Laboratorij za termoenergetiko Energy management Water and steam Exergy Exergy by heat transfer Exergy in the case steam turbine expansion
Properties of water and steam Energy Management 2
Properties of water and steam- density water Moist steam Superheated steam Energy Management 3
Properties of water and steam - volume Saturated steam Moist steam water Energy Management 4
Properties of water and steam - entalphy Superheated steam Moist steam water Energy Management 5
Properties of water and steam – Molliere diagram h-s Energy Management 6
Properties of water and steam - table specifični volumen specifična entropija temperatura specifična entalpija tlak voda para sprememba agregatnega stanja Energy Management 7
Properties of water and steam - table specifični volumen specifična entropija tlak nasičenja specifična entalpija suhost pare: m para x = m para + m voda v = v' + x ( v" - v' ) h = h' + x ( h" - h' ) s = s' + x ( s" - s' ) nasičena para vrela voda Energy Management 8
Exergy Exergy is the convertible part of energy and can be described in several ways it is the energy that can be completely converted into any other form of energy at given surroundings conditions it is the largest quantity of work that can be produces in a technical device from working media with given starting parameters it is the smallest required quantity of work to raise working media from surroundings conditions to any other condition provided that heat is brought into the process only from the environment Exergy depends on surroundings conditions which limits the 'usability' of enery carried by working media. If working media is in balance with the surroundings no energy can be extracted from it without using additional source of energy. Anergy is the part of energy that cannot be converted into any other form of energy including exergy. Internal energy of the environment is pure anergy. Energy Management 9
Exergy Energy Management 10
Exergy Energy Management 11
Specific exergy of working media • internal energy of the working • internal energy of the working media, U 1 ideal media, U amb • volume work for inserting the (reversible) • volume work to eject the work work media into the system, media from the system, process: p 1 V 1 p amb V amb • heat dissipated, Q out = T amb ( S 1 - S amb ) • acquired work W t = W t,max U 1 + p 1 V 1 = U ok + p amb V amb + Q od + W t,max W t,max = H 1 – H amb – T amb ( S 1 – S amb ) w t,max = e = h – h amb – T ok ( s – s amb ) Energy Management 12
Examples of defining properties of water and steam Using the tables of water and water vapor properties, determine the volume of 2.5 kg of water/ steam that has • a temperature of 60 ° C and a pressure of 1 bar • temperature 150 ° C and pressure 1 bar • temperature 150 ° C and pressure 20 bar Determine the state of 4 kg of water/steam at 160 ° C and • pressure 10 bar • volume 0.8 m 3 • specific enthalpy of 2780 kJ/kg Energy Management 13
Examples of determining the properties of water and steam Linear interpolation x x p y y y y p n p x x n p primer parameter 1 parameter 2 iskano p = 20 bar T = 180 °C v = 1 p = 5 bar T = 306 °C h = 2 p = 8 bar h = 3000 kJ/kg T = 3 T = 50 °C s = 6,75 kJ/kgK h = 4 p = 1,9 bar T = 120 °C s = 5 p = 7 bar x = 0,813 v = 6 p = 105,3 bar v = 0,02 m 3 /kg T = 7 Energy Management 14
Examples of determining the properties of water and steam Linear interpolation x x p y y y y p n p x x n p primer parameter 1 parameter 2 iskano v = 0,001127 m 3 /kg p = 20 bar T = 180 °C 1 p = 5 bar T = 306 °C h = 3077 kJ/kg 2 p = 8 bar h = 3000 kJ/kg T = 273,1 °C 3 T = 50 °C s = 6,75 kJ/kgK h = 2163,15 kJ/kg 4 p = 1,9 bar T = 120 °C s = 7,1517 kJ/kgK 5 v = 0,2220 m 3 /kg p = 7 bar x = 0,813 6 p = 105,3 bar v = 0,02 m 3 /kg T = 341,0 °C 7 Energy Management 15
The exergy losses in the case of heat transfer In case of a water-water heat exchanger find the loss of exergy flow and analize dependence of transferred exergy flow and required heat transfer area on inlet temperature of the colder water. The warm water enters with 90 ° C and exits with 60 ° C while mass flow rate is 17 kg/s. Mass flow rate of the cold water is 12,8 kg/s and its inlet and outlet temperatures are 30 ° C and 70 ° C, respectively. Energy Management 16
The exergy losses in the case of heat transfer 2,0 1,8 1,6 relativna površina prenosnika, relativna izguba eksergije 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 10 20 30 40 50 vstopna temperatura hladne snovi / ° C površina izguba eksergije Energy Management 17
Exergy loss in a heat exchanger - mixer For the case of of mixer heat exchanger shown in the figure calculate the global entropy (system and surroundings) if ambient temperature is 20 ° C. Calculate lost exergy due to mixing of both flows? Energy Management 18
Energy and exergy flows in the turbine team is entering a turbine with a pressure of 110 bar and a temperature of 530 ° C and expands to a pressure of 0,06 bar. Steam flow rate is 15 kg/s. Surrounding conditions are 1 bar and 25 ° C. Calculate turbine power - inlet and outlet exergy flows and - energy and exergy balance - for an ideal turbine with thermal efficiency 1 as well as a real turbine where outlet steam dryness is 0,84. Verify the validity of Gouy-Stodola theorem. Energy Management 19
Reduction cooling station For the system shown in the figure find missing parameters as well as energy and exergy flows for two operating regimes: a) all steam from the boiler is directed throgh the turbine b) parameters of superheated steam are reduced in reducing and cooling station Construct a Rant chart for both regimes. Surrounding conditions are 1 bar and 20 ° C. Energy Management 20
Reduction cooling station reducirno-hladilna postaja turbina Energy Management 21
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