With summer upon us, energy efficiency is one of the last things on our minds. Rising temperatures can lead to higher energy bills, especially in southern states. Cooling systems must work harder. Also, hotter weather tends to hide some inefficiencies. Here are a few tips to check out during the hot summer days.
Water cooling systems tend to work harder as cooling demands increase. In some plants, cooling limits rates, which reduces efficiency. Fouling and temperature are working against you.
Fouling requires more control of chemical additives and blowdown. To minimize cost at maximum efficiency automate this process to control blowdown rate and use of chemical additive. Installing an automatic system often provides immediate savings of make-up water and chemicals. More importantly, it provides longer-term savings of equipment and reduced fouling.
Make sure cooling towers are in tip-top shape. Inspect bays and fix systems as the coldest water possible is needed to meet cooling needs. If rates become too limited, attach a supplemental cooling system to your most limited areas.[pullquote]
I had a process unit that was at the furthest point from the cooling tower and at a higher elevation. Every summer, cooling the towers in this area limited the entire plant. Improper cooling of this one area was responsible for inefficiency in the entire plant.
Adding a supplemental cooling system was a short-term solution. The exchangers were cleaned and isolated and a rental water tower was brought in. For even better control, cooling water was replaced with a glycol-water solution to reduce possible fouling. Only the most limited towers were put on this system. The exchanger return was fan cooled before exchanging with water to further reduce load. This system can be costly, but the multiple effect on the entire plant easily paid for it in energy savings and increased capacity. Later, a permanent closed-loop glycol-water system was installed based on saving the rental cost and the positive results of better cooling.
Two of the biggest hidden summer costs are steam and air. Both tend to increase for a variety of reasons. For steam, it’s much easier to spot a leak in the middle of winter in a northern state than the middle of summer. But in summer, sometimes you can hear leaks but just can’t see or know how much steam you’re losing. A steam system audit does the trick. Do a steam trap audit and bring in someone who can look at the whole system. I’m always amazed at how much can be found. In one audit, venting of low-pressure steam occurred while high-pressure steam was let down. The funny part was that these things were happening within five feet of each other.
For air, systems that were fine in winter can expand enough to let all the air out. As a corporate energy director, I would scour utility requisitions every spring looking for requests for air compressor rentals. As a process designer, I knew that air requirements are typically overstated. Compressed air systems are usually bought to meet that requirement at 50%-70% load (depending on how many compressors and redundancy) so only inefficiency accounts for a majority of these requests. When I found the requests, I required a compressed air audit. In one plant, the auditor discovered that 50% of the air was leaking out of the system. The plant had two rental compressors already and was requesting a third. After the audit, all rentals were removed.
Electricity also is tricky during summer. Your local utility probably has a tier on-peak/off-peak program. If so, the money that can be saved can literally cut costs in half. In those systems, it becomes imperative to look at managing load. In one plant, they moved all their oil movement activities to off-peak hours to gain tremendous savings. Plants that generate electricity can likely benefit from reducing electric production during off-peak when rates may be cheaper. In some cases, the utility pays for the changes because they help their off-peak demand management. Software is available with some utilities that provides hour-by-hour current and future buy/sell price plus the next day’s expected price. Incorporating this is a bit of work, but if you’re in an area subject to brownouts, pricing isn’t only good for electric savings, it may also prevent power disruption.
So, enjoy your summer, but first try to take advantage of some easy money.
Gary Faagau is Chemical Processing's Energy Columnist. You can e-mail him at [email protected].