Spirax Sarco helps Provectus with rare decontamination project 12 November 2012
Contaminated land specialist Provectus is reporting success with a novel approach, based on steam, it used to clean up the soil from an old printing works.
The site, located in Somerset, had been contaminated with toluene over many years and developers were looking to extract the flammable solvent so the land could safely be used for housing.
In what is believed to be the first project of its kind, Provectus decided to dig out the soil and treat it above ground using an extensive system of steam heating coils, with help from Spirax Sarco.
The conventional approach for toluene decontamination is to inject live steam into the ground to vaporise the volatile solvent. But the local geology meant there was a risk it might migrate into the surrounding ground.
Hence the decision to treat the soil ex-situ, where it could control the process more effectively. "It meant we could homogenise the material better and improve the transmissivity," explains Provectus director Steve Langford.
"It also prevented any contaminated vapour from migrating into the surrounding area through the fractured geology," he adds.
In addition, using heating coils, rather than direct steam injection, was more efficient in terms of energy and water.
Spirax Sarco engineers devised a series of trombone-shaped coils, laid flat across one of the old concrete factory floors. Several thousand metres of pipework were needed to provide a big enough heating area to treat the batches of soil.
Bristol-based contractor Engineering Services assembled the pipework, according to the Spirax Sarco design, complete with steam traps and associated controls to ensure that the system worked smoothly. The company also provided a 1,250kW containerised boiler to generate the steam.
"It was quite a complex arrangement, but the biggest challenge for us was the physical site conditions," states Bob Clark, managing director of Engineering Services. "We were working exposed to the weather for the whole time."
The process ran over four weeks, heating around 4,000m3 of material and collecting the resulting vapour in plastic sheeting. From there, the solvent passed through a system of activated carbon beds, which absorbed the toluene before discharging clean air to the atmosphere.
Spirax Sarco Ltd
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