4.1 Industry survey
An industry survey was used to gather data to characterise the secondary-metal-processing industry. This study covered a range of ferrous and non-ferrous foundries. The data collected included:
- the type and quantity of metals melted
- processes used, including furnace type
- air pollution controls
- furnace additives.
The survey was initially by mail, with a telephone follow-up. The survey form used is provided as Appendix A. Data was also obtained from regional councils, who hold information on some operations from their monitoring and resource consenting activities. Most of the data was collected from September through to December 2002.
Information sources used to identify metallurgical industry sites were an online telephone book search, [The New Zealand Yellow Pages were searched for scrap metal recyclers, metal smelters and foundries.] the New Zealand Foundry Industry Directory (New Zealand Metal Casting Industry Association, 1995), regional councils, and a list generated from the Accident Compensation Corporation (ACC). The ACC has a database for industry premiums classified by industry type. This was searched for the following categories: basic iron and steel manufacturing; iron and steel casting and forging; aluminium smelting; copper, silver, lead and zinc smelting and refining; basic non-ferrous metal manufacturing; and non-ferrous metal casting. This study therefore represents a comprehensive compilation of the possible sites throughout New Zealand.
A list of 250 potential sites was developed and a survey was mailed to all sites. Information was requested on the basis that data for individual sites would be kept confidential.
Some thermal metallurgical operations were excluded from the survey because they did not meet the process description for the survey scope, or because good PCDD and PCDF emission data already existed. The sites excluded are discussed elsewhere, but are as follows:
- a steel mill using the direct reduction (Lurgi-Steelco) process
- a primary aluminium smelter using the pre-brake Hall-Heroult process
- a 170,000 tonne capacity secondary-steel-processing facility
- a medium-sized lead smelter.
4.2 Survey results
4.2.1 Survey response
Industry data was collated from all the sources discussed above; data for some sites was gathered from more than one source. Data was initially collected from regional council resource consent information, then the mail survey, followed by telephone calls. The telephone was used to gather additional information where data was incomplete and to increase the response rate from the survey.
Ninety-seven of the 250 mailed questionnaires were returned, but 58 respondents indicated the survey did not apply to them. This result gave an indication of the proportion of sites that were within the study scope. Regional council data was available for 32 sites, 11 of which returned the survey. The telephone survey gave data for 19 sites for which no other information was available.
Eighty-two secondary-metal-processing sites were confirmed, although there are data gaps for some of these due to incomplete responses.
Table 1 summarises the response rate achieved from the various information sources.
Table 1: Cumulative return rate for survey
Cumulative return ratea
Postal survey returns
Regional council information
a Five surveys were returned undelivered, so percentages were calculated on the basis of 245 surveys.
Assumptions were needed regarding the 100 or so sites from the survey where no information was obtained. The number of surveys returned from people whose firms did not fit within the survey indicated that it was safe to assume a proportion of the non-returns did not fit within the survey. Information from the New Zealand Foundry Industry Directory and/or the telephone book was used to judge whether the additional sites were likely to be secondary-metal processors.
It was estimated that up to 40 additional sites were likely to fit within the study scope. The additional sites were assumed to be in the small size category, because data on larger sites is generally available from the industry itself and regional councils via their regulatory involvement with such sites. As a result, 122 sites were identified as potential secondary-metal-processing sites.
While a moderate response to the survey was achieved in terms of the number of sites, the response rate in terms of total metal melted is very high at greater than 95%. This is because the large and medium categories are responsible for the majority of the production. Any sites not identified are likely to be small and contribute little to total production. It is therefore expected that not including the additional sites will be within the bounds of error for the total production estimates.
Appendix B gives full summary tables of the survey results. A summary and a discussion of the results are provided below.
Table 2 summarises the number of metal industry sites by region.
|Regional council / unitary authority||Number of confirmed operations||Regional council / unitary authority||Number of confirmed operations|
|Bay of Plenty||2||West Coast||0|
4.2.2 Metal production data from survey returns
Metal production data varied in quality due to either no response or a partial response from industry participants for some questions. Some respondents were unwilling to provide details they saw as proprietary, such as total annual production figures. These figures were estimated by assuming an average number of operating hours per week multiplied by furnace production in tonnes per hour. However, due to the extensive coverage achieved from the survey, the production data collected can be assigned a medium-to-high certainty ranking, in accordance with the certainty rankings for activity statistics used in the 1998 dioxin inventory (Ministry for the Environment, 2000).
Sites were categorised according to the scale categories identified in Table 3. Six 'large' sites produce 71% of New Zealand's total production as measured by the survey. Conversely there are likely to be about 90 small operators that contribute around 3% of the total production.
|Category||Size range |
(tonnes per year)
|Number of sites||Total production (tonnes per year)||Percentage throughput|
|Medium||> 1,000 to 5,000||8||14,791||16|
|Small-medium||> 250 to 1,000||18||8,877||10|
The amount of metal processed by operations according to size category, as a proportion of total industry production, is presented in Figure 2. As discussed in section 1, some very large sites were excluded from this study because emissions data has previously been assembled (Ministry for the Environment, 2000). These include one large steel plant in Auckland processing 170,000 tonnes per year of iron and steel, a large smelter of lead batteries, and a foundry associated with an aluminium producer in the South Island. If these were taken into account the production from plants in the large category would be higher than the 71% shown in Figure 2.
The data for production of various metals by size of industry is provided in Table 4 and the distribution is presented in Figure 3. Copper alloys include copper-based metals such as brass, bronze and gunmetal. "Other" includes lead, zinc, manganese, magnesium and tin.
Table 4: Metal production, by metal type for 82 sites surveyed (tonnes per year)
Metal production (tonnes per year)
Al and alloys
Most of the aluminium processing takes place at large sites (94% of the total). The great majority of copper processing also takes place at large sites (73%). Small-to-medium sites process a relatively large proportion of the secondary iron and steel production (note that the single 170,000-tonne capacity plant is not included).
Figure 4 gives the total metal production for each metal category on a weight percentage basis.
Excluding the 170,000 tonnes of iron and steel from the large Auckland plant, aluminium dominates secondary metal production in New Zealand. Aluminium production is mainly from four large sites, all of which were included in the test programme discussed in section 5 of this report. Iron and steel production is spread throughout a large number of plants of varying production scales and technologies. On this basis, it was considered necessary to measure a relatively larger number of sites processing iron and steel. Consequently this sector was well represented in the test programme. Copper production is mainly from one large site, which was unwilling to participate in the test programme.
4.2.3 Furnace types
Table 5 summarises data on the furnace types used within the industry. The data is only for the sites that identified having a particular furnace type. Some sites will have more than one furnace, and additional furnaces may be of the same or a different type. More detail on the total number of each furnace type was not possible due to limitations in the way that respondents completed the survey. It appears, however, that the most common types of furnaces in New Zealand are electric induction furnaces and oil- or gas-fired crucibles, and that these are used at the smaller sites. In contrast, much of the metal processing is done at large sites, which have resistance, rotary and reverberatory furnaces.
|Furnace||Induction||Oil/gas-fired crucible||Arc||Resistance||Cupola||Rotary||Reverberatory||Tilting rotary||Oil/fuel oven||Other/ unknown|
|Number of sites||35||33||5||4||2||2||1||2||1||13|
Appendix B summarises furnaces used by metal type and size.
4.2.4 Air pollution control
Fabric filtration is the most common form of air pollution control. All six sites in the large-scale category have fabric filtration and five of the eight furnaces in the medium category also have fabric filters. Five sites were identified as having afterburners and three had water scrubbers. Seventy-five percent of smaller sites ventilate directly to atmosphere via extractor fans with no air pollution control.
Fume capture rates to air pollution control equipment varied from less than 50% to 100% capture (as estimated by the survey respondents). A capture rate of 75% or greater was typical.
The New Zealand industry is not known to have advanced pollution control technologies such as carbon injection or quenching prior to filtration or catalytic filtration. Lime injection, however, would normally be used with fabric filtration because of the corrosive nature of the off-gases.
Air pollution control requirements in New Zealand vary from region to region, [For example, in the Proposed Auckland Regional Plan (Auckland Regional Council, 2001) all metal-melting operations other than welding require resource consent for air discharges, while the Otago Regional Plan: Air (Otago Regional Council, 2003) provides a permitted activity for metal processing and foundries less than 250 kg/hour.] depending on the requirements of the applicable regional plan. Operations over a specific size are required to gain resource consent for air discharges in all regions and the emissions are dealt with on a case-by-case basis. Resource consent conditions are likely to specify scrap quality (if used), air pollution control, and emission limits for particulate matter, where appropriate. Below a certain threshold the activity may be permitted by some councils and have a general requirement not to create an objectionable or offensive effect. No regions have any specific requirements relating to PCDD and PCDF emissions from metal processes that fall within the scope of this study.
Air pollution control equipment used within the industry is summarised in Appendix B.
4.2.5 Scrap quality
Data gathered on raw material was of poor quality, with the raw material type and/or quality not identified for 32 of the 82 sites. Where there was data, 78% of the sites indicated that the raw materials were clean (i.e. ingots or internally generated returns). Others stated raw materials were mixed, but did not state the contaminants present.
It is likely that the majority of dirty scrap is going to a few large sites, which are relatively well controlled. Overall the industry appears relatively clean, with little use of contaminated scrap.
Survey returns indicate that two or three sites have thermal scrap pre-treatment processes controlled by fabric filtration. Overall the rate of scrap pre-treatment is very low.
4.2.6 Furnace additives
About 20% of sites indicated that they used additives. Chlorine gas is not known to be used in New Zealand, but a few sites did identify the use of salt and other fluxes. Nitrogen gas was the most common additive identified for aluminium and copper processes. Four iron and steel sites use a combination of chlorides, fluorides and oxygen.