00:00:00.590 [Music] 00:00:03.69000:00:03.700 as we progress through this program you 00:00:06.36900:00:06.379 need to keep in mind that the procedures 00:00:07.92900:00:07.939 will demonstrate our typical of how many 00:00:10.03000:00:10.040 plants handle abnormal and emergency 00:00:11.79900:00:11.809 conditions your plants procedures will 00:00:14.07900:00:14.089 give you specific information on how you 00:00:15.97000:00:15.980 should respond now the chances are 00:00:19.12000:00:19.130 extremely good but if you follow your 00:00:20.92000:00:20.930 plants operating procedures and monitor 00:00:22.78000:00:22.790 your equipment properly your boiler is 00:00:24.88000:00:24.890 not going to explode 00:00:26.14000:00:26.150 however by understanding why boilers 00:00:28.93000:00:28.940 explode and the situations that have the 00:00:30.82000:00:30.830 potential for causing explosions you're 00:00:33.25000:00:33.260 better prepared to anticipate the 00:00:34.63000:00:34.640 possibility of an explosion and act to 00:00:37.60000:00:37.610 keep that explosion from occurring in 00:00:40.21000:00:40.220 general boiler explosions occur when an 00:00:42.52000:00:42.530 abnormally high concentration of 00:00:44.56000:00:44.570 combustibles is suddenly and 00:00:46.39000:00:46.400 uncontrollably ignited inside the boiler 00:00:48.15000:00:48.160 now there are a number of situations 00:00:50.26000:00:50.270 that can lead to a high concentration of 00:00:52.27000:00:52.280 combustibles in the boiler furnace 00:00:54.00000:00:54.010 startup is one example as you know from 00:00:57.72900:00:57.739 earlier training fuel air heat and a 00:01:01.36000:01:01.370 chemical reaction are the four basic 00:01:03.91000:01:03.920 requirements for combustion as this 00:01:07.80900:01:07.819 simplified diagram of a burner port 00:01:09.58000:01:09.590 illustrates in preparation for start-up 00:01:11.73900:01:11.749 and operator first Sparks igniters to 00:01:14.23000:01:14.240 provide the heat source to start the 00:01:15.76000:01:15.770 combustion process the operator next 00:01:18.63900:01:18.649 establishes secondary air flow to the 00:01:20.88900:01:20.899 burner to provide the air requirement 00:01:23.63900:01:23.649 with the igniter sparking and air 00:01:26.19900:01:26.209 supplied for combustion the final step 00:01:28.38900:01:28.399 is the introduction of fuel to the 00:01:29.98000:01:29.990 burner the fuel and air combine to form 00:01:32.41000:01:32.420 a combustible mixture the heat from the 00:01:35.08000:01:35.090 igniter starts the combustion process 00:01:37.44000:01:37.450 now that's the way it's supposed to work 00:01:39.94000:01:39.950 however boiler explosions occur during 00:01:42.51900:01:42.529 unusual conditions let's suppose that 00:01:44.91900:01:44.929 the igniter malfunctions and does not 00:01:46.98900:01:46.999 spark as it is supposed to we'll use the 00:01:49.62900:01:49.639 same illustration to see how an 00:01:51.03900:01:51.049 explosion might occur the operator turns 00:01:54.58000:01:54.590 the controller to start the igniter 00:01:55.98900:01:55.999 sparking however in this case the 00:01:58.59900:01:58.609 igniter is slow to respond and doesn't 00:02:00.45900:02:00.469 spark right away the operator next 00:02:03.33900:02:03.349 establishes airflow to the burner port 00:02:05.19900:02:05.209 and then starts fuel flow the igniter 00:02:09.39900:02:09.409 still doesn't spark the air and fuel 00:02:12.22000:02:12.230 form a combustible mixture 00:02:14.02000:02:14.030 the mixture accumulates in the boiler as 00:02:16.27000:02:16.280 more fuel and air are supplied if the 00:02:19.15000:02:19.160 igniter suddenly begins sparking it will 00:02:21.61000:02:21.620 ignite this abnormally large mixture 00:02:23.47000:02:23.480 the result is an explosion the same 00:02:26.86000:02:26.870 thing can happen if a combustible 00:02:28.21000:02:28.220 mixture is present in the boiler prior 00:02:29.92000:02:29.930 to startup and an operator sparks 00:02:31.99000:02:32.000 igniters without first purging the 00:02:34.48000:02:34.490 boiler an operator can easily avoid 00:02:37.63000:02:37.640 these situations by carefully following 00:02:39.40000:02:39.410 plant procedures and purging the boiler 00:02:41.83000:02:41.840 before sparking igniters then verifying 00:02:45.69900:02:45.709 that the igniters are operating properly 00:02:47.11000:02:47.120 before introducing air and fuel to the 00:02:49.75000:02:49.760 boiler explosive fuel mixtures can also 00:02:52.42000:02:52.430 occur during normal operation if either 00:02:54.97000:02:54.980 the flow of air or the flow of fuel to 00:02:57.01000:02:57.020 the burner port is temporarily 00:02:58.21000:02:58.220 interrupted and then reestablished an 00:03:00.57000:03:00.580 explosion may occur again from earlier 00:03:05.08000:03:05.090 training you know that if one of the 00:03:06.79000:03:06.800 four basic requirements for combustion 00:03:08.53000:03:08.540 is eliminated combustion will cease if 00:03:12.94000:03:12.950 you have established a proper boiler 00:03:14.71000:03:14.720 flame and air flow and fuel flow are 00:03:16.81000:03:16.820 properly matched your burners will 00:03:18.67000:03:18.680 operate the way they're supposed to 00:03:19.87000:03:19.880 however if air flow for example is 00:03:22.33000:03:22.340 interrupted one of the basic 00:03:23.92000:03:23.930 requirements for combustion is 00:03:25.21000:03:25.220 eliminated this will cause the boiler 00:03:27.43000:03:27.440 flame to go out unless the fuel flow is 00:03:30.58000:03:30.590 immediately stopped and the boiler is 00:03:32.11000:03:32.120 purged and abnormally high concentration 00:03:34.53900:03:34.549 of fuel may accumulate near the burner 00:03:36.40000:03:36.410 port if airflow is subsequently 00:03:38.77000:03:38.780 re-established this large concentration 00:03:41.41000:03:41.420 of fuel can ignite suddenly and cause an 00:03:43.96000:03:43.970 explosion 00:03:45.66000:03:45.670 interrupting fuel flow will also 00:03:47.56000:03:47.570 extinguish the boiler flame and unless 00:03:49.69000:03:49.700 steps are taken to correct the problem 00:03:51.22000:03:51.230 according to procedures an explosion may 00:03:53.74000:03:53.750 result when fuel flow is restored 00:03:57.36000:03:57.370 generally an operator has several 00:03:59.35000:03:59.360 indications that make it possible to 00:04:00.85000:04:00.860 verify that a flame is present in the 00:04:02.74000:04:02.750 boiler viewing ports mirrors and 00:04:06.60000:04:06.610 television monitors allow visual 00:04:09.34000:04:09.350 indication that combustion is taking 00:04:11.44000:04:11.450 place typically if an operator discovers 00:04:14.86000:04:14.870 that the boiler flame has gone out 00:04:16.83000:04:16.840 procedures indicate to immediately shut 00:04:19.81000:04:19.820 off the fuel supply and to purge the 00:04:22.06000:04:22.070 boiler for a designated amount of time 00:04:23.86000:04:23.870 before restarting the flame 00:04:27.10000:04:27.110 another situation that can lead to a 00:04:28.83900:04:28.849 boiler explosion is difficult to detect 00:04:31.05900:04:31.069 and may cause an explosion with no 00:04:33.01000:04:33.020 warning whatsoever to give you one 00:04:36.70000:04:36.710 example of how this unusual situation 00:04:38.26000:04:38.270 might occur we'll use a boiler that has 00:04:40.57000:04:40.580 a gas bypass system for steam 00:04:42.42900:04:42.439 temperature control as you learned 00:04:44.74000:04:44.750 earlier 00:04:45.12900:04:45.139 under normal conditions flue gas flows 00:04:48.10000:04:48.110 from the furnace area over the super 00:04:50.46900:04:50.479 heaters and reheater in this section of 00:04:52.36000:04:52.370 the boiler over the economizer and then 00:04:55.36000:04:55.370 through the air preheater x' in a boiler 00:04:58.95900:04:58.969 with a flue gas bypass if the outlet 00:05:01.27000:05:01.280 temperature of the superheated steam 00:05:02.68000:05:02.690 gets too high this damper is open which 00:05:05.95000:05:05.960 redirects a portion of the flue gas away 00:05:08.08000:05:08.090 from the super heaters when superheated 00:05:11.49900:05:11.509 temperature returns to normal the damper 00:05:14.02000:05:14.030 is closed and flue gas flow proceeds 00:05:16.27000:05:16.280 normally gas bypass systems usually do 00:05:20.52900:05:20.539 not require the use of fans flue gas can 00:05:23.35000:05:23.360 be redirected simply by opening a damper 00:05:25.42000:05:25.430 the reason simple the pressure in this 00:05:28.14900:05:28.159 part of the boiler is higher than the 00:05:30.49000:05:30.500 pressure in this part and fluids 00:05:32.95000:05:32.960 naturally flow from an area of higher 00:05:34.57000:05:34.580 pressure to an area of lower pressure 00:05:36.99000:05:37.000 when the damper is closed a dead spot 00:05:40.68900:05:40.699 may occur in the ductwork at the 00:05:42.07000:05:42.080 entrance to the gas bypass system a dead 00:05:45.18900:05:45.199 spot is an area where little or no flow 00:05:47.11000:05:47.120 takes place now let us suppose that for 00:05:51.85000:05:51.860 whatever reason the boiler flame was 00:05:53.82900:05:53.839 momentarily lost and an abnormally large 00:05:56.32000:05:56.330 quantity of fuel entered the boiler the 00:05:58.86000:05:58.870 operator responded properly by cutting 00:06:01.26900:06:01.279 fuel flow to the burners and increasing 00:06:03.18900:06:03.199 air flow to purge the boiler of all 00:06:05.07900:06:05.089 combustibles but let us also suppose 00:06:08.74000:06:08.750 that a portion of the combustibles 00:06:10.57000:06:10.580 accumulated in this dead spot around the 00:06:12.93900:06:12.949 gas bypass damper and were not purged 00:06:15.67000:06:15.680 from the boiler when purging was 00:06:19.54000:06:19.550 complete the operator followed the 00:06:21.76000:06:21.770 proper procedures for reestablishing the 00:06:23.46900:06:23.479 boiler flame but remember combustibles 00:06:25.95900:06:25.969 remained in this dead spot in the 00:06:27.30900:06:27.319 ductwork the boiler continues operating 00:06:29.74000:06:29.750 for some time with nothing unusual 00:06:31.99000:06:32.000 happening however let's suppose further 00:06:34.62900:06:34.639 that the operator needs to adjust 00:06:36.12900:06:36.139 superheater outlet temperature and opens 00:06:38.70900:06:38.719 the bypass damper 00:06:40.14900:06:40.159 the combustibles that have accumulated 00:06:41.79900:06:41.809 in the ductwork are no longer in a dead 00:06:43.98900:06:43.999 spot they are immediately reintroduced 00:06:46.60000:06:46.610 into the flow path of flue gas going to 00:06:48.85000:06:48.860 the economizer or due to some back 00:06:51.21900:06:51.229 pressure around the damper are forced 00:06:53.01900:06:53.029 back into the furnace area of the boiler 00:06:56.00900:06:56.019 the result could be sudden and 00:06:58.57000:06:58.580 uncontrolled combustion in other words 00:07:00.99900:07:01.009 an explosion in either the furnace area 00:07:03.39900:07:03.409 the ductwork or near the economizer now 00:07:07.14900:07:07.159 what we've just done is a lot of 00:07:08.67900:07:08.689 supposing but let me stress that boiler 00:07:10.86900:07:10.879 explosions occur under uncommon 00:07:12.93900:07:12.949 conditions if it is possible to make up 00:07:16.11900:07:16.129 a situation where an explosion could 00:07:17.73900:07:17.749 possibly happen it is also possible that 00:07:20.29000:07:20.300 under rare and unusual circumstances 00:07:22.68900:07:22.699 those conditions can exist and cause an 00:07:25.41900:07:25.429 explosion let me again stress that 00:07:27.99900:07:28.009 boiler explosions are uncommon 00:07:29.94900:07:29.959 occurrences by following your plants 00:07:32.07900:07:32.089 operating procedures the chances of them 00:07:34.32900:07:34.339 happening to you are extremely slim what 00:07:38.46900:07:38.479 you can do to keep explosive situations 00:07:40.17900:07:40.189 from developing is to carefully monitor 00:07:42.18900:07:42.199 your boiler flame and to make sure that 00:07:44.35000:07:44.360 combustion is taking place properly you 00:07:47.49900:07:47.509 should also keep a careful watch on the 00:07:49.02900:07:49.039 fuel flow and air flow to the burners to 00:07:51.10000:07:51.110 make certain that both are being 00:07:52.92900:07:52.939 supplied in proper proportions finally 00:07:56.82900:07:56.839 since the boiler explosions which have 00:07:58.65900:07:58.669 occurred in the past have often been 00:08:00.27900:08:00.289 fostered by a loss of boiler flame 00:08:02.18900:08:02.199 knowing the procedures for dealing with 00:08:04.56900:08:04.579 this situation and the proper procedures 00:08:06.45900:08:06.469 for purging your boiler will prevent 00:08:08.64900:08:08.659 boiler explosions in the next part of 00:08:11.82900:08:11.839 this program we look at some situations 00:08:13.54000:08:13.550 that can lead to the loss of a boiler 00:08:15.51900:08:15.529 flame and the typical procedures for 00:08:17.88900:08:17.899 returning the boiler to normal operation 00:08:19.79900:08:19.809 for now read over the material in your 00:08:22.26900:08:22.279 text on the cause of boiler explosions 00:08:24.10000:08:24.110 and answer the questions did you need 00:08:26.10900:08:26.119 any help with this material ask your 00:08:27.93900:08:27.949 instructor before going on 00:08:30.46000:08:30.470
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