PRESENTATION. Ignition Risk of Biomass Dust Layers. The Fuel and Energy Research Forum. - Washing Pre-treatment on Low Temperature Ignition of Biomass

Transcription

1 The Fuel and Energy Research Forum PRESENTATION Ignition Risk of Biomass Dust Layers - Washing Pre-treatment on Low Temperature Ignition of Biomass Yee Sing Chin Jenny M Jones Slide 1 of 19

2 Background/Introduction Biomass with increase usage of renewables, UK power sector reduced carbon emissions by 13% between * a promising renewable energy source for power generation a reactive solid fuel capable of self-heating, eventually self-ignition, leading to catastrophic fire * REF: Energy in the UK 2016 Delivering jobs, growth and choice through sustainable investment in 2015 Slide 2 of 19

3 Background/Introduction History of biomass fires Motivation: ~ fires related to biomass selfcombustion and ignition of combustible biomass dust had led to growing interest in this research area Port of Tyne South Shields RWE npower, Tilbury Pinnacle Pellet in Armstrong, British Columbia Fire Incidents Laurinburg Nature Earth Plant, North Carolina Shur Fire Energy Norwich Port of Tyne Slide 3 of 19

4 Methodology Experiments & Analyses are in accordance with: BS Electrical Apparatus for Use in the Presence of Combustible Dust Part 2-1: Test Methods Methods of Determining Minimum Ignition Temperature Procedure of determining T LIT * T LIT (minimum layer ignition temperature) BS Electrical apparatus for use in the presence of combustible dust Part 1-2: Electrical apparatus protected by enclosures Selection, installation and maintenance Relating T LIT with MPST * MPST (maximum permissible surface temperature) Slide 4 of 19

5 Methodology Pre-treating Biomass Water-washing pre-treatment - 1g Biomass : 5 ml Distilled Water rpm agitation speed - 60 minutes Slide 5 of 19

6 Methodology Adhering to BS EN Hot Plate Temperature Uniformity Check Free from draught Hot plate Dust Layer Experiment 16 points temp. check hot plate temperature is uniform Slide 6 of 19

7 Methodology Adhering to BS EN Dust Layer TC Adjustment Nut Inconel Shielded TC Ring B, 12.5 mm height Ring A, 5 mm height Slide 7 of 19

8 Methodology Dust Layer Ignition Experiment* Materials Preparation BS: Materials pass through 200 µm aperture This study: materials milled & sieved using 180µm sieve Equipment Placement & Setup Fume Extraction Dust Layer Rig * BS EN Electrical Apparatus for Use in the Presence of Combustible Dust Part 2-1: Test Methods Methods of Determining Minimum Ignition Temperature. Slide 8 of 19

9 Methodology Dust Layer Ignition Experiment Experimental Procedure Hot plate set at estimated ignition temperature Fill ring cavity & level off (all within 2 minutes) Timer & recorder started once dust is levelled off Ignition lowest temperature when visible glow is seen ~ T LIT Experiments in multiples of 10 o C, fresh dust each time Ignition delay time time recorder is started to time glow is observed ~t ig!!! If no ignition observed, wait for minimum 30 minutes, repeat another 2 times as confirmation Slide 9 of 19

10 Results & Discussion - Washing T LIT & t ig of 8 Water-Washed Materials vs Parent Materials Parent materials, Pine & Miscanthus 90wt%Pine:10wt%Miscanthus 50wt%Pine:50wt%Miscanthus Washed Parent material Washing effects: Increased the T LIT by C - 20 C for parent materials - 10 C for blended materials Washed 90wt%Pine:10wt%Miscanthus Washed 50wt%Pine:50wt%Miscanthus Slide 10 of 19

11 Results & Discussion - Washing Acid Digestion dissolving an untreated sample into its constituent elements with acid & heat reactions H 2 SO 4 & HNO 3 acid digest miscanthus & pine Focus: Potassium & Calcium elements that are well known for causing fouling at heat convective boiler regions. Slide 11 of 19

12 Results & Discussion - Washing Atomic Absorption Spectroscopy (AAS) quantification of constituent elements Acid digestates determine concentrations of two major problematic metal elements, K and Ca that occurred naturally in biomass Slide 12 of 19

13 Results & Discussion - Washing Distilled Water Washing - Solid residue taken dust layer test after drying - Leachates taken for Ion Chromatography (IC) Slide 13 of 19

14 Results & Discussion - Washing Ion Chromatography IC on leachates check elements washed out (removed) from biomass washing Slide 14 of 19

15 Results & Discussion - Washing Concentration (mg/kg of Dry Fuel) in Untreated Fuels (AAS Analysis) and K, Ca, and Cl Removed (mg/kg of Dry Fuel) during Water Washing (IC Analysis of Leachates) In Fuel (mg/kg of Dry Fuel) Removal (mg/kg of Dry Fuel) K Ca K + % K Ca 2+ % Ca Cl - PineC Misc(1) decrease of reactivity in washed biomass (increased T LIT ) was due to catalytic potassium and calcium elements being washed out of the biomass Slide 15 of 19

16 Results & Discussions Risk Ranking Thermogravimetric Analysis (TGA) self-ignition risk ranking (E a, T MWL ) 4 Risk Categories: Low risk Medium risk High risk Very high risk * Ramírez, A. et al Experimental Determination of Self-Heating and Self-Ignition Risks Associated with the Dusts of Agricultural Materials Commonly Stored in Silos. Journal of Hazardous Materials. 175, pp Slide 16 of 19

17 Results & Discussions Risk Ranking Self-Ignition Propensity Risk Ranking - by TGA slow combustion * Jones, J.M. et al Low temperature ignition of biomass. Fuel Processing Technology. 134, pp Slide 17 of 19

18 Results & Discussions MPST Industrial Application Maximum permissible surface temperature (MPST) of an equipment ~ prediction for 12.5 mm thick dust deposits MPST Estimation with Three Different Methods: Points T LIT less 75K Curves BS*, 5 mm T LIT Constant at 150 C Power Station Practice * BS EN Electrical apparatus for use in the presence of combustible dust Part 1-2: Electrical apparatus protected by enclosures Selection, installation and maintenance Slide 18 of 19

19 Conclusion Solid fuel biomass dust deposited on hot surfaces T LIT of different species is confined within a narrow range Removal of potassium element that is catalytic to combustion upon washing pre-treatment did make the fuel slightly safer with T LIT increase but still showed high self-ignition risk after washing pre-treatment Treating the MPST as 75K less than T LIT was the most lenient for thin deposits and 150 C was most conservative for thin deposits; as dust thickness increases, the 150 C became the most lenient, opposite to when deposits are thin MPST strongly depends on the situation, but regardless of this, thicker dust layers are more hazardous in terms of ignition risk Slide 19 of 19