**7. Case study: Presentation of small size Waste – to – Energy plant**

The W-t-E plant presented in this chapter is located in Celje, Slovenia.

The technology applied enables energy utilization (the combined heat and power production) of RDF produced from MSW with MBT and mechanically dried sewage sludge. Two stage combustion system has been applied as thermal treatment technology to ensure complete combustion and minimal influence on the environment.

The main goals for the investment were:


The operation of the W-t-E plant reduced the negative effects on the environment – in addition to the utilization of energy in waste. The waste and sludge incineration also substantially reduces the volume needed to landfill.

The W-t-E plant is located on the north-eastern rim of the city. In the urban planning docu‐ mentation its location is declared as an industrial zone. The built surface of the W-t-E plant measures 2.000 m2 while the site of the plant including all the peripheral infrastructure and related technology covers 15.000 m2 . The plant is designed to operate for 25 years and can be seen on Figure 8.

The W-t-E plant annually processes approximately 20,000 tons of RDF and 5,000 tons of sludge from the municipal waste water treatment plant with approximately 25% of solids.

The nominal thermal power of the plant is 15 MW with ability for 2 MW of power production. The power is supplied to the distribution network, while the heat energy is used in the district heating system for the city. The plant is designed to operate 24 hours a day, 7 day a week and 8000 hours per year. The schematic presentation can be seen on Figure 9.

The waste thermal treatment process is conducted in the following stages:


ous screw feeding system, a uniform combustion of fuel is assured and thereby extreme values

Combustion of Municipal Solid Waste for Power Production

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

295

Feeding of fuel commences at startup of plant when the temperature in the furnace is at minimal value of 850°C. To reach this high temperature the natural gas is used. If the temper‐ ature falls below this value or emission values exceeded, then the fuel feed is stopped. Fuel

The combustion technology is the modular incineration on a grate. Waste combustion is conducted in two stages – in the primary and secondary chambers. In the primary chamber

feed is continuously controlled and daily fuel consumption records are taken.

of carbon monoxide and total organic carbon are minimized.

**Figure 9.** Schematic presentation of W-t-E plant

**Figure 8.** Celje W-t-E plant [3]


Prepared and mixed fuel is transported to the hoppers above the fuel screw feed dosing units situated above the furnace. These screw feeders provide a continuous and steady fuel feed into the primary chamber. As compared with discontinuous feeding (ram feed), with the continu‐ Combustion of Municipal Solid Waste for Power Production http://dx.doi.org/10.5772/55497 295

**Figure 8.** Celje W-t-E plant [3]

**7. Case study: Presentation of small size Waste – to – Energy plant**

**•** energy utilization of waste to cover part of the heating energy needs in the city,

**•** sewage sludge disposal generated in the city waste water treatment plant.

The technology applied enables energy utilization (the combined heat and power production) of RDF produced from MSW with MBT and mechanically dried sewage sludge. Two stage combustion system has been applied as thermal treatment technology to ensure complete

**•** meeting the strict requirements regarding the biodegradable carbon content in waste disposed of in the landfill after the year 2008 (base on European landfill directive [5])and

The operation of the W-t-E plant reduced the negative effects on the environment – in addition to the utilization of energy in waste. The waste and sludge incineration also substantially

The W-t-E plant is located on the north-eastern rim of the city. In the urban planning docu‐ mentation its location is declared as an industrial zone. The built surface of the W-t-E plant

The W-t-E plant annually processes approximately 20,000 tons of RDF and 5,000 tons of sludge

The nominal thermal power of the plant is 15 MW with ability for 2 MW of power production. The power is supplied to the distribution network, while the heat energy is used in the district heating system for the city. The plant is designed to operate 24 hours a day, 7 day a week and

**•** transport and dosage of RDF and sludge to the combustion chamber in a ratio of 4:1,

**•** the multi step complete combustion of RDF and sludge mixure producing flue gases and

**•** utilization (cooling) the flue gasses and production of super-heated stem for the combined

Prepared and mixed fuel is transported to the hoppers above the fuel screw feed dosing units situated above the furnace. These screw feeders provide a continuous and steady fuel feed into the primary chamber. As compared with discontinuous feeding (ram feed), with the continu‐

from the municipal waste water treatment plant with approximately 25% of solids.

8000 hours per year. The schematic presentation can be seen on Figure 9.

The waste thermal treatment process is conducted in the following stages:

while the site of the plant including all the peripheral infrastructure and

. The plant is designed to operate for 25 years and can be

The W-t-E plant presented in this chapter is located in Celje, Slovenia.

combustion and minimal influence on the environment.

The main goals for the investment were:

294 Advances in Internal Combustion Engines and Fuel Technologies

reduces the volume needed to landfill.

related technology covers 15.000 m2

heat and power production,

**•** flue gas treatment.

measures 2.000 m2

seen on Figure 8.

ash,

**Figure 9.** Schematic presentation of W-t-E plant

ous screw feeding system, a uniform combustion of fuel is assured and thereby extreme values of carbon monoxide and total organic carbon are minimized.

Feeding of fuel commences at startup of plant when the temperature in the furnace is at minimal value of 850°C. To reach this high temperature the natural gas is used. If the temper‐ ature falls below this value or emission values exceeded, then the fuel feed is stopped. Fuel feed is continuously controlled and daily fuel consumption records are taken.

The combustion technology is the modular incineration on a grate. Waste combustion is conducted in two stages – in the primary and secondary chambers. In the primary chamber the combustion process is managed with an air deficiency – approximately 70% of the theoretically required air, so pyrolysis gasification processes prevail. Volatile and flue gases then travel to the secondary chamber for complete combustion. The temperature of the gases leaving the primary chamber is usually between 650 and 850 ˚C, as a large part of the generated heat is used in endothermic pyrolysis processes. The heterogeneous burning down of solid residue needs to be ensured towards the end of the revolving grate where the amount of air fed is sufficient for the complete oxidation of solid carbon.

prior to injection into flue gases the activated carbon powder is added. The neutralization residues and partially adsorbed heavy metals on activated carbon are removed from flue gases

As the end stage slue gas treatment system the fixed bed activated carbon system is applied. In ensures the final polishing of flue gases and ensures very low emissions of pollutants.

By using state-of-the-art technology all environmental, technical and economic requirements and stipulations are met. The plant is regarded within European legislation as IPPC plant and

Ash and slag from primary combustion chamber are not considered dangerous waste material, therefore are landfilled on local landfill site. The quantity depends on the inorganic content of the waste material input. Flue gas treatment residue stems contain increased quantities of metals and salts. It is therefore classified as dangerous waste. It's disposed at hazardous landfill

Figure 10. Schematic presentation of mass and energy conversion in W-t-E plant

2-stage combustion

13 MWth

Combustion of Municipal Solid Waste for Power Production

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

297

~400 kWe

process

5.000 t/a SS 2,1 MWe

The combustion, gasification or pyrolysis chamber (reactor) needs to be modeled in such way to assure best possible process conditions for the production of complete thermal conversion of waste.

 The thermal conversion process by using municipal solid waste as a fuel in W-t-E plant calls for detailed understanding these phenomena. First, this process depends on many input parameters like proximate and ultimate analyses, season of the year, primary and secondary inlet air velocity and second, on the output parameters such as temperature or mass flow rate of conversion products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieve the optimal conversion conditions with minimal pollutants emission during the plant design phase. To meet these goals, W-t-E plants are in the design phase investigated by using computational fluid dynamics (CFD) approach. The adequate variable input boundary conditions which are based on the real measurement are used and the whole computational work is updated with real plant geometry and the appropriate turbulence, combustion and heat transfer models. Different operating conditions are varied and conversion products are

CFD approach uses for description of conversion process in W-t-E a system of differential equations. Fluid mechanics of reacting flow is modeled with Reynolds Averaged Navier-Stokes equations

*<sup>j</sup> x*

*<sup>p</sup> <sup>h</sup>*

*<sup>j</sup> xt*

*ij*

*j*

 

*k*

*j*

 

*j*

3

2 '

*x*

*xt*

*h*

*t*

*''*

 *<sup>j</sup>*

0

*i*

*j*

*f*

 

Eq. 3

 

 

Eq. 6

*i*

*j*

*j*

 

 

*t*

*j i*

*Ihq*

Eq. 4

*ij ij*

*p*

*x*

*Tjj*

*k k tijij xxx*

*xt*

) are modelled by the introduction of turbulent viscosity

*i*

**9 Case study: W-t-E technology development with modern R&D computational tool** 

For such modeling mostly advanced computer based engineering tools are used. [18][21]

**Figure 10.** Schematic presentation of mass and energy conversion in W-t-E plant

19/27

Eq. 5

*t*:

On Figure 7 is the presentation of operation confirmed yearly of W-t-E plant.

together with fly ash in textile bag filter.

20.000 t/a RDF

has this permit.[8]

site.

predicted and visualized.

Reynolds' stresses ( *ij*

(RANS), presented in the following form:

In the secondary combustion chamber careful supply of secondary air in the mixing zone generates an optimum combustible mixture of air and volatile gases. In the following zone this mixture is ignited. Complete combustion is assured by correct mixing procedure and by supplying tertiary air. A special probe is fixed on the thermal reactor exit, which is used for measuring the oxygen contents in the flue gases, as well as accurate thermocouples. The quantity of the supplied secondary and tertiary air is regulated with reference to the measured value. The temperature of the thermal reactor is between 850 °C and up to 1200°C, with a residency time of at least two seconds. These conditions ensure the complete combustion of organic substances together with the highly toxic polychlorinated biphenyls, polychlorinated dibenzodioxins, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons eventually generated in the primary chamber.

For startup preheating of secondary combustion chamber and to keep up the minimal burning temperature gas burners are installed. The burners are normally not required to operate, as normally the expected energy within the fuel is sufficient to maintain combustion.

The main components of the energy production system are the steam boiler, the steam turbine with the generator, air condenser and heat exchangers.

The feed water is vaporized in the water tube boiler and superheated to the temperature of 350 °C at 30 bars in the super heater. The superheated steam is then passed through the steam turbine, driving the power generator. The steam exiting the turbine is condensed in the heat exchangers for heating up water for district heating or in air condenser. Condensed water is then led over water preparation system and with the help of the boiler feed pump back to the boiler.

A computer controlled variable speed drive induced draft fan ensures correct negative pressure is maintained through the boiler and flue gas treatment system.

From the secondary chamber thermal reactor the hot gasses are ducted to the steam boiler. Just prior to entry into the boiler, ammonia water solution is sprayed in through atomizers. The solution in the high temperatures reacts with NOx, thus reducing it back to nitrogen.

The flue gas treatment system is specially designed to the waste input data. The system removes solid particles (fly ash or dust), acid gases, heavy metals and persistent organic pollutants.

The acid gases are neutralized by alkaline additive injection into flue gases. The removal of heavy metals and persistent organic pollutants is usually done with activated carbon adsorb‐ tion. As alkaline material the sodium bicarbonate is used. The material is grinded on site and

19/27

Eq. 5

*t*:

prior to injection into flue gases the activated carbon powder is added. The neutralization residues and partially adsorbed heavy metals on activated carbon are removed from flue gases together with fly ash in textile bag filter.

the combustion process is managed with an air deficiency – approximately 70% of the theoretically required air, so pyrolysis gasification processes prevail. Volatile and flue gases then travel to the secondary chamber for complete combustion. The temperature of the gases leaving the primary chamber is usually between 650 and 850 ˚C, as a large part of the generated heat is used in endothermic pyrolysis processes. The heterogeneous burning down of solid residue needs to be ensured towards the end of the revolving grate where the amount of air

In the secondary combustion chamber careful supply of secondary air in the mixing zone generates an optimum combustible mixture of air and volatile gases. In the following zone this mixture is ignited. Complete combustion is assured by correct mixing procedure and by supplying tertiary air. A special probe is fixed on the thermal reactor exit, which is used for measuring the oxygen contents in the flue gases, as well as accurate thermocouples. The quantity of the supplied secondary and tertiary air is regulated with reference to the measured value. The temperature of the thermal reactor is between 850 °C and up to 1200°C, with a residency time of at least two seconds. These conditions ensure the complete combustion of organic substances together with the highly toxic polychlorinated biphenyls, polychlorinated dibenzodioxins, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons

For startup preheating of secondary combustion chamber and to keep up the minimal burning temperature gas burners are installed. The burners are normally not required to operate, as

The main components of the energy production system are the steam boiler, the steam turbine

The feed water is vaporized in the water tube boiler and superheated to the temperature of 350 °C at 30 bars in the super heater. The superheated steam is then passed through the steam turbine, driving the power generator. The steam exiting the turbine is condensed in the heat exchangers for heating up water for district heating or in air condenser. Condensed water is then led over water preparation system and with the help of the boiler feed pump back to the

A computer controlled variable speed drive induced draft fan ensures correct negative

From the secondary chamber thermal reactor the hot gasses are ducted to the steam boiler. Just prior to entry into the boiler, ammonia water solution is sprayed in through atomizers. The

The flue gas treatment system is specially designed to the waste input data. The system removes solid particles (fly ash or dust), acid gases, heavy metals and persistent organic

The acid gases are neutralized by alkaline additive injection into flue gases. The removal of heavy metals and persistent organic pollutants is usually done with activated carbon adsorb‐ tion. As alkaline material the sodium bicarbonate is used. The material is grinded on site and

solution in the high temperatures reacts with NOx, thus reducing it back to nitrogen.

pressure is maintained through the boiler and flue gas treatment system.

normally the expected energy within the fuel is sufficient to maintain combustion.

fed is sufficient for the complete oxidation of solid carbon.

296 Advances in Internal Combustion Engines and Fuel Technologies

eventually generated in the primary chamber.

boiler.

pollutants.

with the generator, air condenser and heat exchangers.

As the end stage slue gas treatment system the fixed bed activated carbon system is applied. In ensures the final polishing of flue gases and ensures very low emissions of pollutants.

By using state-of-the-art technology all environmental, technical and economic requirements and stipulations are met. The plant is regarded within European legislation as IPPC plant and has this permit.[8]

Ash and slag from primary combustion chamber are not considered dangerous waste material, therefore are landfilled on local landfill site. The quantity depends on the inorganic content of the waste material input. Flue gas treatment residue stems contain increased quantities of metals and salts. It is therefore classified as dangerous waste. It's disposed at hazardous landfill site.

On Figure 7 is the presentation of operation confirmed yearly of W-t-E plant.

Figure 10. Schematic presentation of mass and energy conversion in W-t-E plant

The combustion, gasification or pyrolysis chamber (reactor) needs to be modeled in such way to assure best possible process conditions for the production of complete thermal conversion of waste.

 The thermal conversion process by using municipal solid waste as a fuel in W-t-E plant calls for detailed understanding these phenomena. First, this process depends on many input parameters like proximate and ultimate analyses, season of the year, primary and secondary inlet air velocity and second, on the output parameters such as temperature or mass flow rate of conversion products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieve the optimal conversion conditions with minimal pollutants emission during the plant design phase. To meet these goals, W-t-E plants are in the design phase investigated by using computational fluid dynamics (CFD) approach. The adequate variable input boundary conditions which are based on the real measurement are used and the whole computational work is updated with real plant geometry and the appropriate turbulence, combustion and heat transfer models. Different operating conditions are varied and conversion products are

CFD approach uses for description of conversion process in W-t-E a system of differential equations. Fluid mechanics of reacting flow is modeled with Reynolds Averaged Navier-Stokes equations

*<sup>j</sup> x*

*<sup>p</sup> <sup>h</sup>*

*<sup>j</sup> xt*

*ij*

*j*

 

*k*

*j*

 

*j*

3

2 '

*x*

*xt*

*h*

*t*

*''*

 *<sup>j</sup>*

0

*i*

*j*

*f*

 

Eq. 3

 

 

Eq. 6

*i*

*j*

*j*

 

 

*t*

*j i*

*Ihq*

Eq. 4

*ij ij*

*p*

*x*

*Tjj*

*k k tijij xxx*

*xt*

) are modelled by the introduction of turbulent viscosity

*i*

**9 Case study: W-t-E technology development with modern R&D computational tool Figure 10.** Schematic presentation of mass and energy conversion in W-t-E plant

predicted and visualized.

Reynolds' stresses ( *ij*

(RANS), presented in the following form:

For such modeling mostly advanced computer based engineering tools are used. [18][21]
