5. OPERATIONAL REQUIREMENTS AND PRECAUTION
Although the physical advantage of hot
Although the physical advantage of hot oil, such as oil, such as a high thermal stability, aa high thermal stability, a low operating pressure at high temperature, and a low viscosity, make its low operating pressure at high temperature, and a low viscosity, make its use as a heat transfer medium highly attractive, there are several points to use as a heat transfer medium highly attractive, there are several points to which attention should be drawn to
which attention should be drawn to ensure trouble-free operation.ensure trouble-free operation.
5.1 Starting the Plant 5.1 Starting the Plant
It should be ascertained that all parts of the plant are correctly assembled, It should be ascertained that all parts of the plant are correctly assembled, and
and thathat t all all spespeciacial l reqrequireuiremenments ts for for venventinting, g, sasafetfety y valvalvesves, , expexpansansionion vessel, etc., have
vessel, etc., have been included. been included. All new equipment shoAll new equipment should be cleaned anduld be cleaned and free from loose rust, scale, dirt or pieces of weld metal. Water should be free from loose rust, scale, dirt or pieces of weld metal. Water should be circulated through the system; afterward, pump strainers should be cleaned circulated through the system; afterward, pump strainers should be cleaned and the syst
and the system thorouem thoroughly dried oughly dried out. t. All pipelAll pipelines and otheines and other parts of ther parts of the equipment should be pressure tested before use, preferably with hot oil equipment should be pressure tested before use, preferably with hot oil rather than water.
rather than water.
Filling with Hot Oil Filling with Hot Oil
Before the initial filling of a plant, it is necessary to ensure that the correct Before the initial filling of a plant, it is necessary to ensure that the correct operating level is clearly m
operating level is clearly marked. arked. Hot oil expands on hHot oil expands on heating and allowanceeating and allowance must be made for the expansion of liquid between the filling and operating must be made for the expansion of liquid between the filling and operating temperatures.
temperatures.
The hot oil is
The hot oil is normally at room temperature when the normally at room temperature when the plant is being charged;plant is being charged;
if th
if the ambe ambienient temt temperperatuature is bere is below 1low 122℃℃, the ho, the hot oil wit oil will reqll requiruire heae heatinting ing in order to liquefy it, and special precautions will be necessary to ensure that order to liquefy it, and special precautions will be necessary to ensure that subsequent solidification does not take place in the pipelines and other parts subsequent solidification does not take place in the pipelines and other parts of the syste
of the system during fillinm during filling. g. When filWhen filling undeling under very cold condr very cold conditionsitions, it is, it is advisable to warm the plant with hot air, and to fill the heater first.
advisable to warm the plant with hot air, and to fill the heater first.
Circulation of hot oil through the heater and its by-pass is then started and Circulation of hot oil through the heater and its by-pass is then started and the hot oil is gradually fed to other parts of the system, the addition of liquid the hot oil is gradually fed to other parts of the system, the addition of liquid hot oil being co
hot oil being continuentinued until the plant is filled to the necesd until the plant is filled to the necessary levesary level. l. If it isIf it is necessary to warm the hot oil before filling the plant, particular care should necessary to warm the hot oil before filling the plant, particular care should be taken that there are no open flames near the filling point.
be taken that there are no open flames near the filling point.
Initial Heating Initial Heating
The first heating of a plant, after commissioning or after a prolonged shut The first heating of a plant, after commissioning or after a prolonged shut down, should be carried out very slowly
down, should be carried out very slowly. . Although plants should be provideAlthough plants should be providedd with a storage and discharge vessel for hot oil in some cases this may not with a storage and discharge vessel for hot oil in some cases this may not have been included, or the plant may have been incompletely drained, so have been included, or the plant may have been incompletely drained, so that some lines are blocked by solid hot oil.
that some lines are blocked by solid hot oil.
If the presence of solid material is suspected, testing must be extremely If the presence of solid material is suspected, testing must be extremely cautious and the temperature of the heater should be kept to a minimum cautious and the temperature of the heater should be kept to a minimum until circulation is established.
until circulation is established.
If gent
If gentle heale heatinting g is not sucis not succecessssfuful l in estain establblisishihing circng circulaulatitionon(s(say 50 ay 50 ℃℃ atat heater coils), heating should be discontinued and the blockage located and heater coils), heating should be discontinued and the blockage located and cleared by applying gentle external heat to the affected portion of line.
cleared by applying gentle external heat to the affected portion of line.
Ex
Extrtrememe e heheat at is is nonot t rereququireired d fofor r clcleaearinring g bloblockckagageses; ; raraisisining g ththe e roroomom temperature will usually be sufficient to clear lines inside a building, while temperature will usually be sufficient to clear lines inside a building, while low-pressure steam is normally adequate for thawing
low-pressure steam is normally adequate for thawing external lines.external lines.
Once circulation has been established, heating can be continued slowly up Once circulation has been established, heating can be continued slowly up to the operating temperature, all flanges and joints being checked for leaks to the operating temperature, all flanges and joints being checked for leaks aft
after eer eververy 50 y 50 ℃℃ risrise. e. All All venvents ats and thnd the bye by-pa-pass to ss to the the safsafety vety valvalve, if fe, if fitteitted,d, should be open until all
should be open until all air pockets have been removed from the air pockets have been removed from the system.system.
Plants operating at atmospheric pressure should not be heated to such an Plants operating at atmospheric pressure should not be heated to such an extent that hot oil is discharged from the vent pipes or from the condenser.
extent that hot oil is discharged from the vent pipes or from the condenser.
Plants operating under pressure should never be heated beyond the hot oil Plants operating under pressure should never be heated beyond the hot oil temperature corresponding to the test pressure of the plant, or in any case temperature corresponding to the test pressure of the plant, or in any case hi
highgher thaer than n 404000℃℃. . MoMost plast plantnts opers operatatining g unundeder r prpresessusure are fitre are fitteted d wiwithth automatic controls limiting the maximum
automatic controls limiting the maximum obtainable.obtainable.
Removal of Extraneous Water Removal of Extraneous Water
The presence of extraneous water in a hot oil system can be dangerous, The presence of extraneous water in a hot oil system can be dangerous, owi
owing tng to tho the hie high vgh vapoapor prer pressussure of re of watwater at er at temtemperperatuatures res aboabove 1ve 10000℃℃. . ItIt is therefore recommended that, after a hydraulic test with water, new plant is therefore recommended that, after a hydraulic test with water, new plant should be thoroughly dried by compressed air before being filled with hot oil.
should be thoroughly dried by compressed air before being filled with hot oil.
Alternatively, the water can be vaporized and vented to atmosphere before Alternatively, the water can be vaporized and vented to atmosphere before the plant system is brought up to its full working temperature.
the plant system is brought up to its full working temperature.
5.2 Supervision of Operation 5.2 Supervision of Operation
The level of hot oil charge in the system should be checked at regular The level of hot oil charge in the system should be checked at regular intervals.
intervals. Changes in Changes in hot oil comhot oil composition arising position arising from prolonged opfrom prolonged operationeration or extraneous c
or extraneous causes should bauses should be periodically checke periodically checked. ed. The changes The changes due todue to pol
polymeymer r forformatmation ion are are besbest t chcheckecked ed by by phyphysicsical al meameasursuremeements nts of of thethe distillation range, crystallization
distillation range, crystallization point or viscositypoint or viscosity. . Where contaminaWhere contamination withtion with process materials is suspected, tests should be made immediately for the process materials is suspected, tests should be made immediately for the chemicals concerned, as most organic chemicals are much more liable to chemicals concerned, as most organic chemicals are much more liable to carbonize than hot oil is, and if
carbonize than hot oil is, and if left in the system will left in the system will impair heat transfer andimpair heat transfer and may even choke pipelines.
may even choke pipelines.
Analysis and Replacement Service Analysis and Replacement Service
When the polymer content, that is the amount distilling at temperatures When the polymer content, that is the amount distilling at temperatures abo
above 26ve 260 0 ℃℃ undunder ater atmosmosphepheric pric presressursure, is in te, is in the rahe rangnge 10 ~ 15e 10 ~ 15%, the h%, the hotot oi
oil l shshouould ld be be rereplplacaceded. . ThThis can is can be be dodone ne eieithther er by by reregegeneneraratinting g ththee degraded material locally or by using the replacement service operated by degraded material locally or by using the replacement service operated by vendor
vendor. . It should be noted thIt should be noted that it may not be pat it may not be possible to regenerate ossible to regenerate hot oilhot oil that has been contaminated by large quantities of material of low thermal that has been contaminated by large quantities of material of low thermal stability
stability, such as , such as greases or tars.greases or tars.
When HTF is decomposed due to thermal degradation, flash point, ignition When HTF is decomposed due to thermal degradation, flash point, ignition point and auto-ignition temperatures are lower than its original properties point and auto-ignition temperatures are lower than its original properties that need to check the
that need to check the following properties.following properties.
(1)
(1) ViViscoscositsityy Viscosity ef
Viscosity effects fluidity and heat transfects fluidity and heat transfer efficient. fer efficient. If it is lower viscosityIf it is lower viscosity,, tha
than n it it givgives es betbetter ter heaheat t tratransfnsfer er and and flufluidiidity ty but but chachanginging ng visviscoscosityity re
revevealals s ththerermamal l dedegrgradadatation of ion of hohot t oioil. l. AlAlonong g wiwith th timtime, e, viviscscosositityy increases in poly-phenyl derivatives and in mineral oils but decreases in increases in poly-phenyl derivatives and in mineral oils but decreases in synthetic paraffin.
synthetic paraffin.
(2)
(2) AciAcid Numd Number ber Hy
Hydrdrololysysis is or or oxoxidaidatition on dedegrgree ee cacan n be be chchececkeked d vivia a acacid id nunumbmberer..
Maximum is 4.0
Maximum is 4.0㎎㎎KOH/g-oil in paraffinic compounds, 1.0KOH/g-oil in paraffinic compounds, 1.0 ㎎㎎KOH/g-oil inKOH/g-oil in poly phenyl compound.
poly phenyl compound.
(3)
(3) Non acNon acetone etone solubsolublele Carbo
Carbon and solidn and solids scale is meas scale is measuredsured. . MaximMaximum is 50um is 50㎎㎎//㎖㎖-oil to avoid-oil to avoid erosion.
erosion.
(4
(4)) WWatater er
Water is the source of increasing light volatile compounds and acidic Water is the source of increasing light volatile compounds and acidic com
compoupoundnds. s. MaxMaximuimum m allallowaowable shouble should ld be 2000pbe 2000ppm pm for syntfor synthetheticic paraffin, 400ppm for aromatic compound.
paraffin, 400ppm for aromatic compound.
(5)
(5) Light vLight volatiolatile materle materialsials This con
This content shotent shows the degrews the degree of thermal dee of thermal degradagradation. tion. If it exceedIf it exceedss 10%, then flash point
10%, then flash point and ignition point should be checked.and ignition point should be checked.
(6) High boilers (Heavy components) (6) High boilers (Heavy components)
This con
This content shotent shows the degrews the degree of thermal dee of thermal degradagradation. tion. If it exceedIf it exceedss 10%, then coke will form.
10%, then coke will form.
5.3 Maintenance of Plant 5.3 Maintenance of Plant
Before performing any maintenance work involving the breaking of joints, all Before performing any maintenance work involving the breaking of joints, all the
the hot hot oiloil shshoulould be draid be drained fned from the prom the planlant into tht into the store storage taage tank. nk. WheWherere welding is required on a plant item, the part should be thoroughly steamed welding is required on a plant item, the part should be thoroughly steamed out to remov
out to remove traces of hot oil befoe traces of hot oil before weldinre welding is started. g is started. Where thWhere the worke work involved is small, it may be possible to do the operation without danger by involved is small, it may be possible to do the operation without danger by filling the section of pipe or plant with nitrogen and maintaining a continuous filling the section of pipe or plant with nitrogen and maintaining a continuous fl
flow ow of of ninitrtrogogen en whwhile ile weweldlding is ing is prprococeeeedidingng. . AfAfteter r anany y mamainintetenanancncee operation the plant should be tested to ensure freedom leaks before being operation the plant should be tested to ensure freedom leaks before being put back into operation.
put back into operation.