The power output of the turbine is 35 MW. In every process, the overall entropy change (of a system and its surroundings) increases. Reheating the steam helps to alleviate this difficulty. As the examples in the previous section illustrated, it should come as no surprise that efficiencies of standard utility boilers are in the 30- to 35-percent range. A large utility steam generator usually has several feedwater heaters, at least a single reheater and condenser that has excess surface area for cooling. if(MSFPhover) { MSFPnav5n=MSFPpreload("../FiremanExams/_derived/fireman_exams.htm_cmp_strtedge110_vbtn.gif"); MSFPnav5h=MSFPpreload("../FiremanExams/_derived/fireman_exams.htm_cmp_strtedge110_vbtn_a.gif"); } where H4 is the actual enthalpy at turbine exit. This equation can be easily understood through a few definitions and simplifications. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. Typical Isentropic efficiencies range from 70-90%. (adsbygoogle = window.adsbygoogle || []).push({}); The Isentropic efficiency of a turbine is a comparison of the actual power output with the Isentropic case. Isentropic efficiency of the steam turbine: The isentropic efficiency of an optimized steam turbine is 90% for an advanced power plant. The Isentropic efficiency of a turbine is a comparison of the actual power output with the Isentropic case. However, the remaining steam takes up a specific volume of 274.9 ft3/lbm. In this case, wt = (1,474.1 – 1,248.1) + (1,526.5 – 1,003.9) = 748.6 Btu/lbm. Although the historical steam turbine was still working fine, the Oxea GmbH in Germany replaces the Siemens steam turbine with a new SST-600 due to increasing overall efficiency. At 1,000,000 lb/hr steam flow, the total work is 582,400,000 Btu/hr = 170.6 MW. The K 200-130-1 steam turbine’s rated thermal efficiency is 44.7%. To calculate these enthalpy changes, you need to know the initial and final states, for example, temperature and pressure, of the working fluid for both the actual and isentropic cases. 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. The first law is that of conservation of energy. // -->. : "http://www. So, at 1,000,000 lb/hr steam flow, a rise of 1 psia in the condenser backpressure equates to a loss of 36,300,000 Btu/hr or 10.6 MW of work. // -->. [Steam Property Calculator] => Specific Enthalpy = 1,218.4 btu/lbm; Step 3: If solve for 'Isentropic Efficiency', Determine Outlet Properties. google_ad_client = "ca-pub-0945984148751929"; "https://ssl." Why must turbine exhaust steam be condensed? One might logically ask how feedwater heating improves the process. Read : The key to this problem is to assume that the turbine is adiabatic. A well-designed reheat system can reduce moisture to low levels in the turbine exhaust steam. An obvious conclusion is that reheat increases the energy output but also the fuel requirements to the boiler. Like enthalpy, entropy values are included in the steam tables. Economically, however, the turbine generates power at the efficiency of the steam boiler. In this case, the turbine work equates to 513.8 Btu/lbm. The electrical generating efficiency of standard steam turbine power plants varies from a high of 37% HHV4 for large, electric utility plants designed for the highest practical annual capacity factor, to under 10% HHV for small, simple plants which make electricity as a byproduct of delivering steam to processes or district heating systems. var pageTracker = _gat._getTracker("UA-7717216-1"); Two important points should be noted about the Carnot cycle and all real world processes. document.write(unescape("%3Cscript src='" + gaJsHost + "' type='text/javascript'%3E%3C/script%3E")); But, at 2,000 psia the turbine exit steam quality is only 77 percent. Efficiency of the feedwater pump: According to manufacturers informations, the overall efficiency of the feedwater pump can be 75-85% according to the size. // -->. pageTracker._trackPageview(); Machine eff = ~20%, System Eff = ~35% • For Cogeneration, 2 useful outputs = Power + Process { Supercritical units may have two reheaters to maximize turbine performance. However, new alloys are being developed that may allow higher steam temperatures, especially for future supercritical boilers. Calculations show that the reheating process improves the turbine exhaust steam quality from 77 percent to 90 percent. 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. Author: Brad Buecker is an air quality control specialist at a large Midwestern power plant. He is a member of the ACS, AIChE, ASME and NACE. In a steam turbine, water is the working fluid which passes through the system. Buecker has a BS in Chemistry from Iowa State University. // -->