Lime kiln environmental protection equipment

Technical route and advantages of environmental protection equipment for lime kiln

Technology roadmap

There are three main links in lime production: limestone calcination; Heat recovery of calciner waste gas; High temperature lime heat recovery. The core is limestone calcination, the main process is calcium carbonate decomposition, and the key point is to improve the calcined calcium carbonate decomposition rate. During the calcination of limestone, the decomposition reaction of calcium carbonate is CaCO ∈→ CaO+CO ∈, which is an endothermic reaction. When the temperature rises to 5500C, calcium carbonate begins to absorb heat, decomposes into CaO and releases CO ∈ gas. With the increase of temperature, the decomposition speed is accelerated, and a large amount of decomposition starts above 7500C. At this time, the heat absorption is 1660kJ · kg-1 (i.e. 397kcal, kg-1). It is calculated that the theoretical heat of formation of finished lime is about 2906 kJ · kg-1 lime, equivalent to 695 cal · kg-1 lime.

The decomposition reaction rate of calcium carbonate is mainly related to calciner temperature, CO  2 partial pressure, calcium carbonate particle size and other factors. The particle size of limestone is the main factor affecting the decomposition reaction rate of calcium carbonate. The larger the limestone particles are, the deeper they reach the interior of the particles, the slower the infiltration of heat and the release of carbon monoxide generated by decomposition, and the slower the decomposition reaction of calcium carbonate. The relationship between the limestone particle size and the calcination time after burning is shown in Figure 1, while the particle size of 0, 1mm limestone at 950oC

The solution time is less than 1s.

Therefore, calcining limestone from lump to powder is an effective method to improve the decomposition reaction rate of calcium carbonate, that is, combining the suspension calciner, multi-stage suspension preheater, multi-stage suspension cooler, etc., to achieve the whole process of preheating, decomposition and cooling of limestone powder in suspension. Suspension preheating decomposition technology has been widely used in China, especially in the cement industry.

In the suspension calciner, powdered limestone and fuel are evenly suspended and dispersed in the air flow combined with jet swirling movement, completing the combustion, heat transfer, decomposition, mass transfer and other processes, improving the reaction speed and thermal efficiency. A cyclone separator is set at the outlet of the furnace to separate and collect the calcined lime powder as the finished product. The function of multistage suspension preheater is to recover the heat of waste gas released from suspension calciner, preheat limestone powder and reduce the temperature of waste gas discharged from the furnace. The waste gas from the cyclone separator at the outlet of the suspension calciner enters the multistage suspension preheater, gradually heats the fed limestone powder, and the preheated limestone powder enters the suspension calciner for calcination. The function of the multi-stage suspension cooler is to recover the heat from the finished powder lime of the suspension calciner. The high-temperature finished powder lime separated and collected by the cyclone separator enters the multi-stage suspension cooler for gradual cooling, and the preheated cooling air enters the suspension calciner as the combustion air.

The number of cyclone separators at the outlet of suspension calciner shall be determined according to the capacity of powdered lime, one or two in parallel, and the corresponding multi-stage suspension preheater and multi-stage suspension cooler shall be in single row or two in parallel. The series stage of the multistage suspension preheater can be determined according to the requirements of the exhaust gas emission temperature of the multistage suspension preheater, and the series stage of the multistage suspension cooler can be determined according to the requirements of the finished lime temperature from the multistage suspension cooler.

Technical advantages

The production process of powdered lime will change from calcining massive limestone to grinding into powder, to grinding massive limestone to powder suspension preheating and calcination cooling, which will reduce the calcination heat consumption and grinding power consumption in the production process of powdered lime, and will also make the lime production green and modern. Compared with the current blocky lime calciner, its advantages are as follows:

(1) High heat exchange efficiency due to preheating, decomposition and cooling in suspension state;

(2) Calcium carbonate is decomposed in powder form, with fast reaction speed and high decomposition degree;

(3) The temperature of suspension calciner is uniform and controllable, and the decomposition reaction is uniform, which further improves the uniform stability of product quality;

(4) The high-temperature preheating, decomposition and cooling process are carried out in a static device that is not running, and the operation is stable and reliable with high operation rate;

(5) The production scale is easy to be large-scale, the unit product occupies a small area, saves investment, and the comprehensive energy consumption and cost are low;

(6) Limestone of various particle sizes can be ground into powder as raw materials to improve resource utilization;

(7) There are mature experiences in construction, operation, management and operation of modern new dry process cement enterprises. At present, the technology of rolling powdery lime into balls is becoming more and more mature, which can roll powdery lime into various balls less than 80mm, which will open up a wider market space for the application of powdery lime.