Chemical process heating systems rely on high-temperature pumps to circulate heat transfer fluids (thermal oil, molten salt, hot water) through reactors, distillation columns, heat exchangers, and process heaters. These pumps operate at 150-400°C with corrosive or hazardous fluids, requiring careful material selection, sealing, and thermal management. This guide covers high-temperature pump selection for chemical process heating systems.
Chemical Process Heating Applications
| Process | Fluid | Temp | Pump Considerations |
|---|---|---|---|
| Reactor heating/cooling | Thermal oil, molten salt | 150-400°C | Precise temp control, low NPSH |
| Distillation reboiler | Thermal oil, steam | 200-350°C | High flow, stable pressure |
| Heat exchanger circulation | Thermal oil, hot water | 100-300°C | Reliable, efficient |
| Process heater circulation | Thermal oil | 250-400°C | High temp, centerline support |
| Molten salt loop | Nitrate salt | 250-550°C | Freeze protection, no elastomers |
| Hot oil system | Mineral/synthetic oil | 150-350°C | Seal cooling, expansion tank |
| Vacuum distillation | Thermal oil | 200-350°C | Low NPSH, precise control |
| Polymerization reactor | Thermal oil, hot water | 100-300°C | Gentle, no dead spots |
Heat Transfer Fluids
Mineral Thermal Oil
- Temp range: -10 to 320°C (some up to 340°C)
- Low cost, good heat transfer, widely available
- Limitations: flammable, oxidation at high temp, coking at film temp >340°C
- Vapor pressure: moderate (need expansion tank, nitrogen blanket)
- Pump: high-temperature chemical pump with mechanical seal + Plan 21
Synthetic Thermal Oil
- Types: diphenyl oxide/biphenyl (Dowtherm A), alkylated aromatic, silicone
- Temp range: -40 to 400°C (some up to 425°C)
- Advantages: higher temp, better thermal stability, lower vapor pressure
- Limitations: higher cost, some are toxic (Dowtherm A), compatibility with elastomers
- Pump: centerline support, metal bellows seal or Plan 32 injection
Molten Salt
- Types: nitrate salt (60% NaNO₃/40% KNO₃), chloride salt, fluoride salt
- Temp range: 220-600°C (nitrate), 400-800°C (chloride)
- Advantages: very high temp, non-flammable, high heat capacity
- Limitations: freeze protection (nitrate melts at 220°C), corrosive at high temp, no elastomers
- Pump: vertical canned pump or magnetic drive, heat tracing
Pressurized Hot Water
- Temp range: 100-250°C (pressurized to prevent boiling)
- Advantages: high heat capacity, non-flammable, low cost
- Limitations: high pressure at high temp, corrosion, freezing
- Pump: standard high-temp centrifugal, 316 or carbon steel
Pump Type Selection
Horizontal Centrifugal (OH2)
- Most common for thermal oil and hot water circulation
- Flow: 10-500 m³/h, head: 20-150 m
- Centerline support for >150°C
- Material: carbon steel (WCB) up to 350°C, 2.25Cr-1Mo up to 450°C, 316 for corrosive
- Seal: single mechanical with Plan 21 (recirculation + cooler)
- Advantages: efficient, reliable, easy maintenance, wide range
Vertical Canned Motor (VS6)
- For high-temperature, high-pressure, zero-leakage applications
- Flow: 10-200 m³/h, head: 50-500 m
- No shaft seal — zero leakage (critical for hazardous/high-temp fluids)
- Material: 316, 310S, Inconel, Hastelloy (depending on fluid)
- Advantages: zero leakage, no seal maintenance, compact
- Limitations: lower efficiency (can losses), high cost, limited power
- For molten salt and hazardous thermal oil: ideal choice
Magnetic Drive Pump
- Zero leakage, no shaft seal
- Flow: 1-100 m³/h, head: 20-150 m
- Temp limit: typically <350°C (magnet material limit)
- Material: 316, Hastelloy, PTFE lining (for corrosive)
- Advantages: zero leakage, no seal maintenance, good for small-medium flow
- Limitations: temp limit, torque limit, eddy current losses
Multistage Centrifugal (BB3/BB4/BB5)
- For high-pressure heating systems (e.g., boiler feed, high-pressure hot water)
- Flow: 50-500 m³/h, head: 200-2,000 m
- Material: 316/17-4PH wetted, carbon steel or alloy casing
- Key: low NPSH first stage, minimum flow protection, high-speed driver
Material Selection
Thermal Oil Service
- Casing: WCB (carbon steel) up to 350°C, 2.25Cr-1Mo (F22) up to 450°C
- Impeller: 316, CF8M, or WCB (non-corrosive oil)
- Shaft: 316, 17-4PH, or 2.25Cr-1Mo
- Shaft sleeve: 316, Stellite, tungsten carbide
- Seal faces: SiC vs SiC (high temp), SiC vs carbon (general)
- Elastomers: limited to <200°C — use metal bellows or PTFE wedge above
Molten Salt Service
- Casing: 316/304 (nitrate, <500°C), Inconel 625/Hastelloy C (chloride, >500°C)
- Impeller: 316, Inconel 625
- Shaft: 316, Inconel 625
- No elastomers — use metal gaskets (spiral wound, camprofile, RTJ)
- Seal: canned motor (no seal) or magnetic drive (if temp <350°C)
- Key: maintain salt above melting point (heat tracing, jacketing)
Corrosive High-Temp Service
- Sulfuric acid at high temp: high-temp sulfuric acid pump (cast iron, 316, or alloy)
- Hydrochloric acid: PTFE-lined or Hastelloy (temp <200°C for PTFE)
- Caustic soda: 316, nickel, or Hastelloy (stress corrosion cracking risk)
- Solvents: 316, cast steel, verify compatibility
- For corrosive + high temp: consult material compatibility chart, consider magnetic drive (zero leakage)
Seal Selection for High-Temp Chemical Pumps
Single Mechanical Seal (API 682 Type A)
- For non-hazardous, non-toxic thermal oil and hot water
- Plan 11: recirculation from discharge (general)
- Plan 21: recirculation + cooler (high temp, cool seal)
- Plan 32: external flush (clean, cool fluid injected)
- Seal faces: SiC vs SiC (high temp), carbon vs SiC (general)
- Springs: Inconel 718 (high temp/corrosion)
- Limit: elastomer <200°C — use metal bellows above
Metal Bellows Seal
- For high temp (>200°C) where elastomers fail
- Bellows material: Inconel 718, Hastelloy C
- No elastomer secondary seal — PTFE wedge or metal
- Plan 21 or 32 for cooling
- Advantages: high temp capability, no elastomer degradation
- Limitations: higher cost, less forgiving of misalignment
Double Mechanical Seal (API 682 Type B/C)
- For hazardous, toxic, or high-value fluids
- Arrangement 3 (pressurized): barrier fluid between seals
- Plan 53A/B/C: barrier fluid system (tank, pressurizer, cooler)
- Barrier fluid: water, glycol, or compatible oil
- Advantages: zero leakage to atmosphere, seal failure protection
- For hazardous thermal oil: recommended
Canned Motor / Magnetic Drive
- No shaft seal — zero leakage
- For hazardous, toxic, or high-value fluids
- Canned motor: higher temp capability (up to 450°C with proper design)
- Magnetic drive: temp limit <350°C (magnet material)
- Advantages: zero leakage, no seal maintenance, no barrier fluid system
- Limitations: lower efficiency, higher cost, limited power/torque
System Design Considerations
Expansion Tank
- Accommodates thermal expansion of heat transfer fluid
- Maintains NPSH for pumps (pressurized with nitrogen)
- Prevents oxidation (nitrogen blanket for mineral oil)
- Sizing: 10-20% of system volume (depending on temp range)
- Location: above pumps, with equalizing line
Minimum Flow Protection
- High-temp pumps must not operate below minimum flow (overheating, cavitation)
- Automatic recirculation valve (ARV): self-contained, opens at low flow
- Orifice plate: simple, but continuous bypass (energy waste)
- Control valve: flow meter + valve + controller (precise, complex)
- For multistage/high-power pumps: ARV is standard
Heat Tracing and Freeze Protection
- For molten salt: maintain >250°C (nitrate melting point ~220°C)
- For high-pour-point thermal oil: maintain >pour point + 10°C
- Methods: electric heat tracing, steam tracing, jacketing
- Pump: jacketed casing or heat tracing on bearing housing
- Preheat pump before startup (avoid thermal shock, prevent solidification)
Piping Design
- Large suction line: velocity <1.5 m/s (reduce NPSH loss)
- Expansion joints: accommodate thermal growth
- Centerline support: pump grows from centerline, piping must flex
- No strainer on suction (pressure drop) — use large mesh if required
- Slope piping to drain (for maintenance, freeze protection)
- Insulate piping (maintain temp, energy efficiency)
Common Issues
- Thermal oil coking: Film temp >340°C (mineral) causes coking. Maintain flow, avoid hot spots, use synthetic oil for >320°C.
- Seal leakage: Elastomer degradation at high temp. Use Plan 21/32 cooling, metal bellows, or canned/magnetic.
- Cavitation: Hot fluid near vapor pressure. Use expansion tank (nitrogen blanket), elevate tank, low-NPSH pump.
- Molten salt freeze: Salt solidifies in pump/piping. Use heat tracing, preheat, maintain temp.
- Thermal growth misalignment: Centerline support, flexible coupling, align cold with target offset.
- Oxidation (mineral oil): Nitrogen blanket expansion tank, minimize air contact.
- Bearing overheating: Heat conduction from casing. Use finned/water-cooled housing, oil circulation cooler.
- Fire hazard (thermal oil): Use double seal or canned/magnetic, leak detection, proper insulation.
Procurement Recommendations
- Provide: heat transfer fluid type, temp range, flow, head, system layout, hazardous classification
- For thermal oil: specify high-temp chemical pump, centerline support, Plan 21 seal
- For molten salt: specify vertical canned pump, 316/Inconel, heat tracing
- For hazardous fluid: specify double seal (Arrangement 3) or canned/magnetic drive
- For high pressure: specify multistage (BB3/BB4/BB5) with minimum flow protection
- Specify material per fluid and max temp (verify compatibility)
- For >200°C: specify metal bellows seal or Plan 32 injection
- Include expansion tank sizing and NPSH calculation
- Specify minimum flow protection (ARV for multistage/high-power)
- Include heat tracing/jacketing for freeze-prone fluids
- Specify centerline support for >150°C
- Require performance test per API 610 / ASME PTC 8.2
- Include spare parts: seal, bearings, wear rings, impeller, gaskets
- Verify supplier has chemical process heating references
Related Industries
Chemical process heating pump principles apply to oil and gas (refinery, upstream), power generation (fossil, nuclear, solar), food and beverage (process heating, CIP), pulp and paper (digester, recovery), pharmaceuticals (reactor, sterilization), and metals processing (furnace, rolling). The core principle — reliable circulation of heat transfer fluid at high temp with proper sealing and thermal management — is consistent across process heating applications.