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Conversion Technologies Is It a Zero Waste Solution? 1.

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1 Conversion Technologies Is It a Zero Waste Solution? 1

2 Separated/Recyclable Materials By-products & Residuals Conversion Technology 2 Electricity, Fertilizer or Chemicals 3 2 MSW Pre- Processing 1

3  Can treat both organic and carbon-based (plastic) materials using higher temperatures (>750°F).  Typically more efficient to generate electricity and has a lower volume of residual byproducts than biological technologies.  In other countries, these residuals are reused that makes the system virtually zero waste. 3

4  Gasification  Pyrolysis  Pyrolysis/Gasification  Plasma Gasification 4

5  Thermal conversion of organic materials at 1,400~2,500°F and with a limited supply of oxygen, producing a syngas  The syngas (primarily H 2 and CO) can be used as a fuel to produce electricity  Inorganic materials are converted to bottom ash or slag 5

6 Gasification Process Emission Control System Gasification Biomass Pre- processing Ash/Slag 1,400- 2,300°F Air/O 2 Clean Syngas Power Generation Electricity Water Quenching Emissions Recyclables 6 Syngas = CO + H 2

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8  Thermal degradation of organic materials using an indirect, external source of heat, at 750-1,650°F, in the absence or almost complete absence of free oxygen, producing syngas or liquid fuel  The syngas (primarily H 2 and CO) or liquid fuel can be used to produce electricity  Byproducts are carbon char, silica, metals, and inorganic materials 8

9 Condenser MSW Pyrolysis Process Refining Carbon Char, Silica, Metals Electricity Syngas CO + H 2 or Liquid MSW Pre- processing Pyrolytic Converter Power Generation Air Emission Control Recyclables Thermal Oxidizer 750~1,650°F 9

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11  Thermal degradation of organic materials using pyrolysis to produce syngas and carbon char as solid byproduct  The byproduct (carbon char) is going through gasification process to produce additional syngas 11

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13 Uses AC or DC electricity to produce an ionizing gas (plasma) at 6,000-10,000 o F and gasify the MSW Utashinai City, Japan Plasma Gasification 100,000 tons/year 13 Ref. reading: Ref. reading: How Plasma Converters Work

14  Garbage is fed into an auger which shreds it into smaller pieces  These are then fed into a plasma chamber - a sealed, stainless steel vessel filled with either nitrogen or ordinary air.  A 650-volt electrical current is passed between two electrodes; this rips electrons from the air and creates plasma.  The byproducts are a glass-like substance used as raw materials for high-strength asphalt or household tiles and "syngas". 14

15  Syngas (which leaves the converter at a temperature of around 2,200˚F) is fed into a cooling system which generates steam.  This steam is used to drive turbines which produce electricity - part of which is used to power the converter, while the rest can be used for the plant's heating or electrical needs, or sold back to the utility grid.  It is self-sustaining after the initial electrical charge is used, is environmentally friendly, and produces materials that have commercial applications or use and thus can generate profit. 15 Should we believe?

16  Can decompose organic materials by biodegradation using low temperatures (< 400° F).  Typically has a higher volume of residual byproduct than thermal technologies. 16

17  Microbes convert MSW into useful products: Compost: a useful soil amendment Biogas: a clean, renewable fuel  Requires careful MSW prescreening to ensure a clean compost 17

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19  Step 1: cellulosic wastes like waste paper can be hydrolyzed to sugar  Step 2: this sugar can then be fermented into dilute ethanol  Step 3: finally, the dilute ethanol can be distilled and processed into fuel ethanol 19

20  Syngas-Ethanol: gasify waste, ferment synthesis gas to ethanol, distill to fuel grade, sell electricity and ethanol; pilot stage  Biodiesel: process fatty waste into a diesel- like fuel 20

21 Gasification Pyrolysis Plasma Gasification Anaerobic Digestion Ethanol Fermentation Syngas-to-Ethanol Degree of Commercialization 21

22  Air Emissions:  Thermal Conversion: Latest emission control systems  Biological Conversion: Little impact – low temperature process (< 400˚F)  Water Discharges: Minimal issue  Solid Waste: Mostly recyclable or compost 22

23  Thermal: 7~10 MW  Biological: 1.2~3.0 MW Efficiency:  Thermal: 650~900 kWh/ton  Biological: 100~250 kWh/ton 23

24  Cost of siting and permitting  Capital cost  O&M cost  Tipping fee  Incentives for conversion facilities  Sale of recyclables  Sale of electricity  Sale of by-products 24

25  Reduced carbon (greenhouse gas) emissions  Increased recycling  Lower air emissions  Offset of fossil fuels  Beneficial use of residuals  Renewable energy 25 Environmental Sustainability

26 Challenges to Implementation  Lack of technology understanding  Air emissions  Variation in designs  Lack of regulatory clarity  Funding/financing hurdles  No operating CT facilities in the U.S. that process MSW 26

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28  Reduces foreign imports from unstable producing countries  Enhances US energy security and independence  Slows depletion of scarce fossil fuel resources  Reduces cost of transportation fuel in era of high oil prices 28

29  Lower greenhouse gas emissions, primarily CO 2  Lower air emissions from gasoline when ethanol is blended as an oxygenate  Positive energy (carbon) balance: Fewer energy units used than energy units produced 29

30  Feedstock/energy material is locally resourced on a sustainable basis  Current ethanol production from: Corn in the U.S. Sugar in Brazil  Next generation ethanol: Agricultural wastes & energy crops Industrial & municipal wastes 30

31  US Gasoline Market 140B gal  US Renewable Fuels 5B gal (99% ethanol, 1% biodiesel)  US Ethanol – Corn 5B gal  US EPA’05 RFS Target 7.5B gal  Pres. Bush’s 2017 Target 35B gal  Maximum potential US Corn Ethanol Production 15B gal  Conclusion: New feedstocks are necessary to meet the U.S. goal of displacing oil imports 31 1 Renewable Fuel Standard

32  Limit on viable corn acreage & supply  Commodity-based corn prices rising rapidly due to demand-push from ethanol (same impact as sugar)  Geographically undesirable corn belt vs. West Coast/East Coast markets for transportation fuel 32

33  Major driver: Limit on corn supply / price  Paradigm shift to cellulosic & waste feedstocks  Emerging technologies (capital cost/gallon still higher than corn ethanol facilities): Hydrolysis – acid/enzyme treatment to separate sugars in cellulose, followed by conventional fermentation & distillation Thermal Conversion – gasification of cellulose & wastes, followed by Fischer Tropsch catalysis of carbon monoxide/hydrogen syngasFischer Tropsch 33

34  Examples: Agricultural wastes: corn stover, sugar cane bagasse, wheat straw, rice straw bagasse Urban/Industrial wastes: wood, pulp, paper, MSW fluff, RDF, sewage sludge, plastics, tires, carpet, waste coal Energy crops: switch grass, miscanthusmiscanthus  Common Denominator: Lower-cost feedstock; higher production per gallon capital cost 34 Switch grass

35  Use waste or cellulosic feedstock Solves waste disposal issues Reduces cost/impact of disposal Extends landfill capacity Creates local economic development Reduces Greenhouse Gases by 85% Provides a very positive energy balance (>3 : 1) due to waste utilization Lowers feedstock cost by 80% Urban/industrial wastes are in the right place 35

36  Technology : Anaerobic thermal conversion with syngas catalysis  Technology Feedstock : any carbonaceous wastes, organic or inorganic, including agricultural waste, MRF residuals, urban wood waste, tires, railroad ties, biosolids, coal, petroleum coke, etc.  Products : 80% ethanol, 20% methanol 36

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38  Thermal Processing: conversion of solid wastes into gaseous, liquid, and solid conversion products, with the concurrent or subsequent release of heat energy  Combustion: a chemical reaction involving the rapid combination of oxygen with the combustible components in a fuel  Gasification: partial combustion of solid waste under stoichiometric conditions to generate a combustible gas containing carbon monoxide, hydrogen, and gaseous hydrocarbons  Pyrolysis: thermal processing of waste in the complete absence of oxygen  Conditions necessary for combustion Time, temperature, turbulence, and oxygen 38

39 Thermal Processing Systems  Major elements in fuels: C, H, O, S, and N Carbon: C + O 2  CO 2 Hydrogen: H + O 2  H 2 O Sulfur: S + O 2  SO 2 Combustion (stoichiomatric or excess air) Mass-fired RDF-fired Fluidized bed Gasification (substoichiomatric air) Vertical fixed bed Horizontal fixed bed Fluidized bed Pyrolosys (no air) Fluidized bed 39

40  Distillation zone: not sufficient oxygen for rapid and complete oxidation; volatile materials present driven off as gases; many organic compounds to thermally crack and form gaseous products; complete exposure of refuse to high temperature; design grates to turn the material over  Incandescent zone: only fixed carbon and ash remain on the grates; at 1,300°F, fixed carbon is ignited and burns (burnout); longer retention time required; heat balance important  Flame zone: very high heat release rates and high temperature; turbulence; mixed with oxygen added with the secondary air supply; complete in 1 or 2 sec.; critical phase in refuse combustion 40

41  Approximate Btu values Btu/lb = 145C (H 2 - 1/8O 2 ) + 40S + 10N C, H 2, O 2, S, and N: percent by weight Ex. Total energy content for the chemical composition of the waste including S and water: C 760 H 1980 O N 12.7 S Solution: Component# of atom/molAtomic wt.Wt. Distribution% Carbon Hydrogen Oxygen , Nitrogen Sulfur Total25, Btu/lb = 145   ( /8) + 40   0.7 = 5,773 41

42 Ex. Determine the heat available in the exhaust gases from the combustion of 250,000 lb/day of solid waste Component% of totallb/day Combustible ,500 60,000 Noncombustible Water ,500 Element% Carbon27.4 Hydrogen3.6 Oxygen23.0 Nitrogen0.5 Sulfer0.1 Water21.4 Inerts24.0 Assumptions As-fired heating value of SW: 5,065 Btu/lb Grate residue: 5% unburned carbon Entering air: 80ºF; Grate residue: 800 ºF Specific heat of residue: 0.25 Btu/lb ºF Water latent heat: 1,040 Btu/lb; C heating value: 14,000 Btu/lb Radiation loss: Btu/Btu of gross heat input All oxygen in waste is bound as water Net H 2 available: % H 2 – 1/8∙%O 2 Moisture in combustion air: 1% 42

43 Solution Carbon = 0.274×250,000 = 68,500 lb/day Inerts = 0.24×250,000 = 60,000 lb/day Total residual = 60,000  0.95 = 63,158 lb/day Carbon in residue = 63,158–60,000 = 3,158 lb/day Net available hydrogen, % = (3.6%–23.0%/8)=0.725% = 1,812 lb/day Bound water = oxygen + hydrogen in bound water = 23%+( )% = % Air required Element Air requirement, lb/day Carbon = (68,500-3,158) × ,740 Hydrogen = 1,812× ,623 Sulfur = 0.001×250,000× ,078 Total dry theoretical air816,441 Total dry air including 100% excess 1,632,882 Moisture = 1,632,882× ,329 Total air 1,649, ,441 lb air/250,000 lb SW = 3.27 lb air/lb SW 43 See next slide

44  Carbon C+O 2  CO 2 (16 x 2)/12/ * = lb air/lb C  Hydrogen H 2 +O  H 2 O 16/(1x2)/ = lb air/lb H  Sulfur S+O 2  SO 2 16x2/32.1/ = 4.31 lb air/lb H * Assume dry air contains 23.15% oxygen by weight. 44

45 Amount of water produced from combustion of available hydrogen Item Value, 10 6 Btu/day Gross heat input 2.5  10 5 lb/day  5,065 Btu/lb Heat loss in unburned carbon 3,158 lb/day  14,000 Btu/lb-44.2 Radiation loss Btu/Btu   10 6 Btu/day -6.3 Inherent moisture 53,500 lb/day  Btu/day Moisture in bound water 64,688 lb/day  Btu/day Moisture from the combustion of available hydrogen 16,308 lb/day  Btu/day Sensible heat in residue 63,158 lb/day×0.25 Btu/lb ºF × (800-80)ºF Total losses Net heat available in flue gases (1, ) ×10 6 Btu/day 1,064.5 Combustion efficiency (1,0645.5×10 6 Btu/day)  (1,266.3 ×10 6 Btu/day) ×100% 84.1% Total efficiency = 84.1% ×85%(boiler efficiency) = 71.5% 45

46  Mass-fired: minimal processing is given to SW before it is placed in the charging hopper of the system; Grate system is one of the most important – move, mix, and injection of combustion air  RDF-fired: typically burned on a traveling-grate stoker; remove metal, glass, and other non- combustible materials; RDF produced in shredded or fluff form or as densified pellets or cubes  Fluidized bed: consist of a vertical steel cylinder, usually refractory-lined, with a sand bed, a supporting grid plate, and air injection nozzles known as tuyeres; versatile; operated on MSW, sludge, coal, and numerous chemical wastes.tuyeres 46

47  Gas stream: H, CH 4, CO, CO 2, and various other gases  Liquid fraction: a tar or oil stream containing acetic acid, acetone, methanol, and complex oxygenated hydrocarbons; use as synthetic fuel oil  Char: pure carbon plus any inert material 3C 6 H 10 O 5 8H 2 O+C 6 H 8 O+2CO+2CO 2 +CH 4 +H 2 +7C Operational problems 1.Failure of the front-end system to meet purity specifications for aluminum and glass 2.Failure of the system to produce a saleable pyrolysis oil 47

48 Gasifier types  Vertical fixed bed: simple and low capital cost; sensitive to type of fuel; densified RDF preferred  Horizontal fixed bed: most commercially available type; starved air combustor (incinerator), modular combustion unit (MCU); primary chamber (substoichiometric, low Btu gas produced, lower velocity and turbulence) and secondary chamber (1200~1600°F, complete combustion)  Fluidized bed: fluidized bed combustion system in substoichiometric mode;  Need further refinement and development 48

49  NO x : NO and NO 2 ; precursors to the formation of O 3 and peroxyacetal nitrate (PAN), photochemical oxidants know as smog; thermal No x by rxn between N and O in the air; fuel No x by rxn between O and organic N.  SO 2 ; formed by combusting sulfur containing fuels; an eye, nose, and throat irritant, related to acid rain and snow  CO: formed during carbonaceous material combustion under insufficient oxygen  Particulate matter (PM): Formed during incomplete combustion of fuel and physical entrainment of non-combustibles Reduced visibility and health effect Particles < 10 μm - critical to lungs  20~40% < 10 μm  7~10% < 2 μm 49

50  Metals: Cd, Cr, Hg and Pb; emitted as particulate matter or vaporized into gaseous forms-Hg vaporizes at > 675°F  Acid gases: formed by combustion wastes containing fluorine and chlorine → HF and HCl; formed by combusting sulfur-and nitrogen-containing wastes; SO 2 → SO 3 → H 2 SO 4 ; NO 2 → HNO 3 in the atmosphere  Dioxins and furans: most complex and controversial issues; dioxin-polychlorinated dibenzodioxins (PCDD). 75 possible isomers; furan-polychlorinated dibenzofuran (PCDF), 135 possible isomers; some isomers-most toxic substances in existence,e.g.,LD 50 of 2,3,7,8-TCDD for guinea pigs ≤ 1 μg/kg of body weight; present in MSW, formed during combustion with chlorinate aromatic precursors, formed during combustion from simpler hydrocarbon and chlorine compounds 50

51  Electrostatic precipitator (ESP): first control device used on MSW combustors for removal of fine (< 10 μm) (99.8% removal) and very fine (< 2 μm) (93% removal) particles; a strong electric field produced by a high negative voltage, 20,000~ 100,000 volts applied to the discharge electrodes-electrostatic attraction and particles removed by mechanical vibration of the electrodes (plates); may not meet requirements of some states such as California  Fabric filter (baghouse): technology of choice on most recently constructed MSE combustion systems in the U.S.; open space - 50~70 μm; filter area, material, and method of cleaning; felted glass, woven glass, and Teflon ® ; < 0.01 grains/dscf  Electrostatic gravel bed filter; hybrid device; < grains/dscf grains/dscf 51 Air Calculations and Conversions Guide, Air & Waste Management Association, 1994

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53 Reverse-air-type fabric filter: used mainly for large industrial sources. Pulse jet fabric filter 53

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56  Source separation of MSW to remove organic nitrogen sources, such as food and yard wastes  Thermal NO X control: flue gas recirculation and low excess-air operation and staging of combustion  Selective catalytic reduction: employs ammonia injection into the flue gas, followed by gas passage over a catalyst bed; at °F NO+NH 3 +1/4O 2 N H 2 O Cu,Ni,Mo,Co and V used as catalysts in pellets or grids; due to contamination by particulates and poisoning by lead, not yet applied to MSW combustion  Selective noncatalytic reduction: Thermal DeNO x ® ; NO+NH 3 +O 2 +H 2 O+H 2 N 2 +H 2 O at 1300~2200°F NH 3 +O 2 +H 2 ONO+H 2 O at >2200°F 56

57  HCl & HF: emitted as fine aerosols  NO 2 & SO 2 : emitted as gases, combined with water droplets in the atmosphere to form HNO 3 and H 2 SO 4 mists reduced visibility, corrosion of metals, and acid rain or fog  Source separation: separate waste components containing large amounts of chlorine and sulfur, such as plastics  Wet scrubbers: wet scrubbing with a lime solution in a venturi scrubber; cool the flue gases by about 90°F prior to the scrubber (to enhance the efficiency) and reheat prior to discharge in the stack (to enhance the buoyancy of the plume)a venturi scrubber  Dry scrubbers: spay drying-pump sodium carbonate and lime solutions, removed in a downstream baghouse along with the fly ash still in the flue gas; removal efficiency: ~98% 57

58 Venturi scrubber 58

59 Spray dryer absorbers Introduce flue gases into an absorbing tower (dryer) where the gases are contacted with a finely atomized alkaline slurry. Acid gases are absorbed by the slurry mixture and react to form solid salts which are removed by the particulate control device. Dry sorbent injection Add an alkaline material (usually hydrated lime or soda ash) into the gas stream to react with the acid gases 59

60  Directly related to combustion efficiency  Function of both design and operation  Caused by incomplete combustion of waste, due to fuel-rich burning (overloading of the furnace) and insufficient temperature caused by high-moisture-content waste Control  Use of excess air  Must be balanced to avoid burning too hot and generating excess NO X emissions via continuous emission monitoring (CEM) of flue gas constituents (CO, CO 2, NO X, HC and O 2 )  CO and O 2 readings are used to balance excess air.  Temp. readings in critical portions of the furnace also used to assist in control  In mass-fired systems, the skill of the crane operator in loading the combustion chamber is critical to optimum combustion –as constant a flow of waste into the combustion unit as possible  RDF systems more automated and less problems 60

61 Dioxins and Furans  Source separation: removal of chlorine-containing wastes, primarily plastics  Combustion controls: principal control strategy; California Air Resources Board –min. temp 1800±190°F with a min residence time of 1 sec: Conditions minimizing generation of CO also minimize generation of dioxins and furans; CO as a surrogate to monitor the emission of dioxins and furans  Particulate control; also good for metals; metallic oxides and chlorides tend to condense on submicron fly ash particles at temp. < 500°F; properly designed fabric filters; Hg not removed because of low volatilization temp.  Can be captured in the filter cake in fabric filters and in wet and dry scrubbers used for SO 2 control if temp. is maintained <284°F, allowing condensation of dioxins and furans. 61

62  Bottom ash: unburned and nonburnable portion of MSW; landfilled without processing ; used for road base construction  Fly ash: particulates removed from flue gases; handled carefully to avoid fugitive dust emissions; moistened and mixed with bottom ash prior to disposal  Scrubber product: sludge produced by a wet scrubber used for SO 2 and acid gas cleanup; calcium and sodium sulfate salts and trace organics and heavy metals; dewatering for volume reduction and subsequent disposal  Heavy metals and trace organics: in the Toxicity Characteristic Leaching Procedure (TCLP test), ash samples are ground to  3/8 in., mixed with a pH 5 acetate buffer, and mixed for 18 hours. The supernatant is then filtered and tested for heavy metals.Toxicity Characteristic Leaching ProcedureTCLP test 62

63 Source: (1) cooling and washwater from wet ash removal systems; (2) wet scrubber effluent from SO 2 and acid gas cleaning equipment; (3) wastewater from sealing, flushing, and housekeeping activities; (4) wastewater from boiler feedwater production; and (5) cooling tower blowdown  Wet scrubber effluent: neutralization, precipitation, and settling  Wastewater from sealing, flushing, and housekeeping activities: small amount; contaminated with oils and greases; settling  Wastewater from boiler feedwater production: water used to make steam in a steam turbine system: requirement for TDS, pH, and alkalinity-water softening, ion exchange, precipitation, and reverse osmosis units; discharges from these systems regulated  Cooling tower blowdown: related to power production; chromium salts used to retard algae growth inside the tower; periodically, the cooling water must be replaced, producing an effluent called discharge to municipal sewers; 10~50 MW power systems generate less blowdown than 500~1000 MW systems. 63

64  Stream turbine systems: most common energy recovery system; scale-down version of a coal- or gas-fired electrical utility plant Stream turbine systems  Gas Turbine generator systems: use gaseous or liquid fuels; supplied by landfill gas, anaerobic digestion of MSW, or by pyrolysis or gasification; efficient and compact; widely used in landfill gas systems Gas Turbine generator systems  Internal combustion engine systems: alternative to gas turbines for gaseous or liquid fuels from the thermal or biological processing of solid wastes; modified versions of industrial engines designed for natural gas of propane; modified carburetors and intake manifolds used to handle the lower quality gas; internal combustion engines are the most common used in landfill gas recovery systems Internal combustion engine systems  Cogeneration systems: generation of both thermal and electrical power; limited by the requirement that a use for the heat recovered must be located at the site with the power generation system. Cogeneration systems 64

65 Ex. Estimate the amount of energy produced from a solid waste energy conversion system with a capacity of 50 ton/day. The system consists of a fluidized bed gasifier-internal combustion engine-electric generator combination. Also estimate the heat rate and overall process efficiency. Assume that the energy value of the solid waste is 5,065 Btu/lb. Note: red – widely accepted engineering values Solution Gross energy available in MSW 50 ton/day  2,000 lb/ton  5,065 Btu/lb  24 hr/day = 2.11  10 7 Btu/hr Chemical energy available from gasifier, cold cleaned gas 2.11  10 7 Btu/hr  0.7 = 1.48  10 7 Btu/hr Mechanical energy available from engine 1.48  10 7 Btu/hr  0.25 = 3.7  10 6 Btu/hr Net electrical energy generation 3.7  10 6 Btu/hr  0.90  3,413 Btu/kWh = 976 kW 65 Low efficiency


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