The fired heater — what it is,
where it sits, and why it matters.
This page gives you the foundations. You'll find what a fired heater actually does in a refinery, the main types you're likely to work with, the hazards that make careful operation non-negotiable, and how to get the most from this reference.
What is a fired heater?
A fired heater — also called a process heater, furnace, or charge heater depending on the application — is a direct-fired heat exchanger. Fuel is burned inside an insulated enclosure, and the heat released transfers through steel tubes to a process fluid flowing inside them.
Unlike shell-and-tube or plate heat exchangers, which move heat from one process stream to another, a fired heater introduces new heat energy into the process from combustion. This makes it both the most powerful and the most hazardous heat transfer device in a refinery.
Heat duties range from a few million BTU/hr for small treater feed heaters up to several hundred million BTU/hr for CDU charge heaters. Despite this range in size, the fundamental operating principles are the same.
Role in the refinery
Fired heaters appear throughout a refinery wherever a process stream needs to reach a temperature that cannot be achieved by heat integration alone. The most common duties are listed below.
| Unit / Service | Common Name | Typical Duty | Typical Outlet Temp. |
|---|---|---|---|
| Crude Distillation Unit | CDU charge heater / atmospheric heater | Partially vaporise crude feed for the atmospheric column | 340–370°C |
| Vacuum Distillation Unit | VDU charge heater | Heat atmospheric residue to near-cracking temperature under tight control | 390–420°C |
| Catalytic Reformer | Reformer charge heater / inter-heaters | Heat naphtha feed and reheat between reactor beds | 490–530°C |
| Hydrocracker / Hydrotreater | Charge heater / reactor feed heater | Heat feed to reactor inlet temperature | 300–430°C |
| Delayed Coker | Coker heater | Rapidly heat vacuum residue to cracking temperature — shortest residence time possible | 480–510°C |
| Visbreaker | Visbreaker heater / soaker heater | Controlled thermal cracking of heavy residue | 440–490°C |
In most of these services, the fired heater is the rate-limiting piece of equipment for the entire unit. If the heater trips, the unit stops. This is why fired heater reliability — and the operator's ability to recognise and respond to problems early — directly determines plant throughput and safety.
Main heater types
Fired heaters come in several configurations. The type you work with affects layout, burner arrangement, draft system, and inspection access — but the combustion and process principles are the same across all of them. Module 01 covers each type in depth; the brief summary below gives you a working picture.
Key zones inside a fired heater
Understanding the two main sections of a fired heater is essential before working through any procedure. All temperature, pressure, and flow references in this library use these terms.
Radiant section
The firebox itself. Burners fire here, and heat is transferred to the process tubes primarily by radiation from the hot flame and from the refractory-lined walls. This is where the highest heat flux occurs — and where tube overheating and coking problems develop. Typical radiant section temperatures range from 750°C to over 1000°C in the gas space.
Convection section
Flue gas leaving the radiant section passes upward through the convection section, where it gives up remaining heat to process tubes and, in most modern heaters, to a preheat coil or steam generation coil. Heat transfer here is primarily by convection — hence the name. Stack temperatures leaving the convection section typically range from 150°C to 350°C depending on heater efficiency and design.
The stack
The vertical flue that carries combustion gases to atmosphere. Stack height creates the natural draft that draws air into the burners. Stack dampers control draft and therefore airflow. The stack is also the source of the most visible indicator of combustion quality — smoke colour and density.
Key hazards
Fired heaters sit at the intersection of flammable process fluids, high temperatures, and a live flame. The hazards below are covered in depth in Modules 03 and 04. Every operator working on a fired heater should be able to describe each of them without prompting.
How to use this reference
This library is organised to support two modes of use: working through it as a structured learning resource, or jumping directly to a specific topic when you need it.
- 01 New to fired heaters? Work through Module 01 (Fundamentals) before moving to Operations. Understanding combustion and draft before you read startup and shutdown procedures will make those procedures much more meaningful.
- 02 Experienced operators can navigate directly to any topic via the sidebar. Procedure pages include context notes that explain the why behind each step — not just the what.
- 03 Procedures use interactive checklists. Tick steps as you work through them. Checklists reset if you navigate away — they are an aid to working through a procedure, not a permanent record. Your site logbook remains the official record.
- 04 Critical steps are flagged in red with a warning symbol. These are steps where an error carries significant risk to personnel or equipment. They warrant a pause and a deliberate confirmation before proceeding.
- 05 This reference is generic. It is written for a general refinery audience and reflects widely-used industry practice. It does not replace your site-specific operating manual. Where your site procedures differ, your site procedures take precedence.