limestone injection for protection of scr catalyst · scr catalyst terence ake, clayton erickson,...

MEGA Symposium May 19 – May 22, 2003, Washington, D.C.

LIMESTONE INJECTION FOR PROTECTION OF SCR CATALYST

Terence Ake, Clayton Erickson, William MedeirosRiley Power Inc., a Subsidiary of Babcock Power Inc.Linton HutchesonDuke EnergyMark Barger, Scott RutherfordCormetech, Inc.

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Introduction & Background

• Gaseous Arsenic Poisoning Predominant Deactivation Mechanism

• CaO Potential Poison at High Percentages• Gaseous As Controllable with CaO from

– Naturally in Coal– Limestone Addition to Fuel– Fuel Blending

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Arsenic Control Through Limestone Addition

• Gaseous Arsenic (AsO3) as Catalyst Poison

• Addition of Limestone (CaCO3) to Coal form solid Non-Poisoning Form ((Ca3(AsO4)2)

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European And Japanese Experience

• Japanese Experience Good, Low As Coals -Dry Bottom Units

• European Experience Good, Low As Coals -Dry Bottom Units

• Bad European Experience, Low As Coals -Wet Bottom Ash Recirculation

• Recirculation Revaporized As to Gaseous Phase

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United States Coals

• USGS Coal Database - 22 ppm As Average• Coal Cleaning Reduces As by 35 to 83%• Utilities Need for Fuel Flexibility

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Arsenic Variation in Coals

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First US Limestone Addition• Large Variation in As Concentration with

Low CaO• Arsenic Levels as High as 24 ppm • Unit Had Past History of Slagging• Approach

– Temporary Limestone Feed System– Measure Gaseous Arsenic (AsO3)– Observe Boiler Performance

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Effect of Limestone Addition

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Limestone Addition Experience

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Limestone Addition Experience

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Duke Energy Cliffside Unit 5

• 50% of Fuels Did Not Require Limestone• Two Fuels Cannot Achieve Continuous

Operation With Limestone Addition• Using Limestone Addition System and Fuel

Knowledge Two Initial Catalyst Layers• Cormetech FIELD Guide Developed for

Fuel Range

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Duke Energy Cliffside Unit 5

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Mark Barger

SCR Catalyst Supplier for Cliffside 5 Project

Project Manager – Cliffside 5

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FIELD Guide

• Fuel Impact and Evaluation of Life Determination

• Unit Design Specific• Assumes Constant Fuel Sulfur Level• For Arsenic poisoning SCR applications

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FIELD Guide

20K+hours

16-20Khours

12-16Khours

0-12Khours

CaO%

As (ppm)

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Cliffside 5 with 2002 fuels plotted

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Cliffside 5 with 2003 fuels plotted

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Linton Hutcheson

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Cliffside Unit 5 SCR Management

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Limestone Injection

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FIELD GUIDE

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Cliffside Unit 5 SCR Management

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Coal Data Information

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Cliffside Unit 5 SCR Management

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Fly-ash Data Information

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Cliffside Unit 5 SCR Management

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CS5’s SCR PI Performance Data

More than 100 Additional SCR Data Points Stored

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Cliffside Unit 5 SCR Management

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Viewing Short Version of PI Data

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Viewing Short Version of PI Data

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Cliffside Unit 5 SCR Management

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Time Passing Across the Catalyst

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Conclusions• Optimum Catalyst Designs are Achievable

With Current and Future Fuel Knowledge• Limestone Addition Reduces Gaseous As• Limestone Addition Protects• Limestone Adds to Fuel Flexibility• Limestone System is Part of an Integrated

SCR Reactor Design, Fuel Purchase, Catalyst Management, and Plant Operation Approach