Particulate matter makeup

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Removal of Particulate Matter. The amount of particulate entering a cooling system with the makeup water can be reduced by filtration and/or sedimentation processes. Particulate removal can also be accompHshed by filtration of recirculating cooling water. These methods do not remove all of the suspended matter from the cooling water. The level of fouling experienced is influenced by the effectiveness of the particular removal scheme employed, the water velocities in the process equipment, and the cycles of concentration maintained in the cooling tower. 

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Major problems inherent in general applications of RO systems have to do with (1) the presence of particulate and colloidal matter in feed water, (2) precipitation of soluble salts, and (3) physical and chemical makeup of the feed water. All RO membranes can become clogged, some more readily than others. This problem is most severe for spiral-wound and hollow-fiber modules, especially when submicron and colloidal particles enter the unit (larger particulate matter can be easily removed by standard filtration methods). A similar problem is the occurrence of concentration-polarization, previously discussed for ED processes. Concentration-polarization is caused by an accumulation of solute on or near the membrane surface and results in lower flux and reduced salt rejection. 

A question must be raised as to why the tap water and the calcium bicarbonate washing treatments give such different results. The alkaline pH of the tap water suggests that calcium carbonate or bicarbonate is present and that the final product deposited in the fiber should be similar to that obtained with the pure bicarbonate solution. However, the chemical makeup of any city tap water is very complex and must contain a number of components that could affect the stability of cellulose. For example, the municipal treatment plant in Ottawa adds large amounts of alum (aluminum sulfate) to the water to settle particulate matter. Because alum makes the water very acidic, lime is then added to raise the pH. The result is that a large amount of calcium sulfate is present in the tap water and must affect the overall chemistry of the salts deposited in the fibers. One may further speculate that the anions present can influence the stability of cellulose as much as the cations. Any comprehensive understanding of the factors involved must include aH parameters. 

The removal of these gases and particulate matter from the makeup air stream is therefore strongly advised. It can be accomplished by treating incoming air streams in the following manner ... 

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