Present situation and development countermeasure of low carbon technology of metallurgical lime

Carbon dioxide recycling technology

Recycling carbon dioxide from lime kiln exhaust gas is the most direct and effective way to achieve carbon emission reduction. Lime kiln exhaust gas CO2 content is generally 14%~38%, the concentration is low, and contains dust, SO2, NOX and other impurities, resulting in certain difficulties in recycling, high investment and operating costs. However, in order to reduce carbon dioxide emissions and realize comprehensive utilization of resources, through the research of technical personnel in the industry, the carbon dioxide recycling technology of lime kiln exhaust gas has achieved certain results. At present, the chemical absorption process with potassium carbonate (sodium) aqueous solution or ethanolamine aqueous solution as absorbent and the pressure swing adsorption process with organic amine series adsorbents are generally used.

In the 1990s, Shaosteel began to explore ways to separate and recover CO2 from lime kiln exhaust gas, and continuously reformed the CO2 recovery system, successively built two sets of pressure swing adsorption devices, and successfully recovered liquid CO2 with purity of more than 99.5% from gas fired lime shaft kiln exhaust gas. Shougang Jingtang Company studied the use of carbon dioxide from the flue gas of sleeve kiln, the use of pressure swing adsorption method to produce food-grade CO2, replace part of nitrogen and oxygen, participate in the converter top blowing and bottom blowing smelting, which can reduce the iron loss of steel slag, improve the recovery rate of ferric resources, and excess liquid CO2 can be exported. A steel plant in Shandong province recycled CO2 from the waste gas of rotary kiln, and used MEDA olamine solution as adsorbent to obtain liquid food-grade CO2 through impurity removal, adsorption and deep purification, and realized resource utilization. Jingye Group used to recover CO2 from the waste gas of rotary kiln after dust removal and desulfurization, and obtained CO2 products with purity of more than 99.5%, which were used as raw materials for salicylic acid production.

Other energy-saving and low-carbon technologies

Through the development and optimization of different kiln structure, thermal system and process technology, lime kiln equipment has been developing towards the direction of energy saving and low carbon.

The rotary kiln is equipped with preheater and cooler at the head and tail of the kiln to make full use of the waste heat of roasting flue gas and lime products, improve production efficiency and realize energy saving and emission reduction. For a long time, there are some misunderstandings about energy consumption of lime rotary kiln in the industry. According to years of research experience, the actual production of rotary kiln process energy consumption is only slightly higher than that of shaft kiln, in the case of raw fuel, production operation, product output conditions are good, lime rotary kiln process energy consumption can be as low as 160 kg standard coal/ton ash ~170 kg standard coal/ton ash.

Double-chamber kiln adopts unique kiln structure, spray gun system layout and heat storage and heat exchange roasting system. The heat supply of kiln cross section is uniform, the waste heat of flue gas is fully utilized, and the heat consumption per ton of product can reach 3.7 GJ or less, making it the kiln with the lowest heat consumption per unit product among all lime kilns.

The sleeve kiln can achieve heat exchange and roasting in two ways: parallel flow and counterflow. The preheated cooling air in the annular joint of the lower inner sleeve is used as the combustion-supporting air for the upper and lower burners, and the driving air preheated by the exhaust gas on the top of the kiln and the cooling air of the lime product are used as the secondary combustion-supporting air for the lower burners, so that the heat in the kiln can be fully utilized and good energy-saving effect can be achieved.

Beam kiln combustion beam has made revolutionary progress. The third generation beam kiln controls the temperature difference of thermal oil within 2 degrees Celsius by adiabatic burning beam, thereby reducing the heat loss caused by heat dissipation of thermal oil and greatly improving the energy utilization efficiency of beam kiln. The third generation beam kiln has been successfully put into the market and widely promoted, and a number of beam kilns have been upgraded with this technology. In addition, the fourth generation beam kiln is undergoing technological advancement, adopting a more energy-saving oil-free cooling combustion beam, completely eliminating the heat consumption index of the combustion beam, and bringing broad space for the energy-saving development of beam kiln.

Low carbon development strategy of metallurgical lime

Gradually improve the level of metallurgical lime equipment

In the current situation of backward elimination, transformation and upgrading, reduced development and high-quality development of the iron and steel industry, energy-saving and environmentally friendly, technologically advanced lime kiln equipment will inevitably become the best choice for metallurgical lime production. Metallurgical lime enterprises should speed up the elimination of existing backward or energy saving and environmental protection of lime kilns, give priority to rotary kiln, double-chamfered kiln, sleeve kiln and other energy saving and environmental protection of lime kiln equipment, improve the overall level of metallurgical lime equipment, and lay a good foundation for energy saving and low-carbon development.