Thermal-oil circulation pumps
A thermal-oil heating system circulates a synthetic or mineral heat-transfer fluid through a fired heater and back to process consumers (jacketed reactors, heat exchangers, calanders). The pump runs continuously at fluid temperatures typically between 200 and 350 °C.
Three constraints dominate pump selection:
- Mechanical seal life at temperature. Standard elastomers fail above 180 °C. Thermal-oil pumps use hard-face mechanical seals (typically silicon carbide vs silicon carbide) with cooled seal flush.
- Bearing temperature. The bearing housing must be thermally isolated from the fluid casing — usually a finned spool piece between casing and bearing housing dissipates heat.
- Flow stability. Thermal-oil systems are sensitive to flow drop — reduced flow at high temperature accelerates fluid breakdown (cracking, coke formation).
Operating envelope of the FB Bombas FBOT line
The FBOT thermal-oil line covers, per the official catalog:
- Sizes: DN25 to DN300
- Flow: up to 2.200 m³/h
- Head: up to 135 m
- Temperature: continuous duty up to 350 °C
- Maximum rotation: 3.500 rpm
- Maximum suction pressure: 10 bar
Construction and shaft-sealing options are configured per application. For the recommended materials and seal arrangement at any specific service, consult the FBOT technical manual (linked from the catalog page) or FB Bombas application engineering.
Common failure mode: fluid degradation
Thermal-oil itself is a consumable. Over time it cracks (long molecules break into smaller volatile fragments) and oxidizes (if air ingresses through a bad seal or expansion-tank vent). Symptoms:
- Rising viscosity → flow drop → temperature spike
- Acid number > 0.5 mg KOH/g → corrosion accelerates
- Carbon deposits in heater coils → hotspots → coil failure
Best practice: sample the fluid every 6-12 months. Replace before the acid number or carbon residue exceeds the supplier’s limits.
What kills thermal-oil pumps
| Cause | Mitigation |
|---|---|
| Dry start | Interlock with expansion-tank low-level switch |
| Air ingress through seal | Maintain expansion tank N₂ blanket |
| Overheating bearings | Verify cooling water flow on the seal flush plan |
| Coked impeller | Replace fluid before coke residue spec is exceeded |
Further reading
References
- API 685-2011 — Sealless Centrifugal Pumps for Petroleum, Petrochemical, and Gas Industry Process Service.
- Therminol & Dowtherm technical bulletins (fluid suppliers’ degradation limits).
- ASTM D2882 — Standard Test Method for Indicating the Wear Characteristics of Petroleum and Non-Petroleum Hydraulic Fluids in Constant Volume Vane Pump (proxy for fluid wear).