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C.5. BEST AVAILABLE TECHNIQUES FOR BATCH

GALVANIZING

In understanding this chapter and its contents, the attention of the reader is drawn back to the

preface of this document and in particular the fifth section of the preface: How to understandand use this document. The techniques and associated emission and/or consumptionlevels, orranges of levels, presented in this chapter have been assessed through an iterative process

involving the following steps:

Identification of the key environmental issues of batch galvanising. Among the importantissues are: emissions to air (HCl from pickling and dust and gaseous compounds from thekettle); spent process solutions (degreasing solutions, pickling baths and flux baths); oilywastes (e.g. from cleaning of degreasing baths) and zinc-containing residues (filter dust,

zinc ash, hard zinc).

Examination of the techniques most relevant to address those key issues. Identification of the best environmental performance levels, on the basis of the available

data in the European Union and world-wide. Examination of the conditions under which these performance levels were achieved; such as

costs, cross-media effects, main driving forces involved in implementation of thistechniques.

Selection of the best available techniques (BAT) and the associated emission and/orconsumption levels for this sector in a general sense all according to Article 2(11) and

Annex IV of the Directive.

Expert judgement by the European IPPC Bureau and the relevant Technical Working Group(TWG) has played a key role in each of these steps and in the way in which the information ispresented here.

On the basis of this assessment, techniques, and as far as possible emission and consumptionlevels associated with the use of BAT, are presented in this chapter that are considered to be

appropriate to the sector as a whole and in many cases reflect current performance of someinstallations within the sector. Where emission or consumption levels associated with bestavailable techniques are presented, this is to be understood as meaning that those levelsrepresent the environmental performance that could be anticipated as a result of the application,in this sector, of the techniques described, bearing in mind the balance of costs and advantages

inherent within the definition of BAT. However, they are neither emission nor consumptionlimit values and should not be understood as such. In some cases it may be technically possible

to achieve better emission or consumption levels but due to the costs involved or cross mediaconsiderations, they are not considered to be appropriate as BAT for the sector as a whole.

However, such levels may be considered to be justified in more specific cases where there arespecial driving forces.

The emission and consumption levels associated with the use of BAT have to be seen togetherwith any specified reference conditions (e.g. averaging periods).

The concept of levels associated with BAT described above is to be distinguished from theterm achievable level used elsewhere in this document. Where a level is described asachievable using a particular technique or combination of techniques, this should beunderstood to mean that the level may be expected to be achieved over a substantial period oftime in a well maintained and operated installation or process using those techniques.

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Where available, data concerning costs have been given together with the description of thetechniques presented in the previous chapter. These give a rough indication about themagnitude of costs involved. However, the actual cost of applying a technique will dependstrongly on the specific situation regarding, for example, taxes, fees, and the technical

characteristics of the installation concerned. It is not possible to evaluate such site-specificfactors fully in this document. In the absence of data concerning costs, conclusions on

economic viability of techniques are drawn from observations on existing installations.

It is intended that the general BAT in this chapter are a reference point against which to judgethe current performance of an existing installation or to judge a proposal for a new installation.In this way they will assist in the determination of appropriate "BAT-based" conditions for theinstallation or in the establishment of general binding rules under Article 9(8). It is foreseenthat new installations can be designed to perform at or even better than the general BAT levelspresented here. It is also considered that existing installations could move towards the generalBAT levels or do better, subject to the technical and economic applicability of the techniques ineach case.

While the BREFs do not set legally binding standards, they are meant to give information for

the guidance of industry, Member States and the public on achievable emission andconsumption levels when using specified techniques. The appropriate limit values for anyspecific case will need to be determined taking into account the objectives of the IPPC Directive

and the local considerations.

This chapter discusses the best available techniques for reducing the environmental impactsfrom batch galvanising. Where possible, the structure follows the logic of the production lineand identifies BAT for individual processing stages. However, some measures, especiallyprimary or preventive measures, cannot be assigned to one single process step and have to beallocated to the plant as a whole. As far as possible and wherever the data available allowed,emission levels, efficiencies or recirculation rates are given an indication of the improvementthat can be expected by implementation of the techniques. For a number of techniques, theobvious positive effect cannot be described by an exact number, but some of these techniquesare nevertheless considered as BAT.

Unless stated otherwise the emission figures presented in the following BAT chapters are dailymean values. For emissions to air they are based on standard conditions of 273 K, 101.3 kPaand dry gas.

Discharges to water are indicated as daily mean value of a flow-rate-related 24-hour composite

sample or a flow-rate-related composite sample over the actual operating time (for plants notoperated in three shifts).

Fordegreasing operations in batch galvanising plants, the following techniques are consideredBAT:

Installation of a degreasing step, unless items are totally grease-free which is rarely the casein job galvanizing.

Optimum bath operation to enhance efficiency, e.g. by agitation. Cleaning of degreasing solutions to extend lifetime (by skimming, centrifuge, etc.) and

recirculation; reuse of oily sludge, e.g. thermally.or

'Biological degreasing' with in situ cleaning (grease and oil removal from degreasersolution) by bacteria.

A primary measure to minimize environmental impact from pickling and stripping is tooperate both in separate treatment vessels, since mixed acids (with both high iron and zinc

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contents) cause problems in regeneration or reuse. As long as there are no suitable treatmentoptions for mixed acid, separate pickling and stripping and reuse of spent stripping liquor(external or internal e.g. to recover fluxing agent) are considered to be BAT for new andexisting plants.

If separation of pickling and stripping is not possible, e.g. when there is insufficient space to

install additional pickling/stripping tanks, external reuse of the mixed acids for flux productionis considered BAT.

One central treatment plant for spent mixed pickle liquors using solvent-extraction and onegalvanizing plant operating this process have been reported (see Chapter C.4.3.8). Where such(external) treatment plants are available, recovery of HCl from spent mixed pickle liquors usingsolvent-extraction may be considered a viable alternative to fluxing agent recovery (see above).

ForHCl pickling the following techniques are considered to be BAT to reduce environmentalimpacts:

Close monitoring of bath temperature and concentration parameters: and operating withinthe limits given in Part D/Chapter D.6.1 Open Pickling Bath Operation.

If operation outside the operational range given in D.6.1 is desired, e.g. if heated or higherconcentrated HCl-baths are used, installation of an extraction unit and treatment of theextraction air (e.g. by scrubbing) are considered BAT. The associated HCl emission level is2 30 mg/Nm.

Special attention to the actual pickling effect of the bath and use of pickling inhibitors toavoid over-pickling.

Recovery of free-acid fraction from spent pickle liquor.or

External regeneration of pickling liquor. Zn removal from acid. Use of spent pickle liquor for flux production.Neutralisation of spent pickle liquor and the use of spent pickling liquor for emulsion splittingare not considered BAT.

Generally, good drainage between pre-treatment tanks is advocated. Furthermore, rinsing after

degreasing and after pickling to avoid carry-over into subsequent process baths and thus toprolong the lifetime of these baths is essential. BAT is:

Static rinsing or rinsing cascades. Reuse of rinse water to replenish preceding process baths. Waste water-free-operation (waste water may be generated in exceptional cases, in which

waste water treatment is then required).

Forfluxing, control of bath parameters and the optimized amount of flux used are important toreduce emission further down the process line as well. For the flux bath itself, side-streamregeneration of the solution (using e.g. H2O2, electrolytic oxidation or ion exchange) or, ifinstallation of a regeneration unit is not possible, regeneration by externals is possible. Bothinternal and external flux bath regeneration are considered BAT.

The main problem arising from hot dipping is air emissions resulting from reaction of the fluxagent during dipping. The following techniques are considered to be BAT:

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Capture of emissions from hot dipping by enclosure of the pot or by lip extraction followedby dust abatement (e.g by fabric filters or wet scrubbers). The dust level associated withthese techniques is < 5 mg/Nm.

Internal or external reuse of collected dust for flux production. As this dust mayoccasionally contain dioxins at low concentration due to upset conditions in the plant (badlydegreased items being galvanised), only recovery processes yielding fluxing agents free of

dioxins are BAT.

Although the opportunities for energy saving by heat transfer from flue gases from thegalvanizing kettles are limited due to low volumes and relatively low temperatures (450

oC), it is

good practice to recover heat from this source either to hot water used elsewhere in the plant or

to air for drying.

For all Zn-containing wastes (dross, hard zinc, and splashes/squirts), separate storage and

protection from rain and wind, and reuse in the non-ferrous metals industry or other sectors torecover the valuable substances they contain are considered to be BAT.