Power Plants, Steel Plants, Petroleum Plants, Paper Mills, so on and so forth; all depend on the processes that define what they are producing. Each of these types of plants and facilities depend on the addition of pure water to these processes. In the old days (30-50 years ago) water chemistry was not an exact science and really was not paid much attention to. How times have changed! Now pure water is not just needed but mandated. Pure water helps plants minimize maintenance issues and maximizes efficiency. By removing impurities from the process water, scale and organic fouling is minimized on heat transfer mediums. Further, less corrosion of susceptible materials adds to the longevity of the plant components.
To obtain pure water for the various processes, plants and facilities either use turnkey systems loaded in trailers delivered to the site or they purify and clean the water with in-house.
Many companies are selling complete turnkey systems loaded into semi-truck trailers. The systems are rolled onto the plant site, a water input pipe is connected and the pure water output pipe is connected to collection tanks or sent directly through to the plant or facility. These trailers contain all of the necessary equipment to produce water that is so pure it is hard to quantify any impurities in it at all!
In lieu of a trailer, cleaning the water typically consists of several steps that are generally used; flocculation/settling, filtration, reverse osmosis, and chemical addition. Flocculation is the process of adding a flocculant chemical to the water that causes sediment to “stick” together making larger particles. The larger particles tend to settle in a slow or non-moving water column. Clarifiers are used to slow the water movement so the “Floc” can have the time to settle in the bottom of the Clarifier so it can be removed.
The next step is filtration. Filters are used throughout the process from traveling screens at the inlet to remove sticks and floating debris in the river to Ultrafiltration that can remove particles as small as viruses! A critical process of any filtration system is a way to clean the filter media. Ultrafiltration units usually have both chemical addition and backwash systems. Chemicals are added (such as acids) to remove salt and/or scale buildup on the filters. Backwashing uses clean water to force water through the system in the opposite direction of the normal flow. The clean water can also be used in conjunction with air scour systems to mechanically clean the filters by “boiling” the water with air in addition to flowing backwards through the filter to knock any items off of the filter so it can be carried away by the backwash water.
The final step in water purification at power plants is usually Reverse Osmosis (RO). The Reverse Osmosis process has a semi-permeable membrane that only allows extremely small particles through. Reverse osmosis semi-permeable membranes allow water to pass through while retaining 90-99% of all the inorganic substances in solution, 95-99% percent of the organic constituents, and 100% of the most finely-divided colloidal matter (bacteria, viruses, colloidal silica, etc.). The efficiency of membranes in the removal of salts varies from 90-99%. To maximize purity, the water is passed through a series of semi-permeable membranes in a reverse osmosis unit.
The flow rate through a reverse osmosis membrane is directly proportional to the effective pressure (the difference between the applied pressure and osmotic head). A pressure in excess of the osmotic pressure is generated by High Pressure booster pumps to obtain a satisfactory flow of pure water through the RO units.
What ends up being produced is water that is extremely pure. Viruses, bacteria, suspended solids, etc. are completely removed so that maintenance, fouling, and scale buildup is virtually eliminated, and the cost associated with those processes become negligible.
Operators and Managers should ensure a trailer that meets their needs is brought on site or that the in-house water purification and cleaning system is updated and operated properly. It is important that operators and managers are properly trained on these systems and operating procedures are up to date. Proper training and updated operating procedures will assist operators in maintaining proper water chemistry throughout various plant processes, which will increase longevity of equipment and maximize efficiency of the facility.