Gas cooler maintenance – a solution

Citation

(2000), "Gas cooler maintenance – a solution", Anti-Corrosion Methods and Materials, Vol. 47 No. 6. https://doi.org/10.1108/acmm.2000.12847fab.003

Gas cooler maintenance – a solution

Gas cooler maintenance – a solution

Keywords Crane Heatex, Brunner Mond, Heat transfer, Coolers, Corrosion prevention

Heat transfer specialist Crane Heatex, part of Crane Co., USA, reports that it has developed a novel solution for preventing corrosion to heat transfer surfaces within three central gas coolers at Brunner Mond's Lostock and Winnington works, which, it believes, not only has made the whole cooling water process easier to maintain, but also has paved the way for cost-effective redesign and reconstruction of the ageing plant.

Two large vertical condensers at Brunner Mond's Lostock works are used for condensing Secheur gas as part of the production process. Originally these were also used to recover medium grade heat into boiler feed water. After the installation of a combined heat and power plant (CHP), however, this function was no longer required.

Owing to continuous premature corrosion of heat exchanger tubes, it became clear that ultimately the condensers would have to be redesigned and refurbished to a higher standard. The changing use of the coolers following the arrival of the CHP further accelerated the need for a solution to the problem.

Crane Heatex approached Brunner Mond with a novel design solution. The principle was that a certain grade of aluminium was known to be resistant to the process conditions, provided that galvanic or reverse galvanic action could be eliminated.

In practice this, we are informed, meant electrically isolating the cast iron or carbon steel structures from the aluminium wherever electrolyte was present and electrically coupling and running both materials to ground where it was not.

River or boiler feed water is only ever allowed to come into contact with one metal, aluminium. All connecting pipework, tubeplates and headers were either replaced in aluminium or coated in an inert material.

This "one metal" principle could not be duplicated on the gas columns, however, as these are built in iron or steel. In this case, a combination of metals has been used. The system was designed so that at no point does aluminium touch iron or steel. Where the electrolyte condensate can bridge the gap, the two metals are electrically coupled and properly earthed outside in dry conditions.

Owing to the age and size of the parent structures, Crane Heatex's designers had to overcome the differential expansion between aluminium and iron and steel in all three planes.

The design had to allow for contraction as well as expansion. To cater for this, Crane Heatex ensured that each 19-tonne flooded tube bundle would float within the main structure, using a system of regenerating elastomeric seals which could accommodate up to 6mm of differential movement without losing vacuum. A further innovation was to make these seals replaceable without detubing.

Crane Heatex had to meet very tight timescales for each installation. The equipment was constructed in kit form at Heatex and assembled on-site by Crane Heatex's sister company Crane Engineering Service (CES). Lack of working space and room for manoeuvring were major problems, which had to be overcome by CES. This involved major rigging and slinging exercises, using large cranes, fast hoists and specially rigged lifting points. Local labour with rigging expertise and site experience, combined with Crane's specialist trades and management skills, was used during the installation to maximise cost-effectiveness.

In summary, the solution provided by Crane Heatex is believed to have produced a system in which electrolytic action and structural stress problems have been "designed out". The problems caused by corrosive chemistry have, it is thought, been avoided, even though the chemical components remain. Furthermore the use of aluminium has reportedly provided a far more cost-effective solution than stainless steel – one that was well inside Brunner Mond's original budget.

Further details are available from Crane Heatex. Tel: +44 (0) 1675 470042.