Chemical Processing - January 2008 - (Page 16) >> EnERgy SavER Resolve to trim that excess air five heater excess-air good practices can lead the way to peak performance Process heating, in the form of fired heaters and boilers, accounts for 65% to 90% of a plant’s energy demand. for those without state-of-the-art controls, these energy hogs represent one of the easiest areas to reduce energy use. Whether using digital, analog or field controls, process heaters require constant attention to run at peak efficiency. there are many ways to improve performance, like better insulation, better convection-section heat recovery, removing process tube scale, improving radiant absorption and better furnace designs. however, excess air is the top controllable reason for poor energy performance. so, to start the new Year with an energy resolution, try implementing five key heater excess-air good practices. these, in most cases, can be implemented without taking the heater off-line. committing many furnace types that discussing how to adjust them in this column isn’t possible, but a good training program will have proper procedures in place for each. 3. Keep burners, registers and dampers in good operating order. i once installed automatic air-register controls on a heater because the oxygen levels were extremely high. even though the operators logged for years that they adjusted the manual registers each shift, i found that 90% of the old registers couldn’t move or were damaged and never repaired. the most effective practice that i’ve seen is where a dedicated maintenance person inspects and maintains the moving parts (yes, they are supposed to move) of the plant’s furnaces. 4. once (preferably twice) a year, bring in a furnace specialist to check your heaters. most plants can’t afford to maintain a full-time furnace expert. But it makes sense to have a third party regularly check heater performance. it tells your operating people that the heaters are being watched and performance counts. it also allows your operators to consult an expert, who also can train them while at your site. some vendors offer this service as do independent consultants or doe consultants. a consultant who can model your furnace is preferred. 5. consider carbon monoxide (co) control or a fully functional co analyzer. in addition to the sampling problem with oxygen, there are more basic problems. air that leaks in from openings in the furnace (peepholes, areas surrounding pipes, improperly sealed manholes) can’t be distinguished from excess air from the register. co can only be created at the burner. maintaining co level between 100 ppm and 400 ppm, depending on the environment, can help in running the lowest possible oxygen level. i’ve seen heaters run 0.5% to 2% excess oxygen with proper co analyzers. they’re also great safety devices. Before following any advice, be aware that all heaters are unique and dangerous. create a management of change document to avoid creating an unsafe situation or violating regulatory or insurance requirements. When dealing with controls or burners, it’s always a good idea to consult the manufacturer before proceeding. CP Gary Faagau, energy columnist gfaagau@icubedenergy.com www.chemicalprocessing.com Keep in mind that all heaters are unique and dangerous. to at least one is a good start to reducing that monthly energy bill. Using all five will help approach top performance. 1. You can’t manage what you don’t measure! an oxygen sensor in the box and a box draft meter are two basic instruments that a process heater needs to be safely adjusted to minimum excess air. But to actually measure stack loss, install a flue gas analyzer and a temperature sensor in the stack (after any exchange equipment). a sensor is your control point to determine heater air requirements. But an analyzer is needed to report stack loss. Both are key for a successful energy program. also oxygen sensors will only measure the oxygen in the area surrounding the sample point. multiple point sampling is always preferred. 2. start a training (or retraining) program on heater adjustments. all operators need to be able to properly adjust furnaces. the process is fairly straightforward but doesn’t get the highest plant priority. i can count on one hand how many times i’ve seen operators voluntarily adjusting a furnace outside of start-up. furnaces should be adjusted once a shift, right after upsets and when the process or weather drastically change. there are so 16 • January 2008 http://www.chemicalprocessing.com
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