Issues in Hazardous Waste Treatment Design
- Preprocessing system
Since hazardous wastes contain some flammable substances, in order to prevent possible fire, explosion and other working conditions during the crushing process of hazardous wastes, the crusher system is equipped with a N2 injection oxygen control system, and the front and rear of the crusher flap valve is equipped with an oxygen content detection function. Once the oxygen content is higher than 6%, the system automatically closes the upper and lower hydraulic gates, and starts the button system to complete functions such as N2 injection, oxygen detection, and discharge. At the same time, in order to ensure the reliable operation of the plug-in valve, the inlet and outlet of the crusher system are equipped with hydraulic plug-in doors for double protection. - Feed sealing and handling
The kiln head feeding system of the rotary kiln is easy to cause the kiln head tempering of the rotary kiln, so it is necessary to design double hydraulic flap doors to ensure the safety during operation. When feeding, the two-stage hydraulic doors cannot be opened at the same time. When the material level of the upper hopper reaches the set value, the upper hydraulic door opens automatically. After the blanking is completed, the upper hydraulic door closes, the lower hydraulic door opens, and the solid waste enters through the chute. Rotary kiln. The intermediate hopper between the feed chute and the two hydraulic doors is cooled with soft water. The entire feeding process operates in a sealed and cooled state to ensure safe operation. - Rotary kiln coking problem and treatment
In the operation of previous projects, the problem of coking at the tail of the rotary kiln often occurred. This is because the burner of the rotary kiln is installed at the kiln head, and the combustion temperature is very high. When the feed contains wastes with low melting point salts, the ash and slag can easily become molten. When the ash and slag are close to the kiln end, the combustion temperature Lower, the molten ash is easy to stick to the refractory material. The length of the rotary kiln designed in this project is 11m, which is also prone to coking problems.
This design is directly optimized. The end of the rotary kiln is inserted into the secondary combustion chamber, which shares a slag outlet with the secondary combustion chamber. The bottom of the secondary combustion chamber is provided with a large opening for slag discharge (3300X800mm), which is convenient for large particle slag to drop slag. At the same time, a multi-component burner is installed at the bottom of the secondary combustion chamber to ensure that the combustion temperature of the secondary combustion chamber is higher than 1100 °C, and at the same time, the temperature of the kiln tail of the rotary kiln is increased. The slag falls directly into the water seal slag scraper at the bottom.
Before the waste is put into the furnace for incineration, appropriate compatibility of the waste into the furnace is carried out. In addition to the calorific value compatibility mentioned above, various wastes need to be tested. For wastes containing low melting point salts, they must be blended before they can be put into the furnace. During operation, the operator needs to adjust the incineration temperature of the second combustion chamber of the rotary kiln, and the reasonable ratio of primary air and secondary air to ensure the stable combustion of the rotary kiln and the second combustion chamber. At the same time, operators should conduct frequent inspections. Once coking is observed from the observation mirror at the end of the kiln, the wastes with high calorific value and no low-melting salts should be replaced for incineration, and the temperature at the end of the kiln should be raised to slowly melt the coke as much as possible. . Both sides of the secondary combustion chamber shall be provided with openable observation holes. At present, after the successful commissioning of the project, there has been no coking incident at the kiln end within half a year of the warranty. - Boiler fouling and corrosion problems and their treatment
Waste heat boiler ash accumulation and heating surface corrosion chamber are common problems in hazardous waste incineration. Common waste heat boiler layouts include horizontal waste heat boiler and vertical waste heat boiler. Horizontal waste heat boilers are rarely used in hazardous waste combustion. Mainly Horizontally arranged waste heat boilers are prone to fouling and corrosion. This project uses a single-drum natural circulation vertical water-tube boiler. The boiler consists of two radiant vertical flues, surrounded by membrane walls, without convection evaporation surface and gas saver to prevent the boiler from accumulating ash. The soot blowing method adopts steam soot blowing, which can effectively remove the ash deposits. During the design, the temperature of the flue gas entering the superheater should not exceed 650°C, to ensure that the temperature of the superheater tube wall is lower than 450°C to avoid high temperature chlorine corrosion of the superheater. At the same time, in long-term operation, the temperature of the secondary combustion chamber should be controlled below 1200 ℃ to avoid superheater corrosion caused by over-temperature operation and excessive nitrogen oxides caused by high-temperature combustion.