June 4, 2019 | 2 minute read
There are a lot of advantages for power generation companies to move to geothermal energy production. For example, by requiring no fuel, they are immune to market volatility. Reduced need of water and a smaller physical footprint than coal, wind, nuclear and oil also make it attractive both economically and environmentally.
However, switching to geothermal energy does have its challenges. Between the incredibly high temperatures and the release of corrosives such as hydrogen sulfide, ammonia, radon, etc., every part of the system needs to be carefully considered.
When one company decided to make the switch to the geothermal energy market, they came to John Crane to find the right mechanical seals to stand up to these extreme conditions.
In 2011, a global leader in the design, manufacture and maintenance of binary Organic Rankine Cycle (ORC) turbine systems entered the geothermal energy market. Binary ORC plants use heat exchange to vaporize fluid to drive turbines that produce electric power without harmful emissions.
Company engineers knew that its existing turbines would be put to the test with new and demanding conditions, including higher output demands as well as temperature and pressure increases. As part of the transition, the company introduced new, silicon-based fluids into the ORC process that not only increased temperature concerns but also presented corrosive condition challenges to the turbines’ double-cartridge seals.
The engineers quickly realized they needed to upgrade the existing seals to reliably stand up to the demanding output, heat and corrosive challenges.
Upon John Crane’s inspection, it appeared the initial turbine design used traditional heavy-duty seals, with primary rings made of plain-face abradable inserts in metal carriers. Based on previous customer experiences with double O-ring pusher seals, John Crane engineers tried a number of solutions that would stand up to the high heat—230° F to 644° F (110° C to 340° C).
The team knew that traditional hydropad technology, while effective in many highpressure applications, did not meet John Crane criteria for the new ORC turbine conditions, including leakage. Other solutions, including different seal mating ring designs, were tested but did not meet the rigid ORC requirements for heat transfer.
John Crane called upon the experience of company engineers based in Germany for a new and effective recessed hydropad technology that had proven itself in other turbine applications.
John Crane quickly sprang into action and upgraded the double O-ring pusher seals with recessed hydropads, which helped increase peripheral shaft speed and enhance heat transfer around the seal rings, thereby preventing overheating. The recessed hydropad technology reduced the risk of uneven contact across the seal interface while providing better and stiffer lubrication, making the seal interface less sensitive to seal ring distortion.
The upgrade to double O-ring pusher seals with recessed hydropads provided all the benefits of the conventional seals, but with much less leakage. The recessed hydropads were an ideal addition to the double pressurized seals that would ultimately deteriorate as oil degraded over time.
Following the upgrade, the ORC turbine manufacturer has met its reliability goals thanks to the help of John Crane’s recessed hydropad technology. Today, seal meantime between maintenance (MTBM) is up to five years.
The company is now able to confidently provide its turbine technology as a reliable income generator to the geothermal energy market.
In addition, following the successful upgrade, the ORC turbine company has successfully incorporated the recessed hydropad design in other larger projects.
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