Incineration ash management Flashcards
what is a rough estimate of the amount of ash produced from 1 tonne of waste?
Bottom ash: 150-300kg Boiler ash: ~5kg Fly ashes: 10-30kg APC residues - dry/semi-dry: 15-60kg (including fly ash) -wet: 0.5-2 (sludge) Gypsum: 1-4
what is the characteristic of ash?
Bottom ash
- raw bottom ash is a granular material that consists of a mix of inert materials such as sand, stone, glass, porcelain, metals and ash from burnt materials that falls through or over the grate
- consists of lithophilic elements (earth-like elements) and looks like gravel; contains iron and aluminium scrap
- not classified as a hazardous waste
Fly ash including APC residues
- fine grained powder, light or dark gray, dusty
- may contain soot particles (or activated carbon)
- classified as a hazardous waste
explain metals in ash?
Metals tend to be distributed differently in fly and bottom ash
- most volatile metals (e.g., arsenic, mercury, lead, cadmium and zinc) tend to be more concentrated or ‘enriched’ in fly ash
- carcinogens: dioxins, furans, PCBS- concentrated in fly ash
- less volatile metals (e.g. aluminium, chromium, iron, nickel, and tin) typically are concentrated in bottom ash
What are the disposal methods for fly ash?
Landfilling
- bottom ash: non-hazardous waste
- fly ash/ APC residues: hazardous waste
(Currently no real utilization, landfilling only after treatment and stabilization and it is hazardous).
reuse in road construction
- bottom ash as a substitute for granular materials (gravel etc) in pavements, embankments, noise barriers, etc.
- bottom ash (occasionally mixed with other ashes) as aggregates in concrete and asphalt
specific utilization
- refilling of mines with APC ashes (Germany): fill cavaity to reduce the risk of collapse
- Neutralisation of waste acid with APC ashes (Norway)
Bottom ash processing for recovery
- application of the CE
- bottom ash contains significant amounts of ferrous and non-ferrous metals scrap
- it is common practice that at least the ferrous metals are recovered
- if it is intended to use bottom ash the burn out should be extended
- the ash is then stored for a few days to allow de-watering * ash quenched in bath to prevent release, avoid fire, stop combustion to stop fugitive emissions
further treatment consists of sieving to remove bulky fractions and magnetic separation of ferrous scrap and eddy-current separation of non-ferrous metals
- the metal fractions, up to 10 wt% of ferrous and approximately 1wt% of non-ferrous scrap, are sold to recycling companies (how is only recovered if the wt percentage is high)
- the ash is then stored for typically three months. This aging (maturation) reduces the alkalinity of the ash by the uptake of CO2 from the air and some respeciation of mineral phases.
Bottom ash recovery
pretreatment
- size classification
- metal separation
- aging/ maturation (improves the qualities of aggregates for construction)
materials recovered
- ferrous metals (high price)
- non-ferrous metals
- aggregates
IBA in construction
- replacement of 100% virgin aggregate in hydraulically bound material
- lightweight aggregate in masonry blacks
- replacement of up to 100% of virgin aggregate in cement bound materials
- replacement of up to 50% of virgin aggregate in asphalt
IBA in waste management
- protection for landfill liner membrane
- drainage systems (sustainable drainage systems)
APC residues
The residues from wet and dry or semi-dry APC systems carry high levels of soluble salts, especially of alkali and alkali-earth chlorides or sulphates
- because of their high solubility, a safe disposal route can only be guaranteed on special disposal sites.
- attempts have been made to utilize parts of the ingredients in order to minimize the disposal problem. This will only be successful if there are long term markets
note
bottom ash management in Europe 2009/2010
utilization as opposed to diposal is larger leaders: Germany France Netherlands
Pyrolysis and gasification
advantages
- by using less oxygen, air emissions can be reduced (smaller volume) : reduced need for flue gas cleaning which can reduce cost
- PCDD/PCDF could be less at some conditions (lower emission)
- The plants are modular (i.e. flexible). They are made up of small units which can be added to or taken away as waste streams or volumes change (e.g. with increased recycling) and therefore more flexible and can operate at smaller scale than mass-burn incinerators, and be quicker to build.
- The processes recover useful energy which can be used either on site, or, following further processing or conversion, elsewhere. the energy recovered from mass burn incinerators can only be used on site (product can be traded or needs a local heat demand)
- the syngas may be used to generate energy more efficiently, is a gas engine (and potentially a fuel cell) is used, whilst incineration can only generate energy less efficiently via steam turbines (higher energy efficiency)- can be up to 40%
- a version of pyrolysis has been proposed that will capture carbon (biochar) from organic material and thereby enable it to be ‘sequestered’ from the carbon cycle. The biochar can then be used for agricultural purposes, or other purposes that prevent, or substantially delay its return to the carbon cycle (carbon capture)
- recovering the chemical value from the waste (rather than its energetic value) with more flexibility (large product variety)
- better public acceptance
disadvntages
- pretreatment of MSW is required in most cases- most cases needs to be reduced in size (break down organic materials)
- impact on recycling
- reliability - still emerging tech for MSW
- emissions - still emits
- climate, GHG and energy efficiency
- costly
Pyrolysis: slow or fast
Slow pyrolysis: with slow heating rates used for producing charcoal (carbonization)
Fast pyrolysis: used for fuel production with high heating rates and low retention times
describe the application of pyrolytic oil
bio-oil
extraction
- whole fractions: i.e. sugar- fermentation (hybrid processing)
- specific compounds
direct use
- turbine or diesel engine fuel
- co-feeding in boilers- upgrading: refinery co-feed- drop in biofuels
Gasification
- syngas platform
describe application of syngas
- 2nd generation biofuels: ethanol, methanol, hydrogen
- heat and power application
- Note that the desirable qualities of syngas is different for different uses- therefore may need a purification process.
