I spend a significant amount of time in petrochemical plants, refineries and process plants. When I review the major on-site energy consumers at these sites, I find myself looking at steam generation and direct-fired process heaters. Depending on the specific plant, these two behemoths can use 70–80% of the total onsite energy. Thermal energy is the engine that drives our processes; plants can implement several energy conservation measures and best practices to optimize its use. Not only does this month’s column deal energy efficiency, but the topic also has a close connection to personnel safety.
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Personnel safety is of prime importance and should not be compromised at any cost. We want to return home safe and sound to our families and friends every day. Every plant has a safety protocol and all of us abide by that protocol when on site. On a daily basis, it’s typical to find, in addition to plant personnel, several contractors on site, as well as other visitors. Our industry’s heavy dependence on thermal energy leads to extremely high temperatures in plants. Hence, we must ensure all high-temperature equipment, components, piping, instrumentation, etc. are properly insulated so their surface temperatures are such that no personnel can be injured if they accidentally or unknowingly happen to touch a hot surface. Note that process heaters, boilers, etc. have refractory on the inside and hot spots on the outside skin can pose a significant burn risk.
Now, let’s talk about the energy efficiency aspect. Radiation and convection energy losses can be significant. They are a function of several factors but primarily process temperature, surface area, geometry, wind speed, ambient temperature and insulation/refractory heat-transfer resistance. Interestingly, the energy loss due to lack of insulation is fixed and does not depend on operating rates. For example, a boiler on hot standby has the same amount of fixed radiation and convection loss (MBtu/hr) as a similar boiler operating at full load with other factors being the same. When I am doing an energy assessment, I see several areas where insulation is damaged or missing and in some instances no insulation is specified at all. Adding insulation reduces surface temperature and minimizes the energy loss, thereby improving energy efficiency. One of the challenges in the field is to be able to estimate the energy loss due to missing or damaged insulation.
To illustrate, consider an uninsulated 10-in. pipe with a 350°F process fluid (or steam). From a personnel safety perspective, adding 1 in. of insulation will bring the outside surface temperature to below 120°F. From an energy efficiency perspective, this 1 in. of insulation will save ~90% of the energy loss compared to uninsulated pipe. You can do these types of analyses very easily using the free 3EPlus Insulation Evaluation software (www.pipeinsulation.org/). One other tool I would highly recommend you have on hand is an infrared thermography camera; use it every time you walk into a plant. (For more on thermography, see “Use Thermal Imagery for Process Problems.")
In addition to piping runs, some of the most common places where I see missing insulation are valves, channel heads of heat exchangers, inspection manways, steam turbines, condensate tanks, level indication and control assemblies, etc. When I ask why these are not insulated, the most common answers include “they need to be serviced often and insulation is always in the way” or “the fittings leak.” In most such cases, I recommend removable insulation materials that can be easily used and wrapped using clips or hook-and-loop bands. The reason for doing this is that ½ in. of insulation can save 70–80% of the energy loss compared to the bare surface. This brings down the outer surface temperature significantly and enhances both personnel safety and energy efficiency.
Improving insulation and adding refractory are low-hanging fruits and should be implemented immediately. As we have discussed, improving energy efficiency by adding insulation leads to improved personnel safety, which is paramount and should never be sacrificed. Insulation projects are like gold filings — collect all of them and you’re bound to end up with a gold nugget!