Innovation: Common Discharge Stack

During the preliminary development of a 6,000 kW (6 MW) backup generation site for a corn processing plant, it was concluded that 42 foot tall stacks would be needed for each unit. The generator sets were sent off for packaging and individual generator enclosures designed to accommodate the weight and wind loading for the stacks. Even though concessions had been made in run-hours to keep the project out of PSD and Title V space, late in the permitting process, the local permitting agency asked for a more extensive computer model. Results from the model revealed that 120 foot tall stacks were needed to meet the 24-hour NAAQS for PM10 (particulate), due to the proximity of the generators to the customer’s property line. As a result, IEA faced the challenge of how to support the weight of the stacks and where to run the guy wiring.

IEA developed a novel solution; rather, than four individual 120 tall stacks, the emission model was rerun with a single (common) 125 foot tall, 42 inch diameter stack that showed compliance with the 24-hour NAAQS for particulate and all other emission limits.

The design called for each generator’s exhaust to be run more or less horizontally and then connected to the bottom of the stack which was mounted to an adjacent building. Even when constructed of stainless steel (for aesthetic purposes), the end result was the exhaust system costs approximately half of what was estimated for the four separate, individually supported stacks.

Challenges to overcome during the project included:

  • Demonstrating (through calculations and then actual test data), that the horizontal runs would not create excess differential pressure (dP) across the turbochargers leading to increased wear and shorter life span.
  • Ensuring mechanisms would not be created to draw air (allowing for condensation) through an idle engine with a cylinder with an exhaust valve open.
  • Determining (through calculations) the proper sizing (diameter) of the individual horizontal exhaust headers.
  • Determining (through calculations) the proper sizing (height and diameter) of the common exhaust stack.

If you have a design challenge, contact IEA to see how we can help you install generation at your location.