market-based advanced coal power systems final report - National ...

Market-Based Advanced Coal Power Systems
quenching spray of reagent. The gas flows upward through a tray, which provides enhanced
contact between gas and reagent. Multiple sprays above the tray maintain a consistent reagent
concentration in the tray zone. Continuing upward, the reagent laden gas passes through several
levels of moisture separators. These will consist of chevron-shaped vanes that direct the gas flow
through several abrupt changes in direction, separating the entrained droplets of liquid by inertial
effects. The scrubbed and dried flue gas exits at the top of the absorber vessel and is routed to
the plant stack. The FGD system for this reference plant is designed to continuously remove
92 percent of the SO2.
The scrubbing slurry falls to the lower portion of the absorber vessel, which contains a large
inventory of liquid. Oxidation air is added to promote the oxidation of calcium sulfate, contained
in the slurry, to calcium sulfate (gypsum). Multiple agitators operate continuously to prevent
settling of solids and enhance mixture of the oxidation air and the slurry. Recirculation pumps
recirculate the slurry from the lower portion of the absorber vessel to the spray level. Spare
recirculation pumps are provided to ensure availability of the absorber.
The absorber chemical equilibrium is maintained by continuous makeup of fresh reagent, and
blowdown of spent reagent via the bleed pumps. A spare bleed pump is provided to ensure
availability of the absorber. The spent reagent is routed to the byproduct dewatering system. The
circulating slurry is monitored for pH and density.
This FGD system is designed for “wet stack” operation. Scrubber bypass or reheat, which may be
utilized at some older facilities to ensure the exhaust gas temperature is above the saturation
temperature, is not employed in this reference plant design because new scrubbers have improved
mist eliminator efficiency, and detailed flow modeling of the flue interior enables the placement of
gutters and drains to intercept moisture that may be present and convey it to a drain.
Consequently, raising the exhaust gas temperature is not necessary.
Technical Requirements and Design Basis
• Number and type of absorber modules = One, 100% capacity, counter-current tower design,
including quench, absorption and moisture separation zones, recirculated slurry inventory in
lower portion of absorber vessel
3.1-15 December 1998