theoretical practice - university of ljubljanalab.fs.uni-lj.si/kes/erasmus/2012energysystems... ·...

Aškerčeva 6 SI-1000 Ljubljana, Slovenia tel.: +386 1 4771200 fax: +386 1 2518567 http://www.fs.uni-lj.si e-mail: [email protected]

University of Ljubljana

Fakulty of mechanical engineering

Department of Energy Engineering

Laboratory for Heat and Power

Energy Systems

Theoretical practice

Program: Erasmus

Authors: Mitja Mori

Mihael Sekavčnik

Ljubljana, 20. august 2010

University in Ljubljana

Faculty of mechanical engineering Askerceva 6, Ljubljana

THERMAL TURBOMACHINERY

Theoretical exercises 2

CONTENTS

1. ENERGY, MASS BALANCES AND REGENERATIVE HEATING OF FEED WATER 3

2. ENERGETIC SYSTEM 5

3. NUCLEAR POWER PLANT 6

4. GAS TURBINE POWER PLANT 8

5. STEAM SUPERHEATING 9

6. NUMERICAL MODELING OF STEAM SUPERHEATING SYSTEM IN IPSEPRO CODE 12





1. Energy, mass balances and regenerative heating of feed

water

On the basis of power plant scheme, given below, determine:

Saving in boiler when regenerative heating is in use, compared to a plant with regenerative

heating disabled;

Difference in power plant efficiency for both cases.

Note: When calculating saving, consider cases with constant turbine power.

Assumptions:

1. Pressure drop in boiler is 10 % of pressure

at inflow.

2. Pressure drops in heat exchangers (feed

water side) are approximately 3 % of

pressure at inflow (0,1 bar).

3. Feed water temperature at regenerative

heater outflow is 1,, TTT isofw , where

T1 = 5 K.

condensationcondensate cooling

feedwater heating

distance

tem

per

ature

Tfw,i

Tc,o

Ts,i

Tfw,o

4. Temperature of condensate from LPRH is 2,, TTT ifwoc , where T2 = 6 K.

7

1

5

2

4

3

12

6 11

LPRH 1LPRH 2

10

8

9

closed

Figure: Schematical image of steam power plant with 2 low pressure regenerative heaters





p T m x h

point bar °C kg/s – kJ/kg

1 200 550 1

2 0,05 2160

3

4 3 33

5

6

7 132

8 3 0,943

9 0,6 0,897

10

11

12





2. Energetic system

Discussing: Energy- and mass-balances, power at the turbine shaft, fuel mass flow, internal

pump power.

On the picture the high pressure and middle pressure part of energetic system is shown. On the

basis of data, shown on the schema calculate following:

a) Calculate steam mass flow and

b) turbine power on the turbine shaft, if internal efficiency of the middle turbine part is

known (0,85).

c) On the basis of boiler heat power calculate fuel mass flow, if boiler efficiency is known

( 9.0K ) and the caloric value of the fuel also known ( MJ/kg 10B ).

d) Additionally calculate the steam mass flow for degasification (point 5) and

e) internal feed water pump power.

8

1

6

5

2

10

7

9

3

4

60500

20350

1.390

80175

310

1.25

82107

20200





3. Nuclear power plant

Given below is a simplified diagram of the Krško nuclear power plant.

1) Draw the upper part of the process in a h-s diagram;

2) Determine steam quality before moisture separator reheater using three different methods;

3) Calculate high pressure turbine and low pressure turbine efficiency, if steam quality before

water drain is x22 = 0,94;

4) Calculate thermal efficiency and estimate complete efficiency of the secondary circuit;

5) Estimate heating surfaces in a two-stage steam reheater, if the overall heat transfer

coefficient is k = 2,5 kW/m2K.

10

1 2

43

6

5

22odv

13

11

20

7

8

21

12

16 17 18 19

1514

9

Schematic view of nuclear power plant





Table: Properties of water/steam in specific points on the scheme

p T x m h

točka bar °C - kg/s kJ/kg

1 65,4 281,3 1 1030 2778,4

2 62,1 277,8 983 2778,4

3 61,5 277,2 47 2778,4

4 8,7 260,5 677,7 2970,7

5 0,053 33,9 561 2405,3

6 17,4 32,9 139,5

7 15,3 171,3 725,3

8 15,3 171,1 724,3

9 77,7 172,2 732,5

10 77,6 220,2 946,0

11 26,9 227,9 104 2665,0

12 9 175,4 64 2509,1

13 60,9 0 47 1218,8

14 8,2 0 101,3 742,7

15 26,8 0 36 979,4

16 3 156 34 2774,1

17 1,2 29 2632,0

18 0,474 14 2528,0

19 0,275 67 2493,0

20 0,268 39,4 165,1

21 15,3 170,7 722,4

22 0,162 0,94 10 232,6





4. Gas turbine power plant

Calculate electrical power and efficiency for the following 5 power plants:

a. Pressure at turbine entry is 5 bar and temperature at turbine entry is 750 °C.

b. Pressure at turbine entry is 5 bar and temperature at turbine entry is 1200 °C.

c. Pressure at turbine entry is 12 bar and temperature at turbine entry is 1200 °C.

d. Pressure at turbine entry is 12 bar and temperature at turbine entry is 1200 °C. Degree of

regeneration is 0,8.

e. Pressure at turbine entry is 12 bar and temperature at turbine entry is 1200 °C. Thermal

efficiency of steam power plant, attached to gas turbine exhaust, is 0,35. Flue gases are

cooled in heat recovery steam generator (HRSG) to a temperature of 120 °C.

Ambient pressure is 1 bar and ambient temperature is 20 °C, compressor efficiency is 0,85, gas

turbine efficiency is 0,87, mechanical efficiency of compressor is 0,97, mechanical efficiency of

gas turbine is 0,98, mechanical efficiency of steam turbine is 0,99 and generator efficiency is

0,98. Pressure drops are: 0,2 bar at compressor entry, 1 bar in combustion chamber, 0,1 bar at

gas turbine exhaust to ambient, 0,2 bar in regenerative air heater (flue gas side and air side) and

0,3 bar in HRSG. Fuel mass flow can be neglected. For determination of air and flue gas

enthalpies use h-s or T-s diagram for dry air.

5

1 14 4

332 2

6

Power plant a, b in c Power plant d

7

14

32

Power plant e





5. Steam superheating

Calculate the efficiency of thermodynamic cycle in optimum working conditions for:

a) the system without repeated steam superheating;

b) the system with one degree repeated steam superheating.

Processes should be represented in T – s diagram. For case b) calculate the optimal temperature

before repeated superheating (T2). The expansion thru turbine is assumed to be isentropic. The

pressure drop in the boiler with superheater is 30 bar and 2 bar in next superheater.

2

77 88

3

11

6b6a

Picture 1: Scheme of the thermodynamic cycle without repeated superheating and the system

with one degree repeated steam superheating.

p T m h

point bar °C kg/s kJ/kg

1 190 540

2

3 540

6a 0,05

6b 0,05

7

8 34

With repeated steam superheating we achieve increase in the thermodynamic efficiency of the

cycle. With regenerative heating of feeding water we increase the average temperature level of

the fluid during heat addition in the region of low temperatures, with repeated superheating we

increase the average temperature level of the fluid during heat addition in the region of high

temperatures.





The connection between the average temperature level of the fluid during heat addition and

efficiency of steam thermodynamic cycle goes out from the steam cycle carnotization.

Carnotization: To the steam cycle the Carnot cycle is ascribed with the same work potential.

That means (picture 2) that shaded surface inside steam cycle (7-8-1-6) that represents the

difference between added and taken heat (gain work) is the same like by the ascribed Carnot

cycle (7-8c-1c-6).

T

s

1

678

8c1c

T

T

m,do

od

Picture 2: Carnotization of the steam cycle.

If the surfaces are the same it means that the average temperature level of the fluid during heat

addition in the case of Carnot cycle is the same value like in the case of steam cycle (Tm,do). The

average temperature level of the fluid during heat addition (Picture 2) is calculated with

81

81,

ss

hhT dom

It is well known that the Carnot efficiency is:

do

odC

T

T 1

So the efficiency of Carnot cycle can be inceased with increasing of the average temperature

level of the fluid during heat addition. From comparison with steam cycle it follows that the

efficiency of steam cycle can be increased also with increasing the average temperature level of

the fluid during heat addition.

Both processes can be shown in T – s diagram. The point 2 is not known that’s why the cycle

with one degree repeated steam superheating in this point cannot be sketched.





0

100

200

300

400

500

0 1 2 3 4 5 6 7 8 9

T

[°C]

7

8

1

2

3

6a 6b

Picture 3: T – s diagram for the cycle without one degree repeated steam superheating

(7-8-1-6a) and the cycle with one degree repeated steam superheating (7-8-1-2-3-6b).





6. Numerical Modeling of steam superheating system in

IPSEPro code

PREPARATIONS

1. Check if IPSE is installed on the computer and elements library (App lib) is updated and

connection with MS Excel is assured.

2. Before you start you should have hardware license key (LPT port).

3. In MS windows you should set dot instead comma (Control Panel -> Regional and

Language Options).

EXCERCISE:

o Start the IPSEpro-PSE program.

o In menu Options -> Set Page set format to A5, landscape.

o In menu Options -> Set Scale set the Scaling Factor to 1.5.

The template could be prepared, where these settings are already set to appropriate values.

Setting of the working fluid

In menu Objects -> New Global Object set the working fluid. There are 3 possibilities:

ambient (for defining the environment)

composition (for defining the structure of the working fluid)

fuel composition (for defining the structure of the fuel)

o Chose composition and write water in the box.

o The structure of fluid is defined in Objects -> Edit Global Object.

o We chose water (composition).

o The basic compounds are given. We define working fluid with prescribing mass ratios for all

compounds. In our case we are dealing with water, so by WATER we chose estimate and set

the value to 1, at all other compounds we chose set and set value to 0. If we chose set by the

water is the system of equations over defined.

The demonstration of the graphical interface

o In library chose source and place it on the right side on the sheet for modeling. On the right

side of the source place sink. With source and sink we define inflow and outflow of the

working fluid. Empty green square represents the outflow connector, full green square

represents the inflow connector.

o Connect source and sink with click from one in other green square. The connection (stream)

represents the fluid path.

o Double-click the connection and under composition chose water.





o Thermodynamical state is defined with two independent variables (pressure, temperature) and

the flow is defined with mass flow.

o Data that we chose to define should be set to set and the values should be inserted, all other

data will be calculated from others terms (mass and energy balance). In our trivial case set the

pressure to 1 bar, temperature to 20 °C and mass flow to 1 kg/s.

o Click the button for calculating and we get the results in the form of crosses.

o In menu Objects chose Add Reference Cross in order to get the legend.

With right-click on the elements we get the calculated parameters.

Making of the scheme and modeling (Appendix 1)

o At the left side we add boiler.

o Delete the existing connection and connect the boiler between source and sink and define

water as composition.

o Regarding to the exercise, define the pressure after boiler 190 bar and temperature 540 °C.

Before boiler the temperature is 34 °C. Mass flow should be set to 100 kg/s.

o The efficiency of the boiler is 1 and pressure losses thru boiler 30 bar.

o Click the button for calculation.

o Add the first turbine and set the mechanical efficiency to 1 and internal efficiency to 1.


o We get error. We can see in the protocol that we have 40 equations and 41 parameters. The

system is not well defined. We forgot to define state after turbine. For the moment we set that

missing state to 100 bar.


o We proceed by adding another boiler and turbine.

o Settings:

pressure drop in superheater 2 bar,

temperature after superheater 540 °C,

pressure after turbine 0,05 bar,

mechanical and internal turbine efficiency 1.

o Add the generator and connect it with turbines.


o We proceed with the condensator: undercooling 0.001, both pressure drops 0.0001.


o Add the pump and numerical connector. The pump mechanical efficiency is 1, internal

efficiency is 0.8.


o We can find out that we have 1 equation too many. If we analyze the state around the pump,

we can find out that the temperature after the pump should be let loose (with internal

efficiency, defined state before pump and pressure after pump, the temperature after pump is





well defined). If we like to have 34 °C after the pump, we should change the internal

efficiency of the pump. Instead 0.8 we set it to 0.9.

o Because the troubles with convergence occurs, we use option Import Estimates in menu

Calculation.

o The scheme is now finished; we should just define state before superheating with temperature

instead with pressure.

The connection with the Excel

o For simplification the particular stream in the program should have the same number as in

the scheme in Appendix 1.

o We run Excel and open template PSEExcel. If the template is not shown, we usually find it in

"C:\Program Files\Microsoft Office\Templates\PSExcel.xlt".

o We set font to 16pt.

o In Excel we create the simple table. In the first column the state is marked in second the

enthalpy will be written.

o With the button Insert Item the enthalpies are inserted.

o In specific cell the equation for cycle efficiency is written:

2381

786321,

hhhh

hhhhhh

Q

PP b

do

čtbkp

o In specific cell the temperature T2 is written and is set as initial value with Add Item to

Sendlist. Insert value and click Calculate button and observe how cycle efficiency is changed.

The automatical variation of the parameter

o In menu DDE chose Create Variation.

o Set to one-parameter variation and T2 as parameter.

o Initial value should be 200, end 500. The step 10 and max. steps 100.

o As required results we set all enthalpies and entropies, that we can calculate the middle

temperature of the heat transfer to the water.

o In IPSE should be done the calculation 200 °C, that we don’t have any problems with

convergence.

o By the column where variation is, add one column for the middle temperature of heat transfer

to the water defined with: 2381

2381,

ssss

hhhhT dom

and one column for cycle efficiency.

o Search the maximum of the middle temperature of heat transfer to the water and we can find

out that it coincide with maximum value of the cycle efficiency.

Draw the diagram Tm (T2).





APPENDIX 1: The scheme that should be modeled

2

77 88

3

11

6b6a

theoretical practice - university of ljubljanalab.fs.uni-lj.si/kes/erasmus/2012energysystems... ·...

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