**6. Environmental impact of W-t-E plants**

The W-t-E plants have an environmental impact. In European legislation [8] is thermal treatment regarded as technology that needs to fulfill integrated pollution prevention control demands.

General image of the thermal treatment technologies is low and the spatial planning for these plants is extremely problematic and needs excellent cooperation among many professionals, from engineers to politicians. The last are very much under the influence of "not in my backyard" and "not in my election term" syndrome. To overcome this, everybody must realize that the complete environmental standards and environmental regulation requirements for such plants are met but still the most common environmental impacts of W-t-E plants are:


STEAM GENERATION

(FLUE) GAS TREATMENT SYSTEM

CHEMICAL (AND PHYSICAL) REAGENTS FOR (FLUE) GAS TREATMENT

(FLUE) GAS TREATMENT REMAINS

SYNTHETIC GAS COMBUSTION CHAMBER

STEAM GENERATION

**Figure 6.** The schematic presentation of complete gasification system with high efficient electrical power production unit

Thermal conversion of waste with combustion can produce only hot water, hot thermal oil or steam (Figure 4). The power production can only be achieved with Rankine cycle with clear limitations of overall efficiency. Even when combustion occurs in multiple stages (chambers) it does not improve power production efficiency. It only improves environmental performance

On the other hand can gasification or pyrolysis process lead to higher power efficiencies since part of energy transformation and utilization takes place in gas engine or turbine with higher overall efficiency. This two processes have also quite some drawbacks especially is question‐

STEAM UTILIZATION FOR POWER AND HEAT PRODUCTION

**Figure 5.** The schematic presentation of complete waste gasification system with immediate combustion of synthetic gas

AIR SUPPLY

(FLUE) GAS TREATMENT SYSTEM

CHEMICAL (AND PHYSICAL) REAGENTS FOR (FLUE) GAS TREATMENT

CONTINUOUS EMISSION MONITORING SYSTEM AND ELECTRONIC CENTRAL CONTROL SYSTEM

> S T A C K

> S T A C K

(FLUE) GAS TREATMENT REMAINS

CONTINUOUS EMISSION MONITORING SYSTEM AND ELECTRONIC CENTRAL CONTROL SYSTEM

> UTILIZATION OF SYNTHETIC GAS IN POWER GENERATOR SET

> > POWER AND HEAT PRODUCTION

AIR SUPPLY

STEAM UTILIZATION FOR POWER AND HEAT PRODUCTION

GASIFICATION REACTOR / CHAMBER

WASTE INPUT

WASTE INPUT

of conversion process.

AIR SUPPLY

290 Advances in Internal Combustion Engines and Fuel Technologies

SOLID REMAINS

GASIFICATION REACTOR / CHAMBER

AIR SUPPLY

SOLID REMAINS


In general the most considered and regarded as most harmful environmental impact is regarded emission to air. This is also the reason for the great opposition toward new plants.

The flue gas treatment includes the removal of dust particles, nitric oxides, acid gasses, potentially present organic substances and heavy metals. The design of the flue gas treatment

Combustion of Municipal Solid Waste for Power Production

http://dx.doi.org/10.5772/55497

293

**◦** selective non catalytic removal with ammonia water injection into combustion chamber

**◦** catalytic removal with ammonia water injection into flue gases at temperatures around

**◦** wet, semi-wet, semi-dry or dry flue gas treatment with alkaline reagents (lime, sodium bicarbonate,…) and removal of neutralization products on fabric or ceramic filters;

**◦** with fabric or ceramic filters together with neutralization products or within wet washer

**◦** coke adsorbent or activated carbon powder for the extraction of organic substances and

During combustion of RDF in W-t-E mass of input waste is reduced for about 90%. The remains of combustion are mostly bottom ash. There are minor amounts of fly ash, boiler ash and flue gas treatment residue all classified as hazardous waste. The bottom ash composition and its amount from W-t-E fed by RDF differ drastically from the bottom ash of conventional mass burning grate incinerators (MBGI) fed by untreated MSW[10] (not RDF). The bottom ash from RDF incineration offers different possibilities for its utilisation with similar composition to

> **Content (wt. %) Cement RDF bottom ash Untreated MSW bottom ash [10]**

SiO2 22.3 24 41.13-56.99 Al2O3 5.83 14.8 9.2-11.35 Fe2O3 2.17 2.7 3.97-8.61 CaO 60.81 39 13.22-19.77 MgO 2.82 1.7 3.46-3.85 Na2O 0.34 0.9 2.84-5.87 K2O 0.72 0.2 1.35-1.57

**Table 7.** Chemical composition of cement and bottom ash produced with incineration of RDF and untreated MSW

system consists of multiple stages, designed for specific emission removal:

**•** reduction of nitric oxides:

**◦** flue gas recirculation,

200°C to 300°C;

**•** reduction of acid gases:

**•** reduction of particles:

heavy metals.

cement as shown in Table 7.

**Oxide**

systems;

at temperatures around 900 °C,

**•** reduction of heavy metals and organic matter:

The emissions of pollutants into the air are strictly controlled by national legislation or in case of European Union, also with Waste incineration directive [7] and are presented in Table 6.

A considerable advantage of advanced thermal conversion technology is the controlled conversion process and the low dust emissions in the gasses, which positively affects the reduction of the catalytic processes of harmful substances being produced during the flue gas cooling process and resulting in smaller quantities of flue gas treatment residue.


**Table 6.** Air emission limit values for waste incineration in European Union [7]

The flue gas treatment includes the removal of dust particles, nitric oxides, acid gasses, potentially present organic substances and heavy metals. The design of the flue gas treatment system consists of multiple stages, designed for specific emission removal:

**•** reduction of nitric oxides:

**•** heat emissions to air and water,

292 Advances in Internal Combustion Engines and Fuel Technologies

In general the most considered and regarded as most harmful environmental impact is regarded emission to air. This is also the reason for the great opposition toward new plants.

The emissions of pollutants into the air are strictly controlled by national legislation or in case of European Union, also with Waste incineration directive [7] and are presented in Table 6.

A considerable advantage of advanced thermal conversion technology is the controlled conversion process and the low dust emissions in the gasses, which positively affects the reduction of the catalytic processes of harmful substances being produced during the flue gas

Total dust [mg/Nm3] 20 10 10

CO [mg/Nm3] 20 10 10

TOC [mg/Nm3] 100 - 50

SO2 [mg/Nm3] 200 50 50

NOx [mg/Nm3] 400 200 200

HCl [mg/Nm3] 60 10 10

HF [mg/Nm3] 4 2 1

Cd, Tl – together [mg/Nm3] 0,05 - 0,05

Hg [mg/Nm3] 0,05 - 0,05

Ag, Sb, As, Pb, Cr, Co, Mn, Ni, V, Sn – together [mg/Nm3] 0,5 - 0,5

PCDD/F [TE ng/Nm3] - - 0,1

**Table 6.** Air emission limit values for waste incineration in European Union [7]

**100 % ½ h**

**97 % ½ h**

**24 h**

cooling process and resulting in smaller quantities of flue gas treatment residue.

**(all parameters calculated on dry flue gas and 11% O2)**

**•** noise,

**•** odor,

**Parameter**

**•** increased traffic,

**•** utilization of space,…

	- **◦** wet, semi-wet, semi-dry or dry flue gas treatment with alkaline reagents (lime, sodium bicarbonate,…) and removal of neutralization products on fabric or ceramic filters;
	- **◦** with fabric or ceramic filters together with neutralization products or within wet washer systems;
	- **◦** coke adsorbent or activated carbon powder for the extraction of organic substances and heavy metals.

During combustion of RDF in W-t-E mass of input waste is reduced for about 90%. The remains of combustion are mostly bottom ash. There are minor amounts of fly ash, boiler ash and flue gas treatment residue all classified as hazardous waste. The bottom ash composition and its amount from W-t-E fed by RDF differ drastically from the bottom ash of conventional mass burning grate incinerators (MBGI) fed by untreated MSW[10] (not RDF). The bottom ash from RDF incineration offers different possibilities for its utilisation with similar composition to cement as shown in Table 7.


**Table 7.** Chemical composition of cement and bottom ash produced with incineration of RDF and untreated MSW
