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SEP-OCT 2018

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INTECH SEPTEMBER/OCTOBER 2018 27 SYSTEM INTEGRATION S team distribution systems support manu- facturing across a huge range of indus- tries, from craft brewing to oil refining and most everything in between. Steam can carry enormous amounts of energy, and it is valuable as a highly controllable heat source. On the oth er hand, producing steam is energy intensive, and an ineffective distribution system can be waste- ful. Boiler designs can be highly efficient, but this efficiency can be rapidly lost with a poor distribution system. Boiler design and efficiency factors have been the topic of countless articles, so here we will concentrate farther downstream and examine the distribution itself, especially steam traps (figure 1). They are the primary tools for sepa- rating condensate from steam. A steam trap failure can be predicted to some extent through nonintrusive ultrasonic acoustic event detec- tion using data generated by a wireless acous- tic transmitter. Fixing failed traps early can also help to prevent problems in downstream equipment caused by passing condensate slugs through traps. Condensate is sent back to the boiler as feed- water, which makes it valuable for two reasons. First, boiler feedwater is heavily treated with expensive chemicals to avoid boiler fouling, so any that can be recaptured saves money. Sec- ond, condensate is usually hot, which reduces the amount of energy needed to turn it back into steam. Consequently, condensate collec- tion is critical for overall system efficiency, and it depends on steam traps. Steam for heat transfer We will explore more about transferring heat from steam in a moment, but steam is also used to capture heat. The term heat-recovery steam generator (HRSG) has become more common with the higher energy costs and carbon foot- print concerns of recent years. Where older plants might have simply blown hot exhaust or process gases out a stack, they are now more commonly channeled into an HRSG and used to generate steam (see sidebar). A prime example is a combined-cycle gas tur- bine power plant. Where a few years ago the hot exhaust from the gas turbine would have been blown to the atmosphere, now it is put through an HRSG and the steam runs a second turbine. This ability to recover what was regarded as waste heat contributes to the high efficiency of these generating units. Steam is typically used to transfer heat to another fluid, such as a large-jacketed reac- tor or kettle used in a brewery (figure 2) or other food-and-beverage applications. Steam flows through passages and heats the product through the kettle walls or an internal coil. This can provide very even and carefully controlled heat, so the product is not burned. During the initial heating phase when the product is cold, steam condenses quickly, and the condensate collects in the lowest point. A steam trap sepa- rates condensate from the incoming steam and sends it back to the boiler as feedwater. This is a critical point in the process and has a major effect on the efficiency of the kettle. To transfer all the heat possible from the steam, all of the steam should condense in the jacket. Ear ly in the heating process, the temperature FAST FORWARD l If not properly monitored and maintained, steam traps waste energy and can often cause catastrophic failure of downstream equipment. l Manual inspection rounds are expensive, labor intensive, and often ineffective. l Wireless acoustic monitors are a better solution, with continuous updates and early warning of impending issues. Figure 1. Steam traps are an important part of a distribution system, but often receive little attention.

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