MODELLING with IpsePro: Feed water regenerative heating Steam superheating

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1 Aškerčeva 6 SI-1000 Ljubljana, Slovenia tel.: fax: dekanat@fs.uni-lj.si Department for energy engineering Laboratory for Heat and Power LABORATORY PRACTICUM MODELLING with IpsePro: Feed water regenerative heating Steam superheating Authors: Boštjan Drobnič Mitja Mori Content - CASE 1: Steam cycle with feed water regenerative heating - CASE : Steam cycle with reheating Ljubljana, October 015

2 CASE 1: Steam cycle with feed water regenerative heating To improve the efficiency of the steam plant from previous laboratory work (such as case - Steam Cycle) we add the system for regenerative heating of feed water. To do so the expansion is interrupted at a pressure of 5 bar and 170 C, the part of the steam is therefore lead in the feed water boiler, the greater part of the steam expands in the second part of the turbine to the condenser pressure. In the first part determine: Electrical power at the generator; Thermal power input with the fuel; The energy efficiency of the power plant (include the power of the pumps which represents its own consumption). In the second part, make an analysis of the of the extraction steam pressure impact on: - Electrical power at the generator; - Thermal power input with the fuel; - Energy efficiency; Draw the dependence of the overall efficiency from the extraction steam pressure of the power plant. r F A r E B1 D B 4 C p = 85 bar T = 490 C. m = kg/s r p= 5 bar T = 170 C 4 p = 0,08 bar 1 x = 0 r T= 10 C r' x= 0 A k = 0,85 B t = 0,88 E č = 0,9 ' r 1 In addition to symbols that you used in previous laboratory exercise, it is necessary to add Splitter Preheater Water Preheater is designed to heat the feed water with the steam that condensate through preheater. We assume that at the preheater outflow is boiling water, set the super cooling temperature difference at a small value, for example dt_sub = 0.01 K (the value must be greater than 0 due to the numerical stability). In addition the pressure drop in pre-heater

3 has to be set for hot side (steam) and cold side (water). In this case the pressure drops are neglected, so delta_p_hot = 0 bar and delta_p_cold = 0 bar. Because the condition of steam after the high pressure turbine is precisely defined (pressure and temperature), the turbine efficiency must not be set. Before analyzing the impact of extraction steam pressure on the operation of the steam cycle, set the internal turbine efficiency as constant. In the original scheme by rightclicking on HPT (high pressure turbine) determine the value of its internal efficiency. Then set the efficiency of HPT in the modified steam cycle as a known (set) value. Since now we have one unknown less, it is necessary to define one of the known parameters into a unknown. This parameter should be temperature after the high-pressure steam turbine, since it is directly related to the internal efficiency. After this change you can vary the pressure at steam extraction and try to determine which optimal pressure is. Questions: Why the thermal power with the fuel does not change? Why there is no convergence in the case, when the pressure is less than.75? Identify and justify the optimal steam pressure at the steam extraction. p r / bar,75,9 4,0 6,0 10,0 0,0 50,0 80,0 Q fuel / kw P el / kw

4 Izkoristek postrojenja University of Ljubljana 4 SOLUTIONS 1. part: Q fuel 789 kw P el = 760,94 kw. part: HPT p r / bar Q fuel / kw P el / kw, ,86 997,96 0,1,9 7891,86 977,9 0,1 4,0 7891,86 850,8 0,11 6,0 7891,86 686,19 0,08 10,0 7891,86 459,17 0,05 0,0 7891,86 015,87 0,99 50,0 7891, ,80 0,87 80,0 7891, ,40 0,78 0,15 0,1 0,05 0, 0,95 0,9 0,85 0,8 0, tlak odjemne pare

5 5 CASE : Steam cycle with reheating In steam cycle from lab 1 (case ) the expansion is interrupted at a pressure of 15 bar and temperature of 75 C. The steam is reheated on the initial temperature, and then expands in the low pressure turbine (LPT) the pressure of 0.08 bar and dryness of In the first part determine the energy efficiency of the plant, using the plant's own consumption (pump). In the second part determine the optimal pressure at which the expansion is interrupted before reheating. p a / bar ,0 0,0 0, A F b a E B D B 4 C p = 85 bar T = 490 C. m = kg/s a p= 15 bar T = 75 C b T= 490 C 4 p = 0,08 bar x = 0,965 1 x = 0 A,F k = 0,85 E č = 0,9 1 For reheater additional boiler is used with equal efficiency eta_b = 0,85 as the main boiler. Same as in the previous task check the internal efficiency of HPT and LPT and set both to constant values (eta_s). The state after turbines will be therefore defined by pressure after turbine and internal efficiency of turbines. Determine the optimal pressure of reheating.

6 6 SOLUTIONS 1. part:. part: HPT LPT p a / bar 1 0,86 0,97 0,0 5 0, ,09 15,0 0,11 0,0 0,11 0,0 0, , , ,00