While striving for efficiency, engineers often overlook poor water quality as a major reason their cooling systems fail to meet high expectations and miss a great opportunity to push the envelope. Poor water quality is draining your process cooling efficiency. How can you regain this lost ground? Process cooling engineers are constantly striving for improved efficiencies and for good reason. Most process cooling systems consume approximately 60 percent of a building’s energy, and seemingly modest gains in efficiency can yield both significant and measurable effects.
Process system designers typically focus on optimizing elements of the actual cooling system. For example, engineers have re-designed the cooling tower fan blades, upgraded the current chiller tube technology, and introduced many other innovations that have yielded improved operating efficiencies. These optimizations have caused notable and important gains in efficiency among the industry.
Why is Water Quality Important?
Water quality is one important aspect of cooling systems that is many times overlooked. Many incorrectly assume that once water reaches the array of systems, the quality will be under control. While this is true to a certain degree, what happens to the wide range of suspended solids that are picked up by the water after it enters the system? Such substances include dust, biofilm and corroded metal particles - suspended solids that can wreak havoc on a process cooling system and drastically reduce efficiencies.
Because most suspended solids find their way into the water stream once the water has actually entered the process cooling system, the best solution is a post-hoc removal system. Most of these fine suspended solids (approximately 95 percent, depending on the system) are smaller than 5 µm in size. This means that the majority of fine particulates remain in the water loop, as traditional filtration systems are not capable of filtering such fine particulate. Therefore, it is necessary to find a system that can either clump or filter particles below 5 microns in size.
- 1. One might use a chemical coagulant in conjunction with a traditional filter to clump small particles into larger particles to increase the removal efficiency.
- 2. Or, an alternative is a cross-flow micro sand filtration system that can capture submicron particles. A micro sand filtration system combines a cross-flow conditioner and micro sand filtration in the same vessel, allowing for high filtration efficiency. This approach to filtration also requires less water for backwash, making it ideal for use as a side-stream filtration solution for cooling water applications.
In these examples, two process plants added a cross-flow micro sand filtration system to help address water quality in process operations. Designers had evaluated several other technologies, including ultra-filtration and cartridge filters. Fouling of reverse-osmosis membranes can seriously affect the filtration system. A proper pre-treatment filter can help to extend the life of reverse-osmosis membranes and ensure the filtration system is operating at the designed efficiency. The best available technology for determining the fouling potential of reverse-osmosis inlet water is by measuring the silt density index (SDI). SDI measurement must be taken prior to designing an RO pre-treatment system.