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Home arrow Environment arrow A Novel SOFC Tri-generation System for Building Applications
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Experimental Method

To start the micro-tubular SOFC CHP system, the gas valve on the propane cylinder is opened. The micro-tubular SOFC electrical output cables are then connected to the battery pack. The micro-tubular SOFC ON button is then pressed. The digital display on the micro-tubular SOFC unit will show the operating voltage of the battery pack and the number of hours of operation the unit has completed to date. The voltage of the battery pack needs to be at 11.8 V for the micro-tubular SOFC unit to begin start-up. If the voltage of the battery pack is greater than this, the electrical load needs to be connected to discharge the battery. Once 11.8 V is achieved the micro-tubular SOFC will go into heat-up mode. Heating of the micro-tubular SOFC system is achieved through the combustion of propane in the afterburner. This takes approximately 20 min. During this time a current flow of 2.95 A from the battery pack to the micro-tubular SOFC is observed: this is due to the micro-tubular SOFC parasitic energy consumption (35 W). Once the system is up to temperature (~600 °C), it goes into power production. Now a current flow of approximately 20 A (when operating at a 250 We output) from the micro-tubular SOFC to the battery pack is observed. It is important that the electrical load (lamps) on the battery pack is maintained during micro-tubular SOFC operation to avoid the battery voltage exceeding 13 V and the micro-tubular SOFC shutting down. Voltage and current readings are taken every two minutes, and the results recorded. The sulphur trap has a lifetime of 250 h. It is essential this is not exceeded as sulphur poisoning will damage the stack. The micro-tubular SOFC unit’s operating hour counter is on a 250 h loop so that the replacement milestones are clear. Throughout micro-tubular SOFC CHP and tri-generation system tests, a constant fuel input of 100 g h-1 is assumed.

During the micro-tubular SOFC heat up period, the pump in the WHR circuit is switched on and the water volumetric flow is set to the required test conditions. During micro-tubular SOFC CHP tests, the water in the WHR is simply circulated from the tank and through the recupertaor plate heat exchanger using the by-pass loop. The WHR inlet and outlet water temperatures are recorded and used to calculate the WHR thermal output. The tank volume is sufficient to act as a thermal load to the micro-tubular SOFC. During tri-generation system testing the microtubular SOFC CHP system is operated in the same manner as described above. However, the water in the WHR loop is diverted through the regenerator plate heat exchanger (PX1) to heat the desiccant solution. The SDCS experimental method has been provided previously in detail in Sect. 6.2.2. The experimental metrics used to evaluate the performance of the micro-tubular SOFC CHP and tri-generation system are provided below.

The DC electrical power output of the micro-tubular SOFC is determined using Eq. 7.1.

The thermal output of the micro-tubular SOFC is determined using Eq. 7.2.

The heat capacity is evaluated using a validated EES function. The electrical efficiency of the micro-tubular SOFC is calculated using Eq. 7.3, and is based on the LHV of the propane fuel (4.635 x 107 J kg-1). The mass flow rate of the fuel input is assumed constant at 0.00002778 kg s-1 (100 g h-1).

The co-generation efficiency of the micro-tubular SOFC CHP system is determined using Eq. 7.4.

The complete tri-generation system efficiency is shown in Eq. 7.5.

During the tri-generation system evaluation, Welec,net is the DC electrical output of the micro-tubular SOFC minus the parasitic energy consumption of the SDCS

(Waux,des).

Section 7.3.4 has provided the experimental method and evaluation metrics used to assess the micro-tubular SOFC CHP and tri-generation system. Section 7.4 presents the experimental results and analysis.

 
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