Environmental protection kiln design technology reference
Basic theoretical parameters of lime calcination
1. When lime is calcined, CaCO3 = CaO (s) + C02 (g) - 178.4KJ/mol
Under normal circumstances, CaCO3 begins to decompose between 880 ° C and 915 ° C. In order to improve the decomposition rate of CaCO3, the calcination temperature of the limestone in the limestone kiln should be maintained in the range of 950 ° C to 1200 ° C, and the maximum temperature is 1250 ° C. During the decomposition process of limestone, the impurity MgCO3 in it is also decomposing. The reaction equation is as follows:
MgCO3 = MgO (s) + CO2 (g) - 177.7KJ/mol
The decomposition point of MgCO3 is much lower than that of CaCO3, and the decomposition reaction speed is accelerated when the temperature reaches 700 ° C. Since there are also impurities such as SiO2, AL2O3 and FeO3 in limestone, the decomposition reaction is also accompanied by the following side reactions. The reaction equation is as follows:
SiO2 (s) + XCaO (s) = XCaO. SiO2 (s)
AL2O3 (s) + XCaO (s) = XCaO. AL2O3 (s)
Fe2O3 (s) + XCaO (s) = XCaO. Fe2O3 (3)
SO2 (g) + CaO (s) = CaCO3 (s)
The heat required for the calcination reaction of limestone is supplied by coke, and the combustion reaction is as follows:
C (s) + O2 (g) = CO2 (g) + 393.8KJ/mol
2C (S) + O2 (g) = 2CO (g) + 219.2KJ/m0l
2CO (g) + O2 (g) = 2CO2 (g) + 570.6KJ/mol
2H2 (g) + O2 (g) = 2H2O (g)
S (g) + O2 (g) = SO2 (g)
The above constitutes the general process of the calcination reaction
2. Limestone consumption: 1.6-1.8t/t * ash
3. Calcination temperature: 900-1250 degrees
After the limestone that has been processed and screened by the mine is transported to the limestone stockyard in the factory, the qualified limestone is transported by the loader to the limestone reserve silo in front of the kiln. Coal is also screened from the stockyard and transported to the coal reserve silo. A reciprocating feeder and a measuring hopper are installed at the lower part of the limestone and coal silos respectively. After the limestone and coal are weighed according to the proportional requirements, they enter the crane and pull up along the inclined bridge. After the crane reaches the top, it is tipped over and poured into the distributor to receive the hopper. The distributor evenly loads the material into the kiln. The raw fuel material is calcined in the kiln through the reduction reaction process of the preheating belt, the combustion belt and the cooling belt. At the bottom of the kiln, the calcined lime is unloaded through a screw cone to be unloaded to the lime belt conveyor, and the belt conveyor transports the lime to the designated location.
Design of fabric equipment
After a uniform mixture, it is lifted from the single-bucket elevator to the top of the furnace and put into the stone unloading bucket. The stone unloading bucket is controlled by an electrical switch, and the angle specified by the four-point fabric starts to rotate. The hopper runs to the bottom of the inclined bridge and presses the pressure bar of the lower bell cap by the weight of the hopper itself, thereby opening the lower bell cap, and the mixture in the receiving hopper is sprinkled into the lime kiln through the distributor.
Calcination measurement and control
Furnace temperature detection: Limestone is calcined in the kiln through three sections, namely the preheating section, the combustion section, and the cooling section. According to the thermal theory of the kiln, the preheating section should account for 25% of the kiln height. The calcination section accounts for 50%, and the cooling section accounts for 25%.%, but it is reflected from the actual operation experience of the kiln. The combustion section is generally 1-2 meters higher. There are 3 layers * 3 thermocouples in these three sections to detect the kiln temperature in the furnace. The ash outlet point is controlled by an ash thermocouple, and the top is controlled by a kiln gas thermocouple.
Monitoring and Automation
The kiln has 6 monitoring points, which are distributed in various key parts of the kiln. The operator can know all kinds of operation conditions of the kiln in the control room and observe the various operation states of the kiln at any time. All processes from the silo to the ash discharge of the kiln are automatically controlled and completed by the control personnel in the control room.
Dust removal system
1. Flue gas dust removal and desulfurization
After the kiln gas is ejected from the kiln, the dust is removed by a multi-rotor separator, and then it is contacted with alkaline water through the desulfurization chamber to remove sulfur dioxide. After cooling and dehydration, it is discharged to the chimney by the induced draft fan.
2. Post dust removal system
After the lime is discharged by the ash extractor, it is collected by the bag filter.