Dry Scrubber – Recycle Ash Systems: Considerations for Recycle Solids

摘要

Present a design approach used for a recent coal fired power plant project in developing aDry Scrubber-Recycle Ash Removal System. The design / sizing criteria for a pneumaticrecycle ash conveying system will be presented along with the actual layout of thepneumatic conveying system that utilizes conventional commercially available blowerequipment. Today's dry scrubber power plant projects that burn Powder River Basin(PRB) coal have substantially increased the quantity of solids in the flue gas stream to becollected in the baghouse or pulse jet fabric filter (PJFF). In an effort to fully utilize theun-reacted lime and reduce operating costs, utilities are recycling a portion of the fly ashremoved in the baghouse/PJFF for re-use in the scrubbing process. As a result,traditional utility-grade fly ash pneumatic conveying systems are approaching theirvacuum pipe design limits, compromising the traditional high design allowable margins,and sub-dividing the vacuum conveying layout into smaller sub-systems and/orcombination vacuum/pressure pneumatic conveying systems. Higher ash generationproduction/capacities, difficult material characteristics and lower operating temperaturesprovide additional design constraints directly resulting in larger/more complicatedpneumatic conveying systems (i.e. larger equipment, more pneumatic pipes, fittings andvalve stations). At the same time, the pneumatic conveying system equipment locationand pipe routing must be arranged and often re-arranged during the design calculationperiod so that the total equivalent conveying length (TEL) including fitting losses, etc isdetermined to be less than the available TEL calculated length up to and including thevacuum exhauster losses. This paper explains the methodology used for developingsystem design criteria, presents design constraints, lessons learned, and the final system /equipment selection and layout for a recent project involving a 600 MW, UltraSupercritical PRB-fired unit with a Spray Dryer Absorber (SDA) and Pulse Jet FabricFilter (PJFF).