Feedstock atomiser design based on aero engine
15 Jan 2000
Aero & Industrial Technology (AIT) has employed aero engine technology to design and manufacture a novel chemical feedstock atomiser/vaporiser.
The AIT client, ICI, required this specialised system for the non-contact vaporisation of heavily fouling organic feedstocks using hot process gas vapour at high pressure. The reaction concerned is the vaporisation of trichlorethylene in the manufacture of the refrigerant, Klea 134a.
Conventional vaporisers, usually of the kettle or thermosyphon type, are not ideal for duties where fouling is a problem.
AIT's initial research indicated that the operating environment for the atomiser/vaporiser was similar to that of a gas turbine combustion system. The atomising techniques used in the aerospace industry seemed a suitable solution.
To prevent contact between the liquid hydrocarbons and any hot metal surface the liquid must be atomised into droplets to ensure that they evaporate rapidly. This was achieved by using a concentric hole airblast atomiser, which utilises an external supply of process gas to produce the desired droplet size.
The spray is injected directly into the main process plant hot gas stream. The atomiser/vaporiser unit is designed to fit into a typical chemical plant conduit with minimum reduction in system pressure. In order to ensure a good spray distribution across the gas stream a venturi was designed to accelerate gas flow and give good mixing.
The diffuser was perforated to allow effusion of the process gas through the wall to prevent the feedstock material reaching the hot metal surface.
Computer droplet analysis, perspex flow modelling and stress and finite element models assessed potential problem areas.
A perspex model with a brass atomiser was designed and manufactured which allowed engineers the opportunity to observe operations. For safety reasons, it was not possible to test the design using process chemicals, so air and aviation kerosene were used to assess droplet size and injection angle.
The units were installed in a fully functioning plant and run continuously for six months with no maintenance involvement. Following inspection, during a scheduled plant overhaul, the units were found to be in pristine condition, with no sign of carbon deposition.
Ian Duerden, AIT's sales and marketing manager, told PE: 'We have started producing the systems for John Brown. The aero engine type atomiser/vaporiser is a technology that many operators in the chemical industry have been seeking for a long time.'
