How to Trap Steam Distribution Systems - Armstrong International, Inc.

How to Trap EvaporatorsEvaporators reduce the water content from a productthrough the use of heat. They are very common tomany industries, especially paper, food, textiles, chemicaland steel.An evaporator is a shell and tube heat exchanger wherethe steam is normally in the shell and the product is in thetubes and in motion. Depending upon the type of productand the desired results, more than one stage or effect ofevaporation may be required. The triple effect is the mostcommon, although as many as five or six can be found onsome applications.Single EffectWhile the product is being forced through the tubes of theevaporator, heat is added to remove a specific amount ofmoisture. After this is completed, both the product vaporand the concentrated product are forced into the separatingchamber where the vapor is drawn off and may be usedelsewhere. The concentrate is then pumped off to anotherpart of the process (Fig. CG-48).Multiple EffectIn using the multiple effect method, there is a conservationof heat as steam from the boiler is used in the first effect,and then vapor generated from the product is used asthe heat source in the second effect. The vapor generatedhere is then used as the heat source in the third effect andfinally heats water for some other process or preheats theincoming feed (Fig. CG-49).There are many variables in the design of evaporatorsdue to their wide application to many different products.The steam capabilities for evaporators can vary fromapproximately 1,000 lbs per hour to 100,000 lbs per hour,while steam pressures may vary from a high of 150 psigin the first effect to a low of 24'' mercury vacuum in thelast effect.Because evaporators are normally run continuously, there isa uniform load of condensate to be handled. It’s importantto remember that traps must be selected for the actualpressure differential for each effect.The three major considerations when trapping evaporators are:1. Large condensate loads.2. Low pressure differentials in some effects.3. The evacuation of air and contaminants.Safety Factor■ When load is fairly constant and uniform, a 2:1 safetyfactor should be adequate when applied to an actualcondensing load in excess of 50,000 lbs/hr.■ Below 50,000 lbs/hr, use a 3:1 safety factor.For single and multiple effect evaporators, automaticdifferential condensate controllers are recommended.In addition to offering continuous operation, DC trapsvent air and CO 2 at steam temperature, handle flashsteam and respond immediately to slugs of condensate.Figure CG-48. Single Effect Evaporator SystemFigure CG-49. Triple Effect Evaporator SystemSteamSteamSteamSteamFeedConcentrateConcentrateFeedChart CG-15. Recommendation Chart(See Page CG-2 for “Feature Code” References.)Equipment BeingTrappedEvaporator SingleEffectEvaporator MultipleEffect1st Choice, Feature Codeand Alternate Choice(s)0-30psigAbove30 psigA, F, G, H, K, M, P DC DCIBLV IBLVAlternate ChoicesF&T F&TA, F, G, H, K, M, P DC DCIBLV IBLVAlternate ChoicesF&T F&TArmstrong Steam and Condensate Group, 816 Maple St., P.O. Box 408, Three Rivers, MI 49093 – USA Phone: (269) 273-1415 Fax: (269) 278-6555www.armstrong-intl.com37CG-32