Brazed Aluminum Heat Exchangers (BAHX) play an important role in cryogenics and are the most compact and energy efficient heat exchangers available for handling a wide range of services. They are particularly valued for their relatively high thermal efficiency, compactness, low weight and low maintenance. BAHX provide low capital, installation, and are key to many cryogenic processes and are at the heart of the plants they operate.

Source: Fives

A Brazed Aluminum Heat Exchanger

Today BAHX’s are used in a variety of applications including:

  • Hydrogen liquefaction
  • Industrial Gas Production (Air Separation Units - ASU)
  • Natural Gas Processing
  • Liquefied Natural Gas (LNG)
  • Olefins & Petrochemicals
  • Helium liquefaction

At Fives, we are proud of our standing as a technological leader in the cryogenics market. We specialize in the design, manufacture, installation and maintenance of brazed heat exchangers, cold boxes, core-in-drums and cryogenic Cryomec® centrifugal and reciprocating pumps.

Our cutting-edge, high-performance and complete product portfolio is specially developed for the gas production and processing industry and has a wide range of applications. These include air separation, distribution, natural gas processing, LNG, petrochemicals and hydrogen.

We have been in the industry for over 60 years, starting under the name ‘Trane’ in France, before joining the group Fives in the late 90s. Today, Fives in cryogenics operates all around the world with the support of local workshops and offices in France, Switzerland, China and the USA.

History and development

BAHX technology actually dates back to World War II when many manufacturing firms in the US, including Trane, changed their focus to manufacturing processes to support military production. One of the applications Trane developed for the US military was for airplanes that needed to cool air from their supercharger by using outside air. While the supercharger could establish the pressure, in doing so a great deal of heat had to be transferred through a heat exchanger (intercooler). Due to weight limitations on board of these planes, Trane turned to brazing aluminum as a possible solution. They developed a very lightweight aluminum exchanger that they were able to successfully braze into an entire intercooler. These intercoolers allowed US planes to maintain performance at higher altitudes. Later this intercooler was also used for the first vehicle on the moon, the lunar rover.

This technology eventually evolved in the 1950s to cryogenic separation and liquefaction of air (ASU) and to production of petrochemicals and treatment of off-gases (especially on ethylene production). Most BAHX have been installed in process plants used to separate a feed gas into its constituents, for example by the partial liquefaction of the feed and subsequent distillation and separation. The products and waste stream are then re-warmed against the feed streams. Condensers and reboilers are associated with distillation columns.

Design and manufacturing process

Source: Fives

BAHX have the design ability to carry multiple streams, occasionally up to 20 or more which allows process integration in multiple industrial processes and their very large surface per unit volume (up to 4 or 5 times as many as conventional heat exchangers) which is particularly advantageous when low temperature differences apply.

BAHX are a unique type of heat exchanger consisting of a stacking of several layers (hundreds), each layer made of corrugated fins inserted between two parting sheets and closed by side bars (Figure 1). Openings inside bars assure inlets and outlets of up to 20 fluids, monophasic and/or diphasic.

Among all operations, exchanger brazing is a key and complicated step in the manufacturing cycle of an exchanger. Mechanical integrity (pressure resistance) and matrix leak tightness are dependent on the control of this operation; these are two essential factors for correct operation of the exchanger according to the client’s process, and in compliance with construction codes.

Full control of this operation has always been considered by Fives as being of paramount importance.

To that end, Fives successively equips its vacuum brazing furnaces with a specific regulation system, allowing predictive control under stress of the brazing thermal cycle from actual temperature cartography of the exchanger at any moment of brazing. Based on a breakdown of heating elements into more than 65 independent zones, this control principle allows real-time adaptation of the individual power of each resistor so as to obtain the shortest possible brazing cycle while complying with all key parameters such as the temperature levels and/or the vacuum quality.

Today, we have gone one step further with the development of new 3D software, allowing the simulation of the entire brazing thermal cycle for the exchanger to be manufactured.

This software package allows optimization of the control parameter inputs before brazing, based on radiation and conduction computing, according to the exact design of the exchanger and the real brazing configuration. In addition to systematic use in operation, this software is a technological improvement for Fives since it allows the optimization of matrix design (cross-section, etc.) during, in particular, the R&D phase.

Flexible by design

Source: Fives

Exchanger brazing

With design pressures of up to 140 bar, our BAHX are available in a wide range of sizes, configurations and fin types. Fives in-house simulation software is the result of more than 20 years of R&D and tests. Thanks to this, we can offer bespoke design and optimization. Our simulation tools are used for the thermal and hydraulic simulation of heat exchangers in order to take into account their process environment and validate BAHX performance.

Fives’ BAHX offer extremely high reliability and, as a result, exceptionally low downtime – less than 0.01%. Clients therefore enjoy greater availability with our solutions, lower maintenance costs and, ultimately, higher productivity and profitability.

Going even further, our CryoSens software is Fives’ proprietary digital solution that enables operators to better understand and monitor our BAHX. Fives’ CryoSens Analytics software identifies and analyzes clients’ heat exchanger components, providing simple, calibrated solutions for improved operation.