MICRO COGENERATION - Dgc

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DEVELOPMENT AND DEMONSTRATION OF DANISH FUEL CELL BASEDMICRO COGENERATIONM. Näslunda*, J. de Wit,a, L. Grahl Madsenb , M. Karlsenc, M. Møller Melchiorsc,K.F. Juelsgaardd, J. Jakobsend and A.H. PederseneaDanish Gas Technology Centre, Dr Neergaards Vej 5B, DK-2790, Hørsholm,Denmark, *corresponding author: mna@dgc.dkbIRD A/S, Svendborg, Denmark, c Dantherm Power, Hobro, DenmarkdSEAS-NVE, Svinninge, Denmark, e DONG Energy, Gentofte, DenmarkABSTRACTDenmark has the largest share of cogeneratedelectricity in the world (60% of electricityproduced). Most of the production units areconnected to district heating systems. The futurepotential of increased cogeneration in Denmarkis within industrial processes and microcogeneration.For a long time Denmark also holds a strongscientific position in fuel cell research. Based onthis, a national demonstration program for fuelcell based micro cogeneration (µCHP) wasstarted in 2005/6 including field tests of up tothree fuel cell technologies. The third phaseends in 2013.Calculations have shown that approximately100% of the annual electricity demand in astandard Danish single-family home can beproduced by a micro cogeneration unit in athermal load-following operation mode. 50% ofthis electricity is exported to the grid. A backupboiler and a storage tank are other importantparts that may be included in the heatingsystem. The overall system performance hasbeen addressed from an early stage of theproject. Storage heat loss, water temperaturesand the internal electricity consumption in thecogeneration unit have been studied.Hydrogenfuelledlow-temperaturePEM(Polymer Electrolyte Membrane) systems (1.5kW e) are field tested in a small hydrogen gridwithin the project. Hydrogen is locally produced.The electric efficiency is 47% (lower calorificvalue, LCV) at full load (H2 AC), and theoverall nominal efficiency is 94%.Natural gas fuelled low-temperature PEM (0.9kW e) are also field tested. The electric efficiencyis approximately 34% at nominal load (naturalgas AC), and the overall efficiency is 95–100% (LCV).The SOFC (Solid Oxide Fuel Cell) systems arethe last to possibly enter field tests. They arenatural gas fuelled, and two versions haveundergone laboratory performance testing withinthe project.The paper will address the following topics: Technical design of the microcogeneration units Data and statistics from the field tests System integration Challenges for the futureKeywords: fuel cells, micro cogeneration,system design, operation, field tests.INTRODUCTIONThe Danish power generation system hasundergone a major reshape during the last 30years. Central coal-fired power plants havepartly been replaced, firstly by gas-firedcogeneration plants in district heating grids andsecondly by wind power. Today, the Danishpower generation is divided between differenttechnologies as shown in figure 1.PJ2001501005001980'85'90'95'00Wind Turbines and Hydro Power UnitsAutoproducersSmall-scale CHP UnitsLarge-scale CHP Units'05'10Large-scale Units, Power OnlyFigure 1: Evolution of Danish power generatingsources 1980-2011.No other country in world has as large a shareof electricity from cogeneration plants asDenmark. The CO2 emission has been reducedfrom 937 g/kWh (1990) to 505 g/kWh (2010) dueto fuel switching, cogeneration and wind power[1]. The long-term Danish political goal is afossil-free energy supply in 2050. One stepworth noticing in the energy agreement in theDanish parliament [2] is that gas boilers aregenerally not allowed in new single-familyhouses from 2013 and oil boilers in single-familyhouses are to be phased out.

Theremainingpotentialforexpandedcogeneration is as industrial cogeneration andas micro cogeneration in the Danish residentialsector. A study [3] shows that the technicalpotential for micro cogeneration in Denmark is1,100 MW e for units connected to the gas gridand with an output of maximum 15 kW e.The electricity and heat production from microcogeneration units has been simulated in orderto evaluate different operation strategies andcogeneration unit sizes. The operatingstrategies are heat controlled and electricitycontrolled. The cogeneration output is controlledby the thermal energy demand in the heatcontrolled operation. Surplus electricity isexported to the grid. The operation is securing ahigh overall efficiency. Selected results for aheat controlled strategy are shown in table 1. Abase load cogeneration unit with an electricaloutput of 1.0 kW e and a larger unit capable ofcovering the heat demand are compared. Thehouse has an annual electricity consumption of5,000 kWh, a space heating demand of 12,000kWh and an annual hot water demand of 5,000kWh. The heat-to-power ratio of thecogeneration unit is assumed to be 2. Itcorresponds roughly to a unit with 30–35%electrical efficiency. The electricity consumptionpattern used in the simulations was based onearlier 15-minute measurements of theelectricity consumption in a number of Danishsingle-family houses.Table 1 shows that a micro cogeneration unitsized for base load will get a satisfactoryutilization time in single-family houses. Theelectricity generation equals approximately100% of the electricity demand in the house.Due to the actual electricity demand 45% will beused in the house and 55% exported to the grid.The larger load-following unit is sufficient for theentire annual space heating and hot waterdemand, but does not supply the entireelectricity demand. Instead, a large part of theelectricity is exported to the grid, which in mostcircumstances will not be financially attractivefor the consumer. A heat storage facility makeslong full-load operation possible, thus reducingload and thermal cycles which are amplifying thedegradation processes in fuel cells.Table 1: Example of calculated microcogeneration electricity and heat productionin a Danish single-family house,heat controlled operation.Base loadLoadfollowingMax. power CHP(kW e)1.03.3Elec. production(kWh/a)4,5458,500Elec. export to grid(kWh/a)2,3075,175Elec. prod. in-houseuse re of elec.demand (%)Heat prod. (kWh/a)Share of heatdemand (%)Full load equiv. (h)Micro cogeneration is one of the possible newgas applications in the residential gas sector.Gas-fired cogeneration reduces the carbonfootprint through a higher utilization of theprimary energy compared to power generationin a steam cycle and separate heating in thedwellings. Other new gas-fired options are directgas-fired heat pumps and hybrid systemsconsisting of an electric heat pump and a gasboiler for peak loads and hot water production.Using solar energy and heat pumps introducesrenewable energy into the gas heating system.These are all examples of new gas-firedtechnologies that improve the primary energyutilization.These new technologies also make it possiblefor greener natural gas to be distributed to thecustomers. Carbon neutral biomethane fromanaerobic digestion is already injected in smallvolumes at several places in for exampleGermany and Sweden. Denmark has currentlyonly one site where upgraded biogas is injectedinto the natural gas grid. In a few years it will bepossible to supply methane from biomassgasification into the gas grid. Excess wind powermay be used for hydrogen production which canbe directly injected into the gas grid or convertedto methane together with carbon dioxide in theSabatier process.A number of examples of integrating the gasand electricity grids into a smart grid arementioned above. Micro cogeneration andhybrid systems (electric heat pumps and gas

boilers) are technologies at the consumer levelthat also give the possibility of external control inorder to use renewable energy as best aspossible. Converting excess wind power intohydrogen is a way to store electricity in the gasgrid.Micro cogeneration is one way to reduce thecarbon emissions. Other new heating and powergenerating technologies also offer s, heat pumps and also districtheating are technologies that compete with fuelcell micro cogeneration. Both technical andpolitical issues will play an important role.DANISH FUEL CELLDEMONSTRATION PROGRAMIn a joint effort to develop micro cogenerationfuel cell units a number of Danish enterprisesare developing and demonstrating such units.The project partners represent the entire chainfrom research companies to gas and electricityutilities. The project started in 2006 and ends in2013.The fuel cells in the field test are installed in twodifferent gas grids, which are shown in figure 2.Natural gas fuelled low-temperature PEM andSOFC units are connected to the natural gasgrid. Hydrogen fuelled low-temperature PEMunits are installed in a more future orientedhydrogen grid in a small village. Hydrogen islocally produced in an electrolyzer.The main difference between the unitsconnected to the natural gas grid and thehydrogen grid respectively is the absence of afuel reformer in the latter case. Hydrogen unitsare expected to show a significantly higherelectrical efficiency than the natural gas fuelledlow-temperature PEM units.A similar ongoing demonstration program is theGerman Callux program.MethodThe method used in the Danish project is astraightforward one. The system integratordevelops the micro cogeneration unit, addingthe necessary balance of plant (BoP) parts suchas heat exchangers, reformer, inverter andcooling. The demonstration program involvessystem integrators that develop the entiresystem from the stack design to systemintegrators using parts from other developers.Danish Gas Technology Centre (DGC) performssafety analysis and laboratory performancetesting. The fuel cell based unit is testedseparatelyregardingperformanceandbenchmark, and later for CE certification in theDGC laboratory.Test plans for each fuel cell version have beendeveloped independently by DGC, based on thefuel cell standard IEC 62282 [4]. The EuropeanUnion Gas Appliance Directive is applicable forthe fuel cell units. The tests include performanceand safety aspects. The CE marking is valid forthe specific test site only. The project partnershave gained in this exercise, much experiencewhich is essential when commercial units ratherthan prototypes are to be built.Field test data is collected and sent to DGC forcontinuous evaluation during the field test. Theproject contains three phases, which can bedescribed as proof of concept, early field testand field test with improved units. Each projectphase contains performance and cost targets.FUEL CELL UNIT DESIGNSThe description of the different fuel cell unitsrefer to the phase 3 design.Figure 2: Two energy system designs for fuelcell operation.Hydrogen low-temperature PEM unitsThe hydrogen fuelled cogeneration units havebeen both laboratory and field tested in projectphase 2 and 3. The hydrogen low-temperaturePEM units are developed and built by IRD. Thestacks are also from the same company. Thestack gross output is 1,660 W DC and net (230 V)output is 1,500 W AC. The stack is water cooled.The performance data from laboratory tests areshown in table 2. The start-up time is defined asthe time from cold start until electricity can bedelivered.

Table 2: IRD hydrogen PEM Gamma 1laboratory performance.ParameterValueStack gross output (W DC)1,660Unit net output (W AC)1,500Unit heat output (W)1,500Gas supply pressure (mbar)400Operating temperature ( C)67Net electric efficiency (%)47Heat efficiency (%)47Overall efficiency (%)94Start-up time (min)2Stand-by power (W AC)15Figure 3 shows at the top an image of the fuelcell unit in preparation for wind tests. The unit isdesigned as a closed unit where air and exhaustis transported in a standard gas boiler balancedflue. The vertical air and flue terminal passesthrough the simulated roof. Air speeds up to 12m/s towards the terminal exit are used to checkthe sensitivity to heavy wind.The inverter in the IRD Gamma 1 version islocated in a separate box to allow flexibility inthe installation. The wall-mounted fuel cellinstalled at a field test site is seen at the bottomof the image.Figure 3: IRD hydrogen PEM Gamma 1 unit forphase 3 in laboratory tests and installedat a field test site.Natural gas low-temperature PEM unitsThe natural gas PEM units are designed andbuilt by Dantherm Power. The unit contains afuel cell stack from Ballard and a Japanesereformer. These units have a fixed output anddo not have the modulation capability like thehydrogen fuel cell. Laboratory performance datais shown in table 3.

Table 3: Dantherm natural gas PEM Betalaboratory performance.ParameterValueUnit net output (W DC)900Unit heat output (W)1,650Gas supply pressure (mbar)20Operating temperature ( C)65Net electric efficiency (%)33.6Heat efficiency (%)54.9Overall efficiency (%)88.5Start-up time (min)56The exhaust flow is cooled as much as possible,and the exit temperature is approximately 10 Khigher than the return water temperature to theunit. The exhaust temperature is then clearlybelow the dew point. Integrated burners areused for heat generation. The NOx emissionsare below the instrument detection limit of 2ppm.Figure 4 shows a phase 3 field test unit in asingle-family house. Natural gas is suppliedthrough the copper piping. The maximumnatural gas input is 2.7 kW. The air and flueterminal is located at the top of the cabinet.There is a potential for significant size reductionin future versions.Natural gas SOFC unitsThe SOFC units have a stack developed anddesigned by Topsoe Fuel Cells. Integration ofthe stack in a micro cogeneration unit is madeby Dantherm Power.Due to the less mature SOFC technologycompared to the PEM technology the units haveso far not been field tested. Tests have beendone at the manufacturer and at DGC. The workhas focused on the stack durability anddegradationissues,acceleratedtests,eliminating the need for protecting gases andsize reduction. The design has evolved from theplanar fuel cell stack and separate balance ofplant parts into an integrated packageincorporating the fuel cell stack, natural gasreformer, start-up burner, off-gas burner, heatexchanger and heat insulation. The unit(PowerCore) generates 1.5 kW DC. The stack isair cooled and operates at approximately 750 C.The required gas pressure is low enough, 20mbar, for the unit to be connected to thedistribution gas grid.FIELD TEST SITE SELECTIONAn important and useful part of thedemonstration project has been to move thecogeneration units from the developer to thecertification laboratory and finally to the field testsites. Invaluable experience has been collectedon the installation and operating aspectsthrough these steps. However, the completeinstallations including the fuel cell unit, heatstorage facility and supplementary boiler werenot tested as a system before the field testbegan. The reason being that existing heatgenerators in the buildings act as back-up orsupplementary heater.Many of the field test sites are ordinary singlefamily homes. The fuel cells will then operate inas real conditions as possible. The test sites willalso present real installation aspects valuablefor the developers, installers and servicecompanies engaged in the project. The test siteswere selected among the consumers thatshowed an interest in the project at presentationmeetings for the inhabitants in a selected area.The energy utilities played an important role inthis selection.FIELD TEST RESULTSFigure 4: Dantherm natural gas PEM Alphain phase 3 installed at a field test site.The cogeneration units’ internal data acquisitionsystems are used in the ongoing field tests. Thesampling frequencies for the field test evaluationare 6 minutes for the hydrogen fuel cells and 60minutes for accumulated and momentary valuesfor the natural gas fuel cells. The internalsampling frequency is 10 seconds. Data istransmitted to DGC for evaluation.

180016001400Power output (WAC)Hydrogen low-temperature PEM unitsThe hydrogen fuel cells are connected to a smallhydrogen distribution grid in the village ofVestenskov 150 km south of Copenhagen. Theoverall grid length is 500 m and the pipematerial in phase 2 is stainless steel. PE(Polyethylene) is used in phase 3. Hydrogen isproduced in commercial alkaline electrolyzers3with a capacity of 32 m /h. Gas pressure in thegrid is 4 bar.5 fuel cells were tested in phase 2, and 30 willbe tested in phase 3. The hydrogen PEM fuelcells are installed with a 200 l heat storage tank.The existing heat generator acts as back-up andsupplementary heater.The faults experienced in the second projectphase for the hydrogen PEM fuel cells areshown in figure 5. It is clearly seen that a largeshare of the faults are related to thecommunication and control system. The fuel cellstack was responsible for only a small part ofthe faults. The fault distribution resembles thefault distribution in early Japanese fuel celldemonstration 19:1200:00TimeFigure 6: Operation pattern for a hydrogenfuel cell CHP unit in a simulated smart-gridsituation (House 1).The two units have obtained the followingoperational hours during the first test year: 6,000and 4,000 hours, respectively. The hydrogenfuelled µCHP unit in continuous operation hasprovided 86% of the house heat and hot waterdemand during the heating season 2011/12; and97% of the demand during the summer 2012.The smart-grid operated unit has provided muchless of the thermal demand, not only because ofthe operational pattern, but mainly due to beinginstalled in an old un-insulated house.Figure 7 shows the operation from October 2011until the end of June 2012 for one selected site.Accumulated data for periods of four weeks areshown in the bar graphs. At the end of theperiod shown in the graphs the unit operationtime had reached 6,500 hours. During thisperiod has the unit produced 6,700 kWhelectricity and 8,900 kWh heat.Figure 5: Fault statistics for hydrogenPEM units, phase 2.800OperationTotal TimeNot ready700Ten (10) hydrogen fuelled micro cogenerationunits are presently installed in Vestenskov.Another 20 units will be installed from December2012 to January 2013. Two of the ten units havebeen in operation for a full year. One of thesetwo units has been operated on a continuousmode basis and one unit has been operatedaccording to a simulated smart-grid operationwith four full thermal cycles a day. Figure 6shows the daily operation during this period. Theoperation pattern is five hours of full loadfollowed by one hour of zero load and cooling.Observe the quick response from the cold stageto full AC power output. The hydrogen fuelledPEM unit fulfils every transient responsenecessary for a smart-grid ready cogenerationunit.Time (h)6005004003002001000Week/YearFigure 7: Operating example for a hydrogenPEM Gamma 1 fuel cell unit (House 18).The unit covers a large part of the heating andhot water demand at the site. Figure 8 showsthe thermal heat demand and the seasonalvariation.

Fuel cell thermal heat1.0008006004002000Week/YearFigure 8: Thermal heat supply from a hydrogenPEM Gamma 1 fuel cell unit and supplementaryheating (House 18).The electric and overall efficiencies of thehydrogen PEM unit are shown in figure 9. Theelectric efficiency is close to the laboratoryperformance. The operating time is currently notlong enough to evaluate the possible field testdegradation.temperatures were 30 C return temperature and60 C forward temperature, high enough for hotwater production. The second and third graphsshow accumulated data for periods of twoweeks. In the beginning the unit was not fullyavailable due to installation aspects. After thatthe unit was operating well until somemaintenance, which stopped the operation for awhile. The rightmost bar indicates that the unitwas stopped for the summer period. The bargraph with the electricity and heat productionshows a fairly constant two-week productionreflecting the constant full load 406003040012020Po

fuel cell standard IEC 62282 [4]. The European Union Gas Appliance Directive is applicable for the fuel cell units. The tests include performance and safety aspects. The CE marking is valid for the specific test site only. The project partners have gained in this exercise, much e

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