New Zealand has signed but not yet ratified the Stockholm Convention on Persistent Organic Pollutants (POPs). [The Government has signalled its commitment to the Convention, and has enacted amendments to the Hazardous Substances and New Organisms and the Imports and Exports Acts to enable ratification.] The Convention covers 12 POPs, including polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), commonly known as dioxin, which are listed in Annex C as being unintentionally produced.
The Convention (UNEP, 2001b) sets out a series of measures designed to reduce releases of unintentionally produced POPs, with the goal under Article 5 of "their continuing minimisation and, where feasible, ultimate elimination". Article 5 requires the development and maintenance of source inventories for the unintentionally produced POPs. Article 11 requires that parties encourage and/or undertake appropriate research and monitoring pertaining to sources and releases into the environment.
Part II of Annex C lists industrial sources with the potential for comparatively high formation and release of PCDD and PCDF to the environment: thermal processes in the metallurgical industry - in particular secondary copper, aluminium and zinc production - are all included. Part III lists thermal processes in the metallurgical industry that are not listed in Part II.
This study aims to contribute to progressing any future New Zealand obligation under the Convention by characterising emissions from thermal processes in the secondary metallurgical industry.
The New Zealand Inventory of Dioxin Emissions to Air, Land and Water and Reservoir Sources (Ministry for the Environment, 2000) identified the secondary metal industry as one of New Zealand's largest industrial sources of PCDD and PCDF. This follows worldwide experience where the secondary metal sector has been identified as an important source of these pollutants.
Ferrous and non-ferrous metallurgical processes have been identified as a source of PCDD and PCDF emissions in many European countries (UNEP, 1999). Based on these national inventories, mainly for industrialised countries, iron and steel (including primary production) were estimated to contribute 10% and non-ferrous metals production 8% of the global flux for the 1995 reference year. There is, however, little information on the proportion contributed from secondary metal production.
The New Zealand dioxin inventory (Ministry for the Environment, 2000) identified uncertainties in emission estimates for non-ferrous metallurgical and foundry processes. The emission factors used were from overseas, and the applicability to New Zealand conditions was considered highly uncertain.
1.2 Study scope
This study covers those sectors within the metal production and processing industry where there were data gaps from the 1998 dioxin inventory. The inventory covered secondary steel from one large plant in Auckland, non-ferrous metals (estimated for all operations based on employee numbers), and secondary aluminium estimates for four large plants. This report updates the emission factors and production estimates for all secondary processing in New Zealand except the large steel plant in Auckland, because there is high certainty associated with that data.
The phrase 'secondary metal processes' in this report refers to processes for melting and refining metals including scrap, ingots, internal returns [Internal returns are offcuts and off-specification product that are generated internally and recycled to the furnace.] and alloying materials. Many of these activities are sometimes referred to as 'foundry operations'. They have been distinguished from metal production processes involving the reduction of ores and smelting. This study covers both ferrous metals and non-ferrous metals, including aluminium and copper. The principal thermal processes in the secondary metals industry encompass furnace operations and thermal pre-treatment of scrap. The study focuses on furnace emissions after an initial industry survey showed there to be limited thermal pre-treatment of scrap undertaken in New Zealand. Nonetheless, one thermal pre-treatment system was included in the test programme.
Primary metal production is considered distinct from secondary metal processing and as such is not included in this study. There are only two primary production sites in New Zealand (one steel and one aluminium), so emissions from this category can be characterised by focusing on the individual sites. There is already good information on primary steel production in New Zealand, which is undertaken by the Lurgi-Stelco direct reduction process from iron sand and coal, with a capacity of 650,00 tonnes per year and an annual PCDD and PCDF emission of approximately 0.10 g I-TEQ per year. Primary aluminium production is approximately 320,000 tonnes per year using the pre-bake Hall-Heroult process, but emissions from this source have not yet been estimated (Ministry for the Environment, 2000).
There is also limited data on secondary metal processing both in New Zealand and overseas. It was therefore considered necessary to study this part of the metals sector in order to enhance knowledge of New Zealand's dioxin emissions to air.
In this study an industry survey was carried out to gather information on the metals sector, including process characteristics, plant sizes and pollution controls. Emission testing was then undertaken at selected sites based on the information from the survey. Sites were selected to investigate the range of small through to large production rates, and furnace and metal types commonly present in New Zealand.