cogen technology

8/13/2019 Cogen Technology

1/15

Introduction :

YesI, you, society, organization, state, nation and world need development. Not simplydevelopment but a Sustainable development and sustainable development benefits social,

economic, technological, and environmental benefits. Power (electricity and !eat plays a ma"orrole for development# it can accept all of us without any drought in our mind. $o produce chefelectricity, lower emissions to the environment, in particular of %& ' , the main greenhouse gas,

better cycle efficiency, improved local and general security of supply, electricity demand andsupply and to increase employment we need better technology for generation of electricity.

es %ogeneration, %ombined !eat and Power (%!P can fulfill it for long way.

What Is Cogeneration,

%ogeneration or %!P (combined heat and power is the simultaneous production ofelectricity and heat using a single fuel such as bagasse, natural gas, coal, waste gas, biomass,li)uid fuels and renewable gases. $he heat produced from the electricity generating process (for

e*ample from the e*haust systems of a gas turbine is captured and utilised to produce high andlow level steam. $he steam can be used as a heat source for both industrial and domestic purposes and can be used in steam turbines to generate additional electricity (combined cycle power . %ogeneration for on+site power and heat is well established overseas, especially in

Scandinavian countries. Its use is gradually increasing in ustralia, although optimistic forecastsof rapid implementation and growth in the last couple of years have yet to be realized.

The Benefits of CogenerationProvided the cogeneration is optimized in the way described above (i.e. sized according to theheat demand , the following benefits can be obtained-

Increased efficiency of energy conversion and use

ower emissions to the environment, in particular of %&', the main greenhouse gasIn some cases, biomass fuels and some waste materials such as refinery gases, process oragricultural waste (either anaerobically digested or gasified , are used. $hese substanceswhich serve as fuels for cogeneration schemes, increases the cost+effectiveness andreduces the need for waste disposal

arge cost savings, providing additional competitiveness for industrial and commercialusers while offering affordable heat for domestic users also

n opportunity to move towards more decentralized forms of electricity generation,where plants are designed to meet the needs of local consumers, providing highefficiency, avoiding transmission losses and increasing fle*ibility in system use. $his will

particularly be the case if natural gas is the energy carrier n opportunity to increase the diversity of generation plant, and provide competition

ingeneration. %ogeneration provides one of the most important vehicles for promotingliberalization in energy mar/ets.

Principle of Cogeneration,Combined heat and power (CHP !

$he principle behind cogeneration is simple. %onventional power generation, on average, is only012 efficient 3 up to 412 of the energy potential is released as waste heat. 5ore recentcombined cycle generation can improve this to 112, e*cluding losses for the transmission and


2/15

distribution of electricity. %ogeneration reduces this loss by using the heat for industry,commerce and home heating6cooling.

In conventional electricity generation, further losses of around 1+782 are associated withthe transmission and distribution of electricity from relatively remote power stations via the

electricity grid. $hese losses are greatest when electricity is delivered to the smallest consumers.$hrough the utilisation of the heat, the efficiency of cogeneration plant can reach 982 or

more. In addition, the electricity generated by the cogeneration plant is normally used locally,and then transmission and distribution losses will be negligible. %ogeneration therefore offersenergy savings ranging between 71+:82 when compared against the supply of electricity andheat from conventional power stations and boilers.

;ecause transporting electricity over long distances is easier and cheaper thantransporting heat, cogeneration installations are usually sited as near as possible to the placewhere the heat is consumed and, ideally, are built to a size to meet the heat demand. &therwisean additional boiler will be necessary, and the environmental advantages will be partly hindered.$his is the central and most fundamental principle cogeneration.


3/15

?ig.7 Separate !eat and Power ?ig.' %ogeneration %ombined !eat and Power.

%ogeneration systems can be powered by a variety of fuels, including natural gas, coal, oil, andalternative fuels such as biomass. In recent years, natural gas has been the predominant fuel for%!P systems, but biomass and opportunity fuels (i.e., wastes or by+products from industrial

processes, agriculture, or commercial activities are e*pected to gain a larger share with growingenvironmental and energy security concerns.@,> Some cogeneration technologies can operatewith multiple fuel types, ma/ing the system less vulnerable to fuel availability and volatilecommodity prices.%ogeneration is appropriate in situations where a facility has a continuous demand for heating orcooling as well as demand for electrical or mechanical power. %ogeneration systems can provideelectricity or mechanical power (e.g., for driving rotating e)uipment li/e compressors, pumps,and fans and heat energy that can be used for- steam or hot water# process heating, cooling andrefrigeration# and dehumidification.

Classification "f #as Turbine

$here are two types of cogenerationABtopping cycle and Bbottoming cycle. $he most common type of cogeneration is the Btopping cycle where fuel is first used to generateelectricity or mechanical energy at the facility and a portion of the waste heat from powergeneration is then used to provide useful thermal energy. $he less common Bbottoming cycle type of cogeneration systems first produce useful heat for a manufacturing process via fuelcombustion or another heat+generating chemical reaction and recover some portion of thee*haust heat to generate electricity. B;ottoming+cycle %!P applications are most common in

process industries, such as glass and steel, that use very high temperature furnaces that wouldotherwise vent waste heat to the environment. $he following description of cogeneration systemsfocus on Btopping cycle applications.


4/15

$our t%pes of topping c%cle cogenerations%stems

&!Combined'c%cle topping s%stem gas turbine or diesel engine

producing electrical or mechanical power followed by a heat recovery boiler to createsteam to drive asecondarysteam turbine

!)team'turbine topping s%stem$he second type of system

burns fuel (any type to producehigh+pressure steam that then

passes through a steam turbineto produce power with thee*haust provides low+pressure

process steam.

*!Heat reco+er% topping s%stem$his type employs heatrecovery from an enginee*haust and6or "ac/et coolingsystem flowing to a heat

recovery boiler, where it isconverted to process steam 6 hotwater forfurther use.

!#as turbine topping s%stem natural gas turbine drives a

generator. $he e*haust gas goesto a heat recovery boiler thatma/es process steam and

process heat.

Bottoming c%cleIn a bottoming cycle, the primary fuel produces high temperature thermal energy and the heatre"ected from the process is used to generate power through a recovery boiler and a turbinegenerator. ;ottoming cycles are suitable for manufacturing processes that re)uire heat at hightemperature in furnaces and /ilns, and re"ect heat at significantly high temperatures. $ypicalareas of application include cement, steel, ceramic, gas and petrochemical industries.


5/15

;ottoming cycle plants are much less common than topping cycle plants. ?igure 9 illustratesthe bottoming cycle where fuel is burnt in a furnace to produce synthetic rutile. $he wastegases coming out of the furnace is utilized in a boiler to generate steam, which drives theturbine to produce electricity.

Cach cogeneration system is adapted to meet the needs of an individual building or facility.System design is modified based on the location, size, and energy re)uirements of the site.%ogeneration is not limited to any specific type of facility but is generally used in operationswith sustained heating re)uirements. 5ost %!P systems are designed to meet the heat demand ofthe energy user since this leads to the most efficient systems. arger facilities generally usecustomized systems, while smaller+scale applications can use prepac/aged units.%ogeneration systems are categorized according to their prime movers (the heat engines , thoughthe systems also include generators, heat recovery, and electrical interconnection components.$he prime mover consumes (via combustion, e*cept in the case of fuel cells discussed belowfuel (such as coal, natural gas, or biomass to power a generator to produce electricity, or to driverotating e)uipment. Prime movers also produce thermal energy that can be captured and used forother on+site processes such as generating steam or hot water, heating air for drying, or chillingwater for cooling. $here are currently five primary, commercially available prime movers- gasturbines, steam turbines, reciprocating engines, microturbines, and fuel cells.Steam turbines and gas, or combustion, turbines are the prime movers (heat engines best suitedfor industrial processes due to their large capacity and ability to produce the medium+ to high+temperature steam typically needed in industrial processes.

#as Turbine Heat -eco+er% Boiler Technolog%!Das turbine systems operate on the thermodynamic cycle /nown as the ;rayton cycle. In a;rayton cycle, atmospheric air is compressed, heated, and then e*panded, with the e*cess of

power produced by the turbine or e*pander over that consumed by the compressor used for powergeneration.Das turbine cogeneration systems can produce all or a part of the energy re)uirement of the site, and theenergy released at high temperature in the e*haust stac/ can be recovered for various heating and cooling


6/15

applications (see ?igure . $hough natural gas is most commonly used, other fuels such as light fuel oil ordiesel can also be employed.

Das $urbine !eat Eecovery ;oiler $echnology

$he typical range of gas turbines varies from a fraction of a 5< to around 788 5


7/15

$he air is delivered through a diffuser to a constant+pressure combustion chamber, where fuel is in"ectedand burned. $he diffuser reduces the air velocity to values acceptable in the combustor. $here is a

pressure drop across the combustor in the range of 7.'2. %ombustion ta/es place with high e*cess air.$he e*haust gases e*it the combustor at high temperature and with o*ygen concentrations of up to 71+742. $he highest temperature of the cycle appears at this point# the higher this temperature is, the higherthe cycle efficiency is. $he upper limit is placed by the temperature the materials of the gas turbine canwithstand, as well as by the efficiency of the cooling blades.


8/15

Process .lternates

&!Bac/pressure Technolog%: $he first type of technology in cogeneration available was the ;ac/pressure, where combined heat and

power (%!P is generated in a steam turbine. $he ?ig. 0 shows the process flow of bac/pressure typecogeneration (%!P .

!01traction Condensing Technolog%: $he second type of technology in cogeneration available was the C*traction %ondensing. condensing

power plant is generating only electricity whereas in an e*traction condensing power plant some part ofthe steam is e*tracted from the turbine to generate also heat.

$he ?ig shows the process flow of C*traction %ondensing type cogeneration (%!P .


9/15

C*traction %ondensing $echnology.

*!Combined C%cle Technolog%: $he forth type of technology in cogeneration available was %ombined cycle. combined cycle power

plant consists of one or more gas turbines connected to one or more steam turbines.$he ?ig. 4 shows the process flow of %ombined %ycle cogeneration (%!P .

%ombined %ycle $echnology.4.Reciprocating Engine Technology:

The fifth type of technology in cogeneration available was Reciprocating Engine.Instead of a gas turbine, a reciprocating engine, such as a diesel engine, can be


10/15

combined with a heat recovery boiler, which in some applications supplies steam toa steam turbine to generate both electricity and heat. In a reciprocating enginepower plant heat can be recovered from lubrication oil and engine cooling water aswell as from exhaust gases.

Eeciprocating Cngine $echnology.

bove technologies are readily available, mature, and reliable. $hree other technologies have recentlyappeared on the mar/et, or are li/ely to be commercialized within the ne*t few years-

2!3icro'turbines:

$his new type cogeneration technology to be commercialised. 5icro+turbines are smaller are smaller thanconventional reciprocating engines, and capital and maintenance costs are lower. $here are environmentaladvantages, including low N&* emissions of 78+'1 ppm (8' 3 712 e)uivalent or lower.5icro+turbines can be used as a distributed generation resource for power producers and consumers,including industrial, commercial and, in the future, even residential users of electricity. Significantopportunities e*ist in five /ey applications-$raditional cogeneration,Deneration using waste and bio+fuels,;ac/up power,Eemote Power for those with ;lac/ StartJ capability,Pea/ Shaving.

4!$uel cells:?uel cells convert the chemical energy of hydrogen and o*ygen directly into electricity withoutcombustion and mechanical wor/ such as in turbines or engines. In fuel cells, the fuel and o*idant (airare continuously fed to the cell. ll fuel cells are based on the o*idation of hydrogen. $he hydrogen usedas fuel can be derived from a variety of sources, including natural gas, propane, coal and renewable suchas biomass, or, through electrolysis, wind and solar energy.

typical single cell delivers up to 7 volt. In order to get sufficient power# a fuel cell stac/ is made ofseveral single cells connected in series.


11/15

Cven if fuelled with natural gas as a source of hydrogen, the emissions are negligible- 8.8:1 ppm N&*, ' ppm %&, : ppm !%.A number of different types of fuel cells are being developed. The characteristics ofeach type are very different: operating temperature, available heat, tolerance tothermal cycling, power density, tolerance to fuel impurities etc. They are also invery different stage of development and some of them have not emerged from thelaboratory. ome are approaching commercial brea!through. This will be coveredby other briefings from "#$E% Europe.

5!)tirling engines!

$he Stirling engine is an e*ternal combustion device and therefore differs substantially fromconventional combustion plant where the fuel burns inside the machine. !eat is supplied to theStirling engine by an e*ternal source, such as burning gas, and this ma/es a wor/ing fluid, e.g.helium, e*pand and cause one of the two pistons to move inside a cylinder. $his is /nown as thewor/ing piston. second piston, /nown as a displacer, then transfers the gas to a cool zonewhere it is recompressed by the wor/ing piston. $he displacer then transfers the compressed gasor air to the hot region and the cycle continues. $he Stirling engine has fewer moving parts thanconventional engines, and no valves, tappets, fuel in"ectors or spar/ ignition systems. It istherefore )uieter than normal engines, a feature also resulting from the continuous, rather than

pulsed, combustion of the fuel.

$here are some low capacity Stirling engines in development or in the mar/et. $he electricalefficiency is still not very high and in the range of 782 (018


12/15

0nerg% 0fficienc% "pportunities in a #as Turbine Cogeneration )%stem

Cnergy efficiency improvements can be made in the following sections of Steam $urbine%ogeneration Systems-

&! .ir Compressor: Please refer to the 5odule %ompressors and %ompressed ir SystemJ! #as Turbine:

Das temperature and pressure- If the gas temperature and pressure conditions at the inletto the gas turbine vary from the design optimum conditions, the turbine may not be ableto operate at ma*imum efficiency. Kariations in gas conditions can be due to errors in

plant design (including sizing or incorrect plant operation.Part load operation and starting L stopping- $he efficiencies of the generating unit at partloads can be maintained close to the design values by paying due attention to all theabove items. !owever, mar/et decisions to operate the generating unit at certain loads for certain periods will have the ma"or influence on its average thermal efficiency. Similarly,mar/et decision on when the plant is to come on and off line also has a bearing onaverage thermal efficiency because of energy losses while starting or stopping the system.

$he temperature of the hot gas leaving the combustors. Increased temperature generallyresults in increased power output#

$he temperature of the e*haust gas. Eeduced temperature generally results in increased power output#

$he mass flow through the gas turbine. In general, higher mass flows result in higher power output#

$he drop in pressure across the e*haust gas silencers, ducts and stac/. decrease in pressure loss increases power output#

Increasing the pressure of the air entering or leaving the compressor. n increase in pressure increases power output.*! Heat -eco+er% )team #enerator: Please refer to the 5odule


13/15

"PTI"8) T" I8C-0.)0 0$$ICI08CY$his section includes the most important energy efficiency options for cogeneration

=sing the e*haust gas to heat the air from the compressor (mainly used in cold weather conditions #

Mivide the compressor into two parts and cool the air between the two parts#

Mivide the turbine into two parts and reheat the gas between the two parts by passing thegas through additional burners and combustors located between the two parts#%ooling the inlet air. $his is mainly used in hot weather conditions#Eeducing the humidity of the inlet air#Increasing the pressure of the air at the discharge of the air compressor#In"ect steam or water into the combustors or turbine#


14/15

&ut of all the variants, cogeneration systems based on combined cycle configurations withcogeneration of power and heat permit the optimal utilisation of fuel energy in the true

sense of Second aw of $hermodynamics. ;esides highest fuel efficiency and by virtue of its low capital cost, the combined cycle based option has been found the most acceptableand economical solution.Steam turbine based cogeneration systems are of greater interest to the industries withmoderately large and stable steam demand, and further where it is necessary to use fuelsof lower )uality li/e coal, lignite, furnace oil, etc which can not be directly fired in gasturbines. $hough high ash bearing dirty fuels li/e residual fuel oil or furnace oil can be firedin gas turbines, but only to some limited e*tent due to inherent problems associated with it.


15/15

H)0 P0-$"-3.8C0

Secure, reliable and affordable energy supplies are fundamental to economic stability and development.$he worsening misalignment between energy demand and supplyAwith ma"or conse)uences on energy

prices, the threat of disruptive climate change and the erosion of energy securityAall pose ma"or challenges for energy and environmental decision ma/ers. 5ore efficient use of primary energysources can help to mitigate the impact of these negative trends. %o+generation represents a proventechnology to achieve that goal.$he average global efficiency of fossil+fuelled power generation has remained stagnant for decades at012 to 0@2. $echnologies already e*ist today to bring the generation fleet closer to :12 efficiency andthe reasons why efficiencies have not edged closer to the :12 mar/ are not dealt with in this report.Doing significantly beyond :12, for a large part, does not reflect a lac/ of incentive to research anddevelop new technologies to e*tract energy stored in fossil fuels in more efficient ways. It has more todo with the intrinsic, theoretical constraints on the conversion of heat into electricity. Notwithstandinggains that could come from research efforts over time, power generation efficiency will plateau belowthe level of overall efficiency that the best co+generation plant can achieve. %o+generation allows @12to >82 of fuel inputs, and up to 982 in the most efficient plants, to be converted to useful energy. $hetwo+thirds of input energy lost globally in traditional power generation (?igure ' represent significantmissed opportunities for savings on both energy costs and %& ' emissions. Implementing co+generationdoes not, in itself, increase the power supply for a given plant# rather it increases overall energyefficiency by supplying useful heat alongside useful electricity. ;y ma/ing more efficient use of fuelinputs, co+generation allows the same level of end+use energy demand to be met with fewer energyinputs.

cogen technology

Documents