Spirax Sarco's expertise helps Provectus with rare decontamination project
15 November 2012, News release from Spirax Sarco Ltd
When contaminated land specialist Provectus decided to take a novel approach to cleaning up the soil from an old printing works, Spirax Sarco provided the steam system expertise to help turn the concept into reality.
The site, located in Somerset, was 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. The contractor brought in Spirax Sarco to design a steam distribution system to do the job.
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 that the toluene would migrate into the surrounding ground, rather than rising to the surface. Provectus also judged that the 24-hectare site was too big to install an effective underground barrier around the operation to prevent such leaks escaping.
The company therefore decided 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," says Provectus Director Steve Langford. "It also prevented any contaminated vapour from migrating into the surrounding area through the fractured geology."
In addition, using heating coils rather than direct steam injection was more efficient in terms of energy and water. Spirax Sarco advised using steam as the heating medium in the coils rather than hot water, because it would remain at a constant temperature, rather than cooling down as it passed through the system.
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 that were piled on top. It was tricky to calculate the necessary heat transfer area, because the ability of the soil to conduct heat changed as the material nearest the heating coils dried, making it more difficult for the heat to flow through to the remaining soil.
Bristol-based contractor Engineering Services assembled the necessary 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 1250kW containerised boiler to generate the steam.
"It was quite a complex arrangement, but the biggest challenge for us was the physical site conditions," says Bob Clark, managing director of Engineering Services. "We were working exposed to the weather for the whole time.
The process ran over the 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.
"We'd never seen a project like this and neither had the Environment Agency personnel who inspected the operation," says Mr Langford. "We'd cleaned up the first batch of soil within two weeks and the site is now suitable for even the most sensitive developments - residential housing with gardens."
"I'm more than happy with the support we got from Spirax Sarco, which helped us to complete the project so quickly and efficiently. The solution prevented us from having to send the contaminated soil off to landfill and bring in replacement material."
"We've worked on projects with Spirax Sarco for over 20 years," adds Mr Clark. "This was the first time anyone had attempted to do a clean-up this way and the results were outstanding."
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