The Influence Mechanism Of Non-isothermal Mixing On Water Networks’ Energy Performances

In order to explore the energy influences of non-isothermal mixing, this paper hasdivided all the mixing patterns into21types according to the pinch temperature, andexcluded the exsitence of three kinds of mixing, which can be testified by therelationship of temperature values involved. Then the effects of the18types ofmixing on the water-using network’s energy performance have been studied byanalyzing their influences in the hot and cold composite curves. Moreover, someeffective non-isothermal mixing rules have been established.Based on the pinch analysis technology, this paper has studied the influence mechanism ofnon-isothermal mixing on heat transfer networks. For water distribution networks, themixing between water streams (isothemal or non-isothermal) will reduce the numberof streams. Moreover, the non-isothermal mixing between water streams will makesome energy transferred directly, which may save some heat exchange areas or evenget rid of some heat exchangers. However, some energy may be transferred across thepinch accompanying with the mixing. If the mixing can make some energy transferredacross the pinch from down to up breaking the limitation of the minimum temperatureapproach, the amount of heat recovery may be improved and the energy-saving effectwill happens. If the mixing can make some energy transferred across the pinch fromup to down, the amount of heat recovery will definitely decrease and the energypunishment effect must occur. If the mixing cannot make some energy transferredacross the pinch, it will never have energy-saving effect.By analyzing the effects of the18types of non-isothermal mixing on systemenergy target, we have concluded some non-isothermal mixing rules. During themixing between hot sreams or between cold streams, no energy will be transferrdacross the pinch, but the heat transfer matches after mixing might change. In addition,some energy may be transferred across the pinch from up to down. Therefore, hot-hotstream mixing and cod-cold stream mixing will have no energy-saving effect.Hot-cold stream mixing can make some energy transferred across the pinch from upto down or from down to up, and it may make no energy transferrd across the pinch.Consequently, this kind of mixing may increase, not change or even reduce the systemenergy target. Obviously, when designing the energy integrated water-using network featured with minimum water and energy consumptions, we should make good use ofthe mixing, which cannot change or save the energy consumption, and avoid that withenergy punishment effect.Finally, we utilized the conclusions we have drew in a case with manynon-isothermal mixing options, and compared the results with those we have got bypinch analysis method. It turned out to be that the non-isothermal rules could be usedto avoid the mixing with energy punishment effect and take all advantages ofnon-isothermal to save water and energy in chemical productive process.