Best Available Technology Document

Preface

The European Asphalt Pavement Association (EAPA), in recognition of rapidly developing EU environmental legislation, decided in 1992 to proactively address the incoming environmental requirements of the industry in order to further enhance its reputation and record in this key area.

It was quickly identified that the focal point of this strategy would be the development of an industry-agreed document describing the technologies and emission limits that were currently accepted to be reasonable, economic and proven in practice. Under EU legislative terminology, this is described as Best Available Techniques, abbreviated as BAT.

After extensive consultation with environmental specialists in 16 European countries, the document was published for wider industry discussion at the Helsinki Symposium in June 1994.

As the title implies, the document is presented in the form of guidelines proposed to be voluntarily adopted by the asphalt industry in all EAPA Member Countries. It is written to be useful to those outside the industry also, in particular the legislators and licensing authorities. Hence it should be useful in promoting understanding and dialogue, as well as being a universal reference document in licensing, monitoring and auditing. The EAPA membership has expressed full support to the recommendations and supports further implementation.

An addendum, reconfirming the main recommendations of the document, but updating on new EU and national legislation and limit values, as well as on updated abatement techniques and measurement values, was issued at the Strasbourg congress in 1996.

The document emphasises that BAT will have different interpretations in different countries, depending on the level of economic development. Interpretation will also vary according to plant location, depending for example whether the plant is located in a remote quarry or a city suburb. Decision on specific limits for each particular plant will, as hitherto, remain a matter for local decision.

The consultation process established that there was in fact a higher degree of consensus on BAT criteria between Member Countries than originally anticipated, and the trend is towards further convergence in the medium term. More significantly, the consultation process also underlined the low environmental impact of the asphalt industry compared to many others, further improvement being anticipated in the years ahead.

Legislative background of the BAT document

Here schematically the main EC environmental legislation up to the present 5th Environmental Action Program is indicated. As part of this Program several new instruments are being formulated with the purpose of encouraging industries of all types to work to "Best Available Techniques" (BAT) on a self-regulatory basis.

Figure: Relevance of BAT guidelines to other EC and national initiatives.

The asphalt industry through this document is seeking to establish agreed BAT guidelines with the purpose of encouraging consistency and a "level playing field" between all European countries. The BAT document will also serve as a valuable reference for environmental auditing and compliance reporting to licensing authorities and the public at large, giving greater consistency throughout the industry. The BAT document therefore reflects the importance that the European asphalt industry attaches to good environmental performance.

It is significant to note that the asphalt industry is not specifically targeted in any of the mentioned EC initiatives, because it is regarded as a low environmental impact industry. Similarly in the US the asphalt industry is categorised in the industry grouping of least environmental impact.

Recommendations

It is recommended that new stationary asphalt plants should be designed, equipped and operated to the guideline values set out below (all values ideally being referred to the commonly used 17% O2 level in exhaust gases measured on a dry basis). It is recognised that the interpretation of what is "reasonable, economic and proven in practice" will vary from country to country, depending on the level of economic development and locational factors. It is recommended that existing stationary asphalt plants should be considered for phased upgrading where economically achievable to the levels appropriate for new plants over a time period yet to be agreed. Based on the current rate of development of technology a period of several years seems appropriate.

For new and existing transportable and mobile mixing plants, some exemptions will apply, the limits imposed being usually delegated to local decision. For cold mix (that is, emulsion based) plants, the relevant emission parameters need to be addressed.

It is recommended that stack particulate emissions should be in the range 20-100 mg/Nm3 (ideally measured according to the draft CEN standard). The choice of limit will depend on plant design, locational requirements, and associated costs (both capital and operational) and benefits. In special cases where the wet scrubbing system is necessary, a higher limit of 150 mg/Nm3 may be the best economically achievable. Measurement every 1 to 3 years of particulate emission usually suffices combined with daily visual inspection and good plant management.

In typical situations, SOx emissions will be significantly less than the guideline value of 500 mg/Nm3, and hence will not require to be measured. Only in cases where high sulphur fuels (for example over 3% sulphur), or where some sulphur containing aggregates are used, will this figure be exceeded. In such cases a higher limit will be appropriate, possibly with associated measurement.

Similarly, under virtually all operating conditions, NOx emissions will be significantly less than the guideline value of 500 mg/Nm3, likewise not requiring measurement. Low-NOx burner technology is still at a development stage, and therefore not widely proven.

It is not possible to give specific guidelines for CO and CO2 emissions as these vary widely according to the type of fuel used and the construction of the burner installation. However both can be optimised by good plant operation. The emission of blue smoke is to be avoided or minimised by temperature control or by covering and ventilation in combination with filtering particularly when recycling.

While measurement data currently available does not indicate concern with PAH emissions, prudence should be exercised to limit such emissions when recycling tar containing materials, in view of environmental, health and safety considerations.

It is desirable to standardise the bases and methods of emission measurements and hence it is important that the work in CEN TC 264 "Air Quality" is successfully completed. Future standards should recognise that good process controls will not only optimise plant performance, but also reduce the frequency of measurements.

Stack height should provide sufficient dispersion of the emissions mentioned above to keep immission levels within acceptable limits. As a rule of thumb, this will require stack heights varying from 10 m for smaller plants to 20 m or more for larger plants. All practical steps should be taken in plant operation to ensure that there is no offensive odour outside the plant boundary or at the nearest dwellings.

Plant design and operation should ensure that fugitive dust emissions do not cause nuisance outside the plant boundary or at the nearest dwelling. It is suggested that further reduction of fugitive dust emissions could be more beneficial then any further reduction in stack emission limits.

Similarly, operating noise levels should not cause nuisance at the nearest dwellings, particularly outside normal working hours. Guideline values (expressed as Leq over 8 hours) are 65 dB(A) during working hours, and 55 dB(A) at other times.

Only in the case of plants with wet scrubbers will there need to be process water settlement facilities in order to meet typical effluent limits. In all plants the usual preventative measures (particularly spill containment for fuel tanks or leachate from stock piles of reclaimed asphalt containing tar) will be required to prevent ground or ground water contamination.

All incidental wastes should be recycled, or minimised where unavoidable, stored and then disposed of according to good practice.

Visual amenity should be maximised by appropriate landscaping, screening or enclosure of plant. Good housekeeping will also pay handsome dividends. Communications with neighbours should be encouraged.

Operation within these guidelines will further demonstrate the low environmental impact of asphalt plants, and will further enhance the image and reputation of the asphalt industry.