## 3 Results and Discussions
### Analysis of Petrochemical Excess Sludge Incineration  
The sludge has different water content, and the amount of auxiliary fuel required for incineration disposal and the amount of incineration flue gas generated are quite different. When the dry sludge has a calorific value of 3500 kcal/kg and a water content of 33.3-80%, the sludge with a dry sludge content of one ton is incinerated. When the incineration temperature is maintained at about 800 \({}^{\circ}\)C, the required auxiliary fuel oil is between 0 and 850 kg, the self-sustained combustion of sludge can be achieved when the water content is less than 33.3%, and the amount of flue gas generated by incineration is about 7000-25,000 m\({}^{3}\)[59]. The higher the moisture content of the sludge, the more auxiliary fuel oil required for incineration, and the greater the amount of flue gas generated, hence the  
Figure 2: Contents of C, H, O, and N in Cq sludge samples. heavier the tail gas treatment burden. Therefore, sludge incineration needs to be dried to reduce the moisture content of the sludge. Drying methods for sludge include convection, conduction, and radiation, or a combination of these technologies. However, no matter which way, sludge has serious natural and dust explosion risks when it is hot-dried. When the solid content of the sludge is more than 80%, it is finely granulated and has a small particle size. The frictional collision between the sludge and the surrounding medium can generate a large amount of dust with a particle size of less than 150 \(\upmu\)m. The dust has a certain oxygen content. Dust explosion is highly prone to occur under conditions such as temperature. Generally, the lower limit of the explosive concentration of organic dust is 20-60 g/m\({}^{3}\). When the protective gas is nitrogen, carbon dioxide, and water vapor, the minimum oxygen content of the dust combustion explosion is about 5%, 6%, and 10%, respectively. Therefore, the sludge is generally dried to a moisture content of about 30%. The petrochemical excess sludge contains a certain amount of petroleum hydrocarbons. For example, the Cq wet sludge has a petroleum hydrocarbon content of 0.564%. When the sludge drying process is selected, the petroleum hydrocarbon content in the gas phase during the drying process needs to be analyzed to prevent flash-explosion. The sludge contains elements such as N, C, S, and P. The contents of elements such as N, C, S, and P of Cq sludge are shown in Figures 2 and 3, respectively. Gases such as CO, CO\({}_{2}\), NO, NO\({}_{2}\), P\({}_{2}\)O\({}_{3}\), P\({}_{2}\)O\({}_{5}\), SO\({}_{2}\), and SO\({}_{3}\) are easily generated during incineration, and the corrosion dew point of the flue gas containing COx-NOx-SOx-POx-H\({}_{2}\)O system is related to the thermodynamic properties of the mixed gas components. The composition fluctuates greatly, causing serious corrosion of the equipment. As can be seen from Figure 3, the content of Cl in Cq sludge is 353 mg/kg. The contents of Na and K are shown in Figure 3. The melting point of NaCl and KCl is low, and the sludge is easy to follow the flue gas during incineration. Entering the exhaust gas, it is easy to react with sulfur oxides in the presence of water and oxygen to form HCl and Cl\({}_{2}\), which is highly corrosive to the equipment. To avoid the generation of dioxin, the temperature of incineration and disposal of solid waste is generally not lower than 850 \({}^{\circ}\)C [49]. In this study, heavy metal elements of ash obtained from the incineration of Cq sludge at 850 \({}^{\circ}\)C is shown in Table 5. It can be seen from Table 5 that the content of Ni, Zn, and As elements exceed the standard. In addition, the contents of uranium and thorium are 5.90 and 1.77 mg/kg, respectively, which are lower than the mean contents of uranium (3.03 mg/kg) and thorium (13.8 mg/kg) in Chinese soil [53]. Furthermore, from the change of Hg content before and  
Figure 3: Contents of S, P, Cl, Na, and K in Cq sludge.