On Biomass Milling for Power Generation. Orla Williams, University of Nottingham

Transcription

1 2015 Technical Session On Biomass Milling for Power Generation Presenter: Co-Authors: Orla Williams, University of Nottingham Dr Carol Eastwick, Prof Ed Lester, Dr Donald Giddings, Prof Ed Lester, Mr Stephen Lormor (EDF Energy plc) Tuesday 6 th October 2015

2 Project Outline 4 year EngD with completed in September 2015 Part of the Efficient Fossil Energy Technologies Centre at the University of Nottingham Research theme: biomass milling in the power generation sector Academic supervision: Dr Carol Eastwick & Dr Donald Giddings (University of Nottingham) Industrial supervision: Stephen Lormor EDF Energy

3 Key Research Areas How different woody, herbaceous, fruit and thermally treated densified biomasses comminute in different mills How mills impact densified biomass particle shape factors Suitability of standard coal grindability test for densified biomass Differences between grindability tests and classification on mill product Investigation of industrial operational issues associated with biomass, such as mill choking and olive caking

4 Samples Used Mixed Wood Eucalyptus Sunflower Miscanthus Olive Cake Steam Exploded Microwave La Loma Coal

5 Planetary Ball Mill Laboratory scale Retsch PM100 planetary ball mill High impact compression forces 100ml of sample milled at 300 RPM for 3 minutes

6 Cutting Mill Retsch SM300 cutting mill Operated at speed of 1500 RPM, feed rate of kg/s, screen size of 4mm Continuous throughout mill fed by vibrating bed feeder Cutting mills use primarily shear forces to reduce the particle size of the material

7 Hardgrove Grindability Index Hardgrove Grindability Index (HGI) most widely used grindability test for coal for vertical spindle mills Test conducted according to BS :1995 [1] Limited data for grindability of densified biomass

8 Bond Work Index Test conducted on a Bond Work Index testing mill The Bond Work Index W i expresses the resistance of the material to grinding to a specified product size (kwh/ton) [2] Study recently published in journal Fuel Investigation into the applicability of Bond Work Index (BWI) and Hardgrove Grindability Index (HGI) tests for several biomasses compared to Colombian La Loma coal [3]

9 Ring-Roller Mill The Lopulco LM 1.6 laboratory scale ringroller mill Continuous through put mill with dynamic classification (separator) No biomass comminution literature published for this type of laboratory scale mill

10 Standard Coal Grindability Tests

11 Energy Consumption Comparison

12 Particle Size and Shape Laboratory scale milling tests assess the grindability of a material to a given size Full scale mills use classifiers to select particles Stokes number of a biomass particle should match that of an equivalent coal particle in order to pass through the classifier [4]. Stokes number is dependent on the sphericity and Reynolds number of the particle Possible for large biomass particles to have similar aerodynamic properties to that of a much smaller coal particle provided it has a sufficiently low sphericity

13 Camsizer Digital Analysis CAMSIZER P4 simultaneously measures both particle size and shape CAMSIZER P4 uses Dynamic Image Analysis principle to detect each particle and record its size and shape

14 Mixed Wood Pellets Particle Size

15 Mixed Wood Pellets Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 975 µm 787 µm 1105 µm 1201 µm Sphericity Symmetry Aspect Ratio Circularity

16 Eucalyptus Pellets Particle Size

17 Eucalyptus Pellets Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 705 µm 751 µm 1171 µm 958 µm Sphericity Symmetry Aspect Ratio Circularity

18 Miscanthus Pellets Particle Size

19 Miscanthus Pellets Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 1181 µm 813 µm 1069 µm 1377 µm Sphericity Symmetry Aspect Ratio Circularity

20 Sunflower Pellets Particle Size

21 Sunflower Pellets Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 1220 µm 757 µm 1145 µm 1523 µm Sphericity Symmetry Aspect Ratio Circularity

22 Olive Cake Particle Size

23 Olive Cake Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Particle Size d µm 1553 µm 589 µm 1461 µm Sphericity Symmetry Aspect Ratio Circularity

24 Steam Exploded Pellets Particle Size

25 Steam Exploded Pellets Particle Shape Characteristic Pre-milled Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 466 µm 346 µm 1412 µm 521 µm Sphericity Symmetry Aspect Ratio Circularity

26 Microwave Pellets Particle Size

27 Microwave Pellets Particle Shape Characteristic Planetary Ball Mill Bond Work Index Cutting Mill Ring-Roller Mill Particle Size d µm 888 µm 1091 µm 538 µm Sphericity Symmetry Aspect Ratio Circularity

28 La Loma Coal Particle Size

29 La Loma Coal Particle Shape Characteristic Planetary Ball Mill Bond Work Index Ring-Roller Mill Particle Size d µm 78 µm 402 µm Sphericity Symmetry Aspect Ratio Circularity

30 Particle Size & Shape Relationship

31 Project Findings Biomass Characterisation Pre-milled biomass pellets are composed of similar particle size distributions, but show a large variance in particle shape Standard coal abrasion index test does not work for biomass as it caused the apparatus to catch fire Standard Coal Grindability Test HGI is a poor indicator of the grindability of biomass in a vertical spindle mill Grindability tests which aim to analyse the grindability of biomass to 75µm are inappropriate should be informed by classifier settings BWI can be used replicate mill choking Biomass pellets should be composed of particles close to the required size

32 Project Findings 2 Olive Caking Olive caking phenomenon is associated with the pulp section of the material Sugar and moisture content of the pulp section are such that when milled a glass transition step occurs which results in the caking of the olive Olive cake fines below 1mm should be sieved out and sent directly to the burner and not comminuted Ring-Roller Mill Strong negative correlation was obtained between comminuted particle size and shape for mill with separator Biomass mill classifiers should be set to the Stokes number requirements for coal rather than a blanket particle size for all biomasses

33 Overall Project Findings The critical particle size for comminution through compression is key to understanding milling behaviour in different mills. By knowing a materials critical particle size and the target size of the specific biomass based on the classifier settings for a mill, it will be possible to tell: i. Whether or not a biomass pellet will break down easily within the mill ii. If the biomass particles which compose the pellet will need extra comminution to reach its required particle size for combustion iii. If the biomass particles will struggle to reduce in size if comminution is required due to their critical particle size being larger than the target particle size for combustion Milling had little impact on particle shape even when an order of magnitude difference was seen in the particle size. Particle shape is inherent to a pellet and is determined by the pre-densified comminution processes.

34 Future Work Follow on Engineering Doctorate currently under way with which is developing numerical models of biomass comminution based on the test results Development of a new standard test to quantify the abrasiveness of biomass in pneumatic conveying systems New HGI test for biomass which incorporates larger volumes and targets s Models to predict the required particle size for a classifier based on the physical characteristics of the pre-milled particles to inform grindability test Need to find the critical particle size for compressed fracture for biomass for all types of biomasses, and compared to the particle size distributions of disintegrated pellets Ring-roller mill: energy consumption and particle size correlations should be compared to those of the full scale Lopulco ring-roller mill at EDF West Burton and the pilot scale ring-ball mill at Doosan [5] for standard materials

35 Thank you for listening The authors would like to thank the University of Nottingham, the Biomass and Fossil Fuel Research Alliance (), and EDF Energy plc for their support during this project. Questions?

36 References [1] The British Standards Institution, BS : 1995 Methods for Analysis and testing of coal and coke Part 112: Determination of Hardgrove grindability index of hard coal. Milton Keynes: BSI. [2] Bond FC. The Third Theory of Comminution. Trans AIME 1952;193: [3] Williams, O., Eastwick, C., Kingman, S., Giddings, D., Lormor, S., & Lester, E. (2015). Investigation into the applicability of Bond Work Index (BWI) and Hardgrove Grindability Index (HGI) tests for several biomasses compared to Colombian La Loma coal. Fuel. [4] Mandø, M., Rosendahl, L., Yin, C., & Sørensen, H. (2010). Pulverized straw combustion in a low-nox multifuel burner: Modeling the transition from coal to straw. Fuel, 89(10), [5] Livingston, W. R., Horne, P. A., McGhee, B. F., Gibson, J. R., & Chakraborty, R. K. (1998). The Characteristics of Coal Blends -Milling Behaviour & Ash Fusion Temperatures