The series of "Long life Large scale Rotary Kiln Castable Integral Lining Technology" developed by Luoyang Luohua Powder Engineering Special Refractory Co., Ltd. in Henan Province has made technological innovation against industrial solid wastes, hazardous wastes and barren ores, and has achieved significant economic, environmental and social benefits.

Li Hongtao

Relevant statistics show that the amount of industrial solid waste and hazardous waste generated in China is about 3.3 billion tons per year, the total amount of industrial solid waste stockpiled over the years exceeds 60 billion tons, covering an area of more than 2 million hectares, and this figure is still growing at an annual rate of about 8%. It is estimated that by the end of 2021, the output of industrial solid waste in China will exceed 4.6 billion tons.  

Industrial solid wastes and hazardous wastes not only waste resources and occupy land, but also bring serious environmental and safety risks, endangering the ecological environment and human health. With the continuous deepening of the environmental protection field in recent years, industrial environmental protection has ushered in a new round of peak for more than 10 years. With the increasing attention paid to industrial environmental protection, the market space of industrial solid waste treatment industry is expected to be further opened and close to the trillion scale, with a good prospect. Luoyang Luohua Powder Engineering Special Refractory Co., Ltd., Henan Province, has developed its own world in the industry by virtue of the series of "long life large rotary kiln castable integral lining technology".

Rotary kiln for solid waste treatment of zinc leaching residue

Environmental pollution caused by industrial solid waste "waste utilization"

Since the reform and opening up, China's economy has maintained steady growth for more than 30 years, becoming the second largest economy in the world, and has made remarkable achievements. With the rapid development of economy and society, China's industry has also made gratifying achievements. But at the same time, the country has paid a huge price for its resources and environment. The problem of industrial solid waste pollution and the lack of comprehensive utilization of follow-up resources have become an important obstacle to the sustainable development of the economy. Industrial solid waste, namely industrial solid waste, generally refers to various waste residues, dust and other wastes discharged into the environment during industrial production. It can be divided into general industrial wastes, such as high furnace slag, steel slag, red mud, nonferrous metal slag, coal slag, salt mud, etc., as well as industrial hazardous solid wastes. At present, industrial solid waste poses a great threat to the environment, and is also regarded by industry insiders as a "misplaced resource". These industrial solid wastes will not only occupy a large area of land resources, but also cause water, soil and air pollution, and even spread diseases through water, gas, biological and other media. How to effectively treat industrial solid waste is one of the key issues in China at present. Its sustainable resource utilization affects the development of China's green circular economy and modern industry. In addition, as China is a typical developing country, heavy industry also accounts for a high proportion, and metallurgical industry is a very common type of industry. The removal of smelting waste residue, a solid waste generated in the production process, will discharge a large amount of tailings with the beneficiation in the early mining process. With the improvement of the utilization of mineral resources, the mineable grade of ore will be reduced accordingly, and the discharge of tailings will also be increased. The amount of tailings discharged by countries around the world every year is about 5 billion tons, while the amount of tailings discharged by China in 2000 was about 600 million tons. At present, the amount of waste stockpiled has reached 20 billion tons, and is increasing at the rate of several hundred million tons per year. In this case, the Party Central Committee and the State Council attach great importance to environmental protection, taking it as an important means to transform the mode of economic development and a fundamental measure to promote the construction of ecological civilization.   As the report of the 19th National Congress of the Communist Party of China put forward, the construction of ecological civilization is the millennium plan for the sustainable development of the Chinese nation, and the construction of ecological civilization is the long-term theme of the future development of our society. The comprehensive utilization of large industrial solid waste resources is an important part of the construction of ecological civilization. In this macro environment, the comprehensive utilization industry of bulk industrial solid waste ushers in a "blowout period". As for the metallurgical industry, every person in the metallurgical industry should continue to decompose and refine the metal barren ore, ore dressing slag, and tailings in the metallurgical process, and conduct physical transformation and energy distribution of metal, non-metal, and other chemical materials in the process of decomposition and refining, so that they can be attributed to the stable structure of nature, be used as new resources again, cherish resources without waste, and do not leave pollution to future generations, It has also become its urgent responsibility and mission.  

Improvement and innovation of rotary kiln are inevitable

In the process of processing a variety of barren ores and industrial tailings in China's environmental protection industry, large rotary kilns have become one of the mainstream equipment for processing industrial solid wastes and hazardous wastes with their remarkable performance of environmental protection, energy saving, easy operation, etc. in process operation. Rotary kiln, also known as rotary calcining kiln, is commonly known as rotary kiln. In the construction process, it carries out mechanical, physical or chemical treatment of solid materials through rotary cylinder equipment, which has been widely used in building materials, chemical industry, environmental protection and many other production fields. In the metallurgical industry, metallurgical rotary kiln equipment also occupies a place, which is mainly used for heating treatment such as sintering and roasting of ores, concentrates and intermediate products. Nowadays, with the vigorous development of China's metallurgical industry, the demand for rotary kilns is increasing, and the specifications are also growing. Then, what are the properties of this "pet" in the eyes of high-temperature metallurgical workers to firmly establish itself in the metallurgical industry—— The equipment is large in size and has strong material tolerance. Whether it is slurry like materials or block like granular materials, whether it is granular or powdery materials, it can be treated by rotary kiln, and various and flexible feeding forms can be used according to the characteristics of materials—— Compared with the materials in the kiln, the working volume of the rotary kiln can be regarded as infinity, which can meet the process requirements of large-scale and large processing capacity—— With the help of the mechanical rotation mode of the rotary kiln, the materials entering the kiln obtain their own kinetic energy and potential energy. Under the condition of keeping the materials in a relatively intense collision, rolling and friction motion, it promotes the transformation of materials in the hot state and reduces the requirements of materials in the rotary kiln on other metallurgical energy. This is also a unique energy-saving mode of rotary kiln—— Rotary kiln equipment can conduct "fine work and slow fire" heating and smelting of materials. Any materials entering the kiln will gradually increase the accumulated value of smelting and chemical field strength to improve smelting and chemical efficiency and reduce energy costs—— In the rotary kiln, materials are added from the kiln tail and run against the generated hot flue gas to stimulate the metallurgical reaction of materials so as to obtain higher metallurgical energy level. This energy-saving form of directly using hot flue gas to improve the "positive feedback" thermal effect of metallurgical process is also unique to the rotary kiln metallurgical process—— The rotary kiln has the characteristics of elastic semi closed working chamber, and has the ability to self recover emergencies, prevent fire and explosion. It is possible to directly feed the activated materials and materials containing liquid substances into the kiln for treatment.  

In addition, the rotary kiln equipment has large volume, relatively small manufacturing difficulty, large output and easy operation, so it is easy to be accepted by investors. The use of large rotary kilns has thus become one of the important equipment in the metallurgical industry. However, because the quality and service life of the traditional rotary kiln lining can not meet the needs of industry, people can only put the rotary kiln in the low-end material processing process at this stage, which can not fully show its many advantages such as energy saving, large output and strong adaptability in the form of metallurgical equipment. Guided by the policy of promoting the spirit of scientific and technological innovation and innovation ability, in order to further deal with the problem of industrial solid waste and hazardous waste, in the field of metallurgical industry, rotary kilns are also facing further improvement and utilization to fully meet the current situation of metallurgical technology.  

Focusing on technology for 30 years, starting a new trend in furnace lining design

The technical performance and operation of rotary kiln, to a large extent, determine the quality, output and cost of enterprise products. The ballad "As long as the big kiln turns, there will be tens of millions" is a vivid description of the importance of rotary kilns in production. In the rotary kiln device, the furnace lining can be regarded as the "heart type" key component that controls its operation strength.

Generally speaking, refractory bricks are often used for lining of traditional rotary kiln. The brick lining has high refractoriness and long service life, and can make its size stable and strength increase to processing and molding according to the calcined raw materials. However, because its mechanical structure is a loose mechanical structure, which is maintained by the side pressure between wedge-shaped refractory bricks. When the rotary kiln is running, slip displacement often occurs, which causes the furnace lining to be in a state of continuous collision and scratch between refractory bricks, between refractory bricks and the outer steel shell, and mutual self damage during the operation of the rotary kiln, The sudden boiler shutdown event caused huge losses to the enterprise, and also made the large-scale rotary kiln equipment in a state of "affordability, unaffordability, and unaffordability".  

Luoyang Luohua Powder Engineering Special Refractory Co., Ltd. (hereinafter referred to as "Luohua Company") in Henan Province is a full industrial chain refractory company specializing in the production of refractory products and the design and construction of furnace linings, and is also the first batch of private high-tech enterprises in China. Since its establishment in 1993, under the leadership of Li Chaoxia, the technical director, the company has accumulatively designed, reconstructed and built nearly 2000 refractory insulation furnace (kiln) linings of various furnaces and kilns, involving nearly 100 types of furnaces in various industries including metallurgy, chemical industry, building materials, electricity, special chemical industry for national defense, barren ore treatment and garbage treatment. In addition to the features of energy conservation and environmental protection, the furnace lining designed and built by it also has the features of significant production expansion, improved equipment operation efficiency, disaster resistance, long-term stable operation for several years and even decades of "zero" maintenance rate.

Up to now, Luohua has obtained 52 patents in refractory products and furnace lining design. Among them, 31 patents for invention, 19 patents for utility models and 2 patents for invention under examination; Won 4 first prizes, 1 second prize and 3 third prizes of China Nonferrous Metals Industry Science and Technology Award; Won 1 science and technology achievement award of China Hi tech Industry Promotion Association; In addition, it was included in one national torch promotion project, one national key new product project, and two national key energy conservation promotion projects. In 2010, Luohua Company was awarded the honor of "China Nonferrous Industry High Temperature Materials and Furnace Technology Center" by China Nonferrous Industry Association.  

The company has made great achievements. Behind the exploration of honor and achievements is the dedication and perseverance of the technicians of Luohua Company for decades. Li Chaoxia, the general technical director of Luohua Company, formerly worked in Luoyang Refractory Research Institute of the Ministry of Metallurgy (now "Sinosteel Refractory Research Institute"), and has participated in several "6.5" and "7.5" refractory research projects of the Ministry of Metallurgy. As early as the 1980s, Li Chaoxia began to study the refractory materials and lining structure of rotary kilns. After mastering a large number of theoretical foundations, Li Chaoxia has successively conducted tests on the construction of monolithic castable linings for different types of rotary kilns in many large and medium-sized smelting enterprises, such as Shenyang Smelter, Kaifeng Zinc Smelter, and No. 1 Smelter of Jinchuan Company, thus accumulating rich and valuable practical experience.  

Over the years, after Li Chaoxia and the technical team members worked hard to tackle key problems, Luohua Company, on the basis of the construction technology of refractory castable and large high-strength castable steel structure refractory concrete, finally invented the construction engineering technology of giant steel structure refractory concrete with refractory castable integral lining replacing refractory bricks - "Long life large rotary kiln castable integral lining technology" series. Compared with the old rotary kiln lining technology, this technology series has carried out subversive transformation and innovation for the lining structure and lining materials, and has shown remarkable superior performance in all aspects:

——According to the research on the damage mechanism of large-scale rotary kiln, the self damage mechanism of rotary kiln lining is named and confirmed by "slip displacement" for the first time. Thus, the form of the furnace lining with the high-strength castable as a whole suspended on the rotary kiln shell and rotating synchronously with the rotary kiln is determined.

——The internal mechanical analysis model of monolithic castable refractory lining is established, which provides the design idea and calculation basis for monolithic castable refractory lining.  

——According to the mechanical analysis model, the efficient and economical anchoring matrix form of "pyramid type" castable integral lining is designed. The whole castable furnace lining will not collapse from the original state at the initial stage of construction to the state of using a 60mm thick thin shell, so that the rotary kiln lining can operate continuously with high load for a long time.  

——According to the principle of inertia and "slip displacement", the cavity interlayer is designed in the rotary kiln steel shell and the rotary kiln lining, so that the rotary kiln lining and the cylinder steel shell can move synchronously and become an elastic integral system, avoiding the scratch and impact of the two in any state. At the same time, the cavity interlayer is also a thermal insulation layer, which makes the rotary kiln more energy-saving and environment-friendly—— Functional components such as material retaining ring, material separating cone and barrier are set for the original rotary kiln shell without control function. These functional components can improve or even change the flow beam shape and running speed of materials, form a higher level of thermal field in the middle and edge of the rotary kiln, and enable the rotary kiln to expand production and save energy.  

——The invention of "long strip continuous construction method" is simple, intuitive, reliable and easy to learn, which is conducive to the rapid standardization and industrialization of this technology.

——In view of the fire resistance and refractory of the huge closed furnace shell, a safe, fast and effective baking and operation supporting technology is designed and configured, which makes this technology can be rapidly translated to the majority of users.  

Through unremitting efforts, in 2015, the series of "Long Life Large Rotary Kiln Castable Integral Lining Technology" passed the scientific and technological achievements appraisal of China Hi tech Industry Association and Hi tech Industry Research Institute, and the experts at the meeting unanimously gave high praise. In 2016, it was finally included in the seventh batch of national key energy-saving low-carbon technology promotion catalogue by the National Development and Reform Commission after the review and evaluation of several experts from the Energy Conservation Division of the National Development and Reform Commission and the National Energy Conservation Corporation. In 2017, this technology was rated as one of the ten key energy conservation and emission reduction promotion projects in China.  

Endless Quality, Creating the Future

During decades of promotion, the running time of the "Long life Large scale Rotary Kiln Castable Integral Lining Technology" series of equipment is obviously better than the national requirements for the shutdown and maintenance rate of large equipment, and a large number of industrial solid wastes, hazardous wastes and barren ores have been disposed, which has obvious economic, environmental and social benefits, so it is loved and recognized by the majority of users.  

For example, lateritic nickel ore is a typical barren ore with a nickel grade of only 0.8%~3%. In 2011, under the recommendation of Beijing ENFI Design and Research Institute, Luohua Company used the "laterite nickel ore reduction converting metallurgy process" in the "long life large rotary kiln castable integral lining technology" to carry out furnace lining design, refractory production, furnace building construction The overall design layout of the drying furnace has been put into operation, and obvious results have been achieved. This project has rapidly improved the popularity of Luohua Company in the industry. Later, Luohua Company was invited to build demonstration projects to more than 10 large laterite nickel iron enterprises, and has been continuously used at full load with a "0" maintenance rate until now, with unexpected excellent results (some enterprises have recently replaced the high-temperature part of the rotary kiln).  

For another example, the zinc leaching residue is the tailings material in the zinc metal smelting process. The zinc leaching residue contains zinc, iron, lead, silver and other metal elements. The factory mainly collects secondary zinc oxide from the leaching residue. In small and medium-sized enterprises, the rotary kiln method is generally used. As zinc leaching residue contains highly polluted leaching solution, it severely damages and erodes the rotary kiln lining. The best brick lining is also used less than 300 days, and the furnace is often shut down for repair several times during use. In order to solve this problem, Luohua Company developed and applied for the "castable lining and zinc leaching slag rotary kiln with this lining" (ZL201) for the treatment of industrial tailings on the basis of "long life large rotary kiln castable integral lining technology"