line just before the auxiliary exhaust steam enters theDFT. In either case, the high-pressure drains end up inthe DFT.These systems have basically the same componentsas the low-pressure steam drain systems. Componentsspecifically designed for high-pressure steam and theaddition of orifices are the only major differences.Whichever system is to be repaired, the system must betagged. When dealing with repairs on both low-pressureand high-pressure steam systems, there should be acontrolled work procedure package. You should reviewthe QA manual concerning repairs on steam systems.Remember you can request assistance from thepersonnel who are trained to do the repairs. For moregeneral information concerning steam plants, readBoiler Technician 3&2, NAVEDTRA 10535-H.DISTILLING PLANTSThis section will deal with inspections,troubleshooting, and repairing of low-pressure steamdistilling plants. The two most common types used bythe Navy are the submerged-tube and the flash-typedistilling plants. Additionally, this section will mentionsome facts about the heat recovery type of distillingplant the Navy also uses.SUBMERGED-TUBE PLANTSLow-pressure submerged-tube distilling plantsdiffer from ship to ship, but the operating conditions andthe maintenance procedures are basically the same. Inalmost all instances, the personnel who stand watcheson the distilling plants are also responsible for themaintenance of the plants. When operating problems dooccur, it is the responsibility of the EN2, ENl, or ENCon duty to locate the trouble and to make the necessaryadjustments or repairs.Distilling plant reliability and consistent operatingconditions are essential for satisfactory results. Exceptunder emergency conditions, no plant should be forcedbeyond its rated capacity. Requirements for highersteam pressures result in higher temperatures, whichwill cause more rapid scaling of the evaporator tubes.During operation, the various elements of any plantdepend on the heat and fluid balances throughout theplant. Adjustment of any one control can producewidespread changes to these balances. For example, anincrease in the feed to the first effect will raise the liquidlevel in the first effect. More heat will be required toraise the feed to the boiling point, so that less heat willbe available for evaporation in the first-effect shell anda smaller amount of heat will flow to the second-effecttube nest. These changes produce a new balancedcondition, and other adjustments would be required tomake the new balance satisfactory. Under suchcircumstances, overcontrolling could require manyreadjustments. The operator will always find it better tomake small adjustments, one at a time. This will allowenough time between each adjustment for all theconditions to become steady.Causes of Low Plant OutputFailure to obtain full rated capacity is one of themost frequent problems encountered during theoperation of a distilling plant. The problem may be verydifficult to remedy since it may result from acombination of things. Adecrease in the distilling outputefficiency may result if any of these factors are not met.Full output requires the following:1. Proper steam pressure above the orificea. Ample steam supplyb. Proper operation of reducing valves2. Highest possible vacuum in the first-effect tubenesta.b.c.d.e.f.No air leaksProper water levels in the evaporator shellsContinuously vented evaporator tube nestsReasonably clean evaporator tube nests(1) Continuous feed treatment(2) Mechanically cleaned tubesDensity of brine overboard not over 1.5/32(1) Reasonably clean overboard piping(2) Proper valve settings(3) Proper operation of brine pump (cleanpiping and strainers, proper speed anddirection of rotation, properly ventedpump, properly packed and sealedgland, and no air leaks in the piping)Properly drained tube nests(1) Proper operation of all drain regulators(2) Proper operation of the tube nest drainpump3. Highest possible vacuum in the last-effect shella. No air leaks8-2
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business