**5. Engineering Application of Rotary Kiln**

The rotary kiln and the entire system have been operated in a pesticide plant in Shandong, China. The incineration system is mainly composed of pretreatment, waste incineration disposal, and a flue gas treatment system. Figure 16 shows the practical engineering application of our rotary kiln.

**Figure 16.** Incineration process and flue gas treatment process.

The incineration disposal disposes the pesticide waste liquid and the solid wastes after pretreatment. Under the continuous rotation of the rotary kiln, the mixed wastes are continuously turned, heated, dried, vaporized and burned in the kiln. The combustion temperature in the rotary kiln is kept at about 850 ◦C, and the residence time of the wastes in the kiln is more than 1 h. Primary dust removal is performed in high-temperature cyclone separator to reduce the particle content in flue gas produced by combustion. After dust removal, the gas enters the secondary combustion chamber. The gas products of the rotary kiln are mixed with the combustion-supporting air of the secondary combustion chamber, and the unburned combustible gas in the rotary kiln is completely burned to remove the toxic organic component. The combustion temperature of the second combustion chamber reaches 1100 ◦C, and the residence time of the flue gas in the second combustion chamber is no more than 2 s. The discharged gas enters the flue gas treatment system.

The flue gas treatment system is composed of heat exchanger, air preheater, quench tower, activated carbon and a calcium oxide injection system, baghouse, and wet desulphurization. The flue gas discharged from the second combustion chamber initially enters the heat exchanger and air preheater, which can fully utilize the waste heat of high-temperature flue gas, save energy and reduce consumption. The outlet gas temperature is 500–550 ◦C. Thereafter, the flue gas enters the quench tower. The high-temperature flue gas contacts directly with the atomized cooling water in the quench tower, and the flue gas temperature drops rapidly to 200 ◦C within 1 s, thereby avoiding dioxin regeneration. Before the flue gas from the quenching tower enters the baghouse, calcium oxide and activated carbon are sprayed successively into the flue. The calcium oxide is used to neutralize the acidic substances in the flue gas. The activated carbon is used to absorb the heavy metal and dioxins in the flue gas. In the baghouse, the suspended particles in the flue gas are intercepted by the filter bag and discharged in the form of fly ash. The flue gas enters the wet absorption tower of the desulphurization unit and contacts with sprayed limestone slurry droplets. The acid substances in the flue gas are absorbed.

An Atmos FIR Fourier infrared multicomponent gas analyzer was used to measure the concentration of SOX, NOX and HCl at the chimney outlet according to GB/T16157-1996. In order to ensure the measurement accuracy, the gas analyzer was calibrated with the target standard gas before measuring. Similarly, automatic smoke sampler with sampling gun was used to measure dust. According to the USA EPA23a method, flue gas sampling was isokinetically collected, and dioxins

were preprocessed and measured [29]. The final flue gas concentration (Table 5) meets the emission standard of waste incineration.


**Table 5.** Measured value of pollutant concentration in flue gas.

The main power consumption equipment in the incineration process of the rotary kiln re the screw conveyor, the motor driving device of the rotary kiln, the draft fan, the ignition burner, the secondary burner, the blower, the slag discharging motor, the quench pump, the lye pump and so on. The total power of the power consumption equipment is 98.29 kW. The hourly waste disposal capacity of the rotary kiln is 1000 kg/h. It takes 353 MJ energy to dispose of a ton of waste. The low calorific value of diesel oil is 42 MJ/L. The diesel oil consumption is 200 L/h. The economic cost of the rotary kiln incineration system mainly includes equipment operation cost, diesel fuel cost, and maintenance cost. The rotary kiln works continuously for 10 h. The power consumption of a rotary kiln is 982.9 kWh per day. The diesel oil consumption per day is 2000 L. There are three workers in total. It costs 691 RMB to treat a ton of waste.

#### **6. Conclusions**

A large amount of liquid and solid wastes generated during pesticide production are urgently needed for disposal. A co-incineration scheme for mixing multi-component wastes in a rotary kiln was proposed for waste disposal from pesticide production. The co-incineration experimental results showed that the residence time of solid and liquid mixtures in the kiln is more than 1 h, and the clinker ignition loss of the slag is less than 5%. Therefore, the co-incineration of solid and liquid wastes is feasible. A numerical study of different particle diameters and different wall rotational speeds was performed to reproduce the configurations of solid flows (i.e., sliding, slumping, rolling, cascading, cataracting, and centrifuging). The rolling or cascading mode was selected as the best operating condition. The numerical simulation revealed the combustion interactions of the co-incineration of mixed wastes, and the results showed that the co-incineration of solid and liquid wastes is feasible by adding auxiliary fuel. The rotary kiln incineration can keep the kiln temperature, mass residue and pollutants within the allowable range. Finally, the rotary kiln incineration process and flue gas treatment process were operated and commissioned. The liquid and solid wastes can be completely burned, and the flue gas concentration after treatment can meet the emission standard of waste incineration.

**Author Contributions:** Investigation, B.Z. and J.H.; methodology, B.Z.; software, C.H.; data curation, W.C.; writing—original draft, J.H.; writing—review and editing, B.Z.

**Funding:** This research was funded by Key Research and Development Program of Shandong Province of China (No. 2019GHY112002).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Nomenclature**



#### **References**


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