Why_Boilers_&_Power Plants_ Explode

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Language: en

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00:00:03.690 00:00:03.700 as we progress through this program you
00:00:06.369 00:00:06.379 need to keep in mind that the procedures
00:00:07.929 00:00:07.939 will demonstrate our typical of how many
00:00:10.030 00:00:10.040 plants handle abnormal and emergency
00:00:11.799 00:00:11.809 conditions your plants procedures will
00:00:14.079 00:00:14.089 give you specific information on how you
00:00:15.970 00:00:15.980 should respond now the chances are
00:00:19.120 00:00:19.130 extremely good but if you follow your
00:00:20.920 00:00:20.930 plants operating procedures and monitor
00:00:22.780 00:00:22.790 your equipment properly your boiler is
00:00:24.880 00:00:24.890 not going to explode
00:00:26.140 00:00:26.150 however by understanding why boilers
00:00:28.930 00:00:28.940 explode and the situations that have the
00:00:30.820 00:00:30.830 potential for causing explosions you're
00:00:33.250 00:00:33.260 better prepared to anticipate the
00:00:34.630 00:00:34.640 possibility of an explosion and act to
00:00:37.600 00:00:37.610 keep that explosion from occurring in
00:00:40.210 00:00:40.220 general boiler explosions occur when an
00:00:42.520 00:00:42.530 abnormally high concentration of
00:00:44.560 00:00:44.570 combustibles is suddenly and
00:00:46.390 00:00:46.400 uncontrollably ignited inside the boiler
00:00:48.150 00:00:48.160 now there are a number of situations
00:00:50.260 00:00:50.270 that can lead to a high concentration of
00:00:52.270 00:00:52.280 combustibles in the boiler furnace
00:00:54.000 00:00:54.010 startup is one example as you know from
00:00:57.729 00:00:57.739 earlier training fuel air heat and a
00:01:01.360 00:01:01.370 chemical reaction are the four basic
00:01:03.910 00:01:03.920 requirements for combustion as this
00:01:07.809 00:01:07.819 simplified diagram of a burner port
00:01:09.580 00:01:09.590 illustrates in preparation for start-up
00:01:11.739 00:01:11.749 and operator first Sparks igniters to
00:01:14.230 00:01:14.240 provide the heat source to start the
00:01:15.760 00:01:15.770 combustion process the operator next
00:01:18.639 00:01:18.649 establishes secondary air flow to the
00:01:20.889 00:01:20.899 burner to provide the air requirement
00:01:23.639 00:01:23.649 with the igniter sparking and air
00:01:26.199 00:01:26.209 supplied for combustion the final step
00:01:28.389 00:01:28.399 is the introduction of fuel to the
00:01:29.980 00:01:29.990 burner the fuel and air combine to form
00:01:32.410 00:01:32.420 a combustible mixture the heat from the
00:01:35.080 00:01:35.090 igniter starts the combustion process
00:01:37.440 00:01:37.450 now that's the way it's supposed to work
00:01:39.940 00:01:39.950 however boiler explosions occur during
00:01:42.519 00:01:42.529 unusual conditions let's suppose that
00:01:44.919 00:01:44.929 the igniter malfunctions and does not
00:01:46.989 00:01:46.999 spark as it is supposed to we'll use the
00:01:49.629 00:01:49.639 same illustration to see how an
00:01:51.039 00:01:51.049 explosion might occur the operator turns
00:01:54.580 00:01:54.590 the controller to start the igniter
00:01:55.989 00:01:55.999 sparking however in this case the
00:01:58.599 00:01:58.609 igniter is slow to respond and doesn't
00:02:00.459 00:02:00.469 spark right away the operator next
00:02:03.339 00:02:03.349 establishes airflow to the burner port
00:02:05.199 00:02:05.209 and then starts fuel flow the igniter
00:02:09.399 00:02:09.409 still doesn't spark the air and fuel
00:02:12.220 00:02:12.230 form a combustible mixture
00:02:14.020 00:02:14.030 the mixture accumulates in the boiler as
00:02:16.270 00:02:16.280 more fuel and air are supplied if the
00:02:19.150 00:02:19.160 igniter suddenly begins sparking it will
00:02:21.610 00:02:21.620 ignite this abnormally large mixture
00:02:23.470 00:02:23.480 the result is an explosion the same
00:02:26.860 00:02:26.870 thing can happen if a combustible
00:02:28.210 00:02:28.220 mixture is present in the boiler prior
00:02:29.920 00:02:29.930 to startup and an operator sparks
00:02:31.990 00:02:32.000 igniters without first purging the
00:02:34.480 00:02:34.490 boiler an operator can easily avoid
00:02:37.630 00:02:37.640 these situations by carefully following
00:02:39.400 00:02:39.410 plant procedures and purging the boiler
00:02:41.830 00:02:41.840 before sparking igniters then verifying
00:02:45.699 00:02:45.709 that the igniters are operating properly
00:02:47.110 00:02:47.120 before introducing air and fuel to the
00:02:49.750 00:02:49.760 boiler explosive fuel mixtures can also
00:02:52.420 00:02:52.430 occur during normal operation if either
00:02:54.970 00:02:54.980 the flow of air or the flow of fuel to
00:02:57.010 00:02:57.020 the burner port is temporarily
00:02:58.210 00:02:58.220 interrupted and then reestablished an
00:03:00.570 00:03:00.580 explosion may occur again from earlier
00:03:05.080 00:03:05.090 training you know that if one of the
00:03:06.790 00:03:06.800 four basic requirements for combustion
00:03:08.530 00:03:08.540 is eliminated combustion will cease if
00:03:12.940 00:03:12.950 you have established a proper boiler
00:03:14.710 00:03:14.720 flame and air flow and fuel flow are
00:03:16.810 00:03:16.820 properly matched your burners will
00:03:18.670 00:03:18.680 operate the way they're supposed to
00:03:19.870 00:03:19.880 however if air flow for example is
00:03:22.330 00:03:22.340 interrupted one of the basic
00:03:23.920 00:03:23.930 requirements for combustion is
00:03:25.210 00:03:25.220 eliminated this will cause the boiler
00:03:27.430 00:03:27.440 flame to go out unless the fuel flow is
00:03:30.580 00:03:30.590 immediately stopped and the boiler is
00:03:32.110 00:03:32.120 purged and abnormally high concentration
00:03:34.539 00:03:34.549 of fuel may accumulate near the burner
00:03:36.400 00:03:36.410 port if airflow is subsequently
00:03:38.770 00:03:38.780 re-established this large concentration
00:03:41.410 00:03:41.420 of fuel can ignite suddenly and cause an
00:03:43.960 00:03:43.970 explosion
00:03:45.660 00:03:45.670 interrupting fuel flow will also
00:03:47.560 00:03:47.570 extinguish the boiler flame and unless
00:03:49.690 00:03:49.700 steps are taken to correct the problem
00:03:51.220 00:03:51.230 according to procedures an explosion may
00:03:53.740 00:03:53.750 result when fuel flow is restored
00:03:57.360 00:03:57.370 generally an operator has several
00:03:59.350 00:03:59.360 indications that make it possible to
00:04:00.850 00:04:00.860 verify that a flame is present in the
00:04:02.740 00:04:02.750 boiler viewing ports mirrors and
00:04:06.600 00:04:06.610 television monitors allow visual
00:04:09.340 00:04:09.350 indication that combustion is taking
00:04:11.440 00:04:11.450 place typically if an operator discovers
00:04:14.860 00:04:14.870 that the boiler flame has gone out
00:04:16.830 00:04:16.840 procedures indicate to immediately shut
00:04:19.810 00:04:19.820 off the fuel supply and to purge the
00:04:22.060 00:04:22.070 boiler for a designated amount of time
00:04:23.860 00:04:23.870 before restarting the flame
00:04:27.100 00:04:27.110 another situation that can lead to a
00:04:28.839 00:04:28.849 boiler explosion is difficult to detect
00:04:31.059 00:04:31.069 and may cause an explosion with no
00:04:33.010 00:04:33.020 warning whatsoever to give you one
00:04:36.700 00:04:36.710 example of how this unusual situation
00:04:38.260 00:04:38.270 might occur we'll use a boiler that has
00:04:40.570 00:04:40.580 a gas bypass system for steam
00:04:42.429 00:04:42.439 temperature control as you learned
00:04:44.740 00:04:44.750 earlier
00:04:45.129 00:04:45.139 under normal conditions flue gas flows
00:04:48.100 00:04:48.110 from the furnace area over the super
00:04:50.469 00:04:50.479 heaters and reheater in this section of
00:04:52.360 00:04:52.370 the boiler over the economizer and then
00:04:55.360 00:04:55.370 through the air preheater x' in a boiler
00:04:58.959 00:04:58.969 with a flue gas bypass if the outlet
00:05:01.270 00:05:01.280 temperature of the superheated steam
00:05:02.680 00:05:02.690 gets too high this damper is open which
00:05:05.950 00:05:05.960 redirects a portion of the flue gas away
00:05:08.080 00:05:08.090 from the super heaters when superheated
00:05:11.499 00:05:11.509 temperature returns to normal the damper
00:05:14.020 00:05:14.030 is closed and flue gas flow proceeds
00:05:16.270 00:05:16.280 normally gas bypass systems usually do
00:05:20.529 00:05:20.539 not require the use of fans flue gas can
00:05:23.350 00:05:23.360 be redirected simply by opening a damper
00:05:25.420 00:05:25.430 the reason simple the pressure in this
00:05:28.149 00:05:28.159 part of the boiler is higher than the
00:05:30.490 00:05:30.500 pressure in this part and fluids
00:05:32.950 00:05:32.960 naturally flow from an area of higher
00:05:34.570 00:05:34.580 pressure to an area of lower pressure
00:05:36.990 00:05:37.000 when the damper is closed a dead spot
00:05:40.689 00:05:40.699 may occur in the ductwork at the
00:05:42.070 00:05:42.080 entrance to the gas bypass system a dead
00:05:45.189 00:05:45.199 spot is an area where little or no flow
00:05:47.110 00:05:47.120 takes place now let us suppose that for
00:05:51.850 00:05:51.860 whatever reason the boiler flame was
00:05:53.829 00:05:53.839 momentarily lost and an abnormally large
00:05:56.320 00:05:56.330 quantity of fuel entered the boiler the
00:05:58.860 00:05:58.870 operator responded properly by cutting
00:06:01.269 00:06:01.279 fuel flow to the burners and increasing
00:06:03.189 00:06:03.199 air flow to purge the boiler of all
00:06:05.079 00:06:05.089 combustibles but let us also suppose
00:06:08.740 00:06:08.750 that a portion of the combustibles
00:06:10.570 00:06:10.580 accumulated in this dead spot around the
00:06:12.939 00:06:12.949 gas bypass damper and were not purged
00:06:15.670 00:06:15.680 from the boiler when purging was
00:06:19.540 00:06:19.550 complete the operator followed the
00:06:21.760 00:06:21.770 proper procedures for reestablishing the
00:06:23.469 00:06:23.479 boiler flame but remember combustibles
00:06:25.959 00:06:25.969 remained in this dead spot in the
00:06:27.309 00:06:27.319 ductwork the boiler continues operating
00:06:29.740 00:06:29.750 for some time with nothing unusual
00:06:31.990 00:06:32.000 happening however let's suppose further
00:06:34.629 00:06:34.639 that the operator needs to adjust
00:06:36.129 00:06:36.139 superheater outlet temperature and opens
00:06:38.709 00:06:38.719 the bypass damper
00:06:40.149 00:06:40.159 the combustibles that have accumulated
00:06:41.799 00:06:41.809 in the ductwork are no longer in a dead
00:06:43.989 00:06:43.999 spot they are immediately reintroduced
00:06:46.600 00:06:46.610 into the flow path of flue gas going to
00:06:48.850 00:06:48.860 the economizer or due to some back
00:06:51.219 00:06:51.229 pressure around the damper are forced
00:06:53.019 00:06:53.029 back into the furnace area of the boiler
00:06:56.009 00:06:56.019 the result could be sudden and
00:06:58.570 00:06:58.580 uncontrolled combustion in other words
00:07:00.999 00:07:01.009 an explosion in either the furnace area
00:07:03.399 00:07:03.409 the ductwork or near the economizer now
00:07:07.149 00:07:07.159 what we've just done is a lot of
00:07:08.679 00:07:08.689 supposing but let me stress that boiler
00:07:10.869 00:07:10.879 explosions occur under uncommon
00:07:12.939 00:07:12.949 conditions if it is possible to make up
00:07:16.119 00:07:16.129 a situation where an explosion could
00:07:17.739 00:07:17.749 possibly happen it is also possible that
00:07:20.290 00:07:20.300 under rare and unusual circumstances
00:07:22.689 00:07:22.699 those conditions can exist and cause an
00:07:25.419 00:07:25.429 explosion let me again stress that
00:07:27.999 00:07:28.009 boiler explosions are uncommon
00:07:29.949 00:07:29.959 occurrences by following your plants
00:07:32.079 00:07:32.089 operating procedures the chances of them
00:07:34.329 00:07:34.339 happening to you are extremely slim what
00:07:38.469 00:07:38.479 you can do to keep explosive situations
00:07:40.179 00:07:40.189 from developing is to carefully monitor
00:07:42.189 00:07:42.199 your boiler flame and to make sure that
00:07:44.350 00:07:44.360 combustion is taking place properly you
00:07:47.499 00:07:47.509 should also keep a careful watch on the
00:07:49.029 00:07:49.039 fuel flow and air flow to the burners to
00:07:51.100 00:07:51.110 make certain that both are being
00:07:52.929 00:07:52.939 supplied in proper proportions finally
00:07:56.829 00:07:56.839 since the boiler explosions which have
00:07:58.659 00:07:58.669 occurred in the past have often been
00:08:00.279 00:08:00.289 fostered by a loss of boiler flame
00:08:02.189 00:08:02.199 knowing the procedures for dealing with
00:08:04.569 00:08:04.579 this situation and the proper procedures
00:08:06.459 00:08:06.469 for purging your boiler will prevent
00:08:08.649 00:08:08.659 boiler explosions in the next part of
00:08:11.829 00:08:11.839 this program we look at some situations
00:08:13.540 00:08:13.550 that can lead to the loss of a boiler
00:08:15.519 00:08:15.529 flame and the typical procedures for
00:08:17.889 00:08:17.899 returning the boiler to normal operation
00:08:19.799 00:08:19.809 for now read over the material in your
00:08:22.269 00:08:22.279 text on the cause of boiler explosions
00:08:24.100 00:08:24.110 and answer the questions did you need
00:08:26.109 00:08:26.119 any help with this material ask your
00:08:27.939 00:08:27.949 instructor before going on
00:08:30.460 00:08:30.470
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