Every fall, northern plants start preparing for the long winter. With outside temperatures dropping, problems can develop because of poor insulation or equipment icing. Typically, sites use heat to keep things from freezing, plugging, or becoming too viscous. Here are a few tips to improve your process.
Short-circuit your cooling water system — In certain areas, cooling water can get too cold and make it difficult to control processes depending on a cooling system. Trying to reduce flow can have devastating effects as slower velocity in exchangers may produce corrosion or plugging problems. Monitor your cooling-water supply temperature to make sure it isn’t getting too cold. The first line of defense is turning off fans in your cooling tower. Some places will actually physically block air flow.[pullquote]
In once-through systems or river water systems, there’s no way to change supply temperature. Instead, feed return water to some supply pumps to control supply temperature. This allows units to operate without closing valves. The only negative is build up of corrosive material, which may cause you to increase blowdown.
Lower your tower pressures – If not limited by compressor inlet pressure or any downstream pressure, recalculate tower pressure to take advantage of cooler accumulator temperatures. A tower at lower pressure would need less reboiler duty to make the same split. So, the colder it gets, the more process energy you can save. Other systems, such as blowers and compressors, may have more capacity as temperature drops. Identify these systems and use them to your advantage.
Conduct insulation audits – After the next heavy rain, check steam and fuel gas usage to see how much more was used. Some meters jump 10%–20%. Many insulation companies have audit programs or you can send someone to them to learn how to audit insulation. I use a thermal camera to help me decide where insulation is needed (For information on thermography, see www.ChemicalProcessing.com/articles/2009/202.html.) But have enough insulation for high temperature systems and make sure insulation is sealed to prevent water from ruining your system. Water in insulation can reduce insulation rating or turn to ice and cause more damage. Surprisingly, bottled foam works well in non-flammable areas. Asphalt, paint and cladding can seal insulation — but your system must be able to “breathe” so moisture can escape.
Heat tracing – The most common two types are steam and electric. I’ve heard arguments for using either and they’re both good. To me it boils down to how well you can maintain your systems. Steam requires a good program to monitor your system and repair leaks and plugs. Electric requires that circuits are working without any breakage. The difference in whether they work well or poorly typically depends upon the attitude of the people using them. Places where they believe the system is important to keep units running smoothly tend to take good care of their tracing and they get great results. Where the system is just another utility to watch there tends to be a lot of waste and trouble.
Before it gets too cold, you’ll need to turn on and test your systems. Hopefully, you’ve segmented it so you can operate each portion separately. For steam tracing, turn on your systems one by one and check each line for flow. Repair any steam leaks you find. Replace traps that have plugs or lines that have been damaged. A good running system can use low-pressure steam where available.
Electric systems are usually three-phase and work even when one phase develops a fault. Electronic systems are best if they’re kept on all year, but if you’re using one for winterizing, remember to turn it on early. They are meant to maintain heat and are slow to heat without a boost system, which is a big energy waster. Because they are electric systems, lights can be used to help determine where problems exist.
The third type of tracing is hot water. These can be real energy savers if water is produced from waste heat. Glycol water for systems that are well insulated or that experience mild winters work best. I know of one plant that circulates hot water to nearby businesses for winter heat. The synergy saves money for both the plant and the businesses.
Winter can cost your company a lot of money if you don’t properly maintain your winter systems. If you have found ways to save energy during the winter, please let me know.
Gary Faagau is Chemical Processing's Energy Columnist. You can e-mail him at [email protected].