Bearings are a vital component in the wastewater industry. Breakthroughs in bearing technologies help wastewater companies extend the life and operational efficiency of critical applications—even when those applications are operating in harsh conditions, with corrosive fluids and under heavy loads. The main problem facing wastewater applications is not the operating fluid itself. It is the ongoing threat of seal failure that causes bearing contamination, ultimately leading to destructive and costly system failure. Many wastewater applications such as transfer pumps, electric submersible pumps (ESPs), stationary pumps, vertical turbine pumps, dredging pumps and injection pumps can operate in demanding and abrasive environments. Unfortunately, a typical sealed bearing must be kept clean and lubricated for the pump to function properly. Even the smallest break in the bearing seal can quickly flood the bearing with abrasive and corrosive working fluids, bringing pumping operations to a halt. Recently, a coastal wastewater treatment facility in Washington demonstrated the effects of running in a corrosive saltwater environment. The biggest difficulty that the facility faced was the intrusion of saltwater into its sewage-outflow pipes."If higher water levels are able to push salty water into the county's wastewater-treatment system, corrosion will worsen. This has already been seen to a certain extent with equipment that should be lasting 50 years breaking down after 20" (Seattle Weekly, "King Tide Shows What Climate Change Has In Store," January 2015). Corrosion is a killer when it comes to application integrity. Bearings and seals have a direct impact on wastewater equipment and system performance. They simply cannot fail. Because these applications generally run in corrosive conditions, wastewater engineers design bearings and seals that are protected from operating fluids. However, these bearings generally require a watchful eye and ongoing maintenance. When a seal fails, operational fluid leaks into the bearing housing quickly, decreasing equipment life, increasing surface friction and energy consumption, and affecting equipment operation.
A New Solution
Faced with these challenges, some companies in the wastewater industry are discovering the benefits of advanced seal-free bearing technology—using polycrystalline diamond (PCD). PCD is an advanced engineering material comprised of individual diamond crystals that have been fused together under extremely high pressures and temperatures. The result is a diamond bearing surface that provides extreme hardness, wear resistance and thermal conductivity—delivering a bearing that can be submerged directly into corrosive and abrasive process fluids. This eliminates the need for seals and lubricants altogether. Instead of designing around corrosive process fluids, diamond bearings can work directly in them. "In our initial testing, we threw sand and gravel into the PCD bearing to see how it would perform. It seemed to like it— just ground up the particles with no problem. In some ways, it actually worked better," said Clayton Bear, president of New Energy Corporation, a builder of Marine Hydrokinetic power generation equipment that typically operates in silt-laden river water and canal water. Another large energy company also saw remarkable results from its adoption of diamond bearing technology. The company reported significant improvements in its chemical mixing application. The application used a traditional foot bearing that was typically failing every three months. Replacing the bearing was time-consuming and difficult. Equipment had to be shut off, tanks had to be drained and cleaned, and maintenance personal had to climb down into the base of the tank to replace the bearing. Company engineers swapped the mixer's foot bearings with diamond radial bearings. After a six-month test, the diamond bearings showed no measurable wear. The chemical mixing application bearings have now run for four years without failure or maintenance.
Table 1. Physical and mechanical property comparison of bearing materials. Sources: Bertagnolli, U.S. Synthetic; Roberts et al., De Beers; Cooley, U.S. Synthetic; Jiang Qian, U.S. Synthetic; Glowka, SNL; Sexton, U.S. Synthetic; Lin, UC Berkeley, MatWeb.com, CercoThe Diamond Advantage
Compared to traditional bearing technology (such as tungsten carbide), diamond bearings offer extended bearing life by four to ten times in the harshest real-world environments. Although diamond bearings are relatively new in the wastewater industry and in pumping applications, this technology offers a reliable, cost-effective and proven solution to make pump operations more robust and maintenance free. Reverse Moineau pump technology used in mud motors in the oil and gas industry represent one application where diamond bearings adoption is already occurring. These motors force particle-laden drilling fluid through diamond radial and thrust bearings within the drill string. In renewable energy, marine hydrokinetic (MHK) generators also currently use diamond bearings in submerged underwater environments. MHKs have the same design as vertical turbine pumps and benefit from the seal-free advantages of diamond bearings. Diamond is known for its high thermal conductivity, low coefficient of friction, high toughness, and other preferred physical and mechanical properties. Having a bearing material with high thermal conductivity reduces localized temperature extremes that lead to bearing degradation.
Figure 1. Comparative data in thermal conductivity and friction co-efficiency (Courtesy of U.S. Synthetic)
Figure 2. Comparative data in fracture toughness and material hardness. (Courtesy of U.S. Synthetic)