Full steam ahead

Energy matters. Almost irrespective of the source, it's expensive and environmentally unfriendly. So inefficiency – and, worse still, waste – add almost criminally to costs, limit your plant's capacity and effectiveness, and damage competitiveness. Steam plant is no exception. Yes, the tendency is simply to assume that, because it's a utility, basic boiler and steam distribution plant maintenance is enough, but there's more to it. And sadly, in many cases, even that isn't being pursued as well as it should. Putting some scale on the problem, steam raising accounts for up to 40% of many manufacturers' and process plants' fuel bills. That's because, in addition to its use for heating raw materials and semi-finished goods, steam is also used to evaporate, distil, boil, brew and react products, as well as to clean and sterilise plant and equipment, and indirectly to provide for space heating. So, for many, it's probably high time you prioritised your steam plant for a review. Best advice is to start by establishing your apparent efficiency of generation, based on overall output versus fuel input and cost. Then temper that with how much steam is actually being used and how much wasted – by walking the plant. That means checking everything, from pipe lagging to steam trap effectiveness, as well as examining the boiler and its ancillaries, the operating regime, water treatment schedule, and the distribution and condensate return set-up. This needn't take forever and, as Paul Mayoh, technical manager with Spirax Sarco, suggests, to keep it sharp you need to bear three aspects in mind. First, the potential for eliminating steam waste is generally great and relatively simple to achieve, with low-cost repairs and/or modifications providing for rapid ROI (return on investment). Secondly, given that steam demand may well have changed since the boiler and its associated plant was installed and commissioned, it makes sense to conduct the review in light of current and foreseeable requirements – which might well indicate further project priorities. And thirdly, just as important, it pays to be aware of technology improvements and their implications for increasing efficiency and further cutting costs. Taking it from the top, Mayoh advises that steam and condensate need to be thought of as a circle. "If anything interrupts that circle – such as leaks or vents from joints or valves, or steam traps failing to operate correctly – then you're losing energy," he warns. "And such losses compound up very quickly, meaning significant excess fuel and emissions." Simple steps first So what simple steps can you take? Spirax Sarco has several recommendations – starting with turning to bellows-sealed valves, instead of glands. "They cost more initially but, once installed there will be no losses and they're maintenance free. So, over the years, the savings will be considerable," states Mayoh. In a similar vein, he points to insulation in the distribution and return lines. "We see damaged insulation all the time. People seem to forget that when it's raining, for example, if the lines aren't sealed correctly, then the whole system becomes saturated, you haemorrhage heat, and fuel consumption rockets." And he reminds us of the importance of replacing broken pressure gauges. "It's very difficult to trim pressure control, without gauges in strategic locations... Many would also consider them safety devices: you need to see a normally low pressure increasing long before a safety valve lifts. And replacing gauges is not expensive." Inevitably, any such basic inspection and repair programme – although about getting the foundation right – will be influenced by your steam demand and technology reviews. For example, replacing glanded valves with bellows-sealed valves is unlikely to be high on anyone's agenda. However, if it turns out that the rated pressure of your existing cast iron valves is no longer appropriate, then it probably should make the to-do list. With the basics done, though, if demand looks set to exceed supply unless the burners are ramped up and/or a standby boiler is fired up, it's time to consider plant modifications. One option is to look at extracting more energy at the point of use, by enabling sub-cooling of the condensate prior to dumping it into the return line. That is all about trimming the point (temperature and pressure) at which hot condensate returns from the process to the boiler feed side – most likely by changing either the rating or type of steam traps, or both. "Hot condensate still contains useful energy," explains Mayoh. "So if it is sub-cooled on the process, instead of being immediately returned, then it gives up more energy, which might well be more efficient for the process." He concedes that the approach is not a fix for everyone. For a start, production might depend on maximum steam temperatures for product quality and/or throughput. Then again, since the eventually returning condensate will be cooler, some plants may need to augment feed water heating in the boiler room. On the other hand, sub-cooling might improve the plant's steam balance by, for example, eliminating excess flash and dealing with choking problems. The bottom line: engineers need to check that the plant can withstand a risk of some water logging resulting from condensate flow. "If the existing steam plant is over-sized – so there is some spare capacity – flooding is unlikely to be a problem in the heat exchanger," comments Mayoh. "But we would offer to look at the process and do that analysis." He also recommends using Spirax Sarco's quick-fit technology and its recently-launched trapping station, which accommodates its full range of traps and sizes, enabling relatively easy tuning for optimum savings. But, if that doesn't appeal, another approach to capacity and/or efficiency issues is to go for flash steam recovery – using, for instance, Spirax Sarco's FREME (flash recovery energy management equipment) system. This is a pressurised, skid-mounted package designed to extract energy from the condensate and flash, and to use it for preheating the boiler feed water downstream of the feed pump (to avoid cavitation issues). Clear benefits include: improved boiler efficiency, which reduces energy costs; the end of condensate dumping; and hence also reduced water supply and water treatment costs. Yet another option is Thermal Energy International's Flu-Ace stack-mounted, direct-contact condensing heat recovery system, proven to recycle up to 90% of the heat normally lost through boiler flue gas stack emissions. TEI claims that its equipment leads to 15-35% reductions in boiler energy consumption and 200-300% greater heat recovery than is possible with conventional recuperator and economiser systems.