**5. Technology background of high efficient Waste – to – Energy thermal conversion process**

The development of the high efficient electrical power production system could go into the direction of utilizing more advanced, high corrosion and stress resistant steels for boiler production or use or corrosion resistant plating on boiler tubes. The other possibility is to modify the whole W-t-E process and this is presently investigated and tested by many researchers and companies. Some technologies have even been marketed with moderate real operating conditions success thus a lot of research and development (R&D) is still needed to get a reliable and lasting operation of new high efficient technology.

Standard temperature probes

**Combustion chamber**

> Flue gas exit

Gas burner (also possible plasma torch)

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Combustion of Municipal Solid Waste for Power Production

Hatch D Hatch U

**Figure 2.** The schematic presentation of gasification and combustion chambers of pilot scale waste gasification unit

Gasification process emerged from combustion process as it is already present in every solid fuel combustor. Depending on the technology and waste (fuel) utilized can be updraft or downdraft system. These two terms define the movement of synthetic gas in co-flow (down‐ draft) or contra-flow (updraft) compared to waste movement. Other types of gasification technology are even more comparable to pure combustion technologies (like fluidized bed,

The schematic presentation of gasification reactor or primary chamber and combustion or

The gasification chambers on Figure 2 and implemented technology can be regarded as modular waste processing on the grate. Waste processing is conducted in two stages – the designed process enables to upgrade the investigated system with utilization of high calorific synthetic gas in gas turbine or internal combustion gas engine instead of burning it in secon‐ dary chamber. The system enables both updraft and downdraft operating regimes, depending on input waste characteristic and reactor operating conditions. The photo of the pilot plant in

In the primary chamber the gasification process is carefully managed with an exact air supply and temperature control. The system operates with air deficiency – compared to the theoreti‐ cally required air for combustion, so pyrolytic gasification processes prevail. This is carefully controlled with under the grate air supply to ensure proper gasification process along the grate. The only possibility to overlook the gasification process along the grate in detail is to measure the temperature of the grate. As the upper side is covered with waste the only possibility is to

Standard temperature probes

**Gasification chamber**

Waste supply

rotary kiln,…).

presented on Figure 3.

measure the bottom side of the grate.

Inclined grate

secondary chamber is presented on Figure 2.

Standard temperature probes

Energy of waste conversion technologies were in the past solely based on combustion process similar to solid fuels combustion technologies. The only plant additions were demanding flue gas treatment devices to clean up the emitting pollutants.

Today, environmentally high efficient systems are based on multi stage thermal conversion process.

At first, two stage combustion systems have been designed for industrial, medical and hazardous waste incineration since in the past the legislation of developed countries had set higher environmental and technical standards for treating these wastes then treating the municipal solid waste. Those incinerators had small capacity and were mostly batch fired. The main intention for installing the second combustion chamber was to improve complete combustion of all organic components in gases leaving primary chamber. [2][13]

Multi stage incineration systems have made their first appearance some fifty years ago. All two (or multi) stage technologies share the common idea of two (or more) divided chambers (reactors). The two chamber combustion technology is in principle based on the air shortage in the primary chamber and excess air in the secondary chamber, what together assures good combustion conditions, low emissions and lower consumption of added fuel. [2][13]

The whole waste thermal treatment process is based on two groups of physical - chemical processes:


Two stage incineration system is in more technical detail presented in chapter Case study: presentation of small size waste – to – energy plant.

Combustion of Municipal Solid Waste for Power Production http://dx.doi.org/10.5772/55497 287

Main emphasis of this work is dedicated to optimize the conversion process to enhance the

**5. Technology background of high efficient Waste – to – Energy thermal**

The development of the high efficient electrical power production system could go into the direction of utilizing more advanced, high corrosion and stress resistant steels for boiler production or use or corrosion resistant plating on boiler tubes. The other possibility is to modify the whole W-t-E process and this is presently investigated and tested by many researchers and companies. Some technologies have even been marketed with moderate real operating conditions success thus a lot of research and development (R&D) is still needed to

Energy of waste conversion technologies were in the past solely based on combustion process similar to solid fuels combustion technologies. The only plant additions were demanding flue

Today, environmentally high efficient systems are based on multi stage thermal conversion

At first, two stage combustion systems have been designed for industrial, medical and hazardous waste incineration since in the past the legislation of developed countries had set higher environmental and technical standards for treating these wastes then treating the municipal solid waste. Those incinerators had small capacity and were mostly batch fired. The main intention for installing the second combustion chamber was to improve complete

Multi stage incineration systems have made their first appearance some fifty years ago. All two (or multi) stage technologies share the common idea of two (or more) divided chambers (reactors). The two chamber combustion technology is in principle based on the air shortage in the primary chamber and excess air in the secondary chamber, what together assures good

The whole waste thermal treatment process is based on two groups of physical - chemical

**•** mixing of the synthetic gases with air, ignition and complete combustion in the secondary

Two stage incineration system is in more technical detail presented in chapter Case study:

**•** warming, drying, semi-pyrolitic gasification of the waste in the primary chamber and

combustion of all organic components in gases leaving primary chamber. [2][13]

combustion conditions, low emissions and lower consumption of added fuel. [2][13]

electrical power production of the waste-to-energy process.

286 Advances in Internal Combustion Engines and Fuel Technologies

get a reliable and lasting operation of new high efficient technology.

gas treatment devices to clean up the emitting pollutants.

presentation of small size waste – to – energy plant.

**conversion process**

process.

processes:

chamber.

**Figure 2.** The schematic presentation of gasification and combustion chambers of pilot scale waste gasification unit

Gasification process emerged from combustion process as it is already present in every solid fuel combustor. Depending on the technology and waste (fuel) utilized can be updraft or downdraft system. These two terms define the movement of synthetic gas in co-flow (down‐ draft) or contra-flow (updraft) compared to waste movement. Other types of gasification technology are even more comparable to pure combustion technologies (like fluidized bed, rotary kiln,…).

The schematic presentation of gasification reactor or primary chamber and combustion or secondary chamber is presented on Figure 2.

The gasification chambers on Figure 2 and implemented technology can be regarded as modular waste processing on the grate. Waste processing is conducted in two stages – the designed process enables to upgrade the investigated system with utilization of high calorific synthetic gas in gas turbine or internal combustion gas engine instead of burning it in secon‐ dary chamber. The system enables both updraft and downdraft operating regimes, depending on input waste characteristic and reactor operating conditions. The photo of the pilot plant in presented on Figure 3.

In the primary chamber the gasification process is carefully managed with an exact air supply and temperature control. The system operates with air deficiency – compared to the theoreti‐ cally required air for combustion, so pyrolytic gasification processes prevail. This is carefully controlled with under the grate air supply to ensure proper gasification process along the grate. The only possibility to overlook the gasification process along the grate in detail is to measure the temperature of the grate. As the upper side is covered with waste the only possibility is to measure the bottom side of the grate.

This reactor design can in constant operation reach over 4 MJ/Nm3 with average composition of RDF produced in Europe. Thus the system allows downdraft (hatch D on Figure 2 closed) or updraft (hatch U on Figure 2 closed) operation to be able to adjust the gasification to the properties of waste treated.

The pilot scale equipment tests have shown that this technology can offer production of

value of the RDF. Test have shown that RDF with around 11 MJ/kg produces synthetic gases

and over.

The syngas is composed of the H2, CO and CH4. These are the main components of the formed syngas, which have the energy value, and together with CO2, N2, O2 and H2O represent more than 93% of the components in syngas. The rest are higher order hydro-carbons (ethane, propane, butane, benzene,...), some cyclical hydro-carbons (benzene, toluene,...) and other gases (HCl, HF, SO2,...). Higher-order hydro-carbons and cyclical hydro-carbons do have higher calorific value than H2, CO and CH4, but are found in the syngas in very low, negligible

Pyrolysis process is again is composed of thermal decomposition of organic matter which occurs in the absence of air. To reach decomposition conditions in reactor heat and sometimes

The pyrolysis gas has at least double the calorific value as gasification synthetic gas both produced from the same waste (fuel). But the overall energy efficiency is not always in favor

To be able to compare all three thermal conversion processes in context of power production

STEAM GENERATION

**Figure 4.** The schematic presentation of single stage combustion with steam generation and utilization

(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

(FLUE) GAS TREATMENT REMAINS

STEAM UTILIZATION FOR POWER AND HEAT PRODUCTION

of pyrolysis as there is pyrolysis gas partially utilized for heat and steam generation.

. The generation of gas is highly dependent of the calorific

Combustion of Municipal Solid Waste for Power Production

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289

and only RDF with calorific value of 15 MJ/kg or over enables the

synthetic gases of over 4 MJ/Nm3

production of synthetic gas of 4 MJ/Nm3

steam need to be introduced to the reaction chamber.

there are schematic presentations on Figure 4 to Figure 7.

COMBUSTION CHAMBER

AIR SUPPLY

SOLID REMAINS

with around 2 MJ/Nm3

quantities.

WASTE INPUT


**Table 5.** Calorific value of synthetic gas produced with air and various gasifier types [17]

This utilization of synthetic gas in gas engine or turbine is only possible if high calorific synthetic gas is produced. The literature shows that the gases with the calorific value of between 4 and 6 MJ/Nm3 can be produced and the complete data is presented in Table 5. [17] The gas turbine can run on gases with calorific values as low as 2.5 MJ/m3 .

**Figure 3.** Pilot scale W-t-E gasification plant during experiments and investigations

The whole process of gasification was controlled with the quantity of waste input into the chamber, the velocity of waste movement along the grate and quantity and distribution of air. The search for optimal operating conditions was based on the known composition of waste and operating experience.

Generated synthetic gases are on the pilot scale system measured in the duct between primary and secondary chamber with Wobbe index analyzer [12]. The temperature in primary chamber needs to be kept more or less constant just over 600 °C and the air supply must be carefully controlled.

The pilot scale equipment tests have shown that this technology can offer production of synthetic gases of over 4 MJ/Nm3 . The generation of gas is highly dependent of the calorific value of the RDF. Test have shown that RDF with around 11 MJ/kg produces synthetic gases with around 2 MJ/Nm3 and only RDF with calorific value of 15 MJ/kg or over enables the production of synthetic gas of 4 MJ/Nm3 and over.

This reactor design can in constant operation reach over 4 MJ/Nm3

288 Advances in Internal Combustion Engines and Fuel Technologies

downdraft 4 – 6 updraft 4 – 6 fluidized bed 4 – 6 fluidized bed - steam 12 – 18 circulating fluidized bed 5 – 6.5 cross flow 4 – 6 rotary kiln 4 – 6

**Table 5.** Calorific value of synthetic gas produced with air and various gasifier types [17]

The gas turbine can run on gases with calorific values as low as 2.5 MJ/m3

**Figure 3.** Pilot scale W-t-E gasification plant during experiments and investigations

and operating experience.

controlled.

properties of waste treated.

of RDF produced in Europe. Thus the system allows downdraft (hatch D on Figure 2 closed) or updraft (hatch U on Figure 2 closed) operation to be able to adjust the gasification to the

**Gasifier type Calorific value of the product gas [MJ/Nm3]**

This utilization of synthetic gas in gas engine or turbine is only possible if high calorific synthetic gas is produced. The literature shows that the gases with the calorific value of between 4 and 6 MJ/Nm3 can be produced and the complete data is presented in Table 5. [17]

The whole process of gasification was controlled with the quantity of waste input into the chamber, the velocity of waste movement along the grate and quantity and distribution of air. The search for optimal operating conditions was based on the known composition of waste

Generated synthetic gases are on the pilot scale system measured in the duct between primary and secondary chamber with Wobbe index analyzer [12]. The temperature in primary chamber needs to be kept more or less constant just over 600 °C and the air supply must be carefully

with average composition

.

The syngas is composed of the H2, CO and CH4. These are the main components of the formed syngas, which have the energy value, and together with CO2, N2, O2 and H2O represent more than 93% of the components in syngas. The rest are higher order hydro-carbons (ethane, propane, butane, benzene,...), some cyclical hydro-carbons (benzene, toluene,...) and other gases (HCl, HF, SO2,...). Higher-order hydro-carbons and cyclical hydro-carbons do have higher calorific value than H2, CO and CH4, but are found in the syngas in very low, negligible quantities.

Pyrolysis process is again is composed of thermal decomposition of organic matter which occurs in the absence of air. To reach decomposition conditions in reactor heat and sometimes steam need to be introduced to the reaction chamber.

The pyrolysis gas has at least double the calorific value as gasification synthetic gas both produced from the same waste (fuel). But the overall energy efficiency is not always in favor of pyrolysis as there is pyrolysis gas partially utilized for heat and steam generation.

To be able to compare all three thermal conversion processes in context of power production there are schematic presentations on Figure 4 to Figure 7.

**Figure 4.** The schematic presentation of single stage combustion with steam generation and utilization

able the durability and reliability of this technologies with RDF operation. Generally these processes operate well with constant quality (properties) of waste (fuel) material without

certain undesired materials that could cause problems along the conversion process.

STEAM GENERATION

**Figure 7.** The schematic presentation of pyrolysis system with high efficient electrical power production unit

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

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:

PYROLYSIS GAS TREATMENT SYSTEM

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

CONTINUOUS EMISSION MONITORING SYSTEM AND ELECTRONIC CENTRAL CONTROL SYSTEM

Combustion of Municipal Solid Waste for Power Production

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

UTILIZATION OF PYROLYSIS GAS IN POWER GENERATOR SET

> POWER AND HEAT PRODUCTION

AIR SUPPLY

S T A C K 291

PYROLYSIS GAS TREATMENT REMAINS

STEAM UTILIZATION FOR POWER AND HEAT PRODUCTION

PYROLYSIS REACTOR / CHAMBER

HEAT (AND/OR STEAM) SUPPLY

WASTE INPUT

demands.

**•** emissions to air,

**•** emissions to water, **•** emissions to ground,

**•** flue gas treatment residue,

**•** electromagnetic radiation,

**•** ash and slag,

SOLID REMAINS

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

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

**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 of conversion process.

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‐ able the durability and reliability of this technologies with RDF operation. Generally these processes operate well with constant quality (properties) of waste (fuel) material without certain undesired materials that could cause problems along the conversion process.

**Figure 7.** The schematic presentation of pyrolysis system with high efficient electrical power production unit
