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Understanding Boiler Pressure Controls - Boiling Point
WEBVTT Kind: captions Language: en
00:00:00.030 one thing I've learned is to get people 00:00:01.40000:00:01.410 a lot smarter than me to talk about 00:00:03.40900:00:03.419 things that I have no clue about well 00:00:06.34900:00:06.359 dude wolf was so popular last week who 00:00:08.60000:00:08.610 thought that we would do something with 00:00:10.00900:00:10.019 him again so this week we're going to 00:00:11.74900:00:11.759 talk about Honeywell pressure trolls 00:00:13.37000:00:13.380 today on the boiling point 00:00:27.76000:00:27.770 pressure controls like this are common 00:00:30.08000:00:30.090 sight on a firetube boiler but often 00:00:33.71000:00:33.720 times it's confusing why we have for 00:00:36.23000:00:36.240 which one does what and having them set 00:00:39.80000:00:39.810 properly is an important part of making 00:00:41.78000:00:41.790 your boiler operate correctly so let's 00:00:44.29900:00:44.309 take a look at these controls and 00:00:45.91000:00:45.920 examine the use the purpose and the 00:00:49.64000:00:49.650 proper setting for each of them like any 00:00:52.39000:00:52.400 important control on a boiler water 00:00:55.40000:00:55.410 level control pressure control we 00:00:57.95000:00:57.960 typically have more than one instrument 00:01:00.62000:01:00.630 doing that job that's just to back up 00:01:02.69000:01:02.700 for safety purposes so with four 00:01:05.57000:01:05.580 controls like this two of them are 00:01:07.76000:01:07.770 dedicated to shutting the boiler off in 00:01:09.85900:01:09.869 the case of high pressure the first one 00:01:13.21900:01:13.229 to normally shut the boiler down on an 00:01:15.68000:01:15.690 increase of pressure is the operating 00:01:17.78000:01:17.790 control the operating control will break 00:01:21.53000:01:21.540 open the limit circuit of the boiler and 00:01:24.38000:01:24.390 turn the burner off when pressure hits 00:01:26.90000:01:26.910 its setpoint 00:01:28.18000:01:28.190 currently this one is set for 60 psi and 00:01:31.76000:01:31.770 we can watch as the pressure increases 00:01:34.77900:01:34.789 we can see that mercury bulb trip once 00:01:38.93000:01:38.940 the boilers firing if there's 00:01:40.46000:01:40.470 insufficient load for the boiler to stay 00:01:42.49900:01:42.509 on that pressure will increase and it 00:01:46.58000:01:46.590 will trip and open up that circuit 00:01:49.24000:01:49.250 oftentimes this operating control is 00:01:51.77000:01:51.780 misunderstood because the name implies 00:01:54.10900:01:54.119 that it determines where the boiler 00:01:55.91000:01:55.920 operates at pressure wise but in fact it 00:01:59.18000:01:59.190 really cuts the boiler off at a certain 00:02:01.43000:02:01.440 limit so typically our operating 00:02:03.68000:02:03.690 pressure control should be set and what 00:02:06.38000:02:06.390 we would want to be the highest pressure 00:02:08.27000:02:08.280 that we want to see on the boiler at any 00:02:10.58000:02:10.590 time so if we operated normally at 120 00:02:13.85000:02:13.860 psi we may want to shut the boiler off 00:02:16.82000:02:16.830 at 140 not because we're trying to hold 00:02:19.37000:02:19.380 140 but because we want the boiler to 00:02:21.74000:02:21.750 stay on as long as possible so that if 00:02:24.08000:02:24.090 the load resumes we don't have to go 00:02:26.44900:02:26.459 through the whole sequence of operation 00:02:28.16000:02:28.170 and start it back up our high steam 00:02:32.27000:02:32.280 pressure limit or high limit is it has 00:02:35.99000:02:36.000 the same function in that it opens the 00:02:37.88000:02:37.890 operating limit of the boiler on 00:02:39.86000:02:39.870 to rise but it's also manual reset so 00:02:43.13000:02:43.140 that if our operating limit fails to 00:02:45.22900:02:45.239 function and we trip on our high limit 00:02:47.75000:02:47.760 we get an indication because we have to 00:02:50.39000:02:50.400 go out there and reset it manually that 00:02:52.39900:02:52.409 something's wrong with our operating 00:02:54.05000:02:54.060 pressure control or that they're set too 00:02:56.11900:02:56.129 close together so we can watch that trip 00:02:59.19900:02:59.209 so as the pressure increases past its 00:03:02.33000:03:02.340 set point it's going to break and that's 00:03:10.30900:03:10.319 going to shut down the boiler even if 00:03:12.80000:03:12.810 the pressure drops on the boiler it's 00:03:14.80900:03:14.819 not going to reset itself it's going to 00:03:18.74000:03:18.750 require a manual reset many original old 00:03:22.97000:03:22.980 controls on earlier generations of 00:03:26.08900:03:26.099 boilers will have these mercury switches 00:03:27.97900:03:27.989 the benefit of a mercury switch is it 00:03:30.28900:03:30.299 gives you a visual indication of whether 00:03:32.44900:03:32.459 the switch is made which is very 00:03:34.46000:03:34.470 convenient but unfortunately they have 00:03:36.47000:03:36.480 mercury in them which is something that 00:03:38.33000:03:38.340 they're frowning on in many facilities 00:03:41.66000:03:41.670 so the replacement for that is a micro 00:03:45.40900:03:45.419 switch style control what we lose is an 00:03:48.37900:03:48.389 actual visual indication of its trip 00:03:52.09900:03:52.109 point and we're going to have to rely on 00:03:54.12900:03:54.139 listening for the boiler to shut down 00:03:56.31900:03:56.329 etc in order to set that up 00:03:59.47900:03:59.489 so these two controls serve the purpose 00:04:02.56900:04:02.579 of starting and stopping the boiler this 00:04:04.69900:04:04.709 one routinely but this one only in the 00:04:06.77000:04:06.780 event that the operating limit doesn't 00:04:08.44900:04:08.459 work the firing the firing rate control 00:04:11.90000:04:11.910 is actually the tool we use to try to 00:04:13.84900:04:13.859 maintain the pressure on the boiler that 00:04:16.09900:04:16.109 we desire when there's a load on the 00:04:17.81000:04:17.820 boiler it actually uses a three wire 00:04:20.96000:04:20.970 configuration commonly referred to a 00:04:23.51000:04:23.520 series ninety has a slide wire 00:04:25.90000:04:25.910 potentiometer in there which gives 00:04:27.89000:04:27.900 information to the firing rate motor to 00:04:30.68000:04:30.690 position the burner to match the load it 00:04:33.08000:04:33.090 has a set point and the set point on 00:04:35.42000:04:35.430 your firing rate controls basically the 00:04:37.27900:04:37.289 point which it will tell the burner to 00:04:39.50000:04:39.510 run at high fire the differential on 00:04:43.40000:04:43.410 this controls referred to as additive 00:04:45.80000:04:45.810 because whatever that differential is 5 00:04:48.92000:04:48.930 pounds 10 pounds 15 pounds that above 00:04:52.13000:04:52.140 the 00:04:53.11000:04:53.120 point is where you're going to be in low 00:04:54.58000:04:54.590 fire so the firing rate control if it's 00:04:58.00000:04:58.010 not properly coordinated with the 00:04:59.77000:04:59.780 operating limit you could have the 00:05:01.93000:05:01.940 boiler tripping on pressure before 00:05:04.27000:05:04.280 getting down to low fire and we call 00:05:06.31000:05:06.320 that short cycling so we always want our 00:05:09.04000:05:09.050 firing rate control set so that the 00:05:11.23000:05:11.240 burners at its minimum input before our 00:05:14.56000:05:14.570 operating limit trips and that's why we 00:05:17.29000:05:17.300 don't set the operating limit at where 00:05:19.39000:05:19.400 we want the fire the pressure to be we 00:05:22.75000:05:22.760 set it where it's at the highest we 00:05:25.81000:05:25.820 would really want to see on the system 00:05:27.76000:05:27.770 an additional control that we often see 00:05:31.15000:05:31.160 on a boiler is a low fire hold and the 00:05:33.79000:05:33.800 point of a low fire hold is basically to 00:05:36.64000:05:36.650 get a certain amount of pressure on the 00:05:39.01000:05:39.020 boiler before allowing the boiler to 00:05:41.59000:05:41.600 come out of the low fire position and 00:05:43.81000:05:43.820 that's important because if we take a 00:05:45.55000:05:45.560 cold boiler and we put full fire into 00:05:49.54000:05:49.550 that unit we're going to thermally shock 00:05:51.49000:05:51.500 it we're going to stress the tubes and 00:05:53.50000:05:53.510 refractory so this is sort of an 00:05:55.65900:05:55.669 insurance policy to prevent us from 00:05:58.17000:05:58.180 firing the boiler hard before we 00:06:00.40000:06:00.410 actually have steam in the boiler so 00:06:03.40000:06:03.410 basically a summary on where these are 00:06:05.50000:06:05.510 set generally are our high steam limit 00:06:08.56000:06:08.570 is going to be set below our relief 00:06:10.54000:06:10.550 valve setting on our boiler and 00:06:12.61000:06:12.620 definitely below the maximum allowable 00:06:14.52900:06:14.539 working pressure of the boiler because 00:06:16.57000:06:16.580 its job is to prevent us from putting 00:06:19.27000:06:19.280 excess pressure on the boiler our 00:06:21.36000:06:21.370 operating limit we're going to put at 00:06:23.77000:06:23.780 the highest pressure we would normally 00:06:25.62900:06:25.639 want to see on our system so we may 00:06:27.79000:06:27.800 operate when we have a load at 110 125 00:06:32.08000:06:32.090 psi something appropriate for your plant 00:06:34.93000:06:34.940 but at some point we're going to want to 00:06:36.93900:06:36.949 turn the burner off so we'll put this at 00:06:40.08900:06:40.099 the highest pressure that we care to see 00:06:42.27900:06:42.289 on the system our firing rate control is 00:06:45.52000:06:45.530 the workhorse 00:06:46.39000:06:46.400 it's what's actually maintaining a 00:06:48.30000:06:48.310 specific pressure on the boiler at any 00:06:51.18900:06:51.199 given load and so this is the go-to for 00:06:55.33000:06:55.340 adjusting our target pressure if we want 00:06:58.06000:06:58.070 five more pounds on the boiler when it's 00:07:00.31000:07:00.320 running we're going to adjust our firing 00:07:02.50000:07:02.510 rate control and then we're going to 00:07:04.30000:07:04.310 adjust our operating control so that we 00:07:05.98000:07:05.990 don't shut 00:07:06.49000:07:06.500 down before we get too low fire on the 00:07:10.12000:07:10.130 firing rate control because that'll be 00:07:11.47000:07:11.480 short cycling the low fire hold on a low 00:07:15.52000:07:15.530 pressure boiler that might be set as low 00:07:17.47000:07:17.480 as two or three pounds on a water-tube 00:07:20.11000:07:20.120 boilers on to come out of low fire until 00:07:23.59000:07:23.600 we've attained a hundred psi to develop 00:07:26.44000:07:26.450 proper circulation on the boiler this is 00:07:29.14000:07:29.150 not a substitute for attending the 00:07:32.80000:07:32.810 boiler and warming it up slowly 00:07:34.60000:07:34.610 and properly it's simply there is a 00:07:36.58000:07:36.590 safeguard in case the boiler is 00:07:39.15900:07:39.169 unattended for some reason while it's 00:07:40.99000:07:41.000 warming up we are pumped that spring is 00:07:44.05000:07:44.060 finally here and it's not so stinking 00:07:46.18000:07:46.190 cold lots of equipment out getting 00:07:48.13000:07:48.140 maintenance ready to go to the next 00:07:49.45000:07:49.460 jobsite Jude Wolfe is always great to 00:07:52.30000:07:52.310 have in fact the last video that we did 00:07:54.75000:07:54.760 2,000 views in just a week and a half or 00:07:57.70000:07:57.710 so so make sure that you check him out 00:07:59.62000:07:59.630 on a lot of our other videos also on 00:08:01.96000:08:01.970 that boiler university video right here 00:08:04.45000:08:04.460 and make sure you check all of our 00:08:06.43000:08:06.440 social media right over here and we'll 00:08:09.46000:08:09.470 see you next time on the boiling point 00:08:29.74000:08:29.750 you
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