Question 2 a steam power plant that operates on an ideal re...

Name: question 2 a steam power plant that operates on an ideal re heat regenerative rankine cycle has an open feed water heater and a closed feed water heater steam enters the turbine at 10 mpa an 82575
Uploaded: 2021-03-15T18:30:38-08:00
Duration: 17 min 35 s
Channel: Eric Mockensturm
Description: question 2 a steam power plant that operates on an ideal re heat regenerative rankine cycle has an open feed water heater and a closed feed water heater steam enters the turbine at 10 mpa an 82575

QUESTION 2 A steam power plant that operates on an ideal re-heat regenerative Rankine cycle; has an open feed water heater and a closed feed water heater. Steam enters the turbine at 10 MPa and 500\deg C is condensed in the condenser at 10 kPa . Some steam is extracted from the high-pressure turbine at 3 MPa for a closed feed water heater and the remaining steam is reheated at the same pressure to 500\deg C. The extracted steam travels through the throttling device into the condenser and then runs through the pump into the open feed water heater to the boiler. And a certain amount of steam is extracted from the lowpressure turbine at a pressure of 200 kPa into the open feed water heater. Consider the work done by the pumps and determine: - 2.1. Plot the T-s diagram inserting all the relevant information. 2.1. the fraction of steam extracted from the turbines. 2.2. the cycle efficiency.

Transcript

00:01 We have another kind of crazy reheat, regenerative with feedwater heater system here.

00:13 This mess here.

00:16 So we're kind of, let me go through the system.

00:19 It's just, it's illustrated in the book, so, but you know, stuff going through the boiler, into the high pressure turbine, come out of the high pressure and driven being reheated in the boiler, going to low pressure turbine.

00:34 Then we have two bleed lines, one going to, the higher pressure one going to a closed feed water heater, the lower pressure one going to open feed water heater, and then the outlet going to the condenser.

00:47 Now, the first pump pumps the pressure back up so that it is the same as at 12, and then it mixes with stuff coming out of, that went through the closed feed water heater and had its pressure dropped.

01:07 So the 2, 7 and 12 all have the same pressure, and then likewise 3 has the same pressure.

01:15 So everything is mixing in here.

01:18 And then we get pump two pumps everything back up to the boiler pressure.

01:23 So the boiler pressure is 15 megapascals.

01:27 Coming out of the high pressure turbine is 1 megapascal, which is what's going into the low pressure turbine.

01:35 The first bleed is at 600 kioskles.

01:38 The second is at 200 kilopascals, and then the condenser operates at 5 kilopascals.

01:46 We have a fraction of y coming off at the first bleed and a fraction c coming off at the second.

01:56 Let's see here.

01:59 So again, our ts diagram is kind of a mess, but again, we can see all of these states, the reheat here, the bleed, the bleed, the feed water heater, the, let's see here, this would be the, from six to seven.

02:17 This is from the expansion valve, get it from this pressure down to this pressure, and then seven, seven, two, and twelve.

02:32 So seven, two, and twelve, all meet up together to go into.

02:39 Come out at 3.

02:42 And it's pumped up.

02:44 And then through the boiler again.

02:46 And so that is our cycle.

02:49 So let's see here.

02:51 We want to analyze.

02:53 We can look at the pump, this low pressure pump.

02:57 So we get us entropy, specific entropy, specific volume.

03:02 We know the pressure change.

03:04 So we can get the power, the specific work into the pump here.

03:08 And that means we can get the entropy coming out of the pump.

03:10 Pump, specific entropy that is.

03:14 Now at 3 here, we're told we have a saturated liquid that is at 200 kilopascals, so we can get the specific entropy -specific volume there.

03:27 And likewise, we know the pressure change across this pump, so we can get the specific work being put into this pump, and also the entropy -specific entropy coming out.

03:42 Now, now across this expansion valve, we have constant enthalpy, assuming there's no heat transfer there, and obviously no mechanical work being done or electrical work.

03:57 So then we have those two things are equal, and we know that six is a saturated liquid.

04:08 So seven, we expand it to a lower pressure, so we wind up with a two phase.

04:15 We get some, basically some boiling in here because of the pressure drop.

04:21 And then we go into here.

04:23 And so we can also get the specific volume at six because we know the saturated liquid and we know the pressure.

04:31 Now, why we need that is if we take a look at this feed water heater here, now we're going to assume that the temperature coming out here is the same as the temperature coming out there.

04:42 So that we basically had perfect heat exchange here.

04:45 Now, the entrop, so we have, let's see here, we have, this is all saturated liquid to be just basically, this is all, you know, or saturated or subcritical liquid.

05:04 So that's one thing to note.

05:06 Everything through here is basically, well, not, not coming in here, but anyway.

05:14 So we can look at this system.

05:16 Here where we have what's coming out here, right, and then it's going through here, and then getting, and then there's pressure dropped and then is increased, right? so we have a difference in pressure here, but the specific volume is basically the same.

05:41 So what happens is in this loop here, basically from here to here, we have a pretty much, we have an incompressible fluid.

05:54 So, and again, we can get that specific volume.

06:00 So the entropy here is the entropy here, plus the work that was done in getting the pressure, the difference in the pressure.

06:10 So that gives us the, the entropy at five going into the boiler.

06:19 All right um so let's see here um we have so basically we're doing a control volume kind of i don't even know how to draw it um cut here cut here and then um everything kind of out here is that what we're doing is that what i'm thinking yeah, yeah.

07:03 It's basically just a weird control volume.

07:06 We're just looking at the flow through here.

07:08 There's a pressure difference in here.

07:10 Specific volume is the same.

07:18 And so we're basically just looking at how this stuff coming out here gets back up to here.

07:26 So it has some enthalpy here.

07:28 And then we put some mechanical work into it because the pressure difference is here.

07:32 We get some.

07:33 And we lose some pressure here, but we gain some pressure here.

07:38 So the thing is, is that it's a saturated liquid here.

07:42 It's also pretty much a saturated liquid here at the same temperature, roughly.

07:50 So it is, let's see here.

07:59 It's not a saturated liquid here, obviously.

08:03 But once it mixes here, it is.

08:05 And so we have just a, he puts up.

08:07 Work we put we put some out put some in and so the net between here and here is the difference in the and the pressure at four is the same as the pressure at five so that's kind of this one here is the same as four so that that's what this equation came from basically looking at at the fluid that's coming out of here and then coming back in in this loop so it's a little weird but uh i hope i hope i hope i explain that.

08:42 Okay.

08:43 Again, coming, let's see here.

08:51 Yeah, it's, um, so we have y coming through here, um, why coming into here.

09:00 Here we have total.

09:03 Um, yeah, but essentially we're just, we're adding, we're adding, we're increasing the, the entropy by adding, um, by adding, um, by adding some by adding pressure to what came out here.

09:24 You can almost think of it as kind of a little internal pump that went from here to here, kind of bypassing that...

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