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.
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.
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
- 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.
We are in the midst of a U.S. shale revolution: advancements in shale oil and gas extraction techniques have led to greater natural gas production levels and a renewed demand for natural gas in industrial and power applications. Because of the increased level of competition in the industry, process efficiency is paramount. Bringing natural gas to market cost effectively hinges on the optimal design and operation of the natural gas sweetening process.
Natural gas produced from reserves in almost never pure; rather, it contains acid gases such as carbon dioxide and hydrogen sulfide. One way to remove these impurities is amine gas treatment. An amine plant (also known as a sweetening plant) is used to remove the carbon dioxide and hydrogen sulfide from the gas solution so that pure natural gas can be efficiently transported to end users via pipeline.
Our latest white paper, Effective Heating Helps Amine Plants Purify Natural Gas, describes how to improve the natural gas purification process with effective heating. It also reviews the optimal conditions and system settings for controlling the amine regeneration temperature and optimizing the efficiency of the process.
The process works like this: the natural gas mixture and amine are combined in an absorber, where the carbon dioxide and hydrogen sulfide are removed. Pure natural gas exits from the top of the vessel and the amine is sent to a regeneration system (consisting of a still and a boiler) where it is filtered for reuse.
Usually, control and bypass valves are used to maintain a constant flow through the thermal fluid heater in the regeneration process. Moreover, the temperature of the system is typically controlled using overhead temperature measurements in the reboiler. There are a few problems with this standard procedure, which are described in detail in the eBook. If these problems are not addressed in the design of the control scheme, the process will not run optimally and the control systems could destabilize.
Using thermal oil as an indirect heat source can significantly increase the life of the amine solution and increase process efficiency. Typically, system operators manually set the flow of thermal oil through the reboiler. This is a convenient solution that prevents any need for frequent fine-tuning, but this conservative approach wastes energy. The eBook discusses the thermal fluid system specifications required to optimize the operation of amine plants.
Sigma Thermal has a long history of providing highly engineered process heating systems and fine-tuning services for existing systems. To learn more about Sigma Thermal’s expertise with amine reboilers, visit our website.
Download your free copy of the full eBook here or click on the button below.
Learn more about Thermal Fluid Heaters in Amine Plants
Fire safety is an ever-present concern for operators of thermal oil heating systems. To understand the scope of the problem, let’s review the salient facts.
First and foremost, this is a relatively rare and well-understood threat to users of thermal oil heating systems. Plant owners and operators have been dealing with fire prevention issues for the better part of a century, according to an article in Chemical Processing magazine. So there are a lot of best practices in place to address this specific risk within the industry.
To discuss the parameters of fire safety in this context, experts rely on three measurements that describe fire phenomena: flash point, fire point, and autoignition temperature. Flash point is the temperature at which vapor from a fluid will temporarily burst into flame (or flash) when exposed to an ignition source. It’s measured by two tests approved by the American Society for Testing and Materials: ASTM D92 and D93. Fire point is the temperature at which such a temporary flame continues to burn the available fuel source. Fire point is typically 40-100°F above the flash point. Both flash point and fire point depend on the presence of an ignition source, such as a spark. Autoignition temperature marks the point at which no ignition source is necessary (as described by ASTM E659-78).
While the physical parameters described are important in understanding the fire risk of thermal fluids, they are actually more helpful to scientists in a laboratory than to plant managers and engineers in an actual chemical processing operation. According to the Chemical Processing article, “Relatively few fires have originated in thermal fluid systems.” Rather, the culprit in most cases is not the overheated thermal fluid but the equipment and systems conveying it. Specifically, blame can commonly be placed on poor choice of insulation materials, loss of flow, cracked heater tubes, or uncontained leakage.
What practical advice is there for such hazards? The complete answer is detailed in the article above, and in well-known industry installation guidelines such as FM 7-99, but here are a few highlights:
- Follow an industry accepted and widely used guideline, such as FM 7-99, to guide system design and installation decisions.
- Most good hot oil system manufacturers and hot oil fluid suppliers have published guidelines for installation and design that should be consulted as well.
- “The most effective precaution against insulation fires is the identification of all potential leak points and the specification of high-temperature closed-cell insulation or no insulation at these points.” Open cell insulation, such as fiberglass, will wick oil away from leak points and can potentially saturate hundreds of feet before a problem is seen.
- “To avoid incidents resulting from loss of flow, low-flow shutdown should be included in the burner safety interlock. . . ..”
- Use a low level alarm in your expansion vessel to notify an operator and shut down the system in the event that oil level in the system is falling below normal levels.
- Centralize major equipment and install containment berms in those areas to contain spills and isolate possibly incident locations when possible
- “To prevent excessive thermal cycling of the heater tube bundle, oversized heaters should be derated by the manufacturer.”
- “To prevent leaks, plants should: Allow expansion joints and flexible hoses to move along their axes, never sideways. Maintain lubrication systems for rotary unions and supply these systems with the correct lubricating oils. Install valves with their stems sideways so any leaks run down the stem and away from the piping.”
For more information on fire prevention practices for thermal fluid heating systems, contact one of our knowledgeable representatives or Application Engineers. We’ll be happy to answer your questions.