Diffusion-bonded Heat exchangers ,Printed-circuit model operation Temperature ranges

Diffusion-bonded Heat exchangers 

Technological innovations continue to extend the range of compact heat exchangers, pushing the temperature threshold to 1,000 degrees Celsius and pressure to 500 bars, depending on the material of construction and type of exchanger. Diffusion bonding creates a block of ``parent metal'' with uniform grain structure throughout the heat exchanger, even across what were once individual plates. The result is a unit with no joints or seams other than the external connection attachments.

Plate-fin model. Produced by a joint venture of Rolls Royce and Alfa Laval, the diffusion-bonded plate-fin exchanger is aimed at applications that require high pressure capabilities and the ability to handle seawater as the cooling medium. Currently available only in titanium, it operates at temperatures to 750 degrees Celsius, and pressures to 500 bars.

Designed for high-pressure gas services on offshore platforms, namely gas compression coolers in the compressor train, the plate-fin model can also be used for high-pressure crude exchangers and gas dehydration duties. The unit can also handle multiple-stream flows, with the number of streams limited only by the size of the equipment. The exchanger is a fraction of both the size and weight of conventional exchangers, which, on an offshore platform, have a large impact on costs.

The large channel size -- up to 5 mm -- means that relatively dirty services, such as raw wellhead gas and seawater, can be handled without plugging problems. Since the channels are integrally bonded together throughout the structure of the exchanger, it is inherently more reliable than tubular exchangers, which can suffer catastrophic failure should a tube rupture.

Printed-circuit model. Aptly named, because the channel-forming method mimics that used to manufacture printed-circuit boards for electronic components, the printed-circuit diffusion-bonded exchanger has been produced for several years in stainless steel, and other iron and nickel alloys. Channels of 0.5-2 mm are chemically etched into flat sheets, which are then diffusion-bonded together, with the connections welded.

Light and compact, the unit can handle pressures to 400 bars and temperatures to 900 degrees Celsius. Feed-effluent exchange, two-phase processes and other applications that lie outside the range of gasketed plate exchangers can be accommodated with this model. Like several other compact exchangers, it can be designed for multiple-pass and multiple-stream construction. However, the unit should only be used for clean services, such as clean-gas cooling, because of its very small channel size. Cooling water must be adequately treated, so that neither scaling nor biological growth plugs the channels.