Bringing tall chimneys down - Bierrum's custom solution at work

UK-based Bierrum International has developed its own specialist solution to the problem of tall chimney demolition. D&RI reports.

Over the years, a variety of different techniques have been used to demolish tall free-standing chimneys, from equipment suspended from cranes, the creation of travelling work platforms inside and/or outside the chimney through to the use of explosives where space and the nature of the site allows.

As a specialist in the design, construction and repair of tall concrete structures, Bierrum International has developed its own specialist solution to the problem of tall chimney demolition in the shape of its Spider platform that was specifically developed to meet the challenges imposed by this type of demolition challenge.

The result is a fully engineered chimney demolition tool that offers a number of key advantages. It allows demolition to be carried out safely, with in-built redundancy, in a controlled and protected environment.

All demolition debris falls down the inside of the chimney, the unit itself is adjustable to cope with tapered walls and the fact that the platform mounts its own hydraulic breaker means that workers do not have to use hand held breakers, limiting their exposure to harmful hand arm vibrations.

The operating principle is simple - both the external work platform and the breaker platform inside the chimney are suspended from six brackets that fit over the top of the concrete windshield.

The external work platform provides workers with full protection from the elements while at the same time sits flush with the chimney to prevent any objects falling outside the structure.

The breaker platform has six telescopic legs but these do not touch the internal wall of the chimney - typically, a gap of 100 mm (4 in) is left between the end of each leg and the wall.

When the breaker is in use, the legs on the opposite side of the platform are pushed against the wall and provide an anchor for the platform.

To lower the platform as work progresses, slots are cut in the windshield and the brackets are repositioned in sequence at the new lower level.

The breaker is used remove the concrete from the rebar in sections, with the rebar then cut using torches to create manageable sized pieces, which are then dropped down inside the chimney to its base.

The resulting debris is then removed by machine from the base of the chimney through holes cut into the windshield and lining, and transported off site for further processing.

Spider in action

The Bierrum spider is now in the final stages of a demanding demolition job at the Rugeley Power Station in Staffordshire, UK, where it has been in use on the removal of a redundant 180 m (590 ft) chimney.

In 2006, Bierrum won a contract from International Power to build a new 180 m multi flue chimney at the power station as part of a new Flue Gas Desulphurisation (FGD) installation.

Unfortunately, this new chimney affected the stability of the older one, and as part of another separate contract, Bierrum installed a mass damper on the old chimney to stabilise the structure.

However, the old chimney could not be used for the new plant and became redundant, so International Power requested bids for its demolition - the contract was again awarded to Bierrum.

The job featured two particular challenges, however, in that the ducts for the new FGD plant ran within 1.5 m (4.9 ft) of the old chimney wall, and the main control cable duct ran under it.

This imposed a number of specific requirements for the job in that no material could be allowed to fall outside the concrete windshield of the structure and protection canopies could not be used.

In addition, the tender stipulated that workers involved in the demolition be protected against the effects of Hand/Arm Vibrations (white finger).

Add to the above a tight timeframe for the removal of the mass damper before the equinox and the presence of asbestos made demolition a major challenge, but one that the use of the Spider was perfect for.

The Spider has worked away steadily on the job, and the chimney is now down to the 12 m (39 ft). The Spider will be every shortly removed, since the presence of flues at the base of chimney mean it cannot work down any further.

Bierrum plans to demolish the remaining stump of the chimney using excavator-mounted breakers.

The work has been carried out on budget and on time, with no accidents or reportable incidents, and with no damage being caused to the ductwork surrounding the old chimney.