THE WOLFSON CENTRE for Bulk Solids Handling Technology STORAGE, HANDLING AND FLOW OF BIOMASS MATERIALS A Review Mike Bradley Rob Berry 0000

THE WOLFSON CENTREfor Bulk Solids Handling Technology

STORAGE, HANDLING AND FLOW OF BIOMASS MATERIALS

A Review

Mike Bradley

Rob Berry

0000

What is biomass?

Organic wasteSewage sludge, shredded refuse

“Coproducts”, “Residues”Waste but avoiding the “W” word!

From food, agricultural, or forest / timber / paper processing

Straw, bits of tree, olive stones etc.

Energy cropsChipped wood, cut elephant grass

The Wolfson Centrefor Bulk Solids Handling Technology

Cereal coproduct: wheatfeed pellets

Pellets and fines

Rounded

Like any other free-flowing bulk solid


Milled nuts

Sticky, cohesive

Particles roughly rounded

Like any other cohesive bulk solid


Chopped straw

Long, stringy particles

Special behaviour


Miscanthus (elephant grass)

Long, stringy particles again

Special behaviour


Forest residue

Long, stringy particles again

Special behaviour

Other examples

Horse or poultry bedding

Whole pallets

Wet leaves

Meat waste

Features

Biomass is not one material!

All different handling properties

No one handling system can deal with all biomass (economically)

Special characterisation techniques available

Biomass macro-economics

Renewable energy costs more

Currently adds around £20 to the household annual power bill

Target is to rise to £50 when about 20% of our power from renewables

Sustainability of biomass depends on cross-subsidy from fossil fuels


The ROCs system

The Renewables Obligation

ROC = Renewables Obligation Certificate

Granted for a certain quantity of power produced from certified renewables (1MWh = 1000 “units”)

Each generator must show a target proportion of their output from renewables

Proof is in submission of ROCs at end of year


ROC trading Generators with a surplus of ROCs can sell them

Those who haven’t earned enough can buy

The market fixes the price

Allows “dirty” generator to carry on making cheap electric from fossil fuels

Whilst they subsidise the “green” generators using wind, biomass etc

ROC bandingOr “When is a ROC

not a ROC?”

More costly renewables are given more ROCs to subsidise themOffshore wind 2

Solar PV 2

Cheaper ones given less ROCsBiomass co-firing 0.5

Conversion of existing power plants from fossil to biomass 1.5 but falling to 1


ROC rebanding

October 21 2011:

Proposed changes to how many ROCs issued per MWh of generation:

http://www.decc.gov.uk/en/content/cms/news/pn11_85/pn11_85.aspx




Renewable electricity technologies Current support, ROCs/MWh[1] Proposed ROC support/MWh[2] Other proposed changes

Advanced gasification 2

2 in 2013/14 and 2014/15; 1.9 in 2015/16 and 1.8 in 2016/17

Call for evidence

Proposed change to definition and merger with advanced pyrolysis

Advanced pyrolysis 2

2 in 2013/14 and 2014/15; 1.9 in 2015/16 and 1.8 in 2016/17

Call for evidence

Proposed change to definition and merger with advanced gasification

Anaerobic digestion 2 2 in 2013/14 and 2014/15; 1.9 in 2015/16 and 1.8 in 2016/17

Biomass conversionNo current band but eligible to claim 1.5ROCs under current banding arrangements

1Call for evidence

Proposal for a new band.

Co-firing of biomass 0.5 0.5 Changes proposed to add fossil derived bioliquids.

Co-firing of biomass (enhanced)No current band but 0.5 ROCs under current banding arrangements

1Call for evidence

Proposal for a new band.

Co-firing of biomass with CHP 1 1Changes proposed to add fossil derived bioliquids, to exclude enhanced co-firing and to close this band to new accreditations from 1 April 2015.

Co-firing of energy crops 1 1Changes proposed to the definition of energy crops and to exclude enhanced co-firing.

Co-firing of energy crops with CHP 1.51.5

Call for evidence

Changes proposed to the definition of energy crops, to exclude enhanced co-firing and to close this band to new accreditations from 1 April 2015.

Dedicated biomass 1.51.5 to 31 March 20161.4 from 1 April 2016

Changes proposed to exclude biomass conversions and to add fossil-derived bioliquids

Dedicated energy crops 22 in 2013/14 and 2014/15; 1.9 in 2015/16 and 1.8 in 2016/17

Changes proposed to the definition of energy crops and to exclude biomass conversion.

Dedicated biomass with CHP 2 2 in 2013/14 and 2014/15Changes proposed to add fossil derived bioliquids, to exclude biomass conversion and to close this band to new accreditations from 1 April 2015.

Dedicated energy crops with CHP 2 2 in 2013/14 and 2014/15Call for evidence

Changes proposed to the definition of energy crops, to exclude biomass conversion and to close this band to new accreditations from 1 April 2015.

Energy from waste with CHP 10.5Call for evidence




Handling and storage issues with biomass

Low density – so large quantities

Poor flow – and all different

Dust emission

Bio-activity – may self-heat

Sensitivity to water – need to keep dry


Energy density by volume

0 5000 10000 15000 20000 25000 30000

Coal

Wood chips (30%MC)

Log w ood (stacked -air dry: 20% MC)

Miscanthus (bale -25% MC)

Wood pellets

Volumetric energy density MJ/m3


Bulk density of raw biomass fuels

Govt of Ontario

Fundamental Issues;Dust Emission

Many biomasses contain high dust levels and have great potential to emit that dust

“Surface dry” at high moisture (even 20%) Coal saturated at about 6% Coal itself becomes more dusty when co-

handled with biomass

Also have lower density and more complex particle shapes

Varies within “same” material in specification


Key dust hazards:

Health

Explosion risk

Mess

Inhalation of Biomass Dust

More mobile than coal dust

Stays suspended better than coal dust

Much greater health danger than coal dust Danger of “Farmer’s Lung”

(Alveolitis) Common in those handling biomass

in agriculture Can stimulate allergic reaction Long term exposure can be

debilitating

Aspergillus Mould

Grows freely on organic matter at +14% moisture approx.

Commonly present still on materials that have been dried

Principal pathogen for Alveolitis

Many other hazardous moulds found in biomass

Wet cleaning and wet dust suppression MUST NOT be used!

E.g. Spilt maize attracted dampness

Mouldy in a few days

Dusty areas must be kept dry

Dust must be kept inside

Reducing dust emission

Mainly at transfer points

Covers required Must be easy to open AND CLOSE! (For

maintenance)

Dust extraction NOT a panacea for inadequate enclosure Poor enclosure will greatly increase air volume to be

extracted

Chute designs

Enclosure of towers Keeping draughts out!


“Hood and Spoon” design

Gentle transfer to avoid knocking dust out of flow

Design curve to suit particle trajectory

Adjustment needed on site

Definitely NO wet sprays!

Martin Engineering

The importance of housekeepingPrimary explosions

initiated by ”ignition sources”Localised, small

Secondary explosions initiated by primary explosions.Utter devastation

Diagram: Dave Price, Gexcon

Dust layershow much dust is too much?

1 mm dust layerfull ceiling height = 5 m, 100 g/m3, ”ceiling height" = 1 m 500 g/m3.

Well into the explosible range!

Calc’s and diagrams by Dave Price, Gexcon


Secondary explosion – utter devastation


Design to aid good housekeeping

1mm of dust?

Open flooring


Sheet over “girts” or add sloping dust-

shedder plates


Dust refuges on top of cabinets

Again, add shedders


Keep heat sources clean

Or risk smouldering fires leading to ignition


Core Flow:Undesirable for

biomass in some circumstances

Flow from top of material

Static material

Discharge through

central flow channel

“first in last out” discharge

“dead” regions of product

erratic discharge caused by product on product shear during emptying

central discharge channel

exaggerates segregation effects of particles

hopper half angle shallower

poor stock rotation

Caking and biological spoilage

high storage capacity for a given headroom – but often not all can be discharged

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Mass flow:Desirable for

biomass

“first in, first out” discharge

all storage capacity is “live”

consistent discharge encouraged by the reduced levels of shear generated as the product discharges against relatively smooth wall material - not static product

degree of remixing during discharge minimises segregation effects

hopper half angle relatively steep – depends on biomass and surface

relatively lower storage volume for a given headroom - but all the product can be retrieved

Requires well designed feeder interface

All material in motion during discharge

Shear occurring at

walls of vessel

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Sometimes the powder flow properties and the equipment design are just not compatible!

2004: Three distinct types of biomassfrom a HANDLING point of view

“CLASS 1”: Rounded particles, free-flowing: Pellets and dry powders (not too fine)

“CLASS 2”: Rounded particles, cohesive: Milled nuts, wet powders; fine powders

“CLASS 3”: Flaky/stringy particles – extreme shape: At least one dimension much smaller than other two!

Chopped straw and grass;

Sawdust, wood shavings, chicken litter

Shredded paper or plastic;

Many wastes from sheet material

Herbaceous materials


Core flow bins with non-free-flowing

materials

Tendency to rat-hole

Not recommended for class 2 or class 3 materials!


Planetary screw discharger


Push floor (sliding frame) discharger

Hydrauliccylinder

Reciprocating framework

Dischargescrew


Push floor discharger

1. Hydraulic Power Pack2. Rear Beam for Cylinder Mounting3. Hydraulic Cylinders4. Push Elements5. Levelling Screw6. Discharge Head7. Metering Discharge Screw8. Fall Chute

Picture:

Saxlund International


Problems with full-live-bottom for flaky/stringy (“class 3”) biomass

High stress at base

Creates great strength in material

High forces on mechanism

Severe wear and screw breakage In planetary or multiple screw machines

Need wide, shallow bunker In sliding-frame type machine

Great expense to get ruggedness needed!


Mass flow as a cheaper option Many “class 3” biomasses

have moderate wall friction Especially against UHMW-

polyethylene lining Mass flow at reasonable

angle

Low stress at outlet Flow occurs by relieving

stress, not by increasing it! Reduced load on feeder

Smaller feeder


Wedge-shaped mass flow bin

Twin screw outlet

Very steep walls for highly frictional material

Most cases do not need such steep walls!


Pelletisation of biomass

Reducing delivery cost

Reducing handling challenges

Reduced variation in handling properties

Lower project cost

Case study:pelletisation versus

chip 10,000 tpa of wood

Delivered 10 miles

Using 8-wheel tipper (body 15m3)

Assumptions: Fuel consumption 6mpg fully loaded, 12mpg lightly loaded Diesel £1.35 per litre Driver cost £24/hr Average speed 15 mph Ignore purchase and depreciation

Pelletiser

5.5kW motor

Produces 0.5 tph

Electricity cost £0.09/kWh11kWh/tonne x 10,000 tonnes x £0.09/kWh

= £9,900 pa electricity cost

Milling energy ignored


Transport costs - for 10 miles delivery

For a transport distance of 10 milesTransport costs: chip pelletisedBody capacity 15 m3Bulk density 180 600 kg/m3Hence actual weight per delivery 2.7 9 tonnesDeliveries per annum 3704 1111 deliveriesMiles light 74074 11111Miles fully loaded 11111Diesel used pa 6173 2513 gallonsCost of diesel £37,500 £15,268 £ paDriver hours per delivery 0.67 0.67Driver hours pa 2469 741Driver cost per hour £24.00 £24.00Driver cost pa £59,259 £17,778Cost of pelletising £0 £9,900 £paTotal costs £96,759 £42,946Transp. & proc. cost per tonne £9.68 £4.29


Characterisation – more critical for biomass

Flow properties

Dustiness testing

Friction

Density

Caking

Moisture

Size and shape

Explosibility


Choice of biomass cases for design

No one system will handle all biomass materials

But experience shows that systems designed for one biomass will soon be burning another!

Consider this in design


Plan for the long term

Change in fuel portfolio is a given

Allow space for retrofit



Contents of the Guide

Coverage: Biomass handling and biomass/coal co-handling

Part I: Basic problems

Part II: Guide to practice on existing coal-handling installations gearing up for biomass

Part III: Guide to practice for new installations

THE WOLFSON CENTREfor Bulk Solids Handling Technology

University of Greenwich

Medway School of Engineering

Tel 020-8331-8646: Fax 020-8331-8647

www.bulksolids.com

Documents

THE WOLFSON CENTRE for Bulk Solids Handling Technology STORAGE, HANDLING AND FLOW OF BIOMASS MATERIALS A Review Mike Bradley Rob Berry 0000