Billet reheating furnaces are an essential component in the steel industry. They are used to heat steel billets to the required temperature for further processing, such as rolling, forging, or extrusion. The heating process in a reheating furnace is a continuous process where the steel billets are heated to a temperature of around 1200°C, which is suitable for plastic deformation of steel and hence for rolling in the mill.

Fundamentals of Billet Reheating Furnaces include the process of heating steel billets to the desired temperature, which is achieved by using various types of reheating furnaces. The operational aspects of these furnaces, such as temperature control, fuel consumption, and material handling, are crucial to ensure the quality of the final product. The types of reheating furnaces commonly used in the steel industry include walking beam furnaces, rotary hearth furnaces, pusher-type furnaces, and others.

Energy efficiency and sustainability are also important considerations in the design and operation of reheating furnaces. The use of advanced technologies, such as regenerative burners, waste heat recovery systems, and automation, can help reduce energy consumption and greenhouse gas emissions. Proper maintenance and safety measures are also essential to ensure the safe and efficient operation of these furnaces.

Key Takeaways

• Billet reheating furnaces are used to heat steel billets to the required temperature for further processing.
• The operational aspects of reheating furnaces, such as temperature control and material handling, are crucial to ensure the quality of the final product.
• Energy efficiency, sustainability, and safety are important considerations in the design and operation of reheating furnaces.

Fundamentals of Billet Reheating Furnaces

Design Principles

Billet reheating furnaces are an essential part of steel plants, used to heat billets, blooms, or slabs to the rolling temperatures of around 1200°C, which is suitable for plastic deformation of steel and hence for rolling in the mill. The heating process in a reheating furnace is a continuous process where the steel stock is heated to the required temperature for the subsequent rolling process. The design of a billet reheating furnace is based on the size and shape of the billets to be heated.

The design principles of a billet reheating furnace include the heating rate, the heating uniformity, and the fuel efficiency. The heating rate is the rate at which the billets are heated to the required temperature, and it is determined by the heat transfer mechanisms used in the furnace. The heating uniformity is the degree of temperature uniformity across the billets, and it is determined by the furnace design and the heat transfer mechanisms used. The fuel efficiency is the ratio of the heat energy supplied to the billets to the fuel energy consumed by the furnace, and it is determined by the furnace design, the fuel type, and the combustion process.

Heat Transfer Mechanisms

The heat transfer mechanisms used in a billet reheating furnace are conduction, convection, and radiation. Conduction is the transfer of heat through the solid material of the furnace walls and the billets. Convection is the transfer of heat through the movement of hot gases in the furnace. Radiation is the transfer of heat through electromagnetic waves emitted by the hot gases and the furnace walls.

The efficiency of heat transfer mechanisms depends on the furnace design and the operating conditions. For example, a walking beam furnace uses convection and radiation for heat transfer, while a pusher furnace uses conduction, convection, and radiation. The choice of heat transfer mechanisms depends on the size and shape of the billets, the desired heating rate, and the required heating uniformity.

Fuel Types and Combustion

The fuel types used in a billet reheating furnace are natural gas, coke oven gas, fuel oil, and coal. Natural gas is the most commonly used fuel due to its high calorific value and low emissions. Coke oven gas is a byproduct of the coke-making process and is used as a fuel in some steel plants. Fuel oil and coal are used in some steel plants where natural gas is not available or is expensive.

The combustion process in a billet reheating furnace is critical for fuel efficiency and emissions. The combustion process should be optimized to ensure complete combustion of the fuel and minimize emissions such as carbon monoxide, nitrogen oxides, and particulate matter. The combustion process is controlled by the air-to-fuel ratio, the fuel injection system, and the furnace design.

Operational Aspects

Temperature Control

Maintaining the right temperature is crucial for the quality of the finished product and energy efficiency. The temperature of the billets should be uniform throughout the furnace. The temperature control system should be accurate and reliable. According to a study by Chen et al. (2005) published in ScienceDirect, the temperature control system can be improved by using a proportional-integral-derivative (PID) controller. The PID controller can regulate the fuel gas and air flow rate to maintain the desired temperature.

Process Optimization

Optimizing the billet reheating process can increase energy efficiency and reduce cost. The pusher-type reheating furnace is commonly used in the steel industry. The furnace can contain up to 138 billets and the billets enter the furnace one or two at a time from the left side. The pushers trigger the billet movement from the entrance to the exit of the furnace. The billet furnace inlet temperature can be very different, in the range 0 to 1200°C (SpringerLink, 2024).

A review by Ma et al. (2019) published in ScienceDirect suggests that process optimization can be achieved by reducing the billet size, increasing the heating rate, and minimizing the heat losses. The review also suggests using heat recovery systems, such as heat exchangers and recuperators, to recover the waste heat and preheat the combustion air.

In conclusion, optimizing the temperature control system and the billet reheating process can improve energy efficiency and reduce cost.

Types of Reheating Furnaces

There are several types of reheating furnaces used in the steel industry. Each type has its own unique features and advantages. The three main types of reheating furnaces are pusher furnace, walking beam furnace, and rotary hearth furnace.

Pusher Furnace

Pusher furnaces are the most commonly used type of reheating furnace in the steel industry. They are designed to heat up steel billets by pushing them through a furnace using a system of pusher rams. The billets are placed on a roller conveyor and pushed into the furnace by the pusher rams. The furnace is heated by burners located on both sides of the furnace. The billets are heated to a temperature of around 1200°C to 1250°C, which is the ideal temperature for plastic deformation of steel.

Pusher furnaces are ideal for high production rates and are capable of heating large quantities of steel billets at a time. They are also highly energy-efficient and can be designed to operate with a range of fuels, including natural gas, coke oven gas, and blast furnace gas.

Walking Beam Furnace

Walking beam furnaces are another type of reheating furnace commonly used in the steel industry. They are designed to heat up steel billets by moving them through the furnace on a series of walking beams. The billets are placed on the walking beams, which move through the furnace at a controlled speed. The furnace is heated by burners located on both sides of the furnace.

Walking beam furnaces are ideal for heating up larger steel billets and can be used for a wide range of steel grades. They are also highly energy-efficient and can be designed to operate with a range of fuels, including natural gas, coke oven gas, and blast furnace gas.

Rotary Hearth Furnace

Rotary hearth furnaces are a type of reheating furnace that uses a rotating hearth to heat up steel billets. The billets are placed on a rotating hearth, which moves through the furnace at a controlled speed. The furnace is heated by burners located on both sides of the furnace.

Rotary hearth furnaces are ideal for heating up small to medium-sized steel billets and can be used for a wide range of steel grades. They are also highly energy-efficient and can be designed to operate with a range of fuels, including natural gas, coke oven gas, and blast furnace gas.

In summary, each type of reheating furnace has its own unique features and advantages. Pusher furnaces are ideal for high production rates, walking beam furnaces are ideal for heating up larger steel billets, and rotary hearth furnaces are ideal for heating up small to medium-sized steel billets.

Material Handling in Reheating Furnaces

Reheating furnaces are crucial pieces of equipment in the steel industry, used to heat ingots, blooms, or billets to a temperature suitable for hot rolling. Material handling is an essential aspect of reheating furnaces, as it affects the quality of the final product and the efficiency of the reheating process.

Conveyor Systems

Conveyor systems are used to transport the billets from the charging area to the furnace and then to the discharge area after reheating. The conveyor system should be designed to handle the weight and size of the billets and to prevent damage during transport. The conveyor system should also be designed to minimize the time required to transport the billets to and from the furnace to maximize efficiency.

Charging and Discharging Practices

Charging and discharging practices are critical in the material handling process of reheating furnaces. The charging process involves loading the billets onto the conveyor system and moving them into the furnace. The discharging process involves removing the billets from the furnace and moving them to the discharge area.

Proper charging and discharging practices can significantly improve the efficiency of the reheating process. For instance, charging the furnace with the correct number of billets at the right temperature can reduce the heating time and energy consumption. Similarly, discharging the billets from the furnace in a timely and organized manner can increase the throughput of the furnace.

In conclusion, material handling is an essential aspect of reheating furnaces. Conveyor systems and charging and discharging practices should be designed and implemented to maximize efficiency and minimize damage to the billets.

Energy Efficiency and Sustainability

Waste Heat Recovery

Waste heat recovery is an important strategy for improving the energy efficiency of a billet reheating furnace. By capturing the waste heat generated during the heating process, it can be reused for other purposes, such as preheating combustion air or water. This can significantly reduce the overall energy consumption of the furnace and improve its sustainability. According to a study published in Energy Reports, a heat balance study and process improvement can increase the energy efficiency of a steel billet reheating furnace by up to 10% [1].

Emission Reduction Strategies

Reducing emissions is another important aspect of improving the sustainability of a billet reheating furnace. One strategy is to use cleaner fuels, such as natural gas or biogas, instead of coal or oil. Another strategy is to optimize the combustion process to minimize the formation of pollutants. This can be achieved by adjusting the air-to-fuel ratio, using staged combustion, or installing flue gas recirculation systems. According to a review published in Renewable and Sustainable Energy Reviews, waste heat recovery and combustion optimization are the most effective strategies for reducing emissions from industrial reheating furnaces [2].

Overall, improving the energy efficiency and sustainability of a billet reheating furnace is crucial for reducing its environmental impact and operating costs. By implementing waste heat recovery and emission reduction strategies, steel manufacturers can not only reduce their carbon footprint but also improve their bottom line.

[1] Increase in energy efficiency of a steel billet reheating furnace by heat balance study and process improvement. (n.d.). ScienceDirect. https://www.sciencedirect.com/science/article/pii/S2352484719305815

[2] Industrial reheating furnaces: A review of energy efficiency assessments, waste heat recovery potentials, heating process characteristics and perspectives for steel industry. (2021). ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S0957582021000549

Maintenance and Safety

Routine Maintenance Procedures

To ensure the efficient operation of billet reheating furnaces, routine maintenance procedures must be carried out regularly. This includes cleaning the furnace and its components, inspecting the refractory lining, lubricating moving parts, and replacing worn-out parts. It is important to follow the manufacturer’s recommendations for maintenance procedures to ensure the longevity of the furnace.

One of the most important routine maintenance procedures is cleaning the furnace and its components. This involves removing any debris or slag that may have accumulated in the furnace, as well as cleaning the burners, fans, and ductwork. Inspecting the refractory lining is also crucial to ensure that it is in good condition and to identify any cracks or defects that may need to be repaired.

Lubricating moving parts such as bearings, motors, and chains is also essential to prevent wear and tear and to ensure smooth operation. Replacing worn-out parts such as thermocouples, thermocouple protection tubes, and burners is also important to maintain the efficiency of the furnace.

Safety Measures and Protocols

Safety is of utmost importance when operating a billet reheating furnace. The following safety measures and protocols should be strictly adhered to:

• Personal protective equipment such as gloves, safety glasses, and heat-resistant clothing should be worn by all personnel working in or around the furnace.
• The furnace should be equipped with safety features such as emergency shut-off switches, fire suppression systems, and gas leak detection systems.
• Regular safety inspections should be carried out to identify any potential hazards or safety issues.
• All personnel should be trained in the safe operation of the furnace and should be aware of emergency procedures in case of an accident or malfunction.

By following routine maintenance procedures and adhering to safety measures and protocols, the billet reheating furnace can operate efficiently and safely for many years.