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Case Study - Kiln Wrecking

Gnat's Brokk 90, 180, 250 and 330 Robotic Demolition machines were deployed to wreck and remove refractory linings during the decommissioning of numerous vessels on a chromium site

A seven-strong fleet of Gnat's robotic demolition machines were centre stage in the decommissioning of a major Teesside chemical plant, where they were deployedin very carefully ‘wrecking’ the linings of several vast steel kilns

Hydraulically operated pecker arms, more at home breaking out heavily reinforced concrete, were used to delicately removing tonnes of contaminated brick linings in a confined-space operation demanding extreme safety precautions

“The bricks were coated with a 50mm thick layer of toxic chromium dust, and our range of versatile Brokk robots proved the most efficient and safe way to remove these linings” explains Nick Turnbull, managing director of specialist demolition contractor Gnat UK. “The current downturn in our industry has created an upturn for us in developing this state of the art decommissioning process.”

Until its closure, the Eaglescliffe based complex was the UK’s only chromium processing plant. For decades it had converted a mix of chromium sulphate and chromic acid compounds into coatings for products ranging from electro plating to ceramic tiles

At the heart of this process were six, up to 100m long, rotating cylindrical kilns used to heat and mix the various feedstock materials. Varying in diameters from 3m to 5m, these horizontal steel kilns had, over the years, built up a thick layer of fine chromic oxide powder known as ‘roast’. Its green pigment has fused onto and into the kilns’ internal lining, formed of bricks laid end-on to create a 250mm thick protection

With the enclosed kilns designated as confined spaces, any proposed lining removal method - known in the industry as wrecking - demanded a severe health and safety regime

Petrol or diesel driven plant would not have been allowed and operators have to wear fully sealed head gear with its own filtered air supply” says Elementis maintenance contracts engineer Bob Armstrong. “Gnat’s electrically powered robots, with operators able to stand some distance back from the working face, have offered an effective and very safe method.”

GNAT UK’s range of Brokks offer varying sized arm reaches and hammer power ideal for tackling all kiln diameters

Access holes were cut in kiln sides and, for the narrowest 3m high vessel some 30m long, Gnat is using one of their smaller robots the Brokk 90. Just 750mm wide, and with a 3.7m reach, the machine boasts an impressive 255 joules hammer power - equivalent to a standard robot three times its size

The slightly larger, 4.5m reach Brokk 180 tackles wider kilns, while two of the fleet’s heavyweight robots, the 250 and 330, tackled the biggest 5m diameter vessels

With removal of these sizeable kilns critical to the plant’s entire £20 million decommissioning and demolition operation, Mr. Turnbull insists on having two back-up Brokks kept instantly available. “But so far they have not been needed as our robots are coping flawlessly” he says

A second opening, cut in the floor of each kiln, allowed bricks and roast powder coating to drop directly into a dump truck standing beneath. Here a simple, yet effective, water spray funnelling arrangement surrounded the drop area with a fine mist ensuring minimal dust escape. “Without this dust suppressant we would have had to totally enclose the loading areas” points out Mr. Turnbull

As the six month operation to remove some 200t of brick and chemical powder contaminant neared its successful end, Elementis’ Bob Armstrong shared his contractor’s satisfaction

Gnat was not the lowest tenderer for this job, but the company has worked well in this plant several times already and both its performance and choice of robots are proving excellent” he says. “Obviously safety on this operation was paramount and the company has shown an exemplary standard.”

The Elementis plant at Eaglescliffe, close to County Durham’s Tees Valley airport, was, until its closure, the European headquarters of the world’s largest chromium product manufacturer with US factories in Texas and North Carolina. The group produces a wide range of coating compounds for use in leather tanning, metal finishing, wood preservation, ceramic tiling and aircraft finishes

The year before the recession suddenly hit us hard in October 2008, our UK plant had a record turnover” recalls Bob Armstrong, who, as maintenance contracts manager, had worked in the plant for 37 years. Bob retired following the plant decommissioning

The Elementis chemical plant was totally demolished in Spring 2012

Above: Banksman guides Bobcat into position to remove kiln rubble, which is then removed via a hole cut into the floor of the kiln onto a dump truck for removal from the site