Pulverized Coal Combustion Particulates and NOx

Coal as a Fuel Advantages Disadvantages

Coal as a Fuel Primary Advantages Primary Disadvantages High Energy Density Widely Available Globally Inexpensive Easily Transported Easily Stored On-Site Good Choice for Baseload Generation Contaminants Mineral Matter Sulfur Nitrogen Trace Elements CO2 Focus of Technology Development

Early Air Pollution in England In 1306, to clean up London's air, King Edward I, outlawed coal burning exclaiming "…whosoever shall be found guilty of burning coal shall suffer the loss of his head." After deforestation, rather than freeze and starve, people began burning c0al again. In 1590, Queen Elizabeth bans burning coal again, without the death penalty

Addressing Pollutants 1930’s: soot and smoke (dirtied cities) Taller stacks 1960’s: partial combustion products, fly ash Precipitators, scrubbers 1980’s: SOx Phase 1: Low sulfur coal, Phase 2: Scrubbers 1990’s: NOx, Phase 1: Low NOx burners, over-fire air, gas recirculation Phase 2: Selective Catalytic Reduction, Non-Catalytic Reduction 2000: Mercury Scrubbers, Activated Carbon Injection (ACI) 2010’s CO2 ?

Pollution Abatement Pollutant Technology Consequence Industry Response Ash Particulates Mechanical capture Increased solid waste Utilization of ash SOx Scrubbers Utilization of scrubber byproduct NOx Low NOx Burners, SCR, SNCR Increased carbon content in ash Beneficiation of ash to remove carbon Mercury Scrubbers, ACI CO2 Capture: Scrubbers Storage: underground injection? Significant energy penalty (30%) Water displacement R&D to improve efficiency ? Reduced emissions (i.e. cleaner air) Increased solid & liquid waste

World’s Tallest Stacks 2nd GRES-2 Power Plant, Ekibastuz, Kazakhstan 1377 ft Inco Superstack at the Inco Copper Cliff smelter, Sudbury, Ontario 1277 ft

Electrostatic Precipitators (ESPs)

ESP Applicable boiler sizes: 25 MW to 1300 MW. Source: babcock.com

ESP Performance Normally applied in several stages (2 to 4) to maximize collection efficiency Source: EPA

Baghouse limited by operating temperature Source: pcsesp.com

Fly Ash Collection Fly Ash Silo

Burner Designs Original Recent Past Current Sources: Babcock and Wilcox Unizar

Principle of Low NOx Burners Fuel and air mixed at an angle Suppression of fuel and air in initial combustion stage Fuel not burned initially mixes with air not used initially Higher temp region cannot develop Lower flame temp and local oxygen partial pressure

Low NOx Burners www.einstrumentsgroup.com www.fluent.com/software

Comparison of Flames Decreasing NOx HT-NR HT-NR2 HT-NR3 Stable, brilliant flame Higher NOx Lower Combustion Efficiency Wider, shorter flame Lower NOx Higher Combustion Efficiency Source: www.bhk.co.jp

Nitrogen Oxides (NOx) Contribute to acid rain Can also form ozone and reduce visibility Formed from 2 sources fuel combustion air Initial control (late 70’s) was staged combustion Fire in stages Restrict oxygen where temp. is highest Led to low NOx burners Installed at 75% of large coal plants Typical NOx reductions of 40 to 60% Source: www.netl.doe.gov/KeyIssues/future_fuel.html

Selective Non-Catalytic Reduction (SNCR) Post combustion process Lower temperature required Typically at top of boiler by-pass Nitrogen-based reagent injected Typically urea or ammonia NOx converted to N2 and H2O Typical NOx reductions of 35-50%

Selective Catalytic Reduction (SCR) Source: procom.kaist.ac.kr

SCR Reactor www.netl.doe.gov http://english.hhi.co.kr www.dom.com

Reaction Mechanism in SCR Reactor Selective Reactions 6NO + 4NH3 → 5N2 + 6H2O 4NO + 4NH3 + O2 → 4N2 + 6H2O 6NO2 + 8NH3 → 7N2 + 12H2O 2NO2 + 4NH3 + O2 → 3N2 +6H2O NO + NO2 + 2NH3 → 2N2 + 3H2O Non-selective Reactions 2NH3 + 2O2 → N2O + 3H2O 4NH3 + 3O2 → 2N2 + 6H2O 4NH3 + 5O2→ 4NO + 6H2O

Global NOx Concentrations

NOx is a precursor to acid rain (HNO3) and ozone (O3)

SO2 Combines with water vapor to form dilute acid Sulfur sources acid rain Sulfur sources coal volcanoes biological decomposition Clean Air Act (1970) reduced SO2 emissions Initial reductions by coal cleaning First US commercial coal-utility scrubber built in 1967 Union Electric, MO Clean Air Act (1977) essentially mandated scrubbers 52 scrubbers operating in 1982 190 scrubbers operating in 2008 Mandatory after 2018 Typical SO2 reductions >90% Source: www.netl.doe.gov/KeyIssues/future_fuel.html

US Coal Production Million tons Source: EIA

Source: EPA

Rainfall pH 1994 2000 2009

EPA Train Wreck Chart

Annual SO2 and NOX Emissions 2005 2009

Source: wattsupwiththat.com

2000-2011 http://iopscience.iop.org/1748-9326/8/1/014003/article

Vintage protest images 1994 ? 1985

There are about 1,500 active volcanoes in the world Emission rates of SO2 from an active volcano range from <20 tonnes/day to >10 million tonnes/day Mount Pinatubo (1991) injected about 20 million metric tons of SO2 into the stratosphere In 2016, US electric plants will emit 1.1 million metric tons of SO2 There are about 1,500 active volcanoes in the world