{"id":2468,"date":"2016-03-14T14:40:05","date_gmt":"2016-03-14T14:40:05","guid":{"rendered":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/?p=2468"},"modified":"2016-03-14T14:40:05","modified_gmt":"2016-03-14T14:40:05","slug":"power-and-refriger-a-tion-cycleshow-can-we-increase-the-efficiency-of-the-rankine-cycle","status":"publish","type":"post","link":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/power-and-refriger-a-tion-cycleshow-can-we-increase-the-efficiency-of-the-rankine-cycle\/","title":{"rendered":"POWER AND REFRIGER A TION CYCLES:HOW CAN WE INCREASE THE EFFICIENCY OF THE RANKINE CYCLE?"},"content":{"rendered":"<div class=\"lqpxc6a0dce4fa276c\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '61e5902552e2353963d8d2f1bd1f4a8f',\n\t\t'format' : 'iframe',\n\t\t'height' : 250,\n\t\t'width' : 300,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/61e5902552e2353963d8d2f1bd1f4a8f\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.lqpxc6a0dce4fa276c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.lqpxc6a0dce4fa276c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.lqpxc6a0dce4fa276c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.lqpxc6a0dce4fa276c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.lqpxc6a0dce4fa276c {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<p align=\"justify\"><font size=\"5\">\u25a0 <b>HO<\/b><b>W CAN WE INCREASE THE EFFICIENCY<\/b><b> <\/b><b>O<\/b><b>F THE RANKINE CYCLE?<\/b><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">Steam power plants are responsible for the production of most electric power in the world, and even small increases in thermal efficiency can mean large savings from the fuel requirements. Therefore, every effort is made to improve the efficiency of the cycle on which steam power plants operate.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The basic idea behind all the modifications to increase the thermal efficiency of a power cycle is the same: <i>Increase the average temperature at which heat is transferred to the working fluid in the boiler, or decrease the average temperature at which heat is rejected from the working fluid in the con- denser. <\/i>That is, the average fluid temperature should be as high as possible during heat addition and as low as possible during heat rejection. Next we dis- cuss three ways of accomplishing this for the simple ideal Rankine cycle.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><b>Lowerin<\/b><b>g the Condenser Pressure (<i>Lowers T<\/i><\/b><b>lo<\/b><b>w<\/b><b>, av<\/b><b>)<\/b><b> <\/b>Steam exists as a saturated mixture in the condenser at the saturation temperature corresponding to the pressure inside the condenser. Therefore, lowering the operating pressure of the condenser automatically lowers the temperature <\/font><font size=\"5\">of the steam, and thus the temperature at which heat is rejected.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The effect of lowering the condenser pressure on the Rankine cycle effi- ciency is illustrated on a <i>T<\/i><i>&#8211;<\/i><i>s <\/i>diagram in Fig. 8\u201343. For comparison purposes, the turbine inlet state is maintained the same. The colored area on this diagram represents the increase in net work output as a result of lowering the con- denser pressure from <i>P<\/i>4 to <i>P<\/i>&#8216;. The heat input requirements also increase (rep- resented by the area under curve 2&#8217;-2), but this increase is very small. Thus the overall effect of lowering the condenser pressure is an increase in the thermal efficiency of the cycle.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">To take advantage of the increased efficiencies at low pressures, the con- densers of steam power plants usually operate well below the atmospheric pressure. This does not present a major problem since the vapor power cycles operate in a closed loop. However, there is a lower limit on the condenser pressure that can be used. It cannot be lower than the saturation pressure cor<\/font><font size=\"5\">responding to the temperature of the cooling medium. Consider, for example<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">a condenser that is to be cooled by a nearby river at 15\u02daC. Allowing a temper<\/font><font size=\"5\">ature difference of 10\u02daC for effective heat transfer, the steam temperature in the condenser must be above 25\u02daC; thus the condenser pressure must be above <\/font><font size=\"5\">3.2 kPa, which is the saturation pressure at 25\u02daC.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">Lowering the condenser pressure is not without any side effects, however. For one thing, it creates the possibility of air leakage into the condenser. More <\/font><font size=\"5\">importantly, it increases the moisture content of the steam at the final stages of the turbine, as can be seen from Fig. 8\u201343. The presence of large quantities of moisture is highly undesirable in turbines because it decreases the turbine efficiency and erodes the turbine blades. Fortunately, this problem can be corrected, as discussed below.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><b>Superheatin<\/b><b>g the Steam to High Temperatures<\/b><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The average temperature at which heat is added to the steam can be increased <\/font><font size=\"5\">without increasing the boiler pressure by superheating the steam to high temperatures. The effect of superheating on the performance of vapor power cy<\/font><font size=\"5\">cles is illustrated on a <i>T<\/i><i>&#8211;<\/i><i>s <\/i>diagram in Fig. 8\u201344. The colored area on this <\/font><font size=\"5\">diagram represents the increase in the net work. The total area under the process curve 3-3\u2032 represents the increase in the heat input. Thus both the net work and heat input increase as a result of superheating the steam to a higher temperature. The overall effect is an increase in thermal efficiency, however, since the average temperature at which heat is added increases.<\/font> <\/p><div class=\"buqxw6a0dce4fa28f6\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '0c1eb4c533eaedb7b996f49a5a4983a9',\n\t\t'format' : 'iframe',\n\t\t'height' : 300,\n\t\t'width' : 160,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/0c1eb4c533eaedb7b996f49a5a4983a9\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.buqxw6a0dce4fa28f6 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.buqxw6a0dce4fa28f6 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.buqxw6a0dce4fa28f6 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.buqxw6a0dce4fa28f6 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.buqxw6a0dce4fa28f6 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<div class=\"hdkdy6a0dce4fa283a\" ><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-0778475562755157\"\n     crossorigin=\"anonymous\"><\/script>\n<!-- 300x600 hydraulics-and-pneumatics -->\n<ins class=\"adsbygoogle\"\n     style=\"display:inline-block;width:300px;height:600px\"\n     data-ad-client=\"ca-pub-0778475562755157\"\n     data-ad-slot=\"3735577695\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.hdkdy6a0dce4fa283a {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.hdkdy6a0dce4fa283a {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.hdkdy6a0dce4fa283a {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.hdkdy6a0dce4fa283a {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.hdkdy6a0dce4fa283a {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n\n<p align=\"justify\"><font size=\"5\">Superheating the steam to higher temperatures has another very desirable&nbsp; <\/font><font size=\"5\">effect: It decreases the moisture content of the steam at the turbine exit, as <\/font><font size=\"5\">can be seen from the <i>T<\/i><i>&#8211;<\/i><i>s <\/i>diagram (the quality at state 4\u2032 is higher than that at 1 <\/font><font size=\"5\">state 4).<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The temperature to which steam can be superheated is limited, however, by metallurgical considerations. Presently the highest steam temperature allowed at the turbine inlet is about 620\u02daC (1150\u02daF). Any increase in this value de<\/font><font size=\"5\">pends on improving the present materials or finding new ones that can with- stand higher temperatures. Ceramics are very promising in this regard.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><b>Increasin<\/b><b>g the Boiler Pressure (<i>Increases T<\/i><\/b><b>high, av<\/b><b>)<\/b><b> <\/b>Another way of increasing the average temperature during the heat-addition process is to increase the operating pressure of the boiler, which automatically raises the temperature at which boiling takes place. This, in turn, raises the av<\/font><font size=\"5\">erage temperature at which heat is added to the steam and thus raises the thermal efficiency of the cycle.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The effect of increasing the boiler pressure on the performance of vapor power cycles is illustrated on a <i>T<\/i><i>&#8211;<\/i><i>s <\/i>diagram in Fig. 8\u201345. Notice that for a <\/font><font size=\"5\">fixed turbine inlet temperature, the cycle shifts to the left and the moisture content of steam at the turbine exit increases. This undesirable side effect can <\/font><font size=\"5\">be corrected, however, by reheating the steam, as discussed in Section 8\u201313. Operating pressures of boilers have gradually increased over the years from about 2.7 MPa (400 psia) in 1922 to over 30 MPa (4500 psia) today, generat<\/font><font size=\"5\">ing enough steam to produce a net power output of 1000 MW or more in a 2&#8242; <\/font><font size=\"5\">large power plant. Today many modern steam power plants operate at super- 2 <\/font><font size=\"5\">critical pressures (<i>P <\/i>&gt; 22.09 MPa) and have thermal efficiencies of about 40 <\/font><font size=\"5\">percent for fossil-fuel plants and 34 percent for nuclear plants. There are about <\/font><font size=\"5\">170 supercritical-pressure steam power plants in operation in the United States. The lower efficiencies of nuclear power plants are due to the lower <\/font><font size=\"5\">maximum temperatures used in those plants for safety reasons. The United States has 112 nuclear power plants, which generate about 21 percent of the nation\u2019s electricity. (In contrast, 75 percent of the electricity in France comes<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0345.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0345\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0345\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0345_thumb.jpg\" width=\"198\" height=\"230\"><\/a><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0346.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0346\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0346\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0346_thumb.jpg\" width=\"183\" height=\"484\"><\/a><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">from nuclear plants.) The <i>T<\/i><i>&#8211;<\/i><i>s <\/i>diagram of a supercritical Rankine cycle is shown in Fig. 8\u201346.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The effects of lowering the condenser pressure, superheating to a higher temperature, and increasing the boiler pressure on the thermal efficiency of the Rankine cycle are illustrated below with an example.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0347.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0347\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0347\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0347_thumb.jpg\" width=\"189\" height=\"240\"><\/a><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0348.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0348\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0348\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0348_thumb.jpg\" width=\"358\" height=\"318\"><\/a><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0350.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0350\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0350\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0350_thumb.jpg\" width=\"560\" height=\"235\"><\/a><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0351.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0351\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0351\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0351_thumb.jpg\" width=\"286\" height=\"484\"><\/a><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0352.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0352\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0352\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0352_thumb.jpg\" width=\"353\" height=\"103\"><\/a><\/font> <\/p>\n<p align=\"justify\">\n<p align=\"justify\"><font size=\"5\"><\/font><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u25a0 HOW CAN WE INCREASE THE EFFICIENCY OF THE RANKINE CYCLE? Steam power plants are responsible for the production of most electric power in the world, and even small increases in thermal efficiency can mean large savings from the fuel requirements. Therefore, every effort is made to improve the efficiency of the cycle on which [&hellip;]<br \/><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/power-and-refriger-a-tion-cycleshow-can-we-increase-the-efficiency-of-the-rankine-cycle\/\" class=\"more-link\" >Continue reading&#8230;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2468"}],"collection":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/comments?post=2468"}],"version-history":[{"count":1,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2468\/revisions"}],"predecessor-version":[{"id":2469,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2468\/revisions\/2469"}],"wp:attachment":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/media?parent=2468"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/categories?post=2468"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/tags?post=2468"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}