The Fuel and Energy Research Forum SCAPE PRESENTATION · The Fuel and Energy Research Forum SCAPE...

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SCAPEThe Fuel and Energy Research Forum

Ignition Risk from Biomass Dust Layers

PRESENTATIONThe Fuel and Energy Research Forum SCAPE

Ignition Risk of Biomass

Dust Layers

- Washing Pre-treatment on Low

Temperature Ignition of Biomass

Yee Sing ChinJenny M Jones

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Background/Introduction

• Biomass

– with increase usage of renewables, UK power sector reduced carbon emissions by 13% between 2014-2015*

– 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

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Background/Introduction

• History of biomass fires…

Fire Incidents

2011

- Pinnacle Pellet in

Armstrong, British

Columbia 2011

- Shur Fire Energy

Norwich

2011

- Port of Tyne2012

- Laurinburg Nature’

Earth Plant, North

Carolina

2012

- RWE npower , Tilbury

2013

- Port of Tyne South

Shields

Motivation:

~ fires related to biomass self-combustion and ignition of

combustible biomass dust had led to growing interest in this

research area

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Methodology

• Experiments & Analyses are in accordance with:– BS 50281-2-1 Electrical Apparatus for Use in the Presence

of Combustible Dust – Part 2-1: Test Methods – Methods of Determining Minimum Ignition Temperature

– BS 50281-1-2 Electrical apparatus for use in the presence of combustible dust — Part 1-2: Electrical apparatus protected by enclosures — Selection, installation and maintenance

Procedure of determining TLIT

* TLIT (minimum layer ignition temperature)

Relating TLIT with MPST* MPST (maximum permissible surface temperature)

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– Water-washing pre-treatment

Methodology

Pre-treating Biomass

- 1g Biomass : 5 ml Distilled Water- 500 rpm agitation speed- 60 minutes

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Methodology

Hot Plate Temperature Uniformity Check

Hot plate

Dust Layer Experiment

Free from draught

↑ 16 points temp. check – hot plate temperature is uniform

Adhering to BS EN 50281-2-1 ……

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Methodology

Ring A, 5 mm height

Ring B, 12.5 mm height

Dust Layer TC

Inconel Shielded

TC

Adjustment

Nut

Adhering to BS EN 50281-2-1 ……

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Methodology

• Dust Layer Ignition Experiment*

Materials Preparation

Equipment Placement &

Setup

• BS: Materials pass through 200 µm aperture• This study: materials milled & sieved using 180µm sieve

Dust Layer Rig

Fume Extraction

* BS EN 50281-2-1. Electrical Apparatus for Use in the Presence of Combustible Dust – Part 2-1: Test Methods – Methods of Determining Minimum Ignition Temperature.

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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 ~ TLIT

• Experiments in multiples of 10oC, fresh dust each time• Ignition delay time – time recorder is started to time glow is

observed ~tig

!!! If no ignition observed, wait for

minimum 30 minutes, repeat another 2

times as confirmation

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Results & Discussion - Washing

• TLIT & tig of 8 Water-Washed Materials vs Parent Materials

Washing effects:

Increased the TLIT

by 10-20˚C

- 20˚C for parent materials- 10˚C for blended materials

Parent materials, Pine & Miscanthus

Washed Parent material

Washed 90wt%Pine:10wt%Miscanthus

Washed 50wt%Pine:50wt%Miscanthus

90wt%Pine:10wt%Miscanthus

50wt%Pine:50wt%Miscanthus

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• Acid Digestion – dissolving an untreated sample into its constituent elements with acid & heat reactions

↑ H2SO4 & HNO3 acid digest miscanthus & pine

Focus: Potassium & Calcium elements that are well known for causing fouling at heat convective boiler regions.

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• 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

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• Distilled Water Washing

- Solid residue taken dust layer test after drying

- Leachates taken for Ion Chromatography (IC)

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• Ion Chromatography

↑ IC on leachates – check elements washed out (removed) from biomass washing

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- decrease of reactivity in washed biomass (increased TLIT) was due to catalytic potassium and calcium elements being washed out of the biomass

In Fuel (mg/kg of Dry Fuel)

Removal (mg/kg of Dry Fuel)

K Ca K+ % K Ca2+ % Ca Cl-

PineC 342 584 130 38 19 3 31

Misc(1) 2998 5409 2709 90 1017 18 2781

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)

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Results & Discussions – Risk Ranking

• Thermogravimetric Analysis (TGA) – self-ignition risk ranking (Ea, TMWL)

* Ramírez, A. et al. 2010. 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.920-927

4 Risk Categories:

Low risk

Medium risk

High risk

Very high risk

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Results & Discussions – Risk Ranking

• Self-Ignition Propensity Risk Ranking

* Jones, J.M. et al. 2015. Low temperature ignition of biomass. Fuel Processing Technology. 134, pp.372-377

- by TGA slow combustion

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Results & Discussions – MPST

• Industrial Application – Maximum permissible surface temperature (MPST) of an equipment

* BS EN 50281-1-2. Electrical apparatus for use in the presence of combustible dust — Part 1-2: Electrical apparatus protected by enclosures — Selection, installation and maintenance

MPST Estimation with Three Different Methods:

• Points – TLIT less 75K• Curves – BS*, 5 mm TLIT

• Constant at 150°C – Power Station Practice

~ prediction for 12.5 mm thick dust deposits

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Conclusion

• Solid fuel biomass dust deposited on hot surfaces …– TLIT 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 TLIT increase but still showed high self-ignition risk after washing pre-treatment

– Treating the MPST as 75K less than TLIT 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

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