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A range of water needs typically exist within a facility, all of which may have different water quality requirements for specific uses. Describe five of these common needs.

Solution. Five common industrial facility water uses include:

1 Cooling Water. Natural and forced-draft cooling towers are generally used to provide the cooling water required at a site unless water can be drawn from a convenient river or lake in sufficient quantity to meet a facility’s cooling demands. Seawater or brackish water can be used at coastal sites but, if used directly, necessitates more expensive materials of construction for heat exchangers because of potential corrosion problems resulting from the high dissolved solids content of this water. Often, this cooling water does not have to be of high purity and can be taken from blowdown streams from boilers or process lines that require much more stringent water quality conditions.

2 Potable and General Use Water. The water required for general purposes on a site is usually taken from a local municipal or private supplier, unless a cheaper source of suitable quality water (e.g. a river, lake, or well) is available. If the cost of this supply is low, incentives for water use reduction will also be low. It should be remembered, however, that the cost of the supply may be a small portion of the overall cost of managing this water, particularly if it is used in process rinsing, general facility cleaning and wash-down, etc. More water use requires more energy to convey it from the source and within a plant. When the water becomes contaminated, costs for its handling increase exponentially. In addition, waste treatment becomes progressively less efficient and more costly as a waste stream is diluted, and load penalties may be incurred based on the volume of waste discharged to publicly owned treatment works (POTWs). It should be evident, then, that numerous benefits can be associated with increased water use efficiency within a plant.

3 Demineralized Water. Water from which all the minerals have been removed by ion exchange must be used where ultrapure water is needed to meet process demands and strict boiler feedwater requirements. Mixed and multiple-bed ion exchange units are used for this purpose, with resins exchanging multivalent cations for hydrogen. Boiler water as condensed steam and process water must be removed on a routine basis (blow down) to prevent the build-up of unwanted constituents within these systems, and this ultrapure water may be effectively reused within a plant for other unit operations that demand much less stringent water quality characteristics, i.e., cooling water, process rinse water, and so on.

4 Refrigeration. Refrigeration is needed for processes that require temperatures below those that can be economically obtained with cooling water. Chilled water can be used to lower process temperatures down to approximately 10°C. For lower temperatures, to -30°C, salt brines (NaCl and CaCl2) are used to distribute the “refrigeration” around the site from a central refrigeration unit. Vapor compression machines are normally used for this purpose. As with boilers, evaluation of the operating conditions of a chiller can lead to significant pollution prevention opportunities. Consider, for example, that a 1% improvement in chiller efficiency can be expected for each 1°F increase in the chiller set point.

5 Steam. The steam for process heating is generated in either fire - or water-tube boilers, using the most economical fuel available. The process temperatures required can usually be obtained with low-pressure steam (typically 25 psig), with higher steam pressures needed only for high process temperature requirements. A significant pollution prevention, energy conservation, and cost reduction opportunity may exist in a facility’s steam generation system, as many facilities operate at higher than necessary steam pressures, increasing their energy demands for steam production and the cost of producing this steam. In addition, repair and replacement of leaking steam and condenser lines will prevent the wasting of steam and the associated energy and cost needed to produce this wasted steam.