Could biomass boilers be operated at higher steam efficiencies (higher temps.)?

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1 Could biomass boilers be operated at higher steam efficiencies (higher temps.)? Sandy Sharp (SharpConsultant, Columbia, MD) Jim Keiser (Oak Ridge National Laboratory, Oak Ridge, TN) Doug Singbeil (FPInnovations, Vancouver, BC, Canada) Jim Frederick (Table Mountain Consulting, Golden, CO) Curtis Clemmons, (MeadWestvaco, Covington, VA) Laurie Frederick, (FPInnovations, Vancouver, BC, Canada)

2 Project tasks Could existing alloys serve in biomass boiler SHs at temperatures 100 Celsius degrees above current operating temperatures? 1. Strategies for managing superheater corrosion 2. Lab and field tests of candidate alloys 3. Would value of the increased power generated justify the costs of the increased steam temperature? 2

3 Project funding and support U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, contract DE-AC05-00OR22725 with Oak Ridge National Laboratory Budget: Research: 1,150,000 ($1,568,000); In-kind: 588,000; Total: 1,730,000 ($2,360,000) Project partners (in-kind contributions): Åbo Akademi University, Andritz Oy, Babcock & Wilcox, Catalyst Paper, Chalmers University of Technology, Domtar Corporation, E.ON UK, FM Global, FPInnovations, Foster Wheeler, Georgia Institute of Technology, Haynes International, Howe Sound Pulp & Paper, International Paper, MeadWestvaco, Metso Power, Outokumpu Stainless, Rolled Alloys, Sandvik Materials Technology, SharpConsultant, Southern Company, Special Metals, Table Mountain Consulting, ThyssenKrupp VDM, University of Toronto Pulp and Paper Centre, Vattenfall Power and the Weyerhaeuser Company. 22

4 Advanced biomass boilers achieve higher steam temperatures using Modified boiler designs Fuel modifications or chemical additions Corrosion-resistant superheater alloys 4

5 Design modification 1a: Remove deposits before SH Add an empty pass between furnace and SH Iglesta CHP boiler Södertälje, Sweden (wood and waste) 5

6 Design modification 1b: Remove deposits before SH Add a Chlorine trap upstream of the SH Molten outer layer of ash may restrict penetration of corrosives WTE boiler, Schweinfurt, Germany Straw-fired boilers (Maribø, Avedøre 2, Denmark; Grenå, Norway) also operate with molten outer layer of SH ash 6

7 Design modification 2: Move CFB SH from flue gases into recirculated fluidizing medium Foster Wheeler INTREX Metso (Valmet) CYMIC Lurgi FBHE 7

8 Design modification 3: Move SH outside boiler and heat it with a less-corrosive fuel Ensted (Åbenrå, Denmark) straw/wood fired boiler raised SH temperature from 470 C to 542 C by installing an external wood-fired SH 8

9 Design modification 4::Design SH for very rapid replacement WTE boiler, City of Amsterdam, The Netherlands, with KEMA 9

10 Design modification 5: Operate SH above ash dew point temp. Raise tube surface temperature to convert NaCl deposits to less-corrosive HCl(g) Skog, et al., 2008 Palonen et al., 2009: Norrköping, Langerbrugge, etc. 10

11 Process modification 1: Dilute corrosive biofuels Simplest approach: dilute corrosive biofuels with less corrosive fuel e.g. diluting straw with 80% coal does not significantly increase SH corrosion 11

12 Process modification 2: Wash corrosives out of biofuels Water-soluble alkali chlorides are among the most corrosive species faced by biomass boiler SHs Water leaching removes >80% of K, Na; >90% of Cl from biomass crop fuels But drying wet fuels can be expensive 12

13 Process modification 3: Convert chlorides to sulfates K 2 SO 4 deposits are much less corrosive than KCl because they have a higher melting temp. - 1,069 C rather than 770 C Sulfation reduces conversion of Cr 2 O 3 to alkali chromate: can halve the corrosion rate can be achieved by SO 2 or SO 3 2KCl(s) + SO 2 (g) + ½ O 2 (g) + H 2 O K 2 SO 4 (s) + 2HCl(g) e.g. WTE boiler, Norrköping, Sweden (NH 4 ) 2 SO 4 SO 3 + 2NH 3 + H 2 O (ChlorOut ) 13

14 Process modification 4: Convert chlorides to silicates Silica or kaolinite additives react with alkali chlorides to form alkali silicates or alkali aluminum silicates silicates have much higher melting temperatures, reduce SH fouling and corrosion e.g. KCl concentrations in FBHE of Grenå CFB boiler (co-firing straw/coal) were reduced by two OOMs by silica or kaolinite additions 14

15 Alloy modifications: use more corrosion-resistant SH alloys Alloy rankings depend on biomass fuel, operational parameters, tube temps. Corrosion rates increase rapidly at ash melting temp. 15

16 Conclusions of tasks 1, 2 SH corrosion control strategies and alloy rankings had been developed for boilers burning wood, straw, black liquor and municipal wastes 3 empirical models had been developed to predict fouling and corrosion in biomass boilers Fuel composition is used to predict ash composition; (T - FMT ) to predict fouling tendency; field data to predict corrosion rate In each of 4 challenging biomass boiler environments, some alloys could have useful lives at 100 Celcius degrees above current limits 16

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18 Is the juice worth the squeeze? Use Rankine cycle software to calculate value of additional power that could be generated by operating typical biomass boilers at higher steam conditions without changing fuel or firing conditions Compare the value of this additional power with the costs of installing more corrosion-resistant superheater alloys, using fuel additives or changing the boiler design 2

19 Specific Available Energy, kj/kg Underlying principle Availability of energy in steam (ability to do work) increases with increasing steam temperature bars 50 bars Temperature, C Increasing our steam temperature by 100 Celsius degrees will increase the energy available from a biomass fuel by 11.4% at 100 bars and 11.0% at 50 bars 4

20 Project collaborators supplied steam data for five biomass boilers Two Black Liquor Recovery Boilers (52,54 MW) Typical data from a boiler manufacturer Process simulation model of 1,500 ODT pulp mill Three wood-fired Biomass Boilers (27,28,43 MW) West Coast pulp mill unit firing sea-floated logs West Coast pulp mill unit firing 2/3 beetle-killed pine, 1/3 sea-floated logs, some construction waste Recently constructed BFB firing wood waste 6

21 Value of increased power in 5 biomass-fueled boilers Conditions Recovery Boilers Biomass Boilers B M C H M +50 C +$1.54m +$2.52m/y +$2.94m/y +$1.33m/y +$3.08m +$5.05m/y +$5.89m/y +$2.66m/y +$2.52m/y +100 C +$2.45m/y +$4.45m/y +$5.61m/y +$2.60m/y +$4.91m/y +$8.90m/y +$11.21m/y +$5.19m/y +$4.84m/y Potential costs of maintaining process steam flows in biomass boilers (likely not large) are not included in these calculations 16

22 Could value of increased power generation justify cost of increasing steam temps by 100 Celsius degrees? Value of additional power generated from hotter steam at constant firing conditions could pay: $5,378/m - $24,911/m for 2,250 m for more corrosion-resistant SH tubes replaced every 5 years (45p x 10t x 5m) $2,420,000 - $11,210,000 per year to remove corrosives from biomass fuel or to apply additives $12m - $56m over 5 years to redesign boiler, upgrade steam turbine 17

23 Project results are available in 7 publications Energy From Biomass Lessons From European Boilers Sharp, Singbeil & Keiser, TAPPI PEERS conference, 2011 Superheater Corrosion Produced By Biomass Fuels Sharp, Singbeil & Keiser, Paper 1308 at NACE Intl. Corrosion/2012 conference Superheater Corrosion In Biomass Boilers: Today s Science and Technology Sharp, Oak Ridge National Laboratory TM-2011/399, 2012 Performance of Alternate Superheater Materials in a Potassium-Rich Recovery Boiler Environment Keiser, Sharp, Singbeil, Frederick & Clemmons, TAPPI J, 12 (7), 45-56, 2013 Could Biomass-Fueled boilers be Operated at Higher Steam Temperatures? 1. Laboratory Evaluation of Candidate Superheater Alloys Singbeil, Frederick, Keiser & Sharp, TAPPI Journal, to be published June 2014 Could Biomass-Fueled boilers be Operated at Higher Steam Temperatures? 2. Field Tests of Candidate Superheater Alloys Keiser, Sharp, & Singbeil, TAPPI Journal, to be published June 2014 Could biomass-fueled boilers be operated at higher steam temperatures? 3. Initial analysis of costs and benefits Sharp, Frederick, Keiser & Singbeil, TAPPI Journal, to be published June 2014

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25 Measuring corrosion rates is difficult Sample temps. are not constant Corrosion is irregular How many cross-sections? Max. or avg. metal loss beneath original surface? Image analysis of cross-sections of lab test specimens produced 28,800 measurements 25

26 Corrosion tests

27 Average Exposure Temperature ( C) Example of field corrosion data 650 Covington Recovery Boiler Goal S31009 N Current max T N08028 N06025 N08120 S21500 S34709 N12160 N ,1 0,1 0,3 0,5 0,7 0,9 1,1 1,3 1,5 Total Material Affected (mm)

28 Nine alloys were selected for exposure in the RB corrosion probe Alloy UNS number Fe Ni Cr Mo Co Mn Al Si C Other 310H SS S31009 Bal Haynes 214 N Bal Y=.004, Zr=.011 Sanicro 28* N CA N Y=0.07, Zr=0.09 HR160 N Bal Inconel 690* N HR120 N N=0.21 Esshete 1250* S Nb=1, V=2.5, B= H SS S34709 Bal *Nominal values

29 Average Exposure Temperature ( C) Conclusion from field and lab tests In SH environments simulating boilers burning sea-floated logs w and w/o demolition waste coal-wood blends kraft black liquor existing alloys could serve useful lives in superheaters operating 100 Celcius degrees above current operating temperatures Covington Recovery Boiler 0 0,5 1 1,5 Total Material Affected (mm) S N N N N S2150 0