Case Study 1 - Furnace FDF Vibration

In July 2002, the maintenance team at Mitsui Chemicals solved a challenging vibration problem in the Furnace Forced Draft Fan (FDF) using ADRE for Windows® in combination with Bently Balance software. ADRE® is a portable diagnostic system designed for test stand applications and for field and laboratory work when machines are not fitted with an on-line condition monitoring system. At the time, the fan was not being monitored by an on-line system.

ADRE detected furnace FDF vibration. A temporary optical pick up was used to measure the pulse signal, and a seismic velocity probe was mounted on top of the bearing. The vibration patterns suggested a typical unbalance condition.

Using the data collected by ADRE, Bently Balance software was used to calculate the amount and angle of balance collection weights. This dramatically decreased the fan vibration level; however, fluctuation in the fan vibration amplitude persisted due to several factors.

The fan was operating very close to its first resonance frequency, so even slight changes in balance could affect the fan vibration level. Further, other fans in close proximity to the FDF contributed to the fluctuating vibration level. ADRE properly diagnosed this condition so additional balance adjustments could be made, keeping the fan in good operating condition.

These prevailing conditions still exist, but today the fan is monitored on-line by GE's System 1 optimization and diagnostic software platform with Trendmaster® Pro. This has facilitated periodic adjustments, further protecting the fan, and helping to avoid an unexpected equipment breakdown.

Trendmaster Pro links transducers and measurement points onto a single-cable sensor network, and brings the data into System 1. The System 1 software enables plant personnel to quickly identify significant events, evaluate the situation, and respond quickly; resulting in increased equipment availability and reduced maintenance costs.

Case Study 2 - Vibration in the Mechanical Drive Steam Turbine

In January 2005, the plant experienced a sudden rise and drop in vibration at the high-pressure side of a mechanical drive steam turbine. At the time, the plant was using a DM2000 on-line machine protection system; however, the system did not have the data collection/analysis capacity to adequately diagnose the problem. The ADRE system was used to measure vibration level and phase pattern.

The data showed obvious signs of rub. Plant engineers determined the cause to be carbonized oil deposits which changed the seal structure. Based on this diagnosis, the operation manager decided to keep the turbine in operation without having to disrupt plant operations with an emergency overhaul. Steps were taken to avoid continued carbonized oil deposits.

Subsequently the plant replaced their DM2000 system with System 1 for greater data capture and analysis capability. System 1 provides long-term data collection to avoid overwriting critical data, supports storage to other computer systems, provides better resolution, and excellent signal-to-noise ratio. The new installation was completed without having to replace transducer and field wiring. With countermeasures in place and System 1 installed, the vibration level has been low and stable.

Future Plans at Mitsui Chemical

With System 1 facilitating a proactive maintenance approach, Mitsui Chemicals Ichihara Works has improved asset reliability while requiring fewer planned maintenance shutdowns. Consequently, the company is moving to increase on-line machine protection capability including plans to install System 1 and Trendmaster Pro in their new plant with a total of 80 measuring points (Acceleration 60, Displacement 14, REBAM 4).