A furnace is an essential piece of equipment in manufacturing many objects, and it is used in heating processes that require temperatures above 4000C. Because there are different processes and raw materials used across the manufacturing industry, there are various heating applications, too. This automatically gives rise to the need for different furnace designs in the market.
So, it is not uncommon to find different types of furnaces for different types of applications, fuels types, heating duties, or methods of introducing combustion air.
Choosing one for your specific application may be a challenge if you aren’t familiar with furnaces. Hence, it is important to understand what each furnace design entails and its capabilities before opting for one.
Considerations for Industrial Furnace Design
There are a couple of factors to consider when choosing a furnace design. Some of them are:
Furnace Operations and Applications
Furnaces are used for two main purposes: to produce heat for industrial chemical reactions or to assist in the production of certain objects. Industrial applications they are used for include annealing, tempering, melting, sintering, brazing, and carburizing metals, among others.
Industrial furnaces come in different designs to suit different applications. Hence, the specific application you want to use a furnace will determine the specific design you should opt for.
In the same way, each application requires a mode of operation. For example, while some processes require direct contact with the heat produced by the furnace, other applications require indirect contact.
Types of Furnace Design
There are different furnace designs available. So, it is important to decide on the one that best suits your manufacturing process.
Generally, there are four types of furnace designs. They are:
Single-Stage Furnace: Also known as single-speed furnaces, this type of furnace design constantly runs at a maximum speed and pumps out hot air at a high velocity. This type of furnace design is relatively simple and inexpensive to install and is, therefore, a good choice if you’re working with a very limited budget.
However, this type of furnace design leads to high energy usage and emits a lot of noise from its blower motor. It is also common to experience mechanical inefficiencies while using it.
Two-Stage Furnace: Unlike single-stage furnaces, a two-stage furnace can run at a low or high speed, depending on the amount of heat needed per time. They are energy efficient and attract lower power costs.
However, this furnace design is more expensive to install than single-stage furnaces, but they are quieter and move air at a lower velocity.
Modulating Furnace: This type of furnace design intuitively emits heat as much as is necessary. As its name implies, it constantly modulates heat and air velocity as needed.
It can do this because it has a burner that adjusts the amount of fuel used at any given time. This type of furnace design is an ideal choice if you’re looking to maintain consistent temperature regardless of external temperature.
Structural Design of the Furnace
A furnace is made up of different parts, which consist of various components. The main parts of an industrial furnace include the radiant section or firebox, convective section, radiant coil, burners, sootblower, the flue gas stack, insulation, the foundation, access doors, electrical and control components.
These components and how they are assembled make up the structural design of a furnace. It is essential to consider the structural design when opting for one.
Two main factors determine the structure of a furnace. They are:
Construction Materials
In designing an industrial furnace, each component is made from different materials based on its function. The heat exchangers are made of stainless steel to make them resistant to corrosion; gas valves are constructed with brass, aluminized steel for the blowers, burners, and the frame. Fiberglass is used as an insulating material for the furnace cabinet, while the electrical wires are made of copper.
Fabrication Methods
After designing the furnace and procuring the construction materials to be used, the next step is to fabricate the furnace.
There are two heat exchangers in an industrial furnace – the primary and secondary heat exchangers. The primary heat exchanger is made from two separate pieces of stainless steel sheet, while the secondary heat exchanger is made from stainless steel fins and tubing. The two exchangers are then crimped to each other through a transition box.
At this point, already constructed burners are attached to every side of the primary heat exchanger. The flue draft blower is also attached to the secondary heat exchanger. Next, the gas control valve is attached to the assembled heat exchanger and burner and connected through a pipe.
A compartment is formed for the air circulation blower using the same method as the primary heat exchanger. Other components of this compartment, such as the motor and squirrel-cage rotor, are then fitted using brackets.
The blower compartment is mounted on the primary heat exchanger using a plate. Apart from this plate, another plate is attached to the blower compartment to allow for the furnace control system and transformer attachments.
Finally, the furnace cabinet is fitted around the entire assembly using bolts and screws, doors are installed, and the new furnace is ready.
Upgrading an Existing Furnace
In some cases, you need to upgrade an existing furnace instead of getting a new one. In this case, you do not need to design a new furnace from scratch.
Upgrades can either involve retrofitting an entire system or replacing one or more components. It is usually done to meet current processing rules and standards, technological advancements, market demands, or to reduce production downtime.
An upgrade helps increase the efficiency and safety of your furnace. There are three main areas of a furnace that can benefit from an upgrade: insulation, combustion, and control systems.
It’s usually easy to determine if the insulation system needs an upgrade, as the indicators are generally obvious. For combustion and control systems, you may need the services of an expert to determine whether you need an upgrade or not. For example, a collapsed furnace roof is obvious and may require an upgrade of the insulation system. In contrast, a clogged burner isn’t immediately apparent to the user.
Calculating Industrial Furnace Temperature
Furnace designs have different heat transfer capabilities, and industrial applications also have standard heat requirements. So, it is crucial to ensure that the combustion process of a furnace can deliver the amount of heat required.
Four main processes contribute to the combustion process in a furnace. They include air flow, combustion, heat, and mass transfer.
When air and fuel enter the combustion chamber, ignition occurs and releases energy, which produces a flame. Heat is then transferred from the flame to the furnace walls. Afterward, the heat is distributed by conduction, convection, and radiation throughout the furnace to process the object.
The heat transfer in a furnace can be calculated using the other parameters that contribute to the combustion process. By comparing the resulting value (in BTU) with the temperature requirements of your application, you can determine which furnace design is best for your production process.
Challenges of Furnace Design for Different Applications
The main goals for every furnace design are to increase energy efficiency by reducing the amount of fuel or electricity required for combustion and to minimize the emission of pollutants, such as carbon mono-oxide and nitrogen oxides. Achieving these goals comes with different challenges. Some of them are:
Meeting Process Expectations
Processes that use furnaces involve running the equipment at high temperatures and for long periods at a stretch. It is an intense process and pushes the materials used in designing the furnace to their limit. So, a furnace designer must source suitable materials and create the right design to meet process expectations.
Beyond meeting process requirements during design, the designer must also consider the reliability and durability of such materials over time to prolong the useful life of the furnace.
Heat Maintenance and Heat Loss
The operation of a furnace is characterized by heat transfer and heat loss, and thus, its efficiency largely depends on these two parameters.
Efficiency is achieved when the object to be processed is heated uniformly at the required temperature at a given time using the least possible amount of fuel or electricity.
A sufficient amount of heat must be liberated in a given time while overcoming possible heat losses. Heat loss from the furnace must also be reduced to the least possible amount.
Heating Design and Operation
The heating design and operation of a furnace involve two primary energy sources – fuels and electricity. For a fuel furnace, its design should ensure that fuels undergo complete combustion. For example, a fossil-fueled furnace should emit carbon dioxide instead of carbon monoxide in its flue gas.
Furnace Controls
Achieving a control system that is safe, efficient, and user-friendly requires sufficient expertise. Usually, this involves evaluating the furnace parameters and the user’s needs.
The furnace control system measures and controls power consumption, temperature, fluid flow, material conveyance, motor control, etc. Thus, the productivity of a furnace depends on its control system. For fueled furnaces, for instance, the pressure control determines its efficiency.
Abbott Specializes in Furnace Design
In choosing a furnace design for your application, it is best to work with a team of furnace designers and engineers that have the required expertise you need.
The team at Abbott Furnace takes the time to understand the specific requirements of your processes and custom designs and engineers the furnace to your specific application.
Experience with Variable Application Furnaces
With over 35 years of designing and producing some of the industry’s most reliable and high-performing industrial furnaces, Abbott Furnace Company has the experience required to manufacture furnaces for different industrial applications.
Contact Abbott Today
Contact us to discuss the right type of furnace design for your specific application today.
