00:00:00.319 one of the key elements of many process 00:00:03.05000:00:03.060 plants is a distillation system it's 00:00:05.57000:00:05.580 important for operators to understand 00:00:07.34000:00:07.350 how distillation systems work because 00:00:09.79900:00:09.809 it's part of their job to make sure the 00:00:11.36000:00:11.370 systems run properly the purpose of any 00:00:14.24000:00:14.250 distillation system is to separate a 00:00:16.43000:00:16.440 liquid mixture into two or more 00:00:18.29000:00:18.300 components the separation takes place in 00:00:21.08000:00:21.090 a distillation column or tower the 00:00:23.81000:00:23.820 liquid mixture is called feed or charge 00:00:26.06000:00:26.070 and the components into which it 00:00:28.16000:00:28.170 separated are called cuts or fractions 00:00:30.75900:00:30.769 let's take a look at a simplified 00:00:32.93000:00:32.940 representation of a distillation system 00:00:34.79000:00:34.800 in this example the feed is stored in a 00:00:38.72000:00:38.730 tank during operation a pump is used to 00:00:42.17000:00:42.180 move the feed from the tank to a pre 00:00:43.85000:00:43.860 heater in the pre heater the mixture is 00:00:47.18000:00:47.190 heated under pressure to just below its 00:00:49.16000:00:49.170 boiling point the pressure in the tower 00:00:51.70900:00:51.719 is lower than the pressure in the pre 00:00:53.63000:00:53.640 heater so when the feed enters the tower 00:00:56.11900:00:56.129 it starts to boil the vapors from the 00:00:59.36000:00:59.370 boiling liquid which primarily contained 00:01:01.72900:01:01.739 the lighter components in the feed rise 00:01:04.16000:01:04.170 in the tower the remaining liquid which 00:01:07.91000:01:07.920 consists primarily of the heavier 00:01:09.56000:01:09.570 components in the feed moves down the 00:01:11.81000:01:11.820 tower and collects at the bottom some of 00:01:15.02000:01:15.030 this liquid is drawn off as the bottoms 00:01:16.96900:01:16.979 product and some of it's routed to a 00:01:19.13000:01:19.140 device called a reboiler which is 00:01:21.28900:01:21.299 connected to the bottom of the tower the 00:01:24.05000:01:24.060 reboiler is usually a heat exchanger 00:01:26.14900:01:26.159 that's designed to vaporize the lighter 00:01:28.19000:01:28.200 components that remain in the liquid 00:01:29.92900:01:29.939 from the bottom of the tower vapors from 00:01:33.17000:01:33.180 the reboiler or in some cases a mixture 00:01:35.60000:01:35.610 of vapors and liquid re-enter the tower 00:01:38.26000:01:38.270 the vapors then rise up in the tower 00:01:41.10900:01:41.119 these vapors and the heat they contain 00:01:44.06000:01:44.070 are often referred to as boil up the hot 00:01:47.96000:01:47.970 boil up provides heat that's needed for 00:01:49.78900:01:49.799 the distillation process to take place 00:01:51.77000:01:51.780 in the tower the vapors that rise up in 00:01:54.85900:01:54.869 the tower are routed to a condenser the 00:01:57.85900:01:57.869 purpose of the condenser is to cool and 00:01:59.99000:02:00.000 condense the vapors into liquid from the 00:02:03.05000:02:03.060 condenser the liquid flows into a 00:02:04.99900:02:05.009 receiver or accumulator the receiver 00:02:07.63900:02:07.649 provides a reservoir for the liquid part 00:02:11.27000:02:11.280 of the liquid from the receiver is 00:02:12.71000:02:12.720 pumped back 00:02:13.73000:02:13.740 to the top of the tower and part of it 00:02:15.89000:02:15.900 is drawn off as the towers overhead 00:02:18.11000:02:18.120 product well we've just looked at one 00:02:21.32000:02:21.330 simple example of a distillation system 00:02:23.33000:02:23.340 not all distillation systems are the 00:02:25.73000:02:25.740 same but most of them have the basic 00:02:28.01000:02:28.020 equipment that we've just seen at the 00:02:30.77000:02:30.780 heart of a distillation system is the 00:02:32.75000:02:32.760 distillation tower basically a 00:02:35.30000:02:35.310 distillation tower is a series of 00:02:37.28000:02:37.290 distillation processes or stills stacked 00:02:40.13000:02:40.140 on top of each other the process of 00:02:42.89000:02:42.900 distillation is sometimes referred to as 00:02:44.86000:02:44.870 fractional distillation or fractionation 00:02:47.63000:02:47.640 and distillation towers are sometimes 00:02:50.45000:02:50.460 called fractionators fractionation is 00:02:53.69000:02:53.700 distillation that occurs at different 00:02:55.46000:02:55.470 levels in a tower this is a simplified 00:02:59.27000:02:59.280 illustration of the inside of one type 00:03:01.13000:03:01.140 of distillation Tower this tower uses 00:03:03.83000:03:03.840 trays called sieve trays to separate 00:03:05.96000:03:05.970 vapors and liquid the trays are spaced 00:03:08.51000:03:08.520 throughout the tower 00:03:09.56000:03:09.570 they're called sieve trays because they 00:03:11.99000:03:12.000 have many openings in them like a sieve 00:03:14.11000:03:14.120 here's a closer view of some of the 00:03:16.55000:03:16.560 trays we've exaggerated the size of the 00:03:19.25000:03:19.260 openings to make them easier to see the 00:03:22.04000:03:22.050 openings in the trays allow vapors to 00:03:23.75000:03:23.760 rise through the trays on their way up 00:03:25.40000:03:25.410 the tower each tray is also designed to 00:03:29.09000:03:29.100 hold liquid dams or Weir's on each tray 00:03:32.12000:03:32.130 allow liquid to build up on the tray 00:03:34.57000:03:34.580 liquid that overflows the Weir's flows 00:03:37.19000:03:37.200 into downcomers the downcomers channel 00:03:40.10000:03:40.110 the liquid from tray to tray down the 00:03:41.90000:03:41.910 tower when the upward moving vapors and 00:03:45.02000:03:45.030 the downward flowing liquid come in 00:03:47.39000:03:47.400 contact on each tray the vapors transfer 00:03:50.21000:03:50.220 some of their heat to the liquid two 00:03:52.16000:03:52.170 things happen the heavier components of 00:03:54.68000:03:54.690 the vapors become cooler and condense 00:03:56.60000:03:56.610 into liquid and the lighter components 00:03:58.73000:03:58.740 of the liquid boil the vapors then rise 00:04:01.58000:04:01.590 toward the next tray as this process 00:04:04.22000:04:04.230 continues the rising vapors contain a 00:04:06.62000:04:06.630 higher concentration of lighter 00:04:08.21000:04:08.220 components and a lower concentration of 00:04:10.76000:04:10.770 heavier components so this is how the 00:04:14.75000:04:14.760 distillation process is repeated on each 00:04:16.94000:04:16.950 tray as the vapors rise through the 00:04:19.09900:04:19.109 tower now not every distillation tower 00:04:21.71000:04:21.720 is designed in the exact same way 00:04:23.53000:04:23.540 however every tower can be divided into 00:04:26.63000:04:26.640 three base 00:04:27.45000:04:27.460 sections the middle section is where the 00:04:30.54000:04:30.550 feed enters the tower and part of the 00:04:32.49000:04:32.500 feed vaporizes this vaporization is 00:04:35.12900:04:35.139 commonly known as flashing so this 00:04:38.01000:04:38.020 section of the tower is often called the 00:04:39.90000:04:39.910 flash zone the section above the flash 00:04:42.80900:04:42.819 zone is called the rectification section 00:04:44.99000:04:45.000 in this part of the tower the 00:04:47.30900:04:47.319 concentration of lighter components 00:04:49.08000:04:49.090 increases the section of the tower below 00:04:52.46900:04:52.479 the flash zone is called the stripping 00:04:54.60000:04:54.610 section in this section the lighter 00:04:57.15000:04:57.160 components are vaporized or stripped 00:04:59.43000:04:59.440 from the heavier liquid if a 00:05:02.10000:05:02.110 distillation tower worked perfectly it 00:05:04.11000:05:04.120 would produce pure products 00:05:06.32000:05:06.330 unfortunately that's not the case 00:05:08.31000:05:08.320 the lighter products usually contains 00:05:10.37900:05:10.389 some heavier fractions and the heavier 00:05:12.48000:05:12.490 products usually contains some lighter 00:05:13.98000:05:13.990 fractions this is sometimes referred to 00:05:16.43900:05:16.449 as overlap distillation systems use 00:05:20.46000:05:20.470 several methods to help maximize the 00:05:22.37900:05:22.389 purity of the products one of these 00:05:24.77900:05:24.789 methods is called refluxing the vapors 00:05:28.14000:05:28.150 coming off the top of the tower are 00:05:29.76000:05:29.770 condensed in a condenser and then 00:05:31.80000:05:31.810 collected in a receiver part of the 00:05:34.37900:05:34.389 liquid from the receiver is sent to 00:05:36.21000:05:36.220 storage or to other units in the plant 00:05:38.21900:05:38.229 as the towers overhead product the rest 00:05:41.46000:05:41.470 of the liquid is pumped back into the 00:05:43.35000:05:43.360 top of the tower the liquid that's 00:05:45.74900:05:45.759 reintroduced into the tower is called 00:05:48.14900:05:48.159 external reflux because it consists of 00:05:51.51000:05:51.520 liquid that was cooled in the condenser 00:05:53.24900:05:53.259 the external reflux is cooler than the 00:05:56.07000:05:56.080 liquid in the top of the tower as the 00:05:58.56000:05:58.570 external reflux cools the top of the 00:06:00.33000:06:00.340 tower vapors made of heavier fractions 00:06:02.76000:06:02.770 condense the liquid made of heavier 00:06:05.12900:06:05.139 fractions flows down the tower and is 00:06:07.62000:06:07.630 referred to as internal reflux meanwhile 00:06:10.95000:06:10.960 the top of the tower is still hot enough 00:06:12.89900:06:12.909 to keep the lighter fractions in vapor 00:06:15.12000:06:15.130 form the vapors are drawn off the top of 00:06:18.02900:06:18.039 the tower and into the condenser 00:06:20.77900:06:20.789 refluxing increases the purity of the 00:06:23.24900:06:23.259 overhead product because condensing the 00:06:25.52900:06:25.539 vapors made of heavier fractions keeps 00:06:27.81000:06:27.820 them out of the stream of vapors that 00:06:29.33900:06:29.349 leaves the top of the tower another 00:06:32.49000:06:32.500 method used to maximize product purity 00:06:34.62000:06:34.630 is called reboiler the bottoms liquid 00:06:38.18900:06:38.199 that's drawn off from the tower is sent 00:06:40.14000:06:40.150 to a heater called a 00:06:41.27900:06:41.289 boiler the rest of the bottoms liquid is 00:06:43.92000:06:43.930 sent to storage or to other units in the 00:06:46.04900:06:46.059 plant as the towers bottoms product the 00:06:49.52900:06:49.539 reboiler heats the liquid it receives so 00:06:51.89900:06:51.909 that a mixture of vapors and liquid is 00:06:53.60900:06:53.619 formed depending on the system either 00:06:56.45900:06:56.469 vapors or the mixture of vapors in 00:06:58.46900:06:58.479 liquid is then reintroduced into the 00:07:00.54000:07:00.550 tower the hot vapors cause any lighter 00:07:03.60000:07:03.610 fractions in the liquid at the bottom to 00:07:05.82000:07:05.830 vaporize and move up the tower this 00:07:08.67000:07:08.680 reduces the amount of lighter fractions 00:07:10.70900:07:10.719 in the bottoms product the reboiler 00:07:13.79900:07:13.809 provides the major portion of the heat 00:07:15.80900:07:15.819 that's required to make the distillation 00:07:17.33900:07:17.349 process work in the type of system we've 00:07:20.48900:07:20.499 been discussing the heat supplied by 00:07:22.58900:07:22.599 preheating the feed is not sufficient 00:07:25.10900:07:25.119 for proper distillation the reboiler is 00:07:27.98900:07:27.999 needed to provide enough additional heat 00:07:29.85000:07:29.860 to vaporize the lighter fractions in the 00:07:32.07000:07:32.080 tower so that the products meet 00:07:33.77900:07:33.789 specifications although all distillation 00:07:36.92900:07:36.939 towers serve the same basic function 00:07:39.02900:07:39.039 they don't all have the same internal 00:07:40.73900:07:40.749 components one type of tower uses trays 00:07:44.12900:07:44.139 called sieve trays to separate vapors 00:07:46.25900:07:46.269 and liquid that type of tower is covered 00:07:48.77900:07:48.789 in the tower operation part of this 00:07:50.45900:07:50.469 program in this part will look inside 00:07:53.51900:07:53.529 two other types of distillation towers 00:07:55.82900:07:55.839 and see how their internal components 00:07:58.07900:07:58.089 differ let's start with a tower that 00:08:00.95900:08:00.969 uses trays with bubble caps the holes in 00:08:04.73900:08:04.749 each tray are covered with caps called 00:08:06.65900:08:06.669 bubble caps the slots in these bubble 00:08:09.44900:08:09.459 caps disperse the rising vapors through 00:08:11.79000:08:11.800 the liquid on the tray each bubble cap 00:08:14.90900:08:14.919 has many slots and each tray has many 00:08:17.39900:08:17.409 bubble caps to spread out the vapors 00:08:19.18900:08:19.199 this ensures a maximum contact between 00:08:22.01900:08:22.029 vapors and liquid so that maximum heat 00:08:24.54000:08:24.550 transfer can take place 00:08:26.86900:08:26.879 another type of tower called a packed 00:08:29.54900:08:29.559 tower contains layers of devices called 00:08:32.06900:08:32.079 packing instead of trays with bubble 00:08:34.11000:08:34.120 caps there are many different types of 00:08:36.95900:08:36.969 packing some towers have sections that 00:08:40.07900:08:40.089 are filled with cylindrical rings like 00:08:41.90900:08:41.919 the one Illustrated here it's known as a 00:08:44.24900:08:44.259 rash agreeing another type of packing is 00:08:47.22000:08:47.230 known as a burl saddle the packing 00:08:50.63900:08:50.649 breaks up the liquid so that it flows 00:08:52.23000:08:52.240 over a large amount of surface area 00:08:54.70000:08:54.710 this exposes more of the liquid to the 00:08:56.59000:08:56.600 vapors and increases heat transfer from 00:08:58.99000:08:59.000 the vapors to the liquid packing can be 00:09:02.01900:09:02.029 made for many different materials 00:09:03.07000:09:03.080 including porcelain copper aluminum and 00:09:06.40000:09:06.410 iron the main requirement is that the 00:09:09.22000:09:09.230 material must be compatible with the 00:09:10.96000:09:10.970 liquid in the tower and the conditions 00:09:13.09000:09:13.100 under which the Tower is operated this 00:09:16.00000:09:16.010 is a section of another type of packing 00:09:18.01000:09:18.020 from a distillation Tower it's called a 00:09:20.17000:09:20.180 packing grid each layer in the grid has 00:09:23.68000:09:23.690 spaces for vapors to rise through the 00:09:25.63000:09:25.640 packing on their way up the tower liquid 00:09:28.32900:09:28.339 flows over these surfaces which channel 00:09:30.73000:09:30.740 the liquid as it flows down the tower 00:09:32.28000:09:32.290 the packing grid provides a great deal 00:09:34.75000:09:34.760 of surface area where contact between 00:09:36.63900:09:36.649 the vapors and the liquid can take place 00:09:38.86000:09:38.870 so heat transfer is maximized some of 00:09:42.34000:09:42.35000:09:44.23000:09:44.24000:09:46.38900:09:46.39900:09:48.55000:09:48.56000:09:50.82000:09:50.83000:09:53.41000:09:53.42000:09:55.44900:09:55.45900:09:57.16000:09:57.17000:10:00.40000:10:00.41000:10:02.86000:10:02.87000:10:05.49000:10:05.50000:10:08.37000:10:08.38000:10:11.32000:10:11.330 are often referred to as boil up
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