Ash utilisation - Startsidamzevenho/portfolj/undervisning... · Fly- and bottom ash Bottom ash –...
Transcript of 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
http://www.varmeforsk.se/files/program/askor/Korpijrvi_workshop_Finland.pdf
Utilisation of ash
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
http://www.varmeforsk.se/files/program/askor/ECN_Pels_final.pdf
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.
http://www.varmeforsk.se/files/program/askor/Korpijrvi_workshop_Finland.pdf
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
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
http://www.varmeforsk.se/files/program/askor/Korpijrvi_workshop_Finland.pdf
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
http://www.varmeforsk.se/files/program/askor/Korpijrvi_workshop_Finland.pdf
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.