Waste to Energy: MSW Combustion and Dioxin Control

Debajyoti Bose

M Tech - REE, UPES

ENERGY TRENDS

Energy security, economic growth and environmental protection are the three paramount entities for any nation

The dwindling community of fossil fuels apart from leaving us with its destructive cumulative effects will put an enormous strain on energy infrastructure and life itself

Such catastrophic outcomes require efficient and effective solutions

Hence debates on low carbon alternatives and other energy conversion processes are now being considered

THE ATOM ECONOMY

Energy supply and waste management are great challenges that humans have faced

To meet these challenges we must move to an atom economy where every atom is utilized in the best possible manner

Waste to Energy builds the foundation for this

To achieve this goal, a fundamental understanding of the underlying mechanisms and processes of energy and waste generation is necessary

FEEDSTOCK TESTING FOR WASTE TO ENERGY

NECESSITY:

Testing will yield data required for combustor design

Air pollution control system

The waste properties will affect the air- to-fuel ratio

The need for lime or caustic soda in the air pollution control system

The need for pre drying if the moisture content is too high and the heating content is too low

MAJOR WASTE STREAMS:

FOR MSW INCINERATORS

MSW

RDF

Biomass and organic waste

Plastics (from production waste and mixed with other wastes)

Bio-solids (wastewater sludge, animal wastes)

Liquid wastes

Industrial and commercial wastes

Landfill allocation and remediation waste

TDF

Hazardous waste (coal tars from manufactured gas plants)

ASTM COMBUSTION & THERMAL PROPERTY TESTS

NOTE : Relevant Literature can be followed to get the rest

WASTE PRETREATMENT STEPS Basic Screening Processes:To minimize the entry of bulky and hazardous materials onto the combustion grates

Pit Fluffing:o In storage area the crane operator uses the loading claw to pick up several tons of MSW and

redistribute it across the pit

o This process has the twofold effect of breaking bags and mixingthe waste, resulting in a more homogeneous fuel, which can be fed more fluidly into the hopper

In situations where source separation is not common practice and MSW is disposed of in a mass burn facility, all glass, metal and non- combustibles are passed through the moving grate furnace. The result of this is a bottom ash that is typically disposed of in a sanitary landfill

SOME COMMERCIALIZED PROCESSES OVERVIEW

BASIC: Fluidized bed combustion boilers A sulfur absorbing chemical, such as limestone or dolomite, may be

added to the bed Additional scrubbing equipment is necessary in waste to energy

facilities“Municipal waste contains various constituents and impurities that induce

corrosion attacks on boiler tubing”

Table: Chemistry of common alloys used in waste to energy boilers

WASTE BOILERS

Solid Waste Management Waste is not an ideal fuel

Common to waste boilers is the concept of the capacity diagram

Determines the limits of thermal capacity (energy input) for a particular boiler

The Rankine Cycle

HEATING VALUES (FEED) CAPACITY DIAGRAM

WASTE BOILERS (CONTINUED)

Source: ECN, 2012; Patel et al. , 2001; Vølund, 2009

ENERGY RECOVERY & DISTRICT HEATING

When a WTE facility has access to a large district heating network, such as insome cold weather countries like Denmark, Sweden and Finland, it is common toestablish back- pressure turbines, where all the steam exiting the turbineis used to produce district heat

OPTIMIZING WTE FACILITIESBoiler efficiency (generating more steam): Lowering the excess air ratio and lowering the flue- gas temperature will

lower the resulting thermal loss to the chimney, and hence produce more steam

Water steam cycle optimizations: Using feed water and condensate preheaters, as well as preheating the

combustion air, can increase the thermal cycle efficiency

Turbine back-pressure: Besides the live steam temperature, the turbine back- pressure can be

decreased, for instance by having larger condensers

AIR CLEANING EQUIPMENTS Cyclone Separator

Scrubbing Systems (Wet & Dry)

Electrostatic Precipitator

Bag Filters

THE SEVESO ACCIDENT In 1976 di-benzo-p-dioxins (PCDDs) and di-benzo-furans (PCDFs) in filter ashes

from three Dutch municipal solid waste combustors were detected Initiated violent public discussions concerning waste combustion, especially in

Europe

Initiated extensive R&D activities to understand the formation of these compounds and to develop countermeasures

Triggered the waste authorities to issue tighter legislative regulation of air emissions

“This was a strong driver for the development of improved technology”

DIOXINS The group of 75 polychlorinated di-benzo-p-dioxins and 135 di-benzo-furans

A group of some (but not all) highly toxic compounds

Olie, Vermeulen and Hutzinger were the first to report on the dioxins found in filter ashes from three Dutch municipal solid waste combustors (Olieet al.,1977)

Mass flow of dioxins in a waste combustor in the early 1980s

ABOUT DIOXINS & FURANS Are formed when two six carbon benzene rings are joined by

two oxygen atoms Significant exposure to dioxin like compounds can result in the acute

disfiguring condition known as “chloracne” Medical follow ups on people exposed have not resulted in definitive links to

an increased incidence of cancer

The molecular structure of these chlorinated compounds has the geometric configuration to damage DNA

These compounds are currently listed by the World Health Organization as probable carcinogens

DETAILED INVESTIGATION OF THE REACTION MECHANISM

Stieglitz and Vogg,1987; Hagenmaier et al. , 1987; Hiraoka et al. , 1987; Vogg et al. , 1987; Gullet et al. , 1990 all concluded that:

The ingredients and conditions necessary to form dioxins are:

Products of incomplete combustion (PICs), e.g. soot Halides, mainly chlorides, but also bromides An oxidizing atmosphere A catalyst – copper salts being most effective.

“This slow reaction is called de novo synthesis and mainly takes place in the dustdeposits in the backend of the boiler and, if the dust removal system is operated at

temperatures above 200°C”

OBSERVATIONS MADE Careful investigations in test plants carried out by Hunsinger et al., 2002

confirmed that dioxins fed into the combustor along with the waste are totally destroyed inside the combustion chamber

The dioxins found in the flue gas were newly synthesized in the boiler

“On the basis of this knowledge, strategies were soon developed to minimize their formation by suitable measures”

CONSIDERATIONSVogg et al., 1991 suggested the following counter measures:

Optimization of combustion control to achieve a better burn out and hence to reduce the content of PICs in the raw gas, in the fly ashes and in the deposits inside the boiler

Reduction of the gas velocity in the fuel bed to minimize the release of fly ash Adequate cleaning of the boiler to minimize the deposition of fly ash Operation of the dust removal system at low temperature

“Reeck et. al, 1991 reported that it was possible in most existing plants in Germany, without major upgrades, to reduce dioxin emissions easily, quickly and

without additional costs in the order of around 1–5 ng (I-TE)/m³ “

INTERNATIONAL STANDARD International dioxin emission limits is of the order of 0.1–0.3 ng(I-TE)/m³ Secondary abatement measures are needed

Dannecker and Hemschemeier, 1990 suggested that it needed to be removed by additional process stages like adsorption on charcoal fixed- bed filters

Hiraoka et al., 1989 suggested that catalysts if operated in oxidative mode, can have a high destruction potential for dioxins

DRY SCRUBBING WET SCRUBBING

SCRUBBING SYSTEMS

The REMEDIA® process Uses a device in dry scrubbing

systems

Bonte et al., 2002 claimed by incorporating a low temperature catalyst in the cloth of the filter, it can be used to eliminate gaseous organic compounds

Operates between 140-260°C

Medical and MSW plants in Europe & Japan use this

Carbon-filled plastic material called Adiox® has been developed

Andersson et al., 2003 showed that it can be used a s tower packing & demisters

The plastic absorbs dioxins and other low volatile organic pollutants

The dioxin loaded packingcan be burnt in the plant’s furnace to destroy the dioxins totally

Thermal treatment plants

Vehlow, 2005 showed that the emission of dioxins from state- of-the- art plants is in most cases well below 0.01 ng(I-TE)/m³ in Europe

Concentrations of PCDD/F in bottom ashes from grate furnaces; the shaded area indicates typical concentration ranges in natural soil in Central Europe (adapted from

Vehlow et al. , 2006)

WTE BENEFITS Output can be heat, electricity and CHP Efficient way to reduce waste volume

Outputs State Quantity by wt of Original Wt

Comment

Incinerator bottom ash

Solid residue 20-30% Potential use as aggregate replacement or non biodegradable, non hazardous waste for disposal

Metals (Ferrous and Non Ferrous)

Requires separation from MSW or IBA

2-5% Solid for re-smelting

APC residues (including fly ash, reagents and waste water)

Solid residue/liquid

2-6% Hazardous waste for disposal

Emission to atmosphere

Gaseous 70-75% Cleaned combustion product

LIMITATIONS TO WTE Heavy investment and high operating cost

Waste incineration is applicable if certain requirements are met.

The composition of waste in developing countries is questionable and its suitability for auto combustion

Plant requires skilled staff

Well maintained landfill for ash disposal

OVERVIEW: ENDING REMARK Waste combustion is a key component in waste management strategies

An efficient and reliable process for inertizing that fraction of residential waste that is left over after material recycling

The technology is well developed and different processes can be applied according to local conditions

The control of dioxins has been developed to a degree that the air emissions as well as the concentrations in bottom ash cause no harm

Emissions now are very low and have no discernible impact on human health and the environment

REFERENCES STM Test Methods , American Society of Testing and Materials, 100 Barr Harbor Drive,West

Conshohocken, PA, www.astm.org/DIGITAL_LIBRARY/index.shtml. 2009. North American Combustion Handbook , Volume I third ed, 1986, Volume II third ed, 1997, North

American Manufacturing Company, Division of Fives, Cleveland, Ohio, www.namfg.com/comb- handbook/gra49.pdf.

Perry’s Chemical Engineers’ Handbook (8th Edition), 2008, McGraw-Hill, NY. Steam, Its Generation and Use , Babcock & Wilcox, 41st ed., Barberton, Ohio, shop.

fullpond.com/bwco/pdf/STEAM41orderform.pdf. Harvey , A. , Gavis , J. , Renard , L.M. ( 1981 ) Design models of trommels for resource

recovery processing ,Resources and Conservation 6 , 223 – 240 . Hasselriis , F. ( 1984 )Refuse- derived Fuel Processing , Boston: Butterworths (available from

Amazon). Lorange , R. , Redon , E. , Lagier , T. , Hebe , I. , Carre , J. ( 2007 ) Performance of a low cost MBT

prior to landfi lling: Study of biological treatment of size reduced MSW withoutmechanical sorting ,Waste Management 27 , 1755 – 1764.

REFERENCES Mata-Alvarez , J. , Mace , S. , Llabres , P. ( 2000 ) Anaerobic digestion of organic solid waste. An

overview of research achievements and perspectives ,Bioresource Technology 74 , 3 – 16. Savage , G.M. , Trezek , G.J. ( 1974 ) On grinder wear in refuse comminution ,Compost Science , 15

( 4 ), 51 – 53. Shiflett , G.R. , Trezek , G.J. ( 1979 ) Parameters governing refuse comminution ,Resource Recovery

and Conservation 4 , 31 – 42. Schlesinger, MD ( 2007 ), Fuels and Furnaces, in Avallone , E, Baumeister , T, and Sadegh ,

A ,Marks’ Standard Handbook for Mechanical Engineers , 11th edition, New York , McGraw Hill , p. 7 – 6.

Stoller , P and Niessen , W ( 2009 ), Lessons learned from the 1970s experiments in solid waste conversion technologies ,17th Annual North American Waste to energy Conference , NAWTEC17-2348, 1.

Velzy , C and Grillo , L ( 2007 a), Fuels and furnaces , in Avallone , E , Baumeister , T , and Sadegh , A ,Marks’ Standard Handbook for Mechanical Engineers , 11th edition, New York , McGraw Hill , pp. 7-48 – 7-53.

Velzy , C and Grillo , L ( 2007 b), Waste to energy combustion , in Kreith , F and Goswami , D ,Handbook of Energy Effi ciency and Renewable Energy , Boca Raton , CRC Press , pp. 24-1 – 24-42.

REFERENCES

Patel N , Gordon G , Howlett L , 2001 , Accomplishments from IEA Bioenergy Task 23: Energy from Thermal Conversion of MSW and RDF

Vølund , 2009 , 21st century advanced concept for waste-fi red power plants , Babcock & Wilcox Andersson S , Kreisz S and Hunsinger H ( 2003 ) Innovative material technology removes dioxins

from fl ue gases ,Filtration and Separation , 40 , 22 – 25 Bonte J L , Fritsky K J , Plinke M A and Wilken M ( 2002 ) Catalytic destruction of PCDD/F in a

fabric fi lter: Experience at a municipal waste incinerator in Belgium ,Waste Management , 22, 421 – 426.

Dannecker W and Hemschemeier H ( 1990 ) Level of activated- coke technology for fl ue gasdust collection behind refuse destruction plants looking at the problem from the specialaspects of dioxin separation ,Organohalogen Compounds , 4 , 267 – 272

THANK YOU !!!

A PRESENTATION BY

DEBAJYOTI BOSE

M TECH REE, UPES

INTERN AT ABELLON CLEANENERGY