Operational Improvementsat the

Grant Town Power Plant

Presented By:Steve Friend

Sr. Plant EngineerEdison Mission O&M

2005 ARIPPA Technical Symposium

Improvements at the Grant Town Power Plant

• Fuel Handling and ProcessingRo-Pro FacilitySilt System

• Ash HandlingBottom Ash Screw CoolersBottom Ash Piping

• Limestone ProcessingDFM

• BoilersGrid NozzlesTube ErosionCyclonesNOx Control

• DCSFoxboro Migration

Fuel Processing and Handling

• Addition of the Ro-Pro facility has added flexibility to the fuel production process and additional means for final product cost

• Removal of the wet circuit equipment from the original preparation plant eliminated excessive reject and reduced costs of product – dewatering chemicals and equipment no longer used

• Silt system installation and modifications have allowed facility to maximize amount of lowest cost fuel to be added into final fuel blend – higher silt percentage = minimum fuel costs

Ro-Pro Fuel Processing Facility

Ro-Pro Screener

Silt Feed System

Bottom Ash Handling Improvements

• Screw Cooler capacity was approximately 20% lower than design with a 6” Pitch Auger – required running the screw cooler at higher RPM for adequate bed level control

• 7” Pitch Auger allowed screws to be slowed down – reduced erosion rates on the cooler components

• Addition of rifle bars has helped to control trough erosion but has increased wear rate on the auger

• Application of weld overlays, wear strips, and thicker materials has helped control auger wear

Bottom Ash Screw Cooler Troughwith Rifle Bars

Bottom Ash Screw CoolerInlet Section of Trough

Bottom Ash Piping Modifications

• Initial design was sweep elbows on both the primary and redundant pressurized bottom ash conveying systems

• Sweep elbows had very low mean time between failures due to erosion – on the order of a few weeks

• Reconfiguration of the system using blinded tees for the direction transitions has reduced maintenance costs.

• Effective pipe rotation program has helped to further reduce ash conveying system maintenance costs

Bottom Ash Blinded Tees

Limestone Handling System

• Williams Direct Fired Mill for processing limestone for injection into the CFBs

• Velocity Cone did not have any impact on final product size

• Optimization of air flow though the mill has helped to produce more ideally sized product

• Installation of VFD on the product cyclone rotary valve has helped to minimize transport line pluggage and system processing delays

DFM

Boiler Modifications

• Erosion Control

– Sootblower lane shielding

– Economizer hanger tube tube monitoring/shielding/replacement

– Flame Spray

– Pad Welding

– Refractory Extensions

– Stainless Steel Overlay

Combustor Tube Erosion

Refractory Extensions

Combustor Tube Weld Overlay

Boiler Modifications

• Arrowhead Nozzles

– Provide nominal improvement in limestone utilization

– Backsifting is a BIG problem

– Internal stand pipe erosion now becoming a major concern

– Increased maintenance costs offsetting any benefit realized in reduced limestone consumption

– Considering repair/replacement options

Arrowhead Nozzles

New Nozzle being Considered as Arrowhead Replacement

Boiler Modifications

• Cyclones

– Segmented Vortex Finders

– Narrowing of cyclone inlet opening

– Design of vertical bullnose on the cyclone inlet to narrow the opening about 10%

– Narrowing of the opening has increased inlet velocity to >75 ft/sec

– Both changes had major impacts on limestone consumption – improvement of about 20% in total when paired with the DFM optimizations.

Vortex Finder Deformation

Segmented Vortex Finder

Bullnose Modification to Narrow Cyclone Opening

Ammonia Unloading/Storage

Ammonia Injection Skid

DCS Modifications

• Foxboro Migration Package

– Poor availability of Bailey replacement parts and support

– Electrolytic capacitor failures

– No changes to I/O wiring

– Low cost alternative to wholesale DCS replacement

I/O Rack

DCS Processor Rack