Preliminary+Research

Boilers University of Alabama Engineering

Three Types of Boilers: 1) Fire Tube Boilers: combustion products pass through tubes surrounded by water Peak pressure=300 psi Used for heating systems

2) Water Tube Boiler: water passes through combustion products in tubes Water pipes are smaller Can reach pressures of 2000 psi Need insulated refractory wall

3) Waterwall Boiler: water tube boiler with tubes forming an integral part of the boiler wall Wall is water cooled Used for all large boilers

Four Components of Fuel combustion 1) Air supply 2) Fuel air mixture—better for liquid fuels 3) Temperature—higher temp=higher efficiency 4) Combustion time: larger for larger particles

Solid Fuel Firing Stoker Boilers: automatically add more fuel 1) Chain Grate Stoker: fuel fed from hopper along gate 2) Vibrating Gate: like chain grate, but not a loop: sections vibrate 3) Underfeed stokers: use rams to feed fuel from below 4) Spreader stokers: fed from rotating wheel: spreads out fuel

Pulverized Fuel Boilers Use 25 um particles is a dispersion. “Sprayed” from nozzle. Better response to changing loads & more efficient More expensive and harder to use

Coal Combustion Ultimate analysis—elemental composition of coal Primary elements—C, H, O, N, S Air to fuel ratio—A/F Additional information on coal combustion

The Rankine Cycle: Workhorse of the Coal-fired Utility Industry Steve Voss and Greg Gould

Subcritical Rankine Cycle Increasing temperature increases efficiency—increases distance between bottom and top of cycle Typical pressures at 2400 psi & typical temperatures are 1000 or 1050 Reheat cycle increases efficiency Subcritical vs Supercritical: “critical point” is where the fluid is no longer classified as strictly a liquid or a gas—just above 3200 psi for water Efficiency increases: 10,000 Btu/kWh increase 2400 to 3500 psi improves heat rate by 1.5% 4% increase in efficiency (with double reheat) $1.2 per million btu fuel w 80% annual capacity=$2 million cost savings per year

Supercritical Benson Cycle: once-through—shorter start-up time and ramp rates Why aren’t there more? 1) History—more subcritical have been built, dropped off in 70s b/c of nuclear power; had problems 2) Suffered from increases in size in unit size—these problems have been resolved 3) Needs better quality water 4) Controllability more difficult 5) Higher capital cost

Where is this headed? 4500 psi, 1500 F with 20% better efficiencies Few coal plants built in US in last 20 years—80% of plants built outside the US are supercritical

Tracking New Coal-Fired Power Plants National Technology Laboratory Office of Systems Analyses and Planning—Erik Shuster June 30, 2008

Overview of coal-fired power plants currently under production

Historically, predicted capacity much higher than actual capacity (36000 vs 4500 in 2007) Regulatory uncertainty (climate change) Project delays/cancellations Primarily a graph based-resource (difficult to summarize) Net increase of 3745 MW (16%) on progressing projects during 1st half of 2008 Coal-fired plants commissioned averaged 976 per year btw 1990 to 2007 More traditional subcritical plants in development (earlier start) PC and IGCC reflect more recent developments Increase in electricity demand could strain natural gas reserves (no longer true) 2 plants operational during 1st half of 2008 (590 MW)

U.S. Department of Energy. __Fourth Quarterly Report: Boiler Materials for Ultrasupercritical Coal Power Plants__. USC Materials, 2003.

Principal objective of the project is to develop materials technology for use in ultrasupercritical (USC) plant boilers capable of operating with 750ºC (1400ºF), and 35MPa (5000psi). This will allow increase of efficiency of coal based power plants to increase from 35% to 47% all while reducing CO2 and other fuel emissions by as much as 29%. World faces challenge of providing abundant cheap electricity to meet the needs of a growing global population while preserving the same values to the environment. New fuels and technologies must be developed so that the US will have adequate electricity supplies in the future. Coal is low cost but emit pollutants and CO2 at high relative levels. New materials must be looked into on a variety of properties:

Mechanical Properties – mechanical characterization, effects of fabrication variables, weldment performance, fatigue and thermal fatigue behavior. Allowable Stress in boiler maker Long Term Creep Strength – long term characteristics of creep and damage accumulationMicro-structural Analysis – are microstructural changes leading to strengthening, weakening, internal damage? Modeling of Weld Joints Assessment of Creep-Fatigue properties Steamside Oxidation tests performed – behavior of materials predominantly controlled by the alloy chromium concentration. Coating Tests – coated specimens for steamside oxidation testing, and coating feasibility (internal tube coating techniques), Process Scaleup – coating trials at an intermediate scale between lab and commercial size Based on steamsie oxidation test results, practical temperature limits for materials tests will be determined Fireside Corrosion – lab tests on alloys exposed to various deposits representative of the three coals at the range of temperatures expected for the USC plant Steam Loop Design, Construction and Testing – must withstand temp and be corrosion resistant

Alstom, Electric Power Research Institute. __Progress Report: Pleasant Praire Carbon Capture Demonstration Project__. Oct. 8, 2009 Purpose: a pilot field test for an advanced chilled ammonia process for capturing CO2 from the exhaust of a coal power plant in Pleasant Prairie, WI. The “What’s Next” section mentions environmental/ economical estimating for technologies. The three companies involved are Alstom, We Energies, and the Electric Power Research Institute. Background: - 1/3 US greenhouse gas emissions today come from electricity generation - Other environmental control systems at the plant include: o Selective catalytic reduction system: controls nitrous oxide emissions o Wet flue gas desulfurization system: controls SO2 emissions o Pollutants contribute to smog, acid rain, and fine particulate matter

Experimental Procedure: · Withdraws 1% of the exhaust gas just before it reaches the stack · Gas is cooled (condense & remove moisture and residual pollutants) · Enters CO2 absorber where ammonia-based solution separates CO2 from the exhaust gas (also called flue gas) · CO2 solution is heated to release a stream of pure CO2 · In commercial application, gas is compressed for transportation for use in industrial processes or underground · Pilot system captures 2 tons CO2/hour which equivalents to 15,000 tons/year at full capacity · Overtime the flue gas was increased to 100%

Results: · Demonstrated > 90% CO2 removal at design conditions · At design gas flow, consistently measured less than 10 parts per million (ppm) and normally less than 5 ppm ammonia released · Produced high-purity CO2 with low ammonia (< 10 ppm) and water content (< 2,500 ppm); other impurities require further testing/evaluation. · Operated for more than 7,000 hours, since September 2008 it has reliably operated 24/7. (Only two unplanned outages for pilot plant maintenance)

What’s Next: · Underground storage testing, electric removal testing system (will remove 110,000 tons and pipe into storage under facility), commercial scale testing · Ammonia is one of three technologies (advanced amines and oxy firing) · Carbon capture is just one tool for reducing carbon emissions. EPRI has developed analyses, (Prism and MERGE available at www.epri.com, report # 1019563), that show a full portfolio of electricity sector technologies could simultaneously address the challenge of growing load demand while meeting carbon constraints and limiting increases in the cost of power.

· A full portfolio could reduce the economic cost of reducing emissions in the United States by more than $1 trillion by 2050. · Talks about upgrading to new technologies and mixing new technologies

Energy Nexus Group. __Technology Characterization: Steam Turbines.__ Environmental Protection Agency, 2002

Summary · Conventional steam power plants generate most of energy in US · Steam turbines are important for combined heat and power (CHP) applications Application · Not typically competitors of gas turbines and reciprocating engines · using lower cost fuels or avoided disposal costs of waste fuels · facilities operate continuously · fuel at low or negative costs (waste fuels) Disadvantages: · High cost of per kW capacity basis · Low power to heat ratio · Costs of boiler, fuel handling, overall steam system, custom installation · Can only be used in large scale industrial system with high capital return Technology · Rankine cycle · Heat source: converts water to high-pressure steam · Turbine expands pressurized steam to lower pressure · Steam is exhausted to a condenser or steam distribution system · Condensation enters feedwater pump for continuation Types of turbines · Condensing – most common, max power and electrical generation efficiency. Exhausts steam into a condenser under vacuum conditions, cooled by external water supply. · Non-condensing (back-pressure) - exhaust steam at atmospheric pressures. Power generation capabilities much lower than condensing turbines. · Extraction – contains openings for extraction of a portion of steam at an intermediate pressure before condensing. Accommodates the specification of the plant. Design Characteristics · Custom design: Steam turbines are designed to match CHP design pressure and temperature requirements and to maximize electric efficiency while providing the desired thermal output. · Thermal output: capable of operating over a range of steam pressures. Utility steam turbines operate with inlet steam pressures up to 3,500 psig and exhaust vacuum conditions as low as one inch of Hg (absolute). Steam turbines are custom designed to deliver the thermal requirements of the CHP applications through use of backpressure or extraction steam at appropriate pressures and temperatures. · Fuel flexibility: variety of fuel sources including coal, oil, natural gas, wood and waste products. · Reliability and life: Steam turbine life is extremely long. When properly operated and maintained (including proper control of boiler water chemistry), steam turbines are extremely reliable, only requiring overhauls every several years. They require controlled thermal transients to minimize differential expansion of the parts as the massive casing slowly heats up. · Size range: Steam turbines are available in sizes from under 100 kW to over 250 MW. · Emissions: Emissions are dependent upon the fuel used by the boiler or other steam source, boiler furnace combustion section design and operation, and built-in and add-on boiler exhaust cleanup systems. Performance · Electrical efficiency – 37% HHV (large plants) to less than 10% HHV (small plants). · Thermodynamic efficiency – 65 – 90% · Operation – leaks; steam out, air in. Continuous operation due to slow start up · CHP system efficiency – overall efficiency 70-85% depending on boiler type, age, fuel, duty cycle, application, steam conditions · Steam reheat – higher pressures and steam reheat increase power generation efficiency per unit mass flow. Temp limited by condensation and practical limit of materials: 800 – 900 F. · Combustion air preheating – heat recovered from boiler exhaust preheats combustion air, reducing fuel consumption. Capital Cost · 25% boiler · 25% fuel handling, storage and preparation system · 20% stack gas cleanup & pollution control · 15% steam turbine generator · 20% field construction and plant engineering · Significant cost reductions can only be made in fuel handling/storage/preparation · Complete plant costs over $1,000/kW · Steam tubines/plants more expensive on smaller scale, less attractive to market · Boiler stop valve – few materials options = expensive Maintenance · Operational life > 50 years · Lubrication, proper temperatures, clean fluids · Long warm ups and cool downs · $0.004/kWh maintenance cost · Solid wastes from boiler deposit on turbine nozzles degrades turbine efficiency o Manual removal o Cracking off by cooling turbine o Water soluble deposits – water washing with turbine running Fuels · Wood, coal, natural gas, oils, municipal solid wastes, sludge · Fuel handling, storage, preparation add significant cost · Requires high annual capacity or disposal required due to space occupancy problem Availability · 99% bc few shutdowns for maintenance Emissions · Depends on source of steam · NOx, SOx, particulates, CO, CO2