Energy Systems. Program: Erasmus

Transcription

1 University of Ljubljana Fakulty of mechanical engineering Aškerčeva 6 SI-000 Ljubljana, Slovenia tel.: fax: dekanat@fs.uni-lj.si Department of Energy Engineering Laboratory for Heat and Power Energy Systems Theoretical practice Program: Erasmus Authors: Mitja Mori Mihael Sekavčnik Ljubljana, 0. august 00

2 Theoretical exercises CONTENTS. ENERGY, MASS BALANCES AND REGENERATIVE HEATING OF FEED WATER. ENERGETIC SYSTEM 5. NUCLEAR POWER PLANT 6 4. GAS TURBINE POWER PLANT 5. STEAM SUPERHEATING 9 6. NUMERICAL MODELING OF STEAM SUPERHEATING SYSTEM IN IPSEPRO CODE

3 temperature University in Ljubljana Theoretical exercises. 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:. Pressure drop in boiler is 0 % of pressure at inflow.. Pressure drops in heat exchangers (feed water side) are approximately % of pressure at inflow (0, bar).. Feed water temperature at regenerative heater outflow is Tfw, o Ts, i T, where T = 5 K. T s,i T fw,o condensation feedwater heating distance 4. Temperature of condensate from LPRH istc, o Tfw, i T, where T = 6 K. condensate cooling T c,o T fw,i 9 closed LPRH LPRH Figure: Schematical image of steam power plant with low pressure regenerative heaters

4 Theoretical exercises 4 p T m x h point bar C kg/s kj/kg , ,94 9 0,6 0,9 0

5 Theoretical exercises 5. 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 (0,5). c) On the basis of boiler heat power calculate fuel mass flow, if boiler efficiency is known ( K 0. 9) and the caloric value of the fuel also known ( B 0 MJ/kg ). d) Additionally calculate the steam mass flow for degasification (point 5) and e) internal feed water pump power

6 Theoretical exercises 6. Nuclear power plant Given below is a simplified diagram of the Krško nuclear power plant. ) Draw the upper part of the process in a h-s diagram; ) Determine steam quality before moisture separator reheater using three different methods; ) Calculate high pressure turbine and low pressure turbine efficiency, if steam quality before water drain is x = 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 =,5 kw/m K odv Schematic view of nuclear power plant

7 Theoretical exercises Table: Properties of water/steam in specific points on the scheme p T x m h točka bar C - kg/s kj/kg 65,4, 00,4 6,, 9,4 6,5, 4,4 4, 60,5 6, 90, 5 0,05, , 6,4,9 9,5 5,, 5, 5,, 4, 9,,,5 0,6 0, 946,0 6,9, ,0 9 5, , 60,9 0 4, 4, 0 0, 4, 5 6, , ,, 9 6,0 0,44 4 5,0 9 0,5 6 49,0 0 0,6 9,4 65, 5, 0,,4 0,6 0,94 0,6

8 Theoretical exercises 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 50 C. b. Pressure at turbine entry is 5 bar and temperature at turbine entry is 00 C. c. Pressure at turbine entry is bar and temperature at turbine entry is 00 C. d. Pressure at turbine entry is bar and temperature at turbine entry is 00 C. Degree of regeneration is 0,. e. Pressure at turbine entry is bar and temperature at turbine entry is 00 C. Thermal efficiency of steam power plant, attached to gas turbine exhaust, is 0,5. Flue gases are cooled in heat recovery steam generator (HRSG) to a temperature of 0 C. Ambient pressure is bar and ambient temperature is 0 C, compressor efficiency is 0,5, gas turbine efficiency is 0,, mechanical efficiency of compressor is 0,9, mechanical efficiency of gas turbine is 0,9, mechanical efficiency of steam turbine is 0,99 and generator efficiency is 0,9. Pressure drops are: 0, bar at compressor entry, bar in combustion chamber, 0, bar at gas turbine exhaust to ambient, 0, bar in regenerative air heater (flue gas side and air side) and 0, 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 Power plant a, b in c Power plant d 4 Power plant e

9 Theoretical exercises 9 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 (T ). The expansion thru turbine is assumed to be isentropic. The pressure drop in the boiler with superheater is 0 bar and bar in next superheater. 6a 6b Picture : 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 a 0,05 6b 0,05 4 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.

10 Theoretical exercises 0 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 ) that shaded surface inside steam cycle (---6) that represents the difference between added and taken heat (gain work) is the same like by the ascribed Carnot cycle (-c-c-6). T c T m,do c T od Picture : Carnotization of the steam cycle. 6 s 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 (T m,do ). The average temperature level of the fluid during heat addition (Picture ) is calculated with T m, do h h s s It is well known that the Carnot efficiency is: T C T od do 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 is not known that s why the cycle with one degree repeated steam superheating in this point cannot be sketched.

11 Theoretical exercises T [ C] Picture : T s diagram for the cycle without one degree repeated steam superheating (---6a) and the cycle with one degree repeated steam superheating (-----6b). 6a 6b

12 Theoretical exercises 6. Numerical Modeling of steam superheating system in IPSEPro code PREPARATIONS. Check if IPSE is installed on the computer and elements library (App lib) is updated and connection with MS Excel is assured.. Before you start you should have hardware license key (LPT port).. 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.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 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, 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.

13 Theoretical exercises 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 bar, temperature to 0 C and mass flow to 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 ) 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 90 bar and temperature 540 C. Before boiler the temperature is 4 C. Mass flow should be set to 00 kg/s. o The efficiency of the boiler is and pressure losses thru boiler 0 bar. o Click the button for calculation. o Add the first turbine and set the mechanical efficiency to and internal efficiency to. o Click the button for calculation. o We get error. We can see in the protocol that we have 40 equations and 4 parameters. The system is not well defined. We forgot to define state after turbine. For the moment we set that missing state to 00 bar. o Click the button for calculation. o We proceed by adding another boiler and turbine. o Settings: pressure drop in superheater bar, temperature after superheater 540 C, pressure after turbine 0,05 bar, mechanical and internal turbine efficiency. o Add the generator and connect it with turbines. o Click the button for calculation. o We proceed with the condensator: undercooling 0.00, both pressure drops o Click the button for calculation. o Add the pump and numerical connector. The pump mechanical efficiency is, internal efficiency is 0.. o Click the button for calculation. o We can find out that we have 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

14 Theoretical exercises 4 well defined). If we like to have 4 C after the pump, we should change the internal efficiency of the pump. Instead 0. 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. 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 6pt. 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: kp, b Pt Pč Q do h h h h6b h h h h h h o In specific cell the temperature T 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 T as parameter. o Initial value should be 00, end 500. The step 0 and max. steps 00. 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 00 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: T m, do h h h h and one column for cycle efficiency. s s s s 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 T m (T ).

15 Theoretical exercises 5 APPENDIX : The scheme that should be modeled 6a 6b