Various substances used in the adsorption dryer have to be replaced in the course of its operating life. In addition to this, the operation of an adsorption dryer leads, to further by-products in addition to the substances consumed. The concept of consumable material shows clearly that, in the first place, economical i.e. operating and works economy aspects, are reviewed. The enforcement of new waste product laws means that essential aspects of compressed air purification also have to be considered.
Figure 9.4.1
Apart from the priority attached to the avoidance of waste products, there is also the responsibility of the manufacturer concerning the responsible disposal of the product manufactured by him. At the same time, there must be information made available about any by-products concerned and applicable safety data must be stated. Every operator is obliged to avoid pollution or, at least, to reduce it to an absolute minimum. Compressed air dryers generate clean, dry compressed air but also by-products which cannot be avoided. By-products and residual substances arising from the operation of compressed air dryers are those groups of waste materials arising mainly at service intervals from the replacement of operating aids such as filter elements and drying material.
Figure 9.4.2
Oil free compression promotes acid formation within the condensate and oil lubricated compression also becomes a polluting factor. Oil saturated prefilter elements may have to be disposed of as special waste products in accordance with legislation concerning used oil. Contamination of the drying material with oil residues has to be looked at. Oil lubricated systems are always protected by coalescing oil removal filters. Assuming an inlet temperature of 30°C, the drying material is polluted by 0.015 mg/m3 of oil (see Diagram 4.8.4.1) and at the same time charged with 30 g/m3 of water (see Diagram 2.5.3.1). The proportion between oil loading and water loading thus amounts to 1:2000.000. The pollution of the drying medium (see section 4.8) with oil vapour is considerably less than often assumed. In its new state, drying material can be classified in accordance with the DIN safety data sheet. After some years of service life, the operator must carry out a new assessment.
Figure 9.4.3
As drying materials have a catalytic effect, the disposal of harmful substances must be considered. The best precaution is a conventional layout of the installation which usually leads to a prolonged service life of the filling where service lives (see Diagram 5.5.3.3) of 3-5 years are typical. In accordance with European waste products legislation, every manufacturer is obliged to take back all material such as filter elements and drying materials, as pollution of the operating materials during service life in part drastically changes these materials so that they no longer correspond to the original product. Only officially licensed waste disposers are permitted to receive materials contaminated by the system.
Figure 9.4.4
If in doubt, the disposal recommendations mentioned in the waste product catalogue should be applied. According to the latest European regulations, waste product removers or disposers are no longer allowed to accept waste products without disposal documentation approved by a waste product authority office. Adsorption dryers are, in most cases, regenerated by means of their own or by outside air. We are thus dealing with regeneration air as well as with air which re-enters the atmosphere upon depressurisation. The fraction of the airflow which is released by heatless as well as internally heat regenerated dryers, as well as the regeneration and blower air of externally heated dryers are all exhaust air. Such exhaust air is released to the environment as a by-product or ducted via a suitable pipe. The regeneration air of both processes can include not only moisture but also dust, caused by the catalytic effect of the adsorption mass. With heat regenerated installations, one also has to consider the residual heat of the regeneration air. Various locations and industrial areas presuppose that the exhaust air meets the requirements of TA-air. For pressure releases and depressurisation processes it is important that the exhaust filters retain dust particles which could otherwise enter the atmosphere. With closed loop installations, which regenerate at operating pressure, such exhaust air does not arise. As compressed air is being dried, another by-product arises naturally, i.e. the condensate (see Part 11). Depending on the type of application and the design of the compressor, one has to deal with acidic condensate or oil/water emulsions. Responsible disposal or regeneration of condensate by means of Oil/Water Separators, filter installations or effluent water treatment forms part of the installation requirement. Figs. 9.4.1 to 9.4.4 shown in this section represent the most important adsorption dryer processes complete with their characteristic by-products and residual substances. This data is based on operating experience with the systems shown.
