Indirect-fired heaters are an essential piece of equipment in many industrial settings. They provide a reliable and efficient way to heat fluids, gasses, and airstreams for a variety of applications. In this blog post, we will take an in-depth look at what indirect-fired heaters are, how they work, their components, different types, applications, advantages and disadvantages, and critical design considerations. Whether you are looking to purchase a new indirect-fired heater or learn more about optimizing an existing one, this guide covers all the essential details about indirect-fired heaters that you need to know.
What are Indirect Fired Heaters?
Indirect-fired heaters, also known as indirect heat exchangers, are process heating equipment that use an external heat source to heat a fluid, gas, or air stream. Indirect Heaters transfer heat through a dividing wall from an external combustion chamber to the material being heated. The combustion chamber and heating chamber are separated with a pressure-tight, gas-tight tube sheet, preventing combustion gasses from mixing with the fluid being heated.
This differs from direct-fired heaters, where the combustion gasses come into direct contact with the process fluid. The critical advantage of indirect heating is that it prevents any contamination between the heating medium and the process fluid.
Main Components of an Indirect Fired Heater
Indirect-fired heaters have several main components that work together to safely and efficiently transfer heat to the target fluid or gas stream:
- Combustion Chamber - This is where fuel combustion takes place, producing heat that gets conducted through the tube sheets. Different types of burners may be used based on the fuel source.
- Tubesheet - The tubesheet divides the combustion chamber from the heating chamber and facilitates heat transfer. It must be pressure-tight and gas-tight.
- Tube Bundle - This network of tubes contains the process fluid and runs through the heating chamber, allowing the tube sheet to transfer heat. Different materials and configurations are used based on temperatures and pressures.
- Stack - Exhaust gasses exit via the stack after transferring heat.
- Casing - This enclosure houses all heater components and provides thermal insulation.
How Indirect Fired Heaters Work
Now that we understand the primary components, let's look at how indirect-fired heaters actually work:
- Fuel (natural gas, oil, etc.) and combustion air enter the combustion chamber, where the burner ignites the mixture.
- This controlled burning creates flames and hot combustion gasses within the chamber.
- The tube sheets transfer heat from these hot gasses to the tube network containing the process fluid.
- The fluid flows through the tubes, getting heated by the conducted heat.
- Combustion exhaust gasses exit via the stack while the heated fluid flows out of the tube network to its destination.
- The casing encloses the entire heater, retaining heat and protecting operators.
This indirect heating keeps the process fluid isolated from the products of combustion. By optimizing flows and heat transfer, high efficiencies can be achieved.
Types of Indirect Fired Heaters
There are a few main types of indirect-fired heaters that are designed for various uses:
- Tubular Heat Exchangers - Long steel tubes encased in a refractory-lined furnace and commonly used for higher temperatures/pressures.
- Box-Style Cabinets - A box-shaped heater with a flat top and short vertical tubes. They are used for heating air or gasses at lower temperatures.
- Packaged Water Tube Units - Self-contained heaters with straight water tubes, circular headers, and removable channel tops. Offer fast turndown and modular configurations.
- Steam Heaters - Explicitly designed for producing steam, these heat water in long bent tubes within a pressure vessel.
- Fluidized Bed Heaters - A bed of inert particles gets fluidized by airflow for excellent heat transfer to tubes immersed in the bed.
- Electric Heaters - Instead of combustion, electric heating elements are used. Clean and easily controlled, it is better for small or portable units.
The right heater type depends on parameters like capacity, temperatures, pressures, flows, and kind of heating medium. Consulting experts are advised to match the heater design to your specific process needs.
Critical Applications of Indirect Fired Heaters
Now that we have covered the basics of how indirect-fired heaters work and the main types available, what are some of the most common applications? Here are some of the industries and uses where indirect-fired heaters are indispensable:
Oil & Gas - Used extensively at refineries, petrochemical plants, and processing facilities to heat hydrocarbons for fractionation and reactions and required to achieve precise temperature control and clean heating.
Chemical & Pharmaceutical - Critical for achieving chemical reactions, distillations, and separations. Sanitary heating is essential to prevent contamination.
HVAC & Air Drying: Heated fresh air and processed air streams need precise temperature and humidity control provided by specialized air heaters.
Power Generation: Steam generation, turbine inlet heating, and boiler feedwater heating all require industrial-scale indirect-fired heaters.
Food & Beverage: Food processing, brewing, and pasteurization rely on indirect heaters for product safety and quality.
Asphalt Production: Efficient heating of asphalt is achieved via indirect firing, preventing local overheating.
From critical industrial processes to large-scale utility and energy applications, indirect-fired heaters serve a vital role in many sectors. Their versatility, efficiency, and reliability make them an indispensable technology.
Advantages of Indirect Fired Heaters
There are many good reasons why indirect-fired heating is preferred over direct firing in industrial processes. Some of the main advantages include:
- No Contamination - The process stream never contacts combustion gasses, preventing fouling, corrosion, and contamination.
- Versatility - Indirect heaters can heat a wide variety of fluids, gasses, and particulates.
- Efficiency - Well-designed units can achieve thermal efficiencies of over 90%, providing substantial energy savings.
- Temperature Control - Precise control overheating is possible by controlling firing rate and fluid flows.
- Lower Emissions - Since heat is transferred through a barrier, lower NOx emissions are achievable.
- Operator Safety - Isolating the process stream from combustion enhances operator safety.
- Longer Tube Life - Avoiding direct contact with flames increases tube life significantly.
- Design Flexibility - Many custom tube materials, shapes, and configurations are possible.
For processes that demand clean, efficient, and controlled heating, indirect-fired heaters provide significant advantages over direct firing options. Long-term benefits justify their upfront cost.
Potential Disadvantages of Indirect Fired Heaters
Despite their many benefits, indirect-fired heaters also come with some potential downsides to consider:
- Higher Capital Costs - The specialized construction makes indirect heaters more expensive upfront than comparable direct-fired units.
- Space Requirements - Indirect heaters tend to be larger due to lower heat transfer coefficients through the tube walls.
- Longer Startup Time - It takes longer to heat the thermal mass of the tube sheets when starting up an indirect heater.
- Lower Temperatures - Maximum temperatures are ultimately limited by tube metallurgy. Other methods can achieve higher temperatures.
- Tube Failures - Mechanical or material failures in the tubes or headers can result in downtime and lost production. Proper maintenance is critical.
- Fouling Risks - Scale buildup and fouling on the tube side can reduce heat transfer over time. Chemical treatment may be needed.
While these downsides are manageable, they should be factored into the total cost of ownership. Weighing the pros and cons of a given application is recommended.
Key Design Considerations for Indirect Fired Heaters
If an indirect-fired heater is determined to be the right solution for a heating process, proper design is critical for performance and safety. Here are some of the most important design factors to consider:
- Temperature Requirements - Max/min temperatures dictate tube metal selection and furnace design.
- Heating Load - The required heat transfer rate determines the overall heater size.
- Fluid Properties - Density, viscosity, corrosiveness, and fouling tendency affect design.
- Pressure Rating - Tube thickness and joints must withstand maximum pressures.
- Flow Volumes - Tube diameter and flows dictate fluid velocity and residence time.
- Fuel Type - Impacts burner selection and combustion chamber design.
- Safety Factors - Proper codes and standards must be incorporated in the design.
- Control System - Precise flow, temperature, and firing rate controls are needed.
- Inspection/Cleaning - Access doors and ports should allow for visual and mechanical inspection.
- Thermal Expansion - The design must compensate for the expansion of tubes and casings at temperature.
- Emissions - Low NOx burners and proper exhaust treatment may be required.
Consulting qualified engineers during the design phase is highly recommended to ensure optimal sizing, efficiency, and functionality of the indirect-fired heater.
Conclusion
Indirect-fired heaters, such as those offered by Preferred Climate Solutions, are pivotal in diverse industrial settings, delivering efficient and dependable heating solutions while safeguarding the purity and integrity of the process fluid or gas. These heaters operate by transferring heat from an external combustion chamber through a tube sheet to the material being heated, thereby averting contamination and upholding stringent quality standards.
Name: Preferred Climate Solutions
Address: 14818 Park Almeda Dr, Houston 77047, Texas, USA
Phone No: 713–305–6239
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