Some time back TNO developed a heat exchanger in the form of a twisted tube into a reactor: the TNO Helix®. The efficient heat transfer gave those involved the idea of refining the technique further and modifying it for continuous processes in the chemical industry. The Helix is suitable for various compounds and can be combined with existing equipment such as separation devices or other reactor types
The twisted form of the Helix has a considerable advantage over a straight tube. The reactor comprises a tube which winds in a spiral form around a central axis. The short bends lead to a secondary flow (Dean vortices) which causes local mixing. As a result, the flow begins to act like an ideal plug flow and the retention time of the molecules in the tube can be better defined than in a straight tube, even under the lower speeds of a laminar flow. The radial mixing also improves the heat transfer, which contributes to better process control. Because of the dimensions of the channels in the Helix, the production speed can easily be adjusted to continually produce the desired quantities of the required substance. The characteristics of the particles are easier to control in the Helix reactor than in a stirred vessel or straight tube, giving better guarantees of the quality of the product.
The main added value of the reactor can be found in highly exothermic and temperature-sensitive reactions and multi-phase reactions. TNO has shown the applicability of the Helix in successful experiments with alkylation reactions, emulsion polymerizations and processes with concentrated suspensions. Another useful application for which the Helix can be used is crystallization. The mixing in the reactor is so fine that it prevents particles from sinking or adhering to the walls.
The Helix is one of the many examples of an application developed by TNO for a specific process or product which, after various modifications, has resulted in a surprising solution in other domains. Besides the original objective, that is, cooling by efficient heat transfer, a number of lab tests have led to new possibilities and unexpected applications. The breakthrough came from the discovery of the unusual flow pattern in the reactor which resulted in the formation of particles of equal sizes. Different manufacturers have now successfully applied Helix technology in their production processes and thus significantly improved the quality of their products.