January 1995, Volume 1

We design and manufacture a wide range of products for a multitude of industries including iron and steel, cement, mining, pulp and paper, power, aluminum, lime and chemical. Our newsletter will include general topics of interest from these industries and, although the market may not be specific to your needs, a power engineer could have an interest in cement plant projects because the commonality between these two processes is the combustion of fuel and a generation of flue gas.

Case Study
Process Equipment was recently awarded a contract to design, manufacture and install a replacement forced draft impeller of considerable size. The replacement was a result of an unusual vibration problem and cracks in the impeller. Cracking can occur in these large fan impellers after prolonged operation from either low cycle or high cycle fatigue. Low cycle fatigue failure originates from the starting and stopping or the variation in the speed of the impeller. High frequency fatigue failures occur from the multitude of occasions that a fan blade passes the cutoff of the housing when natural frequency excitation can occur to the various fan impeller components. In this instance, the large fan impeller required replacement because of unusual and unpredictable vibrations that occurred during operation at the upper 10% speed range of the turbine drive. For over a year, the utility hired consultants in an effort to determine the cause of this unpredictable vibration. Because no one could isolate a cause for the problem and minor cracking was discovered in the impeller, the utility decided to purchase a replacement impeller from Process Equipment.

During the commissioning of the replacement fan impeller, the same mysterious vibration problem recurred. After three days of continuous attempts to analyze the vibration problem, it was decided that the adding and deleting of balance weights would not provide a satisfactory solution. One of the Process Equipment engineers isolated the vibration problem which is commonly found on fans of this size. It was hypothesized that a natural frequency problem might be occurring at the oil interface between the journal and the shaft. It was ultimately discovered that custom-designed bearing oil seals had been added by the plant personnel in an effort to eliminate a serious oil leakage problem. This oil seal design consisted of a fabric type material which was bolted to the inboard face of each bearing. As these bolts were tightened, force between the fabric material and rotating fan shaft was increased.

We determined as torque was released on these bolts and the pressure reduced at the interface of the fabric filter and shaft journal, the vibration problem disappeared. Regardless of origin, we are proud that our persistence to help solve this problem characterizes the fact that we are not strangers to solving difficult problems.

Combustion Air and Lime Kiln I.D. Fan Flow Rate Slide Rule
Because many of our products are utilized as auxiliary components to boilers and kilns, we have developed an expedient way of calculating flue gas flow rates and combustion air requirements. All of these calculations have been simplified on a slide rule which is available at no charge. One side of the slide rule provides computations for combustion air requirements and flue gas flow rates when burning wood, oil, gas or a combination of these fuels. The other side of the slide rule is intended for the pulp and paper mill engineer who is interested in determining lime kiln flue gas flow rates.

Combustion Air Calculation Side of Slide Rule

Lime Kiln I.D. Fan Flow Rate Calculation Side of Slide Rule

This information is useful in troubleshooting either fan problems or in analyzing stack particulate noncompliance problems. Often, particulate emission violations occur because of the undersizing of air pollution control devices. The analysis of such a problem begins with the determination of the actual flow rate through the air pollution control device and the comparison of this value to original equipment specifications.

If you are interested in receiving one of these slide rules with the instruction manual, please contact us at (205) 663-5330 or E-mail to: information@process-equip.com