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Lime production technology

Date:2019-08-26 15:16 Source:cementepcViews:

Lime is a necessary auxiliary material in the process of steelmaking, and its quality will directly affect the amount and quality of steel.

Although our country is energy superpower, but due to backward technology, especially the old kiln burning limekiln type and soil pollution, poor quality, high energy consumption, low yield, short of steelmaking requirement about the quality of the white, compared with the mechanical automatic calcined in the world, the gap is quite big, at present our country 70% lime kiln kiln is no environmental protection measures, protected by local survival, but all regions, all kinds of industrial pollution has caused the state attaches great importance to, thus eliminating soil lime kiln burning,To build our own modern white ash kiln with energy saving, environmental protection and high efficiency is not only the requirement of national environmental protection, but also the imperative measure of hundreds of thousands of lime production enterprises in China.The following is a simple analysis of lime raw material, calcining fuel, calcining equipment and process.

 

1 raw limestone


Limestone is a kind of rock formed from sedimentary source, which is alkaline rock and is mainly composed of calcium carbonate, calcium magnesium carbonate or a mixture of calcium carbonate and magnesium carbonate.Limestone has good processing, polishing and good cementing performance, insoluble in water, soluble in saturated sulfuric acid, can react with strong acid and form corresponding calcium salt, and release CO2 at the same time.
 

1.1 impurities in limestone


Because limestone (CaCO3) is a natural mineral, it contains impurities that are not conducive to calcination.The impurities are mainly SiO2, AL2O3, Fe2O3, K2O, P, S, etc.
 

1.2 size of limestone


In the process of limestone calcination, the influence of the particle size of raw limestone is very large. Because CO2 separation is carried out slowly from the surface of limestone to the interior, the calcination with large particle size is more difficult and takes longer time than that with small particle size.Through scientific test and analysis, the calcining time at a certain temperature is proportional to the square of the thickness of limestone, and the calcining time of 80mm stone is 4 times that of 40mm stone.Practice shows that the best effect is to choose limestone with particle size of 40-80mm for shaft furnace and 10-30mm for rotary kiln.
 

1.3 selection of limestone


Limestone with high density of calcium is not easy to burn, but the lime and gray matter after calcination is good. On the contrary, limestone with low density of calcium is easy to burn, but the gray matter after calcination is poor.The content of calcium and other substances in limestone is determined by chemical analysis, wear test and calcining test.Generally, the CaO content of high-quality limestone is more than 52%, MgO content is less than 3%, and SiO2 content is less than 1%.

Lime production

2 fuel


There are many fuels for calcining limestone.There are solids, liquids, gases and so on.

Solid fuels are mainly coal and its processed products.Coal is an important energy source and chemical raw material.The best coal for calcination of limestone is the one with high calorific value and low S content.But using coal as fuel is costly and polluting.

Liquid fuels are petroleum and processed products.Most of them are atomized and diffused by atomizing devices.But also because the production cost is too high pollution is generally not used.

There are many kinds of gas fuels, such as coking gas, producer gas, natural gas, blast furnace gas, converter gas and so on.Gas fuel is beneficial to improve thermal efficiency and save energy.Compared with coal burning, gas fuel can increase thermal efficiency by 2 times, and oil by 1 times.And gas fuel is conducive to protect the atmospheric environment to reduce NO Χ and SO2 emissions.Therefore, it is recommended to use gas as fuel for calcining limestone.

 

(1)Gas burning lime kiln to save energy


Especially the use of residual blast furnace gas and coke oven gas, and other industrial furnace residual gas is the largest energy conservation and utilization.
 

(2)Favorable environmental protection


Because the gas kiln does not have a large number of harmful gases discharged after solid fuel combustion, and the original gas discharged to the atmosphere also reduces the emission of pollution to the atmosphere after fuel, so it is very beneficial to environmental protection.
 

(3)The temperature in the furnace is uniform


The calcined lime is of good quality.The gas fuel can be burned in all the voids in the limestone without any dead space, and the temperature may be high or low if the coal is used as fuel.Because the flame of gas burning is uniform and at the same time exothermic, it can achieve fast combustion and fast cooling, so the lime activity is good.
 

(4)In addition, it is convenient for detection and good operation


Because the temperature, gas, air flow and pressure of the gas kiln can be measured by the instrument, the furnace operator can master the furnace state and adjust the furnace state according to the test data, unlike the solid fuel is difficult to control, even if the furnace stopped the gas is still burning, the gas kiln adjustment cycle is short, the solid fuel kiln adjustment cycle is long.

The most ideal gas fuel is blast furnace and coke oven gas, but coke oven gas calorific value is too high, and must take off tar, so it is not easy to control the use.

 

3. White ash calcining equipment -- white ash kiln


There are many kinds of old furnace type white ash kilns.Such as earth kiln, common shaft furnace, rotary kiln and so on.Among them, the earth kiln and the common shaft furnace type ash kiln, which USES coal as calcining fuel, are elimination equipment.Nowadays, shaft kiln and rotary kiln which use gas as fuel are mostly used.According to the furnace volume, the normal vertical kiln can be divided into 25, 50, 140, 180 and 300M3.Smaller is easier to master.Now take 140M3 white ash kiln of common gas fired shaft furnace for analysis:

The outer diameter of annular concrete foundation wall is 3.95m, the wall thickness is 400mm, the upper elevation is 4.9m, the outer diameter of steel kiln shell is 4.29m, the highest elevation of the upper roof is 26.55m, that is, the metal kiln shell is 22.05m high, the inclined bridge top is 31.25m(elevation), the kiln inner diameter is 3m, the material column is 20m high, and the effective volume is 140m3.There are 6 test thermocouples, one at the position of 5.6m, two at the position of 10.8m, two at the position of 14.8m, and one at the position of 23.5m.There are 16 burners at elevation 13.3m and 16 nozzle (burners) at elevation 10.8m.Combustion air casing 16 side shape, diameter 325mm, opposite to the burning nozzle center, cooling air casing 300*250;Blast hole ф 250250 tossing in the ground operation;Cooling fan, combustion fan 6.3a,30Kw. Hoist 3 tons 18-22kw.

 

Design requirements:

raw material particle size 40-80mm, gas calorific value 860*4190KJ/m3, flow 7000m3/ hour, design utilization coefficient >0.6.
 

To be continued


Ratio of gas and air in the 2-1 and 1:2. 5, calculate the cycle of the furnace, put the ashes of time, according to the cycle regulation 130 cubic grey interval generally in a lime shaft kiln, such as the gas pressure, when air pressure is 10000 mpa, 60 minutes, put on a gray one-time about 7 tons of stone, keep good stable material surface, plus or minus not more than 10 centimeters, can be a good grey.

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