Non-contacting labyrinth seal bearing isolators for industrial rotating equipment can be a key to energy conservation – and saving money.
By changing from contact lip seals to non-contact seals in industrial rotating equipment, the U.S. could save billions of dollars in electrical power costs and conserve over 5,500-MW of energy each year.
38 million contacting lip seals are used in U.S. industrial applications, including pumps, gearboxes, fans, paper machine rolls, and other types of rotating equipment. Each lip seal consumes an average of 147-watts of power and has a 100 percent failure rate.
After approximately 2,000 hours of operation (or 2.7 months), a lip seal will fail, lose contact with the rotating shaft, and stop consuming power. When a lip seal fails, it must be replaced or the rotating equipment will operate until the bearings become contaminated or run out of oil. This is akin to running your car on a flat tire until it self-destructs.
Contacting seals, including magnetic face seals, account for 6000-MW of power consumption – assuming they are functioning and effectively sealing. To add to the problem, industrial electric motors were, for a long time, manufactured and placed into severe duty services without adequate bearing protection. Only a close clearance between the shaft and end-bell served to limit contamination ingress into the bearing environment. Reliability suffered as life cycle costs for energy and maintenance had significant negative impact on the process industries’ production members.
However, some relief has come in the way of industrial electric motors. In 1994, the Institute of Electrical Engineers introduced their IEEE-841 Motor, a unit designed to improve reliability, efficiency, performance, and energy consumption. One year later, a process plant that switched to 2,000 of these new motors discovered $5 million in savings through efficiency and enhanced reliability.
A good deal of the savings in the IEEE-841 comes from its use of non-contact seals, or bearing isolators, as part of its specification.
Invented in the 1970s, the bearing isolator is a non-contacting labyrinth seal, which provides permanent bearing protection and eliminates the need for continual maintenance.1 The non-contact situation between the unitized rotor and stator result in no consumption of energy. In addition, bearing isolators never wear out, so they can be used over and over for many years.
The IEEE-841 and the NEMA Premium motor both are available with bearing isolators to enhance reliability and reduce MTBF (mean time between failures). Documentation calculates an internal rate of return of more than 100 percent.
Approximately 40 million industrial-grade electric motors are in use in the U.S. On average, these motors will last 5.7 years before they need to be repaired or replaced. The vast majority of the time, the root cause of electric motor failures is mechanical rather than electrical. Pure and simple, bearing-protected motors have proven to last at least twice as long as the motors that they replaced, because the major documented cause of motor failure remains bearing deterioration.
The insulation on the windings could be good for 130 years because it is designed for sever resistive heating that does not present itself in the modern day super efficient motor.
If the 38 million contacting lip seals in the U.S. were replaced with non-contacting, non-energy consuming bearing isolators, the net energy savings in the U.S. would be about 5,586-MW, or the equivalent of 10 fossil fueled power plants.
Tons of carbon dioxide, said to be a major contributor to global warming, would no longer be produced. The economic savings would also be substantial – the process industries would save over $3.7 billion per year in electrical power costs. Bearing isolators have been known to stay in service for at least 20 years, eliminating the duty cycle and replacement expense and stabilizing operating costs. The benefits would be innumerable.
1 The bearing isolator was invented under patent #4,022,479.
Pumps & Systems, November 2006
