Open recirculation

Figure 1.3 Schematic of open recirculating cooling system.

FIGURE 4.39 Cooling water system (open recirculation). 

Open recirculating systems These are more amenable to inhibition since it is possible to maintain a closer control on water composition. Corrosion inhibition in these systems is closely allied to a number of other problems that have to be considered in the application of water treatment. Most of these arise from the use of cooling towers, ponds, etc. in which the water is subject to constant evaporation and contamination leading to accumulation of dirt, insoluble matter, aggressive ions and bacterial growths, and to variations in pH. A successful water treatment must therefore take all these factors into account and inhibition will often be accompanied by scale prevention and bactericidal treatments. 

Lichen is in fact a symbiose between a weed and a fungus. They are not found in swimming pools. Mostly they are present in open recirculating cooling water systems. 

Figure 8-3 Three basic types of cooling water systems. Top the once-through system where the cooling water is used once and then discharged. Middle the open recirculation system where the water is cooled and recycled through a system in which it comes in direct contact with air. Bottom a closed recirculation system where the water is cooled and recycled without coming in direct contact with the atmosphere.

Cooling Towers—5. Problems in Replacing Chromate as a Corrosion Inhibitor for Open-Recirculating Cooling Waters... 

Widespread practice has always existed, unfortunately, by owners and operators of cooling systems, or their general contractors and consultants, to specify chemical treatment operating standards in isolation, with little or no actual contact with prospective vendors of water treatment service companies before the issuance of such standards. There is now a growing tendency for particularly low corrosion rates to be specified as a part measure of the quality of water treatment and technical services to be provided in water management contracts (say below 1 mpy for steel in closed-loop systems and below 2 mpy for steel in open-recirculating systems). These low rates are often unattainable in practice. 

This section is primarily concerned with the reviewing water treatment program selection process for open recirculating cooling systems and demonstrating the kind of information that may then be represented in a vendor s standard program selection guide. 

Precommission Cleaning and Passivation of Open Recirculating Systems... 

There are many open recirculating cooling systems that still do not have chemical dosing pumps available. This represents a serious risk, as the... 

See also Chapter 9, Section 4, and the notes on Process Contamination in Section 10.8.28). Techniques for the on-line cleaning of open recirculating cooling water systems are often similar to those for preoperational cleaning in that generally there is a two-stage approach ... 

Almost all open recirculating cooling water systems operate within a pH range of 6.5 to 9.5. Occasionally this may be as low as 6.0 or as high as 10.0. Typically, however, water treatment programs are designed to function within only a narrow pH band of 0.5 to 1.0 pH unit or less. The specific... 

Fig.4.3-7. An open recirculation system with divided flow...

The following scheme is an open recirculating system with a recycle of magnitude Qzi. 

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