What is a white ash kiln?

1. The significance of developing new technology lime kilns now

The steel industry, calcium carbide industry, alumina industry, refractory materials and other industries are all major consumers of lime. These industries have been developing rapidly in the past two years. Annual output is basically growing at a rate of more than 20%. However, the main material (auxiliary material) they need, lime, has not increased accordingly, which has caused a shortage of lime, which has stimulated the society to launch a large number of soil-fired lime kilns. The proliferation of soil-fired kilns has also caused serious pollution to the environment. Under this situation, the national and local governments have successively issued a series of policies and regulations to rectify earth-fired kilns, but it is difficult to achieve the expected results because of the stimulation of demand. Therefore, in order to completely control the pollution of earth-fired kilns, modern new technology lime kilns must be implemented to solve the problem of demand. The so-called modern new technology lime kiln is a modern lime kiln with environmental protection, energy-saving functions and a high degree of mechanization and automation. Because it adopts modern technology, it can make full use of cheap energy, especially gases that originally polluted the environment as the main energy source, turning waste into treasure. This not only protects the environment, but also produces lime of good quality and low cost. For enterprises that utilize this new technology, economic benefits will increase significantly. This is the practical significance of promoting new technology lime kilns.

2. New technology lime kiln types

According to the fuel, there are mixed kilns, which burn solid fuel, coke, coke powder, coal, etc. Japanese kiln. Gas-fired kilns include burning blast furnace gas, coke oven gas, calcium carbide tail gas, producer gas, natural gas, etc. According to the kiln shape, there are vertical kilns, rotary kilns, sleeve kilns, West German Vimaster kilns, Maerz kilns (Switzerland), Fokas kilns (Italy), etc. At the same time, there are positive pressure operation kilns and negative pressure operation kilns. Linzhou Modern Technology Center has developed and designed mixed-fired kilns with a capacity of less than 300 cubic meters and gas-fired kilns with a capacity of less than 140 cubic meters, especially the XD-type energy-saving and environmentally friendly lime kiln that burns blast furnace gas and coke oven gas. The combustion problems of high calorific value and short flame of coke oven gas are overcome, and the remaining coke oven gas can be fully utilized. The original coke oven gas "lit the sky lanterns", which polluted the environment, has become a valuable energy source that creates benefits for enterprises. It is a very effective way to save energy, protect the environment and increase efficiency for small and medium-sized steel companies, coking companies, calcium carbide companies, and refractory materials industries.

3. The basic principle and thermal process of burning lime

The main component of limestone is calcium carbonate, while the main component of lime is calcium oxide. The basic principle of burning lime is to use high temperature to decompose calcium carbonate in limestone into quicklime of calcium oxide and carbon dioxide. Its reaction formula is

CaCO3 CaO+CO2——42.5KcaI

Its process is as follows: limestone and fuel are loaded into the lime kiln (if the gaseous fuel is sent through pipelines and burners After entering), it starts to decompose at 850℃ after preheating, and completes the calcination at 1200℃. After cooling, it is discharged from the kiln. That is, the production of quicklime products is completed. Different kiln shapes have different preheating, calcination, cooling and ash discharge methods. But several process principles are the same: high raw material quality, good lime quality; high fuel calorific value and low quantity consumption; limestone particle size is directly proportional to calcination time; quicklime activity is inversely proportional to calcination time and calcination temperature.

4. The basic structure and main ancillary equipment of a lime kiln

A lime kiln is mainly composed of a kiln body, a feeding device, a distribution device, a combustion device, an ash unloading device, electrical appliances, an instrument control device, a dust removal device, etc. Different types of lime kilns have different structural forms and calcining forms. The process flow is basically the same, but the equipment value is very different. Of course, the effects of use are definitely different.

5. Quality and Quantity Consumption of Limestone

Industrial lime has two main quality requirements for limestone: First, it requires a high calcium carbonate content, which is generally required to be above 97%. Second, its structural grains should be small, because the limestone crystals with small grains are not tight, and when it contains organic matter, the organic matter is burned to form a porous shape, and carbon dioxide is easily separated, so it is easy to calcine. Third, there are few impurities, especially harmful ingredients such as silica, magnesium oxide, aluminum oxide, iron oxide, sulfur and phosphorus. If these components are one percent in limestone, they are eighteen percent in calcined quicklime.

Theoretically, it takes 1.78 tons of limestone to burn one ton of lime. However, there is a certain difference between the "raw" and "over" burning levels during calcination and the quality of the limestone.

6. Quality standards of quicklime:

The general standards of lime quality are: calcium oxide content, raw and burnt rate, activity, harmful component content, etc., but more importantly, different industries and different uses There are different standards. For example, the calcium carbide industry places special emphasis on activity, that is, soft ash, while the iron-making industry emphasizes strength, so hard ash is required, while steelmaking requires soft ash. Therefore its indicators are also different. Generally, the calcium oxide content of standard quicklime should reach more than 97%, the raw and burnt rate should be less than 10%, and the active calcium should be more than 300mi.

7. Energy-saving and environmentally friendly lime kiln fuel and combustion

There is a wide range of fuels for burning lime, including solid fuel, gas fuel, and liquid fuel. However, the combustion principle of the new technology lime kiln is which fuel is the most economical. Which fuels are more environmentally friendly and which fuels can save more energy are the key to new technology lime kilns. The most commonly used ones now are coke and gas. As far as new technologies are concerned, the most ideal fuel is coal gas, including blast furnace gas, converter gas, coke oven gas, calcium carbide tail gas (coal gas) generator gas, etc., which are the best fuels for lime kilns. Because these gas fuels are waste utilization and are of circular economy nature. In particular, most coke oven gas is now released, and the resources are very rich, followed by blast furnace gas, and then calcium carbide tail gas. If these gases are utilized, a large amount of energy can be saved, and the environment can be protected. More importantly, enterprises can Received good economic benefits. If these gas-fired lime kilns are developed in large numbers, the problem of environmental pollution from earth-fired kilns will naturally be solved. Why is such a good project developing so slowly now? The main reason is that gas-fired lime kiln technology has been developed in our country for a relatively short time, and any matter has a process of development and understanding. Especially coke oven gas, due to its high calorific value, short flame, Lime kilns are prone to over-burning and under-burning. As a result, some companies are afraid to use it boldly. In fact, this is not a difficult problem to solve. Linzhou Modern Science and Technology Center has now developed the technology of external mixing long flame burner and lime kiln self-circulation dilution of high calorific value gas. It can completely solve the problem of burning lime from coke oven gas. The amount of fuel used to burn lime is related to the furnace type and the calorific value of the fuel. The heat required to calcine lime is obtained from the combustion of fuel. The main component of the fuel, the molecular formula of the combustion process of carbon is C+O2 = CO2. The gaseous fuel is calculated based on its calorific value. According to actual experience, approximately 960kcal is needed to produce one kilogram of lime. However, there are differences due to the different production equipment and process conditions of each factory. Generally speaking, it takes about 1600m3 of blast furnace gas to burn one ton of ash, and about 300m3 of coke oven gas. Calcium carbide exhaust gas needs about 360m3, natural gas needs about 120m3, and generator gas needs about 900m3.

8. Distributors, burners and other ancillary equipment of lime kilns

The main ancillary equipment of lime kilns include feeding mechanisms, distributors, air supply devices, combustion devices, ash discharge devices, etc. Relatively speaking, mixed firing Lime kiln distribution is very critical, because when fuel and limestone are loaded into the kiln at the same time, the distribution must be used to achieve a reasonable distribution of the furnace materials in the kiln, eliminate the furnace wall effect, balance the resistance in the furnace, and strive to "heat" the entire furnace section. Uniform and consistent. Therefore, the form and use effect of the distributor have a great impact on the production efficiency of the lime kiln. There are now a variety of distributors, including rotating distributors, conch-shaped distributors, fixed distributors, etc. Among them, the three-section bell-type distributor developed by Linzhou Modern Technology Center uses the "funnel throat effect" and "inverted W stacking" The combination of the "angular effect" principle and the adjustable baffle plate has a simple structure and is very effective in solving the problems of uniform mixing of raw materials and fuel and reasonable distribution of particle sizes. It also has many advantages such as high temperature resistance, wear resistance and convenient maintenance. It is especially suitable for the configuration of small and medium-sized lime kilns. The main accessory equipment of a gas-fired kiln is the burner, because its gas fuel is to mix the combustible gas and the required oxygen (air) in a certain proportion through the burner. It is then sent into the furnace for combustion, and different gases require different amounts of air. Different furnace types and different heating methods require different types of flames. Such as premixed, semi-mixed, externally mixed and oxidizing flame, neutral flame, reducing flame, etc. Therefore, the burner of the gas fired kiln determines the calcining effect of the lime kiln to a certain extent.

Of course, other ancillary equipment is also very important, such as the wind cap. It is easy to see the similarity, but it must ensure that the air volume in the kiln it supplies is distributed across the entire kiln section to achieve good results.

9. Lime kiln air supply and fan selection

Whether a mixed-fired kiln or a gas-fired kiln requires a certain reasonable air supply, because any fuel combustion must meet three conditions, namely fuel, air (oxygen), And open flame, without any of these conditions, it will not burn. The amount of air used is calculated based on the oxygen demand of the combustible component of the fuel. If the air supply is not fuel, the fuel will not be sufficient. If the air supply is excessive, the excess air will become a large amount of heat in the flue gas, thus causing an increase and waste of fuel. Its air volume is generally calculated according to the formula: (calculation formula omitted) Its pressure should be calculated based on the different resistances formed by different kiln types and different raw material particle sizes. Generally speaking, the resistance of a shaft kiln can be calculated according to the formula of

40-70 H2O/effective height (m)

. However, there are differences in the particle size of raw materials and fuels. Therefore, the selection of fans must be based on both theoretical calculations and specific furnace types and actual experience. Only in this way can we have good use effect.

10. Dust removal and environmental protection in lime kilns

The smoke emitted when lime is calcined contains a large amount of harmful gases and dust below 10 microns. The dust also contains SO2; F2O3; AIO3, etc. These harmful gases and dust are very harmful to the human body. If people inhale it for a long time, it will cause respiratory diseases such as bronchus and lungs, which is more serious in young children. Moreover, the dust floating in the air also contains carcinogens. If the average concentration of breath in 24 hours Harmful dust exceeding 150mg/m3 can cause fatal harm to the human body. The main advantages of the new technology lime kiln are low energy consumption, high output and good quality. The biggest advantage is that it is easy to remove dust. Because the entire calcination process is equivalent to being carried out in a sealed container, its flue gas can be discharged from the flue gas pipe on the top of the kiln, purified through dust removal, and then achieve harmless, pollution-free emission standards. eleven. Automated control

Automated control is an important feature of the new technology lime kiln. Its feeding, batching, air supply, air supply, and ash unloading are all completed through computer automation control. However, national conditions, factory conditions and value costs must also be considered. The higher the degree of automation, the better. The final effect should be the principle.