Hot Oil Heaters & Oil Heating Systems

Review of Thermal Oil

Industrial and commercial closed loop heat medium systems typically use water or thermal oil. While both media will carry high levels of heat energy, water-based systems require high pressurization at temperature above 212F. As the water heats up, the water converts to steam and begins to expand. This pressurized steam can be extremely dangerous, especially in aging or improperly sealed systems, where steam may burst through weak joints or other weak spots in the system and cause damage or injury. Steam systems also require frequent maintenance and protection from water impurities that can cause mineral deposits to form within the steam system.

Unlike steam heating, thermal oil absorbs heat energy without significantly changing pressure levels. The low-pressure operation creates a much safer operating environment and reduces strain on the system components. Built to the standards specified in ASME Section VIII, a thermal oil system doesn’t typically require a licensed boiler operator on site. Organic thermal oils can safely manage temperatures up to 600°F, and some synthetic thermal oils will reach 800°F.

System Name Clarification

Hot oil heaters go by a variety of names. Some of these include:

• Thermal oil boiler
• Thermal oil heater
• Thermal oil system
• Thermal fluid heater
• Thermal fluid system
• Hot oil boiler
• Hot oil heater
• Hot oil system

All of these names mean the same thing: A closed-loop, high temperature, liquid phase heat transfer system. Though owners and operators frequently call hot oil systems “boilers,” most liquid phase heat transfer mediums (typically organic or synthetic thermal oils) don’t vaporize the way water does in a steam system. Thermal fluid remains in liquid form during all temperature cycles through the system. The usage of the term boiler is simply derived from earlier water-based heating systems.

Basic Operation of Hot Oil Heater

Ultimately, a thermal fluid heating system supplies heat to process systems throughout a commercial or industrial facility. Because the fluid travels at low pressure, a thermal oil system supports a broader range of process heating tasks with less complexity than a high-pressure water heater system. The heated thermal oil flows throughout the closed-loop system and gets regularly reheated to replenish lost heat energy.

The three stages of hot oil heating include:

• Initial heating. The system’s combustion chamber contains a fuel fired burner or an electric immersion heating element. The gas fired burner or electric heating coil heats the thermal oil in the nearby fluid coils. The burner or electric heating element will modulate its output to control a constant fluid outlet temperature for the circulated thermal oil.
• Fluid & energy transfer. Once the newly heated thermal oil leaves the combustion chamber, it circulates throughout the closed loop to other process heating equipment. This process heating equipment includes a wide range of indirect heat transfer devices such as heat exchangers, jacketed reactors, press platens, calendar rolls, or many others.
• Fluid return & expansion. After delivering its energy to the process users, 100% of the thermal oil will return to the heater for reheating. Any unused energy is kept within the system and reused. This differs from steam systems where valuable heat energy is often lost through devices like steam traps and processes like blow down. A thermal fluid system does require an expansion vessel because it is a closed loop and the fluid expands when heated.

While most thermal oil heaters operate on the same principles, heater manufacturers differ on specific details of their designs. As with any product, there are trade offs between cost and performance that must be made. Some areas to consider include:

• Surface area. Efficient hot oil systems maximize the available heating surface area to capture as much of the available heat energy as possible. With a larger heat transfer area and a properly designed heater, more of the available energy is transferred to the oil, and less heat gets expelled from the system as waste. In similar thermal oil heaters with identical heat capacities and operational specifications, increasing the heat transfer surface in one of the systems will ultimately increase its efficiency over the heater with the smaller surface area.
• Combustion chamber size. A larger combustion chamber does more than accommodate the increased size and surface area of the thermal oil coils. Increasing the chamber size also helps control the burner flame by increasing the distance between it and the thermal fluid, which reduces the film temperature and extends the fluid’s useful lifespan.

Typical Applications

Some of the most common applications of hot oil heaters in commercial and industrial applications include:

• Autoclaves
• Building heaters
• Calendar roll heating
• Crude oil heating
• Heated molds or dies
• In-line gas heating
• In-line liquid heating
• Indirect steam generators
• Jacketed vessel heating
• Natural gas heating
• Ovens and fryers
• Plate/press heating
• Process reboilers
• Reactor vessel heating
• Suction heating
• Tank heating

At Sigma Thermal, we can create a fully customized thermal system based on your project or facility’s needs.

Sigma Thermal’s Groundbreaking Hot Oil Heater Project

Sigma Thermal helped design and build hot oil heaters for the first U.S. export-focused liquified natural gas (LNG) plant. We completed this project on a very tight timeline, including multiple site specific customizations. The finished result included:

• Four custom 100MM BTU/hour hot oil heaters
• Four exhaust stacks
• A fuel train and controls
• A flue gas recirculation (FGR) duct
• A complete combustible air system

We managed the entirety of the project, creating a heating system that could operate with six different types of gases and varying mixtures of those materials.

Sigma Thermal’s Hot Oil Heaters

Sigma Thermal designs and produces a wide range of hot oil heaters to fit virtually any industrial application. The following systems are two of our most popular.

• HC-1 Thermal Fluid Systems. These systems come in horizontal, vertical up-fired, and vertical down-fired options and the sizes range from 1–100 MM BTU/hour. We also offer custom heater designs to meet specific project needs.
• HC-2 Thermal Fluid Systems. HC-2 systems are also available in horizontal, vertical up-fired, and vertical down-fired configurations. Sizes range from 1-100 MM BTU/hour, with custom designs available upon request.
• SHOTS Electric Thermal Fluid System. Sigma Hot Oil Transfer Systems (SHOTS) use electrical power for circulation heaters and low-watt density immersion bundles. This capability enables the creation of heat without fuel sources such as natural gas, fuel oil, or biomass fuel. SHOTS systems provide power in configurations from 30-800kW. These electric thermal fluid systems can accommodate increased power from 800kW to 4MW and higher with customization.

Choose Sigma Thermal for Complete Hot Oil Heater Services

Our team of expert designers and engineers at Sigma Thermal have decades of experience designing and creating process heating systems. Our full portfolio of maintenance and repair solutions will help you to keep your system in excellent condition. We specialize in:

• Biomass fired energy systems
• Direct fired process heaters
• Electric process heaters
• Indirect process bath heaters
• Parts and retrofits/upgrades
• Support services
• System automation
• Thermal oil and thermal fluid heating systems

To see how our expertise can benefit your operation, please contact us, or request a quote today.