FGD and DeNOx
NEWSLETTER       

February 2011
No. 394

Jeffrey Energy Center FGD Upgrade

Over a period of 18 months (Spring 2008 through Spring 2009), Westar’s 3 x 800 MW Jeffrey Energy Center upgraded the existing FGD systems to remove greater than 95 percent of the SO₂. Burns & McDonnell was contracted to provide detailed engineering, procurement and construction management services for the project. In addition to upgrading the absorbers by way of new internals, new slurry recycling pumps and conversion to forced oxidation, the scope of the project also included upgrading the existing ID fans, new ductwork from the ID fan outlet through to the stack breaching, and conversion to accommodate “wet stack” mode of operation and forced oxidation. The project also included the addition of new limestone preparation and feed systems, new gypsum dewatering and a new FGD blowdown treatment system. The approximate cost of the project was $435 million, reported Kristin Collier of Burns & McDonnell and Stuart Bailey of Westar Energy at Power-Gen 2010.

Upgrades included:

· The internals of each module were replaced in their entirety. All new module internals were of Alloy 2205 construction. The existing spray headers were replaced in kind, with two levels of spray. Headers were constructed of Alloy 2205 internal to the module and fiberglass-reinforced plastic (FRP) external to the module. A contact tray was added to improve the liquid/gas (L/G) contact and reduce the slurry spray requirement. Wall rings were installed to prevent gas sneakage and to direct sprays back toward the center of the towers.

· The original mist eliminators and retractable lance wash system were replaced with high efficiency mist eliminators and a fixed grid wash system. The new mist eliminators have a velocity limit of about 22 feet per second (fps), as compared to the original system’s limit of 10 fps.

· Each module has a dedicated reaction tank. As a result of degradation over time, all tanks were replaced. The new tanks are carbon steel with ceramic tile lining the walls and floor. The new tank roof was constructed of 316L stainless steel.

· The upgraded system includes one spray pump per spray level, or two per module. Each pump is rated at 20,5000 gpm.

· Due to increased pressure drop across the absorber modules, the ID fans needed to be upgraded. New rotors and variable inlet vanes were installed in the existing fan housings. New 8900-hp motors were also installed as part of the upgrade.

· The required limestone grind for the revised FGD system is 95 percent passing 325 mesh. To accomplish this, two new 48 tph ball mills were installed, one running, one spare. The new ball mills were sized so that grinding for a 24-hour-period could be accomplished in one 8-hour shift. Two new limestone slurry storage tanks and new forwarding system, pumps and slurry piping loop were included as part of the upgrade.

· Hydrocyclones, one cluster per module, were added for primary dewatering. Three 55 tons/hr vacuum filters were installed as part of the upgrade, two operating, one spare, sized so that a day’s worth (24 hours) of spent slurry can be dewatered in 12 hours.

After the outage for Unit 3, the scrubber was not achieving the desired SO₂ removal efficiency. Several attempts were made to increase removal by way of altering operating parameters such as pH, stoichiometry and reaction tank density with limited success. The final solution was to increase the pressure drop, and therefore liquid/gas contact time, across the contact tray by reducing the open area from 40 to 30 percent. Figure 1 (see insert) shows emissions from Unit 3.

After the upgrade there were vents of foaming from the reaction tanks. The probable cause was bridging between fine particulates. To counteract the foaming, the limestone slurry storage tanks were dosed with an anti-foaming agent as a plant-wide solution. A purge valve on the hydrocyclone overflow, now opened to remove fines from individual reaction tanks when required, substantially reduces foaming events.

When the secondary dewatering system was first operated, there was a persistent failure to produce filter cake. The filter cloth was blinding after a couple of revolutions of the drum. The blinding was not permanent — the filter could be shut down and the cloth cleaned, which ruled out significant amounts of flyash as a fouling source. The fines layer (secondary peak at 10 micron or less) was attributed to a high level of inerts in the limestone. The limestone supply was changed to a source with fewer inerts and performance of the vacuum filters dramatically improved. A permanent chemical feed system was installed to accommodate upset conditions.

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