# Flue Gas Composition and Treatment Potential of a Waste Incineration Plant
## 2 Methods and Materials
### Prediction of the Real CO\({}_{2}\) Volume in the Flue Gas  
According to [23], there are three methods for predicting and calculating CO\({}_{2}\) emissions. As is well known, it is the CO\({}_{2}\) emissions that are of concern due to their effect on the climate and atmosphere. Therefore, it is essential to predict the amount of CO\({}_{2}\) emitted from a waste incineration plant at the design stage. Such predictions require specific data about the volume of flue gas generated, the gas fractions in the flue gas, the excess air, and the composition of the waste. These days, such data are widely available as waste composition is being thoroughly investigated. For example, there are reports from the Inter-governmental Panel on Climate Change (IPCC) [24] and the EC which specify regulations for waste incineration [13,25]. With more than 500 installations for treating around 25-30% of the EU's municipal waste as well as other types of waste such as hazardous waste or sewage sludge [26], there are plenty of data accessible directly from the websites or from the environmental ministry of each candidate country. The prediction of CO\({}_{2}\) emissions as a function of the oxygen fraction in flue gas constitution was one of the three methods chosen for this research, and the other two can be found in [23]. The selected method depends on the elementary fraction of the composition of the MSW and its energy content (calorific value) in addition to the oxygen fraction, as shown:  
\[F=\frac{227.2*H(\%)+95.5*(C\%)+35.6*S(\%)+8.7*N(\%)-28.7*O(\%)}{GCV} \tag{13}\]  
\[F_{c}=\frac{2*C\ (\%)}{GCV} \tag{14}\]  
\[CO_{2}(\%)=100\ \frac{F_{c}}{F}\ \frac{20.9\ (\%)-O_{2}(\%)}{20.9\ (\%)} \tag{15}\]  
where, \(F\) is the fraction of flue gas flow per unit of energy [m\({}^{3}\)/M]]. \(F_{c}\) is the fraction of carbon flow per unit of energy [m\({}^{3}\)/M]]. \(GCV\) is the higher calorific value [M]/kg]. The percentage of the volumetric flow of oxygen in the flue gas can be calculated depending on the calculation of the theoretical flue gas volume or based on the data available from real waste incineration plants. Some of the available data shown were adapted from [23]. Regarding the gross calorific value (\(GCV\)), this can be found in two ways; either by laboratory analysis using the bomb calorimeter, or by using the available equations model to calculate the value. Both were used here, and it was found that the value was in the range 17,000-24,000 kJ/kg. The equation used to calculate this value is as follows [27]:  
\[GCV=19.2880-0.2135\ \left(\frac{VM}{FC}\right)-1.9584\ \left(\frac{AC}{VM} \right)+0.0234\ \left(\frac{FC}{AC}\right) \tag{16}\]  
where, \(VM\) is the volatile matter (%), \(AC\) is the ash content (%), and \(FC\) is the fixed carbon (%). Table 6 shows the CO\({}_{2}\) emissions from real incinerators. Waste normally includes oxygen and different organic compounds such as cellulose (C\({}_{6}\)H\({}_{10}\)O\({}_{5}\)), which is the main component of paper. In the previous calculations for burning 1 kg of carbon, the required air was all used for the complete combustion of carbon. No excess air was discharged from the interaction, (this amount of air is known as stoichiometric air), and as a result, 11.43 kg of air was required as stoichiometric air for burning 1 kg of carbon. The fraction of air considered as stoichiometric air implies a burning process of 100% efficiency, which means that air is in full contact with the waste surface such that none of it is wasted. In reality, the amount of stoichiometric air is not sufficient to achieve the complete burning process, and therefore, the amount of air must be increased. For burning solid waste, excess air of 100 to 200% stoichiometric air is required [20]. The chemical equation for the cellulose combustion process is shown below (according to [20]):  
\[\text{C}_{6}\text{H}_{10}\text{O}_{5}+6\text{O}_{2}+(6*3.76)\text{N}_{2}\to 6 \text{CO}_{2}+5\text{H}_{2}\text{O}+22.56\text{N}_{2}\]  
As can be seen in Table 7, 5.09 kg of air is required to burn 1 kg of cellulose.