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Type of Waste to be treated
Source Separated Organic Waste
Source Separated Packaging
Mixed MSW
Min Capacity (in tonnes)
>5.000
>12.500
>50.000
ALL
Secondary Products or Energy Production
FE
AL
Plastic
Paper
Glass
Wood
RDF
SRF
Compost
Biogas
Max Residues (%)
0-10%
10-20%
20-30%
30-40%
Capital Expenditure € tn of total feedstock on wet basis
0-100
101-200
301-400
601-700
Annual operation and maintenance cost € tn of total feedstock on wet basis
21-40
41-60
61-80
81-100
Land requirement m2 per tn of total feedstock
0-0.2
0.21-0.4
0.41-0.6
0.61-0.8
0.81-1
Water consumption m3 per tn of total feedstock
0-0.05
0.051-0.1
0.11-0.15
Incineration PDF Print E-mail
1.  General
2. Types of incinerators
3. Air emissions
4. Wastewater
5. Solid residues
6.  Mass and energy balances
7.  Market potential for products
8.  Environmental impacts
9.  Economic data
10.  Applicability in the target area
References

 

1. General

Incineration, which is commonly referred as combustion, is the oxidization of the chemical compounds with oxygen (O2) in order to transform the chemical energy of solid waste organic matter into thermal energy. The incineration of carbon-based materials can be implemented in an oxygen-rich environment (greater than stoichiometric), typically at temperatures higher than 850oC. The incineration of waste is one of the oldest thermal treatment technologies and the most commonly used worldwide.

 

The process produces a waste gas comprised primarily of carbon dioxide (CO2) and water gas (H2O). Air emissions also include nitrogen oxides, sulphur dioxide, etc. The most important factor during the process is the presence of oxygen. During the full combustion there is oxygen in excess and, consequently, the stoichiometric coefficient of oxygen in the combustion reaction is higher than the value “1”. In theory, if the coefficient is equal to “1”, no carbon monoxide (CO) is produced and the average gas temperature is 1,200°C. The reactions that are then taking place are:

In the case of lack of oxygen, the reactions are characterized as incomplete combustion ones, where the produced CO2 reacts with C that has not been consumed yet and is converted to CO at higher temperatures.

The scope of this thermal treatment method is the reduction of the volume of the treated waste with simultaneous utilization of the contained energy. The recovered energy can be used for:

  • heating
  • Steam production
  • Electric energy production

 

In order to achieve the complete incineration of solid waste, a number of preconditions have to be satisfied. These include the following:

 

  • adequate fuel material and oxidation means at the combustion heart
  • achievable of the ignition temperature
  • suitable mixture proportion
  • continuous removal of the gases that are produced during combustion
  • continuous removal of the combustion residues
  • maintenance of suitable temperature within the furnace
  • turbulent flow of gases
  • adequate residence time of waste at the combustion area (Gidarakos, 2006).

 

The method could be applied for the treatment of mixed solid waste, as well as for the treatment of pre-selected waste. It can reduce the volume of the municipal solid waste treated by 90% and its weight by 75%. The incineration technology is viable for the thermal treatment of high quantities of solid waste (more than 100,000 tn/year).

2. Types of incinerators

 

There are two main types of incinerators (combustion units). The facilities which need minimum pre-treatment of waste before they are placed for the incineration process (mass-fired) and the facilities which operate with specific waste fractions that are derived from pre-treatment of municipal solid waste (Refused-Derived Fuel (RDF) and Solid Recovered Fuel (SRF).

 

Mass-burn incineration (Figure 3) is currently the most widely deployed thermal treatment option, with almost 90% of incinerated waste being processed through such facilities. As the name implies, waste is combusted with little or no sorting or other pre-treatment.

There are, of course, many dangers that this process may face, such as the introduction of dangerous and high-volume objects. These dangers, though, can be handled with careful monitoring of the whole process by the facility personnel or by interrupting the process manually when/if needed. The energy contained in waste also depends on the period of the year, climate and waste composition.

 

The second type of facilities described above are those which use a mixture of specific waste fractions from the whole municipal solid waste mixture that derive from the pre-treatment of waste in MBT facilities (MBT: mechanical biological treatment) and is comprised of materials, such as: organics, paper, textiles, leather, rubber materials, etc. The facilities under this type are less (in terms of number worldwide) than the mass-fired facilities because of the fact that a pre-treatment facility for the production of (RDF/SRF) is needed.

 

Their advantages compared to the mass-fired units are:

  1. Faster boiler response than mass burn.
  2. Units can be designed for cofiring.
  3. Higher thermal boiler efficiency because of the lower excess air requirements.
  4. Boiler and overall plant costs are generally lower than those referring to mass burn units.
  5. Potential for sewage sludge disposal.
  6. RDF-fired units are easier in use
  7. Less space is needed for their installation
  8. Finally, the pre-treatment of municipal solid waste gives the chance to remove materials such as PVC and metals that contribute to the production of dangerous gases which are transferred along with the gases produced from the combustion unit.

These facilities have the following disadvantages:

 

  1. The need to build, own, and operate a prepared fuel system is required.
  2. Because of the required processing facility, the overall facility horsepower requirements may be higher than those for mass bum units.
  3. Depending on the process, some combustible material may be lost in processing.

 

The process target is the production of a final mixture with high calorific value. This is why there are quality specifications which the produced RDF must come in line with. More specifically:

  • The minimum of the calorific value should be equal to 4,000 kcal/g (16.744 MJ/kg)
  • The moisture content should not exceed 20%
  • The paper and plastic content should exceed 95% (dry weight).

 

The process in this type of facilities takes place in special combustion chambers with total capacity between 8 and 25 t/h (Vehlow 2006).

 

In Germany the total waste capacity of the first category was 21.5 million tons of waste in 2009 in addition to the 3.3 million tons of waste of the second category. In terms of economy the municipal solid waste incinerators are better in terms of mean energy values (as today), while the second type of incinerators provide better economic results in the case of high energy values when the pre-treatment cost is relatively small (Fiege & Fendel 2010).

 

The incineration facilities represent the main municipal solid waste thermal treatment method used today. In these units the lignite and cement industries in which specific waste fractions are used are also included (Fiege & Fendel 2010). In Table 1 the operational incineration facilities in the United States of America can be seen:

 

Table 1: Operation incineration facilities in the USA

Type

Number of Units

Capacity,(tons/day)

Capacity Million (tons/year)

Mass-fired

65

78,489

24.3

RDF Incineration

15

22,022

6.9

 

The total population that the incineration facilities serve is estimated to 31 million. This estimation is based on the assumption that each inhabitant generates 1.3 tons of municipal solid waste on annual basis.

Energy and environmental advantages of waste incineration

By using 1 ton of municipal solid waste in a modern incineration facility approximately 550 kWh are produced, while the use of at least 250 kg of carbon or the use of 160 liters of oil is prevented. Furthermore, this technology is the only solution against landfilling of non-recyclable waste, since landfilling produces CH4 which is an important greenhouse gas, where the 40% of methane produced is being released to the atmosphere even in modern landfills. The methane that escapes has a dynamic (GHG - Greenhouse Gas Potential) 23 times greater than that of the same CO2 volume.

 

Considering the electricity produced and the CH4 emissions minimization (due to the minimization of waste being landfilled), the incineration facilities help the reduction of «Greenhouse gases» by 1.1 to 1.3 tons CO2 per ton of municipal solid waste being incinerated instead of being disposed at landfills.

 

Besides the energy advantages that this treatment method provides, thermal treatment contributes to the minimization of greenhouse gases. This reduction for just the case of the USA is estimated to 40 million tons CO2.

 

In 2004 the incineration facilities produced 13.5x109 kWh of electricity, an energy amount which was more than any other existing source of renewable energy (besides hydroelectric and geothermal facilities). For instance, wind energy produced 5.3x109 kWh, while solar energy produced 0,87x109 kWh (Table 2).

 

Table 2: Electrical Energy production from Renewable Energy Sources in USA in 2002 (except hydroelectric) (DOE-EIA, Annual Energy Outlook 2002)

Energy Source

Production in 109 kWh

% Energy from RES

Earth (Geothermic)

13.52

28.0%

Waste*

13.50

28.0%

Biogas*

6.65

13.8%

Wood/Biomass

8.37

17.4%

Sun (Heat)

0.87

1.8%

Sun (Photovoltaic)

0.01

0.0%

Wind

5.3

11.0%

Total

48.22

100.0%

* http://www.eia.doe.gov/cneaf/solar.renewables/page/mswaste/msw.html

At European level incineration facilities provided the electricity network with 19 x 109 KWh in 2007, amount of energy which is capable of providing the necessary electricity for the operation of 148 million lambs (15W) for a whole year. If these lambs were set in a line, they would cover the distance from Brussels to Honolulu (11,800 km).

There are various types of incinerators with various advantages and disadvantages. The most widely used are: The moving grate, the fixed grate, rotary-kiln, fluidized bed, etc.

Moving grate incinerator

The grates are placed to the combustion chamber wall and they implement the following operations:

  • Movement of the solid waste stream throughout the facility
  • Provision of air amount at quite steady rate
  • Material stirring at the main combustion zone
  • Transfer of the ash produced during the combustion process

The grates must be covered with materials with high tolerance to mechanical movements, thermal and chemical reactions. Emphasis must be given to the materials tolerance to S and Cl which are corrosive when combined with high temperatures. The stages of the main process are:

  • Drying: evaporation of the moisture contained within waste with the use of fire, heated air, eradiation
  • Vaporization of most of the VOCs (volatile organic compounds) with temperature rise.
  • Combustion: The heat needed is provided with the use of irradiation from the flame and the flame chamber wall.
  • Gasification and burning: Because of the waste combustion, a great number of substances turn into gas. The remaining C is fully oxidized, while the gases from the combustion and gasification process are burnt.
  • Combustion completion: the end solid product is obtained at the end of the grate.

Modern incinerators consist of turbines for the hot combustion gases that pass through the heat exchange sections of the combustion chamber, to be turned into electric energy or heat.

 

Rotary kiln Incinerators

This type of incinerator processes a variety of waste streams that other technologies cannot. This design of incinerator has two chambers: a primary chamber and a secondary chamber. The primary chamber in a rotary kiln incinerator consists of an inclined refractory lined cylindrical tube. The movement of the cylinder on its axis facilitates the movement of waste. In the primary chamber, there is conversion of the solid fraction to gases, through volatilization, destructive distillation and partial combustion reactions. The secondary chamber is necessary to complete gas phase combustion reactions. The unit consists of a system of gaseous emissions control.

 

The clinkers spill out at the end of the cylinder. A tall flue gas stack, fan, or steam jet supplies the needed draft. Ash drops through the grate, but many particles are carried along with the hot gases. The particles and any combustible gases may be combusted in an "afterburner".

 

The chamber has to be covered by materials with tolerance to high temperatures, while a continuous flow of waste is necessary. The temperature inside the chamber is between 800 and 1,400οC, while the effective combustion is achieved through absolute control of the temperature and the waste movement inside the facility. Generally, the higher the temperature, less time is needed for the waste to remain in the combustion chamber.

 

Because of the fact that the gases produced inside the chamber remain for a short period in order to achieve full combustion, a chamber for afterburning is placed. The residues of the chamber are then led to the cooling system.

 

The agitation of waste inside the chamber depends on the time remaining, because this is where the agitation takes place. The gases must be low in CO and H/C considering that the chamber operates with excess of O2 (Gidarakos 2006).

 

The main parameters of this type of incinerators that should be considered include:

  • The temperature of the rotary kiln which leads to the combustion of waste
  • The internal pressure of the chamber that must be negative in order to avoid gaseous emissions and particles to the atmosphere
  • The provision rate for O2 and the waste flow rate so that the process conditions are suitable.

Fluidized bed Incinerators

A strong airflow is forced through a sand bed. The air seeps through the sand until a point is reached where the sand particles separate to let the air through and mixing and churning occurs, thus a fluidized bed is created and fuel and waste can now be introduced.

 

The sand with the pre-treated waste and/or fuel is kept suspended on pumped air currents and takes on a fluid-like character. The bed is thereby violently mixed and agitated keeping small inert particles and air in a fluid-like state. This allows all of the mass of waste, fuel and sand to be fully circulated through the furnace. Evaporation takes place due to the O2 provided, the mixing and the high temperature.

 

Temperature is the main operation parameter for this type of incinerators. It depends on the waste treated, the gases produced, while the temperature varies from 750°C to 850°C.

 

The O2 needed and the retention time are the most important parameters inside the chamber. The determination of these parameters depends on the waste provided for processing. The O2 concentration is controlled in order to achieve a perfect combustion. With this incinerator, temperature variations inside the chamber can be avoided and, as a result, the production of gases due to incomplete combustion can also be avoided.

 

Fuels rich in ash and moisture can also be used for the production of energy. The rate that fuel is turned to energy becomes even higher and, thus, the need for air becomes less (55% compared to the common 100%) (Yassin et al. 2009).

Typical incineration facility

A typical incineration facility includes the following parts:

 

A Weighing System

This system is for weighing solid waste for the better control and recording of the incoming waste streams and, thus, it is designed to be practical in order to minimize the time that vehicles remain at this point.

 

A Reception Site

Due to the fact that waste does not arrive on continuous basis (contrary to the feeding of the facility), the existence of waste reception and temporary storage site is considered essential. The design of the site is made in a way that the following are ensured:

 

  • The unloading time is as little as possible
  • All transferred waste is received
  • The homogeneity of the waste that will be used as feeding material is achieved
  • The smooth feeding of the facility is ensured.

 

Moreover, the design of the reception site should be based on the minimization of the environmental impact. For instance, the solid waste should remain for a maximum of two days in order to avoid the relevant odors, while the bottom of the site has to be characterized by weathering to allow the leachates and washing wastewater to go away.

 

Feeding System

The feeding system has to be adapted to the feeding rate and velocity of the installation.

 

Combustion Hearths

The ignition of solid waste at incineration facilities is achieved through the use of specific burner, which operates with secondary fuel. Basic parameters for the appropriate operation of the combustion hearths are:

 

  • Achievement of the minimum desired temperature
  • Adequate combustion time
  • Achievement of turbulence conditions / homogenous waste incineration.

Boiler

The boiler is the system with which the energy content of the fuel material (hot off-gases) can be utilized in a suitable way through steam production (e.g. at neighboring industrial facilities or for the heating of the neighboring urban areas. Pressure, temperature and steam production rate are basic parameters for the effective operation of the boiler. Its construction has external insulation in order for the system not to lose temperature during the process. The materials used for its construction must also be tolerant to high temperatures (and temperature differences) between the inside and the outside of the facility.

 

System for the removal of residues

Residues represent 20 - 40% of the weight of the initial waste and are categorized as:

 

  • Residues that go out of the grates: 20 - 35%
  • Residues that go through the grates: 1 - 2%.

 

The residues are collected at hoppers where they are transferred with the use of specific cooling system.

 

Emission control system

The role of the emission system control focuses on particles, HCl, HF, SO2, dioxins and heavy metals and is discussed below (Niessen, 2002). After the emissions pass through the boiler, the gaseous emissions pass through a cleaning facility and, then, they are emitted to the atmosphere. In the cleaning systems a large number of different technologies for the removal of flying particles, NOx, SΟx, etc. that are considered to be safe and secure can be applied.

 

The incineration process can be presented with a mass balance diagram for a typical incineration facility. The waste streams percentages depend on the composition of the incoming waste and the emissions control system that is used.

 

In particular for the production of energy from waste incineration it is estimated that 1 ton of waste produces approximately 300kWh electricity and 600kWh of thermal energy.

 

Air emissions, wastewater and solid waste are the result of the process of waste incineration. A detailed analysis of the composition and properties is provided below.

 

3. Air emissions

The gases produced by incineration facilities contain N2 and excess O2, dust particles, the typical products of combustion and other harmful substances, depending on the composition of the incoming waste. The main ones are: SO2, NOx HCl, HF, heavy metals and polycyclic H/C, which are the most dangerous pollutants in the exhaust gases, such as dioxins and furans.

 

An average of 4,000 – 5,000 m³ per tonne of waste gas with a temperature of 1,000°C are generated from the incineration, which in the first phase of cleaning of the produced gas drops sharply to 350°C.

 

The limit values of air emissions are listed in Tables 3, 4, 5 and 6.

Table 3: Daily average values of air emission limit values

(Directive 2000/76/EC on the incineration of waste)

Total Dust

10 mg/m3

Gaseous and vaporous organic substances, expressed as TOC

10 mg/m3

HCl

10 mg/m3

HF

1 mg/m3

SO2

50 mg/m3

NO & NO2, expressed as NO2, for existing incineration plants with a nominal capacity exceeding 6 tonnes /hour or new incineration plants

200 mg/m3

NO & NO2, expressed as NO2, for existing incineration plants with a nominal capacity

400 mg/m3

Table 4: Half-hourly average values of air emission limit values

(Directive 2000/76/EC on the incineration of waste)

 

(100 %) Α

(97 %) Β

Total Dust

30 mg/m3

10 mg/m3

Gaseous and vaporous organic substances, expressed as TOC

20 mg/m3

10 mg/m3

HCl

60 mg/m3

10 mg/m3

HF

4 mg/m3

2 mg/m3

SO2

200 mg/m3

50 mg/m3

NO & NO2, expressed as NO2, for existing incineration plants with a nominal capacity exceeding 6 tonnes /hour or new incineration plants

400 mg/m3

200 mg/m3

 

Table 5: Average values over the sample period of a minimum of 30 minutes and a maximum of 8 hours

(Directive 2000/76/EC on the incineration of waste)

Cadmium and its compounds (Cd)

total

0,05 mg/m3

Thallium and its compounds (Tl)

Mercury and its compounds (Hg)

0,05 mg/m3

Antimony and its compounds (Sb)

Total

0,5 mg/m3

Arsenic and its compounds (As)

Lead and its compounds (Pb)

Chromium and its compounds (Cr)

Cobalt and its compounds (Co)

Copper and its compounds (Cu)

Manganese and its compounds (Mn)

Nickel and its compounds (Ni)

Vanadium and its compounds (V)

Dioxins and Furans

0.1 ng/m3

 

Table 6: Limit values of CO concentrations

(Directive 2000/76/EC on the incineration of waste)

Daily average value

50 mg/m3 of combustion gas

at least 95 % of all measurements determined as 10-minute average

values

 

150 mg/m3 of combustion gas

all measurements determined as half-hourly average values taken in any 24-hour period

100 mg/m3 of combustion gas

 

The concentration of CO in combustion gases (excluding the start and stop) does not exceed the above limit values.

 

The competent authority may grant exemptions for incineration plants using fluidised bed technology, provided that the authorized emission limit value for CO equals to 100 mg/m3 hourly maximum.

 

Then, further reference is made to dioxins and furans, which are among the most dangerous pollutants because characterized by high toxicity (Allsopp et al. 2001).

Dioxins: They include two aromatic rings joined with a pair of individuals O.

The toxic effects of dioxins (Yang & Kim 2004) and furans had not been understood worldwide until the late 80's. With the implementation of MACT regulations, a "toxic equivalent» (TEQ-Toxic equivalent) of dioxin emissions from Waste-to-Energy Facilities in the U.S.A. has decreased since 1987 1,000 times in a value of less than 10 gr TEQ per year (Figure 6). On the other side and in direct relation to the above, the main source of dioxins, as recorded by US EPA (Figure 7) is the uncontrolled burning of waste, which emits about 600 gr per year.

In Germany in 1990 1/3 of dioxin emissions originated from incinerators, and in 2000 the relevant figure was less than 1% although the amount of MSW incinerated more than doubled in relation to 1990. Overall the level of dioxins from 400gr in 1990 was limited to less than 0.5 gr in 2000.

 

Furans: They differ from the dioxins only in that the two aromatic rings are joined by an atom of O.

 

A total of 75 compounds known as polychlorinated dibenzo-p-dioxins (PCDD) and 135 dibenzofurans (PCDF) are classified in this group of compounds.

 

Reference to exposure to dioxins is meant exposure to a mixture of PCDD and PCDF, the toxicity of which is determined by the toxic equivalency factors (Toxic Equivalent Factors, 1 - TEF), which are calculated in relation to the toxic effects of 2,3,7,8 TCDD, also known as the Seveso poison.

 

Dioxins and furans are produced in almost all processes of combustion in the gas phase, while the exact mechanism of their formation remains unknown. It is known that a temperature of formation is 300°C, in which two reactions are possible, the formation and decomposition. The presence of chlorinated organic compounds in the waste to be incinerated and the increased levels of O encourage their creation. The operating conditions of the incinerator affect decisively the creation of dioxins and not the composition of the waste and the quantity of PVC contained in them.

 

They can affect humans through respiration or absorption through the skin, in case they are released to close proximity to the recipients. In other cases their introduction in the body is caused by consumption of food and particularly fruit and vegetables.

 

There is evidence for the contribution of dioxins and furans to processes of carcinogenicity in humans, making it necessary to take measures to reduce their concentrations in the air emissions.

 

Primary measures

-       Improvement of the incineration of waste and suspended particles (products of incomplete combustion).

-       Optimization of the requirement of O2.

-       Improvement of thermal control systems to ensure control of the combustion air

-       The use of improved grates.

-       Adaptation of appropriate systems of grates to changes in the composition of the waste (e.g. calorific value).

-       Control of the temperature of crossing through the filter at a level lower than that of the formation of dioxins (200°C).

Secondary Measures

-       Improvement of the cleaning of steam boilers (continuous cleaning).

-       Preliminary collection of particulate phase before cooling (high temperature removal of particulate matter).

-       Interference in the temperature of the electrostatic filter to reduce the formation of dioxins.

-       Improvement of the systems for the purification of gases by improving the collection of particulate matter and pollutants.

-       Removal of PPDD / PCDF by adsorption of active C.

 

Gas cleaning systems

The existing technologies on the management of air pollutants are summarized in Table 7.

 

Table 7: Existing technologies for the management and treatment of gaseous pollutants

Pollutant

Abatement Technology

Suspended Solids

Cyclones

Electrostatic filters

(Wet - dry)

Bag Filters

Acid Gases

Dry Adsorption

Semi-Dry Adsorption

Wet Sparying

Nitrogen Oxides

Selective non-catalytic reduction

Selective Catalytic Reduction

 

In order to achieve the removal of particulate and gaseous pollutants different methods of cleaning are employed. These include deposition chambers, which remove 40% of airborne particles, wetting screens (efficiency 95%), cyclones (efficiency 60-80%), fluid absorption towers (efficiency 80-95%), electrostatic precipitator (efficiency 99-99.5%) and bag filters (efficiency 99.9%).

Next, the main systems for determining the composition of the gas produced during the incineration of waste are described (Figure 8).

Bag filters: The gases pass through porous materials, where the particulates are trapped. Depending on the requirements, hardware filters are made ​​of natural fibers, plastic fibers, glass, minerals, etc. The dust which is concentrated in cells of the filter is removed by vibration or shock or air in countercurrent (Figure 9).

Electrostatic precipitator (electric filters): The electrostatic precipitator (Figure 10) consists of the cathode, which may be a simple thin wire and the anode, i.e. the inner casing of the electric filter. Another device consists of a system of parallel plates with a potential difference between them. Between cathode and anode voltage develops at 30-80 kV. When particles enter the field of the cathode, they become electrically charged and those negatively charged move towards the positive pole (anode). The speed of the particles depends on their mass and the Coulomb forces that are developed.

Cyclones: The cyclones are based on the development of centrifugal force in the entry of gases in a symmetric space, which at the bottom is cone-shaped. Particles due to centrifugal force and the rotational flow are driven to the wall and, then, removed to the bottom. The cyclones are often deployed along with electrostatic precipitators.

 

Besides the removal of suspended solids, the removal of other pollutants is often necessary, e.g. acid gas, if their content is higher than the relevant acceptable limits. Emphasis is given on the HCl, generated mainly from the combustion of PVC, and oxides of nitrogen, sulfur, phosphorus. The only effective and appropriate way is in this case the operation of towers of wet and dry absorption (scrubbing). The liquid absorption towers are necessary in any case for incinerating toxic and hazardous waste.

 

The process of liquid absorption is based on absorption of gaseous pollutants using a selected washing fluid (solvent). The effectiveness of the process depends mainly on the available surface of the solvent, which controls the mass transfer from gas to liquid phase. To this end, various techniques are employed, such as:

 

  • Venture type scrubbers
  • filling Towers
  • disc Towers
  • absorption-type film Towers (thin layer).

 

Most incinerators in central Europe are using the same technology of liquid absorption. The process takes place in different units consisting of two phases, an initial acid absorption phase and a second phase, neutral or slightly alkaline. The configuration of the acid absorption is often spray or venturi type and in that phase reduction of the temperature of flue gas from 180-200oC to 63-65oC is achieved. For the second phase (neutral or slightly alkaline) filling towers are mainly used. Commercially available absorption tower systems operate with or without producing waste.

 

Such two-phase systems are quite effective in removing waste gases from the incineration of halogen hydrides, HF, HCl, HBr, the Hg and SO2. With this technology the initial concentrations of these compounds in the waste gases are reduced well below the statutory limits.

 

The dry or semi-dry absorption towers (Figure 11) based on simple and low cost technologies exist and are operational in many facilities in the world. In most cases, the adsorbent medium is either injected directly into the flue gas duct or through spray towers in dry or semi-dry form. The products of absorption are removed, in a second phase through a membrane filter. The process of absorption can be performed with various reagents (limestone, CaCO3, calcium oxide, CaO, lime, Ca(OH)2, etc.).

Today, the technology of absorption towers using dry CaCO3 is gradually abandoned, as the composition of air emissions produced by the treatment does not comply with strict statutory limits (Dvorak et el. 2009).

4. Wastewater

 

Wastewater is generated by the use of water during the incineration process and in particular:

  • ash quenching (0.1 m3 H2O / t waste)
  • gas cooling (2 m3 H2O / t waste)
  • liquid absorption towers (2 m3 H2O / t waste)
  • In some electrostatic precipitator to remove particulates from the collection points.

The wastewater contains suspended particles, inorganic and organic in solution. They are toxic and need treatment before discharge into drains. The most common methods of treatment are the precipitation and then adjustment of the pH.

 

Wet gas cleaning system: The liquid comes in contact with the gases where migration of substances from gases in the liquid phase takes place. The absorption depends on surface transport, residence time and type of fluid. The fluid system is developed so that it ensures the removal of ultrafine particles that are not easy to remove through the application of dry systems, e.g. filters. The main wet cleaning systems are:

  • flush Towers (scrubber)
  • Ventouri scrubbers
  • Rotating sprinklers.

 

The limit values ​​of pollutant parameters for discharging wastewater from the cleaning of exhaust gases are summarized in Table 8.

 

Table 8: Emission limit values for discharges of waste water from the cleaning of exhaust gases

(Directive 2000/76/EC on the incineration of waste)

Polluting Substances

Emission limit values expressed in mass concentrations for unfiltered samples

Total suspended solids as defined by Directive 91/271/EC

95% / 30mg/L

100% / 45 mg/L

Mercury and its compounds (Hg)

0.03 mg/L

Cadmium and its compounds (Cd)

0.05 mg/L

Thallium and its compounds (Tl)

0.05 mg/L

Arsenic and its compounds (As)

0.15 mg/L

Lead and its compounds (Pb)

0.2 mg/L

Chromium and its compounds (Cr)

0.5 mg/L

Copper and its compounds (Cu)

0.5 mg/L

Nickel and its compounds (Ni)

0.5 mg/L

Zinc and its compounds (Zn)

1.5 mg/L

Dioxins and furans

0.3 ng/L

 

5. Solid residues

 

The secondary solid residues that are generated during incineration can be categorized as follows:

  • Fly ash: The ash is composed of the lightest part of the ash, which drifted from the exhaust and is collected by special filters. The ash has high concentrations of heavy metals, soluble salts, organic and the higher content of all residues of chlorinated organic compounds.
  • Bottom ash: This is the residue that is collected at the bottom of the furnace.
  • Ash from the boilers
  • dust filter cleaning
  • solid residues from flue gas purification process (WASTESUM, 2006).

 

The solid residues stream must be treated before its final disposal, while a main portion of their quantities could be recycled by applying specific processes.

 

If the bottom ash is not used, it may be released under the same conditions as MSW without any problem.

 

Technologies for the inactivation of fly ash, which is considered hazardous waste, are in development. Most common is the conversion to material useful for road construction, structural applications, etc. The use of ash in road construction - paving is common practice in Europe. The disposal in a landfill must take into account the leachability of the different components. If a method of inactivation is not implemented, it should be placed in hazardous waste disposal site.

 

For the treatment of filters dust various systems are used such as heat (high temperature). The purpose of working at high temperatures is to melt the filter dust and transform it into material that is glassy state, which may be allocated to different uses or placed as inactive.

 

In order to ensure the complete control of emissions, sampling and analysis is required for the determination of the composition of the incoming waste, the generated solids (residue - fly ash), the produced gas and wastewater generated during the processing of waste gases.

 

Quantifying the environmental impact of the implementation of incineration

The method of combustion can cause a variety of environmental impacts taking into account that there are emissions into the environment as gas, liquid and solid pollutants. Table 9 summarizes all the amounts of solid waste, wastewater and air emissions during operation of combustion plants.

 

Table 9: Summary of quantities of solid waste, wastewater and gases produced during the operation of an incineration plant

Solids (ash, metals, glass, other non-combustible materials)

25-40% by weight of

waste

Gases: Dust, CO, CO2, H2O, NOx, SO2, dioxins, furans)

4-5,000m3 gas /

tonne of waste

Wastewater: (suspended particles, organic-inorganic breakdowns)

~ 4m3 water / tonne waste

 

The efficiency of the removal of hazardous components of waste treated in incinerators must be at least 99.99% and is defined as:

 

DRE = Win - Wout / Win * 100%

 

Where DRE = efficiency of the incinerator

Win = rate of supply of a particular substance waste

Wout = rate of emission of that substance in the waste gas

 

The legislation for hazardous waste incinerators does not allow the production of gas with a concentration of solid particles greater than 180 mg / dscm, for O2 content of 7%. To monitor compliance with that restriction in a variety of conditions, current conditions are extrapolated to the conditions of the legislation, according to the formula below:

 

Pc = Pm * 14 / (21 - Y)

Where: Pc = corrected concentration of particulate matter (mg / dscm)

Pm = the measured concentration of particulate matter (mg / dscm)

Y = the measured concentration of O2 in the flue gas chimney (%)

 

The emission factors vary depending on the type of treatment of the produced gases. Also, heat and electricity are considered to have separate emissions (Gidarakos 2006, Niessen 2002).

 

6. Mass and energy balances

 

According to a typical mass balance of the incineration process, for one tonne of input MSW, 200-350 kg is assumed to be bottom ash (10% by volume and approximately 20 to 35% by weight of the solid waste input), 35-45kg flue gas cleaning residue including fly ash and 25-30 kg metals.

The rest of the input is converted into energy. The typical amount of net energy that can be produced per tonne of domestic waste is about 0.7 MWh of electricity and 2 MWh of district heating.

 

7. Market potential for products

Produced heat and electricity may be exploited with a reciprocating engine or microturbine often in a cogeneration arrangement in order to feed the incineration system. Excess electricity can be sold to suppliers or put into the local grid. Electricity produced by incineration systems is considered to be renewable energy.

The produced bottom ash may be used in construction of roads, embankments and landfills, in accordance with the local legislation. At present, the ways to use bottom ash and fly ash as additives in cement plants are under research. The metals may be used in metal recycling industry.

 

 

8. Environmental impacts

The incineration of solid waste generates pollutant emissions (gases, ash, dust and smoke), wastewater, slag and odors. The possible presence in the waste of Cl, F, S, N and other elements could contribute to toxic or corrosive gases. The wastewater that originates from the treatment of exhaust gases and quenching of incinerator ash contains heavy metals and inorganic materials with increased acidity or alkalinity and temperature, while its disposal is permitted only after pertinent treatment and compliance with applicable regulations. Dioxins and furans can be products of incomplete combustion and may be decomposed completely by pyrolysis. The particulate emissions, acid gases (HCl, HF, SO2) and heavy metals (Hg, Cd, Pb) are of significant importance. Novel incineration technologies completely decompose dioxins and furans, neutralize toxicity and stabilize the residue, which could be used in the construction sector. Released aerosols mainly consist of ash absorbing other toxic pollutants; these reduce atmospheric visibility, resulting in public complains, and minimization of aerosol emissions is a must.

If electricity and heat generated from incineration is used, the waste replaces natural resources used for conventional production of energy. The production of energy from renewable sources has positive consequences on nearly all environmental impact categories, because of savings in or compensation for non-renewable energy.

 

 

9. Economic data

 

According to the Carbon Finance Unit of the World Bank in 2008, the capital cost of an incineration system with a capacity of 1,300 tonnes per day is 20-120 /tone, while the operation and maintenance cost is 55-80 /tonne. For the case of Romania, the Neamt Master Plan of the year 2008 considers that an average value for the application of the relevant thermal technology is 120-140 €/t for a capacity of 150,000 t/a. According to EU data the financial cost of incineration, including the annualized capital, O&M expenditures as well as other specific costs or revenues from sale of the energy, ranges between 58 to 104 €/tonne (EC, 2010).

 

10. Applicability in the target area

In general, thermal management practices are characterized by higher cost in relation to other management solutions. This together with the existing economic crisis can be a reason why Romania, Bulgaria and Greece have not yet decided to apply any thermal waste management method exclusively for municipal waste. Furthermore, in many cases the public opinion is not really ready to accept the option of incineration being afraid mainly for the air emissions, but it is considered that these fears and skepticisms will be gradually overcome. On the other hand, it has to be noted that incineration is a well tested method which is widely applied in all advanced in waste management issues European countries that at the same time achieve high recycling rates. Furthermore, the modern incineration plants can be located even at the centre of big cities like in Paris, Vienna, etc. provided that their operation is monitored as required by the relevant Directive on the incineration of waste (2000/76/EC). It is also important to ensure that incineration units have high energy performance so that the relevant treatment can be considered as recovery and not disposal. Finally, energy production through incineration plants can contribute to reducing CO2 emissions.

 

Most specifically, in Romania the incineration practices are already applied but there are still no incineration facilities just for treating municipal solid waste. The relevant data for incineration units in Romania are summarized in Table 10.

Table 10: Synopsis on data on incineration units in Romania

No.

Name and address of facility

Capacity

(tones/year)

Cost

Waste streams incinerated

Public opinion

1.

OLTCHIM- VALCEA county

11.445 tones /year. Co-incineration of the own waste generated

 

 

It was accepted by the population.

2.

S.C.STEMAR S.R.L.Vaslui - Vaslui

966 tones /year. Co-incineration of the own waste generated

 

 

It was accepted by the population.

3.

VRANCART S.A.- Adjud, Vrancea County

17.199 tones /year. Co-incineration of the own waste generated

 

 

It was accepted by the population.

At national level, the total capacity of Co-incineration of the own waste generated is of 29 610 tones/year.

4.

CARPATCEMENT HOLDING SA – Sucursala Bicaz

 

419 432 tones/year

 

Co-incineration in cement kilns

It was accepted by the population.

5.

SC LAFARGE ROMCIM SA - MEDGIDIA, Constanta County,

203 000 tones/year

 

Co-incineration in cement kilns

It was accepted by the population.

6.

SC CARPATCEMENT HOLDING SA – Bucuresti- Fieni, Dambovita County

REPA does not have information about capacity

 

 

It was accepted by the population.

7.

HOLCIM (ROMANIA) SA CIMENT – CAMPULUNG, Arges County

26 208 tones/year

 

 

Co-incineration in cement kilns

It was accepted by the population.

8.

SC CARPATCEMENT HOLDING SA BUCURESTI - Deva- Cement Factory Chiscadaga, Hunedoara County

131.400 tones/year

 

 

Co-incineration in cement kilns

It was accepted by the population.

9.

Holcim (Romania) SA - Ciment Alesd, Bihor County

 

77.000 tones/year

 

Co-incineration in cement kilns

It was accepted by the population.

10.

LAFARGE CIMENT (ROMANIA) S.A. BUCURESTI – Hoghiz, Brasov County

20. 788 tones/year

 

Co-incineration in cement kilns

It was accepted by the population.

Total authorized capacity of co-incineration in Romania is of 907,438 tones/year.

Incinerators

11.

SC CHIMCOMPLEX SA Borzesti –- Bacau County

680 tones/year

 

incineration of their own waste

It was accepted by the population.

12.

SC ANTIBIOTICE SA IASI  - Iasi County

432 tones/year

 

incineration of their own waste

It was accepted by the population.

13.

S.C.KOBER SRL – Turturesti- Neamt County

 

1.248 tones/year

 

incineration of their own waste

It was accepted by the population.

14.

COMPANIA NATIONALA,, IMPRIMERIA NATIONALA" SA,BUCURESTI- Bucuresti

28 tones/year

 

incineration of their own waste

It was accepted by the population.

15.

SC CHIMESTER BV.SA

Bucuresti

126 tones/year

 

incineration of their own waste

It was accepted by the population.

At national level, the total authorized capacity of incineration of facilities’ own waste generated is 2,514 tonnes/year.

Incinerators for hazardous contaminated packaging waste

16.

S.C. MONDECO SRL, Suceava- Suceava County

10.800 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

17.

SC PROD IMPORT CDC SRL ALTAN TEPE, COM.Stejaru- TULCEA County

1.500 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

18.

Compania Nationala Administratia Porturilor Maritime Constanta SA - Constanta County

2.628 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

19.

SC PRO AIR CLEAN SA, TIMISOARA- Timisoara County

3.577 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

20.

SC IF TEHNOLOGII SRL CLUJ- Cluj County

 

1.430 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

21.

SC IRIDEX GROUP IMPORT EXPORT SRL- Bucuresti

6.000 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

22.

S.C. AVAND S.R.L., Iasi- Iasi County

 

11.300 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

23.

SC SUPERSTAR COM SRL-

SUCEAVA County

2.010 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

24.

S.C. ECO FIRE SISTEMS SRL-

CONSTANTA County

10.080 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

25.

SC GUARDIAN SRL- Dolj County

4.620 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

26.

ENVISAN NV BELGIA- SUSCURSALA PITESTI- Arges County

 

93.312 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

27.

SC ECOBURN SRL- PLOIESTI- Prahova County

4.000 tones/year

 

hazardous medical waste and hazardous industrial waste

It was accepted by the population.

The Romanian total authorized capacity of waste incineration is 156,789 tonnes/year.

 

In Greece, no incineration techniques have been applied for the case of municipal solid waste. In fact, there is only one incineration facility which operates in the Attica Region in order to treat hospital waste. It should also be noted that less hospital waste treated than its capacity allows. Referring to municipal solid waste, it has to be noted that the academic society organizes events in order to deal with the skepticisms about the application of incineration (www.wtert.gr). Furthermore, some peripheral waste management plans foresee the construction and operation of incineration units, but have not yet been implemented. For instance, the relevant scheme for Crete Region foresees the operation of an incineration unit with capacity to treat 170,000 tonnes of treated municipal solid waste (SRF and RDF). There are also supporters of the incineration option for the case of Attica Region who have organized events in order to explain the reasons for doing so and the relevant benefits.

 

In Bulgaria, there is total absence of thermal treatment facilities and no significant progress is anticipated in the years to come due to the unwillingness to adopt such practices yet, as well as the economic crisis. Unfortunately, landfilling is expected to continue to be the main treatment method used for the management of municipal solid waste.

 

In Slovenia there is only one incinerator for municipal solid waste. Furthermore, there were two cement kilns having environmental permit. Within 2011 one cement kiln lost the environemental permit for co-incineration of municipal solid waste, so now there is only one cement kiln with the environmental permit for co-incineration. Regarding the incinerator for municipal solid waste, there can be incinerated only treated municipal solid waste. The capacity for the incinerator is 25.000t of treated municipal solid waste. It can be said that the public opinion does not accept the installation and operation of incineration facilities until now.

 

 

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