Understanding Thermal Fluids & Thermal Fluid Systems

The demand for process heating and temperature control in the industry continues to increase as manufacturers and industrial facilities grow, expand, and seek to improve their existing operations. These process heating systems must perform consistently, safely, and with minimal downtime over time.

Industrial facilities that use plant-wide distributed process systems typically have one of two process systems: steam boilers or thermal fluid heating systems. Boilers were often the default choice in the past, but thermal fluid heating systems are a better solution for many applications, offering improved flexibility, control, and reliability.

Thermal Fluid Management

Thermal fluid heating systems operate in a closed-loop with the thermal fluid (also referred to as heat transfer fluid) in constant circulation. This continuous circulation at a constant supply temperature provides a heat source that users can access as needed. Users can be controlled individually, and thermal fluid temperature can be varied (user to user) through secondary control loops. In most systems, the thermal fluid or heat transfer fluid stays in a liquid state throughout the loop, although there are vapor phase fluids available for some niche applications that can benefit from latent heat over simple heat.

Types of Heat Transfer Fluids

Thermal oil, water, and water-glycol solutions are all commonly used in thermal fluid heating systems. All of these heat transfer fluids offer various advantages and disadvantages depending on the operating temperature and performance requirements of a system. It is important to understand what each fluid option is so a correct choice can be made for each application.

• Hot water and water-glycol. Water is the best possible heat transfer medium available when considering thermophysical properties, but it also comes with a number of drawbacks. Principally that it can be corrosive, contain contaminants, boils at 212ºF and freezes at 32ºF. Adding glycol in solution with water both increases the boiling point and decreases the freezing point, although that comes with some reduction in heat capacity.
• Thermal oil. Thermal oils tolerate higher temperatures than water-based formulas without boiling or unduly increasing system pressure. Natural oils can reach temperatures up to 600° F, while some synthetics allow oil-based systems to reach 800° F. These conditions allow oil-based heating systems to comply with ASME Section VIII, creating long-term savings since heat systems certified under ASME Section VIII don’t typically need a licensed boiler operator on site. Thermal oils are also typically non-corrosive and don’t need to be treated like water to prevent hard water deposits from forming in the system.

Advantages of Thermal Fluid Heating Systems

Thermal fluid heating, and thermal oil systems, in particular, have several advantages over their traditional boilers. These advantages include:

Achieving High Temperatures at Low Pressures

Thermal fluid systems offer a greater range of temperatures and a higher maximum temperature. These systems can reach temperatures of 0–750° F when using thermal oil, whereas steam-based systems only operate up to 350° F before operating pressures exceed 425 PSIG. Thermal fluid systems using water-glycol solutions can also reach 32–350° F at somewhat lower pressures than steam, which still offers significantly more flexibility than traditional systems.

While the temperature range is important, the low pressure is just as valuable. Most hot oils operating below 600° F don’t require any vapor pressure, and the maximum system pressure is only what is generated by the centrifugal circulation pumps. Even high-temperature synthetics operating as high as 750° F require less than 100 PSIG of vapor pressure. A steam system at 750° F would require over 3,200 PSIG of operating pressure.

Minimal Maintenance

Aside from regular flashpoint tests, thermal fluid heating systems require relatively little maintenance.

The circuits are simple and the fluid doesn’t require frequent adjustments or additions provided it is cared for and tested periodically to identify any potential issues. Also, thermal fluid systems don’t need blowdown, re-tubing, steam trap maintenance, or water treatments like traditional boilers do.

No Attendant Needed

Due to the increased safety concerns regarding boilers near workers, more industrial, state, and local regulations require the presence of a stationary engineer in boiler rooms. Many plants across the country have to keep at least one employee with specialized training in the boiler room during active periods to monitor the boiler’s operation. This is most commonly required for fire-steamed boilers.

Facilities that use thermal fluid heaters and an unfired steam generator often don’t need a stationary attendant. This advantage depends on specific state and local requirements.

Outdoor Installation

Thermal fluid systems create indirect heating power, which means they can be installed in remote indoor locations or outdoors. Keeping the heater and primary system components away from other key production areas helps to improve overall plant safety.

Thermal fluid systems are easy to install outdoors, though there are additional installation considerations. Cold start provisions must be considered when sizing a circulation pump and motor. It may also be necessary to pour slabs, weatherproof outdoor piping and equipment, and more.

Utilize Central Plant Heating

Larger or multi-purpose facilities may have high-temperature processes in conjunction with open-loop steam injection requirements. Traditionally, these facilities would need a thermal fluid heater and a steam boiler. Today, however, these facilities can use heat exchangers and rely solely on the thermal fluid heating system instead.

Certain types of heat exchangers coupled with a readily available hot oil can produce near-instantaneous steam as thermal fluid flows into them. Operators may use this steam for sterilization, wash downs, and other processes. The advantages of a central plant heating system with a heat exchanger(s) include:

• Lower maintenance
• Fewer expenses (because there is no boiler)
• A heat system that achieves high temperatures at low-pressure levels

Types of Thermal Fluid Heaters

Thermal fluid heating systems are ideal for facilities that need to consistently achieve high temperatures. Oil-based systems go by many names, but they all refer to the same type of closed-loop oil-based heating system. Other common names include:

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

Of note, thermal oil-based systems are still often referred to colloquially as “boilers” even though they do not actually boil the process fluid. For closed-loop indirect heating systems with lower process temperature requirements, hot water and water-glycol mixtures are commonly used as heat transfer fluids.

Thermal Fluid Heater Options

At Sigma Thermal, our range of systems includes the following:

• 

  SHOTS Electric Heater

  

  Thermal Fluid Heater

  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/hr. Custom heater designs are available 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 and custom designs are available.
• SHOTS Electric Thermal Fluid System:  Sigma Hot Oil Transfer Systems (SHOTS) use electrical power for circulation heaters and low-watt density immersion bundles. This creates heat without requiring fuel sources such as natural gas, fuel oil, or biomass fuel. These systems provide power in configurations from 30kW–800kW. Custom units can be constructed to provide increased power ranges from 800kW–4MW or even higher.
• Biomass Fired Thermal Fluid Heaters: These heaters achieve the same high-temperature, low-pressure heat of our most popular thermal fluid systems. Facilities can use these systems alongside other biomass energy systems to meet green energy benchmarks. Sigma Thermal provides installation, training, and equipment servicing to support these systems and help our customers meet their sustainability goals.

Work with Sigma for Your Process Heating Needs

Sigma Thermal is a leading provider of thermal fluid heating systems, parts, and supporting services. We offer high-quality equipment that supports the energy, heating, and process needs of our customers in a broad spectrum of industries.

• Thermal fluid heating system installations
• Retrofit services
• Training
• Maintenance
• Part programs

Talk to our engineers and technicians today about your facility’s heating needs, including maintenance, parts, and full systems. Request a quote today to get your project started.