Waste to Energy. Anders Damgaard. Thanks to Jiri Hyks and Thomas H Christensen DTU for some slides

Transcription

1 Denmark (Thomas Astrup) Denmark (COWI) Waste to Energy Anders Damgaard Austria (CEWEP) Thanks to Jiri Hyks and Thomas H Christensen DTU for some slides Copyright Anders Damgaard & Morton A. Barlaz, NC State University 1

2 The Destructor Nottingham 1874 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 2

3 Waste Combustion Outline Combustion systems Air pollution control Combustion ash Copyright Anders Damgaard & Morton A. Barlaz, NC State University 3

4 US Thermal Treatment (WTE) ~7% of MSW in US is treated by waste-to-energy No new facilities coming on-line in U.S. Globally about 200 between 1995 and 2008 Facilities are concentrated in the northeast and Florida, few west of Colorado (115 operating plants in 2010) Capacity tons/day Not economical Copyright Anders Damgaard & Morton A. Barlaz, NC State University 4

5 WtE facilities in Europe: > 400 Total amount of waste treated: about 53 million tonnes/year Copyright Anders Damgaard & Morton A. Barlaz, NC State University 5

6 WTE and Recycling Copyright Anders Damgaard & Morton A. Barlaz, NC State University 6

7 WTE Process Thermal oxidation of organic matter (C a H b O c N d S e Cl f ) + O 2 + N 2 ---> CO 2 + H 2 O + NO x + SO x + HCl + N 2 + Heat - Inorganics remain intact Copyright Anders Damgaard & Morton A. Barlaz, NC State University 7

8 Why burn? Advantages Reduction of volume (85-95%) Reduction of mass (70-85% the mass leaves through the stack) Reduction of hygienic risks Energy recovery Can be located close to the waste source Disadvantages Air pollution? Costly Destroys resources that otherwise could be recovered? Copyright Anders Damgaard & Morton A. Barlaz, NC State University 8

9 Incineration: Processes & Technology Copyright Anders Damgaard & Morton A. Barlaz, NC State University 9

10 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 10

11 Waste storage and feed Must maintain enough refuse to run incinerator 24 hours/day Typically 7 day storage Refuse unloaded into a pit or onto a tipping floor Copyright Anders Damgaard & Morton A. Barlaz, NC State University 11

12 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 12

13 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 13

14 Control Room Copyright Anders Damgaard & Morton A. Barlaz, NC State University 14

15 Combustion processes Wet waste Drying Burning Pyrolysis Gasification Burnout, cooling Incineration Pyrolysis, gasification and thermal oxidation occur in one chamber Waste temperature Copyright Anders Damgaard & Morton A. Barlaz, NC State University 15

16 Combustion technologies Mass burning of heterogeneous waste: waste incinerators (moving grate systems) rotary kilns (e.g. cement production) Burning of homogenized waste: fluidized bed incinerators co-combustion in power plants /cement kilns (better energy efficiency) Copyright Anders Damgaard & Morton A. Barlaz, NC State University 16

17 Waste pretreatment Mass-burn incinerators: Removal of bulky items to avoid blocking of feeding systems Occasional shredding of waste (rare) Mixing of waste with low and high heating value Combustion of homogenized waste (fluidized bed, co-combustion): Source separation Shredding and maybe screening Removal of metal objects Waste incinerators are relatively robust! Copyright Anders Damgaard & Morton A. Barlaz, NC State University 17

18 Moving Grate (Reverse Acting) Inlet of Solid Waste RB n : reciprocating bar (step) FB n : fixed bar (step) FB 1 RB 1 L=7 m 26 o Outlet of Ash 18 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 18

19 Rotary kilns Copyright Anders Damgaard & Morton A. Barlaz, NC State University 19

20 Heating values Definition: the amount of energy released when a fuel is burned completely. Two heating values are defined - depending on the state of the water in the burned waste: Higher heating value (HHV) = Energy content in waste with water in its liquid phase after combustion Lower heating value (LHV) = Energy content - energy used for evaporation of water The water consist of the moisture content of the waste and the water generated during combustion H high = H low + (W% + H% 8.937) kj/kg W = wet weight moisture content H = % hydrogen The lower heating value is generally used! Copyright Anders Damgaard & Morton A. Barlaz, NC State University 20

21 Determining heating values Calculated from ash content, volatile solids, moisture content: LHV = H awf *0.01*VS *W [kj/kg] VS is on a wet weight basis (%) H awf = ash and water free; ~20,000 kj/kg Calculated form elemental composition using Schwanecke's (empirical) formula: LHV = 348 C% H% S% + 63 N% O% H 2 O% [kj/kg] Calculated from material fractions Measured on the incinerator using mass and energy balances Copyright Anders Damgaard & Morton A. Barlaz, NC State University 21

22 Waste fractions Fraction basis Heating values Material fractions % of Moisture Solids Ash Volatile solids H awf LHV In wet waste Waste W % TS% A% VS% kj/kg kj/kg Food and organic waste Plastics Textiles Paper & cardboard Leather and rubber Wood Metals Glass Inerts Fines Weighted average Crude oil, oils, diesel, jet fuels (40-45 MJ/kg), Natural gas (40 MJ/Nm 3 ), Coal (25 MJ/kg), Copyright Anders Damgaard & Morton A. Barlaz, NC State University 22 Wood (5-17 MJ/kg)

23 Effect of constituents and moisture on heat value of MSW (Themelis, Kim, Brady 2002) Copyright Anders Damgaard & Morton A. Barlaz, NC State University 23

24 Tanners diagram Supports combustion without addition of fuels Copyright Anders Damgaard & Morton A. Barlaz, NC State University 24

25 Grate system Good mixing, leveling of waste Good burnout Distribution of primary air (not too much air...) Grate is divided into a number of individually adjustable sections for better control of incineration Grate length is determined by burnout criteria Grate width determines the capacity Copyright Anders Damgaard & Morton A. Barlaz, NC State University 25

26 Grate system Flexible air supply system Future: advanced monitoring, regulation control algorithms, feedback loops, etc. Important for emissions, residues, maintenance Copyright Anders Damgaard & Morton A. Barlaz, NC State University 26

27 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 27

28 Furnace/secondary combustion Sufficient retention time (2 sec at 850 C) Completion of gas phase reactions Turbulence/vortex Furnace temperature: C Wall materials (ceramics, inconell/alloys, water cooling) Corrosion and fouling risks CFD modeling to ensure retention time and temperature distribution Copyright Anders Damgaard & Morton A. Barlaz, NC State University 28

29 Furnace-air Flue gas recirculation (higher efficiency, less flue gas, emissions reduction) Primary / secondary air intake (low pressure in waste bunker) Auxiliary burners (ensure 850 C at all conditions) Copyright Anders Damgaard & Morton A. Barlaz, NC State University 29

30 Energy recovery/boiler Transfer of energy in the waste to water Three types of boilers: hot-water low pressure steam high pressure steam Energy products: Hot water for district heating ( C) Process steam for industries ( C, 20 bar) Electricity (400 C, 40 bar) Corrosion and fouling limits energy recovery! Copyright Anders (increasing Damgaard & Morton with temperature/pressure) A. Barlaz, NC State University 30

31 Energy technologies Overall efficiencies above 100%? Modern plants: Electricity: 24% Heat: 63% varying Electricity only: up to 35% recovery, surplus heat is cooled Combined heat and power (CHP): 25% electricity % heat = up to 90% Flue gas condensation: extra 10% (low district heating return temperature required) Copyright Anders Damgaard & Morton A. Barlaz, NC State University 31

32 Design Parameters Copyright Anders Damgaard & Morton A. Barlaz, NC State University 32

33 Combustion Chambers Field Units Field constructed units Waterwall - wall lined with tubes full of water or steam Generally requires >500 tons/day for economy Refractory lined for insulation for corrosion and erosion protection Hot off-gas passes through a boiler Copyright Anders Damgaard & Morton A. Barlaz, NC State University 33

34 Combustion Chambers - Modular Modular units (shipped complete) ~50 ton/day capacity per unit is typical May be ideal for areas with seasonal populations Typically two combustion chambers Primary chamber operated below stoichiometric O 2 (1200 F) Secondary chamber with excess air (1800 F) All combustion chamber size based on BTU/ft 3 -hr (KJ/m 3 -hr) Copyright Anders Damgaard & Morton A. Barlaz, NC State University 34

35 Design Strategy Facilities are designed with at least two combustors with a common tipping floor Facilities need to be operated at or near (85%) of design capacity to maintain temperature Plant operates 90-95% of the time 5% down for scheduled maintenance and 5% for unplanned events As turn down, supplemental fuel requirements increase (expensive) Major control levers to maintain temperature: changing waste load changing excess air Copyright Anders Damgaard & Morton A. Barlaz, NC State University 35

36 Energy Recovery Source of green energy - thermal recycling Fossil (~34%), biogenic (~66%) Direct use of steam for heating Generation of electricity - typical in U.S. National average $0.046/kw-hr (2-8) Overall efficiency of electricity recovery: heat rate of BTU/kwh-hr After meeting house load 4800 BTU/lb 550 kwh/ton U.S. average Europe: CHP (combined heat and power) is more common ~1000 kwh/ton electricity plus steam Copyright Anders Damgaard & Morton A. Barlaz, NC State University 36

37 Residue handling Ash is typically water quenched to control dust Fe recovered (to a degree Al, Cu) 98% of ash in U.S. is buried, Use as a road base and in concrete blocks under development Ash must be tested to determine whether it is a hazardous waste (TCLP and alternatives) Fly ash - 5% - 15% of total ash will contain - Pb, Cd, Hg, Zn, As (greater potential to be hazardous) Bottom ash % of total ash will contain - Al, Cr, Fe, Ni, Sn In U.S., most facilities combine bottom ash and fly ash and it passes TCLP Copyright Anders Damgaard & Morton A. Barlaz, NC State University 37

38 Cost Tipping fee ($44-$68 in Biocycle) High initial cost $250,000 per ton per day of capacity Operating and Maintenance - $57/ton Long-term contracts to supply waste are typical Owner will capitalize the facility Copyright Anders Damgaard & Morton A. Barlaz, NC State University 38

39 AUXILIARY BURNERS ( for start-up and shut-down ) 39 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 39

40 40 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 40

41 Brescia WTE site after construction 41 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 41

42 Build WTEs that are Beautiful esthetically; beautiful functionally 42 Copyright Anders Damgaard & Morton A. Barlaz, NC State University 42

43 Hiroshima, Japan 600 tons tons/day 43 Yoshio Taniguchi, Architect Copyright Anders Damgaard & Morton A. Barlaz, NC State University 43