prevent oxidation
6. For long shutdown: flush with compatible fluid if needed

Maintenance

• Daily: Bearing temp, seal temp/leakage, vibration, pressure, cooling water flow.
• Weekly: Oil level/condition, cooling system, insulation integrity.
• Monthly: Alignment (hot), performance verification, vibration analysis.
• Quarterly: Bearing inspection, seal inspection, cooler cleaning.
• Annually: Complete overhaul — impeller, wear rings, bearings, seals, shaft.
• Cooling system: Clean coolers quarterly — scale reduces cooling efficiency.
• Thermal oil: Test oil annually (viscosity, flash point, acid number) — degradation indicates overheating.

Common Failures

• Seal failure: #1 issue — high temp, dry running, cooling failure. Use Plan 23, verify cooling, preventive replacement.
• Bearing failure: Heat conduction, lubrication breakdown. Water-cooled housing, high-temp lube, RTD monitoring.
• Cavitation: Hot fluid, high vapor pressure, insufficient NPSH. Elevate suction, use inducer, insulate suction.
• Thermal distortion: Uneven heating, thermal shock. Gradual warm-up, centerline support, expansion joints.
• Shaft breakage: Thermal fatigue, misalignment, cavitation. Hot alignment, proper warm-up, material selection.
• Coking/carbonization (thermal oil): Overheating, air ingress. Control temp, maintain pressure, test oil.
• Solidification (jacketed): Jacket failure, cold startup. Preheat, maintain jacket temp, flush before shutdown.
• Corrosion (hot acid): Wrong material. Use PTFE/Hastelloy, verify concentration/temp.

Procurement Recommendations

1. Provide: fluid, temp, pressure, flow, head, SG, vapor pressure, NPSH available
2. Specify API 610 (ISO 13709) compliance for critical high-temp pumps
3. Specify centerline support for pumps > 150°C
4. Specify material per temp and fluid: cast steel, 316SS, duplex, alloy steel
5. Specify seal plan: Plan 23 for hot clean fluid, Plan 53B for hazardous, Plan 32 for dirty
6. Specify high-temp seal faces (SiC/SiC) and elastomers (PTFE/Kalrez)
7. Include bearing housing cooling (water jacket or fins)
8. For crystallizing fluids: specify jacketing (steam/electric) and preheat provisions
9. Include NPSH margin — specify inducer if needed
10. Specify baseplate with thermal growth accommodation
11. Include instrumentation: RTDs, pressure gauges, vibration sensors
12. Require factory performance test at operating temperature (or cold with correction)
13. Include spare parts: seal, bearings, wear rings, impeller, gaskets
14. Verify supplier has high-temperature pump references

Related Industries

High-temperature pump technology applies to many industries: power generation (boiler feed, condensate), oil and gas (refinery, hot oil, reactor feed), chemical manufacturing (hot acid, caustic, solvents), food processing (hot oil, steam), and solar thermal (molten salt). The core challenge — handling hot fluids with proper materials, sealing, cooling, and NPSH management — is consistent across industries.