Spiral

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Description

 

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Nexson Group - Spiral Plate Heat Exchangers: GreenSpiral, Liquid-liquid Heat Exchanger, Biphasic Heat Exchanger, Sludge and biosolid treatment SPHE.

The concept of a spiral heat exchanger is as simple as it is sophisticated. Two or four long metal strips, onto which spacer studs are welded, are wound around a core, thus creating two or four equally spaced single-passage channels.

The concentric shape of the flow-passages and the studs yield turbulence at low Reynolds numbers. By optimising the flow pattern, heat transfer is enhanced, whilst fouling is reduced. This yields a compact and space-saving construction that can be readily integrated in any plant and reduces installation costs.

Because of the all-welded and robust design, and the low fouling properties, maintenance costs are reduced to a minimum. From the viewpoint of Total Cost of Ownership, the spiral heat exchanger is frequently the most cost-effective solution.

As the channel geometry can be varied with great flexibility, a spiral heat exchanger can be adapted ideally to the existing requirements and desires. Notwithstanding varying mass flows and desired temperature differences, a spiral heat exchanger often enables heat transfer in a single unit and offers an excellent turn-down ratio. The long single-flow passage channels offer almost any desirable thermal length by which difficult process flows can be heated or cooled in a single device, while avoiding any sharp turns of flow that so often cause blockages.

HES have developed a wide range of cores, each of which is tailored to accomplish specific tasks, which enables us to choose the right solution for any application.

An important feature of our design is the use of continuous strips from core to shell that enables internal and almost unreachable welding seams to be avoided entirely.

The execution of a unit can be chosen freely to our, or to the Rosenblad design, which enables us to offer replacements units for all applications without the need of costly piping adjustments.

Application

Liquids and slurries

Because of the single-flow passages, the spiral heat exchanger is State-of-the-Art-Technology especially in the case of fouling, viscous and/or particle-loaded fluids and is therefore frequently the first, if not the only choice. This is because bypassing is intrinsically avoided resulting in a self-cleaning effect by which potential blockages are washed away before they become a problem. Also as a result of its execution in the case of `difficult´ fluids, high heat-transfer coefficients are established and, in case of particle-loaded fluids sedimentation is avoided.

The spiral heat exchanger is almost free of dead-space and can be executed without any dead spaces. Cold- and/or hot-spots are therefore excluded and temperature differences between the fluids of less then 3°C can be reached. In particular, for sludge or sludge-like applications the spiral heat exchanger is executed without spacer studs so that the risk of blockages is reduced to the absolute technical minimum.

Leakage is practically excluded by the all-welded channel construction. For this reason the spiral heat exchanger is ideal in the case of sensible, dangerous and/or aggressive fluids. Because of the single-flow passage, chemical cleaning is extremely effective. The covers are mounted with hook-bolts to enable easy access to the channels, which can also be readily cleaned mechanically. In particular for sludge or slurry applications, covers can be executed with hinges or davits, thus enabling very fast access that reduces down-time.

Condensation and Evaporation

In case of condensation applications, the spiral heat exchanger demonstrates its versatility. It is almost the ideal condenser, especially in case of condensing mixed vapours, with or without inert gases. The concentric, single-flow passage constitutes a perfect geometry for this task and is therefore a basis for maximised product recovery.

For condensation applications, there are three possible flow arrangements: Counter-current, co-current and a mixture of both.

If pressure-drop is allowed, a unit with counter- or co-current flow is a good solution. Vapour, particularly with a high inert gas concentration, needs a sufficiently long condensation path, which can be realised by means of a spiral heat exchanger. In addition, the condensate and/or inert gases can be sub-cooled within the same unit.

In the case where pressure-drop needs be minimised, such as in near-vacuum applications, the vapour is condensed in a cross-flow arrangement with the cooling fluid. As a result of the short flow passage but high cross-sectional area available, high flow rates of vapour can be condensed at pressure-drops of less than 1 mbar. Also in this case, inert gases can be removed readily.

In the case where the condensate needs be sub-cooled, while having only a small pressure-drop at disposal, the combination of cross-/counter-flow is used.

An outstanding advantage of the spiral heat exchanger as a condenser is that it can be flanged or welded directly onto a column as an overhead condenser. It is also frequently used to realise multiple-stage condensers. The assembly of the spiral condenser onto a column greatly reduces installation costs because connecting pipework is reduced to the minimum.