Taking the converter circulating water system as the research object, the high-pressure surplus energy head is used to start or accelerate the natural circulation, realize the optimized energy use of the system, and achieve the win-win effect of energy saving and longevity of the tail flue.
The structural defects of the front flue are studied and analyzed, and the anti-large splash slag hanging technology and follow-up sealing device are developed to increase the life of the front flue by more than 2 years and reduce the nitrogen consumption by about 90%.
A series of high-efficiency and energy-saving core power equipment has been developed and applied, solving the common technical problems of low steam production and poor quality in the vaporization cooling system, so that the steam production per ton of steel is increased to 100-130kg, the heat loss of the sewage system is reduced by 50%, and the heat loss of the deaerator exhaust steam is reduced by 50%.
Converter steelmaking accounts for about 70.8% of the global steelmaking process and is the main form of steelmaking production. A large amount of flue gas is generated during converter steelmaking, with a total heat of up to 1116.2 MJ/t, which is an important secondary energy source.
At present, vaporization cooling technology is widely used to recover the waste heat of converter steelmaking flue gas, which can reduce the flue gas temperature and recover steam.
The existing vaporization cooling technology has problems such as high system energy consumption, high equipment failure rate, short flue life, low steam output and poor quality, which can no longer meet the needs of upgrading and transformation of the steel industry.
In order to achieve energy conservation and emission reduction, green development, and respond to the call for dual carbon, technical innovation is carried out on the converter vaporization cooling system.
Converter vaporization cooling system and energy-optimized combined cycle
Converter Evaporation Cooling System
The converter vaporization cooling system is mainly used to recover the waste heat of high-temperature flue gas generated by converter smelting. The converter vaporization cooling device consists of vaporization cooling flue, steam drum, circulating water pipeline, deaerator, feed water pump, high-pressure circulating water pump, low-pressure circulating water pump, etc.
Among them, the vaporization cooling flue is the only channel for high-temperature flue gas transportation and is the core equipment of the entire system. The converter vaporization cooling system can be roughly divided into circulating water system, steam heat storage system, feed water system, nitrogen sealing system, sewage system and miscellaneous system according to the medium channel.
Among them, the circulating water system absorbs heat from the high-temperature flue gas side through heat exchange with the flue, and is the core system of the vaporization cooling system. There are three circulation modes of the circulating water system: low-pressure forced circulation, high-pressure forced circulation and natural circulation.
Optimizing energy use combined cycle
The steam-water cycle generally includes natural circulation and forced circulation. The natural circulation relies solely on the density difference of the working medium (water and steam-water mixture) to overcome the resistance loss along the way and the local resistance loss and form a cycle.
The power of the forced circulation system is the density difference between the forced circulation pump and the steam-water medium. The power generated by the density difference between the forced circulation pump and the medium needs to overcome the total resistance loss along the way and locally, and leave a certain margin.
In the early stage of smelting, the density difference of the natural circulation medium is small, the circulation power is insufficient, and bubbles are easily accumulated at the tail corner where the resistance is large. The circulation is blocked, which makes the temperature at the corner higher. The flow rate and heating of the same section of the tube bundle are uneven, resulting in inconsistent expansion and contraction of the tube bundle, and finally deformation and damage at the corner, affecting the life of the flue.
In order to avoid the above problems, combining the characteristics and advantages of forced circulation and natural circulation, an optimized energy composite cycle is proposed: in the initial stage of natural circulation, the density difference is close to zero, and the natural circulation power is insufficient. The surplus dynamic pressure head of the forced circulation is migrated to supplement the power source of the natural circulation, improve the uneven flow velocity distribution and insufficient power of the natural circulation, and enable the tail flue to achieve rapid switching between natural circulation and forced circulation according to the smelting cycle.
Compared with the traditional circulation system, the energy-optimized compound circulation system uses key equipment (jet device) to migrate the surplus energy head in the forced circulation pump to start or accelerate the natural circulation to achieve the system’s optimized energy use, provide reliable power for the initial stage of natural circulation, alleviate the problem of uneven heat load in the tail flue, and ensure that the tail flue circulation is reliable and effective. The energy-optimized compound circulation system solves the technical difficulties of system energy saving and flue longevity, and improves system energy efficiency while ensuring circulation.
Engineering practice shows that: on the basis of not increasing electricity consumption, the converter flue gasification cooling energy optimization composite circulation system strengthens the circulation effect of the tail flue, improves the cooling effect of the heated tubes, reduces water and steam leakage in the flue, increases steam production, reduces the flue maintenance rate, and extends the life of the flue.
Flue longevity and energy saving technology
New follow-up sealing device
The movable smoke hood is placed directly above the furnace mouth. The converter flue gas treatment method based on the unburned method requires the movable smoke hood to be lifted and lowered smoothly and have good sealing performance to ensure efficient and high-quality recovery of coal gas.
The seal between the movable smoke hood and the fixed section of the furnace mouth belongs to the dynamic and static surface seal. At present, the sealing forms usually adopt water seal, N2 seal and mechanical seal.
The water seal is easy to be blocked by dust accumulation in the water seal groove, with a high failure rate and safety hazards.
The N2 seal has a simple structure, little maintenance workload, and easy operation, but it has the disadvantages of large sealing port and high N2 consumption. The mechanical seal has low energy consumption, and the periodic smelting of the converter is easy to cause the mechanical seal to deform. There are safety hazards such as smoke hood jamming and gas leakage, high failure rate and short service life.
In view of the above-mentioned sealing defects, we conducted in-depth research on the problems existing in the sealing structure of the movable smoke hood, and drew on the solutions for dynamic and static surface sealing in other fields. We developed and applied a movable smoke hood follow-up sealing structure by reducing the gap between the fixed section of the furnace mouth in the front flue and the movable smoke hood, supplemented by N2 sealing.
The movable smoke hood follow-up sealing structure uses the elastic force of a specific mechanism to make the sealing surface fit the flue wall over a large area. The end roller structure can roll up and down relative to the fixed section of the flue wall, and the tiny gap with the wall is sealed with the help of N2, which greatly saves the consumption of N2.
The application of the movable smoke hood follow-up sealing structure effectively solves the common technical problems of the movable smoke hood, such as poor sealing effect, high N2 consumption, and poor lifting and lowering, and can greatly improve the safety and economy of the movable smoke hood.
Flue duct splash and slag prevention technology
Small and medium-sized converters generally have problems such as overload production leading to pipe bursts and water leakage in the fixed section of the furnace mouth.
Through on-site collection, the damaged heating tubes were analyzed by macroscopic appearance, metallographic microscope, and scanning electron microscope. The slag on the heating surface of the fixed section caused uneven heating of the heating tubes and deteriorated heat transfer, causing the heating tubes to burst.
In order to solve the problem of easy slagging in the fixed section of the furnace mouth, a large splash slagging prevention technology, also known as the supersonic coating technology for the heating surface, was developed and applied.
A flue heating surface alloy spray protective coating is applied on the flue gas side of the heating tube, which can effectively reduce the direct erosion and wear of the large particles of converter flue gas on the heating surface, reduce the surface roughness of the heating tube, and prevent the heating surface from slagging when the converter splashes.
The application practice of multiple project projects shows that the large splash slagging prevention technology can effectively avoid slagging on the heating surface, protect the heating tube, and increase the life of the flue.
High-efficiency and energy-saving power equipment
Steam filter cleaner
The periodic smelting of the converter causes large changes in the load of the vaporization cooling system and the water level of the drum, resulting in excessively high water content in the steam separated from the drum. Water hammer is prone to occur in the pipeline that transports high-temperature and high-pressure steam, damaging the steam pipeline and valve.
The steam filter is a filtering device before the steam external supply heat accumulator. It is installed on the steam pipeline at the drum outlet, between the drum and the heat accumulator. Engineering practice shows that the steam water rate can be reduced to 1%, which effectively improves the steam quality, avoids the water hammer phenomenon caused by water in the steam pipeline, increases the pipeline transmission rate by 5% to 10%, and the filtered clean condensate can be recycled, reducing the maintenance volume by 90% and reducing the heat loss of the system.
Pressure variable spherical steam accumulator
The heat accumulator is the core equipment of the vaporization steam heat storage system. The variable pressure steam horizontal heat accumulators commonly used in current projects generally have problems such as large floor space, high steam moisture content, large drainage volume, and high failure rate. In view of the disadvantages of horizontal spherical storage, the variable pressure spherical steam heat accumulator was developed and applied.
In-depth and detailed research has been conducted on the stress field of the spherical steam accumulator structure, the temperature field of the large steam-water circulation space, the fatigue of thick metal under frequent alternating hot and cold working conditions, and the durability of internal impacted components. Breakthroughs have been made in conventional technologies in terms of heat charging, liquid level, steam dehydration, etc., with the following characteristics:
(1) A stable circulation heat charging mixing system is set up inside, which is evenly distributed in a ring-shaped multi-layer to ensure that there is no temperature stratification, no heat charging dead zone, and smooth and uniform heat charging;
(2) The steam-water separation device adopts a modular design and a double separation structure. The steam space is twice that of the traditional horizontal accumulator, which reduces the steam moisture content and meets the user’s steam quality requirements;
(3) The ring pipe layout of the water replenishment and discharge device keeps the accumulator liquid level within a reasonable range. The liquid level measurement adopts a guided wave radar liquid level transmitter that is easy to install and maintain.
Compared with horizontal heat accumulators, the pressure-variable spherical steam heat accumulator saves 50% to 70% of space and reduces heat dissipation by 50%. The material usage of the supporting system is reduced by 50%, and the overall investment is reduced by 25% to 30%. The steam space is large and the steam moisture content is low. The structure is simple and the maintenance is small.
Integrated long-term deaerator
Existing thermal deoxidation generally uses a deaerator with a deaerator head. In order to make the boiler feed water reach the specified oxygen content, the deaerator with a deaerator head requires at least about 15% to 27% of the rated evaporation capacity of the boiler. The deoxygenated steam is directly discharged, which consumes a lot of energy.
At the same time, the water tank is equipped with a deaerator head, which occupies a large space, has a complex piping structure, and is inconvenient to connect and repair.
The integrated long-term deaerator uses a high-efficiency composite spring nozzle and an internal device in the water tank to replace the deaerator head of the traditional thermal deaerator. The atomizing nozzle is adjusted by a spring, so that the feed water can form a good film under 10% to 110% load conditions, better adapt to variable working conditions, and reduce deoxidation steam consumption and exhaust steam loss.
The integrated long-term deaerator consists of a deaerator body, a platform staircase and accessories. The deaerator body consists of a shell, a support, a water supply device, a spring nozzle, a baffle, a heating steam device, a reboiling device and a recirculation pipe. The design without a deaerator head simplifies the structure of the conventional deaerator, reduces the installation difficulty of the conventional deaerator and the design requirements of the plant platform.
Innovation to improve equipment life
In order to meet the requirement that the circulating water piping of the movable smoke hood is lifted up and down with the movable smoke hood, the movable smoke hood and the circulating water pipeline are usually connected by metal hoses, metal compensators, etc. Because the movable smoke hood is frequently lifted and lowered, the metal hoses or metal compensators are very likely to be fatigued and damaged.
A single furnace requires about 6 metal compensators, which occupy a large installation space and are inconvenient for maintenance. In view of the disadvantages of the old connection method, a flexible device for the movable smoke hood is developed and applied. Only 2 units are needed for a single furnace, and the service life is extended by 2 to 3 years compared with the old connection method. At the same time, it has the advantages of safe operation and no leakage.
In order to improve the service life of the vaporization cooling pump group, a direct drop multi-filter decontaminant is developed and applied, which is installed at the pump inlet. It not only solves the problem that the conventional pipeline filter structure cannot withstand high temperature and high pressure, but also solves the shortcomings of the traditional decontaminant with simple structure, high filtration flow rate and easy clogging.
In order to prevent impurities in the circulating water pipeline from entering the flue and affecting the service life of the flue, a new filtering device is set at the entrance of each section of the circulating water pipeline of the flue—the anti-blocking device of the heated pipe. A filtering device is arranged in the anti-blocking device for the heated pipe. The force on the filtering device is dispersed through multi-point support, and it has better pressure-bearing capacity. This fundamentally solves the problem that the heated pipe of the flue is easily blocked by the installation of a temporary filter, reduces the number of inspections and replacements of the flue, and ensures the normal and safe operation of the entire circulating water system.
Application Effect
Energy saving, emission reduction and extended flue life
Combining the environmental protection and energy saving of natural circulation, the good circulation effect of forced circulation and the long life of flue, the optimized energy compound circulation cooling system realizes the comprehensive utilization and balanced allocation of resources in the whole system. Compared with similar product technologies, the system reduces consumption by 30%, investment by about 50%, and operating costs by more than 50%; the life of flue is greatly improved, the life of movable smoke hood, fixed section and movable section is increased from 1 to 2 years to 3 to 5 years, and the life of middle section and end section is increased from 5 to 6 years to more than 10 years. The application of follow-up sealing device reduces the amount of N2 used for sealing movable smoke hood by 90%.
Reduce system failure rate
The supersonic coating technology for the heating surface overcomes the technical defects of the movable smoke hood, the heating surface of the fixed section and the movable section of the flue, the easy slag hanging, the easy explosion of the heating tube and the water leakage, and the easy deformation of the movable smoke hood ring beam, which leads to frequent failures, reducing the risk of production safety accidents and ensuring smooth production. Compared with similar technical products at home and abroad, the water side resistance of the heating tube is reduced by 15%, and there is no steam blockage and explosion failure; the splashing and hanging of slag is reduced, which greatly reduces the occurrence of overheating and explosion accidents.
Improve cooling effect and steam recovery quality
By integrating technologies such as optimized energy utilization compound cycle, integrated long-term deaerator, and variable-pressure spherical steam accumulator into conventional converter vaporization technology, the quantity and quality of steam output can be improved while reducing the external energy input of the system. The steam output of the vaporization cooling system can reach up to 130kg/t, the heat loss of sewage discharge is reduced by 50%, the heat loss of deaerator exhaust steam is reduced by 50%, and the deaerator self-use steam is saved by 3%.
Benefit
The technological innovations of the vaporization system series embody the green development economic concept of saving electricity, water, materials and environmental protection. It has the characteristics of low energy consumption, high efficiency and low emissions. It can save energy by about 14.11kgce per ton of steel, reduce CO2 emissions by about 35.19kg, reduce SO2 emissions by about 0.12kg, and reduce NOx emissions by about 0.104kg. It responds to the call of the national dual-carbon policy and helps enterprises reduce carbon and produce green production.
