A new technology for high efficient Waste-to-Energy plants

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1 6 th International Conference on Combustion, Incineration/Pyrolysis and Emission Control (i-cipec 2010), Kuala Lumpur, Malaysia, July 26-29, 2010 A new technology for high efficient Waste-to-Energy plants Hans Hunsinger Karlsruhe Institute of Technology (KIT), Campus Nord Institute for Technical Chemistry Thermal Waste Treatment Division Postfach 3640, D Karlsruhe, Germany hans.hunsinger@kit.edu KIT University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

2 Strategy of waste management in EU27 and Germany Avoidance of land filling of untreated waste Increase of recycling and material recovery Environmentally sound and high efficient energetic utilization of the residual waste Municipal waste management in EU27 Municipal waste management in Germany 100% 100% 80% 60% 40% 20% composting recycling incineration landfill 80% 60% 40% 20% composting recycling incineration landfill 0% 0% Data source: Germany: Landfill ban: 1 st of June 2005 Landfill limit: TOC <1% no landfill of untreated waste 2 H. Hunsinger - ICIPEC 2010

3 Situation of MSW incineration in Germany Today more than 70 MSWI plants Total incineration capacity of 20.3*10 6 tons per year Avg. LHV of municipal waste 10 MJ/kg Energy content of annually burnt municipal waste 56.4 TWh 50-60% of the total MSW-carbon is biogenic origin significant renewable energy source 30 TWh Efficiency of energetic utilization at German MSWI plants heat utilization 27% (average, all plants) net efficiency of power generation η el. 10% (average, all plants) net efficiency of power generation η el. 18% (modern plants) 3 H. Hunsinger - ICIPEC 2010

4 Examples of power generation efficiencies of advanced solid fuel combustion processes 50 MSW/RDF Biomass Coal Nordjylland/DK 290bar/580 C 76bar/580 C 19bar/580 C electric efficiency (%) RDF (grate) Rüdersdorf/D 90bar/420 C 23bar/420 C MSW (grate) AVI Amsterdam/Nl 130bar/440 C 14bar/320 C modern grate MSWI 40bar/400 C CFB grate CFB no intermediate superheating 1x intermediate superheating 2x intermediate superheating MSW, sewage sludge, biomass (grate) Brescia/IT 61bar/450 C steam temperature ( C) 4 H. Hunsinger - ICIPEC 2010

5 Boiler corrosion in MSWI limits max. steam temperature Chloride rich ash deposits on the boiler surface cause chlorine induced corrosion strongly increasing with temperature corrosion rate acid dew point corrosion corrosion below ash deposits (chlorides) low corrosion corrosion of gas phase Seier, J., Albert, F.: VDI-Berichte 1390, (1997), S boiler wall temperature C current design of MSWI: Economic compromise of maintenance costs and power generation steam T max. 400 C 5 H. Hunsinger - ICIPEC 2010

6 Evaluation of new WtE processes upgrading the steam temperature 400 C C >500 C steam temperature modern grate MSWI corrosion-resistant boiler material (Inconel -Cladding) Chemical inhibitation of boiler corrosion (SO 2 -rec. process) Waste (RDF) gasification (cleaned syngas combustion) extra super heater at low corrosive locations - sand loop of CFB - divided combustion chamber in grate furnace Combined steam cycles of MSW with fossil fuel fired power plants 6 H. Hunsinger - ICIPEC 2010

7 Measures for maximized electricity generation from MSWI Optimization of the Rankine cycle approach to Carnot efficiency High temperature steam generation at low boiler corrosion Intermediate steam reheating (high/low pressure steam cycle) Low pressure/temperature of steam condensation (no heat utilization) Regenerative condensate preheating Minimized heat loss Low excess air combustion Low flue gas temperature at boiler exit Low energy consumption of the plant Avoidance of pollutant formation (NO x, PCDD/F reduced efforts in flue gas cleaning) Low quantity and good quality of residues (TOC, PAH) like in modern MSWI (no residue treatment) 7 H. Hunsinger - ICIPEC 2010

8 Characteristics of MSW combustion in a grate furnace T ( C) O 2 C T O 2 (Vol.%) C (%) 0 MSW λ>1 drying λ<1 pyrolysis gasification λ>1 fixed carbon burnout 0 0 bottom ash zone 1 zone 2 zone 3 zone 4 grate fuel bed primary air 8 H. Hunsinger - ICIPEC 2010

9 Characteristics of MSW combustion in a grate furnace steam boiler flue gas λ>1 flue gas burn out zone secondary air λ<1 λ<1 MSW λ>1 drying λ<1 pyrolysis gasification λ>1 fixed carbon burnout bottom ash zone 1 zone 2 zone 3 zone 4 fuel bed primary air 9 H. Hunsinger - ICIPEC 2010

10 Axial O 2 profile in the flue gas above the grate over the grate length at different excess air ratios O 2 O 2 (Vol.% wet) grate length p primary air stoichiometry λ p Example: Low calorific MSW: LHV 7.4MJ/kg 10 H. Hunsinger - ICIPEC 2010

11 Products of uncompleted combustion (PICs) Soot particles 8 6 CO soot (g/m 3 wet) CO (Vol.% wet) grate length grate length Primary air stoichiometry λ p p 2.5 Primary air stoichiometry λ p p 30 C n H m 2.0 H 2 C n H m (g/m 3 wet) 20 H 2 (Vol.% wet) grate length grate length Primary air stoichiometry λ p p Primary air stoichiometry λ p p 11 H. Hunsinger - ICIPEC 2010

12 Axial profile of LHV in the flue gas above the fuel bed LHV (only gaseous compounds) 2.5 LHV (MJ/m 3 wet) grate length p Primary air stoichiometry λ p At λ p 0.8 flue gas shows heating values up to 3 MJ/m 3 at the O 2 minimum Example: Low calorific MSW: LHV 7.4MJ/kg 12 H. Hunsinger - ICIPEC 2010

13 Concentrations of organic compounds in the flue gas above the grate at the main combustion zone soot particles CnHm methane ethene ethyne benzene toluene naphthalene phenanthrene anthracene fluoranthene pyrene pyridine C14H10 C16H10 C16H10 C5H5N C10H8 C14H10 CH4 C7H8 Σ CnHm soot C6H6 C2H4 C2H2 Volatile org. compounds gas phase Low volatile PAH mainly adsorption on soot particles Concentration (g/nm 3, dry) average 13 H. Hunsinger - ICIPEC 2010

14 Concentration of TOC and PAH in ash particles collected by filtration of the fuel gas at the main combustion zone TOC concentration (%) German regulation PAH concentration (mg/kg) German regulation ΣEPA 16 PAH <20mg/kg 0 TOC TOC 6% 1 phenanthrene anthracene fluoranthene pyrene German regulation for underground disposal (VersatzV 2002) TOC 6%, ΣEPA 16 PAH <20mg/kg No disposal of gasification ash possible, treatment necessary! 14 H. Hunsinger - ICIPEC 2010

15 Release of corrosive elements and HCl in the flue gas above the fuel bed Example: Low calorific MSW: LHV 7.4MJ/kg at λ p H. Hunsinger - ICIPEC 2010

16 Concentration of N-compounds in the flue gas above the fuel bed NH 3 20 NO, NH 3 (mg/nm 3 ) NO O O 2 (Vol. %) 0 grate zones 0 Hunsinger et al., 5 th i-cipec, December 2008, Chiang Mai, Thailand 16 H. Hunsinger - ICIPEC 2010

17 Summary of flue gas characterization at the main combustion zone (O 2 -Minimum) Calorific value (LHV) is sufficiently high for separate energetic utilization (= fuel gas) Raw fuel gas contains corrosive compounds and pollutants Volatile corrosive chlorides (Pb, Zn, K, Na etc.) HCl, H 2 S Ash particles removal prior energetic utilization soot particles and adsorbed C n H m (PAH) to be burnt (after separation) NH 3 should be converted to N 2 (minimizing NO x formation) 17 H. Hunsinger - ICIPEC 2010

18 Fuel gas cleaning and energetic utilization Flue gas NO x 4) Heat utilization for steam super heating 3) Combustion of the cleaned fuel gas air 2) Hot gas filtration + dry sorption of HCl (H 2 S) 1) Cooling to T 400 C (Condensation of volatile chlorides, avoiding tar condensation) Ca(OH) C air Raw fuel gas gasification ash (chlorides, soot, PAH) + CaCl 2 18 H. Hunsinger - ICIPEC 2010

19 Emission Flue gas cleaning Water-/steam cycle Raw gas Economizer p=40bar/t=400 C Condenser Steam generator Super heater Evaporator Q el. Secondary air Flue gas λ>1 Flue gas burnout Steam turbine Fuel λ<1 Solid fuel burnout Main furnace Primary air Bottom ash standard process scheme 19 H. Hunsinger - ICIPEC 2010

20 Emission Flue gas cleaning Bypass process Water-/steam cycle Raw gas 4) Super heater SH 2 p=120bar/t=540 C Economizer p=120bar T=400 C air 3) Secondary combustion chamber Condenser Steam generator Super heater SH 1 2) Hot gas filtration + dry sorption Evaporator Ca(OH) C ash (soot) + CaCl 2 Q el. Secondary air Flue gas λ>1 Flue gas burnout air 1) Heat exchanger Steam turbine Fuel (MSW) λ<1 Solid fuel burnout Fuel gas 900 C Bypass flue gas 600 C Main furnace Primary air Bottom ash scheme of new process 20 H. Hunsinger - ICIPEC 2010

21 Reduction of pollutants Ash from fuel gas filtration TOC and PAH are burned when feeding back into the combustion chamber of the main furnace (prior secondary air supply) Heavy metals, chlorides and formed HCl will be collected in the flue gas cleaning system of the main furnace Flue gas of the bypass combustion process NH 3 in the fuel gas forms NO x during combustion in the bypass furnace NO x will be destroyed when injecting the by-pass flue gas back into the reducing atmosphere of the main furnace prior secondary air supply 4NO + 4NH 3 + O 2 4N 2 + 6H 2 O 2NO + 2CO N 2 + 2CO 2 SNCR Re-burn 21 H. Hunsinger - ICIPEC 2010

22 Rankine cycle of usual process in the T-s Diagram T ( C) T=400 C T k p K h I =3214KJ/kg SH T=250 C Evaporator Steam turbine Eco h 0 =105KJ/kg T=25 C Wet steam area Condenser h 1 =2250KJ/kg s (kj/kg K) 22 H. Hunsinger - ICIPEC 2010

23 Rankine cycle of the new process in the T-s Diagram 12% heat transfer in SH II 120bar/540 C T ( C) h 0 =105KJ/kg T=25 C T=540 C T=400 C T=325 C T=250 C Eco h II =3455KJ/kg h=3051kj/kg p K T k SH 1 SH 2 SH Evaporator Wet steam area Condenser h I =3214KJ/kg Steam turbine h 1 =2250KJ/kg Energy transfer to steam (%) Extra super heater (SH 2 ) Main boiler Eco, Evaporator SH 1 s (kj/kg K) 23 H. Hunsinger - ICIPEC 2010

24 Power generation by an axial steam turbine Standard process: 40bar/400 C Example of the new process: 120bar/540 C h II =3455kJ/kg h t 120bar/540 C h t 40bar/400 C h (kj/kg) h I =3214kJ/kg Steam turbine η T 0.83 T=24 C Increase of η el. 4% points h=2250kj/kg s (kj/kg K) 24 H. Hunsinger - ICIPEC 2010

25 Adiabatic combustion temperatures in the flue gas burnout zone of the main furnace Heat transfer in the bypass super heater total excess air can be lowered (λ = ) 1400 Adiabatic combustion temperature ( C) T max. refractory Regulation: T=850 C / t=2s Example LHV waste =7.4MJ/kg LHV waste (MJ/kg) normal combustion O 2 dry 8.6Vol.% new process with bypass furnace (heat transfer in super heater SH 2 ) O 2 dry 7.5Vol.% reduced energy loss in the off gas η el. +1.5% points 25 H. Hunsinger - ICIPEC 2010

26 Economic benefit (for the example) MSWI with thermal capacity of 50MW Operation time per year: 8000h Price for electricity in Germany: 50 /MWh Increase of power generation +5.5% points Additional profit: 1.1 million per year 26 H. Hunsinger - ICIPEC 2010

27 Further increase of power generation efficiency T ( C) T C 40bar/400 C T SH K Evaporator Eco Wet steam area Condenser Super heater p 1 s (KJ/kg K) Steam turbine T ( C) T C T»500 C Eco T SH K Evaporator Wet steam area Condenser Super heater p 1 Steam turbine s (KJ/kg K) The new process allows high steam super heating (T»500 C) avoiding chlorine induced boiler corrosion and super heater fouling Intermediate steam reheating Rankine cycle (high/medium/low pressure) like in modern power plants η el. >35% possible T ( C) T C T SH T»500 C Eco K Evaporator Wet steam area Condenser Super heater p 1 p 2 s (KJ/kg K) Steam turbine T ( C) T C T»500 C T SH Eco K Wet steam area Super heater Evaporator Condenser p 1 p 2 p 3 s (KJ/kg K) Steam turbine 27 H. Hunsinger - ICIPEC 2010

28 Application in various combustion systems Fuels: MSW, Biomass etc. Flue gas Flue gas Secondary air λ>1 Flue gas burnout zone air Cyclone λ<1 Flue gas II Recirculation Gas cleaning Combustion Super heating ash λ>1 Flue gas burnout zone Secondary air MSW Primary air λ>1 Z1 Z2 λ<1 Z3 Z4 Fuel gas λ>1 Bottom ash sand + coarse ash MSW + sand λ<1 λ<1 Fuel gas Bottom ash + sand Flue gas II Recirculation Gas cleaning Combustion Super heating ash air Primary air Grate furnace Fluidized bed furnace 28 H. Hunsinger - ICIPEC 2010

29 Summary and conclusions Energetic utilization of the total residual waste without pre-sorting. Steam can be heated up to very high temperatures at high pressures comparable to fossil fuel fired power plants avoiding super heater corrosion and fouling. This is the basis for further improvements like intermediate superheating of the steam. The excess air of total combustion process can be minimized resulting in reduced energy loss of the exhaust gas flow. The formation of pollutants particularly of NO x can be lowered significantly. As result the efforts in NO x control can be minimized or even avoided. All environmental aspects like low stack emissions, minimized amount of residues with good qualities allowing utilization or land filling are ensured. As overall optimization a very high efficiency of power generation (η el. >35%) from a mono-fuel fired WtE plant can be realized. 29 H. Hunsinger - ICIPEC 2010