Pure hydrogen electric heating design scheme matched with hydrogen-based shaft furnace

Abstract

The invention relates to a design scheme suitable for an electric heating device matched with a hydrogen-based shaft furnace for reducing iron ore, belongs to the technical field of hydrogen metallurgy for directly reducing a hydrogen-based shaft furnace, and aims to solve the problem that the service life of a heating furnace is influenced by aging of a heating rod due to high-temperature reaction between hydrogen and the heating rod. The hydrogen electric heating furnace adopts a separated structure design, hydrogen flows in a nickel-based alloy heating pipeline, and a silicon carbide rod is arranged in a heating furnace cavity, so that the surface of the heating rod is prevented from reacting with high-temperature hydrogen and water vapor; the heating furnace tube adopts a snake-shaped structure, so that the heat exchange area is increased, the deformation of the high-temperature furnace tube is compensated, and the stability of the whole heating furnace is improved; the heating furnace adopts multi-zone temperature control, and heating elements are uniformly distributed in the furnace, so that the temperature in the heating furnace is uniform, and the precision temperature control of + / -5 DEG C of the hydrogen outlet temperature is realized; the heating furnace cavity is protected by nitrogen, inlet hydrogen supply is cut off in time when hydrogen leaks, a safety linkage nitrogen valve is used for purging, and the overall safety of the heating furnace is improved. Through the design mode of the heating furnace, the durability and the safety of the pure hydrogen electric heating equipment are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen metallurgy for direct reduction of iron ore in a hydrogen-based shaft furnace, and in particular relates to an electric heating device matched with the hydrogen-based shaft furnace for reducing iron ore. Background Art

[0002] In 2023, my country's crude steel output reached 1.019 billion tons, accounting for 54% of the world's crude steel output. As a high-energy-consuming and high-emission industry, the steel industry's carbon emissions account for about 15% of the country's total carbon emissions, making it the industry with the largest carbon emissions among the 31 categories of manufacturing.

[0003] my country's steel industry has long been dominated by the long blast furnace-converter process, resulting in high carbon emissions. Blast furnace ironmaking still accounts for over 95% of my country's total iron production. Blast furnace ironmaking is the process with the highest carbon dioxide emissions, accounting for approximately 70% to 90% of the total carbon dioxide emissions from the entire steel production process. Compared with the traditional "blast furnace + converter" smelting process, the shortened direct reduced iron (DRI) + electric furnace process offers significant carbon emission reduction advantages. Hydrogen metallurgy uses hydrogen instead of coke as a reducing agent, significantly reducing carbon dioxide production and contributing to low-carbon, green steel production.

[0004] Hydrometallurgy, which replaces carbon with hydrogen, is becoming a strategic technology option for green and low-carbon development in the domestic and international steel industry. Hydrogen-based shaft furnaces use hydrogen to reduce iron oxide, resulting in metallic iron and water vapor as the primary products, without other carbon-containing reducing gases like CO. This enables low-carbon, green steel production. With the increasing adoption of green electricity such as photovoltaic and wind power and the rapidly declining cost of hydrogen production through water electrolysis, hydrogen metallurgy, which uses hydrogen as a reducing agent instead of carbon, is a key approach to reducing CO2 emissions from long steelmaking processes and ensuring the green and sustainable development of the steel industry.

[0005] The reaction of hydrogen reducing pellets inside the hydrogen-based vertical furnace is an endothermic reaction. In order to maintain the high-temperature reduction conditions inside the vertical furnace, a large amount of heat must be added to the vertical furnace. The heat is circulated by heating the hydrogen to a higher temperature. At this time, the heated hydrogen temperature must reach 950-1050°C. The shell material of the heating furnace must have long-term high-temperature resistance and hydrogen corrosion resistance. Hydrogen is flammable and explosive. The temperature and pressure must be strictly controlled during the heating process to prevent hydrogen leakage and ensure good equipment sealing.

[0006] Electric heating generally uses silicon carbide rods to heat hydrogen. When used in a high-temperature, oxidizing atmosphere, a dense quartz (SiO2) glass film quickly forms on the surface of the silicon carbide rods. This film protects the inner layer of the silicon carbide rod from further oxidation, thereby extending its service life. However, in a reducing atmosphere such as hydrogen, this protective film may be destroyed, thus shortening its service life. In addition, the hydrogen produced after purification of the top gas from a hydrogen-based vertical furnace contains a certain proportion of water vapor. At high temperatures, this water vapor will react with the silicon carbide rods, accelerating their aging. Summary of the Invention

[0007] The purpose of the present invention is to provide a structural solution of an electric heating device suitable for a hydrogen-based shaft furnace iron ore reduction process, so as to improve the durability and safety of pure hydrogen electric heating equipment.

[0008] To achieve the above objectives, the present invention provides the following design and calculation scheme:

[0009] 1. Hydrogen flows in the nickel-based alloy heating pipe, and the silicon carbon rod is arranged inside the heating furnace. The heating form of radiation heat exchange is adopted. The heating rod does not come into contact with hydrogen and water vapor, avoiding reaction with high-temperature hydrogen and water vapor, thereby improving the life and stability of the heating system.

[0010] 2. The heating furnace tube adopts a serpentine structure, which not only increases the heat exchange area but also compensates for the deformation of the high-temperature furnace tube. It is made of high-temperature alloy steel with a temperature resistance of >1300℃, which improves the stability of the heating process of the heating furnace.

[0011] 3. The heating furnace adopts multi-zone temperature control, and the heating elements are evenly distributed in the furnace to make the temperature uniform in the heating furnace. The precision temperature control of the hydrogen outlet temperature can be achieved within ±5℃, and the hydrogen heating temperature can reach 1050℃.

[0012] 4. The heating furnace is protected by nitrogen, the shell is equipped with an explosion relief valve, and a pressure detection system is equipped to monitor the pressure inside the heating furnace tube in real time. When hydrogen leaks, the inlet hydrogen supply is cut off in time, and the safety interlock nitrogen valve is used for purging to improve the overall safety of the heating furnace.

[0013] Compared with existing technologies, this invention offers the following technical advantages: A design that isolates hydrogen from the heating element prevents direct contact between high-temperature hydrogen and the heating rods. Multi-zone, segmented temperature control ensures uniform furnace temperature. Heating tube pressure measurement and nitrogen safety interlocks effectively prevent hydrogen leakage, improving the safety and stability of the heating furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the main process flow chart of the pure hydrogen electric heating furnace

[0015] Figure 2 The internal structure diagram of the pure hydrogen electric heating furnace

[0016] Figure 3 The three-dimensional structure diagram of the pure hydrogen electric heating furnace DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0018] The purpose of the present invention is to improve the stability of the equipment by adopting a partitioned pure hydrogen electric heating furnace design, and to improve the safety of the heating furnace by adopting effective nitrogen purge.

[0019] The process of electrically heating hydrogen does not produce carbon dioxide or other harmful substances, which is a true zero-carbon emission method. At the same time, the use of electric heating reduces the energy consumption of preparing the heating gas, significantly improving the overall energy utilization rate of the system.

[0020] Hydrogen-based shaft furnace reduction process of hematite: 1 / 2Fe2O3+3 / 2H2=Fe+3 / 2H2O

[0021] Hydrogen-based shaft furnace reduction process of magnetite: 1 / 3Fe3O4+4 / 3H2=Fe+4 / 3H2O

[0022] The above two reactions are endothermic reactions. A high reaction temperature must be maintained in the hydrogen-based vertical furnace to ensure the smooth progress of the reaction. Excess hydrogen must be continuously heated to maintain the internal temperature balance so that the reduction reaction can proceed continuously and efficiently.

[0023] The main process flow of pure hydrogen heating furnace is as follows Figure 1 As shown, the hydrogen electric heating furnace in this scheme is composed of a heating shell, a heat exchange pipe, a furnace and other structures.

[0024] The hydrogen heating furnace shell adopts a box-type structure, which consists of two parts: the shell and the lining. The shell of the hydrogen heating furnace is made of carbon steel welded components, and the lining is made of refractory masonry to ensure that the temperature of the heat transferred to the shell does not exceed 80℃.

[0025] like Figure 2 The diagram shows the internal structure of a pure hydrogen electric heating furnace. Hydrogen enters the furnace through the heating pipes, where it is divided into six heating channels. The heating tubes utilize a serpentine structure, which increases the heat exchange area, compensates for high-temperature tube deformation, and improves the stability of the heating process. The heating tubes are made of a specially customized high-temperature alloy steel, which is resistant to temperatures exceeding 1300°C and exhibits high strength and corrosion resistance under high-temperature conditions. The heating tubes enter the furnace from one side above the furnace body. Inside the furnace, the ends of the tubes connect to form a set of pipes that pass through the other side of the upper end of the furnace shell, where they are insulated by a thermal insulation layer and then into the shaft furnace.

[0026] like Figure 3The figure shows the three-dimensional structure of a pure hydrogen electric heating furnace. Thirty-six silicon carbide rods are evenly distributed throughout the furnace, arranged crosswise with the heat exchange coils to ensure uniform radiative heat exchange. The compact structure maximizes furnace space utilization. The silicon carbide rods heat the hydrogen, achieving an operating temperature of up to 1450°C. Radiation heats the heat exchange tubes, which then transfer heat to the hydrogen through a combination of radiation and convection. The furnace is divided into two temperature-controlled zones to ensure uniform heating throughout the furnace: the intermediate and high-temperature zones. These zones are separated by high-temperature refractory bricks. A dividing wall supports the heating tubes midway, preventing significant tube deformation and improving overall pipe flexibility, thereby enhancing pipe stability during the heating process. The intermediate zone can heat the hydrogen to 800°C, while the high-temperature zone heats the hydrogen to 1050°C. This hydrogen is then supplied to the downstream hydrogen-based vertical furnace unit for iron ore reduction.

[0027] The heating furnace is equipped with a number of necessary safety auxiliary equipment such as observation holes, nitrogen inlet holes, nitrogen discharge holes, and is also equipped with an explosion relief valve device to ensure the safety of equipment use.

[0028] Hydrogen enters the heating furnace from the heating pipe inlet. The hydrogen pipe inlet is equipped with a manual valve, filter, pressure gauge, pressure transmitter, and electric shut-off valve to monitor hydrogen pressure in real time and automatically cut off the hydrogen supply in the event of a system failure. At the furnace inlet, the hydrogen pipe is divided into six branches leading to the furnace for heating. Each branch is equipped with a pressure gauge and a manually adjustable stopcock valve to adjust the pressure and flow uniformly on each branch.

[0029] The nitrogen purge pipeline consists of a ball valve and solenoid valve, and is primarily used to purge the hydrogen pipeline and automatically purge the heating furnace chamber. The nitrogen release pipeline is equipped with an electric butterfly valve, which is used in conjunction with the nitrogen purge to purge and release the furnace chamber during furnace startup and in the event of a fault.

[0030] In the hydrogen metallurgical shaft furnace process for producing sponge iron, the hydrogen circulation process involves freshly introduced hydrogen and purified top gas from the shaft furnace being mixed in a buffer tank. The room-temperature hydrogen is then heated by an electric heater. The heated hydrogen then enters the shaft furnace from the lower reduction section, where it reacts with the freely falling iron ore to produce sponge iron. The sponge iron is then discharged through the shaft furnace's lower outlet. Some of the hot hydrogen reacts to produce water vapor, which mixes with the majority of the unreacted hydrogen and flows to the top of the shaft furnace. It is then discharged through the shaft furnace's exhaust gas purification system, where the top exhaust gas temperature is approximately 400°C. The exhaust gas purification process involves water washing, pressurization, and dehydration. The purified gas is then evenly mixed with the freshly introduced hydrogen before entering the heating system for heating, completing the shaft furnace's hydrogen circulation process.

[0031] Four S-type thermocouples are installed on the heating furnace body to monitor and control the temperatures on both sides of the medium-temperature and high-temperature zones of the heating hearth. A thermocouple is installed at the reducing gas outlet to monitor and control the temperature of the reduced gas output after heating. This temperature is displayed and controlled locally by the power control cabinet, and the feedback signal is transmitted remotely to the vertical furnace control system, enabling real-time adjustment of the vertical furnace and heating furnace temperatures to meet the hydrogen-based vertical furnace reduction process routes for different raw materials such as lump ore, sintered pellets, and cold-pressed pellets. A pressure gauge and pressure transmitter are installed at the reducing gas inlet to monitor the reducing gas temperature and pressure in real time.

[0032] Before entering the heating furnace from the heating pipes, hydrogen is divided into six heating channels. Thirty-six silicon carbide rods are evenly distributed throughout the furnace, intersecting the heat exchange coils. The pressure within the tubes is maintained at a constant 0.4 MPa, heating the hydrogen from 25°C to 1050°C. Nitrogen is continuously introduced into the furnace for gas protection, allowing the high-temperature silicon carbide rods to heat the hydrogen without contact. Because the purified gas contains some water, prolonged use at temperatures above 1000°C results in water vapor that reacts chemically with the silicon carbide rods to form silicon dioxide, causing component aging. This electric heater utilizes an isolated design to prevent aging of the silicon carbide rods from contact with water vapor, extending the heater's service life.

[0033] Nitrogen enters the middle temperature zone and high temperature zone of the heating furnace through the pipes below the heating furnace box, and is discharged from the heating furnace through the pipes above the heating furnace. When heating hydrogen, nitrogen is introduced to replace the gas components in the furnace. The low flow of nitrogen ensures the slow flow of gas in the furnace, which is convenient for the monitoring system to monitor the status of the furnace. The pressure fluctuation is detected by the pressure measurement system, and the flow rate of nitrogen is adjusted to ensure the stability of the pressure inside the heating furnace.

[0034] The heating furnace is equipped with a hydrogen detector. When hydrogen components are detected in the furnace, the system will activate the heating furnace safety interlock system. The system will perform the following instructions:

[0035] 1. Cut off the heating power of the silicon carbon rod and stop heating the heating furnace tube;

[0036] 2. Cut off the reducing gas inlet ball valve and let the reducing gas flow into the furnace top exhaust pipe through the bypass. Open the nitrogen ball valve (equipped with a check valve) and let it flow into the heat exchange pipeline to displace the hydrogen in the heating furnace tube and discharge it out of the heating furnace.

[0037] 3. Adjust the solenoid valve of the nitrogen inlet pipeline to introduce a large amount of nitrogen into the heating furnace. At the same time, open the emergency release electric butterfly valve to completely replace the gas inside the furnace to prevent explosion.

[0038] The above operations can effectively ensure the stability and safety of the electric heating system.

[0039] The advantages of this hydrogen-based vertical furnace equipped with pure hydrogen electric heating design are:

[0040] 1. Hydrogen flows in the heating pipe, and silicon carbon rods are arranged in the heating furnace. The heating form of radiation heat exchange is adopted to avoid the silicon carbon rods from contacting and reacting with high-temperature hydrogen and water vapor, thereby improving the life and stability of the heating system.

[0041] 2. The heating furnace tube adopts a serpentine structure, which increases the heat exchange area and compensates for the deformation of the high-temperature furnace tube. It is made of high-temperature alloy steel with a temperature resistance of ≥1300℃, which improves the stability of the heating process of the heating furnace.

[0042] 3. The heating furnace adopts multi-zone temperature control, and the heating elements are evenly distributed in the furnace to make the temperature uniform in the heating furnace. The precision temperature control of the hydrogen outlet temperature can be achieved within ±5℃, and the hydrogen heating temperature can reach 1050℃.

[0043] 4. The heating furnace is protected by nitrogen, the shell is equipped with an explosion relief valve, and the pressure detection system monitors the pressure inside the heating furnace tube in real time. When hydrogen leaks, the inlet hydrogen supply is cut off in time, and the safety interlock nitrogen valve is used for purging to improve the overall safety of the heating furnace.

Claims

1. A structural scheme of an electric heating device suitable for hydrogen-based shaft furnace iron ore reduction process, characterized in that: include: 1) Hydrogen flows in the heating pipe, and the silicon carbon rods are arranged in the heating furnace. The heating form of radiation heat exchange is adopted to avoid the silicon carbon rods from contacting and reacting with high-temperature hydrogen and water vapor; 2) The heating furnace tube adopts a serpentine structure to increase the heat exchange area and compensate for the deformation of the high-temperature furnace tube. It is made of high-temperature alloy steel to improve the stability of the heating process of the heating furnace; 3) The heating furnace adopts multi-zone temperature control, and the heating elements are evenly distributed in the furnace, so that the temperature in the heating furnace is uniform, and the precision temperature control of the hydrogen outlet temperature can be achieved within ±5°C, and the hydrogen heating temperature can reach 1050°C; 4) The heating furnace is protected by nitrogen. When hydrogen leaks, the inlet hydrogen supply is cut off in time, and the safety interlock nitrogen valve is used for purging to improve the overall safety of the heating furnace.

Images