Waste heat recovery (WHR) systems capture and reuse thermal energy from industrial exhaust, process streams, and equipment exhaust. High-temperature pumps circulate heat transfer fluids through heat recovery exchangers, organic Rankine cycle (ORC) systems, and thermal distribution loops. This guide covers high-temperature pump selection for waste heat recovery systems.
Waste Heat Recovery Applications
| Source | Temp Range | Heat Transfer Fluid | Pump Type |
|---|---|---|---|
| Gas turbine exhaust | 400-600°C | Water/steam, thermal oil | Multistage, high-temp centrifugal |
| Engine exhaust (gas/diesel) | 300-500°C | Thermal oil, water/glycol | High-temp centrifugal |
| Process furnace exhaust | 300-800°C | Thermal oil, molten salt | High-temp centrifugal, canned |
| Glass/cement kiln | 300-600°C | Thermal oil, water | High-temp centrifugal |
| Steel mill (furnace, sinter) | 300-1000°C | Water, thermal oil | Multistage, high-temp |
| Data center (IT exhaust) | 30-60°C | Water/glycol | Standard centrifugal |
| ORC system | 80-300°C | Refrigerant, thermal oil | Sealless, high-temp |
| Steam condensate return | 80-150°C | Condensate | Vertical multistage |
Heat Transfer Fluids in WHR
Water/Steam
- Most common for high-temp WHR (HRSG, boiler)
- High heat capacity, non-flammable, low cost
- Temp: 100-550°C (pressurized or steam)
- Pumps: boiler feedwater (high pressure), condensate (low NPSH), cooling water
- For boiler feed: multistage boiler feed pump
- For condensate: vertical can-type multistage (low NPSH)
Thermal Oil
- For medium-temp WHR (150-350°C), liquid phase only
- Mineral oil: up to 320°C; synthetic: up to 400°C
- Advantages: low pressure at high temp, precise temp control, no phase change
- Limitations: flammable, coking at high film temp, expansion tank needed
- Pumps: high-temp chemical pump with centerline support
Molten Salt
- For high-temp WHR and thermal energy storage (250-600°C)
- Nitrate salt: 220-565°C; chloride salt: 400-800°C
- Advantages: very high temp, high heat capacity, non-flammable, storage capability
- Limitations: freeze protection, corrosive at high temp, no elastomers
- Pumps: vertical canned pump with heat tracing
ORC Working Fluid
- Organic Rankine Cycle uses refrigerant or hydrocarbon (R245fa, pentane, toluene)
- Temp: 80-300°C (low-temp heat recovery)
- Flammable/toxic (depending on fluid) — require zero-leakage pumps
- Pumps: magnetic drive pump or canned motor (zero leakage)
- Key: high pressure (condenser to evaporator), precise flow control
Pump Type Selection by WHR System
HRSG (Heat Recovery Steam Generator)
- Recovers heat from gas turbine/engine exhaust to produce steam
- Pumps:
- Boiler feedwater: multistage centrifugal, 50-200 bar
- Condensate: vertical can-type multistage, low NPSH
- Cooling water: horizontal split case, large flow
- Chemical dosing: diaphragm metering
- Key: high reliability (CHP critical), N+1 redundancy, VFD for load following
Thermal Oil WHR Loop
- Recovers heat via thermal oil circulated through exhaust heat exchanger
- Pump: high-temp centrifugal (OH2, centerline support)
- Flow: 50-500 m³/h, head: 30-100 m
- Temp: 200-350°C (mineral) or 250-400°C (synthetic)
- Seal: Plan 21 (recirculation + cooler) or double seal (hazardous)
- Key: expansion tank (nitrogen blanket), minimum flow, centerline support
Molten Salt WHR and Storage
- Recovers high-temp heat, stores in molten salt tank (CSP, industrial WHR)
- Pumps:
- Hot salt pump: vertical long-shaft, submerged in hot salt tank (560°C)
- Cold salt pump: vertical long-shaft, submerged in cold salt tank (290°C)
- Circulation pump: vertical canned or magnetic drive
- Material: 316/304 (nitrate <500°C), Inconel 625 (chloride >500°C)
- Key: freeze protection (heat tracing, jacketing), no elastomers, preheat
ORC System
- Converts low-temp heat (80-300°C) to electricity via organic fluid
- Pumps:
- Working fluid pump: magnetic drive or canned (zero leakage, high pressure)
- Heat source pump: thermal oil or water/glycol circulation
- Cooling pump: water/glycol circulation
- Key: zero leakage (flammable/toxic fluid), high pressure ratio, precise control
Jacket Water Recovery (Engine)
- Recovers heat from engine jacket water (80-120°C)
- Pump: standard centrifugal or vertical inline
- Fluid: water/glycol (antifreeze, corrosion inhibitor)
- Temp: 80-120°C (low pressure)
- Key: reliable, low head, moderate flow
Material Selection
Water/Steam Service
- Boiler feed: 316/17-4PH wetted, carbon steel or alloy casing
- Condensate: 316/bronze wetted
- Cooling water: cast iron/bronze (fresh), 316/duplex (seawater)
- For high-press feed: 2.25Cr-1Mo or F22 casing (high temp/pressure)
Thermal Oil Service
- Casing: WCB (carbon steel) up to 350°C, 2.25Cr-1Mo up to 450°C
- Impeller: 316, CF8M, or WCB
- Shaft: 316, 17-4PH, or 2.25Cr-1Mo
- Seal: SiC faces, Inconel springs, metal bellows (>200°C)
Molten Salt Service
- Nitrate salt (<500°C): 316/304 stainless
- Chloride salt (>500°C): Inconel 625, Hastelloy C
- No elastomers — metal gaskets (spiral wound, RTJ)
- Shaft: 316 or Inconel 625
- Bearing: grease-lubricated (outside salt) or product-lubricated (canned)
ORC Working Fluid
- Refrigerant (R245fa): 316, cast iron, aluminum (verify compatibility)
- Hydrocarbon (pentane, toluene): 316, cast steel
- Zero leakage: magnetic drive or canned motor
- Seal: if mechanical seal, double seal with barrier fluid
WHR-Specific Considerations
Variable Heat Source
- WHR heat source varies with engine/gas turbine load, process changes
- Pumps must handle variable flow and temperature
- Use VFD for flow control (match heat input)
- Thermal shock: gradual load changes, preheat systems
- For thermal oil: maintain minimum flow (prevent coking at low flow)
Thermal Cycling
- WHR systems cycle with production (startup/shutdown daily or weekly)
- Thermal cycling causes fatigue, seal wear, alignment changes
- Design: centerline support, flexible coupling, proper warm-up
- Material: fatigue-resistant (avoid brittle materials, use stabilized stainless)
- For molten salt: maintain temp above melting point during shutdown (heat tracing)
Efficiency Optimization
- WHR system efficiency depends on pump efficiency (parasitic load)
- Select pump near BEP, use VFD for part load
- Parallel pumps: stage for efficiency at variable load
- High-efficiency motors (IE3/IE4)
- Proper sizing: avoid oversized pumps
Redundancy
- WHR often integrated with production — pump failure = lost revenue
- N+1 redundancy for critical pumps
- Dual power supply (utility + emergency generator)
- Quick-change design (cartridge seal, back pull-out)
- Condition monitoring (vibration, temperature, pressure)
Common Issues
- Thermal oil coking: Low flow or high film temp. Maintain minimum flow, use synthetic oil for >320°C.
- Molten salt freeze: Heat tracing failure, cold startup. Maintain temp, preheat, redundant tracing.
- Cavitation (condensate/feed): Low NPSH at variable load. Use low-NPSH pump, deaerator pressure control.
- ORC fluid leakage: Flammable/toxic fluid. Use magnetic drive/canned, double seal, leak detection.
- Thermal cycling fatigue: Daily startup/shutdown. Use centerline support, fatigue-resistant materials, gradual warm-up.
- Bearing overheating: High temp conduction. Use finned/water-cooled housing, oil circulation.
- Variable load vibration: Off-BEP operation. Use VFD, parallel pumps, minimum flow protection.
- Heat exchanger fouling: Reduced heat transfer, increased pump head. Monitor differential pressure, clean periodically.
Procurement Recommendations
- Provide: heat source type, temp range, variability, heat transfer fluid, system layout
- For HRSG: specify multistage boiler feed pump, vertical condensate, N+1 redundancy
- For thermal oil WHR: specify high-temp chemical pump, centerline support, Plan 21 seal
- For molten salt: specify vertical canned pump, 316/Inconel, heat tracing
- For ORC: specify magnetic drive pump (zero leakage), high-pressure rating
- Specify VFD for variable heat source applications
- Include N+1 redundancy for critical WHR pumps
- Specify centerline support for >150°C
- Include minimum flow protection (ARV for multistage)
- For molten salt: include heat tracing/jacketing, preheat system
- Specify material per fluid and max temp (verify compatibility)
- Require performance test per API 610 / ASME PTC 8.2
- Include condition monitoring (vibration, temperature)
- Include spare parts: seal, bearings, wear rings, impeller
- Verify supplier has WHR/thermal oil/molten salt references
Related Industries
Waste heat recovery pump principles apply to power generation (CHP, geothermal, solar), oil and gas (refinery, upstream, pipeline), chemical processing (process heating, reactor), metals processing (furnace, rolling, sinter), glass/cement (kiln, furnace), food and beverage (process heat, boiler), and pulp and paper (recovery boiler, digester). The core principle — reliable circulation of heat transfer fluid under variable thermal conditions — is consistent across WHR applications.