Kiewit Engineering Group Reduces Emissions at Commercial Power Plant with Arrow

• Industry: Power Generation
• Region: North America
• Focus: Reducing power plant emissions through
  auxiliary steam system optimization 

Each year new and stringent emissions requirements are being placed on power generation facilities. The goal for any of these facility owners is to adhere to the new regulations without significantly impacting costs and continuously supply power to the grid with their existing facility. One such company hired Kiewit Engineering Group to study an existing auxiliary steam system for a commercial power plant.

The plant wanted to determine if they reactivated an old glycol heating system, whether existing header and steam letdowns were capable of supplying the glycol system in addition to other future users and current worst-case demands.

More recent emissions regulations have driven the plant to utilize a system that cuts down emissions, but results in the formation of acids that precipitate during cold weather startup and damage the air preheater. Kiewit’s customer desired to reactivate the glycol system to alleviate the issue; the idea is the exhaust gas is heated far enough above the acid-gas dew point that when it enters the air preheater to exchange heat with the incoming cold air, it does not drop down below the acid dew point.

The steam system spans four aging coal boilers. During the cold winters in the 1970s, the plant utilized a glycol heating system that provided energy to the boiler stacks. The glycol (antifreeze) would heat the incoming exhaust gas. Later improvements to the boiler made this system obsolete, and it was partially removed and partially abandoned-in-place.

The goal of the model was to determine which letdowns would need to be increased in size to allow for more steam flow to the auxiliary steam system.

Kiewit started with a crosstie line that was 6” (15 cm) (Figure 1). Of the four aging coal boilers, Unit 4 is the largest and supplies most of the auxiliary steam to the system. As Units 2 and 3 trip, are offline, or cannot supply steam to the auxiliary header, Unit 4 will need to supply these demands. The 6” (15 cm) red crosstie piping was predicted to be too small to allow enough steam to be supplied to users closer to Units 1, 2, and 3, even if the letdowns were increased in size.

Kiewit used the Datacor Arrow Scenario Manager to run various simulations to analyze different conditions. A base scenario represented the as-designed system. Child scenarios were created to reflect variations in Unit configurations, steam supplies, etc. Some scenarios increased the size of the crosstie to 10” (25 cm) and they re-ran restricted scenarios where either