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

Heat insulation technology of kiln

The heat dissipation loss of lime kiln body is an important aspect affecting its energy consumption. For refractory materials of rotary kiln, in order to improve its service life, heat preservation performance and reduce heat transfer coefficient, technicians have developed new refractory materials and kiln lining structures such as special phosphate brick, prefabricated brick and castable mixed brick.

The use of special phosphate brick instead of traditional magnesia-aluminum spinel brick can improve the service life of resistant materials, reduce the maintenance times and time of rotary kiln, avoid the energy consumption caused by frequent kiln opening and stopping, and significantly reduce the kiln skin temperature and save fuel consumption, which has played a good energy-saving and emission reduction effect, and has been promoted in a number of metallurgical lime production lines with good results.

Innovative kiln lining construction method. The composite prefabricated brick is fixed to the kiln shell by anchoring parts, which can reduce the pressure of thermal insulation materials, and can lay low thermal insulation materials close to the surface of the kiln body. At the same time, the prefabricated brick is filled with lightweight high-strength castable and wear-resistant castable to ensure the integrity and fastness of the kiln body, solve the problem of "casting bricks" in the rotary kiln, and improve thermal stability, reduce maintenance rate, and significantly reduce the temperature of the kiln skin.

Waste heat utilization technology

In recent years, in order to reduce energy consumption, save energy cost and avoid energy waste, the waste heat utilization of low-quality flue gas has been paid more and more attention. The available waste heat of lime kiln includes calcination waste gas heat, rotary kiln barrel radiation heat and beam kiln heat transfer oil heat.

Utilization of waste heat from calcined waste gas. The heat taken away by the calcination gas of lime kiln can reach 30% of the total heat of lime kiln, which has good utilization value. The exhaust gas temperature of lime kiln is usually between 160 degrees Celsius and 350 degrees Celsius, and the exhaust gas temperature is affected by the equipment structure of lime kiln, the type of calcined fuel and the production and operating conditions. There are generally the following ways to utilize calcined waste gas waste heat:

First, supporting waste heat boiler and steam turbine/screw generator set for power generation. Due to the low exhaust gas temperature is easy to affect the efficiency of power generation, this technology is suitable for high temperature (≥250 degrees Celsius) waste gas recovery, so it is more than used for lime rotary kiln, it is understood that there are more than a dozen lime rotary kiln waste heat power generation transformation.

The second is to adopt organic Rankine (ORC) cycle technology for power generation. Lime kiln ORC power generation technology is proposed in recent years for 130 degrees Celsius ~300 degrees Celsius flue gas waste heat recovery technology, the main principle is that the waste gas through the heat exchanger to produce hot water, hot water heating organic working medium to boiling, boiling working medium into the turbine unit power generation. ORC power generation technology provides the conditions for the high value-added utilization of waste gas and heat from lime shaft kiln.

Third, it is used for heating and bathing through the flue gas-water heat exchanger. This method has low requirement on flue gas temperature and simple system configuration, and has been widely used in lime production enterprises.

Fourth, the use of high-efficiency heat exchangers to preheat combustion air and fuel, increase fuel temperature, to achieve the purpose of strengthening combustion, improve heat utilization, reduce exhaust gas exit kiln temperature, reduce fuel consumption. This technology has been widely used in rotary kiln and shaft kiln.

Utilization of residual heat radiated from rotary kiln barrel. The surface temperature of the lime rotary kiln cylinder is generally 250 degrees Celsius ~280 degrees Celsius, in order to collect the heat emitted by the surface of the cylinder, the arc collector can be installed above the rotary kiln cylinder, and the collected radiation heat is converted into hot water through the heat exchanger for heating and bathing. This technology is mature, reliable, simple and effective, and has been widely used in lime rotary kilns.

Residual heat utilization of heat transfer oil in beam kiln. At present, the beam kiln used in the production and application generally uses thermal oil to cool the fuel beam, the temperature of thermal oil out of the kiln is generally 150 degrees Celsius ~180 degrees Celsius, and the temperature difference of thermal oil is 10 degrees Celsius ~20 degrees Celsius. After the heat conduction oil out of the kiln, it needs to be cooled by the axial flow fan, and the heat loss caused by it can reach more than 200 kcal, accounting for about 20% of the total heat of the beam kiln. The research shows that the waste heat utilization of the heat transfer oil is realized by using the heat transfer oil-steam heat transfer device to heat water into low saturated steam, and then through the configured turbine generator set to generate electricity. This technology has high return on investment, simple construction and transformation, and is an effective way to utilize the waste heat of beam kiln.