Circular economy What comes around goes around. This lecture. Ash utilisation

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1 Circular economy What comes around goes around European parliament Circular economy "closing the loop" of product lifecycles through greater recycling and reuse, making better use of raw materials, products and waste, and therefore shifting away from the more conventional but unsustainable linear economy. A circular economy keeps products and materials at their highest utility and value, with benefits for both the economy and environment. The circular economy: practical steps to enhance the EU package Mauro Anastasio October 2016 This lecture Ash utilisation Maria Zevenhoven March 2017 Amount of ash Properties Ash utilisation Coal ash Waste ash Biomass ash 1

2 How much ash? Waste ash Co-combustion ash Bio ash ASH UTILISATION Coal ash Ash forming matter Coal Waste Composition of ash Wood The presence of Cadmium (Cd) and to a lesser extent Zink (Zn) in ash is of particularly relevance due to its potential environmental impacts. About 35 to 65% of the total amount of Cd and 35 to 55% of Zn in the ash is concentrated in the fine fly ash fraction of fixed bed furnaces. 2

3 Composition of ash Composition of ash Significant differences in the nutrient and heavy metal content between bottom ash, coarse fly ash and fine fly ash. Volatile heavy metals such as Zn, Pb and Cd as well as the semi-volatile nutrient K in the fine fly ash, Non-volatile elements like Ca, Mg, Si, show the highest concentrations in the bottom ash. Combustion temperature in fluidized bed furnaces is usually lower (between 800 and 900 C) than in fixed bed furnaces (900 to 1,050 C) -> the enrichment of volatile elements in the fly ash fractions of fluidized bed furnaces is less pronounced compared to fly ashes from fixed bed furnaces. Temperatures in pulverised coal furnaces are highest. Most ash released as fly ash Trace metals in fuels Ash properties Ivan Deviatkin, Jouni Havukainen, Mika Horttanainen Optimal Recycling Combination of Ash in South-East Finland ARVI Material Value Chains,

4 Properties of ash Different boilers produce different types of ash ash Total and leachable heavy metals contents are the major environmental parameters Forest fertilization content of nutrients, neutralizing value, ph, etc.), Civil engineering content of heavy metals, content of CaO, particle size distribution, etc. Ivan Deviatkin, Jouni Havukainen, Mika Horttanainen Optimal Recycling Combination of Ash in South-East Finland ARVI Material Value Chains, 2016 energia.fi/files/397/tuhkien_tilastokysely_2014_loppuraportti.pdf Leachibility of ash COAL ASH F1 water-soluble fraction (H2O, ph=4), F2 exchangeable fraction (CH3COOH), F3 easily reduced fraction (NH2OH-HCl), F4 oxidizable fraction (H2O2 + CH3COONH4), and F5 residual fraction (HF + HNO3 + HCl) Ivan Deviatkin, Jouni Havukainen, Mika Horttanainen Optimal Recycling Combination of Ash in South-East Finland ARVI Material Value Chains,

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6 WASTE ASH 6

7 MSW bottom ash production MSW ash composition bottom ash (IBA) contains about 9% of ferrous scrap, 63% of sintered ash and slug, 8% of stones and others, 18% of glass/ ceramic, 1% of non-ferrous metals (mainly aluminum) and 1% unburned MSW MSW ash reuse metal present in bottom ash Landfill structure Road construction Concrete Marine structures Noise barriers Foundation Material for recycling: for example Netherlands 50% of ash will be clean 2017 ISWA Report Bottom ash from WtE plants Metal recovery and utilization,

8 Bottom ash treatment Conventional method (used in most of the WtE plants in Europe) bottom ash is removed from the grate by a wet discharge and follows a dry treatment process. In this approach the final goal is to achieve a high quality material that can be used as a secondary construction material in selected applications. J-P Born et al., 7 th CEWEP Waste-to-Energy Congress 2014 Bottom ash treatment: new Removes the bottom ash from the grate by a wet discharge and follows a wet treatment process. The goal is to further improve the quality of the secondary construction material and recyclability of the metals Washing / fractionating based on wet soil cleaning technology Can remove salts from bottom ash Uses water/ needs water A sludge with heavy metals (< 63µm) fraction (10-15%) has to be landfilled. J-P Born et al., 7 th CEWEP Waste-to-Energy Congress 2014 Indaver process ISWA Report Bottom ash from WtE plants Metal recovery and utilization,

9 Bottom ash treatment: new In two WtE plants in Switzerland (KEZO, Hinwill and SATOM, Monthey) bottom ash is removed from the grate by dry extraction and can follow a dry treatment process: + metal separation and metal quality higher leaching values for Sb, Br and Pb J-P Born et al., 7 th CEWEP Waste-to-Energy Congress 2014 Dry bottom ash treatment: Switzerland under development BIOMASS ASH 9

10 Biomass ash ASH UTILISATION Growth mediated acidification

11 Relationship between soil ph and nutrient availability In acidic soils, some nutrients may be insufficiently available for optimal plant growth and aluminium may become toxic. 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 Solution: Recycling of nutrients through ash utilisation Mass balance Mass balance Deposition Weathering Harvest Leakage Mass balance account: Weathering + Deposits = Harvest + Leakage Risk of acidification if: Weathering + Deposits < Harvest + Leakage 11

12 Requirements of wood ash It should contain all the macronutrients It should not cause an accumulation of metals or any other harmful substance in the soil. It should not cause direct harm when spread processing forest%20and%20soil.html Bottom ash ph Poor lime effectiveness Higher content Si and Al (sand) Recyclable ash Fly- and bottom ash Fly ash ph Good lime effectiveness Higher content K and S (volatile) Higher content heavy metals Higher content unburned organic material Bottom ash from grid boilers Fly ash from CFB and spread stoker boilers Smaller stations often mix these What is in the ash? Ash from ForestResidue (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 Oxides Hydroxides Sulphates Chlorides Silicates Carbonates Phosphates 12

13 Ash that is used as a forest fertiliser must have a combined concentration of phosphorus (P) and potassium (K) exceeding 2% at least 6% of calcium (Ca). the cadmium concentration may not exceed 25 mg/kg, arsenic concentration must not exceed 40 mg/kg. Limits for ash utilisation in agriculture-finland Decree of the Ministry of Agriculture and Forestry on Fertiliser Products (24/2011, amendments up to 7/2013 included) Ash is very soluble= leaches too easily Processing of ash Ash needs to be stabilised before recycled. handling, transport and spreading. leaching properties. With a slow release of the ash content drastic changes in ph and the salt content in the soil are avoided. In some cases the ash must be reburned in order to reduce the content of unburned carbon Carbon reduces the self hardening properties of the ash dramatically increases the ash volume. 13

14 Processing of ash There are currently three main methods for processing wood ash: Self-hardening and crushing Compaction Granulation Ash treatment adding water 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. forest%20and%20soil.html Hardening process Hardening means that: Oxides in the ash Hydroxides and carbonates Secondary mineral such as ettringit The ash is less soluble The ph of the ash is lowered The particle size increases Examples: CaO Ca(OH) 2 CaCO 3 A reduced solubility rate and reduced risk of damage to soil and vegetation 14

15 Self-hardening in heaps the most common method Ash treatment - pelleting T Claesson, 2004, Kalmar Högskola [University of Kalmar] Granulation and pelleting Ash analysis A more unified, homogeneous product A more stable product The products are easier to spread involve heavy investment higher operating costs Before treatment After treatment Unburnt material Nutrients and heavy metals Possibly Cs and PAH Solubility rate Texture and water content 15

16 Soil particle Ash recirculation What happens to the ash in the soil? Decreases soil acidity Causes a long-lasting increase in the total nutrient stores of the surface soil. P is the slowest to dissolve, K and B are quick to dissolve in soil water. Soil heavy metal concentration also rises after ash fertilisation, but due to the alkalinity of ash the heavy metals remain in a very slowly dissolving form. Ash fertilisation speeds up soil decomposition, which in the long term promotes the decomposition of organic soil matter and the release of nitrogen to plants. What happens to the ash in the soil? H + H + Ca 2+ Al 3+ ash Ca 2+ Mg 2+ K + Acid substance neutralised ph raised Lime effectiveness 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 growth 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. 16

17 Examples of damage to vegetation Utilisation of ash in Finland t/a in cement production (coal fly ash) t/a as binder material in concrete production (coal fly ash) t/a as filler in asphalt (coal fly ash) t/a as fertilizers in forests in agriculture (wood, peat and biomass ashes) Earth construction applications ~ (?) t/a Lot of ashes are used in construction of landfill sites, storage fields etc. 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 elementsmanipulating chemical properties Make ash spreadible easily with machines- Manipulating physical properties Spreading in woods Other possibilities Concrete Filler material in roads, landfills etc. Retrieval of metals 17