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The Materials Innovation and Recycling Authority (MIRA), formerly the Connecticut Resources Recovery Authority (CRRA), works to convert municipal solid waste (MSW) into a clean energy source. Last year, an innovative product—Centritec seals— were installed into the facility’s combustion fan system. The change has allowed the plant to improve efficiency and reduce downtime. Centritec seals have improved bearing lubrication and reduced parasitic drag, thereby requiring less power in the operation, and most importantly, reduced maintenance, which has allowed MIRA to lower its operating costs while continually delivering energy to its customers.

Centritec Seals, a division of The Carlyle Johnson Machine Co. (CJM), based in Bolton, Connecticut, provides shaft seal designs for new or retrofit applications for both horizontal and vertical shaft applications. The Centritec Seal design is frictionless, which the company says makes it highly efficient, highly tolerant of vibration, self-venting, easy to install and requires minimal maintenance.

MIRA is a leading local resource for managing municipal solid waste (MSW), and has been instrumental in Connecticut converting more trash to energy than any other state in the U.S. The organization, which is located in Hartford, Connecticut, collects MSW from 51 cities and towns in the area and converts it into a refuse-derived fuel (RDF). The MSW is sent to be processed and separated at the waste processing facility (WPF), and then the RDF moves by conveyor to the Power Block Facility (PBF). It is at the PBF that the fuel is burned to create steam that powers a steam turbine, which generates electricity.

MIRA’s steam boilers produce 62,000 kilowatts (kW) of electricity, which is enough to power more than 50,000 homes in central Connecticut. During the steam generation process, the combustion air system uses fans to pull the odorous air from the WPF and to move the air into the PBF’s combustion boilers, thermally destroying odors while providing oxygen for the burning process.
 

The problem

Prior to installation of the new seals, bearings on the combustion fans were not being consistently and properly lubricated, leading to costly repairs and resulting in downtime.

The plant utilizes two combustion fans, which are mounted on pillow-block bearings and driven by a 1,000-boiler-horsepower (BHP) motor. These high capacity fans are located outdoors, 25 feet from ground level, and are exposed to very harsh environmental conditions including dirt, snow, rain and widely fluctuating temperatures. The addition of this environmental moisture into the bearing housing was causing the grease to break down and lose its lubricating properties. The lack of lubrication caused increased vibration levels that compromised the integrity of the bearings. When lubrication, condensation and vibration reached unacceptable levels, the bearings failed, which caused an outage of the fan and resulted in severe repercussions—including extensive downtime for repair of the fan drive system. The cost to replace just two failed bearings is $15,000.

The bearing isolator seals formerly used by MIRA were routinely failing after eight to 10 months of use and were causing fan outages because of insufficient lubrication and condensation control. These seals did not stop moist, ambient air from entering during the bearing heat-up and cool-down cycles and also trapped moisture in the pillow block bearing housing. This contaminated the grease inside the bearing and poorly lubricated the bearings. To address this problem, MIRA decided to install and test Centritec seals.
 

The solution

MIRA tested Centritec seals on one combustion fan, which required four sets of double-sided seals. The seals are noncontact, centrifugal-pressure seals that prevent lubricant leakage and allow ambient air to circulate throughout the bearing housing. The seals provide continuous, cool bearing operation without moisture entrapment in the housing. With their patented centrifugal-pressure principles and unique ability to support both horizontal and vertical shaft installations, Centritec Seals solved many of the problems presented by MIRA.

The MIRA application utilized a double-seal design to keep lubricants in and containments out, even when idle. Centritec seals are designed to offer less maintenance, inherent moisture expulsion and self-ventilation to eliminate heat buildup, which are all crucial for MIRA’s air system fans to work properly.

After one year of continuous and monitored operation, the seals show no signs of failure or impending failure. This initial installation demonstrated that using the noncontact centrifugal-pressure design allowed for more breathability (to eliminate the buildup of moisture), better heat dissipation (allowing air flow through the pillow block bearing housing) and an expanded tolerance of vibration (resulting in less wear on components). The fan’s current operational vibration data indicates that grease is no longer breaking down, which signifies that the bearings are being properly lubricated.

In addition, Centritec seals provide increased operational efficiency compared with other seal options, such as contact lip seals and hybrid contacts seals. Unlike other seals, which generate heat (caused by friction), Centritec seals dissipate heat, which reduces negative effects on lubricant quality and reduces parasitic drag. The parasitic drag created by a typical contact lip seal requires as much as 60 watts of energy more than a Centritec seal in its operation, because of energy that is dissipated as heat at the seal interface.
 

Summary

Before the installation of Centritec seals, MIRA’s two combustion air system fans had to be shut down and maintained every eight to 10 months because of bearing damage. Fan dependability is crucial to energy production, and this untimely shutdown was labor-intensive and expensive. Now, the bearings and seals have a longer lifespan with no lubrication leakage from the bearing housing, no moisture or heat buildup in the housing and no wear on the components due to vibration frequency.

“So far, after one year of use, the Centritec seals are doing what we need them to do. They have been crucial in keeping the fans running smoothly,” says Rich Quelle, chief engineer of MIRA. “We certainly plan to continue to use Centritec Seals in the future.”

The article was submitted by Centritec Seals, a division of The Carlyle Johnson Machine Co. (CJM), Bolton, Connecticut. For more information, contact Doug Rode at [email protected] or 860-643-1531 ext. 117.