GRINDABILITY OF BIOMASS FOR FUEL APPLICATIONS

SIMON LEISER AND ANDRE VAN ZOMEREN

• Grindability is important to estimate time and energy needed for industrial grinding of biomass for energy

• No established grindability test for (non-torrefied) biomass

• Hardgrove index is limited to very brittle materials and specific mills (ring/roller/ball mills)

• Required fuel specs are different for (torrefied) biomass than required by HGI procedure (for coal)

• No grindability index for (torrefied) biomass available for typically used mill types (i.e. hammer mills)

• TNO method for non-torrified biomass: relatively easy and simple to use

• Potential for international standard within ISO/TC238/WG4 to complement the existing draft standard (ISO/AWI

21596- Hardgrove type method for thermally treated biomass fuels)

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BACKGROUND

TNO GRINDABILITY TEST METHOD (1)

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• Principle:

• based on a cutting mill RETSCH SM 2000

with a nominal electric capacity of 2 kWe

• motor rpm kept constant and

active power consumption registered

• milled product is then (dry) sieved

• result: curves relating the specific power

consumption with the particle size

distribution

• Quick and easy procedure

• Batches of 250 gram of sample are ground

with cutter mill to 4 different particle size

distributions (PSD)

• Product PSD is determined

• Integration of active mill power

consumption yields specific grinding energy

as function of product fineness

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TNO GRINDABILITY TEST METHOD (2)

Condux HM23/20/N5 hammer mill with nominal electric power of 4 kWe

Used for testing, validation and “production”

Equipped with active power consumption measurement and weighing equipment

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TNO GRINDABILITY TEST METHOD (3)

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TNO GRINDABILITY TEST METHOD: RESULTS

• PAL industrial bench scale hammer mill

• 25 kWe, throughput ~1.5 t/h pellets

• 4 industrial wood pellet types were tested with

two different millings (sieve sizes)

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TNO GRINDABILITY TEST METHOD:

VALIDATION AGAINST INDUSTRIAL HAMMER MILL (1)

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TNO GRINDABILITY TEST METHOD:

VALIDATION AGAINST INDUSTRIAL HAMMER MILL (2)

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TNO GRINDABILITY TEST METHOD:

VALIDATION AGAINST INDUSTRIAL HAMMER MILL (3)

Validation against industrial scale hammer mill

Validation against ring and ball/ vertical spindle mill

Correlation with Hardgrove Index

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TNO GRINDABILITY TEST METHOD: FUTURE

New method was developed for grindability of (non-torrefied) biomass

Very good agreement between comminution data from cutter mill and hammer mill, despite:

• Batch grinding vs. continuous operation

• Cutting vs. impaction milling

Further validation of grindability test for dedicated biomass mills, i.e. hammer mills and vertical

spindle mills

New method is complementary to grindability measurement for torrefied materials for use in PF

mills and hammer mills

Applications in both energy and biorefinery markets possible

Potential for development of international standard within ISO/TC238/WG4. Feedback needed from

mirror committee

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CONCLUSIONS

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