Abstract:
In this passage, a contrastive analysis is made on coke oven gas and blast furnace gas, and gasifier gas to calcine metallurgical active lime. And then the feasibility of coal gas for this technology is clarified briefly. Also, it dissertates synthetically in the aspects of its running cost in fuel，environmental protection and energy saving standards and durative availability of fuel. At last, we can get the final conclusion of the high promotion value of coal gas in calcining metallurgical active lime industry.
Key words:
Coal gas     Metallurgical active lime     Technology   Economy environmental protection and energy saving     Durative availability Feasibility
Introduction:
With the deepening development of national economy in our country, about production requirements, the steel enterprises are becoming to pay more attention to its particular production cost and good quality than straightforward pursuit of volume. Also, their requirement to metallurgy materials including active lime is higher. The quality’s improving of metallurgy active lime could reduce the consumption of steel, reduce the cost of steel-making, improve the quality of molten steel and so that can gain more economic benefits.
At present, fuels used widely in China that to calcine the metallurgy active clime are mainly two methods---coal/coke and gas. Using coal or coke as fuel, some problems exist: difficult to control the uniformity of temperature; bad activity of lime; environment pollution, etc. So this calcining method will be replaced before long. Gas fuel has lots of advantages: it can combust in everywhere inside the limekiln; its flame is even; it can release caloric at the same time when it combusts; it also can combust and cool down quickly; the activity of lime will be good. Compared with the coal or coke calnining method, gas limekiln has the characteristics of great air current, high activity of lime, even temperature inside kiln, easy control of temperature, lower requirement for the choice of fuel, lower-effect to environment, etc. It is one of perfect choices of calcining method.
The range of fuel choices for gas-fueled limekiln is very wide, such as coke oven gas, blast furnace gas, gasifier gas, LPG, natural gas, etc. At present, some enterprises use coke oven gas, blast furnace gas or mixture of coke oven gas and blast furnace gas to calcine lime. Normally, these enterprises are underling enterprises of big steel factories or they are near to the gas supply places, which mean they have the advantage of favorable geographical position and support of people. However, most of enterprises don’t have these advantages. They should not only consider the feasibility of technology and the environmental protection problems, but also the cost of investment, running cost of fuel and the supply durative of fuel. After synthetical analysis, reassuring gas would be selected.
1. Technical feasibility of calcining metallurgy activity lime with gasifier gas 
Active lime is a kind of good quality light-combusted lime with active chymic character, strong reacting capability, speedy molten rate in the course steel-making and fewer contents of sulfur, phosphorus and other harmful elements. It is characterized by small cubage and density, many air holes, big surface, small calcium oxide crystal and strong reacting capability. On the choice of fuel, the calcination process and temperature control affect activity of the lime greatly. Too high temperature or too long holding time will make calcium oxide crystal to grow well, which will reduce the activity of lime.
Coke oven gas has higher calorific value, the flame is shorter when combusts, and it combusts quickly when get out from burner. These characteristics will make the temperature is too high around burners, the lime that close to burners will be over baked, even the furnace liner will lump inside, while the lime in the center part of furnace is still fresh. The shortcut to solve the problem is to mix inert gas or low calorific value gas in, so that the mixed fuel’s calorific value could be lower. Practical application proved that the better fuel to calcine lime is the gas whose calorific value is about 6270-7500 KJ/M3, and the more suitable length of its flame is 2-4m. Another way is to change the heating method of lime kiln, and heat with fire boxes radiation, so that the heat value and temperature of flame can be adjusted by combustion chamber. But, radiation heating method requires very strictly to the diameter of furnace. If the diameter is not suitable, it can’t achieve better Calci