Even plant piping can cause waste, and simple piping changes can result in major reductions. The process changes described next are options for preventing pollution from piping.
A scraped-wall exchanger consists of a set of rotating blades inside a vertical, cylindrical, jacketed column. They can be used to recover salable products from viscous streams. A typical application is to recover a monomer from polymer tars.
Exchanger fouling does not always occur steadily. Sometimes an exchanger fouls rapidly when plant operating conditions change too fast or when a process upset occurs. Other actions, such as switching pumps, unloading tank cars, adding new catalysts, or any routine action, can influence fouling. However, estimating the effect is possible.
The first step in reducing or eliminating the fouling causes is for the company to identify the causes by continuously monitoring the exchanger and correlating any rapid changes with plant events.
In many plants, various streams are combined and sent to a waste treatment facility as shown in Figure 3.10.6. A company should consider each waste stream individually. The nature of the impurities may make recycling or otherwise reusing a stream possible before it is mixed with other waste streams and becomes unrecoverable. Stripping, filtration, drying, or some type of treatment may be necessary before the stream can be reused.
If a process stream contains temperature-sensitive materials, a company should review both the amount and temperature level of line and vessel tracing and jacketing. If plant steam levels are too hot, a recirculated warm fluid can prevent the process stream from freezing. A company should choose a fluid that does not freeze if the system is shut down in winter. Electric tracing is also an option.
Using Noncorroding Tubes
Corroded tube surfaces foul more quickly than noncor-roded tube surfaces. Changing to noncorroding tubes can significantly reduce fouling.
Controlling the Cooling Water Temperature
Excessive cooling water temperature can cause scale on the cooling water side.
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