To specify the proper thermal fluid heater for process applications, it is important to think about external influences.
Although thermal fluid heaters are a good choice for industrial applications, it is important to important to consider external influences that can impact the capabilities and performance of the system when selecting the heater. Doing so will ultimately help you select a heater that can provide the best return on your investment. This article will discuss some of the important considerations, including fuel choice, heater location, and environmental and code requirements.
Because fired thermal fluid heaters require a gaseous or liquid fuel to produce heat, finding ways to reduce fuel usage or use alternative fuels are of interest.
Is the fuel you plan to use in your system a commonly purchased commodity? If fuel is purchased, heater efficiency should be a primary consideration when investing in a thermal fluid heater. Generally, more surface area will yield a more efficient model, but other options are available. Preheating the combustion air for the burner is one way to boost a heater’s efficiency and save fuel. Another is to operate the system at a lower temperature when possible. In systems with multiple heaters, setting up a lead-lag computer PLC system to strategically fire each heater optimally will both reduce cycling and save fuel.
Another option is sourcing “free” fuel that normally would not be used - or even considered - as a source of heat. It is quite common to encounter waste fuels being burned in thermal fluid heaters by direct firing, or by blending with commercially sold fuels such as No. 2 oil or natural gas. Most burners can be set up with appropriate controls to safely and efficiently burn common waste fuels such as heavy oil, vent gas and other combustible byproducts of chemical processing with sensible heating values.
Waste heat reclamation also can save the operator money (reduce fuel usage) by capturing heat that would normally go up the stack. Several incineration applications that destroy residual process waste are well suited for use to exchange heat with the heating coil of a thermal fluid heater, allowing reclamation of waste heat for use in other sensible applications. Typical incineration applications suited for waste heat reclamation include syngas incineration in biomass or waste oil recycling processing industry.
Identifying alternate sources of energy to fuel the heating system up front can impact heater selection and reduce costs during heater operation.
Intelligent process monitoring control allows the thermal fluid heater to be located and observed remotely. Tracking performance data provides an early warning of potential trouble.
When selecting a heater, keep in mind any special circumstances that may exist in your specific installation. For instance, do you plan remote or unmanned operations? In particular, remote locations such as thermal fluid heaters in terminals on islands or unmanned ocean-going barges require special consideration. Typically, these applications require detailed operator training on all equipment and an adequate inventory of spare parts. Some operators even monitor the thermal fluid systems remotely via PLC integration to trend system performance and predict when a problem may occur. Many problems - an out-of-tune burner, for example - can be discovered by noting changes in fuel usage, stack temperature or even diminished heating quality.
In the marine industry, unmanned barges on ocean-going vessels require additional redundancies that a manned process heater or inland river barge fleet does not require. Typically, these redundancies include a spare pump onboard as well as nitrogen snuffing equipment and expansion tank overflow safeties. This equipment is required because service may not be as readily available at sea.
Simplicity is a common guideline with remote or unmanned applications. An uncomplicated, straightforward control system may help provide ease of maintenance, fewer parts to stock as spares, and less equipment to troubleshoot when a problem occurs.
A thermal fluid heater equipped to harvest waste heat from syngas incineration allows processors to capture heat that would otherwise escape up the exhaust stack.
What will the unit be exposed to in the field? Knowing and adhering to environmental requirements are crucial to thermal fluid heating system longevity.
Environment temperature should be considered in sizing the insulation on the thermal fluid piping. The expected or average outdoor temperature also should be considered when sizing a thermal fluid heater. For instance, heaters installed in the Midwest may require seasonal tuning to ensure proper combustion with changes in air temperature. Heaters installed at altitude will require a closer look at the blower for the burner to ensure adequate air is available for combustion. Heaters installed in corrosive environments such as seaside terminals and barges require a premium coating of all equipment to safeguard against rust. Soot produced from heavy oil-fired units can foul sensitive electrical equipment if not properly protected.
In addition to application-specific factors that define fuel choice, location and environment, every application has specific code requirements that govern thermal fluid system equipment. In general, the National Fire Protection Association (NFPA) Standard 87 will cover most requirements for thermal fluid heaters. However, NFPA 87 should only be used as a starting point. Be sure to check with any authorities having jurisdiction to determine code requirements specific to your process, location, fuel choice, operating environment and application.
For instance, thermal fluid heaters used for natural gas processing typically require special component selection based on the potential for hazardous gas exposure. The United States Coast Guard (USCG) requires a rigorous inspection of each thermal fluid heater on a heated river barge prior to service, which includes a professional engineer review of the design, a certified test procedure and USCG presence during inspection. In another example, the American Bureau of Shipping (ABS), the jurisdiction for ocean-going heated barges, further requires an on-site inspection of all pressure pipes at appropriate hold points during construction. And of course, across the continental United States, depending on the state, the heating coil may require American Society of Mechanical Engineers (ASME) Section I or ASME Section VIII code compliance.
Take the time to familiarize yourself with the factors that can affect thermal fluid heater selection and you can find the system you need to heat your product or process effectively. PH
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