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Heat Exchangers Operations of shell and Tube types
WEBVTT Kind: captions Language: en
00:00:11.550 many industrial processes must heat or 00:00:14.64000:00:14.650 cool fluids to produce products heating 00:00:17.46000:00:17.470 and cooling are often accomplished by 00:00:19.17000:00:19.180 transferring heat between fluids heat 00:00:22.23000:00:22.240 transfer between fluids occurs in heat 00:00:24.60000:00:24.610 exchangers there are many types of heat 00:00:26.93900:00:26.949 exchangers but one of the most common 00:00:29.16000:00:29.170 types is a shell and tube heat exchanger 00:00:31.47000:00:31.480 shell and tube heat exchangers can be 00:00:34.04900:00:34.059 used for a variety of processes and 00:00:36.06000:00:36.070 operating procedures may vary with each 00:00:38.34000:00:38.350 heat exchanger what you'll see here is 00:00:40.92000:00:40.930 intended to be a guide to the steps that 00:00:43.02000:00:43.030 often have to be taken in the startup of 00:00:45.47900:00:45.489 a shell and tube heat exchanger after it 00:00:47.78900:00:47.799 has been shut down for maintenance but 00:00:50.07000:00:50.080 remember always follow your facility's 00:00:52.53000:00:52.540 operating procedures when you're 00:00:54.11900:00:54.129 starting up any heat exchanger the unit 00:00:57.29900:00:57.309 we'll be using is part of a mixing 00:00:59.18900:00:59.199 process and is used to cool the process 00:01:01.61900:01:01.629 liquid the heat exchanger has cooling 00:01:04.85900:01:04.869 water inlet and outlet lines process 00:01:10.14000:01:10.150 liquid Inlet and outlet lines a series 00:01:15.48000:01:15.490 of isolation valves a vent valve and 00:01:20.31000:01:20.320 drain valves before starting up the heat 00:01:25.31900:01:25.329 exchanger the operator inspects the unit 00:01:27.89900:01:27.909 to see if it's ready he checks the 00:01:29.78900:01:29.799 valves to make sure that all of the 00:01:31.56000:01:31.570 isolation vent and drain valves are shut 00:01:34.76000:01:34.770 after he completes the initial 00:01:37.28900:01:37.299 inspection he establishes the cooling 00:01:39.59900:01:39.609 water supply to the unit he does this by 00:01:42.56900:01:42.579 calling the control room operator and 00:01:44.55000:01:44.560 having him open the shell side vent then 00:01:48.33000:01:48.340 he partially opens the shell side water 00:01:50.73000:01:50.740 inlet valve to slowly fill the shell 00:01:53.06900:01:53.079 side then he calls the control room to 00:01:56.24900:01:56.259 have someone there start the cooling 00:01:57.89900:01:57.909 water pump when the cooling water pump 00:02:00.33000:02:00.340 is started cooling water will fill the 00:02:02.60900:02:02.619 shell side of the heat exchanger any air 00:02:05.21900:02:05.229 that is trapped on the shell side 00:02:06.71900:02:06.729 escapes through the open vent valve as 00:02:08.94000:02:08.950 the shell side of the heat exchanger 00:02:11.30900:02:11.319 fills the operator listens for air 00:02:13.62000:02:13.630 escaping when the shell side is 00:02:15.51000:02:15.520 completely filled he calls the control 00:02:17.82000:02:17.830 room and has them shut the vent valve 00:02:20.14900:02:20.159 then the operator opens the shell side 00:02:22.97900:02:22.989 in 00:02:23.46000:02:23.470 valve the rest of the way at that point 00:02:25.74000:02:25.750 he informs the control room that the 00:02:28.26000:02:28.270 shell side is lined up and that they can 00:02:30.33000:02:30.340 establish the proper flow rate through 00:02:32.22000:02:32.230 the shell on the heat exchanger shown in 00:02:35.28000:02:35.290 this example there is no isolation valve 00:02:38.01000:02:38.020 on the outlet of the shell side some 00:02:40.59000:02:40.600 shell and tube heat exchangers have an 00:02:42.54000:02:42.550 isolation valve on this outlet with 00:02:45.39000:02:45.400 those heat exchangers the isolation 00:02:47.67000:02:47.680 valve must be open to complete the flow 00:02:50.01000:02:50.020 path through the unit the next step is 00:02:52.53000:02:52.540 to line up the tube side of the heat 00:02:54.36000:02:54.370 exchanger first the operator opens the 00:02:57.42000:02:57.430 tube side vent valve then he partially 00:03:00.51000:03:00.520 opens the tube side inlet valve to allow 00:03:03.27000:03:03.280 the tube side to fill with process 00:03:05.16000:03:05.170 liquid and to remove any air or other 00:03:07.38000:03:07.390 gases that might be trapped on the tube 00:03:09.48000:03:09.490 side of the unit when the tube side is 00:03:11.85000:03:11.860 filled the operator closes the vent 00:03:14.25000:03:14.260 valve and opens the inlet valve the rest 00:03:17.79000:03:17.800 of the way then he opens the outlet 00:03:21.09000:03:21.100 valve at this point the startup is 00:03:24.39000:03:24.400 complete and the heat exchanger is in 00:03:26.49000:03:26.500 operation after the operator reports to 00:03:29.40000:03:29.410 the control room that the unit is in 00:03:31.02000:03:31.030 operation the control room establishes 00:03:33.60000:03:33.610 flow through the unit shell and tube 00:03:35.69900:03:35.709 heat exchangers are commonly used in a 00:03:37.83000:03:37.840 variety of processes and each may have a 00:03:40.29000:03:40.300 different operating procedure but 00:03:42.47900:03:42.48900:03:44.79000:03:44.800 operating procedures when shutting down 00:03:46.80000:03:46.810 any heat exchanger during shutdown the 00:03:50.16000:03:50.170 side of the heat exchanger with the 00:03:51.87000:03:51.880 hotter fluid is usually shut down first 00:03:54.06000:03:54.070 this helps to prevent the heat exchanger 00:03:56.72900:03:56.739 from being overheated and damaged let's 00:03:59.72900:03:59.739 watch an operator as he takes a heat 00:04:01.77000:04:01.780 exchanger out of service in this example 00:04:04.25900:04:04.269 the heat exchanger which cools a product 00:04:06.78000:04:06.790 from a reactor is being shut down for 00:04:09.09000:04:09.100 maintenance the tube side fluid is the 00:04:11.43000:04:11.440 hotter fluid to shut down the heat 00:04:14.43000:04:14.440 exchanger the operator closes the tube 00:04:16.89000:04:16.900 side inlet valve first and then the tube 00:04:19.92000:04:19.930 side outlet valve when the tube side has 00:04:23.61000:04:23.620 cooled the operator opens the tube side 00:04:26.25000:04:26.260 drain and vent valves this allows air to 00:04:30.03000:04:30.040 enter the tube side and drains the 00:04:31.98000:04:31.990 process fluid the operator then shuts 00:04:35.37000:04:35.380 the shell side inlet valve 00:04:37.38000:04:37.390 on the heat exchanger shown in this 00:04:39.21000:04:39.220 example the shell side has no isolation 00:04:42.03000:04:42.040 valve on its outlet some shell and tube 00:04:45.03000:04:45.040 heat exchangers have an isolation valve 00:04:47.04000:04:47.050 on this outlet with those heat 00:04:49.11000:04:49.120 exchangers the isolation valve must be 00:04:51.60000:04:51.610 shut to completely isolate the heat 00:04:53.67000:04:53.680 exchanger after the isolation valve is 00:04:56.85000:04:56.860 shut the operator opens the cooling 00:04:59.43000:04:59.440 water drain in vent valves once all of 00:05:02.52000:05:02.530 the fluid is drained from the heat 00:05:03.99000:05:04.000 exchanger the operator closes the vent 00:05:06.66000:05:06.670 and drain valves to complete the 00:05:08.55000:05:08.560 shutdown now if the heat exchanger 00:05:10.83000:05:10.840 that's being shut down handles flammable 00:05:13.56000:05:13.570 liquids it may have to be purged to 00:05:15.78000:05:15.790 reduce the possibility of a fire or an 00:05:18.18000:05:18.190 explosion caused by flammable vapors 00:05:20.45000:05:20.460 purging means forcing the process fluids 00:05:23.40000:05:23.410 out of the heat exchanger by a substance 00:05:25.89000:05:25.900 that won't react with the process fluid 00:05:28.08000:05:28.090 very often steam or nitrogen is used 00:05:30.69000:05:30.700 when a heat exchanger is in operation 00:05:33.05000:05:33.060 operators must routinely check the unit 00:05:35.82000:05:35.830 to ensure that its operating properly 00:05:37.89000:05:37.900 this may include checking temperature 00:05:40.20000:05:40.210 and pressure instruments to make sure 00:05:41.88000:05:41.890 that their readings are within normal 00:05:43.56000:05:43.570 operating ranges as well as checking the 00:05:45.90000:05:45.910 condition of the heat exchanger itself 00:05:48.71000:05:48.720 by checking a heat exchangers 00:05:51.06000:05:51.070 temperature instruments an operator can 00:05:53.31000:05:53.320 tell how the temperatures of the fluids 00:05:55.14000:05:55.150 change as they pass through the unit 00:05:56.91000:05:56.920 these values can also be used to 00:05:59.22000:05:59.230 determine the difference in temperature 00:06:01.02000:06:01.030 or delta T for each fluid the delta T 00:06:04.71000:06:04.720 can be used to see if the unit is 00:06:06.33000:06:06.340 operating properly for example if the 00:06:09.72000:06:09.730 delta T across the tube side of a heat 00:06:11.91000:06:11.920 exchanger is supposed to be 10 degrees 00:06:13.98000:06:13.990 but it is only 5 degrees it could be an 00:06:17.04000:06:17.050 indication that the tubes in the unit 00:06:18.87000:06:18.880 are becoming fouled or that one or both 00:06:21.18000:06:21.190 of the flow rates are not correct for 00:06:23.31000:06:23.320 proper operation in any event the cause 00:06:26.46000:06:26.470 of the problem should be investigated 00:06:28.38000:06:28.390 and supervisory personnel should be 00:06:30.45000:06:30.460 informed another way that temperatures 00:06:32.97000:06:32.980 can be checked is on a temperature 00:06:34.83000:06:34.840 recorder the recorder plots temperature 00:06:37.56000:06:37.570 values on a chart which allows an 00:06:39.66000:06:39.670 operator to see if a trend is developing 00:06:42.14000:06:42.150 additional information about a heat 00:06:44.25000:06:44.260 exchanger can be obtained by checking 00:06:46.47000:06:46.480 the units pressure instruments by 00:06:48.90000:06:48.910 reading the pressure instruments and 00:06:50.81000:06:50.820 operator can often detect problems with 00:06:53.12000:06:53.130 flow through the unit anytime there's 00:06:55.79000:06:55.800 flow through a heat exchanger there will 00:06:57.95000:06:57.960 be a specific drop in pressure across 00:07:00.02000:07:00.030 the unit this pressure drop is often 00:07:02.75000:07:02.760 referred to as differential pressure or 00:07:05.21000:07:05.220 Delta P any change in differential 00:07:08.12000:07:08.130 pressure could be an indication of a 00:07:09.92000:07:09.930 problem as the tubes become blocked or 00:07:12.50000:07:12.510 fouled the differential pressure will 00:07:14.57000:07:14.580 increase above the normal value once 00:07:17.03000:07:17.040 again the cause of the problem should be 00:07:19.10000:07:19.110 investigated and supervisory personnel 00:07:21.23000:07:21.240 should be informed on many units 00:07:24.17000:07:24.180 temperature and flow are controlled by 00:07:26.12000:07:26.130 automatic systems these systems may 00:07:28.73000:07:28.740 provide indications locally and in a 00:07:31.19000:07:31.200 control room the indications in the 00:07:33.41000:07:33.420 control room can be compared to the 00:07:35.51000:07:35.520 indications on instruments located at 00:07:37.73000:07:37.740 the heat exchanger to verify that the 00:07:39.98000:07:39.990 heat exchanger is operating properly if 00:07:42.71000:07:42.720 a problem is detected it could be the 00:07:44.99000:07:45.000 result of the control valves not 00:07:46.79000:07:46.800 operating properly or valves being out 00:07:49.85000:07:49.860 of position or it could be an indication 00:07:52.91000:07:52.920 that other equipment associated with the 00:07:54.98000:07:54.990 heat exchanger is not operating properly 00:07:57.37000:07:57.380 for example a low Inlet pressure could 00:08:00.77000:08:00.780 indicate a problem with a pump that 00:08:02.63000:08:02.640 supplies the heat exchanger besides 00:08:05.51000:08:05.520 checking instrument readings an operator 00:08:07.94000:08:07.950 should also check for leaks and for 00:08:10.91000:08:10.920 damaged or missing insulation problems 00:08:14.30000:08:14.310 such as these could affect the operation 00:08:16.40000:08:16.410 of the heat exchanger and pose hazards 00:08:18.47000:08:18.480 to personnel working in the area in this 00:08:21.14000:08:21.150 topic we looked at some basic procedures 00:08:23.48000:08:23.490 for the startup and shutdown of a 00:08:25.28000:08:25.290 typical shell and tube heat exchanger we 00:08:27.77000:08:27.780 also looked at some operator 00:08:29.30000:08:29.310 responsibilities associated with 00:08:31.25000:08:31.260 operating a shell and tube heat 00:08:32.57000:08:32.580 exchanger now let's try a few practice 00:08:35.24000:08:35.250 questions when the cooling water pump is 00:08:37.49000:08:37.500 started cooling water will fill the 00:08:39.62000:08:39.63000:08:42.20000:08:42.21000:08:43.73000:08:43.74000:08:45.95000:08:45.96000:08:48.32000:08:48.33000:08:50.60000:08:50.61000:08:52.52000:08:52.53000:08:54.83000:08:54.84000:08:57.13000:08:57.14000:08:59.96000:08:59.970 inlet valve the rest of the way at that 00:09:02.48000:09:02.490 point he informs the control 00:09:04.48900:09:04.499 that the shell side is lined up and that 00:09:07.06900:09:07.079 they can establish the proper flow rate 00:09:09.01900:09:09.029 through the shell to shut down the heat 00:09:11.56900:09:11.57900:09:14.02900:09:14.03900:09:17.05900:09:17.06900:09:20.71900:09:20.72900:09:23.35900:09:23.36900:09:27.16900:09:27.17900:09:29.20900:09:29.219 process fluid as the tubes become 00:09:31.57900:09:31.589 blocked or fouled the differential 00:09:33.61900:09:33.629 pressure will increase above the normal 00:09:35.62900:09:35.639 value once again the cause of the 00:09:37.99900:09:38.009 problem should be investigated and 00:09:39.64900:09:39.659 supervisory personnel should be informed 00:09:42.03900:09:42.049 fouling is a term that's often used to 00:09:44.50900:09:44.519 describe the build-up of deposits on the 00:09:46.66900:09:46.679 internal surfaces of the heat exchanger 00:09:48.97900:09:48.989 when fouling occurs the result is an 00:09:52.03900:09:52.049 additional layer of material that heat 00:09:54.04900:09:54.059 must pass through this additional layer 00:09:56.47900:09:56.489 reduces the ability of the unit to 00:09:58.63900:09:58.649 transfer heat also if the buildup 00:10:01.39900:10:01.409 becomes excessive the flow of fluids 00:10:03.67900:10:03.689 through the unit may be restricted 00:10:05.43900:10:05.449 fouling can be caused by many things one 00:10:08.53900:10:08.549 common cause is impurities in the fluids 00:10:11.26900:10:11.279 passing through the heat exchanger for 00:10:13.54900:10:13.559 example in a process that uses water 00:10:16.17900:10:16.189 impurities such as calcium can come out 00:10:18.94900:10:18.959 of the water and form an additional 00:10:20.96000:10:20.970 layer of material another source of 00:10:23.50900:10:23.519 fouling is small plants and animals that 00:10:25.66900:10:25.679 enter the heat exchanger many forms of 00:10:28.33900:10:28.349 algae and bacteria can live and grow 00:10:30.71000:10:30.720 inside the unit and form a layer of 00:10:33.01900:10:33.029 slime on the internal surfaces of the 00:10:35.08900:10:35.099 heat exchanger gases dissolved in the 00:10:38.05900:10:38.069 fluids that flow through a heat 00:10:39.37900:10:39.389 exchanger can also cause fouling for 00:10:42.10900:10:42.119 example some gases react with the metal 00:10:44.68900:10:44.699 inside a unit to cause a type of 00:10:46.42900:10:46.439 corrosion the corrosion forms a layer 00:10:49.09900:10:49.109 that acts as an insulator just like 00:10:51.31900:10:51.329 impurities or algae different techniques 00:10:54.67900:10:54.689 can be used to minimize fouling for 00:10:56.89900:10:56.909 example filters and screens can be used 00:10:59.32900:10:59.339 to remove particles from the fluids 00:11:01.27900:11:01.289 before they enter the heat exchanger 00:11:03.01900:11:03.029 fouling can sometimes be minimized by 00:11:05.68900:11:05.699 adding chemicals to the fluids passing 00:11:07.87900:11:07.889 through a heat exchanger for example 00:11:09.94900:11:09.959 chemicals such as chlorine are often 00:11:12.43900:11:12.449 added to cooling water to reduce the 00:11:14.65900:11:14.669 amount of algae or other organisms 00:11:16.63900:11:16.649 inside a unit 00:11:17.87000:11:17.880 in some situations fouling can become 00:11:20.68900:11:20.699 bad enough to restrict the fluid flow 00:11:22.63900:11:22.649 this problem may show up on the heat 00:11:24.92000:11:24.930 exchangers instruments as an increase in 00:11:27.43900:11:27.449 the pressure drop or as a gradual 00:11:29.60000:11:29.610 decrease in the flow through the 00:11:31.16000:11:31.170 affected side of the unit 00:11:32.60000:11:32.610 fouling may also affect the temperature 00:11:35.18000:11:35.190 of both fluids passing through the heat 00:11:36.98000:11:36.990 exchanger when fluid flow is restricted 00:11:39.74000:11:39.750 the heat exchanger must be cleaned one 00:11:42.71000:11:42.720 way that heat exchangers can be cleaned 00:11:44.48000:11:44.490 is by using chemicals when this is done 00:11:46.93900:11:46.949 a chemical solution is passed through 00:11:48.94900:11:48.959 the heat exchanger to dissolve the 00:11:50.99000:11:51.000 fouling on the walls of the tubes 00:11:53.07900:11:53.089 fouling on tube walls can also be 00:11:55.79000:11:55.800 removed by scraping or by spraying with 00:11:58.40000:11:58.410 high-pressure water or steam however 00:12:00.94900:12:00.959 these methods require the heat exchanger 00:12:03.37900:12:03.389 to be shut down and taken apart in some 00:12:06.41000:12:06.420 heat exchangers cleaning can be 00:12:08.18000:12:08.190 accomplished using a technique called 00:12:09.80000:12:09.810 back washing back washing is the 00:12:12.71000:12:12.720 reversing of flow through the heat 00:12:14.50900:12:14.519 exchanger this technique is effective in 00:12:17.09000:12:17.100 temporarily dislodging materials from 00:12:19.28000:12:19.290 the ends of the tubes and the tube 00:12:21.17000:12:21.180 sheets tube leakage is a problem that 00:12:24.37900:12:24.389 can seriously affect the operation of a 00:12:26.54000:12:26.550 heat exchanger it's usually caused by 00:12:29.09000:12:29.100 the failure of a tube as a result of 00:12:31.46000:12:31.470 overheating erosion or corrosion 00:12:34.56900:12:34.579 corrosion is the wearing away of tube 00:12:37.46000:12:37.470 metal caused by the flow of fluids or by 00:12:40.16000:12:40.170 solid impurities in the fluids some 00:12:42.92000:12:42.930 fluids that pass through a heat 00:12:44.24000:12:44.250 exchanger may contain abrasive particles 00:12:46.49000:12:46.500 as these fluids flow through the heat 00:12:48.55900:12:48.569 exchanger the particles come into 00:12:50.48000:12:50.490 contact with the tube metal and erode 00:12:52.61000:12:52.620 the tubes eventually the tube wears away 00:12:55.30900:12:55.319 in a spot and a leak forms corrosion 00:12:58.49000:12:58.500 chemically deteriorates to metal to 00:13:00.76900:13:00.779 create a leak corrosion is caused by a 00:13:03.43900:13:03.449 chemical reaction between the metal in 00:13:05.50900:13:05.519 the heat exchanger and either the fluid 00:13:07.69900:13:07.709 passing through the unit or impurities 00:13:09.94900:13:09.959 in the fluid the corrosion weakens the 00:13:12.35000:13:12.360 metal until a leak forms the biggest 00:13:15.19900:13:15.209 problem that can result from leaks in a 00:13:17.24000:13:17.250 heat exchanger is the mixing of one 00:13:19.42900:13:19.439 fluid with the other fluid for instance 00:13:22.10000:13:22.110 if cooling water mixes with oil and a 00:13:24.71000:13:24.720 lube oil cooler the water could damage 00:13:27.01900:13:27.029 the equipment that the oil lubricates to 00:13:29.87000:13:29.880 prevent this type of damage from 00:13:31.40000:13:31.410 occurring leeks must be detected one way 00:13:34.24900:13:34.259 to check for tube leaks is to take and 00:13:36.43900:13:36.449 analyze a sample of the lower pressure 00:13:38.44900:13:38.459 fluid when a leak occurs the 00:13:40.79000:13:40.800 high-pressure fluid leaks into the 00:13:42.61900:13:42.629 low-pressure fluid in some cases you may 00:13:45.86000:13:45.870 be able to tell there's a leak by just 00:13:47.60000:13:47.610 looking at the sample in other cases a 00:13:49.85000:13:49.860 lab test may be required to prevent 00:13:52.91000:13:52.920 leaks in some applications the process 00:13:55.10000:13:55.110 fluids pass through filters or strainers 00:13:57.86000:13:57.870 to remove impurities that can erode the 00:14:00.13900:14:00.149 tube metal also chemicals may be added 00:14:02.80900:14:02.819 to the fluids to control corrosion 00:14:04.72000:14:04.730 another method of controlling corrosion 00:14:07.40000:14:07.410 involves using a device called a 00:14:09.43900:14:09.449 sacrificial anode when a sacrificial 00:14:12.11000:14:12.120 anode is used impurities in water tend 00:14:15.01900:14:15.029 to react more readily with the anode 00:14:17.11900:14:17.129 than with the metal of the heat 00:14:18.65000:14:18.660 exchanger so the sacrificial anode 00:14:21.05000:14:21.060 corrodes while the heat exchanger is 00:14:23.38900:14:23.399 less affected heat exchangers that are 00:14:25.79000:14:25.800 used with water often have sacrificial 00:14:28.10000:14:28.110 anodes made up of zinc plates mounted 00:14:30.29000:14:30.300 inside when a leak does occur some type 00:14:33.55900:14:33.569 of corrective action must be taken if 00:14:35.84000:14:35.850 only a few tubes in a heat exchanger 00:14:37.42900:14:37.439 have leaks it may be possible to plug 00:14:40.37000:14:40.380 the affected tubes this prevents the 00:14:42.74000:14:42.750 tube side fluid from passing through 00:14:44.56900:14:44.579 those tubes and effectively eliminates 00:14:47.24000:14:47.250 the leak 00:14:47.87000:14:47.880 however plugging tubes reduces the heat 00:14:50.66000:14:50.670 exchangers heat transfer capacity if a 00:14:53.90000:14:53.910 lot of tubes are leaking the unit will 00:14:55.99900:14:56.009 have to be shut down and the affected 00:14:58.18900:14:58.199 tubes will have to be replaced when air 00:15:01.54000:15:01.550 non-condensable gases or other vapors 00:15:04.06900:15:04.079 are trapped inside a heat exchanger they 00:15:06.25900:15:06.269 can prevent the unit from operating 00:15:08.26900:15:08.279 efficiently this is because the air or 00:15:10.75900:15:10.769 gas can either blanket the tubes or 00:15:13.30900:15:13.319 block the tubes off and prevent fluid 00:15:15.67900:15:15.689 from flowing through them the effect is 00:15:18.11000:15:18.120 the same as the effect created by 00:15:19.61000:15:19.620 fouling less heat can be transferred 00:15:21.92000:15:21.930 across the tubes gas trapped on the tube 00:15:25.12900:15:25.139 side of the heat exchanger can block off 00:15:27.35000:15:27.360 tubes and prevent fluid from passing 00:15:29.42000:15:29.430 through them gas trapped on the shell 00:15:31.81900:15:31.829 side can displace the shell side fluid 00:15:33.88900:15:33.899 at the top of the heat exchanger this 00:15:36.25900:15:36.269 can reduce the amount of tube surface 00:15:38.17900:15:38.189 area that is exposed to the shell side 00:15:40.22000:15:40.230 fluid and thus reduce the amount of heat 00:15:42.62000:15:42.630 that can be transferred there are men 00:15:44.90000:15:44.910 ways that air or other gases can get 00:15:47.06000:15:47.070 trapped inside a heat exchanger for 00:15:48.80000:15:48.810 example this can happen during the 00:15:50.96000:15:50.970 startup of the unit during startup the 00:15:53.93000:15:53.940 heat exchanger should be vented to 00:15:55.70000:15:55.710 remove unwanted gases if the vetting is 00:15:58.40000:15:58.410 not complete gases will remain inside 00:16:01.10000:16:01.110 the unit another source of gases as the 00:16:04.01000:16:04.020 process itself in some situations the 00:16:06.65000:16:06.660 process can produce vapor bubbles as the 00:16:09.68000:16:09.690 process fluid passes through the heat 00:16:11.51000:16:11.520 exchanger the vapor collects inside the 00:16:14.18000:16:14.190 unit when maintenance is performed on 00:16:16.58000:16:16.590 process equipment air may be trapped in 00:16:19.04000:16:19.050 the piping or shell as the equipment is 00:16:21.08000:16:21.090 put back together when the equipment is 00:16:23.24000:16:23.250 restarted the air can make its way to 00:16:25.46000:16:25.470 the heat exchanger and become trapped 00:16:27.26000:16:27.270 inside no matter how error other gases 00:16:30.50000:16:30.510 get trapped inside a heat exchanger they 00:16:32.78000:16:32.790 can cause it to become air bound or 00:16:34.73000:16:34.740 vapor bound there are several symptoms 00:16:37.04000:16:37.050 to indicate this for example when 00:16:39.53000:16:39.540 trapped gas blocks flow to some of the 00:16:41.60000:16:41.610 tubes the outlet temperatures of the two 00:16:44.09000:16:44.100 fluids may change this is because the 00:16:46.61000:16:46.620 gas is restricting flow into the tubes 00:16:48.68000:16:48.690 and the restricted flow causes less heat 00:16:51.68000:16:51.690 transfer surface area to be available 00:16:53.86000:16:53.870 the decrease in heat transfer surface 00:16:56.69000:16:56.700 area will cause the outlet temperature 00:16:58.91000:16:58.920 of the process fluid to increase since 00:17:01.34000:17:01.350 less heat will be removed from the fluid 00:17:03.61000:17:03.620 there are also situations where the 00:17:06.05000:17:06.060 pressure inside a heat exchanger may be 00:17:08.03000:17:08.040 affected for example this can occur in 00:17:10.70000:17:10.710 heat exchangers that are used to 00:17:12.29000:17:12.300 condense processed vapors in this 00:17:14.78000:17:14.790 situation non condensable gases 00:17:17.15000:17:17.160 partially fill the unit reducing the 00:17:19.73000:17:19.740 amount of heat transfer area that the 00:17:21.86000:17:21.870 process vapor can come in contact with 00:17:23.78000:17:23.790 in turn this reduces the amount of vapor 00:17:26.96000:17:26.970 that can be condensed the flow of vapor 00:17:29.51000:17:29.520 will start to decrease and the pressure 00:17:31.76000:17:31.770 inside the unit will start to increase 00:17:34.57000:17:34.580 regardless of how gases get into the 00:17:36.98000:17:36.990 heat exchanger the unit must be vented 00:17:39.32000:17:39.330 to allow them to escape repeated venting 00:17:42.17000:17:42.180 may be necessary to ensure that the heat 00:17:44.39000:17:44.400 exchanger remains free of air and other 00:17:46.79000:17:46.800 undesirable gases however excessive 00:17:50.72000:17:50.730 venting can cause its own problems for 00:17:53.21000:17:53.220 example each venting may allow a small 00:17:55.52000:17:55.530 amount of the process fluid to be lost 00:17:57.44000:17:57.450 from the process 00:17:58.64000:17:58.650 this reduces the efficiency of the 00:18:00.44000:18:00.450 process venting may be only a temporary 00:18:02.78000:18:02.790 fix if the source of the gas is the 00:18:05.72000:18:05.730 process there may be a problem with the 00:18:08.03000:18:08.040 process or with one of the components in 00:18:10.31000:18:10.320 the process in this topic we looked at 00:18:12.77000:18:12.780 some of the basic problems that can 00:18:14.45000:18:14.460 affect a typical heat exchanger 00:18:16.00000:18:16.010 including fouling tube leaks and air and 00:18:19.28000:18:19.290 vapor binding we also looked at the 00:18:21.50000:18:21.510 causes and effects of these problems and 00:18:23.45000:18:23.460 we saw how they can be dealt with 00:18:25.37000:18:25.380 let's take a moment now and try some 00:18:27.44000:18:27.450 practice questions 00:18:28.52000:18:28.53000:18:30.83000:18:30.84000:18:33.23000:18:33.24000:18:35.33000:18:35.34000:18:37.79000:18:37.80000:18:40.01000:18:40.02000:18:41.99000:18:42.000 inside a unit corrosion chemically 00:18:44.51000:18:44.520 deteriorates tube metal to create a leak 00:18:47.05000:18:47.060 corrosion is caused by a chemical 00:18:49.22000:18:49.230 reaction between the metal in the heat 00:18:51.14000:18:51.150 exchanger and either the fluid passing 00:18:53.51000:18:53.520 through the unit or impurities in the 00:18:55.52000:18:55.530 fluid the corrosion weakens the metal 00:18:57.95000:18:57.960 until a leak forms regardless of how 00:19:00.59000:19:00.600 gases get into the heat exchanger the 00:19:02.81000:19:02.820 unit must be vented to allow them to 00:19:04.73000:19:04.740 escape repeated venting may be necessary 00:19:07.31000:19:07.320 to ensure that the heat exchanger 00:19:09.62000:19:09.630 remains free of air and other 00:19:11.48000:19:11.49000:19:15.41000:19:15.42000:19:17.90000:19:17.91000:19:20.21000:19:20.22000:19:22.10000:19:22.110 from the process this reduces the 00:19:24.23000:19:24.240 efficiency of the process
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