Some auxiliary systems should be placed inside the steam and power generation for monitoring reasons, like all air systems. Compressed air systems consist of compressors, air treatment and storage drums. Design conditions always adopt the premise that it will supply clean, dry and stable air at the appropriate pressure to consumers. Among opportunities for energy efficiency in air compressing systems can be cited the use of multiple stage and modulating compressors. This reduces the compressed air temperature between stages, improving compressing efficiency and allowing better control of the energy consumption. Normally, these compressors are electric power driven and operate for continuous long periods, so the choice of high efficiency motors has an attractive payout. Also recovering waste heat from interstage coolers can help save plant energy. Collecting the coolest and cleanest air possible increases compressor efficiency and reduces the need for air treatment. Constant monitoring of pressure drop across the air filter and regular cleaning reduces energy waste.
An additional and indispensable auxiliary utility system is wastewater treatment, which must comply with environmental regulations. Industry operation generates liquid effluents that are quite often discarded. Direct discharge to any water body can cause pollution and environmental degradation, so law restricts this practice to some maximum permitted parameters that must be complied with at wastewa-ter treatments.
The treatment method is a consequence of plant processes and is divided between source segregation and pretreatment of concentrated wastewater streams. Typically it may include diverse steps depending on contaminants. If oils are present, grease traps or oil water separators are needed; if floatable solids, skimmers and air flotation are used; filtration and sedimentation is necessary for suspended solids reduction. The presence of organic matter implies biochemical oxygen demand requiring biological aerobic treatment. If waste water is to be fully recycled, eventual disinfection by chlorination may be required. And dried residual solid materials from wastewater treatment should be disposed in landfills. Not to forget that a maximum disposable temperature can be fixed to effluent streams. Needless to mention that it is not only the core process that generates liquid wastes, utilities do it too; just remember all blowdown streams mentioned in this chapter.
Concerning operation, wastewater treatment resembles water treatment units, but with a great difference. The biggest opportunity for efficiency in waste water is actually to avoid its need, by better management of the operations that produce the waste. Assuring compliance with the many recommendations cited so far, can allow an optimal operation that reduces wastewater treatment flow by a good deal. And another option is to recycle treated waste water as make- up water, for a process with less critical quality standards. It is becoming more likely nowadays to use waste water as cooling water make -up. And there is a good chance, that sometime in the not so faraway future, the only liquid effluent flow that will be allowed to an industry will be the water evaporated at a cooling tower.
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