**9. Conclusion**

Figure 14 shows analyses that help us to determinate the interaction among maximal ash temperature versus secondary air velocity and oxygen mass flow rate at secondary air inlet. The maximal ash temperature from secondary air velocity from 27 m/s to 29 m/s increases rapidly and picked the maximum ash temperature at 1,850 K. On the other hand, there is no significant dependence of oxygen mass flow rate in region from 0.255 to 0.21. In this way we

Figure 15 show results of temperature field comparison by different operating condition with different oxygen mass flow rates in case of enriched oxygen combustion. The temperature in secondary combustion chamber increases when oxygen enriched air is used [4] and this phenomena is clearly seen by temperature comparison on this picture. On the other hand, we have to be sure that the maximum ash temperature was not exceeded the ash melting point and we have to avoid fly ash deposit on heat exchangers walls which can cause a great damage.

Figure 16 shows 3D ash temperature particle tracking through the W-t-E. The ash temperature changing through the W-t-E and it was picked in the secondary combustion chamber where the oxygen enhanced combustion is used. In addition, the ash temperature has fallen due to the wall cooling. It was found out when the flaying ash clashes into the walls the probability

**Figure 15.** Temperature field by different oxygen mass flow rate at secondary enriched air inlet

of ash deposit at these sections is high.

304 Advances in Internal Combustion Engines and Fuel Technologies

can predict and avoid the possible damages cause by fly ash flagging on boiler tubes.

Waste presents a source of energy. The energy utilization is possible with the appropriate integrated waste management system and utilization of appropriate technologies within the legally permissible environmental impact. Such system can create power and heat or cold, which is distributed to the citizens or industry.

Future waste management is going to depend on W-t-E technologies for the high calorific part of the waste stream, not suitable for recycling. The energy in waste will be utilized as the energy prices are not only high but are in constant rise. But the decision making process for the technology selection should not stand only on presented energy efficiency of the technology, thus only full scale long term tested technologies with proven environmental impact should be applied.

Utilization of waste in W-t-E plants means reducing greenhouse gas emissions, more rational management of energy and limited space for waste disposal.

**Abbreviations**

**Symbols**

2D - two dimensional MSW - municipal solid waste 3D - three dimensional PEHD - high-density polyethylene CFD - computational fluid dynamics PET - polyethylene terephthalate

EU - European Union R&D - research & development

LDPE - low-density polyethylene RDF - refuse derived fuel MBGI - mass burning grate incinerator W-t-E - waste – to – energy

*C*η - constant ρ¯ - mean value of density *C1* - constant *<sup>h</sup>*¯ - mean value of enthalpy *C2* - constant υ*<sup>j</sup>* ¯ - mean value of fluid velocity <sup>σ</sup>*k* - constant ρυ' ¯*<sup>j</sup>* <sup>φ</sup> ' - Reynolds' fluxes σε *- constant* ρυ' *<sup>j</sup>* <sup>υ</sup>' ¯*i* - Reynolds' stresses

*cp* - specific heat *<sup>f</sup> ui* ¯ - sum of all volume forces

*k* - turbulent kinetic energy η*t* - turbulent viscosity *Mk* - molecular mass of the component *k Rk* - chemical reaction rate *p* - pressure Sc*t* - turbulent Schmidt number

Dk - molecular diffusion coefficient of component k ε - turbulent kinetic energy dissipation

*f* - function Δ*H°f,k*- standard heat of formation of component *k I*ε - turbulent kinetic energy dissipation source/sink term ωk - formation/consumption rate of component k *Ik*- turbulent kinetic energy source/sink term ν''*k* - stoichiometric coefficients of component k for

*k* - component ν'*k* - stoichiometric coefficients of component k for

products

reactants

IPPC - integrated pollution prevention control RANS - Reynolds Averaged Navier-Stokes

¯ - chemical source term



¯ - combustion source/sink term

Combustion of Municipal Solid Waste for Power Production

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

307

Eq. - equation PS - polystyrene

MBT - mechanical and biological treatment

*<sup>a</sup>* - constant *<sup>I</sup>*ξ*<sup>k</sup>*

b constant *IT*

*c* - constant *q*¯ *<sup>j</sup>*

*d* - constant τ¯ *ij*

Pr*t* - turbulent Prandtl number

Operational data of most W-t-E plants show the following positive effects:


The produced heat of such systems should be used for the needs of the city district heating or industry. The power is partially used for the facility's own consumption and the surplus is placed in the power distribution network.

The correct operation approach and inclusion into city utility services makes the W-t-E plant more acceptable to the society and with such integral management generated MSW no longer present a problem but rather an energy and material source opportunity.

The heat of 1 ton of RDF approximately corresponds to 500 Sm3 of natural gas thus a lot of money and fossil fuel can be saved by proper utilization of this alternative fuel source.

The regional integrated waste management strategy can be utilized in cost and environmental benefit for the citizens of populated region from around 200.000 inhabitants. The concept and technologies utilized in this work presented concept are completely in accordance to European legislation and strategic waste management documents. Each technology discussed is also a "Best available technology" for the segment considered.

Waste gasification and pyrolysis processes results on experimental devices show clear potential for high efficient electrical power production compared to standard waste incinera‐ tion (combustion). The process solutions proposed should be real environment and full scale tested thus present environmentally and financially safe investment. The achieved calorific values of synthetic gases are in the acceptable range for utilization in gas engine or turbine what gives a good utilization potential. Such solutions will raise power production from RDF well over 30%.

The applicability of advanced engineering computer simulation tools should become standard for every R&D in W-t-E technology design. CFD can provide analyses results, comparable to tests on full scale equipment. The CFD approach and the numerical optimization can be used to identify the appropriate conditions to achieve complete conversion conditions, minimize the environmental impact, operating troubleshooting and keep operating costs on reasonable level.

CFD approach can offer huge benefits and provide numerical optimization of the operating conditions without expensive and long duration measurements and different operating conditions. In this way, this optimization can be used not only for operating parameters prediction of built W-t-E but also in the project design phase which would reduce the research and development costs.
