INVENT – Integrated Waste Management modules for different courses of graduate studies

Waste treatment technologies I

- Mechanical treatment, waste recycling, thermal treatment -

INVENT – Final Meetings

INVENT – Integrated Waste Management modules for different courses of graduate studies

Content

1. Waste recycling - basics

2. Mechanical waste treatment

- Size reduction

- Screening

- Sorting

- Compaction

3. Thermal treatment

- Combustion

- Pyrolysis

- Hydrolysis

- Drying

INVENT – Integrated Waste Management modules for different courses of graduate studies

Waste recycling - basics

• relevance of recycling:

- keep items out of landfills and conserve natural resources

- goal of every recycling process: use or reuse materialsfrom garbage in order to minimize the amount of solidwaste

• recycling of waste allow:

- production of potential recyclables

- separation of potential recyclables out of the waste stream

• recycling methods:

- different waste collection systems separation intodifferent waste streams

- mechanical waste treatment: size reduction, classification, sorting and compaction

- thermal waste treatment: combustion, pyrolysis, hydrolysis, drying

INVENT – Integrated Waste Management modules for different courses of graduate studies

• Size reduction:

- to conduce to increase the specific surface area

- influence of the properties of the material on the aggregate

(grain size, hardness, brittleness, cleavage property, application of the products, required properties of the products (e.g. grain size distribution, grain shape))

- aggregates: hammer mills, impact crusher, cutting mill, rotary shear, jaw crusher, cascade mill

Mechanical waste treatment

rotary shearbasic product final product

INVENT – Integrated Waste Management modules for different courses of graduate studies

Size reduction

• principle of a hammer mill:

- used for size reduction of municipalsolid waste, commercial waste,

waste wood and car wrecks

- advantages: no requirements onthe grain size of the waste, high

delivery rates, all-purpose

- disadvantages: high rate of abrasion, loud, danger of dust-explosions, high energy consumption

INVENT – Integrated Waste Management modules for different courses of graduate studies

Screening

• Screening:

- screening is split into sieving and air classifier

• Sieving:

- divides particles of different grain sizes

- separation is effected by specific length of the particlesand the separation plan of the sieve

- during the sieving emerge a fine grit (fall through the separation plan) and a coarse grit (remain on the separation plan)

- examples: trommel screen, oscillating screen, bucketsieve, ballistic separator

• Air classifier:

- separator divide the particles due to their decantationrate which is addicted by the grain shape and the

specific weight of the particles

- examples: zig-zag air classifier, cross-flow and horizontal air classifier, suction hood

trommel screen

principle of a

counter flow

ballistic separator

light fraction

dense fraction

INVENT – Integrated Waste Management modules for different courses of graduate studies

Sorting

• Sorting:

- using the differences of physical properties of the materials

- aggregates: density sorter, magnetic and electric separator, optical sorter, flotation

• Magnetic separation:

- using magnet separator for removal of ferrous components out of the waste stream (cross-flow or parallel to the conveying direction of the waste)

- necessary pre-treatment: prior size reduction, gapping

- often used for pre-sorting the household wastes

principle of a magnetic separator magnetic separator

• Eddy current separation:

- induction of eddy currents

in metal objects in response

to an electromagnetic field

(e.g. to sort tin plate)

INVENT – Integrated Waste Management modules for different courses of graduate studies

Sorting

• Optical sorting:

- developed to sort crushed glasses into differentcolours (recognize the colour and use a blast ofcompressed air to sort out)

- nowadays it can also be used to sort different kindsof plastics

• Flotation:

- is used to remove contaminants in plastics (inGermany: used in paper mills to produce highquality graphic paper

• Density Sorting:

- 2 methods: float-sink method and hydrocyclones

- principle: heavy fractions sink to the bottom andlight fractions swim on top of the liquid medium

• Manual Separation:

optical sorter

manual separation

INVENT – Integrated Waste Management modules for different courses of graduate studies

Compaction

• primary goal: reduce surface and increase bulk

• 2 principles are used: build-up agglomeration, compaction agglomeration

• important for the cost of transport and storage

• aggregates: bale press, compactor, pellet press, briquette press

- a bale is made by pressing the waste against a movable wall

- e.g. pellet presses for producing refuse derived fuels (RDF)

bale press compactor for landfills pellet press

INVENT – Integrated Waste Management modules for different courses of graduate studies

Thermal treatment

• thermal treatment includes combustion, pyrolysis, hydrolysis and drying of waste

• goals of combustion of waste as the main method:

- treatment of non-recyclable residuals

- inertisation of the residuals minimization of the emissions

- destruction of organic contaminants and accumulation of inorganic contaminants

- decrease the volume of the waste send to landfill

- energy recovery of household wastes by using the heating value

- conversion residues to useable secondary raw material to prevent the resources (cycle of materials)

• Pyrolysis:

- thermal decomposition of organic wastes under air tight to produce storable andenergetic products

- currently at experimental stage for treatment of household waste

• Hydrolysis is for treatment and utilisation of residuals of refinery processes

• Drying is especially used for drying sewage sludge

the methods of cleaning the flue gases of the combustion processes will not be explain

INVENT – Integrated Waste Management modules for different courses of graduate studies

Combustion

• Principle: combustion of household waste (grate firing)

delivery hall waste storage boiler house flue gas cleaning chimney

control

unit,

laboratory

INVENT – Integrated Waste Management modules for different courses of graduate studies

Combustion

drying

biomass

degasification

burnout

cooling

ash

post-combustion secondary

air

primary air

• Principle of the grate firing:

INVENT – Integrated Waste Management modules for different courses of graduate studies

Combustion

• Principle of a rotary kiln:

- used for hazardous wastes which can be solid, liquid andpasty

- rotary kiln can reach high temperatures with a long dwellperiod for the waste

- it is necessary to install a post-combustion (1000-1200 °C)behind the rotary kiln to ensure the complete combustion

INVENT – Integrated Waste Management modules for different courses of graduate studies

Combustion

• Fluidized-bed combustors:

- burn waste in a hot bed of granular material, suchas sand

- injection of air into the bed creates turbulencesresembling a boiling liquid

- turbulences distributes and suspends the waste

- the design of a fluidized-bed reactor increases heattransfer and allows for operating temperaturesbelow 950 °C, reducing nitrogen oxide emissions

- fluidized-bed combustors can handle high-ashfuels, agricultural residues and sewage sludge

air

ash

flue gas

combustion

bed ash

secondary

air

waste

secondary

air

INVENT – Integrated Waste Management modules for different courses of graduate studies

Pyrolysis and gasification

• Pyrolysis:

- conversion of the organic components of the waste with lack of O2 and influenced by heat (150 - 900 °C)

- emergence of solid, fluid and gaseous products which can use for energy recovery

- advantages: recovery of pyrolysis gas which has a high energy density and canbe used to burn the emerged pyrolysis coke

- currently: no established pyrolysis treatment of waste

• Gasification:

- conversion of organic components of the waste to gaseous fuels by high temperatures and the use of a reactive gas (steam, CO2, O2, air)

- production of lean gas or water gas for energy recovery

- the produced pyrolysis coke is oxidised in the firebed (more than 800 °C) withdeficient of air

INVENT – Integrated Waste Management modules for different courses of graduate studies

Hydrolysis and drying

• Hydrolysis / hydrogenation:

- conversion of substances (e.g. coal, chemical macromolecule, old plastics) withH2, pressure (300 bar) and raising temperatures (440 – 480 °C)

splitting of chemical bonds with water

- advantage: this method produce the best products (synthetic crude oil), producenew plastics by hydrogenation of old plastics

- disadvantage: quiet expensive

• Drying:

- high relevance for drying sludges (e.g. sewage sludge)

- aggregates: fluidized-bed reactor (for stinky sludge), exhaust vapours, convectivedrying in an open system (for non-stinky sludge)

- used mediums: hot flue gases, superheated steam, air

- employed processes:

- direct contact (drying medium has contact with the sludge)

- indirect contact (wall between drying medium and sludge)

INVENT – Integrated Waste Management modules for different courses of graduate studies

Thank you for your attention!