It is an important direction for the development of cement industry in China in recent years and in the future. At present, there are more than 160 cement kiln waste disposal production lines in China, including 60 domestic waste disposal lines with an annual disposal capacity of 7 million tons, more than 40 sludge collaborative disposal lines and more than 60 hazardous waste disposal lines. How to identify and reduce the impact of collaborative disposal of waste on cement kiln, and optimize and improve the ability of cement kiln to dispose waste, is a concern of many cement enterprises. The official account is to introduce a series of articles on cement kiln co disposal of waste, and explain the problems related to cement kiln disposal.
The way of feeding waste into cement kiln and its influence
In short, all wastes entering the cement kiln can be divided into three categories: gas entering (such as domestic waste gasifier), liquid injection (domestic waste leachate injection, etc.) and solid addition (almost all). In this paper, three kinds of waste adding into the kiln are described, and the influence on the kiln operation is discussed from the perspective of technology.
1. Gas in
The gas produced by the waste mainly includes the gas produced when the gasifier is used to treat the domestic waste, the odor generated during the pretreatment of the domestic waste, the gas generated during the sludge drying, and the gas generated during the desorption of the contaminated soil.
These gases usually need to be sent to the calciner for further incineration. Its impact on the system includes the following points:
(1) Balance between resistance of gasifier and pipeline system and resistance of kiln system (2) influence of gas inlet temperature, flow rate and composition fluctuation on stable operation of calciner (general) (3) influence of flue gas generated by gas combustion on preheater system resistance and high temperature fan (general) (4) influence on temperature distribution of kiln tail system (general) (5) gas (combustible gas) The problem of mixed combustion with tertiary air after entering the calciner will definitely produce a large amount of CO gas if it can not be burned. (6) the influence of harmful components carried by the gas on the crust blockage (general) (7) other problems, such as pollutant emission and impact on denitration system, etc
2. Liquid injection
The liquid in waste disposal mainly includes landfill leachate and some waste liquid (such as acid liquor and alkali liquor).
This part of the liquid is usually sprayed into the high temperature part of the furnace for disposal. As the liquid disposal capacity is generally small, its impact is relatively small, mainly including the following points:
(1) The influence of some components in the liquid on SNCR denitration system (such as ammonia nitrogen), the influence on the stable operation of the kiln (such as alkali, chlorine, etc.) (2) the heat consumed by the gasification of a large amount of water in the liquid and the resulting large amount of flue gas on the pressure distribution, temperature distribution and high temperature fan of the kiln tail system; (3) the influence of the fluctuation of liquid flow and composition on the kiln (4) Other effects: such as corrosion of equipment.
3. Solid addition
Almost all cement enterprises dealing with waste involve solid addition, including domestic waste, dried sludge, solid hazardous waste and so on. For solid waste (part or all) into the furnace, it is usually added to a part of the calciner. The details are as follows
Among them, 1) after being added into the calciner, the heavy waste will fall into the flue gas chamber due to the unstoppable flue gas; 2) part of the waste with higher calorific value will be mainly burned at the kiln head (less in China at present); 3) after being added into the calciner, the lighter weight of the waste will move up with the flue gas of the calciner, some of which will be burnt out in the calciner, and some may continue to enter the kiln with the raw material; 4) some of them are larger in size The waste is directly fed into the tobacco room for disposal (rarely in China at present)
Therefore, 1) and 3) are the focus of the discussion. For 1), the key is how to reduce the amount of particles falling into the smoke chamber! The influence of heavy particles falling into the smoke chamber on the kiln is mainly as follows:
The carbon containing components in the waste are burned here, causing local reduction atmosphere, leading to massive decomposition of sulfate and aggravating sulfur cycle, which affects the normal operation of the kiln.
The ash size of large-scale waste is also large, which may affect the quality of clinker if it is mixed into clinker;
The combustible components in the waste are burned here, and the high temperature makes the liquid phase of clinker appear ahead of time, and the kiln end forms a circle;
It may affect the ventilation in the kiln.
For 3), the key point is to improve the burn out rate of waste at the outlet of calciner! Its influence on kilns mainly includes the following aspects:
If part of the waste goes into the kiln with hot raw material, the effect is as described in 1)
Part of the waste is not burned out at the outlet of the calciner, which indicates that the heat enthalpy of the waste is not effectively utilized, and the fuel substitution value brought by the waste disposal will be reduced;
If it is not burned out, the CO concentration at the outlet of calciner will increase significantly, which will make the overall temperature of preheater rise, and the temperature of C1 outlet will increase more significantly;
If it is not burned out, the excessive CO concentration in the flue gas will affect the SNCR denitrification efficiency;
If it is not burned out, it may affect the emission of other pollutants;
In addition, the addition of solid waste will also produce some common problems, including: the impact of solid flow and composition fluctuation on the stable operation of calciner (general); the influence of flue gas generated by combustion on the resistance of preheater system and high-temperature fan (general); the influence on the temperature distribution of kiln tail system (general); the influence of harmful components carried on the crust blockage Ring (Universal).
In general, from the perspective of technology, no matter what form of waste is added into the kiln, it will inevitably affect the air consumption, temperature distribution and stable operation of the kiln tail system. However, for the gas form, the key is to balance the resistance of the pipeline system and ensure the full mixing and combustion of combustible gas and tertiary air; for the liquid form, when its disposal capacity is large, it is necessary to pay attention to the calculation of heat budget and large amount of steam; for the solid form, try to reduce the large-scale waste directly into the smoke chamber, and improve the waste in the decomposition furnace Burn out rate is the key!