Mechanical degradation of wood pellets during long term stockpile storage

Transcription

1 Mechanical degradation of wood pellets during long term stockpile storage Shalini Graham (Final year EngD) Dr Carol Eastwick, Professor Colin Snape (University of Nottingham Efficient Fossil Energy Technologies Engineering Doctorate Centre) Dr Will Quick (E.ON Technologies (Ratcliffe Ltd.)) ECCRIA Conference, 16 September 2014

2 Contents Introduction Project objectives Methodology Experimental data capture Results and discussion Key messages Acknowledgements

3 Introduction Large scale use of wood pellets in decarbonising power generation which uses coal as a feedstock predicted to grow Challenges of wood pellet storage Formation of hot spots and self heating Emission of volatile gases Moisture intolerance Loss in pellet strength and stiffness Dust formation Handling and conveying issues

4 Project Outline 4

5 Methodology First set of pellet stock piles Apr 2011 Two thermally treated wood pellet piles (2.4x2.4x1.5m) indoor and outdoor 1.5m 1.5m 2.4m 2.4m 2.4m 2.4m 5

6 1.5m 1.5m Efficient Fossil Energy Technologies Methodology Second set of pellet stock piles Nov/Dec 2011 White wood pellet pile indoor (2.4x2.4x1.5m) New thermally treated wood pellet pile outdoor (2.4x2.4x1.5m) 2.4m 2.4m 2.4m 2.4 m 6

7 Experimental Data Capture In situ temperature and weather measurements Wind speed & direction Ambient temp & humidity o Monthly sampling (surface and middle of pile) o Mechanical tests (durability, shear and compression, SEM) o Chemical tests (thermogravimetric analysis, bomb calorimetry) o Biological tests (fungal count and identification) Rainfall

8 Chemical degradation Dry ash free calorific value, dry ash free volatile content and dry ash % show no significant variation with time in storage Moisture content varies significantly, impacted by weather

9 Mechanical degradation Phase 1 Fresh thermally treated pellets Reflected in durability, shear and compression tests and SEM Indoor pellets 3 months Outdoor pellets 3 months Outdoor pellets 12 months 9

10 Mechanical degradation Phase 2 Fresh thermally treated pellets Reflected in durability, shear and compression tests and SEM Outdoor pellets 3 months Outdoor pellets 6 months Outdoor pellets 12 months 10

11 Mechanical degradation Phase 2 Fresh white wood pellets Reflected in durability, shear and compression tests and SEM Indoor pellets 1 month Indoor pellets 4 months Indoor pellets 6 months 11

12 Structural changes in thermally treated pellets Phase 1 Circular cross section of fresh pellet April 2011 Circular cross section of degraded pellet from surface of outdoor pile October 2011 after six months in storage

13 Durability test Dural (II) tester (tumbler) Designed by the Agricultural Process Engineering Laboratory at the University of Saskatchewan and manufactured by McEwan Machining Ltd. 100g of pellets rotated at 1600 rpm for 30 seconds Then sieving in a 4.75mm sieve Durability = Oversize fraction x 100 Total sample weight

14 Durability % Efficient Fossil Energy Technologies Durability Phase Thermally treated pellet Apr-11 Aug-11 Dec-11 Apr-12 Aug-12 Dec-12 Outdoor surface Outdoor middle Indoor surface Indoor middle 14

15 Durability % Durability % Efficient Fossil Energy Technologies Durability Phase 2 90 Thermally treated pellet Middle Edge White wood pellets surface Sep Dec Apr Jul Oct Jan

16 Shear Thermally treated pellets phase 1 Three point force 5kN load cell, ramp rate 1mm/min 16

17 Shear thermally treated pellets phase 2 Three point force 5kN load cell, ramp rate 1mm/min 17

18 Mechanical degradation summarised Significant drop in pellet integrity for untreated white wood pellets in long term exposure to high humidity and heat For thermally treated wood pellets, loss in durability, pellet strength and stiffness lower than for white wood pellets. Mechanical degradation process also slower and more gradual Exposed thermally treated pellets on surface of pile degraded significantly more than those in the inner core of pile 18

19 Main conclusions on wood pellet storage No significant temperature variations in wood pellet piles Both pellet types showed no sign of chemical degradation Severe mechanical degradation of white wood pellets Thermally treated pellets ok for indoor storage In outdoor storage, significant mechanical degradation on surface of pile Weather/season impacts mechanical strength 19

20 Acknowledgements Research Councils UK (RCUK) E.ON Technologies (Ratcliffe) Ltd. Efficient Fossil Energy Technologies (EFET) Engineering Doctorate Centre

21 Thank you for your attention Questions are welcome 21