CogenerationLounge Nishkam DhimanAsst Prof : Electrical and Electronics EngineeringChitkara University, PunjabntroductionCogeneration means se!uential conversion of energy contained in fuel into t"o or more usable forms# $# Energy from coal is converted to heat in boiler to %roduce steam, this steam %roduces electricity, in addition %rovides heat for manufacturing %rocess# 'as is used in gas turbine to generate electrical energy, the remaining heat is used to %roduce steam in a heat recovery boiler "hich can be used for manufacturing %rocess#(hus a conventional system %roduces either Electrical or thermal energy#)ut a cogeneration system %roduces both the energies#A cogeneration system can either be an in%lant %o"er generation system or a reject heat utili*ation system#n%lant %o"er generation system (he industry needs both %rocess steam and electricity# n conventional system, steam is %roduced by a boiler, electricity is either %urchased or %roduced by diesel engine#In cogeneration: the boiler is made to %roduce steam at higher tem%erature and %ressure than needed for manufacturing %rocess, this steam is used in a turbine generator set to %roduce electricity# (he e+haust steam is used for manufacturing %rocess#Reject heat utilization system.(he reject heat utili*ation system is used in %o"er %lants# ,ome steam is e+tracted from the turbine-at suitable tem%# and %ressure. and su%%lied to an adjacent industry for manufacturing %ur%oses#Topping and Bottoming Cycles Topping Cycle: /uel is burnt in the boiler to %roduce high tem%erature steam# (his steam is e+%anded in a turbine cou%led to a generator to give electric %o"er# (he reject heat from the turbine is used for manufacturing %rocess#Electrical energy is %roduced first#,ince steam re!uired for manufacturing %rocess need lo" tem% therefore to%%ing cycle is mostly used#Efficiency: 012Efficiency of se%arate systems: 112Bottoming Cycle:/uel burnt in the boiler to %roduce steam# (he steam is used for manufacturing %rocess# (he reject heat from %rocess is used to generate %o"er#3eat energy is %roduced first#)enefits(a)Fuel Economy: 4ess consum%tion of %rimary fuel#/ueleconomyresultsfromhigherthermodynamicefficiencyofa cogenerationsystemascom%aredtose%arate%o"er%roducingandheat %roducing systems#-b.o!er capitalcost:ndustryneedingsteamhastoinvestonboilers, thee+trainvestmentneededtou%gradeboilersothatelectricitycanalso begeneratedis%rettysmallascom%aredtothecostofboiler#(hus cogeneration results in enormous savings in ca%ital costs#-C.o!gestationperiod:Autilityneeds5yrstoaddathermal generation system# 6hereas, installation of a cogeneration system by and industryneedsonly7yrs#(helo"ergestation%eriodresultsinsavingin interest, early utilisation of facility, early return on investment#-D. ,aving to industry from %o"er cuts and %o"er su%%ly interru%tions#Cogeneration (echnologies(he cogeneration technologies used for to%%ing cycles are:,team (urbine ,ystem'as (urbine ,ystemCombined Cycle systemDiesel Engine ,ystem,team(urbine ,ystem Uses system similar to thermal %lant# /uel may be oil, coal or "ood# (he higher %ressure steam %roduced by the boiler drives turbine and then generate electricity# (he lo"er %ressure e+haust form steam turbine is used for industrial %rocess a%%lication# )ack %ressure steam turbines are used as they e+haust lo" %ressure steam and are more efficient# $72 energy saving # f steam8turbine cogeneration is used# /uel fle+ibility'as (urbine ,ystem(he e+haust from the combustion chamber is used as %rocess heat# f necessary the hot gases can be used to raise steam in "aste heat recovery boiler "here the heat of gasses is transferred to "ater#Due to less availability and high cost of %etroleum %roducts, the cost of electricity %roduced is high#'as turbines need more maintenance than steam turbines# Energy ,avings of about &12 is obtained using cogeneration.Combined Cycle ,ystemt is a combination of gas turbine and steam turbine system#(he gas turbine e+haust is used in "aste heat boiler to raise steam#(he steam from the boiler is used in a back %ressure turbine "hich drives another alternator to %roduce electricity# (he lo" %ressure e+haust from steam turbine is used as %rocess steam# (his system has greater fle+ibility for to%%ing %rocess steam#Energy saving of about 712 is done by combined cycle cogeneration system#Diesel Engine ,ystem(hissystemusesadiesel engine "hich drives the electric generator#(heenginee+haust andjacketcoolingareusedas heatsourcesforthe"asteheat boiler"hichconverts"ater into %rocess steam#(hissystemhashigher electricitytothermalratiothan thatre!uiredbymost industries,used"hen electricity can be sold#Energy saving is about &52 "ith diesel engine cogeneration.