Particulate And VOC Emissions From Foundries

Last updated: (February 2005)

Introduction

Many foundry processes result in the generation of significant emissions of particulates and volatile organic compounds (VOCs). This Reference Note outlines the processes where such pollutants may be emitted, the potential environmental impact of the emissions, and the legislative controls that may be applicable, both current and pending.

Background

The importance of preventing and minimising pollution has increased progressively throughout the 20th century.

Particulates, including smoke, dust and fume, have always been a major constituent of air pollution, although the control of such pollutants has improved enormously following the imposition of a wide range of regulatory controls on industrial, domestic and traffic sources.

The reasons why such pollutants require control are as follows:

• Particles may be inhaled by people or animals, leading to respiratory and other diseases, and, in some cases, are believed to be responsible for premature deaths.
• Deposition of particles can interfere with the rate of photosynthesis in plants, and also their rate of gas exchange
• Dust deposition can cause local damage and nuisance, including soiling of buildings, abrasion to building fabric, damage to vehicle finishes, and nuisance to people.

Fine particles are of particular concern with regard to their impact on human health. These particles are normally described by the size range referred to, eg PM10 (particulates of 10 microns or less) PM2.5 (particulates of 2.5 microns or less) etc. The finer particles are believed to be the most dangerous as they are able to penetrate into the deepest part of the lungs where gases are exchanged with the blood stream.

Volatile organic compounds, or VOCs, are a large class of carbon-containing compounds, which vary in their effects on human health and the environment. They are under considerable scrutiny internationally, and work is being co-ordinated between countries to reduce emission levels.

At present, the main concern about VOC pollution relates to its contribution to the formation of ozone at ground level. Ozone is an aggressive ground level pollutant that is formed by a reaction between VOCs and nitrogen oxides in the presence of sunlight. It can induce respiratory distress in about 10% of the population and also damages crops and building materials. In addition, some VOC emissions can cause odour nuisance to the localities around a foundry. The most notorious substance in this respect is the amine used to catalyse phenolic urethane cores. Breakdown products from the casting of moulds made with phenol-based chemical binders have also been implicated in some cases.

Other organic compound emissions are of concern due to their toxic effects on humans and animals (eg dioxins) or their contribution to global warming (eg chlorofluorocarbons).

Emissions from Foundry Processes

Both particulates and volatile organic compounds are emitted from a wide range of foundry processes. Some examples are given below.

* The actual compounds emitted vary according to the chemical binder system used. Not all substances shown will be emitted from all mould and coremaking processes.

Benefits Of Control

Good control of pollution from foundry processes not only enables companies to comply with legislative requirements, but also:

• prevents nuisance to neighbours
• improves the internal work atmosphere and reduces risks to worker health
• minimises the environmental impact of the operations
• improves the company image.

Legislation

Control of emissions to air from foundry processes is covered by existing legislation in the UK. The introduction of further controls under the new EU Directive on Integrated Pollution Prevention and Control will affect all European foundries, as well as a wide range of other industrial processes. The following legislation is applicable:

England, Scotland and Wales

Environmental Protection Act 1990: Part I, which divides prescribed processes into:

- Part A: Integrated Pollution Control

- Part B: Air Pollution Control.

Most foundries are classified for control as Part B processes under Local Authority control, and are subject to the standards set out in the Secretary of State’s Process Guidance Notes. The guidance notes include emission limits for particulates and other air pollutants, which represent legally enforceable standards of control.

Controls on emissions of particulates

The general requirement is to prevent any releases of persistently visible emissions, where persistent is defined as continuous and/or trailing past the process boundary. Where particulate generation is significant, control of such emissions can only be achieved by capture and abatement. However, where only clean charge materials are melted and the method of melting is electric or gas, some melting operations may not require capture or abatement.

The current emission limits for particulates from foundry processes range from 10 mg m-3 for some Part A processes to 115 mg m-3 for some Part B cupolas, where the type of abatement technology in use is considered acceptable in the short to medium term due to the high cost of replacement. Most processes are expected to meet emission limits of 20 mg m-3 (dry bag filtration) or 50 mg m-3 (wet collectors).

Controls on emissions of volatile organic compounds (VOCs)

Although VOCs are considered to be the source of significant environmental problems, it is not considered cost-effective to capture or abate the VOCs produced from most foundry processes. One of the main sources in foundries is the casting process, and, in jobbing foundries in particular, containment of such emissions is impractical. Even where containment and capture are possible, eg at shake-out, the cost of abatement is usually considered excessive relative to the concentration of VOCs emitted.

Consequently, emission limits for VOCs are only applied to two foundry processes at present: investment shelling processes and thermal sand reclamation plants. The application of a VOC limit to solvent-based investment shelling is deemed appropriate as there are alternative water-based shelling systems available that have been widely adopted within the industry. Thermal sand reclamation plants are gas-fired, and some VOCs will be emitted as a result of the process of burning off the binder resin. However, provided that the plant is operated correctly, including good temperature control and burner maintenance, emissions should be easily controllable to below 20 mg m-3.

Northern Ireland

A system of integrated control similar to EPA 1990 has recently been introduced in Northern Ireland by the Industrial Pollution Control (Northern Ireland) Order 1997. This created a three tier system of control and enforcement is shared between the Environment and Heritage Service of the Department of the Environment for Northern Ireland (DOE(NI)).

Practical Emission Reduction Measures

There is usually more than one way of eliminating or reducing emissions of particulates and VOCs, and it does not always have to involve abatement, which is the ‘end of pipe’ solution. Some alternative ‘cleaner technologies’ are shown below.

The Future

Some tightening of the regulatory requirements associated with foundry processes are anticipated over the next eight years as a result of the following new legislation and international agreements:

• revision of the Process Guidance Notes
• the requirements of the new National Air Quality Standards
• UK implementation of the EU Directive on Integrated Pollution Prevention and Control
• UK implementation of the EU Solvents Directive
• other proposed standards and protocols