June 2015
Exchange Issue 16
Waste to Energy Technology
Guest Authors: Eng. Maffeo Felice Giovanni and
Eng. Amelio Stefano
Engineers at IREN Ambiente, felicegiovanni.maffeo@
gruppoiren.it and [email protected]
1 Introduction
Waste to Energy (WtE) is now an available and well-known
procedure to treat a very wide range of waste. The WtE
sector has undergone a rapid technological development
over the last 10 to 15 years. This change has been driven
in order to control industries’ policies, and in particular,
imposing limits on pollutants produced by individual
installation. A continual process development is ongoing:
at the moment, the sector is exploiting techniques which
aim to limit costs and to improve environmental
performance. The intention of waste incineration is to treat
wastes so as to reduce their volume and hazard, destroying
potentially harmful substances that are, or may be,
released during incineration. Incineration processes allow
not only recovering energy, but also mineral and/or
chemical content from waste. Basically, waste incineration
is the oxidation of the combustible materials contained in
the waste. Waste is generally a highly heterogeneous
material, consisting essentially of organic substances,
minerals, metals and water. The incineration produces
flue-gases whose energy is in the form of heat. The organic
fuel substances in the waste burns once the necessary
ignition temperature is reached and there is enough
oxygen. In this condition the combustion process takes
place.
Referring to 2011, among the 27 European Member States
(MS), the amount of Municipal Solid Waste (MSW) suitable
for thermal waste treatment is approximately 253 million
tons. The scale of use of incineration as a waste
management technique (i.e. percent of solid waste treated
via incineration) varies significantly from place to place
ranging from zero to 65%. The average value in the same
year was approximately 20 %. The target of thermal
treatment is to provide an overall environmental impact
reduction that might arise from the waste. WtE usually
includes a complex set of interacting technical components
which, when considered together, effect an overall
treatment of the waste. Each of these components has a
slightly different main purpose, the main ones as below:
• volume reduction of residues and destruction of organic
substances
• evaporation of water to recover energy
• evaporation of volatile heavy metals and inorganic salts
• production of potentially exploitable slag
• removal and concentration of volatile heavy metals and
inorganic matter into solid residues
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• residues, sludge from waste water treatment
• minimizing emissions
Basics on the technology and IREN
references
The structure of a WtE plant may include the following
operations. Some details of these main operations
are described as follows:
• incoming, waste reception and storage of waste;
• pretreatment of waste, where required;
• loading of waste into the process;
• thermal treatment of the waste;
• energy recovery;
• flue-gas cleaning residue management;
• flue-gas monitoring and stack outlet;
• waste water control and treatment;
• ash management and treatment;
• solid residue discharge/disposal.
Figure 1: Waste to Energy plant operations
Delivery and bunker
Incineration and steam generation:
The waste delivery area is the location where the
delivery trucks, trains, or containers arrive in order
to dump the waste into the bunker. In this phase the
waste is usually subject to a visual control, to check
for radioactivity followed by the weighing operations.
The dumping occurs through openings between the
delivery area and the bunker. Tilting and sliding beds
may be used to help waste transfer to the bunker.
The openings can be locked, and therefore also
serve as odor and seal locks, as well as fire and
crash-protecting devices. The bunker is a waterproof,
concrete bed. The waste is piled and mixed in
the bunker using cranes equipped with grapples.
The mixing of waste helps to achieve a balanced
heat value, size, structure, composition, etc. of the
material dumped into the incinerator filling hoppers.
The bunker area and the feeds system are equipped
with fire protection system.
Grate incinerators and recovery boilers usually have
the following components:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
waste feed chute;
waste feeder;
incineration zone;
main incineration zone
separator for large kernels;
bottom ash discharger;
riddling;
boiler ash remover;
primary air supply;
secondary air supply;
The incineration grate should guarantee a good
distribution of the incineration air into the furnace,
according to combustion requirements. A primary air
blower forces air through small grate layer openings
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into the fuel layer. More air is generally added above
the waste bed to complete combustion. The burning
waste remains for almost an hour on the incineration
grate.
Figure 2: WtE combustion and recovery boiler typical diagram
Figure 3: Boiler and ash remover WtE Plant (Parma)
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Flue Gas Treatment (FGT) - gas cleaning
chimney:
The FGT is designed to clean the combustion gases
coming from grate and boiler to reach the environmental performance stated by the Authority in accordance to the: “Incineration Directive 200/76/EC”.
Individual components of a Flue-Gas Treatment system are combined in different ways to provide an
effective overall system for the treatment of the pollutants in flue-gases. Below is a summary of some
application in the WtE sector. The applied system exploits different technologies according to the waste
streams. For example in the WtE plant in Parma, the
flue-gases treatment is designed in five single steps:
- First Dry-type reactor for the injection of lime and
activated carbon in the flue-gas stream;
- Bag filters for the collection of combustion by-products and reaction products from flue-gas treatment
reactions;
- Second Dry-type reactor for the injection of sodium bicarbonate and activated carbon in the flue-gas
stream;
- Bag filters for the collection of combustion by-products and reaction products from flue-gas treatment
reactions;
- DeNox Selective Catalyst Reactor for the reduction
of nitrogen oxides concentration.
Table 1: Number of MSWT plants withvarious flue - gas treatment systems
WtE plants by-products
The waste to energy treatment produce refuses, as
by product, in consequence of:
• combustion process (metal debris and scraps);
• flue-gas treatment FGT (fly ashes and compounds
of sodium).
The refuses, almost 21% of the inlet waste in weight,
are the residual fraction of the waste: once these
residuals are dropped from the grate, they are cooled
down and transferred to a special waste pit. During
the transfer, a set of electromagnets separate the
metal debris in order to recycle.
The scraps are then treated by experienced
companies which are able to recycle the resulting
material and transform them into building material.
Due to the fact that the residuals from flue-gas
treatment (fly ashes and compounds of sodium) are
hazardous pollutants according to the European
Waste Catalogue (EWC), they are transferred to
authorized facilities for disposal. According to the
Italian law, these facilities are required to submit an
environmental authorization, which in Italy is called
AIA “Autorizzazione Integrata Ambientale”.
Energy recovery:
The majority of the energy produced during
combustion is transferred to the flue-gases which are
collected into a recovery boiler, in order to produce
superheated steam that is inputted in a steam turbine
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power generator.
The characteristics of steam (pressure and
temperature) or hot water (district heating DH) are
determined by the local energy requirements and
operational limitations.
The following factors have to be taken into account
when determining the local design of an energy
recovery system:
Electricity
• national grid or industrial network and plant selfconsumptions;
• price of electricity significantly influences investment;
• subsidies or loans at reduced rates can increase
investment;
• technical requirements: voltage, power, availability
of distribution;
Heat
• the end-users: to communities (DH) or to private
industries;
• geographical constraints; delivery piping feasibility;
• duration of the demand, duration of the supply
contract;
• obligations on the availability of the heat supply;
• steam/Hot water conditions: pressure (normal/
minimum), temperature, flowrate;
• season demand curve;
• subsidies can influence economics significantly;
Figure 4: Steam Turbine Power Generator WtE Plant (Parma)
IREN has developed its own practice in WtE plant in
northern Italy. The following images show the main
references:
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Figure 5: Aerial view of Tecnoborgo WtE Plant (Piacenza)
Figure 6: Aerial view of PAI WtE Plant (Parma)
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Figure 7: Aerial view of Gerbido WtE Plant (Turin)
Key process data:
continental Europe (Niessen, W., 2002).
In Europe, the waste treated in WtE plants is mainly
the non – recyclable share of the separated waste.
This amount is usually evaluated in term of tons/year
(t/y). In order to set the size of the plant, a key figure is
the range of low heating value (LHV) of waste, which
is identified through its chemical compounds. LHV is
the energy release that is reported in the literature of
With these characteristics (waste capacity and LHV),
it is possible to estimate the electrical and thermal
supply in the plant design. It is also important to
evaluate environmental benefits in terms of fuel
saving, normally expressed in toe (tonne of oil
equivalent) per year. The table below shows the
design characteristics of three implemented WtE
plants in Italy:
Table 2: characteristics of three implemented WtE plants in Italy
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Live example from monitoring equipment
of air pollutants
The updated application in WtE monitoring system
at the stack is based on Fourier Transform InfraRed
(FT-IR).
Some of the infrared radiation is absorbed by
the sample and some of it is passed through
(transmitted). The resulting spectrum represents
the molecular absorption and transmission, creating
a molecular fingerprint of the sample. Knowing that
each molecular fingerprint is unique, the infrared
spectroscopy is useful for several types of analysis.
So, the information provided by FT-IR are: the
quality or consistency of a sample and the amount of
components in a mixture.
Check the following links in order to see the real
time values of IREN plants: www.trm.to.it www.
irenambiente.it (as an example).
These following screenshots present an example
of the charts published daily on the IREN website
containing the list of information that the end user
can find:
Table 3: Examples of live monitoring charts of PAI WtE Plant (Parma)
Table 4: Examples of live monitoring charts of PAI WtE Plant (Parma) 2
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Table 5: Examples of live monitoring chart of Gerbido WtE Plant (Torino)
Table 6: Examples of live monitoring charts of Gerbido WtE Plant (Torino) 2
Benefits in terms of heat and electricity
The main benefit in WtE is using waste as fuel
to produce thermal and electric energy, and
consequently a saving of traditional fuel.
However, the generation of electricity is limited by:
the high-temperature corrosion that may occur in the
heat conversion area due to the presence of certain
materials, including chlorine, in the waste fouling
of the boiler. Above approximately 600 to 800 °C
the ashes are sticky due to the presence of some
smelting substances.
The steam generation parameters (and hence
electrical efficiency) of incineration plants are
therefore limited. A maximum steam pressure of 60
bar and a temperature of 520 °C can be considered
the maximum at present. These limitations can
be dealt with through the adoption of special and
expensive measures to limit corrosion.
For electricity production from MSW, the typical
features of superheated steam conditions are 40
to 45 bar and 380 to 400 °C. Only for particular
conditions due to the presence of hazardous waste,
steam conditions are generally less than 30 bar and
300°C in order to avoid corrosion risk by acid fluegas.
Average rates of electricity production and distribution
referred to each inlet MW by waste combustion:
in case of no District Heating: - from 22% to 28%
in case of District Heating - from 15% to 20%
Considering that, in both cases, the WtE process
electrical self-consumption is approximately 15% of
the electricity produced.
Average rate of thermal production and distribution,
referred to each inlet MW by waste combustion, is
estimated between 50% and 55%.
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Environmental implications and social
acceptability
According to the U.S. Environmental Protection
Agency, waste-to-energy plants produce electricity
with “less environmental impact than almost any
other source of electricity.” Clearly, today’s wasteto-energy plants are nothing like those old, polluting
incinerators of the past. While the combustion of
waste as a method of disposal dates back centuries,
it was not until 1975 that the combustion of waste
for the purposes of generating energy became
commercially available in the U.S.A. In fact, the first
commercial waste-to-energy plant opened in 1975
and still operates in Saugus, Massachusetts. It was
recently however, updated with stringent emissions
control systems in accordance with the most stringent
state and federal standards.
Waste-to-energy plants today are much more
advanced than the incinerators dating years back.
First, as their name implies, waste-to-energy facilities
extract energy from the trash, whereas incinerators
only attempted to reduce the volume of the trash.
Waste-to-energy plants use high temperature
combustion, as much as possible, to reduce the
volume of the trash by 90%, decreasing the need for
valuable landfill space.
IREN, in its plants implementations has had to ensure
the social acceptability of WtE plants. The main aim
is to persuade the “third party”. Therefore, it is very
important to meet the people residing in the area
and clearly detail the project’s characteristics: WtE
methods, technologies and processes.
It is very important to show the residents the social
advantages of WtE. The most important of which:
• high level of process and environment monitoring,;
• a really proven worldwide technology,;
• fuel for energy is obtainable cheaply,;
• current landfill material used as fuel.;
Economics of the technology
The economic aspects of WtE change significantly
between regions and countries, not only due to
technical aspects but also depending on the waste
treatment process implemented.
The main costs of WtE plants are generally
conditioned by the following factors:
• Scale (disadvantages for small scale operation);
• Costs of land acquisition;
• The actual requirements for the treatment of fluegases/effluents, (e.g. emission);
• Requirements by the local Authorities (usually
environmental performances) and energy recovery
efficiency (heat and power). The main process data
are designed to provide both. Therefore, a particular
technology has to be selected. Cost effects are:
- the treatment and disposal/recovery of
ashes residues are mainly conditioned by:
i. the market;
ii. the owners of these authorized
plants;
- the efficiency of energy recovery / benefits
received for the energy delivered. The Business Plan
has to clarify the trade-off between:
iii. the cost to improve the technical choices;
iv. the benefits derived by the energy
market;
• The recovery of metals and the revenues received
from this operation;
• Taxes or subsidies received for incineration and/or
imposed on emissions - direct and indirect;
• Taxes and subsidies on waste at check point (gate
fees), which range varies from 10% to 75% of the
inlet waste price; the pay-back period may be highly
influenced.
• Architectural requirements; the architectural type
of the WtE plants mirrors the same architectural
characteristics of the area:
I. Parma: the WtE plant’s architecture is a
typical brick factory.
II. Turin: the WtE plant’s architecture has
been designed by Gruppo Bertone , one of the best
known company specialized in car styling founded in
Turin;
• Development of the surrounding area for waste
delivery access, and other infrastructures;
Based on IREN experiences, WtE plants costs
are divided into the following phases: engineering
constructions, commissioning and start up, and lie in
the ranges:
• 0.70 – 0.75 thousand €/t in the case of large plant
size with capacities reaching 421,000 t/y as seen in
the WtE plant in Turin’s
• 1.00 – 1.10 thousand €/t in the case of small plant
size such as Piacenza and Parma
The cost are expressed in thousand €/t of MSW inlet.
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The European situation
2012).
Currently, there is a huge gap in the WtE development
in Europe, resulting in several EU countries already
experiencing a hold in the expansion of the WtE due
to a possible national overcapacity, while the majority
of the EU countries still have under-capacities or no
waste incineration at all. The result is a significant
decrease in the overall investments into the WtE
technology in Europe, since the investment into
waste in the countries with most developed Waste
Management seems to be slowing down (Malek, S.
A report made by ISPRA (Istituto Superiore per
la Protezione e la Ricerca Ambientale) considers
the percentage subdivision of the principle waste
management methods for each EU country (Eurostat
data). The report underlines that almost 24% of
the urban waste is incinerated. During the period
2010-2012, a stringent implementation of European
waste management policies intended to reduce the
utilization of landfill has influenced the trend of waste
disposal methods.
Figure 8: Percentage subdivision for MW methods in EU - 28
In 2012, among the European states, almost 57
million tons of waste has been treated by incineration.
A percentage of 97.7% of these has been incinerated
by the states composing EU 15. Compared to 2011, a
reduction of 4.1% on the total amount of MSW treated
by incineration is registered. Concerning the data
on incineration, it is evident that a heterogeneous
situation exists among the European states: almost
28.6 million tons are incinerated in Germany and
France (equal to 50.2% of the MSW total amount),
(3)
whereas for example, 5 member states (Bulgaria,
Grecia, Cipro, Lettonia and Romania) do not exploit
incineration methods. The situation in kg per capita
of MSW treated by incineration during 2010-2012
in Europe is described in fig.8 .The utilization of
WtE method is most common in Denmark (349 kg/
inhabitants per year), Netherlands (270 kg/inhabitants
per year) and Sweden (239 kg/inhabitants per year)
(ISPRA, 2014).
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Figure 9: MSW treated by incineration (in kg per capita) in EU - 28 (Eurostat, 2012)
An expansion of WtE is also expected in Eastern
Europe. The trend has been set by many announced
plans for WtE implementations in the coming years.
Since the region has no waste incineration plants, it
could represent a big potential market in the next five
years.
According to the estimations of the Waste-to-Energy
Research and Technology Council Germany (WtERT
Germany), more than 50 WtE and Refuse-DerivedFuel projects are in progress and/or planned in
Eastern Europe. However the realization of planned
capacities is still rather uncertain. Furthermore,
some European countries have a policy which limits
incineration. This can be related to the countries’
economic situation, which at the moment is not ready
to guarantee a complete chain of waste treatment:
separate collection systems, disposal for by-products.
It is therefore fair to conclude that, in spite of overall
insufficient WtE capacities in Europe, the development
of the market is still facing many challenges. Main
investing states in WtE are dealing with overcapacities,
while the states with under-capacities attempt to deal
with the public acceptance of the technology, the
lack of a Waste Management strategy or the lack of
investment potential. It is therefore difficult to estimate
the growth of WtE market as well as its speed. The
forecast regarding the expansion of WtE is mostly
related to each national waste production trend.
Taking into consideration all possible circumstances
that can affect waste generation in the future, such
estimation is full of uncertainties.
References
- Saša Malek (2012) Waste to Energy in Eastern and
South Eastern Europe. Springer
- ISPRA (Istituto Superiore per la Protezione e la
Ricerca Ambientale) Rapporto rifiuti urbani Edizione
2014;
- Eurostat (2012) Eurostat.ec.europa.eu: municipal
waste generated and treated in (Online). Available
from http://epp.eurostat.ec.europa.eu/
IPPC: Integrated Pollution Prevention and Control –
Waste incineration – August 2006
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Copyright © UNDP/CEDRO - 2015
The findings, interpretations and conclusions
expressed in this report are those of the authors
and do not necessarily represent those of the
United Nations Development Programme (UNDP).
The Consultant does not guarantee the accuracy
of the data included in this report. The boundaries,
colors, denominations, and other information shown
on maps and images in this work do not imply any
judgment on the part of the Consultant or UNDP
concerning the legal status of any territory or the
endorsement or acceptance of such boundaries.
The United Nations Development Programme and
the Consultant assume no responsibility of any kind
for the use that may be made of the information
contained in this report.”
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