CARBON DIOXIDE EMISSIONS Electric Utility Generating Units (EGU) are one of the main sources of CO 2 emissions. CO2 is about three-fourth part of GHG emissions around the Globe and 84% of U.S. GHG emissions.
Sector/Source 2012 Electricity Generation2,064 Transportation1,837 Industry1,278 Agriculture614 Commercial353 Residential321 U.S. Territories58 Total6,523 GHG Emissions in CO 2 Equivalent (million metric tons)
Source: EPA Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2012. April 2014 GHG’s Emissions 2012 (Million Metric Tons CO 2 equivalent)
Source Total Emissions Coal1,511 Natural Gas492 Fuel Oil19 Geothermal0.4 Total2,023 CO 2 Emissions 2012(million metric tons)
http://www.vox.com/2014/6/1/5770556/EPA-power-plant-rules-explainer Sources of Carbon Dioxide Emissions 2012
EPA Regulations According to Clean Air Act section 111(d) Section 111(d): Emission Guidelines for GHG’s from existing EGU’s. Section 111(b): Emission Guidelines for GHG’s from Constructed & Modified EGU’s.
EPA proposed two goals in achieving lower emissions of CO 2. State-Specific rate-based goal. Emission guidelines for States to develop plans to attain State- Specific goals. Existing EGU’s Guidelines
State-Specific Goals EPA proposed four building blocks in achieving State-Specific goals Reducing the Carbon intensity at individual affected EGU’s through heat-rate improvements. Reducing emissions to lower the Electric system’s overall Carbon intensity by shifting generation among existing EGU’s. Reducing the Carbon intensity generation by expanding low Carbon and renewable generating capacity. Lowering the Carbon emissions by reducing the Electric generation required(Improving demand side efficiency).
SubcategoryEmission limit Reconstructed Utility Boilers and IGCC (Integrated Gassification Combined Cycle) Units (heat input rating > 2,000 MMBtu/h) 1,900 lb CO 2 /MWh-net Reconstructed Utility Boilers and IGCC Units (heat input rating <= 2,000 MMBtu/h) 2,100 lb CO 2 /MWh-net Reconstructed Natural Gas-Fired Stationary Combustion Turbines (heat input rating > 850 MMBtu/h) 1,000 lb CO 2 /MWh-gross Reconstructed Natural Gas-Fired Stationary Combustion Turbines (heat input rating <= 850 MMBtu/h) 1,100 lb CO 2 /MWh-gross Proposed Guidelines for Reconstructed EGUs
SubcategoryEmission limit Not Subject to State CAA 111(d) Plan Modified Natural Gas-Fired Stationary Combustion Turbines (heat input rating > 850 MMBtu/h) Modified Natural Gas-Fired Stationary Combustion Turbines (heat input rating <= 850 MMBtu/h ) 1,000 lb CO 2 /MWh-gross 1,100 lb CO 2 /MWh-gross After Becoming Subject to State CAA 111(d) Plan Modified Natural Gas-Fired Stationary Combustion Turbines (heat input rating > 850 MMBtu/h) Modified Natural Gas-Fired Stationary Combustion Turbines (heat input rating <= 850 MMBtu/h ) 1,000 lb CO 2 /MWh-gross and 111(d) requirements 1,100 lb CO 2 /MWh-gross and 111(d) requirements Proposed Guidelines for Modified EGU’s
Control technologies Kansai Mitsubishi Carbon dioxide Recovery Process (KMCDR) : Carbon dioxide reacts with an ammine solvent before being captured, isolated and compressed into a liquid. Carbon dioxide capture and sequestration is another technology used by Electric Utility Generating Units(EGU) to reduce emissions.
Mercury Emissions in US due to Utilities Source Category1999 Estimated Emissions Tons/year Percent of total US inventory Coal Utility Boilers 47.840.8 Oil Utility Boilers 0.50.4 Natural Gas 0.440.4
When coal is burned in power plants, mercury passes along with flue gas into atmosphere and falls back to earth in rain, snow etc. Mercury presents a serious problem because when it enters water supply, bacteria converts it into methylmercury. Getting exposed to methylmercury by eating fish which is contaminated by that may cause neurological disorders.
Emission Control Technologies EPA implemented emission control technologies to reduce stack mercury emissions by capturing most of the mercury before it leaves the stack. NALMET 1689 is identified as a promising treatment for metals removal and Nalco 71301 is a high molecular weight cationic emulsion, for effective solids settling. Mercury discharge from plants is reduced from 1336 pounds per year to 17 pounds per year due to NALMET treatment.
Emission Control Technologies Contd. Development of low cost and innovative scrubbers effectively control hg emissions. More than 20% of US. Coal fired utilities use this wet scrubber. Removal efficiency of wet scrubber depends on how much mercury is present in Hg 2+ form because this form is water soluble. Usage of SCR (Selective Catalytic Reduction) catalyst to oxidize hg 0 can enhance the capture of mercury.
Although potential emissions are calculated to be 75 tons per year based on Hg content in coal, actual current emissions are estimated to be 48 tons per year due to Hg capture. ACI (Activated Carbon Injection)with an ESP (Electrostatic precipitator) and a retrofit fabric filter has a potential to achieve 90% Hg reduction. Standard activated carbon injection also controls mercury emission.
Regulations Section 112 of Clean Air Act establishes a two part- process for regulating HAP emissions. First Phase: Defines emission standards that define maximum achievable control technologies (MACT). Second Phase: Residual risk assessment. On December 6,2011, EPA finalized MACT standards to reduce HAP emissions