Economically, however, the turbine generates power at the efficiency of the steam boiler. Isentropic efficiency of the steam turbine: The isentropic efficiency of an optimized steam turbine is 90% for an advanced power plant. Using these simplifications and definitions, the energy equation for steady flow operation reduces to: But this equation represents the ideal scenario and here is where the second law steps in. This concept has some limitations in complex systems and an example is outlined later. { h 1 = Suction enthalpy calculated at P 1, T 1, and composition (z i) h 2 = Discharge enthalpy calculated at P 2, T 2, and composition (z i) h 2Isen = Isentropic discharge enthalpy at P 2 (or T 2), S 2 Isen =S 1, and composition (z i) = Mass flow rate Equation 2 (the first law, steady-state energy equation) becomes for the turbine, wT = m(h1 – h2). So, in the real world, Equation 3 becomes. An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. A well-designed reheat system can reduce moisture to low levels in the turbine exhaust steam. if(MSFPhover) { MSFPnav14n=MSFPpreload("../_derived/Trade Books.htm_cmp_strtedge110_vbtn.gif"); MSFPnav14h=MSFPpreload("../_derived/Trade Books.htm_cmp_strtedge110_vbtn_a.gif"); } Consider the common drum boiler, where the steam leaving the drum is saturated. The benefits are efficiency related. 1301 steam turbine’s rated thermal efficiency is 44.7 %. Isentropic Efficiency of Turbines Schematic of a Turbine. Machine eff = ~20%, System Eff = ~35% • For Cogeneration, 2 useful outputs = Power + Process The overall work is then 425,000,000 Btu/hr = 124.5 MW. To borrow an old phrase, such savings “are not chicken feed.”. MSFPhover = To put this into practical perspective, assume steam flow (m) to be 1,000,000 lb/hr. If you continue to use this site we will assume that you are happy with it. Our industrial steam turbines are designed for easy constructability, fast start-up and economical operation. Let’s increase the steam pressure to 2,000 psia from Example 2, where the condenser pressure was 1 psia. The heat input (qB) is equivalent to the difference in enthalpy of the condensate entering the boiler vs. that of the main steam exiting the boiler. 2. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage. This is less than the work obtained in Example 4 (603.1 Btu/lbm), which had no feedwater heater. At 1,000,000 lb/hr steam flow, the total work is 582,400,000 Btu/hr = 170.6 MW. Thermal Efficiency of Steam Turbine. Many more examples are possible, but this one conveys the essence of the second law. Two important points should be noted about the Carnot cycle and all real world processes. The K 200-130-1 steam turbine’s rated thermal efficiency is 44.7%. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The classic energy equation for a simple system (defined as a control volume in textbooks)1,2 is: Q – WS = m2[V22/2 + gz2 + u2 + P2v2] – m1[V12/2 + gz1 + u1 + P1v 1] + dEc.v./dt Eq. Thermodynamic calculations show that the work output of the turbine drops from 582.4 to 546.1 Btu/lbm. The first law is that of conservation of energy. An obvious conclusion is that reheat increases the energy output but also the fuel requirements to the boiler. QL in a conventional steam generator is heat removed in the condenser. In modern nuclear power plants the overall thermal efficiency is about one-third (33%), so 3000 MWth of thermal power from the fission reaction is needed to generate 1000 MWe of electrical power. The values for H3, S3 and H 4 ′ are 1272.995 kJ/kg, 0.958 kJ/kgK and 428.005 kJ/kg, respectively. The temperature to which the steam is raised above saturation represents the degree of superheat. First, let us examine condenser performance. if(MSFPhover) { MSFPnav11n=MSFPpreload("../Energy Tips/_derived/20_ways_save.htm_cmp_strtedge110_vbtn.gif"); MSFPnav11h=MSFPpreload("../Energy Tips/_derived/20_ways_save.htm_cmp_strtedge110_vbtn_a.gif"); } Maximum steam temperatures in even the most advanced supercritical units have been limited to about 1,100 F due to materials performance issues. Step 3: If solve for 'Isentropic Efficiency', Determine Outlet Properties Using the outlet specific enthalpy, calculate the isentropic efficiency: if(MSFPhover) { MSFPnav6n=MSFPpreload("_derived/QASteamturbines.htm_cmp_strtedge110_vbtn.gif"); MSFPnav6h=MSFPpreload("_derived/QASteamturbines.htm_cmp_strtedge110_vbtn_a.gif"); } Thermodynamic calculations indicate that the exiting enthalpy from the turbine is 1,080.9 Btu/lbm (steam quality is 93 percent). Remember that it takes nearly 1,000 Btu to convert a pound of water to a pound of steam in utility steam generators. Steam Turbines. This type of turbine is mainly used in the power production facilities; lback-pressure turbines, in which vapor pressure is expanded from HP pressure (> 40 bar) at low pressure (about 4 bar). Why must turbine exhaust steam be condensed? efficiencies are defined to be less than 1, the turbine isentropic efficiency is defined as T a s Actual turbine work Isentropic turbine work w w 1 2 1 2 a T s h h h h Well-designed large turbines may have isentropic efficiencies above 90 percent. Another point is that if the steam from Example 1 were rerouted directly to the boiler, the power requirements and size for the feed pump would be huge. } catch(err) {}, . The heat input required by the boiler to produce the required steam is only 1,149.1 Btu/lbm (1,474.1 – 325.0), as the feedwater temperature is much warmer. The turbine work output rises to 603.1 Btu/lbm (176.7 MW at 1,000,000 lb/hr steam flow), and the efficiency increases from 40.6 percent to 42.9 percent. However, the remaining steam takes up a specific volume of 274.9 ft3/lbm. wt = (inlet steam enthalpy – cold reheat enthalpy) + (hot reheat enthalpy – turbine exhaust enthalpy). Second, in a steady flow process such as a steam generator, the system does not accumulate energy, so dEc.v./dt is zero. Second, the efficiency (η) of a Carnot engine is defined as. // -->. Thermal Efficiency of Steam Turbine. For example, a warm cup of coffee placed on a kitchen table does not become hotter while the room grows colder. The main steam enthalpy becomes 1,474.1 Btu/lbm and the turbine exhaust enthalpy is 871.0 Btu/lbm. The h-s Diagram of the Actual and Isentropic Processes of an Adiabatic Turbine Click to View Movie (50 kB) For an adiabatic turbine which undergoes a steady-flow process, its inlet and exit pressures are fixed. The unit work output equates to 1,505.9 – 923.4 = 582.4 Btu/lbm. In this case, wt = (1,474.1 – 1,248.1) + (1,526.5 – 1,003.9) = 748.6 Btu/lbm. Ten percent moisture at the turbine exhaust is typically an upper limit. This is why proper cooling water chemical treatment and condenser performance monitoring are important.3. Enthalpy is a measure of the available energy of the fluid, and enthalpies have been calculated for a wide range of steam and saturated liquid conditions. Supercritical units may have two reheaters to maximize turbine performance. As a market leader for industrial steam turbines, we offer a comprehensive range of reliable and versatile steam turbines for the power output range from 2 to 250 MW. if(MSFPhover) { MSFPnav1n=MSFPpreload("../_derived/home_cmp_strtedge110_vbtn.gif"); MSFPnav1h=MSFPpreload("../_derived/home_cmp_strtedge110_vbtn_a.gif"); } For simple steam generating systems, general efficiency is represented by this equation: The energy required by the feedwater pump is much less than the work produced by the turbine, so it is often left out in basic energy calculations. Much less work is required to pressurize a liquid than a gas. 1. if(MSFPhover) { MSFPnav12n=MSFPpreload("../_derived/Steam Turbines.htm_cmp_strtedge110_vbtn.gif"); MSFPnav12h=MSFPpreload("../_derived/Steam Turbines.htm_cmp_strtedge110_vbtn_a.gif"); } Author: Brad Buecker is an air quality control specialist at a large Midwestern power plant. (Efficiency gain through higher pressure is a primary reason why supercritical have become popular for coal-fired boilers.) google_ad_slot = "9340173143"; A large utility steam generator usually has several feedwater heaters, at least a single reheater and condenser that has excess surface area for cooling. The turbine work equals the enthalpy difference between the main steam and extraction point (1,474.1 – 1,299.7 Btu/lbm), plus the remaining steam (79.2 percent) that passes to the turbine exhaust (0.792*[1,299.7 – 871.0] Btu/lbm). One can also look at this example from a physical perspective. [Steam Property Calculator] => Specific Enthalpy = 1,218.4 btu/lbm; Step 3: If solve for 'Isentropic Efficiency', Determine Outlet Properties. if(MSFPhover) { MSFPnav3n=MSFPpreload("../Jobs/_derived/JobHotline.htm_cmp_strtedge110_vbtn.gif"); MSFPnav3h=MSFPpreload("../Jobs/_derived/JobHotline.htm_cmp_strtedge110_vbtn_a.gif"); } The resulting power generation efficiency (modern steam boilers operate at approximately 80% efficiency) is well in excess of the efficiency for state-of-the-art condensing turbines, where steam is completely expanded at a pressure of about 0.02 to 0.04 bar, and then liquefied in a condenser cooled by ambient air or by water. Determine the enthalpy at exit and calculate the flow rate of steam in kg/s. Where . These values may be found in the standard ASME steam tables, where saturated water at 0C has been designated as having zero enthalpy. In The Efficient Use of Energy (Second Edition), 1982. google_ad_client = "ca-pub-0945984148751929"; The efficiency calculates to 44.5 percent, which is 2 percent higher than the non-reheat example. // --> Stea… A typical Ts diagram for a steam turbine is shown below. I would like to know if you considered to introduce a correction factor to simulate steam turbines with part-load conditions. In the paper a calculation methodology of isentropic efficiency of a compressor and turbine in a gas turbine installation on the basis of polytropic efficiency characteristics is presented. First, in many systems and especially steam generators, potential and kinetic energies are very minor compared to other energy changes and can be neglected. This means that 23 percent of the fluid exits as condensed water droplets. // -->