A Compact, Self-Sustaining Fuel Cell Auxiliary Power Unit Operated on Diesel Fuel

A complete fuel cell-based auxiliary power unit in the 7.5 kWe power class utilizing diesel fuel was developed in accordance with the power density and start-up targets defined by the U.S. Department of Energy. The system includes a highly-integrated fuel processor with multifunctional reactors to facilitate autothermal reforming, the water-gas shift reaction, and catalytic combustion. It was designed with the help of process analyses, on the basis of which two commercial, high-temperature PEFC stacks and balance of plant components were selected. The complete system was packaged, which resulted in a volume of 187.5 l. After achieving a stable and reproducible stack performance based on a modified break-in procedure, a maximum power of 3.3 kWe was demonstrated in a single stack. Despite the strong deviation from design points resulting from a malfunctioning stack, all system functions could be validated. By scaling-up the performance of the functioning stack to the level of two stacks, a power density of 35 We l−1 could be estimated, which is close to the 40 We l−1 target. Furthermore, the start-up time could be reduced to less than 22 min, which exceeds the 30 min target. These results may bring diesel-based fuel cell auxiliary power units a step closer to use in real applications, which is supported by the demonstrated indicators.

Modeling functioning of the pressure regulator in the fuel processor of the air-independent power plant

В статье на основании упрощенной имитационной модели топливного процессора выполнены расчетные исследования в среде LabVIEW с учетом полученных экспериментальных данных. В основу структуры регулятора давления положен ПИ-регулятор с задаваемой зоной нечувствительности сигнала рассогласования заданного и фактического давления парогазовой смеси, составляющей 3 – 3,5% от величины сигнала задания. При этом коэффициенты усиления пропорциональной и интегральной составляющих управляющего сигнала устанавливаются в зависимости от значения задаваемого давления в соответствии с предложенной расчетной программой. Рассмотрена возможность использования привода регулирующего клапана без обратной связи по положению регулирующего органа. Для обеспечения требуемого качества переходных процессов по параметрам установки рекомендовано ограничивать скорость перемещения привода величиной 5 мм/мин., а формирование управляющего сигнала регулятора производить по рассогласованию между заданным и фактическим значениями давления с использованием установленной величины зоны нечувствительности 3 – 3,5%. In the article, on the basis of a simplified simulation model of a fuel processor, computational studies are performed in the LabVIEW programming environment, taking into account the experimental data obtained. The structure of the pressure regulator is based on a PI-regulator with a set dead zone for the signal of the mismatch between the set and actual pressure of the steam-gas mixture, which is 3 – 3.5% of the value of the set signal. In this case, the gains of the proportional and integral components of the control signal are set depending on the value of the set pressure in accordance with the proposed calculation program. The possibility of using a control valve actuator without feedback by the position of the control body is considered. To ensure the required quality of transient processes according to the parameters of the plant, it is recommended to limit the speed of movement of the drive to 5 mm per min, and the formation of the control signal of the regulator is carried out by the mismatch between the set and actual pressure values using the set dead zone value of 3 – 3.5%. The results of the work are described extremely accurately and informatively. The main theoretical and experimental results, actual data, discovered relationships and regularities are presented.

Comparison of integrated fuel processing options for biogas-fed solid-oxide fuel cell plants

The Solid-oxide fuel cell is a highly efficient prime mover for biogas conversion, but a part of biogas needs to be reformulated externally to facilitate the electrochemical conversion, easy control of reforming conditions, and thermal management of the stack. Carbon deposition and external mineralcarrying water should be avoided to ensure the durability of the fuel processor and stack catalysts. This paper investigates four plant layouts with different anode off-gas recirculation schemes and biogas reforming methods: (1) pre-reforming with hot recirculation (HR), (2) pre-reforming with cold recirculation (CR), (3) no pre-reforming and hot recirculation (NR), (4) partial oxidation with hot recirculation (PO). All the schemes feature an electrolyte supported SOFC working at 860°C and 0.23 A/cm2 current density. A sensitivity analysis of the plant efficiency as a function of the Recirculation Ratio (RR) and the Reformer Temperature (RT) is performed. The results show that HR and CR schemes achieve the highest efficiency (58-63%). The HR scheme benefits from the recirculated water and does not require external water for RR > 50% and RT > 600°C; the CR scheme achieves the same result for RR > 80% and RT > 700°C. The optimal RR is within 50 – 80% for the highest system efficiency, as a trade-off between the overall fuel utilization and electrochemistry performance. The RT should be between 600 and 700°C. The HR scheme is the overall best performing if the re-circulator and stack designs do not limit the flow rates at a high RR.

Simplified imitation model of fuel processor in composition of air-independent power plants

В статье представлена упрощенная имитационная модель, описывающая работу топливного процессора в составе воздухонезависимой энергетической установки. Рассмотрено блочное моделирование отдельных составляющих ВНЭУ, в частности, высокотемпературного реактора, блока очистки газа от серы и сажи, первого и второго блоков конверсии, сепаратора и регулирующего клапана. Имитационные модели отдельных элементов ВНЭУ позволяют рассчитывать динамические характеристики энергоустановки и создавать алгоритмы управления клапанами подачи водорода в переходных режимах. Теоретические зависимости для определения массовых расходов реагентов, температур и давлений приведены для идеальных газов с целью представления в среде LabVIEW с учетом полученных экспериментальных данных для проведения расчета маневров по регулированию давления на заданных режимах работы ВНЭУ при различных условиях ее работы. The article presents a simplified simulation model that describes the operation of the fuel processor as part of an air-independent power plant. Block modeling of the individual components of an air-independent power plant, in particular, a high-temperature reactor, a unit for cleaning gas from sulfur and soot, the first and second conversion units, a separator, and a control valve, is considered. Simulation models of individual elements of an air-independent power plant allow you to calculate the dynamic characteristics of a power plant and create algorithms for controlling hydrogen supply valves in transient conditions. Theoretical dependencies for determining the mass flow rates of reagents, temperatures and pressures are given for ideal gases for the purpose of presentation in the LabVIEW environment, taking into account the obtained experimental data for the calculation of maneuvers for regulating pressure at specified operating modes of an air-independent power plant under various operating conditions. The results of the work are described extremely accurately and informatively. The main theoretical and experimental results, actual data, discovered relationships and regularities are presented.