Success Case of Co-firing of Biomass and Coal

Transcription

1 Success Case of Co-firing of Biomass and Coal Luca Rigoni Thermal Services Boiler 29/05/2012

2 Index of Contents Introduction Biomass Fuels Categories Options for Biomass Firing Alstom success case: Fiddlers Ferry Conclusions

3 Introduction There is a worldwide recognition that there is a need for urgent global action to prevent climate change by reducing the emissions of greenhouse gases from power plants. Firing of biomass fuels in existing power plants is an attractive option as the overall cycle efficiency exceed that of smaller dedicated biomass plants for generating electricity. Italy forecast: 20 TWh in 2020 Ref. EEA (European Environment Agency)

4 Introduction Firing these fuels can also increase fuel flexibility and lead to reductions in SO2 and NOx emission. Compared to coal, biomass fuels contain more volatile matter and moisture, less ash and thus result in a lower calorific value. 1.2 Coal 14% biomass Relative Fraction CO 2 SO 2 NOx UBC

5 Biomass Categories Untreated Biomass Treated Biomass Untreated Biomass Energy Crops Residues and Waste Derived Fuels Fire wood Forest residues Wood pellets Olive pellets Short rotation/ coppice/forestry (Willow/Poplar) Residues from agriculture and industry Straw Cereals Demolition wood Palm kernels Miscanthus Sewage sludge Waste derived fuels, RDF

6 Biomass Fuels Logs ~45% H 2 0 Woodchips 15-45% H 2 0 Pelletised wood ~10% H 2 0 Miscanthus ~20% H 2 0 Coppiced Willow ~45% H 2 0

7 Fuel Variability and Acquisition Fuel Coal Wood Miscanthus SRC Form Pellets Logs Bales Wood chips Average moisture % Calorific Value MJ/kg Dimensions mm <25 Dia <12, 50mm long 100 dia 2000 long 1200x1000x Density kg/m Relative storage volume Relative gas flow

8 Proximate Analysis Biomass fuels usually typically contain 70 to 80% volatile matter, whereas coal consists of 10 to 50% volatile matter. Typically processed biomass fuels all have similar calorific values, which are around 70% of a bituminous coal. Constituent (%) Coal Volatile matter Fixed carbon Moisture Ash Wood pellets Palm kernels Olive pellets Willow Miscanthus

9 Fuel Comparison The chemical properties of coal depend upon the relative proportions of the chemical constituents present in the plant debris and this applies even more so for biomass fuels. Coal rank indicates the relative proportions of volatile matter and fixed carbon present in the coal. The C/O and C/H ration increases throughout the coal formation process. Anthracite is almost all carbon compred to youger Lignite. Typically the biomass fuels contain a proportion of hydrogen and oxygen compared to coal.

10 Options for Firing Biomass Co-firing of biomass fuels in large utility boilers is a fuel substitution option whereby the coal burn in the plant is reduced. There are three main options for utilizing biomass as a renewable energy source and include: Blending with coal and co-milling Direct Injection Gasification

11 Biomass Co-milling Blending with Coal and Co-milling typically fire up to 10% mass Lowest cost Blend with coal before milling Use existing mills, limits output Stringy material can be problematic Can reduce overall boiler capacity Coal Pre-treated biomass (pellets) Milling Cofired burner Utility boiler Steam turbine Flue gas cleaning

12 Dedicated Biomass Co-firing Direct Injection with dedicated systems - > 10% by mass More flexible, higher throughputs Equipment can be specifically tailored for biomass Minimal outage requirements Pre-treated biomass (pellets) Milling Biomass burner Utility boiler Flue gas cleaning Coal Milling Coal burner Steam turbine

13 Indirect Firing Indirect systems (gasification) Lower availability and reliability Higher costs Need of larger area for plant installation Biomass Coal Gasifier Milling Gas burner Coal burner Utility boiler Flue gas cleaning Steam turbine

14 Effect of Biomass Thermal Input on Firing Rate The biomass firing brings some issues on delivery, storage and preparation of the fuels. The figure below considers a 500 MWe boiler having 200 t/h coal feed at maximum load. The heating values and bulk density of biomass fuels are generally 50-70% and 20% of coal respectively, leading to overall fuel density of biomass in MJ/m3 approx 10% of coal. Considering a replacement of 5% thermal energy, 15 t/h biomass flow is necessary requiring a 2000 m3 bulk storage area. Biomass Flow (t/h) MJ/kg 10 MJ/kg Biomass Fired (% thermal)

15 Alstom Success Case: Fiddlers Ferry Power Plant: 4 x 500 MWe T fire Client: Scottish & Southern Energy (SSE) In operation since 1970 Biomass Co-Firing since 2007 Biomass input up to 20% of MCR Wide range of Biomass (i.e olive residues, wood and cereal co-product)

16 Plant Design Considerations Broad areas to be considered for biomass co-firing: Biomass fuel consumption target Biomass fuel type and flexibility Biomass fuel quality, variability and handling Boiler performance and operation including: Mills restriction Impact on furnace slagging and fouling Impact on performance Impact on emissions Impact on auxiliaries (ID fans & precipitators) Location of biomass burners Dust control and dust explosion prevention Biomass transport system (lay-out)

17 Performances IMPACT on BOILER PERFORMANCES To determine the impact of co-firing, a boiler model was developed. The output of boiler model were the following: RH temperature increase by 2 C Boiler efficiency decrease by 0,7% (higher temp of gas leaving the boiler, lower fuel calorific value, higher moisture loss for H content in the biomass. Lower heat transfer by the furnace when firing biomass. Total air flow remained the same SH spray flow increased by 14% and reduced by increasing steam outlet temperature set-point

18 Fouling & Slagging IMPACT on FOULING and SLAGGING For slagging, fouling, erosion and corrosion considerations it was assumed that the coal and biomass material behave as blends. This reduces the concentration of elements associated with slagging and fouling due to the dilution of coal ash. The assessment concluded that co-firing wood and palm kernel would not increase the slagging and fouling potential significantly and would be controllable through soot-blowing.

19 Delivery System DESIGN OF FUEL DELIVERY SYSTEM Volumetric capacity of the feed equipment such as conveyor and feeders was calculated based on a lower bulk density of 400 kg/m3 Two modular assembled towers each housing a day silo, milling equipment, fan and auxiliaries were installed To prevent explosion the following precautions were taken: explosion vents on the silo, water deluge fire protection for conveyors. The silo safety system monitors both Carbon Monoxide or High Temperatures. Should levels of these parameters get high, an alarm is activated that block the biomass flow and inject CO2.

20 Delivery System (2) DESIGN OF FUEL DELIVERY SYSTEM

21 Mills MILLING PLANT Previous experience with vertical spindle, roller mills has indicated that the squeezing and rolling action by the roller mill builds up a layer of material quickly on the milling table reducing the output severely. Hammer type mill is utilized for this type of application. This type of mill breaks up biomass particles by cutting/ripping motion and utilises screens for product classification

22 Fuel Characteristic Shapes 75% < 75µm Pulverised Coal 70% < 1000µm 70% < 1000µm Wood Palm Kernels

23 Pneumatic transport PNEUMATIC TRANSPORT SYSTEM Cold air is used for carrying the biomass. Since the amount of cold air into the furnace is relatively small, the impact on boiler efficiency is negligible. On each boiler unit, the milled biomass is conveyed to the burners by four independent pulverised fuel piping systems for each mill hopper outlet.

24 Burners BIOMASS BURNER Ignition energy for biomass is lower than coal, therefore position of ignition is different. The following are considered for the biomass burner design: velocity at the nozzle tip to control the ignition position velocity at nozzle throat to ensure no fire back air stoic. for ignition, NOx control and burnout tilting angle material selection for erosion

25 Burners (2) BIOMASS BURNER In this boiler biomass burner is installed between second and third coal compartments from top The location of the biomass burner is based on the following: physical restriction of current wind-boxes to ensure burnout of larger particles, which might fall through the vortex flame to allow biomass firing on lower loads to operate in a higher temperature region of the furnace improve stability of the biomass flames at lower loads

26 Burners (3)

27 Conclusions The installation of dedicated biomass firing has achieved the design parameters and performance expected. From initiating a biomass start it takes only approximately 6 minutes to achieve full biomass load of 60 ton/h. Co-firing biomass results in a small decrease in boiler efficiency (- 0,4%) due a combination of increased gas temperature and volume leaving the boiler (+ 5 C), increased moisture loss arising from the higher moisture content and higher hydrogen content in the biomass. No adverse effect on ESP system Lower biomass flame temperature contributes to the reduction in thermal NOx formation. Overall the reduction was around 5% Performance of ID fan and precipitator have not been affected

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29 Air Quality Control Systems Our R&D Capabilities Växjö (Sweden) ABCD Dedicated R&D facilities are manned by highly-skilled teams offering: Applied physics / Fluid dynamics Chemical engineering Analytical laboratory Instruments / measuring techniques Laboratory for pilot plants and flow model testing Experimental workshop for test equipment and special services Alstom Power October 2011 Focus on providing state of the art technology

30 Alstom Power Solutions for W2E & Biomass Pulse Jet Fabric Filter Gas Distribution ABCD FF Service area Outlet duct Inlet duct Pressure tank with Optipow valves Outlet damper poppet type Gravimetric gasflow Optimised ratio bag/cage Inlet damper flap type Alstom FF Inlet Arrangement Alstom Power October 2011

31 Alstom Power Solutions for W2E & Biomass Pulse Jet Fabric Filter Gas Distribution ABCD Gravimetric gasflow Optimised gas/dust distribution Alstom FF Gas Distribution in Bag Nest Alstom Power October 2011

32 Alstom Power Solutions for W2E & Biomass Pulse Jet Fabric Filter Cleaning Principle ABCD Conventional High Pressure 5 7 Bar Alstom Advanced Low Pressure 2 3 Bar Ejected Pulse Secondary air 6 7 times the Volume of primary air flow Long pulse Slow pulse Short bag length Direct pulse Primary air expands direct Into the bag Secondary Air 1 2 times the primary Air Fast and short pulse Deep pulse enables longer bags Alstom FF Pulse Cleaning Effect Alstom Power October 2011

33 Alstom Power Solutions for W2E & Biomass Pulse Jet Fabric Filter Cleaning Equipments ABCD Basic Features: Pulse cleaning: Time & Diff. Pressure control Pulse Setting Time, Order & Interval Time Advanced Features: Filter Drag Control Bag Status Monitoring Valve Fault detection Equipment required: Diff. Pressure sensor Alstom EFFIC FF Controller Alstom Power October 2011

34 Alstom Power Solutions for W2E & Biomass ElectroStatic Precipitators ABCD Wet and Dry Electro Static Precipitators More than installation over the world (since 1939) R & D facility in Vaxjo (Sweden) Easy maintenance operation Alstom ElectroStatic Precipitators Alstom Power October 2011

35 Alstom Power Solutions for W2E & Biomass ElectroStatic Precipitators ABCD ESP Codes FAA Steel casing, bottom rapping FTA Steel casing, top rapping FPA Steel casing, top rapping discharge electrodes Bottom rapping collecting electrodes FAC Concrete casing, bottom rapping FTC Concrete casing, top rapping FAV Wet ESP Electrode spacing = The distance between two rows of collecting electrodes. F=250 mm J=325 mm G=275 mm K=350 mm H=300 mm L=375 nn M=400 mm F, H and M spacings are most common. Alstom ElectroStatic Precipitators Alstom Power October 2011

36 Alstom Power Control Systems ABC AB CD Alstom Remote Assistance HMI ProMo RTU Ethernet/Fläktbus Input signals -Vibration -Sound -Opacity -Boiler load etc.. Input signals EPIC III Control unit for T/R\s EFFIC Control unit for Fabric Filter EPICAB FF ESP Control of T/R, rappers, heaters etc. SIR HV energization and control of rappers, heaters etc Conventional T/R Alstom Power October Pressure drop -Opacity etc..

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38 Alstom Power Electronic - SIR ABCD Traditional Hz Single phase 2000 kg 600 Litre Oil T/R Set Comparison High Frequency khz 3-phase kg 50 Litre Oil Peak to Trough Ripple as high as 50% of average voltage Peak to Trough Ripple less than 5% of average voltage RMS value maximized RMS value reduced Typical 2-19 msec recovery from spark over Typical msec recovery from spark over kv Controls & Cabinets built in SIR ESP Voltage kv Peak kv ( ) Spark level Conv. T/R Valley kv 220 Kg. Alstom Power October Kg. S Conv. T/R SIR ESP Current ma

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40 Biomasse Italia - Crotone ABCD End product silo Electrostatic Precipitator Bicarbonate injection Alstom Power October 2011