YOUR EMISSION... should you intercept it

'Adverse climate change is perhaps the most serious environmental threat facing the world today, with the potential for devastating disruption to human society, the global economy, human health and the natural environment.' So said Michael Meacher, environment minister, to a recent seminar on controlling industrial emissions. As a politician, Meacher is concerned with the horse-trading and compromise in negotiations to set the standards that plants must reach. But, as ever, it's down to the chemical engineers to find ways to meet those standards..

The Institution of Chemical Engineers' recent London seminar on industrial emissions sought to find ways to fulfil this function. David Fisk of the Department of the Environment, Transport and the Regions pointed out that the change of government in the UK has led to an appreciable difference in the regulatory climate: 'After only a few months in office,' he said, 'it's become clear that the Labour government is committed to a radical new approach in the environment.' The institution of Integrated Pollution Prevention and Control (IPPC), supplementing and eventually replacing Integrated Pollution Control (IPC) is one example of this, bringing a wider range of industries under a system of permits and inspections, including food production and landfill (see PE September 1997, p29).

However, it's only the latest in a long line of changes, pointed out Chris Haigh of ICI Chemicals and Polymers in Runcorn. Emission control legislation has been around for almost 100 years now and ICIhas the dubious honour of being the original reason for it. 'The original Alkali Inspectorate was formed to control the emissions from the then-formative chlor-alkali industry of North West England, from which ICI eventually emerged,' he said.

These days, ICIexpects to commit around a third of its development resources to environmental improvement for the foreseeable future, says Haigh, and a large part of these funds will be devoted to data handling. One way currently being explored to reduce this cost is to use techniques borrowed from the accounting department, he commented; these techniques provide 'audibility and confidence in automatically produced data.'

But 'traditional' problems still occur, especially when best practice contradicts safe operation. For example, Haigh said, flammable liquid storage silos are only safe if there are no sources of ignition anywhere near their vent streams; but the best practice for disposing of vented liquids is incineration, which uses a continuous source of emission. This means that the design has to incorporate 'flame arrestors or other sorts of non-intrinsic safety protection.'

The cement industry is also facing ever-greater challenges, said Lawrie Evans of Blue Circle Industries. 'The number of emission species which have become of concern has spiralled during the '80s and '90s; NOx, SOx, heavy metals, dioxins and furans to name but a few,' he said.

Previous best-practice techniques, such as electrostatic precipitators to collect dust from the kiln exhausts, are now being supplanted. The problem with this equipment, explained Evans, is that the dust has a very high electrical resistivity, and the precipitators won't work unless the exhaust fumes have been treated with water. Under 'cold conditions', such as start-up and when the kilns are operating at low production rates, this is not possible, which leads to unacceptably high emissions. Since 1980, many precipitators have been replaced by baghouse filters, said Evans. Emission levels from single kilns have dropped from 200 1000mg/Nm3 during start-up and 50 100mg/Nm3 during normal running to an average of just 30mg/Nm3.

For some industries, pollution control can be an opportunity to increase profits. Eric Hutton of British Steel's technology centre in Rotherham explained that his company now focuses on sustainability which he defines in making the most efficient and profitable use of resources. Steel is, after all, 'the world's most recyclable material,' he pointed out.