I. Introduction:

 At the annual meeting of China Lime Industry Society held on January 18,2021, Tangshan Jinquan Complete Equipment Co., Ltd. was authorized to use the new generation of domestic double-chamber lime kiln series technology with complete independent intellectual property rights system led by China Lime Industry Society exclusively, enjoying the rights of independent development and application. At present, both parties have formally signed an exclusive license agreement, and relevant technical documents and drawings have been handed over.

 Based on this, the editor conducted an exclusive interview on the technical sources, cooperation models and development prospects of the above-mentioned cooperation projects, so that everyone can have a further understanding of this technology.

 II. Development and current application of double-chamber vertical kilns

 Double-chamber lime kiln was invented by Austrians. The technology of double-chamber vertical kiln in China was originally introduced from Melz Offenburg Company in Switzerland. * As early as 1980s, it was introduced into China by the Ministry of Metallurgy. It is commonly known as Melz kiln in China. The lime kiln is in the leading position in the world in terms of production efficiency, floor space, energy saving, environmental protection and economic benefits. nbsp;

 Parallel flow and heat storage are its main characteristics. The parallel flow regenerative double-chamber lime kiln has two kiln chambers, which alternately calcinate and preheat ores. A connecting channel is arranged between the bottom of the calcination zone of the two kiln chambers to communicate with each other. The working state of the kiln chamber can be changed by reversing once every certain time. During operation, the two kiln chambers are alternately charged with ore, fuel is respectively fed from the upper part of the two kiln chambers, and the fuel is uniformly distributed on the cross section of the whole kiln chamber through a plurality of spray guns arranged at the bottom of the preheating zone, so that the raw ore is uniformly calcined. The fuel used is fluid fuel, such as gas, oil, pulverized coal and so on. In raw material application, this kiln type has a wider range of particle size selection, capable of calcining 30 100mm particle size, this feature is more important in China limestone resources become less and less.

 Main characteristics and economic indicators:

 1. Calcium oxide has good quality and low overburn rate:

 Due to the use of double chamber kiln body alternate calcination production, so that the calcination time is longer, product homogeneity is better, calcium oxide content can be controlled in the range of 88%~94%, the product overburning rate can be controlled below 5%.

 2. Low CO2 residue rate and high product activity

 Since fuel and combustion air are introduced from the upper part of the kiln body, the calcination flame flows in parallel with the ore in the calcination zone. In all vertical kilns, the co-current zone of the double-chamber kiln is long. Due to the co-current calcination of the long stroke, the lime quality is very good: residual CO2 1.5%, activity can be guaranteed at 370ml of 4NHCl for 10 minutes (product quality mainly depends on the raw material);

3, low energy consumption, low operating costs:

 Due to the alternate reversing operation of the two kiln bodies, the waste gas directly preheats the ore, and the heat is fully utilized. The heat consumption per unit product is * low, and the heat recovery rate exceeds 83%; the heat loss can reach 800-890Kcal/kg(3350-3720kJ/kg);* Low heat consumption means * Low operating costs, for example: when using pulverized coal production, the standard coal consumption is 114kg-120kg of coal per ton of lime product. Compared with the traditional old-fashioned shaft kiln, the fuel consumption per ton of lime product is at least 20-40kg.

 The disadvantages of the parallel flow regenerative double chamber lime kiln imported from abroad:

 The double chamber kiln is a positive pressure kiln. The production of lime kiln is restricted not only by the temperature of calcination zone, but also by the system pressure. In the lime kiln with low calorific value fuel, the system pressure is the main factor restricting the production.

 Double-chamber kilns have connecting channels, and the permeability of channels is an important factor affecting production. The two important factors of channel permeability are gas flow rate and channel temperature. The larger the gas flow rate in the channel, the faster the gas flow velocity, and the easier the channel is to be blocked. The mechanism lies in: high flow rate, high flow rate of gas will bring a lot of dust into the channel, and accumulated in the corner of the channel, a long time, it will block; the higher the channel temperature, will accelerate the accumulation of dust sintering together, the easier the channel is blocked.

 When pulverized coal is used as fuel in production, it will not cause negative effects on system pressure and channel permeability. In gaseous fuels, when the fuel calorific value is not lower than 2400kcal Nm, it will not cause negative effects on the system pressure and channel permeability. When the calorific value of the gas fuel is lower than 2400kcal Nm-3, it will accelerate the passage blockage to a certain extent, increase the overall pressure of the system, and cause the system to be difficult to control.

 3. Optimization Design and Innovation of Domestic Double Chamber Lime Kiln

 China Lime Industry Society is responsible for the development and authorization of Tangshan City Fengnan District Jinquan Metallurgical Energy New Technology Development Co., Ltd. and Tangshan Jinquan Complete Equipment Co., Ltd. under Tangshan Jinquan Metallurgical Science and Technology Industry Group. After many years of research, improvement and upgrading, the new generation of domestic double-chamber shaft kiln technology and the new generation of coal-electricity integrated double-chamber shaft kiln technology have been comprehensively developed. After The technology is now officially available:

 This technology maintains the process structure and characteristics of the original traditional double-chamber vertical kiln, and mainly makes the following process improvements and innovations:

1,simplify the raw material feeding system:

Simplify the raw material feeding system, adopt the bin in front of the kiln to feed directly, and realize stone screening, cleaning and grading into the furnace during the feeding process, which can save 40%-50% of the investment in the raw material system.

2.Optimize pulverized coal injection and ignition system:

 1) Intelligent pressure equalization distribution is adopted for pressure distribution of pulverized coal injection pipeline, reasonable design of pipeline diameter reduces fluctuation of air flow in pipeline, makes air flow more stable, pulverized coal transportation and distribution more uniform, improves flame distribution effect in kiln chamber and improves product quality.

 2) Change the traditional pulverized coal distributor mechanism, from disc distributor to cavity three-dimensional space injection structure, high injection accuracy, stable injection, will not be affected by the change of material characteristics and the fluctuation of kiln pressure;

 3) The unique rotary feeding structure design ensures smooth and undulation-free pulverized coal injection system, ensures uniform and stable injection of pulverized coal in the pipeline, and does not block;

 4) Select a unique spray gun with self-protection function, which can freely adjust the nozzle position, reduce the failure rate, and improve the controllable performance and service life of the spray gun. solve that problems that the spray nozzle of the traditional spray gun is continuously expose in the kiln body and continuously subjected to airflow scouring, so that the spray nozzle is seriously worn, has short service life, is blocked and the like.

 5) The new pulverized coal direct ignition technology is selected to solve the problems of traditional double-chamber kiln ignition burner using liquid fuel, slow heating, long time and large consumption, thus optimizing ignition and lime kiln start-up operation, ensuring engineering quality, reducing labor intensity, shortening ignition solid fuel and lime kiln start-up time, and saving ignition cost.

3. Design and application of new type furnace top charging device:

 The conventional double-chamber lime kiln generally adopts a rotary hopper at the top of the furnace to carry out charging, the overall structure of the equipment is relatively complex, the investment cost is high, the fault points are many, dust is easy to rise in the charging process, so the surrounding environment is polluted, and environmental protection is difficult to control. It also leads to unstable roof pressure, so it is difficult to meet the production process requirements.

 The new type of furnace top charging device adopts the split section sealing charging method, which has the advantages of low investment, high practicability, complete sealing and easy maintenance, and meets the requirements of charging and calcining process of double-chamber lime kiln. Moreover, the device is easy to install, convenient to operate, strong in applicability, greatly reduces the number of faults generated in production and operation, and is in a completely sealed state in production and operation, so dust is completely eliminated, and environmental protection requirements are met.

4. Innovative design and application of furnace support technology:

 Different from the traditional lime shaft kiln, the calcination zone and preheating zone of the double-chamber shaft kiln body are cylinders with different diameters, so the connection and support of the calcination zone and the cooling zone of the kiln body are the key technologies, which is also the biggest difference from the traditional mixed burning shaft kiln and other straight lime shaft kilns. The internal support mode of imported double-hearth kilns mainly adopts corbel support structure developed by Myers Company in the early stage and hanging cylinder structure developed by many domestic companies in the later stage. Another is the angle ring unsupported structure developed by Simone Italia.

 Double-chamber lime supported by corbels needs to be shut down for about 2 hours every week to clean the middle flue gas channel due to high channel resistance, so the labor intensity is high and it is unfavorable to the stability of production. The suspension cylinder structure can solve the problem of annular flue gas channel blockage well; however, the intermediate channel still needs to be cleaned regularly (15~20 days); moreover, the suspension cylinder design structure is complex, the manufacturing process is complex, the construction is difficult, and the price is expensive; moreover, the maintenance is difficult and the risk of accident is large, and even the whole collapse phenomenon will occur in serious cases. The angle ring unsupported structure completely solves the problem of blocking the annular flue gas channel and the intermediate channel, and the annular channel and the intermediate channel do not need to be cleaned during operation. The disadvantages are that the inner diameter of the lower part of the kiln chamber is doubled, and the steel structure engineering quantity and civil engineering quantity are increased greatly. The angle ring structure design structure is complex, the manufacturing process is complex, the price is expensive, and the manufacturing cycle is long. The corner ring special pendant and special refractory design uses a large number of special bricks, special material requirements, manufacturing difficulty, and high cost, and is not conducive to subsequent maintenance and replacement.

 The annular wind guide wall support structure innovatively applied overcomes the defects of the prior art, and designs a furnace internal support and wind guide calcining device which is simple in structure, convenient to manufacture and convenient for field construction; the technology adds an air guide wall device, improves an annular channel process, reduces resistance of the annular channel, improves flow velocity of hot flue gas at the middle channel, makes ash deposition difficult to occur in the middle channel, solves the problem of ash deposition in the furnace or the middle channel in the production process, and ensures continuity of production. Moreover, the cooling problem of the internal support structure is solved at the same time, and the structure is simple and difficult to malfunction. At the same time, compared with the same structure investment of imported technology from abroad, the investment has been greatly reduced.

 The main output of this series of kilns is: 400 tons per day, 500 tons per day and 600 tons per day.

  IV. Optimization Design and Innovation of Multifunctional Domestic Double Chamber Lime Kiln

 China Lime Industry Society is responsible for the development and authorization of Tangshan City Fengnan District Jinquan Metallurgical Energy New Technology Development Co., Ltd. and Tangshan Jinquan Complete Equipment Co., Ltd. under Tangshan Jinquan Metallurgical Technology Industry Group. After years of research, the new generation of coal-electricity integrated double-chamber vertical kiln technology has been optimized and upgraded again on the basis of the new generation of domestic double-chamber vertical kiln technology, realizing the application of various fuels in double-chamber lime kiln and further extending the economic benefits of users.

 1. Gas-coal dual-purpose double-chamber vertical kiln:

 The existing double-chamber lime kilns generally adopt single coal gas or pulverized coal as fuel medium to carry out lime calcination. For the lime kilns which adopt coal gas as fuel medium alone, the utilization rate of low calorific value gas is relatively low, and the low calorific value gas (such as blast furnace gas) cannot be fully used. For the lime kilns which adopt pulverized coal as fuel medium alone, a large amount of pulverized coal is consumed, and the production cost is relatively high.

 The new type of gas-coal dual-purpose double-chamber vertical kiln is designed with the function of gas-coal mixed combustion, which can effectively realize the mixed combustion of gas and pulverized coal, realize the diversity of fuel medium of lime kiln, improve the utilization rate and application range of lime kiln, improve the utilization rate of low calorific value gas, and save the use cost of fuel.

 This technology mainly uses inert gases such as carbon dioxide gas and nitrogen gas and the design combination of pulverized coal spray gun and gas spray gun to make the dual fuel of gas and pulverized coal mixed combustion, realize the diversity of fuel medium of lime kiln, and improve the utilization rate and application range of lime kiln. The kiln model can also be used alone when a single gas or pulverized coal medium for production.

 2. Natural gas type double-chamber vertical kiln:

 Natural gas is clean, efficient and in ample supply, and is currently the most suitable alternative fuel for dual chamber kilns. Natural gas double-chamber vertical kiln and pulverized coal injection double-chamber vertical kiln have basically the same process structure, but the combustion system (including injection and fuel transportation) process is different. At present, the technology of natural gas combustion system of double-chamber kiln has been developed abroad. The technical scheme of natural gas combustion system transformation is high investment and technical monopoly. Therefore, it is very necessary to develop our own natural gas combustion device of double-chamber lime kiln.

 The newly-designed natural gas combustion system consists of natural gas transmission pipeline, gas supply station, pressure regulating device, flow regulating device, safety protection device, gas ring pipe, cooling air pipe ring pipe, high pressure steam pipeline, high pressure inert gas pipeline, spray gun, ignition device, combustion regulating device, spray gun bracket and spray gun. The spray gun in the furnace is provided with a plurality of spray pipes which are combined and arranged in parallel and form a combustion device, the spray pipes are uniformly distributed in the combustion device, and the annular pipe of the gas device surrounds the outer circumference of the combustion device.

 The utility model has the advantages of simple structure, less equipment quantity, low failure rate in the production process, automatic control, simple and convenient operation and maintenance, less post staff requirements, short overall construction period and relatively low investment cost.

 The main output of this series of kilns is: 400 tons per day, 500 tons per day and 600 tons per day.

 3. Transformation of mixed-material vertical kiln into double-chamber vertical kiln:

 At present, due to the limitation of fuel structure characteristics in China, the main production kiln type of shaft kiln is mainly solid fuel mixed lime shaft kiln, contributing more than 70% of the output. However, due to the acceleration of China's economic transformation and development and ecological civilization construction, the production capacity, energy saving, environmental protection and automation control of some ordinary mixed-type shaft kilns and equipment have not met the national requirements for green development of lime industry, technological progress and structural adjustment and elimination of backward shaft kilns The pace of kiln type has been significantly accelerated, and the time for technical upgrading and upgrading of ordinary mixed-type shaft kilns and equipment has arrived.

 However, if such ordinary shaft kilns are demolished and replaced, it will waste a lot of resources or cost a lot of money, and even some lime enterprises may be severely damaged, which is very unfavorable to the development of lime industry. How to make full use of the existing mixing-type ordinary shaft kiln process structure for transformation and utilization has become the focus of attention in the industry.

 In   view of the above problems, a new technology for“ transforming a mixed vertical kiln into a double-chamber vertical kiln” has been developed, and a variety of vertical kilns have been designed to transform ordinary vertical kilns into co-current calcination and counter-current heat storage devices and their transformation methods. The furnace body structure of two single-cylinder vertical kilns has been combined, and high temperature flue gas circulation devices, fuel conveying devices, external furnace control devices, furnace combustion devices, two-way airflow circulation devices, and high pressure cleaning devices have been added, thus changing the previous production process, ensuring production capacity and product quality, and achieving energy conservation and environmental protection. And do not need to dismantle the original ordinary lime shaft kiln, greatly reducing the investment. The device can be used for pulverized coal injection and gas production.

 At present, the fourth generation coal-electricity integrated lime shaft kiln project promoted and applied by Tangshan Jinquan Company since 2019 has all reserved some process interfaces for transformation into double-chamber shaft kiln, among which * important kiln structure parts, including bottom two-way air supply device and kiln body civil engineering foundation, have been designed and constructed according to the process requirements of double-chamber shaft kiln, which is of great transformation and utilization value.

 It is worth explaining that, except the fourth generation AHA compound kiln type of Tangshan Jinquan Company and some third generation kiln types of Jinquan Company can be transformed, due to the limitation of transformation technology, other kiln types that can be transformed at present are mainly straight-tube structure vertical kilns, and vase type vertical kilns cannot be transformed. The reconstruction can only be carried out if the two kilns are coaxial or the center distance between the two kilns is within the range of connection.

 The main output of this series of modified kilns is 300 tons per day and 400 tons per day.

 4. Development and application of coal-electricity integrated double-chamber vertical kiln:

 This technology is a new generation of calcined lime technology independently researched and developed by Xinxin, focusing on the blank of existing technology, using carbon dioxide gas generated in lime production to generate electricity and calcining lime with electric energy, collecting and recycling all carbon dioxide gas in lime production, realizing zero emission of carbon dioxide.

 The lime production system is designed as a double-chamber or multi-chamber, which has the functions of parallel flow and heat storage of the traditional double-chamber kiln, mainly adds an electric energy conversion heat storage chamber, adopts electric heating to generate hot air and high temperature air to calcine lime, and includes an electric burning heat storage chamber, a high temperature flameless combustion device and the like. The key point of the invention is that the process devices with different functions of the double-chamber vertical kiln are arranged in a combined body to form a complete novel multifunctional furnace body integrating heating, parallel flow, heat accumulation and calcination. The invention solves the problems that heat energy converted by electric energy cannot directly heat a heated body when electric energy is adopted to produce lime, heat energy cannot be stored, and heat load and hot air temperature cannot be accurately controlled, production units with different functions are combined according to specific requirements, energy can be stored and heat can be recovered and reused by using heat storage mode converted by electric energy, and high temperature air can be directly provided to a combustion chamber in a furnace, To achieve high temperature air combustion.

 The invention is a further extension and deepening of the double-chamber vertical kiln technology, so as to realize more methods for electrically burning lime. At present, Tangshan Jinquan Company has completed a number of industrial experiments and completed a number of patent applications. With the continuous improvement and maturity of the technology, the technology will be gradually applied to the coal-fired double-chamber shaft kiln. On the basis of the production process of coal or gas, the electric burning function will be added, and the final goal will be to achieve the independent electric burning function.

 Data Editor:

 China Lime Industry Society

 Sun Fei

         2021.01.20