Power-Station

CHALLENGE

Conditions in this paper mill were hot, humid, and miserable. The process equipment would heat the building to incredibly high temperatures. More than 120 F at the mezzanine, with additional elevated temperatures throughout the work line.

The reason for this was obvious; the ventilation system was simply insufficient. Inoperable make-up air units failed to bring any fresh air into the building. That meant that the roof fans, the ones that worked that is, made for a negative pressure environment.

To complicate matters even further, the building is about 100 years old, with a very weird roof. Parts of it were concrete, others were metal. There were even some degraded, rotting support purlins. All of that made any building construction improvements a challenge.

When they decided to replace their roof, however, they decided that they decided that it was also the time to replace their poor ventilation system. Fortunately, they got a recommendation from a sister mill in another state who got their ventilation solution from Moffitt.

DESIGN

The high temperatures and tall roof made this building a prime candidate for natural ventilation. Opening the roof and walls would greatly improve air flow and quality. In addition to removing the hot air, it would also remove the pressurization problems as well.

Moffitt took temperature readings throughout the facility to get a complete picture of the situation. That data was then used to design a computational fluid dynamics (CFD) model. The model illustrated where the hot air was gathering and where intake air was most needed.

The old building structure provided an extra challenge for the design, and ultimately Moffitt revised the design many times to get it to work. Custom louver sizes were needed to best fit the walls. In fact, the Moffitt team inspected the building several times to ensure that the louvers would fit as needed.

The CFD model predicts results at the 5 ft elevation, mezzanine level, and roof. The model illustrates a temperature drop of approximately 13 degrees at the mezzanine. Down from 120 to 107.

INSTALLATION

Moffitt advised Fagen on the installation of the MV. The unit was assembled on the ground and hoisted into place, several long sections at a time. This avoided extended work on the roof of the building.

RESULTS

Moffitt continues to work with the contractor and engineer through start-up and commissioning of the plant. The ventilation equipment is installed and commissioned on building 1, with building 2 scheduled for completion shortly. Everything seems to be working as designed so far but the real test will come this summer when the generators are activated.