PAC Injection Upgrades: Don t Live with Problem Systems EUEC 2017 San Diego, CA Feb. 8, 2017
Introduction PAC systems were installed for Hg compliance. Newest are about a year and oldest are around 5 years. Equipment is simple silo, metering, transport, and injection. But.. Maintenance can be a headache.
Problem Areas PAC Leaks are messy Plugged Lines and Lances Inconsistent / Inaccurate Flow Rates Bromine Corrosion Erosion
Problem: PAC Leaks & Line Plugs
Common Causes: Insufficient Blower Pressure Long Lines & Lots of Bends Insufficient Blower Volume Plugged Eductor Debris from Silo PAC flooding of Eductor
Solution: PAC Leaks & Line Plugs Change to PD Blowers: Centrifugal blowers have decreased air flow as pressure drop increases. Centrifugal Blower Reduced Air Flow Fall-out from low velocity Higher Pressure Drop Investigate Line Design: Minimize pressure drop. Too many turns, not using long-radius elbows, too small. PD Blower
Solution: PAC Leaks & Line Plugs Monitor Eductor Vent Line Pressure shut down blower at positive pressure Monitor Transfer Line shut down blower at low pressure Add Pressure Transmitter
Lessons Learned: Line Plugs In general, lines must be kept as short as possible with as few bends as feasible. Know the limits of your eductor. Pipe diameter should be sized to allow a velocity not less than 3,600 ft/min for PAC. PD Blowers should be used air flow is not reduced as backpressure increases. VFD control is useful to allow for changing air flow rates in the event that installed system requirements are different from design values. The VFD is set and forget and not varied with material flow or unit load changes.
Solution: PAC Leaks & Line Plugs Next Generation Design - Separate feed function of eductor from transport of the blower. Reduces the load on the blower. Pressure drop across eductor does not impact transport to lances.
Another Cause of PAC Leaks: PAC is small and lightweight, so it will follow air if you have an air leak, you have a PAC leak. Silicon caulk is your friend.
Problem: Lance Pluggage Cause: Inadequate velocity at lance Moisture in line Fly Ash buildup at lance outlet Transition from large-to-small diameter in multiplepipe lances
Solution: Lance Pluggage Ensure adequate flow to maintain velocity. Revise lance design to maximize open area and reduce wear. Bayonet lance has proven effective on applications not requiring pin-point distribution.
Lessons Learned: Lance Pluggage Keep blower operating at all times: Prevent ash buildup in lines and lances. Keeps temperature of lines elevated to reduce risk of condensation of water in lines. Install lance isolation system that allows compressed air to be blown through lance. Automated or manual This can be modified to monitor lance pluggage also.
Lance Cleaning w/plug Detection Compressed air can both clear lances and detect stubborn plugs. System can be automated or manual.
Problem: Inconsistent/Inaccurate PAC Flow PAC floods into the system past the screw feeder. Increase in PAC feed demand not related to variations in fuel. PAC hanging up in system, getting stuck in hopper.
Causes: Inconsistent/Inaccurate PAC Flow Density is not constant throughout the injection process. Regardless of design density, it changes at each handling point. Design: 35 lb/ft3 During truck unloading/silo fill: 25 lb/ft3 In silo after settling: 35 lb/ft3 Feed process through auger: 15-25 lb/ft3 Use lower density value when calculating capacity of auger-feed system. Volume-based augers may under-deliver if PAC density is lower than design assumption.
Causes: Inconsistent/Inaccurate PAC Flow PAC can act like water and pour (flood) through the auger. Isn t detected without a gravimetric system. Design the ratio of length-to-diameter to minimize flooding. Use double-helix auger to maximize auger contact.
Problem: Variation from Design Feed Rate Injection systems are often designed for worst-worstcase scenario instead of probable-worst-case scenario. Overdesign of equipment size can create its own problems. Examples: Design: 372 lb/hr Actual: 35 lb/hr Design: 255 lb/hr Actual: 7 lb/hr Increases in Demand should be investigated: Variations of Hg in coal expected. Increase with no apparent cause: Flooding of PAC through feed system. Change in Distribution at Lances Wrong density used to determine auger speed.
Lessons Learned: Variation from Design Feed Rate Design auger with VFD and motor with high-turndown capacity (6 60 Hz). Provide auger with interchangeable screws and tubes to provide different capacities that allow direct replacement. At one facility, we replaced a 2.5 auger with a 1 auger. If load variations create a range too wide for a single auger, consider having one train for high flow (2.5 auger) and convert the redundant train for low flow (1 auger).
Problem: Bromine Corrosion The B of BPAC is Bromine (From 0% to 10% by weight). Bromine facilitates oxidation of Hg, allowing better collection efficiency by carbon particles. Generally, more bromine allows lower BPAC flow. It is in the same family of chemicals as Chlorine, and is water soluble and corrosive. Bromine + presence of water (humidity in air) lead to problems.
Results of Bromine Corrosion The rotors of Rotary Air Locks (RAL) would freeze after only a few days out of service if BPAC left in system.
Results of Bromine Corrosion Corrosion of silo walls can create structural concerns. Pitting on Inside Leads to Holes on Outside
Lessons Learned: Bromine If possible, keep RAL turning even when train is out of service don t give corrosion a chance to bridge between rotor and case. BPAC should not be left in the system for long periods: Empty silo prior to planned outage. Allow operating train to run empty prior to switching to redundant train. Carbon steel components and pipes need to be carefully monitored and tracked. Stainless steel can extend service life, but is not immune. Measure and track wall thickness of carbon steel silos. Watch for thinning spots.
Lessons Learned: Bromine (Cont.) Cycle valves as frequently as feasible make sure they are not frozen. Reduce Bromine levels in PAC as low as possible while maintaining compliance at an economic injection rate. Consider periodic 3 rd party testing of BPAC to confirm proper levels of bromine are being supplied.
Problem: Erosion Although it feels soft and powdery, PAC is erosive. Pressure and flow can create channeling, pitting, and wear. All parts in contact with moving PAC are potentially subject to erosion and need regular inspections: RAL (rotor and body) Auger blades Auger tubes Butterfly valves Eductor internals Pneumatic transfer and fill lines
Erosion
Lessons Learned: Erosion Use long-radius bends and wear-back elbows on all bends and changes in flow direction. Frequent inspection of components with moving parts. Use ceramic-lined eductors to extend life. Modify process/equipment material if wear is consistently observed. Rotor blades eventually wear and allow PAC to flow uncontrolled past the airlock.
Bonus Freebie Keep large pieces of cardboard out of the auger.
QUESTIONS? Contact Information Contact: Corporate Address: Mike Gregory 4800 Lamar Avenue Mission, Kansas 66202 Corp Tel: (913) 384.5511 E-Mail: mgregory@iac-intl.com Sales Tel: (800) 334.7431 Corp Fax: (913) 384.6577 Cell: (913) 216.3000 Web: www.iac-intl.com