Lecture 9 - Coal and Stationary Power PDF

Coal News Vox, why there are more solar jobs than coal jobs https://www.youtube.com/watch?v=lasXF7bFElw California Energy Commission, Tracking Progress, California's Declining Reliance on...

Coal News Vox, why there are more solar jobs than coal jobs https://www.youtube.com/watch?v=lasXF7bFElw California Energy Commission, Tracking Progress, California's Declining Reliance on Coal, Overview, updated October 2018 Coal and Stationary Power ME 4180 – Energy Systems and Sustainability Prof. Mario Medina Department of Mechanical Engineering Sept. 28, 2020 Agenda Agenda Stationary power plants Coal properties: rank, grade Example: coal impact Comparison to petroleum fuel Stationary power generation Exclusively for the stationary power Has different needs than the transportation sector Two categories: Large and centralized Small and distributed EPA, https://www.epa.gov/energy/about-us-electricity-system-and-its-impact-environment Stationary power generation Exclusively for the stationary power Has different needs than the transportation sector Two categories: Large and centralized Small and distributed EPA, https://www.epa.gov/energy/about-us-electricity-system-and-its-impact-environment Electricity generation Coal supplies the electricity sector Coal has historically been the dominant energy carrier use for generating electric power There are huge loses associated with the stationary power sector ~70-80% Source : U.S. DOE., EIA Coal supplies the electricity sector The gap between coal and natural gas is closing. In terms of energy production, natural gas has already exceeded coal Why? Source : U.S. DOE EIA What is coal? Coal is a complex hydrocarbon structure with trace species integrated into the structure Model proposed by Ladner for a vitrinite with 82% carbon, representative of a high volatile bituminous coal (from S. Niksa and A. R. Kerstein, Energy & Fuels 1991, 5, 647-665). Types of coal Type Carbon content Heating value [Btu/lb] anthracite 86-98% 13,500-15,600 (high rank coal) bituminous 46-86% 8,300-15,600 (low, medium and high (a,b,c) volatile bituminous and sub bituminous) sub-bituminous 8,300-11,500 (a,b,c) lignite (a,b) 46-60% 5,500-8,300 (low rank coal) Coal is classified based on heating value and carbon content (rank) All types of coal contain sulfur and nitrogen Coals are also classified by grade (based on ash content, sulfur content, etc.) Coal grade is independent of coal rank Data sources: http://science.jrank.org/pages/1533/Coal-Composition-coal.html; Combustion Engineering, by Borman and Ragland Types of coal Typical compositions and heating values: Ultimate analysis (daf, % wt) (daf: dry ash-free) bituminous lignite wood H 5 5 6 C 78 68 50 S 2 1 0.1 N 2 1 0.1 O 13 25 44 Higher heating value (Btu/lb) 14,000 10,000 8,700 Proximate + ultimate analysis (%wt) bituminous sub bituminous H 5 3.3 C 67.0 48.2 S 1.5 0.4 N 1.5 0.7 Ash: inorganic material, non-combustible (SiO2) O 8.7 11.9 ash 9.8 5.3 moisture 6.7 30.2 Higher heating value (kJ/kg) 28,400 19,400 Data sources: http://science.jrank.org/pages/1533/Coal-Composition-coal.html; Combustion Engineering, by Borman and Ragland Comparing energy content © Wooldridge, University of Michigan Comparing emissions Averages from U.S. power plants, 1996, statistics from U.S. DOE and EPA © Wooldridge, University of Michigan Example: Impact of coal use in the power sector A power plant operates using bituminous coal a) If the plant is rated for 500 MW, with a 1st law thermodynamic efficiency of η = 36% and a plant capacity of 65%, how much coal is burned in one year? b) How much ash and sulfur is generated in one year? Example: Impact of coal use in the power sector Assuming all S is converted to SO2 we can estimate the SO2 produced too. We really need chemical equilibrium to determine trace exhaust gas species, but we can calculate an upper limit determined by atom balance 1 mol S 1 mol SO2 MWS [g/mol] = 32 MWSO2 [g/mol] = 64 2 to 1 ratio 1.5×107 kg of S yields 3.0×107 kg of SO2 1×109 kg coal  3.0×107 kg SO2 annually Example: Coal combustion vs. petroleum-based fuels? How much air Proximate + ultimate analysis (%wt) is required for bituminous H 5 complete C 67.0 S 1.5 C0.47H0.42S0.004N0.009O0.045Ash0.014 combustion N 1.5 O 8.7 + 0.03 moisture (H2O) of bituminous ash 9.8 moisture 6.7 coal? Higher heating value (kJ/kg) 28,400 butiminous MW (g/mol) ni(moles) Xi=(ni/ζ)*100 H 5 1 5 42% C 67 12 5.6 47% S 1.5 32 0.047 0.4% N 1.5 14 0.11 0.93% O 8.7 16 0.54 4.5% ash 9.8 60 0.16 1.4% moisture 6.7 18 0.37 3.1% HHV (kJ/kg) 28,400 Total = ζ= 11.8 Example: Coal combustion vs. petroleum-based fuels? Now we need the global reaction for coal combustion, just like combustion of liquid fuels: C0.47H0.42S0.004N0.009O0.045Ash0.014 + 0.03H2O + z(O2+3.76N2)  aCO2 + b H2O + c N2 Some food for thought The total annual US coal power capacity is ~340 GW That is about 50% of the total power generation in US 90% of these power plants are over 25 years old At least 25% (~50 GW) of the coal-fired capacity is likely to be retired in the next 10 years Nuclear is expected to retire another 40 GW or more in the same time period