Presentation on theme: "Comparison of Transport and Reaction Phenomena in Waste-to-Energy (WTE) Power Plants Prof. Nickolas J. Themelis, Director, and Olivier L.R. Morin, Research."— Presentation transcript:
Comparison of Transport and Reaction Phenomena in Waste-to-Energy (WTE) Power Plants Prof. Nickolas J. Themelis, Director, and Olivier L.R. Morin, Research Associate Keynote Presentation at WASTEENG 2014 Rrio de Janeiro, August 25-28
Origin of this study: Comparison of geometry and operating parameters of existing MSW and biomass WTE operations FeedstockShredded MSW MSW MSW2 MSW3Wood chipsCoal slurry,Shredded MSW4 TechnologySEMASSMass burn 57% H2O, FB 39% H2O, CFB48.4%H20, CFB Plant locationRochester MABresciaUnion, NJEssex, NYArchangelskKaritaCixi, China Starting year Unit capacity, tons/day Height of combustion chamber, Length of grate, m Width of grate,m Grate area, m Combustion chamber cross sect. area, m Volume of combustion chamber, m^ Flue gas flow, Nm3/ton Process gas volume, Nm3/hour Assumed ave gas temperature, °C950 Velocity of gas in comb. chamber, m/s Average minimum residence time, s Grate combustion capacity, tons/h/m Heat value of fuel, MJ/kg Heat value of fuel, MWh/ton Thermal flux, MW/m2 of grate area Fluid bed power plants burning wood chip slurries (40% water): Heat flux of 4-9 MW/m2; Moving Grate power plants burning MSW (30% water: Heat flux of 1-2 MW/m2
kWh,el/ton MW el +0.1 MW el The EEC hierarchy of waste management
Energy recovery from “wastes”(waste-to energy or WTE) is equivalent to recycling Today, several countries such as Japan, Austria, Switzerland, Germany, the Netherlands, Korea and Singapore use WTE as the main process for treating post-recycling municipal solid wastes (MSW).
Thermal treatment (WTE): 200 mill. tons Sanitary landfill, partial CH4 recovery: 200 mill. tons Landfilled without CH4 recovery: >800 mill. tons Estimated land use for sanitary landfilling: 10 tons MSW per square meter Estimated global disposition of urban post-recycling municipal solid wastes (total: 1.2 billion tons; 2012)
Conservation of land near cities Energy recovery: 0.5 MWh/ton, over LFG recovery Reduction of Greenhouse Gas (GHG) emissions: ton CO2 per ton MSW (vs landfilling) Esthetically more acceptable to communities; in fact only acceptable option in most developing countries. There are only two options for managing post- recycling wastes: Sanitary landfill or thermal treatment (WTE) WTE advantages:
Dissemination of wrong information by some environmental organizations (“God recycles but devil burns”) Some of these organizations were formed at a time (before 1990) when incinerators were major emitters of heavy metals and dioxins. However, their opposition has not changed as the Air Pollution Control systems of WTEs have improved to the point that total toxic emissions of WTEs have decreased by factors of 1000 to For example total toxic dioxin emissions of U.S. are now <5 grams/year. Initial capital investment There are only two options for managing post- recycling wastes: Sanitary landfill or thermal treatment (WTE) WTE disadvantages:
Waste-to-Energy (WTE) Facility IN 100 cubic yards of waste OUT 10 cubic yards of (inert) ash 90% volume reduction Reducing the Volume of Waste & Generating Energy 13,000 KWh generated E = M x C 2 Energy is mass times a constant
The economics of WTE plants – Sources of revenues Both sanitary landfills and WTE plants need a “gate fee” (e.g., $/ton) to support them. This fee ranges from $100/ton MSW, in some highly developed nations, to as low as $20/ton for partially sanitary landfilling in Latin America. The second source or revenue for WTE plants is the sale of WTE electricity; for Latin America it is projected to be about $50/ton MSW.
The economics of WTE plants – Sources or revenues (cont.) Truly sanitary landfills can recover methane gas and use it to produce electricity. Generally, this amounts to about 0.1 MWh/ton MSW, i.e. about $10/ton.
The economics of WTE plants: Revenues According to the numbers presented earlier, future WTE plants in Latin America will enjoy a revenue of $70/ton of MSW, while the revenue of sanitary landfills will be only $30. However, what tips the balance in favor of sanitary landfilling is the high capital cost of WTE plants.
A WTE problem: Capital investment In contrast to landfills, which can be expanded year after year (“cell by cell”), a WTE plant requires an initial, very large investment. Therefore, in a less than five years horizon, a community needs to spend a much smaller sum to start a sanitary landfill than a WTE power plant.
The economics of WTE plants – The cost of repaying the capital investment Modern WTE plants, equipped with Air Pollution Control systems that meet the E.U./U.S. standards cost over $600/ton of annual capacity. In order to pay this amount back over a period of 20 years (usual contract) requires a capital charge of about $60/ton. Therefore, communities who only pay a “gate fee” of $20/ton MSW cannot afford a WTE plant.
CONCLUSION FOR LATIN AMERICA: It is necessary to use a WTE technology that requires a lower capital investment than the Moving Grate technologies offered currently
Most common WTE technology: Combustion on moving grate Over 700 operating plants. I n , there were built over 120 new grate combustion plants (over 25 million tons of new capacity) Emerging WTE technology: Circulating Fluid Bed Developed and used mostly in China: Suitable for high organic, high moisture urban wastes (Zhejiang University, Hangzhou: Chinese Academy of Sciences, Beijing)
Reasons for dominance of Moving Grate WTE Simplicity of operation Technology gradually developed over 100 years and constantly advancing Very high plant availability (>8,000 hours per year Low personnel requirement (<70 for a one- million tons/year plant) and ease of training of personnel of new plants
The Moving Grate technology
Forward Acting Grate (FAG) -Von Roll type - RB 1 FB 1 Outlet of Ash FB n : fixed bar RB n : reciprocating bar 30 Inlet of MSW roller Inlet 30 o Outlet Roller Grate (RG) - Duesseldorf/Babcock Grate - Reverse Acting Grate (RAG) - Martin type - Three types of Moving Grate systems RB 1 FB 1 Outlet 26 o Inlet FB n : fixed bar RB n : reciprocating bar Grate Types FAGRAGRG Push ForwardReverse Convey in proportion to friction (shear stress) Reciprocation Same direction Main differences
MSW Size Distribution and Cumulative Distributions MSW Particle Size DistributionCumulative Distributions Cumulative Density Distribution of Gamma Function F(d): Particle Size Cumulative Density Distribution of Gamma Function F(d 3 ): Particle Volume Source: M. Nakamura, M.J. Castaldi, and N.J. Themelis, "Numerical Analysis of size reduction of municipal solid waste particles on the traveling grate in a waste-to- energy combustion chamber," Proc. 14th annual North American Waste To Energy Conference (NAWTEC14), pp , Tampa, FL (2006)
Smaller MSW particle size increases greatly the rates of heat transfer and combustion T=973 K T=773 K T=1173 K Temp, K Source: Nakamura M., Zhang H., Millrath K., and Themelis N. J., "Modeling of Waste-to-Energy Combustion with Continuous Variation of the Solid Waste Fuel," 2003 ASME ICMEE, Washington, D.C. (2003) From Masato Nakamura PhD Thesis, Columbia University, 2008: Rx time for 95% combustion proportional to (d particle ) 1.62
What is a Fluidized Bed? It is an operation blowing solid particle swarms with gas or liquid, making solid particles turn into fluid-like state. The gravity on the particles is offset by drag imposed on fluid, so particles are at the state of semi-suspended. With the addition of airflow speed, solid particles show different flow state.
Types of MSW Fluid Bed furnaces Vertical flow Spiral-shaped Downward spiral-shaped Upward spiral- shaped Circulating fluidized bed is more suitable and originally developed for low heating value waste.
In contrast to MG, CFB requires shredding of the MSW Shredding, as applied in the RDF WTE plants in the 20 th century, was by means of hammermills; it was complex and very costly in construction and operation
Low-speed, high-torque shredders have been developed since the U.S. RDF plants of the early nineties
Cixi WTE advance: Low-Speed, High- Torque shredder is part of MSW bunker. Shredder is fed as- received MSW by overhead crane and shredded outflow is fed by crane to CFB unit. Shredder energy: <10 kWh/ton MSW
Particles in ZJU CFB are engaged in two flows:r Heavier particles are reacted in bubbling flow; lighter, smaller particles are reacted in circulating flow Schematic diagram of CFBI Bubbling flow fuel outer cycle Different density Different size High moisture Exit point of bottom ash The CFB technology of Zhejiang University for burning materials of:
Comparison of various WTE plants in China (Huang, Chi, and Themelis, 2013) Plant Ningbo Fenglin Shanghai Pudong Shanghai Hongqiao Cixi, Zhejiang TechnologyMultistage MGReverse MG CFB Unit capacity, t/d Grate/Plate area, m Grate/Plate feedstock load, kg/m2/h Thermal energy flux, MW/m
Waste to energy (WTE) plants in China (ref. Zheng, 2014) 77 plants use Moving Grate MG) technology 59 plants use Fluidized Bed Combustion technology (Zhejiang, U,; Chinese Academy of Sciences: Tsing Hua U.) Total operating WTE/incineration plants: 136 The Cixi 899 ton/day unit is based on Zhejiang U. technology.
Comparison of some operating parameters of MG and CFB Parameter Typical results for MG Reactors 800 ton/day CFB unit in Cixi plant Reactor type MGCFB Fly ash amount (as a percentage of waste input)3%12% Bottom ash amount (as a percentage of waste input) 22%16% Average particle residence time in bubbling bed1 hour54 minutes Average gas residence time in combustion chamber8 seconds3.8 seconds Excess air amount %40%
Very rough capital investment costs (ref. various sources including Columbia thesis of Ling Qiu (2013) Technology, location Capital investment, US$/ton annual capacity Moving grate expansion, U.S. 600 Moving grate, greenfield, Canada 700 CFB, China CFB, outside China???
If you are interested in learning more about CFB and WTE: Try to attend the ICIPEC International Conference in Hangzhou, China, October (www.icipec2014.org) Try to attend the WTERT 2014 Meeting at Columbia University in the City of New York, October 9-10 (www.wtert.org).