Fluidized bed Oxy-fuel combustion and CCS

Transcription

1 Fluidized bed Oxy-fuel combustion and CCS Third APP Oxy-fuel Capacity Building Course Yeppoon, Queensland September 2011 Sankar Bhattacharya Associate Professor Department of Chemical Engineering

2 Contents of the presentation Coal-fired power generation current status Circulating fluidised bed (CFB) combustion current status characteristics advantages Oxy-CFB current status charasteristics advantages CCS implications and development needs Concluding comments

3 Coal-fired power generation capacity MWe 1,800,000 Global Installed Capacity (MWe) Operational Coal-fired power plants 1,600,000 1,400,000 1,200,000 1,000, , , , , , , , ,408 45,384 1,651, , Years Years Years Years >40 Years Unknown age TOTAL Global Coal-fired power generation capacity ~ 1650 GWe at the end of 2010 MWe Global Installed Capacity (Mwe) Regional distribution of Coal-fired power plants ASIA AFRICA ANZ OCENIA RUSSIAN EUROPE CONTINENT LATIN AM ERICA NORTH AM ERICA M IDDLE EAST TOTAL Source: Platts, 2011

4 Circulating fluidised bed (CFB) combustion 25,000 Operating Circulating Fluidised Bed Power Plants Installed Capacity (MWe) 20,000 15,000 10,000 5, MWe MWe MWe MWe MWe >500 MWe 10 Years Years Years Years >40 Years Unknown age Global CFB capacity 46.5 GWe at the end of GWe at the end of ,000 Installed Capacity, MWe 30,000 25,000 20,000 15,000 Operating Circulating Fluidised Bed Power Plants Regional distribution (MWe) fuels anthracite to lignite, biomass, pet coke 10,000 5,000 0 ASIA AFRICA ANZ OCENIA RUSSIAN CONTINENT EUROPE LATIN AM ERICA NORTH AM ERICA M IDDLE EAST Source: Platts, 2011

5 What is CFB combustion Characteristics Low operating temperature, around 900 C, relative to pulverized coal combustion Secondary Air Bed materials and coal/char particles circulating throughout the furnace and return leg at high velocity, 3-8m/sec Longer residence time of the circulating solids External Heat Exchanger Lower excess air relative to pulverized coal combustion Staged combustion Air, fuel, sorbent feed Aeration air Efficiency of CFBC units is similar to pulverized coal-fired units under identical steam conditions Ash/ bed material

6 Advantages of CFB combustion Low operating temperature, around 900 C, relative to pulverized coal combustion, low NO x Fuel flexibility from high to low-grade fuels, biomass and opportunity fuels Uniform heat flux Excellent load-following capability In-situ sulphur dioxide capture rather than flue gas desulphurisation as in pulverized coal combustion, and higher calcium utilization Lower NO x formation relative to pulverized coal combustion due to lower operating temperature Compact boiler size Simplified fuel feeding, pulverization is not required, crushing is sufficient Ideal for Oxy-fuel CCS

7 Schematic of a CFB combustion pilot plant coal feeder additive feeders combustor cyclone convection section combustor air heater flue gas cooling fan air fabric filter screw conveyor external heat exchanger fluidising air flue gas coolers (three) stack bed media removal heat exchanger media removal natural gas secondary air primary air electric air heater PD blower fly ash discharge to stack ID fan convection section cooling fan Used for First -of -its -kind trials in Australia using high moisture and high /low ash lignites

8 Chronology of CFB Scale-up Largest operating 460 MWe, supercritical steam parameter, unit at Lagisza Recently awarded four 550 MWe, supercritical steam parameter, units in Korea Designs up to 800 MWe available Source: Utt, 2008; Business Wire, 2011

9 Oxy CFB introduction and simplified schematic Convection section Secondary gas Inerts Preheater Dust collector Fuel and sorbent feed Ash Recycle fan Gas purification CO 2 compression CO 2 to storage/use O % Mixer Impurities Ash/ bed material Air ASU N 2 /Ar variant of air-cfb fluidization and combustion by mix of oxygen and recycled flue gas bed and gas temperatures to the same level in an air-fired CFB unit reduces recirculation of flue gas due to recirculating solids in the riser-loop

10 Oxy CFB - advantages Strong mixing in the furnace and long residence time due to recirculation of solids allow high carbon burnout; clearly suits low-reactive coals Recirculation of the cooled solids from the external heat exchanger allow a Oxy-CFB boiler to operate with lower flue gas recycling compared to Oxy-PF systems Reduction of flue gas recycling, thereby reducing the size of the boiler island, and some of the auxiliaries consumption. This may potentially allow more compact and less expensive CFB boilers Direct sulfation of limestone will occur due the high partial pressure of CO 2 and the right thermodynamic temperature for sulfur capture; calcium conversion under direct sulfation is usually higher than that under calcination/sulfation due to the better porosity of product layer

11 Oxy CFB - advantages Fans and blowers consume less power as the draft system handles higher molecular weight gas Oxygen concentration in the recycled flue gas can be kept to a low and safe level, while additional oxygen can be introduced through oxygen nozzles separate from the burner or the secondary gas inserting points. Transition from air-mode combustion to oxy-mode combustion is potentially easier relative to oxy-pf, because CFB has large amount of inert bed material that also helps in controlling the bed temperature. CFBC s operated at slightly over atmospheric pressure, possibility of air-in-leakage is greatly reduced.

12 Oxy CFB - developments Air-fired CFB COMPOSTILLA Oxy-fired CIUDEN 2015 first Oxy-CFB development started in 1986! Adapted from Utt, 2008

13 Major Oxy-CFB Facility - CIUDEN first ever integrated facility

14 Major Oxy-CFB Facility CIUDEN boiler Source: Lupion, 2010

15 Smaller Oxy-CFB Facilities VTT facility (0.1 MWth) CANMET facility (0.8 MWth)

16 Oxy-CFB development issues Coal Quality issues Boiler design issues Gas Cleaning/ Impurity removal Material Issues Gas environment ASU- Cost of O 2 generation Integrated Operation/ control issues Overall economics Integrated demonstration necessary

17 Oxy CFB coal quality coal quality issues related to its development Emissions from the riser Fouling superheater economiser Recarbonation Trace metal emission Recycle fan Gas purification CO 2 compression O 2 Mixer Unburnt carbon / lime Bed Agglomeration Heat transfer Air ASU Sulfur capture N 2 Unburnt carbon

18 Oxy CFB coal quality coal quality issues issues results so far Coal devol & ignition delay No significant issues on all types of coals Heat transfer Gaseous emission Trace element emission Source: Bithi Roy et al., 2011 Depends on solids effects, not on gas composition No major issues on all types of coals CO somewhat higher; High CO 2 hinders CO oxidation NO x lower; NH 3 injection further reduced NO x emission In-bed SO x capture possible and better than in Air-CFB, however further tests necessary Least known; For some bituminous coals Hg and major trace metal emission same as in air-cfb combustion; modeling suggests the same Further investigation necessary for a wide range of coals

19 Oxy CFB coal quality coal quality issues issues results so far Recarbonation Evidence of recarbonation with some bituminous coals Little known for coals with high Ca content Systematic investigation necessary for a wide range of coals Fouling No evidence with some bituminous coals Systematic investigation necessary for a wide range of coals S - transformation For some bituminous coals in bed capture is higher than in air-cfb combustion Overall higher Ca-utilisation, supported by modeling However, SO 3 emission is higher Further investigation necessary for a wide range of coals having different types of S (organic/inorganic)

20 Oxy CFB coal quality coal quality issues issues results so far Bed agglomeration No evidence with bituminous coals or pet coke; Could be issues with lignites containing alkali, calcium, sulfur and chlorine; modeling suggests increased agglomeration; Further investigation necessary with such coals 650 µm 14 0µm µm 3 h61 4 Source: Bithi Roy et al., 2011

21 Oxy CFB materials and boiler design issues Same issues as in Oxy-pf combustion different combustion atmosphere high CO 2 and H 2 O vapour also CO, H 2 S, SO 2, SO 3, HCl however temperatures are lower environment is much more abrasive from the recirculating solids Burner design unlikely to be significantly different from air-cfb Oxy CFB air separation issues Same developmental issues as in Oxy-pf combustion oxygen purity issues and subsequent effect on CO 2 quality same as in Oxy-pf

22 Oxy CFB gas cleaning issues. Similar issues as in Oxy-pf combustion limited information on release of Hg and trace metals on a range of coals under oxy-cfb condition the recirculating char and the flyash is likely to carry these species eventually to the bed discharge and bag filter fundamental experimental work necessary to establish the extent of emission of Hg, S-species, and trace metals in oxy-cfb condition compared to air-cfb condition Sealing of the boiler and air in-leakage CFB boilers are usually operated under slight overpressure, water gauge this is likely to minimize air-ingress into a properly maintained Oxy-CFB boiler

23 Major Retrofit needs for CO 2 capture in an air-cfb unit Case by case study needed Heat fluxes and heat transfer areas can largely be matched New equipment for the CFB boiler new gas recirculation system oxygen supply piping CO 2 product ductwork gas processing system new control and instrumentation system Air separation unit New space for the new equipment

24 Concluding comments Air-CFB advantages also exist in Oxy-CFB Low furnace temperatures Long solid residence times Hot recirculating solids Uniform heat flux and efficient heat transfer Fuel flexibility Good fuel burnout and S-sorbent utilization NO x and SO x reduction without flue gas desulfurization Simple feed systems Ability to operate in air-firing or oxy-fuel mode for CCS 90% CO 2 in off-gas at 3% O 2 level can potentially be achieved Reduced boiler size Demonstration at CIUDEN is critical to: Identify research and development issues fuel/gas processing/materials Gain experience on stable operation Minimise cost and cost uncertainty for new and retrofits

25 Innovation : Chemical Looping Cycle N 2, O 2 CO 2, H 2 O flue gas MeO (+ Me) Air reactor Fuel reactor 2 Me (+ MeO) 1 3 H O 2 Air Fuel air fuel bleed noncondensible gas CO2 Longer-term : extended from CFB experience 1 CFB riser 2 Cyclone 3 Heat exchanger

26 Bibliography E. J. Anthony and L. Jia. Agglomeration and strength development of deposits in CFBC boilers firing high-sulfur fuels. Fuel 2000;79: T Eriksson et al., Development of Flei-Burn CFB technology aiming at fully integrated CCS demonstration, PowerGen Europe, 2009 A. Hotta, Foster Wheeler s solutions for large scale CFB boiler technology, Proc of the 20 th Int Conf on Fluidized bed combustion, 2009 L Jia, Y Tan, C Wang, and E. J. Anthony, Experimental study of oxy-fuel combustion and sulphur capture in a mini CFBC, Energy & Fuels, 21, 2007 M Lupion, 2nd APP Oxyfuel Capacity Building Course, March 2010 G Özkan and G Dogu. Combustion of a high ash and sulfur containing lignite in a pilot circulating fluidized bed combustor and its pollution characteristics. Chemical Engineering and Processing 2002;41: A Robertson, S Goidich, Z Fan, 1300F 800 MWe USC boiler design study, Proc of the 20th Int Conf on Fluidized bed combustion, 2009 B Roy, WL Choo, S Bhattacharya, Prediction of selective trace element emissions during Oxy-CFB combustion of Victorian brown coals,, ICCST, 2011 B Roy, WL Choo, L Chen, S Bhattacharya,thermodynamic modeling of agglomeration during oxy-cfb combustion of Victorian brown coal, Chemeca 2011 C S. Zhao, L. B. Duan, X. P. Chen, and C. Liang. Latest evolution of Oxy-fuel combustion technology in circulating fluidized bed. Proc of the 20th Int Conf on Fluidized Bed Combustion, World Electric Power Plants database, Platts, 2011