Overview:
Proper airflow is critical to the paper manufacturing process. Exhausting gas from paper machines requires a high level of precision engineering. Typically, hoods for a paper machine’s drying section are situated within sheet metal enclosures to conserve heat. In most paper production facilities, a series of roof-mounted exhaust fans positioned above the dryer section remove the hot, moist and often caustic exhaust from the process.
Problem:
A leading producer of container board, corrugated, and consumer packaging paper products was dealing with issues associated with removing exhaust from one of its paper machines at a particular facility. After experiencing frequent maintenance issues and persistent bearing failures, the plant needed a more dependable solution.
If the exhaust system in a paper facility does not operate properly, the steam and heat from the paper machine drying section are not removed and the paper won’t dry. Furthermore, steam in the building reaches the ceiling, condenses, and drips down on everything including people, equipment, as well as the paper.
The hood exhaust system at this particular facility consisted of multiple exhaust fans mounted along the roof. The ducts from the paper machine’s drying section were designed to penetrate the roof vertically, turn 90 degrees, and come to a dead end at the edge of the roof.
Inadequate by current standards, the previous design had each of the existing 72-inch axial fans mounted on one side of the 8-foot square horizontal duct section. A 10-foot jack shaft passed through and protruded from the opposing side of the duct. A sheave, V-belt, and motor provided the necessary rotation for the shaft and fan. A flange-type bearing and seal were installed on the drive side of the duct, along with two bearings within the fan housing.
The shaft was prone to bowing and was difficult to maintain, particularly with the excessive heat and moisture in the environment. Bearing alignment was also very difficult, given that the three bearings had to be kept in direct alignment and one was 11 feet away from the other two.
Solution:
An Aerovent Model TABD tubeaxial fan was selected to provide the solution. The 72-inch, 15 HP, 900 RPM fan installed for the paper machine exhaust system is a belt-driven unit capable of supplying up to nearly 60,000 CFM at 0.75 inch static pressure, depending on system design and ductwork configuration. In this application, the fan is rated at 50,000 CFM at 0.50 inch static pressure.
The new proposal included:
- Eliminating the trans-duct jack shaft
- Removing the old fan
- Installing the new TABD Aerovent fan where the old fan was removed
- Locating the fan motor on the same side of the duct as the new fan
- Sealing the hole where the bearing protruded on the opposite side of the duct
Aerovent designed a special belt driven short-case fan to match the ductwork opening height and mount on the existing structure. The new fan is equipped with a 304 stainless steel propeller to inhibit corrosion.
Result:
The Aerovent tubeaxial fan is reliably removing exhaust from the container board facility. The Aerovent TABD tubeaxial fan provided the best performance for the money in this application. In addition to robust performance, the plant received a highly reliable industry-leading fan, an up-to-date system design that eliminates the reliability and maintenance issues associated with running a jack shaft through ductwork, and the assurance that the high quality of the container board products it manufactures will be maintained.