Ash utilisation - Startsidamzevenho/portfolj/undervisning... · Fly- and bottom ash Bottom ash –...

Ash utilisation

This lecture

Ash utilisation Biomass ash recirculation: Why, How? Problems with ash utilisation

ASH UTILISATION

http://www.varmeforsk.se/files/program/askor/Korpijrvi_workshop_Finland.pdf

Different boilers produce different types of ash

Boiler Bottom ash (%) Fly ash (%)Grid 70-80 20-30

Spread Stoker 40-50 50-60

CFB 10-20 80-90

http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf

Utilisation of ash


Utilisation of ash in Finland

50 000 – 80 000 t/a in cement production (coal fly ash) 50 000 t/a as binder material in concrete production (coal fly

ash) 20 000 t/a as filler in asphalt (coal fly ash) 40 000 t/a as fertilizers in forests 30 000 in agriculture (wood, peat and biomass ashes) Earth construction applications ~ 250 000 (?) t/a Lot of ashes are used in construction of landfill sites, storage

fields etc.


ASH UTILISATIONBiomass ash

http://www.energiaskor.se/pdf-dokument/presentationer%202006/Belgrad%20Sv%20EA.pdf

What is soil?

Mineral particles

Organic materialAirWater Root hair

Fungi myceliaBacteriaSoil organisms

0.2 mm

Cation exchange

The amount of acid substances increases in the soil fluid

Soil

part

icle

s

Nutrients are forced out from the soil participles into the soil fluid Soil fluid

Growth mediated acidification

Soil fluid Roots

The absorption of positively charged nutrients > the absorption of negatively charged nutrition

The absorption of nutrients is acidified

Acidification becomes permanent if the biomass is harvested

Deposition

WeatheringHarvest

Leakage

Mass balance

Mass balance account:Weathering + Deposits = Harvest + Leakage

Risk of acidification if:Weathering + Deposits < Harvest + Leakage

Mass balance

Potential effects of acidification

• Acid groundwater with increased levels of e.g.aluminium and cadmium

• Leakage of acid substances and heavy metals such as aluminium into lakes and watercourses

• Leaching of nutrients from the soil • Effect on terrestrial flora• Effect on future stand growth

http://www.energiaskor.se/pdf-dokument/presentationer%202006/Belgrad%20Sv%20EA.pdf

Fly- and bottom ashBottom ash– pH 10-11– Poor lime effectiveness– Higher content Si and Al(sand)

Fly ash– pH 12-13– Good lime effectiveness – Higher content K and S(volatile)

– Higher content heavy metals– Higher content unburntorganic material

Bottom ash from grid boilers Fly ash from CFB and spread stoker boilers Smaller stations often mix these

Recyclable ash

What is in the ash?Ash from FR contains:• the bulk of the nutrients originally found in

the FR (not nitrogen).• carbon • heavy metals+Cs• polyaromatic hydrocarbons (PAH)• Basic cations

and trace elements OxidesHydroxidesSulphatesChloridesSilicatesCarbonatesPhosphates


Limits for ash utilisation in agriculture-Finland

Ash is very soluble= leaches tooeasily

Technology

• Rotating concrete mixers, or with knives to break up the aggregate.

• Horizontal cylinder with a rotating shaft where shovels/blades have been fitted (similar to a helical conveyer).

• Paddle mechanism where mixing is carried out with shovels or blades.

Ash treatment – adding water

Hardening process

Oxides in the ash

Hydroxides and carbonates

Secondary mineral such as ettringit

Examples:CaO Ca(OH)2 CaCO3

Hardening means that:

A reduced solubility rate and reduced risk of damage to soil and vegetation

• The ash is less soluble • The pH of the ash is lowered • The particle size increases

Self-hardening in heaps - the most common method

Ash treatment – crushing & sifting

Ash treatment - pelleting

T Claesson, 2004, Kalmar Högskola [University of Kalmar]

Ash treatment - granules

+ A more unified, homogeneous product+ A more stable product + The products are easier to spread

- involve heavy investment - higher operating costs

Granulation and pelleting

Ash analysis

Before treatment

Unburnt material

Nutrients and heavy metals

Possibly Caesium and PAH

After treatment Solubility rate

Texture and water content

Ash recirculation

What happens to the ash in the soil?

Soi

l par

ticle

Lime effectiveness

Ca2+

Mg2+

K+

H+

------

H+

Ca2+

Al3+ Acid substance neutralised pH raised

ash

Positive effects of spreading ash

• Reduced leakage of acid water and water containing aluminium into lakes and watercourses.

• Compensation for the nutrition and lime effects lost due to the removal of FR

• The continual removal of forest fuel may increase -the use of fossil fuels may diminish

• The cycle of nutrients is completed. Ash becomes a resource and not waste.

• Resistance to soil acidification increased.

Risks when spreading ash• Increased amount of traffic with an increased risk

of vehicle damage to soil and roots. • Poorly stabilised ash products can cause damage

to vegetation.• Stable ash products can cause scorching of tree

trunks.• In some poorer areas, there may be a risk of

reduced accretion since the availability of N is reduced.

• If the wrong sort of ash is recycled, there is a risk of build-up of heavy metals and other toxic substances in the soil.

Examples of damage to vegetation

Legislation in Finland

Regulated by Fertilizer Product Act 539/2006 & Ministry of Agriculture and Forestry Decree on Fertlizer Products 24/11& Ministry of Agriculture and Forestry Decree on the operations concerning fertilizer products and their suppervision 13/07

Fly and bottom ashes from combustion of biomass and peat Maximum values for minor elements Maximum loads for Cd and As Minimum values for nutrients

– Forestry: K+P 2 % & Ca 6 %– Other use: Neutralising value 10 % (Ca)– Addition of nutrients in the form of inorganic fertilizers

products is allowed to granulated ash fertilizers


Problems on the horizon

Ash from combustion and incineration may fall under the new European Union regulations REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) and CLP (Classification, labelling and packaging of substances and mixtures).

This lecture Why ash utilisation

– Ash is not a waste but can be a product with value– Nutrients from woods need to be replaced– De-acidification

Biomass ash recirculation: – Check composition and mobility of ash elements-

manipulating chemical properties– Make ash spreadible easily with machines-

Manipulating physical properties– Spreading in woods

Other possibilities– Concrete– Filler material in roads, landfills etc.

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