With the of all time increasing demand for energy all over the universe, the fuel cell, as a sustainable energy beginning, is considered as one of the most dependable beginning in electric power. A fuel cell system based on a proton exchange membrane fuel cell should be applied in the country of residential combined heat and power unit. They are non merely characterized by higher efficiency, but besides environmentally clean, because they have about zero emanation of oxide of N and S and have really low noise.
At present, the available fuel cell can be categorized by temperature: low-temperature, medium-temperature, and high-temperature [ 2 ] .The low-temperature fuel cell contains alkalic fuel cell ( AFC ) , and solid polymer fuel cell ( SPFC ) or proton exchange membrane fuel cell ( PEMFC ) . The medium-temperature category has the phosphorous acid fuel cell ( PAFC ) . The high-temperature category has the liquefied carbonate fuel cell ( MCFC ) and solid oxide fuel cell ( SOFC ) .
Applications for residential combined heat and power system.
The cardinal demand
At the minute, there are two methods to bring forth H utilizing natural gas. Hydrogen is the ideal fuel for a PEM fuel cell because it simplifies the system integrating [ 3 ] . Both has its advantage and disadvantage. The cardinal demand is that convent methane to a H rich gas. The heat required during the reaction can be obtained from both external beginning ( allothermal reforming ) or internal ( antothermal reforming ) , severally.
In the instance of autothermal reforming, a mixture of methane ( natural gas ) , air, and H2O is fed into the reactor. A fraction of the methane reacts with O and provides the heat. The allothermal reforming reactor is fed with methane and steam merely. The endothermal energy is supplied by an external burner.
The chemical reactions are shown:
Due to the high H output with the high reformist efficiency, there is a PEM fuel cell system assembled [ 4 ] , the fuel processor can be classified into 5 chief constituents:
- Reforming reactor,
- Heat money changer,
- CO transition displacement reactor,
- CO methanisation reactor.
In the reforming procedure mentioned above, it is been powered by natural gas. The H2O is preheated with the procedure of methanisation and single-shift, which takes topographic point at the recess and the mercantile establishment of the CO cleansing unit. The waste air from the fuel cell is used to set to an optimal temperature scope for the CO cleansing unit. However, the unpersuaded H in the stock is so flow back and burned in the reformist burner.
Furthermore, there is another component exist in the fuel, the heat, and the power direction system as a compact control unit. Then, the instance of application shown below:
First of wholly, as mentioned before, the reforming procedure takes topographic point with the constituents of H2O and methane, to bring forth H, C dioxide, and C monoxide. The energy produced in this procedure can be used to preheat the H2O etc. Then, a 2nd heat exchange transportation the remainder of heat to heat around the house and the burning gas leaves the system. After reformist, the gas is cleaned in a catalytic reactor and so fed back to the fuel cell. The unpersuaded H is fed back to the reformist burner. The energy can be besides used to heat the imbibing H2O. The PEM fuel cell non merely provides warming and hot H2O, but besides electricity. The grid integrated into the system to guarantee changeless fuel cell operation, and the storage armored combat vehicle is used to maintain the fresh thermic energy.
Different fuel cell based systems.
The cogeneration is widely considered as the major option to accomplish energy, and utilised for residential and supply commercial application. During the research, proton exchange membrane ( PEM ) fuel cell has been detected as the suited engineering among other similar applications. This type of fuel cell can run at a temperature of up to 90 & A ; # 8451 ; , and the stuff been used is besides really flexible with no job, for case, fictile foil can be the electrolyte. There is such a batch of advantages, which make advocates of this engineering expect a important cost decrease. This is really of import for the reformer engineering that is much more complicated and expensive than for the solid oxide fuel cell ( SOFC ) . Mentioning to the present application of 3 kilowatts electrical power, its electric efficiency changing from 35 to 40 per centum and with a entire efficiency of 90 % [ 5 ] .
In the SOFC procedure, due to their high operating temperature mediate 600 & A ; # 8451 ; and 1000 & amp ; # 8451 ; , a broad assortment of fuel cell can be processed [ 6-8 ] , and it is evidently requires particular stuff, which may besides means the stuff is reasonably expensive. For illustration, the electrolyte is made of high engineering ceramic. With an electric efficiency of 40 % which perform better than PEM engineering, however, it takes much longer in start-up and chilling stages which affects clip and costs for installing, care and fix. Commercial units of PEM and SOFC system need a boiler and a hot H2O armored combat vehicle to run in domestic or commercial applications.
The Proton Exchange Membrane ( PEM ) system has extremely fabricating coats and complex H2O direction issues. The stack contains H, O and H2O. If dry, the input opposition is rather high and H2O must be added to acquire the system maintain on traveling, nevertheless, excessively much H2O leads deluging. Freezing can besides damage the stack and the warm up is slow and the public presentation is hapless when cold, the chilling systems are besides expensive.
As mentioned before, the PEM fuel cell necessitate some heavy accoutrements, such as operating compressor, pumps and other equipments consumes up to 30 % of the energy generate. And the life span is short caused by intermittent operation. The PEM fuel cell requires pure H which means there is small tolerance for contaminates such as sulfur compounds or C monoxide. Carbon monoxide can poison the system. Finally, the complexness of mending a fuel cell stack becomes evident when sing that a typical 150V, 50 kilowatt stack contains about 250 cells.
Most fuel cell systems presents would be required to run on H produced by reforming hydrocarbon dodo fuel, the primary beginning of energy today and in the foreseeable hereafter. This could ensue in a loss of public presentation due to the toxic condition of PEM fuel cell anodes by the CO nowadays in the fuel watercourse. Operating PEM fuel cell at a temperature greater than 120 & A ; # 8451 ; would extenuate the consequence of CO on the fuel cell public presentation by weakening the CO chemosorptions.
Increasing the operating temperature besides provide advantages such as sweetenings in the anode and cathode reaction dynamicss, handiness of high quality waste heat, less expensive chilling system, system start-up and shut-down without liquid H2O, and other system integrating advantages.