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FCCU — Transcript

by Harikrishnan P · 3,306 words · 572 segments · language en · Watch on YouTube

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0:05the American petroleum Institute and HL
0:08training
0:09present an introduction to fluid
0:12catalytic
0:14cracking crude oil it starts out here in
0:18the ground formed by organic materials
0:21that have been compressed under the
0:22Earth's surface for millions of
0:25years and ends up here powering cars
0:28trucks ships and
0:31airplanes and here heating houses
0:34churches schools and Office
0:37Buildings and even here in clothes
0:41solvents Plastics and
0:44chemicals but to get to all of these
0:46places the crude must first be pumped
0:49piped processed and
0:51refined this program is about one of the
0:54processes catalytic cracking that
0:57changes oil into products we can use
1:01to understand and appreciate the
1:03catalytic cracking process you need to
1:05know how crude oil is
1:07structured crude oil is made up of
1:10hydrogen and carbon atoms that have
1:12bonded together to form molecules called
1:16hydrocarbons the hydrocarbons found in
1:19crude come in a variety of shapes and
1:21sizes they range from small simple
1:24compounds to large complex molecules
1:30different types of hydrocarbons have
1:32different
1:33characteristics small or light
1:35hydrocarbons like methane and propane
1:38are easy to ignite so they make good
1:41fuels heavy hydrocarbons like Doane are
1:45thick or viscous which makes them ideal
1:47lubricating
1:50oils the goal in most Refinery
1:52operations is to maximize the production
1:55of light hydrocarbons because they can
1:57be used in products like gasoline and
2:00petrochemical feed stocks that sell for
2:02the highest
2:04prices catalytic cracking helps us to
2:06meet this goal by converting heavy
2:09hydrocarbons into smaller more useful
2:14molecules the cracking of hydrocarbons
2:16is accomplished by a chemical reaction
2:19that uses heat moderate pressure and a
2:22catalyst to break down the
2:25molecules the catalyst is a substance
2:28that promotes the cracking of oil
2:30when the reaction is complete the
2:32Catalyst comes out just like it went in
2:35except for some hydrocarbons and Coke
2:38that are deposited on its surface the
2:40Catalyst can then be cleaned and
2:44reused heat is an essential part of the
2:47process it is the source of energy that
2:50keeps the cracking reaction going
2:53temperature in the cat cracking vessel
2:55is usually in the area of 900° f
3:01a cat cracking unit consists of three
3:03major sections or
3:05parts these are the reactor the
3:08regenerator and the
3:11fractionator let's take a step-by-step
3:13look at how the whole process
3:16works the cat cracker feed is usually a
3:20heavy gas oil or a vacuum gas oil
3:24normally the first step in processing is
3:26to preheat the feed in a furnace or a
3:29series of heat
3:32exchangers next the feed is mixed with
3:34hot Catalyst in a line called a
3:37riser the heat from the Catalyst
3:39vaporizes the oil as it enters the Riser
3:43and cracking begins as soon as the
3:45Catalyst makes contact with the oil
3:49Vapors the oil Vapors fluidize the
3:52Catalyst allowing the mixture to flow up
3:54the Riser into the
3:56reactor by this time most of the desired
3:59cracking reactions have already occurred
4:02so the Catalyst and oil Vapors are
4:05usually separated as soon as they enter
4:06the
4:08reactor sometimes however the separation
4:10is purposely delayed so that further
4:13cracking will
4:15occur the catalyst is separated from the
4:18oil Vapors by passing the mixture
4:20through Cyclones located inside the
4:23reactor as the oil Vapors and Catalyst
4:26swirl through the Cyclones catalyst
4:29partic particles are deposited on the
4:31Cyclone
4:32walls these particles slide down to the
4:35bottom of the reactor while the cracked
4:37oil Vapors flow out the top and are sent
4:40to a fractionating
4:42tower in the fractionating tower the
4:45hydrocarbons are separated by their
4:47respective boiling points into products
4:50such as gas gasoline Napa light and
4:53heavy cycle oils and slurry
4:56oil this separation process is known as
5:01stallation the bottom product or slurry
5:04oil contains Catalyst particles that are
5:07carried over from the
5:09reactor this stream is sent to a slurry
5:11settler where the Catalyst settles out
5:15Catalyst and oil from the bottom of the
5:17settler are then mixed with Fresh Feed
5:20and recycled back through the system
5:23this is called a slurry
5:27recycle let's return to the reactor
5:30we said that hydrocarbons and Coke are
5:32deposited on the Catalyst during the
5:34cracking
5:36reaction these deposits deactivate the
5:38catalyst so they must be removed before
5:41the catalyst is
5:43reused two different methods are used to
5:45clean or regenerate the
5:49Catalyst the first step in regeneration
5:52is to pass the spent Catalyst through a
5:54steam stripper the steam removes
5:57hydrocarbons from the surface of the
5:59cataly CST by vaporizing them the vapors
6:02are then channeled back to the
6:06reactor next the Catalyst flows into the
6:10regenerator combustion air is
6:12intentionally added to this vessel to
6:14burn the coke off the
6:17Catalyst the burning of coke produces a
6:20flu gas and also releases a great deal
6:23of heat before leaving the regenerator
6:26the gases pass through another set of
6:28cyclones to separate out any Catalyst
6:31particles that are carried with
6:34them from the regenerator the flu gas
6:37may be sent to a CO boiler the co boiler
6:41Burns carbon monoxide in the flu gas
6:44into relatively harmless carbon
6:48dioxide sometimes the flu gas is passed
6:51through an electrostatic precipitator to
6:53recover small particles of catalyst the
6:56Catalyst particles are given an
6:58electrical charge which causes them to
7:00collect on magnetic plates inside the
7:05precipitator back in the regenerator the
7:07catalyst is ready for reuse after the
7:10coke has been burnt off it the
7:13regenerated catalyst is mixed with Fresh
7:15Feed and the same basic process repeats
7:19itself much of the energy that is needed
7:22to continue the reaction is provided by
7:24The Catalyst which has absorbed heat
7:26during the Regeneration stage
7:31you can see that the Catalyst circulates
7:33continuously throughout the system from
7:36the Riser up to the reactor across to
7:39the
7:40regenerator then back to the Riser the
7:43Catalyst flows in a cycle from one part
7:45of the system to the
7:48next let's review how the cracking
7:51process works and consider in more
7:53detail some of the factors that affect
7:55this process stop the tape and turn to
7:59work book period
8:031 first part of the program we looked at
8:06the various components that make up a
8:08cat cracking unit and consider the
8:11function of each of these components in
8:13relation to the total
8:15process in this section we'll discuss
8:18the operating conditions or variables
8:20that affect cat cracker yields and look
8:23at how these factors are
8:25controlled you already learned that the
8:28goal in cat cracking is to convert heavy
8:30hydrocarbons into lighter more useful
8:34molecules to determine how much cracking
8:36occurs in a unit we use a measure called
8:40conversion conversion tells us what
8:42percent of the feed has been cracked
8:44into material that boils below 430°
8:49F the boiling temperature the cat
8:51cracker feed ranges from around 600° fah
8:55to 1,000° F so cat cracker product
8:59prodcts that boil below 430° F must be
9:03composed of hydrocarbons that have been
9:05broken down from larger
9:09molecules conversion is normally
9:11calculated by measuring the yield of
9:13products that boil above 430° F and then
9:18subtracting this figure from
9:20100 in this example 40% of the cat
9:24cracking products boil above 430° F so
9:29the percent conversion is 100us 40 or
9:3660% there are a number of factors or
9:39variables that affect conversion in the
9:41catalytic cracking
9:42process one important factor is the type
9:45of catalyst that's
9:47used different catalysts produce a
9:50different range of products some
9:52catalysts maximize the production of
9:54high octane
9:56gasoline others increase the yield of
9:58jet fuel
10:00the term catalyst selectivity is used to
10:03describe the product distribution that
10:06can be realized from a given
10:09Catalyst the ability of the Catalyst to
10:12actually convert the feed into lighter
10:14products is called The Catalyst activity
10:18the more active the Catalyst the higher
10:20the rate of
10:23conversion high regenerator temperatures
10:25or contaminants in the feed can
10:27gradually reduce the C Catalyst activity
10:30and seal activity fresh catalyst is
10:34added as needed to maintain the desired
10:36activity and seal activity and also to
10:39make up for Catalyst losses in the flu
10:41gas and fractionator
10:45bottoms another important operating
10:47variable is the Catalyst circulation
10:50rate Catalyst circulation can be
10:53measured by two different methods the
10:56first is called weight per hourly space
11:00velocity the space velocity is
11:03determined by dividing the pounds per
11:05hour of feed charged to the unit by the
11:08total pounds of catalyst hold up in the
11:12reactor the space velocity is usually
11:14Changed by adjusting the Catalyst level
11:17or hold up in the
11:20reactor when the Catalyst inventory in
11:23the reactor is increased there is a
11:25corresponding increase in
11:28conversion this however may not be
11:30desirable because increasing the contact
11:33time between the oil and the Catalyst
11:35often leads to
11:37overcracking when the oil is over
11:39cracked less gasoline is produced in
11:42return for higher gas and Coke
11:46yields the majority of cat cracking
11:49units in operation today are pure Riser
11:52crackers in these units a bed of
11:55catalyst is not maintained in the
11:57reactor so space veloc
11:59or hold up is not a relevant Factor
12:03Instead The Catalyst circulation is
12:05determined by measuring the Catalyst to
12:08oil
12:09ratio the Catalyst to oil ratio is
12:12simply the Catalyst rate divided by the
12:15feed
12:16rate as more catalyst is circulated
12:19through the system the Catalyst to oil
12:22ratio
12:23increases you can see from the graph
12:25that conversion increases as the
12:28Catalyst to oil ratio
12:32Rises a third operating variable is the
12:35reactor
12:36temperature the temperature in the
12:38reactor is controlled by adjusting the
12:40feed temperature by changing the amount
12:43of bottom product recycled or by
12:46changing the Catalyst circulation
12:49rate this chart shows the relationship
12:52between reactor temperature and
12:55conversion generally High reactor
12:58temperatures are desirable because they
13:00increase the gasoline yield and octane
13:05number a fourth operating variable is
13:08the regenerator
13:10temperature the regenerator temperature
13:12is a function of several other variables
13:15such as the amount of coke on the spent
13:17Catalyst the degree to which carbon
13:19monoxide is combusted to carbon
13:22dioxide the Catalyst circulation rate
13:24through the regenerator and the amount
13:27of air supplied by the air BL
13:30lower high regenerator temperatures are
13:33often maintained because they reduce the
13:35amount of coke on the regenerated
13:38Catalyst the high regenerator
13:40temperatures also increase the amount of
13:42heat that the Catalyst absorbs so less
13:46Catalyst can be circulated to meet the
13:48process heat
13:51requirements the amount of coke that
13:53remains on the regenerated catalyst is
13:55also considered an operating variable
13:59this is because Coke deactivates the
14:01Catalyst conversion decreases as the
14:05amount of coke on the regenerated
14:06catalist
14:09increases another variable that affects
14:11yields is the amount of bottom product
14:14that is returned to the reactor from the
14:17fractionator this variable is called the
14:20recycle
14:22rate increasing the amount of recycle
14:25results in higher conversion and greater
14:28yields of gas and Coke in most
14:31operations however a low recycle rate is
14:34used because of the problems caused by
14:36the
14:38Coke the feed preheat temperature is
14:42also a factor that affects the unit
14:44operation raising the feed temperature
14:47means that less heat is needed from the
14:49catalyst so the Catalyst circulation
14:52rate can be reduced this reduces the
14:55coke yield and increases the unit's
14:57capacity to process Fe
14:59feed the maximum feed preheat
15:02temperature is normally around 800° F
15:06temperatures higher than this will cause
15:08thermal cracking inside the
15:12heater the air to the regenerator is
15:15another operating variable the burning
15:18air rate is set by the amount of coke
15:20produced enough air must be added to the
15:23regenerator to burn the coke off the
15:26Catalyst but if too much air is added
15:29excessive burning will cause high
15:31regenerator
15:34temperatures pressure in the reactor and
15:36the regenerator must be controlled to
15:39maintain the proper Catalyst
15:42circulation these variables however have
15:44little effect on product yields so they
15:47are normally not adjusted to influence
15:52conversion the composition of the feed
15:54affects what types of products a
15:56particular unit will produce the this is
15:59because different types of hydrocarbons
16:01crack in different ways by carefully
16:04analyzing the feed we are able to
16:06predict the product
16:09yields most variables in the cat
16:11cracking process are measured recorded
16:14and controlled with automatic
16:16instruments this allows an operator to
16:19Monitor and adjust the process from a
16:21central control
16:23room let's take a look at a simple
16:26example of how this instrumentation
16:28works
16:30suppose the variable we are controlling
16:32is the reactor temperature a measuring
16:35instrument like this thermocouple is
16:37used to sense the temperature inside the
16:41reactor this measurement information on
16:43Reactor temperature is then sent to a
16:46device
16:47called a controller that is located in
16:50the control
16:51room the controller is programmed to
16:54keep the reactor temperature at a
16:56desired value called set point
16:59if the temperature has deviated from set
17:01point the controller sends a
17:04signal to a valve on the regenerated
17:08Catalyst line telling it either to open
17:11or
17:12close this changes the amount of hot
17:15Catalyst entering the Riser and brings
17:18the reactor temperature back to set
17:21point during normal operations the
17:24instrumentation automatically adjusts
17:27the process variables to keep the unit
17:29running smoothly if it is necessary to
17:32change the condition of a process
17:34variable an operator can adjust the set
17:37point value at the control
17:40board let's review the operating
17:42variables in the cat cracking process
17:45and take a closer look at how the system
17:47is controlled stop the tape and turn to
17:51workbook Period
17:542 in the normal operation of a catalytic
17:57cracking unit an operator makes Minor
17:59Adjustments to the process to keep the
18:01conversion rates at the desired value
18:04these adjustments are for the most part
18:06routine so when the unit is operating
18:09normally it is fairly easy to
18:13control an operator is faced with a
18:15greater challenge when the unit is
18:17operating abnormally there may be
18:20several different reasons for abnormal
18:22operations so an operator must develop
18:25troubleshooting skills to identify and
18:28solve these types of
18:30problems in this part of the program
18:32we'll take a look at what causes some of
18:35these abnormal operating situations and
18:38how they affect the system in the
18:40workbook period we'll talk about the
18:42corrective actions that should be taken
18:44for each of these
18:48problems the feed is usually preheated
18:50in a furnace or heat exchanger so that
18:53it will thoroughly vaporized when it's
18:55mixed with the
18:57Catalyst there are a number number of
18:59problems that can cause a reduction or
19:01loss of the feed
19:03preheat these include a failure in the
19:05instrumentation system a cut off of the
19:08fuel or steam Supply ruptured or fou
19:12tubes in the furnace or heat exchanger
19:15and water in the
19:18feed when the feed preheat is reduced or
19:21lost there may not be enough heat to
19:23vaporize the oil in the Riser if this
19:26occurs a mixture of liquid hydrocarbon
19:29and Catalyst May muddy up the Riser and
19:32force the unit to be shut down and
19:35cleaned
19:36out another abnormal situation is after
19:40burning in the
19:42regenerator air is added to the
19:44regenerator to burn Coke off the
19:46Catalyst but if too much air is
19:48available the flu gas may also
19:52combust this uncontrolled burning of flu
19:55gas is called after burning
19:59the primary symptoms of after burning
20:01are a sudden increase in regenerator
20:03temperature and pressure these high
20:06temperatures can damage the Catalyst the
20:09Cyclones and other metal hardware inside
20:12the
20:13regenerator a feed or charge pump is
20:16responsible for moving oil into the unit
20:20a loss of power or a mechanical problem
20:23may cause this pump to
20:26fail if the feed pump fails the flow of
20:29oil to the unit will stop and without
20:32oil Vapors flowing up the Riser the
20:34Catalyst will not be able to circulate
20:37properly as a result the reactor
20:40temperature pressure and Catalyst level
20:42will rapidly
20:44decrease obviously normal operation of
20:47the unit cannot continue without a
20:49source of
20:51feed an air blower provides combustion
20:55air to the regenerator a failure of this
20:58component may be caused by a mechanical
21:00problem or a loss of steam or electrical
21:04power if the air blower fails it will
21:07not be possible to burn carbon off the
21:10catalyst so there will be a sudden
21:12decrease in the regenerator temperature
21:14and
21:15pressure this will reduce the
21:17differential pressure across the
21:19regenerated Catalyst
21:21valve since the oil cannot be cracked
21:23with a spent Catalyst the unit will have
21:26to be shut down unless the situ is
21:30corrected another condition that will
21:32cause the unit to operate abnormally is
21:35a failure of one of the valves that
21:37control the flow of flu gas spent
21:39Catalyst or regenerated
21:42Catalyst a valve failure can result from
21:45problems in the instrumentation system
21:48such as a controller malfunction or a
21:50loss of hydraulic fluid pressure or the
21:53valve may fail because of mechanical
21:55problems within the valve itself
22:00the flu gas valve controls the
22:02regenerator pressure by regulating the
22:04flow of flu gas out of this vessel if
22:08this valve fails the regenerator
22:10pressure may change suddenly this could
22:13result in a loss of differential
22:15pressure across the regenerated Catalyst
22:17valve or the spent Catalyst valve and
22:21lead to a flow
22:23reversal an equally serious situation
22:26will occur if either the spent Catalyst
22:29valve or the regenerated Catalyst valve
22:31fails a failure in one of these valves
22:34throws the whole system out of balance
22:37the problem must be immediately
22:40corrected to prevent a major upset and
22:42possible flow
22:45reversal gases in the fractionator and
22:48the reactor are removed by a gas
22:51compressor a loss of power or a
22:53mechanical problem can cause the
22:55compressor to lose some or all of its
22:58capacity to compress
23:00gases if this happens there will be a
23:03sudden increase in fractionator and
23:05reactor pressures this interferes with
23:08fractionating efficiency and limits the
23:11amount of feed that can be processed
23:13through the cat cracker it also changes
23:16the differential pressure that exists
23:18across the spent and regenerated
23:20Catalyst
23:22valves another situation that will cause
23:25a major upset is a loss of power a power
23:29loss is usually due to problems outside
23:31an operator's control such as an
23:34accident lightning or a short at a
23:36junction
23:38box in the event of a power failure
23:41electrically driven pumps compressors
23:43instruments and valves will fail unless
23:46a backup power system is available a
23:49loss of power means that the unit must
23:52be shut
23:54down problems in the fractionator can
23:57also cause a cat cracking unit to
23:59operate
24:00abnormally for example if a fractionator
24:03becomes flooded with liquid hydrocarbons
24:06there will be pressure surges inside
24:08this vessel these pressure surges will
24:11back up into the reactor and cause it to
24:14operate
24:15erratically sometimes the outlets at the
24:18bottom of a fractionator will become
24:20plugged with Coke deposits if this
24:22happens product cannot be drawn from the
24:25tower so the unit must be shut down and
24:28the deposits cleaned
24:30out let's review the causes and effects
24:33of abnormal operating problems and
24:36consider the corrective actions that
24:38should be taken for each of these
24:41situations stop the tape and turn to
24:44workbook period
24:463 you learn that the purpose of
24:49catalytic cracking is to convert heavy
24:51hydrocarbons into smaller more useful
24:54molecules we showed you the hardware
24:57that is used to do this job and
24:59discussed how each piece of equipment
25:02works then we introduced you to the
25:04major operating variables in the cat
25:06cracking process and talked about how
25:09these operating conditions affect
25:11product yields and
25:14conversion finally we looked at a number
25:16of abnormal operating situations such as
25:19an air blower failure or a loss of the
25:22feed preheat and discuss the symptoms
25:25and solutions for each of these problems
25:29this concludes our program on catalytic
25:32cracking work through the review and
25:35self- test at the end of your workbook
25:38it will help you remember the main
25:40points of the program

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