Reducing Blowdown Volume

Chromate waste generation can be reduced either through reducing the volume or chromate content of the blowdown stream. Blowdown volume is dependent to a significant extent on the quality of the feedwater added to the cooling system. Impurities in the feedwater such 

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While minimizing blowdown volumes can be quite effective in reducing waste, removing the hazardous metals component of the waste stream can have a more dramatic effect on reducing the impact of the blowdown on the environment. Chromate based corrosion inhibitors have historically been the mainstay of cooling water treatment systems. But in recent years, some plants have elected to use nonchromate inhibitors in order to reduce the potential environmental problems associated with chromates. Types of nonchromate inhibitors that have proved useful and that have in some situations performed as well as chromates include (Roti 1985) ... 

Following the feed step at the higher pressure, the pressure in the column is reduced to the lower pressure by counterflow blowdown. At this reduced pressure the column is purged (counterflow to the feed) using part of the pure product gas. Since pure product gas is used as a purge, the purge product (or waste) gas contains both adsorbate and carrier gas. The volume of purge gas required for the Skarstrom cycle is. 

Field tests have demonstrated that the use of ozone in place of chemical treatment can reduce the need for blowdown, and in some cases, where makeup water and ambient air are relatively clean, can ehmi-nate it. As a result, cost savings accrue from decreased chemical and water use requirements and from a reduction of wastewater volume. There are also environmental benefits, as fewer chlorine or chlorinated compoimds and other chemicals are discharged. 

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