Technology
Wiped-Film Evaporation (WFE) for Used-Oil Re-Refining
Short-residence, high-vacuum evaporation for heat-sensitive and viscous feeds.
Overview
Balaji Consultants designs and integrates Wiped-Film Evaporation (WFE) systems for the high-vacuum recovery of valuable lubricating-oil fractions from used-oil feedstocks. The WFE creates a continuously renewed thin liquid film over the heated surface, enabling high-boiling fractions to be recovered under vacuum with short residence time and controlled thermal exposure.
Within a complete re-refining plant, WFE is integrated with feed preparation, dehydration, upstream distillation, vacuum generation, condensation, residue handling and downstream base-oil upgrading or finishing systems.
In the context of used-oil re-refining, WFE systems replace or supplement conventional vacuum distillation where higher thermal sensitivity, higher residue viscosity, or the need for continuous uninterrupted residue discharge makes a conventional column unsuitable. They are the preferred distillation technology for medium-to-large continuous re-refining plants and for modular skid-mounted systems where a compact footprint is important.
How It Works
1
Feed Preheating
Dehydrated feed oil is preheated to near-operating temperature in a dedicated feed preheater before entering the evaporator body. Correct entry temperature reduces the thermal load on the evaporator heating surface, prevents feed-distribution problems at the top of the rotating wiper assembly, and ensures the film forms correctly from the point of initial contact with the heated wall.
2
Feed Distribution & Film Formation
The preheated feed is introduced at the top of the heated cylindrical body through a feed distributor. In a WFE, a motor-driven rotor with wiper blades continuously spreads the incoming liquid across the inner heated wall, creating a thin, turbulent film that is continuously renewed as fresh feed enters from above. The turbulence generated by the wipers significantly improves heat transfer compared to a static thin film. Film thickness — controlled by wiper blade design, rotor speed and feed rate — is the primary parameter governing residence time and evaporation rate.
3
Evaporation
Heat is transferred from the heating jacket (carrying thermic fluid or steam) through the cylinder wall into the thin oil film, causing the lighter, more volatile fractions to evaporate. The short residence time — typically 2–15 seconds depending on the design — prevents thermal cracking and colour degradation of the distillate. Operating pressure is held in the range of 0.5–5 mbar absolute to reduce the evaporation temperature to a level that the thermic-fluid heating system can achieve safely.
4
Vapour Separation & Condensation
Evaporated vapours travel from the film surface radially inward across the vapour space to the condenser. In internal-condenser WFE designs, a cold-finger condenser mounted axially inside the evaporator body receives the vapour with minimal pressure drop — critical at very low operating pressures. In external-condenser designs, a large-bore vapour duct connects the evaporator to a separate condenser vessel. The condensed distillate — the recovered base-oil cut — drains to a receiver and is pumped forward to the next processing stage.
5
Residue Discharge
The non-evaporated fraction — comprising heavy residues, carbonaceous matter, asphaltenes and other high-boiling components — accumulates at the bottom of the evaporator body and is continuously discharged by a pump or gravity drain to the residue storage system. Continuous residue discharge is a key operational advantage of WFE systems over batch vacuum stills: the evaporator never needs to be shut down and emptied to remove residue, allowing uninterrupted processing at the design throughput.
Key Equipment
WFE evaporator body with driven rotor assembly
High-temperature thermic fluid or steam heating system for evaporator jacket
Internal cold-finger condenser or external shell-and-tube condenser
High-vacuum generation package (two-stage: dry screw pump + liquid ring pump)
Distillate receiver with transfer pump
Residue receiver with heated discharge pump
Feed preheater heat exchanger
Condenser coolant circulation system
Vacuum instrumentation and pressure control valves
Process Configurations
A
Internal Condenser WFE
The condenser is mounted centrally inside the evaporator body, minimising the vapour travel path and pressure drop between the evaporating film and the condensing surface. Used where very low operating pressures (below 1 mbar) are required to achieve the necessary separation at an acceptable wall temperature. The standard configuration for high-vacuum lube-oil re-refining applications.
B
External Condenser WFE
The condenser is a separate vessel connected to the evaporator body by a large-bore vapour duct. Allows a larger condenser heat-transfer area and more flexibility in condenser design, including the use of multiple condenser stages for fractional condensation. Suitable for higher vapour loads and applications where the modest additional pressure drop from the connecting duct is acceptable.
C
Short-Path Distillation
An extreme-vacuum variant in which the condenser surface is located inside the evaporator body at a distance equal to or less than the mean free path of vapour molecules, eliminating vapour-phase pressure drop entirely. Used for highly heat-sensitive materials where even the low pressure drop of an internal-condenser WFE would raise the evaporating temperature above the thermal stability limit of the product.
Selection Considerations
- Preferred for heat-sensitive feeds requiring very short thermal residence time
- Continuous residue discharge avoids shutdown cycles required by batch stills
- Higher capital cost than batch stills; justified at medium-to-large throughputs
- Requires consistent feed to maintain stable film formation and throughput
See It in Operation
Commissioned projects where this technology is part of the installed plant.
Related Technologies
Not sure which process configuration is appropriate?
Process selection depends on feedstock composition, required product quality, capacity, utilities, operating philosophy and project economics. Share your available feedstock data with our engineering team for an initial technical evaluation.
Submit Feedstock InformationDiscuss Your Project
Connect with our engineering team to review your feedstock, required capacity, and process objectives.