Application of Rotary Kiln Incinerators in Hazardous Waste Management

With the rapid development of human society and economy, industrial and other sectors have produced a large amount of hazardous waste during production and construction processes. These wastes pose various hazards and present significant threats to society. Hazardous waste can be classified into several categories based on its characteristics and sources, including organic waste, inorganic waste, medical waste, chemical waste, etc. These wastes are highly toxic, corrosive, flammable, or radioactive, and need to be safely and effectively disposed of to prevent harm to the environment and human health. With increasing environmental awareness and stricter laws and regulations, finding efficient and environmentally friendly hazardous waste treatment technologies has become a pressing need for all industries.

Incineration is the current mainstream thermal treatment technology for hazardous waste disposal. The principle is to deeply oxidize and completely decompose the toxic and harmful substances in hazardous waste in a high-temperature furnace, effectively achieving harmless and reduced waste. Currently, commonly used hazardous waste incineration technologies include rotary kiln incinerators, mechanical grate furnaces, and pyrolysis gasification furnaces.

Among these, the rotary kiln incinerator, as an advanced high-temperature incineration equipment, is most suitable for treating industrial hazardous waste due to its high efficiency, stability, wide adaptability, and environmental friendliness. Mechanical grate furnaces, due to their numerous moving parts which are prone to corrosion, complex equipment maintenance, and high investment, are mostly used for incinerating municipal waste. Pyrolysis gasification furnaces, due to current technical limitations, can only be used for small-scale treatment scenarios such as less than 10 tons per day, with higher project costs.

Rotary Kiln in Hazardous Waste Incineration

The main part of a rotary kiln incinerator is a horizontal steel cylinder, slightly inclined to the horizontal line and lined with refractory materials. The feeding end of the cylinder is slightly higher than the discharging end, and the cylinder can rotate around its axis. During operation, waste enters from the higher end and moves toward the kiln tail under the rotation of the cylinder, being uniformly heated and incinerated by the flame inside the kiln. The incinerated residue is discharged from the lower end.

Rotary Kiln Incinerator

When used for hazardous waste treatment, a rotary kiln incinerator usually needs to be equipped with a secondary combustion chamber. Hazardous waste can only achieve complete harmless combustion under conditions of sufficiently high temperature, adequate gas retention time, good turbulent contact, and excess oxygen (6%~10%). This process can be completed in two steps: first, in the rotary kiln, the waste undergoes drying, gasification, and combustion at a relatively lower temperature, separating ash residue; then, the flue gas is further burned at high temperature in the secondary combustion chamber. It is hard to achieve complete incineration of hazardous waste in one step, unless we use a very large-volume, high-temperature-resistant rotary kiln, which would increase project costs and energy consumption.

To avoid radiation and overheating of the secondary combustion chamber shell, it is designed as a cylindrical body composed of steel plates and refractory materials. According to incineration theory, to ensure sufficient combustion of flue gas, the 3T+1E principle must be followed: ensuring sufficient temperature, adequate residence time, sufficient turbulence, and adequate excess oxygen. The first three functions are achieved by the secondary combustion chamber. Secondary air and two combined burners are set at the lower part of the secondary combustion chamber to ensure the flue gas temperature reaches the standard and the flue gas has sufficient turbulence.

Classification of Rotary Kiln Incinerators

According to the flow direction of gas and solids in the rotary kiln, it can be divided into co-current and counter-current types.

In a co-current rotary kiln, the movement directions of materials and flue gas are the same. The drying section, combustion section, and burnout section of the materials in the kiln are relatively distinct. Currently, the majority of rotary kiln incinerators are of the co-current type because the feed, air intake, and auxiliary burners of co-current rotary kiln incinerators are simple to arrange, easy to operate and maintain, and conducive to feeding and pre-treatment of waste. In the co-current mode, the residence time of the waste gasification components in the kiln is also relatively long.

In a counter-current rotary kiln, the movement directions of materials and flue gas are opposite. The drying, combustion, and burnout of materials in the kiln do not have clear divisions. Counter-current rotary kilns are suitable for sludge with high moisture and low combustibility. The counter-current design can provide optimal gas-solid mixing and contact, high heat transfer efficiency, and can increase the combustion rate. However, due to the large relative velocity between gas and solid phases, the dust content in the flue gas is relatively high.

Process Flow of Using Rotary Kiln to Incinerate Hazardous Waste

The rotary kiln has a pushing device at the feed inlet to ensure continuous feeding. Hazardous waste is fed into the rotary kiln body through the feeding mechanism for high-temperature calcination, and incinerated into high-temperature flue gas and ash residue. The rotation speed of the rotary kiln can be adjusted, and maintaining a stable ash layer of about 50 mm can protect the refractory layer.

Hazardous Waste Incineration with a Rotary Kiln Incinerator

The high-temperature flue gas and ash residue enter the secondary combustion chamber from the kiln tail, and the incinerated ash residue enters the slag remover, which is periodically sent to the stabilization/solidification workshop for treatment. The exit temperature of the rotary kiln is 800-850℃.

After the flue gas enters the secondary combustion chamber, the secondary air is tangentially injected around the secondary combustion chamber, forming a strong vortex field in the chamber, ensuring that the combustible components in the flue gas can be fully burned. The flue gas temperature at the secondary combustion chamber exit is greater than 1100℃, and the residence time in the high-temperature zone is more than 2 seconds, ensuring the complete decomposition of harmful components in the flue gas, including dioxins, meeting the requirements for hazardous waste incineration.

Advantages of Rotary Kiln Incinerators in Hazardous Waste Management

The rotary kiln incinerator has been widely used in the current hazardous waste incineration industry mainly due to its numerous advantages, including:

Great flexibility in feeding:

The rotary kiln incinerator can effectively handle solid waste, liquid waste, colloidal substances, and gaseous pollutants, making it highly adaptable to various incineration materials. This flexibility allows the rotary kiln incinerator to meet diverse hazardous waste treatment needs, improving efficiency and scope.

Efficient heat transfer:

During the incineration process, the materials tumble and move forward in the kiln due to the rotation of the cylinder, achieving the coexistence of radiation, convection, and conduction heat transfer modes in the kiln. This efficient heat transfer method achieves uniform temperature distribution and high heat utilization in the kiln, ensuring that hazardous waste can be fully burned and decomposed, and reducing the emission of harmful substances.

Continuous ash discharge design:

The rotary kiln incinerator can continuously discharge ash residue during the incineration process without affecting normal operation. This ensures continuous incineration and reduces the frequency of shutdowns for cleaning, improving equipment operational efficiency.

Precise control of material residence time:

By adjusting the rotation speed of the kiln body, the residence time of materials in the furnace can be precisely controlled. This control method makes the incineration process more flexible and controllable, allowing adjustments to incineration conditions according to the characteristics of different hazardous wastes to achieve optimal incineration results.

About GEMCO Energy

As a professional waste management equipment manufacturer, GEMCO Energy has been committed to researching and producing high-performance rotary kiln incinerators for many years, providing clients with comprehensive hazardous waste treatment solutions. Through continuous technological innovation and practical accumulation, our rotary kiln incinerator has won a good reputation and wide application in domestic and foreign markets.

Get In Touch

Get in touch with us for a free consultation or request a customized quote, our expert engineering team is always ready to help. Together, we can build a clean, efficient, and sustainable future.

Customized EPC Projects

Reply Within 24 hours

After Sales Services