The Side Manway Constraint
A process tank has the single side manway of 300mm diameter-too small for the standard PTFE heat exchanger grid. The tank cannot be cut or modified. The heat exchanger must enter through the manway and be assembled inside. The coiled tubing design solves this: the PTFE tube bundle is fabricated as the compact coil that passes through the manway and is uncoiled inside the tank.
The design takes advantage of the PTFE's flexibility-the same property that enables the tight bend radii and the elastic recovery after the coiling.
The Coiled Bundle Design
The PTFE heat exchanger is a single continuous tube-or the several parallel tubes-formed into the flat spiral coil. The coil diameter in the transport configuration is 280mm, just under the 300mm manway. The coil is 400mm high.
Inside the tank, the coil is unrolled into the flat spiral of 1,200mm diameter. The unrolling is performed by the technician through the manway, pulling the coil outward and securing it to the support hooks on the tank floor.
The tube is the 10mm OD × 1.0mm wall modified PTFE-the grade selected for the tight coiling without the kinking. The minimum bend radius of 25× the tube OD (250mm) is maintained in the transport coil. The flat spiral in the service has the larger radii-no kinking risk.
| Coiled Bundle Parameter | Specification |
|---|---|
| Manway diameter | 300mm |
| Transport coil diameter | 280mm |
| Transport coil height | 400mm |
| Service spiral diameter | 1,200mm |
| Tube OD × wall | 10mm × 1.0mm |
| Tube length | 18m (single continuous) |
| Minimum bend radius | 250mm (maintained throughout) |
| Total surface area | 0.57 m² |
| Heating duty at 3 barg steam | 5 kW |
The Field Uncoiling Procedure
The transport coil is passed through the manway into the empty tank. The technician enters the tank-with the confined space permits-and uncoils the spiral. The coil is laid on the tank floor and unrolled outward. The support hooks-the pre-installed PTFE anchors on the tank floor-hold the spiral in the expanded position.
The steam and the condensate connections are made at the two ends of the tube, which exit through the manway. The flexible connections accommodate the movement during the uncoiling.
The Limitations and Applications
The coiled design provides the limited surface area-the single continuous tube of 18m provides 0.57 m². The design suits the small tanks, the low heat duties, or the supplementary heating. For the larger duties, the multiple coils can be installed through the same manway, each coil the separate circuit.
The design is ideal for the retrofit of the existing tanks where the access is the constraint and the modification is not possible. The compact transport enables the installation in the locations where the standard equipment cannot fit.
Summary
A coiled PTFE heat exchanger solves the small side manway retrofit challenge. The tube is fabricated as the compact spiral that passes through the 300mm manway and unrolls into the 1,200mm service spiral inside the tank. The design leverages the PTFE's flexibility and the elastic recovery. The surface area is limited but sufficient for the small duties or the supplementary heating. The installation requires no tank modification.
Engineering support for the coiled tubing design is available upon submission of the manway dimensions, the tank geometry, the heating duty, and the tube specifications.
