With increasing demand of green energy supply with high efficiency and low CO2 emission, solid oxide fuel cell (SOFC) is an attractive choice, thus get more attention of researchers and has been intensively developed in recent years [1]. Its advantages include variety of fuels, high electrical efficiency and full utility of heat, quiet operation and versatility in the electrolyte material [2]. It provides an high electrical efficiency of about 60% in normal operation and up to 90% in combined heat and power operation [3]. It also has the flexibility to be integrated with another power generation source, water heating device and cooling device used in residential homes [4]. To further its application for large scale, the integration of SOFC with gasification using coal or biomass as feedstock shows potential in power generation [5–7]. And it seems a feasible and prospective way for integration gasfication with fuel cell (IGFC).
Most of researches on SOFC focus on materials for the development of anode, electrolyte and cathode as well as performance test of cell [8, 9]. And different cells have been developed for better chemical stability and electrochemical performance. As the performance of cells improving, SOFC stacks consisting of multi-layer cells should obtain more attention to widen the applications, while not much research work on them. Lim et al. fabricated and characterized an anode-supported flat tubular SOFC stack for intermediate temperature operation and the result show a maximum power of nearly 921W at 750℃ using H2 (fuel utilization ratio = 25.2%) as the stability test period is about 200 h [10]. Fang et al. conducted durability test and investigated degradation behavior of a 2.5 kW SOFC stack with internal reforming of LNG [11]. They also tested two stacks of different design under high utilization of up to 90% with humidified hydrogen or 10% pre-reformed LNG, and the results found that high fuel utilization could introduce polarization and a high risk of fuel starvation [12].The fuel utilization ratio is between 64%~80% and mostly about 70% while the feeding fuels of the anode side are H2 or simulated reformate gas, and the stability test period is more than 5000 h under 700℃. Edison R&D center built a 5 kW SOFC system and conducted life test for 1500 h at fixed power output (1500W) over four start-up/shutdown cycles, and the system power was upt to 3000W during the first test sessions. [13].
Researches also have been explored on combine SOFC with gasfication to widen the application in more fields for heat utilization besides electrical supply. Lim et al. constructed a pressurized 5 kW class anode-supported planar SOFC power generation system with a pre-former for a fuel cell/gas turbine hybrid system [14]. The results show that the output of the SOFC stack was 4.7 kW for the pre-performed gas while the output increased to 5.1 kW at 3.5 atm (abs.). Modelling of common hybrid configuration of the SOFC-Gas turbine system illustrated a significant efficiency upgrade. The combined SOFC-Gas turbine system produces an electric efficiency up to 50% and better syngas utilization compared to the implementation of each single technology [15]. Subotic et al. discussed the applicability of the SOFC technology for coupling with biomass-gasifier systems, using commercial SOFC single cells of industrial size fueled with different representative producer gas compositions of industrial relevance at two relevant operating temperatures [7]. The results show that feeding SOFC with a producer gas from a downdraft gasifier, with hot gas cleaning operating temperature of 750 °C represents the most favorable setting, considering system integration and the highest fuel utilization.
There are still few commercial SOFC stacks available in market. To build a demonstration of SOFC power generation system in MW class scale, hundreds of stacks should be well assembled and it is important to distribute the fuel gas for each stack in order to prevent fuel starvation. When coupled with gasfication to use practical produce gas as fuel, long term durability of stacks should be tested as most research using simulated produce gas. As there still lack of performance results of multi-stacks SOFC system using syngas as fuel from industrial gasfiers fed with coal, we fabricated a test rig of 5 kW SOFC system using practical syngas from industrial gasifier as fuel to explore the feasibility of a MW class IGFC demonstration equipment. As syngas used as fuel for the anode side, it has been reported that it might lead to fast degradation phenomena due to the impurities such as hydrogen sulphide or tars as well as coke deposition [16–19]. Thus an long term test using practical industrial syngas under high fuel utility was conducted to investigate the influence of syngas on the performance of stacks in this work.