Start-up time

Another critical issue affecting end-users acceptance is the start-up time of the fuel processor. This is affected mostly by the time demand for heating to the operating temperature. Three main options to get the individual devices of the fuel processor to the appropriate temperature exist  

Electrical heating requires power supply by an interim storage device, i.e. a battery. Even though batteries exist as buffer devices in most fuel cell system concepts, their size would need to increase considerably to meet the demands for start-up. Therefore, battery power is a less viable option especially for hydrocarbon reforming systems, where high operating temperatures of the reformer exceeding 600 °C need to be achieved. 

Another option is direct heating through the flow path of the fuel by applying catalytic or conventional burners, which may be either part of the power supply system of the fuel processor or additionally installed devices (start-up burner). By direct contact of the combustion off-gas with the various devices, rapid start-up of even larger scale fuel processors seems to be feasible [10], However, a major drawback is the restriction to catalyst systems which can tolerate hot combustion off-gases. 

Indirect heating by a start-up burner through a dedicated flow path avoids the direct contact of the catalysts with combustion off-gases. Here micro structured channel systems offer unique possibilities at low overall pressure drop of the start-up system. 

---

The failure rates and times-to-restore developed used a variety of data sources and data construction methodologies and are presented in Section 2. The principal methodology used is a kind of failure mode analysis for each component several principle modes of failure are analyed by characteristics including frequency of occurence, repair time, start-up time, and shut-down time. From these an average failure rate is developed and expressed as failures per million hours and mean time between failure(MTBF). 

P 53] Before operation, a start-up time of about 10 min was applied to stabilize pressure in the chip micro reactor ([R 6]) [20]. As a result, a stable flow pattern was achieved. The reactant solutions were filled into vials. Slugs from the reactant solutions were introduced sequentially into the micro chip reactor with the autosampler and propelled through the chip with methanol as driving solvent. The flow rates were set to 1 pi min The slug volume was reduced to 2.5 pi. 

The transient viscosity f] = T2i(t)/y0 diverges gradually without ever reaching steady shear flow conditions. This clarifies the type of singularity which the viscosity exhibits at the LST The steady shear viscosity is undefined at LST, since the infinitely long relaxation time of the critical gel would require an infinitely long start-up time. 

The start-up time does not depend on the longest relaxation time of the material even if it is orders of magnitude larger than the period In/co [115]. This is an important prerequisite for an experiment near LST. 

Start-Up Time and Transient Response for Storage Systems.336... 

A power failure exceeding the time limit is most critical during MD. In this case a standby power generator with a start up time of e. g. 1 min either for the operation of the whole plant or at least for the critical components is the only answer. The sequence of importance for the components can be ... 

All of the drive power of the Sequel is in an 11-inch-high chassis. The individual powered wheels provide excellent control on snow, mud, ice and uneven terrain. GM s start-up time in freezing conditions is less than 15 seconds at -20°C. GM knew that if they are going to put these cars into the marketplace, they would have to start in the middle of a northern winter. 

Besides the PEMFC being developed for vehicle propulsion, SOFC are being considered for APU applications in vehicles, since they operate at very high temperatures and therefore require long start-up times (an hour or more). In APU applications, the fuel cell can be left running most of the time, or could be started far in advance of an anticipated stop. The principal attraction of SOFCs is their high tolerance to hydrocarbon fuels. The heat of the SOFC can be used in the air-conditioning unit, either as heat or as cold. 

In stationary applications, the cost targets for fuel cells, at approximately 3000/kW, are not as stringent as in fuel-cell cars. For instance, the costs of MCFCs and SOFCs are currently in the range of 8500- 20 000/kW. The start-up time and the load... 

In order to minimize system volume, (and minimize the associated system weight and start-up time) integration of the system components is a key design issue. By recycling the entire anode tailgas to provide steam, a water management system can be avoided, though a hot gas recirculation system is required. 

Flow-injection and continuous-flow systems are very similar. The major differences are outhned here. Continuous-flow systems are characterized by a relatively long start-up time prior to instrument stabilization, whereas the flow-injection approach requires little more time than that needed to stabilize the detector output. Tubing diameters on a flow-injection manifold are usually much smaller and the samples are injected into the flow line rather than aspirated. No wash cycle is employed in the flow-injection regime, since the sample is a discrete slug. Flow rates in continuous-flow manifolds are often larger than in the flow-injection regime. 

Heinzel et al. [77] compared the performance of a natural gas autothermal reformer with that of a steam reformer. The ATR reactor was loaded with a Pt catalyst on a metallic substrate followed by a fixed bed of Pt catalyst. In the start-up phase, the metallic substrate was electrically heated until the catalytic combustion of a stoichiometric methane-air mixture occurred. The reactor temperature was increased by the heat of the combustion reaction and later water was added to limit the temperature rise in the catalyst, while the air flow was reduced to sub-stoichiometric settings. With respect to the steam reformer, the behavior of the ATR reactor was more flexible regarding the start-up time and the load change, thus being more suitable for small-scale stationary applications. 

Other simulation studies reported on the differences between ATR and SR fuel processors for liquid hydrocarbons [82]. The results showed that a fuel processor based on the SR technology gives a higher power than an ATR-based fuel processor. However, this higher performance is counterbalanced by a much higher plant complexity, resulting in increased cost and an impact on system controllability and start-up time. 

A compact design for a gasoline fuel processor for auxiliary power unit (APU) applications, including an autothermal reformer followed by WGS and selective oxidation stages, was reported by Severin et al. [83]. The overall fuel processor efficiency was about 77% with a start-up time of 30 min. 

A 2kW hydrogen generation unit, developed and tested by Cipiti et al. [84], included an ATR unit followed by intermediate WGS and preferential oxidation stages. Preliminary experimental results showed that propane was completely converted and that the CO content in the outlet stream was 0.2% (dry basis). However, a start-up time of about 50 min was observed. 

PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast start-up time, low sensitivity to orientation, and favourable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses. 

Develop a 45% efficient reformer-based fuel cell power system for transportation operating on clean hydrocarbon or alcohol-based fuel that meets emissions standards, a start up time of 30 seconds, and a projected manufactured costof 45/kW by 2010 and 30/kW by 2015. 

A go/no go decision for on-board fuel processing work is scheduled for 2004. The primary criteria for this decision will be the identification of a credible path to achieve a 30-second start-up time target. 

Toto industries, in Japan, manufacture micro-tubular SOFCs that are 15 cm long. The operating temperature is around 500°C. Start up time at room temperature is possible in 5 minutes. These systems are well suited to provide power in the small range size. The electrical efficiency is around 55% (Saito et al., 2005). 

Lockett et al. (2004) present one of the first models on micro-tubular SOFCs that are 10 cm long. Although the cell is very short, there is a temperature gradient along it this means that in some areas of the cell the temperature is not optimal. The advantage of these cells versus the longer ones is that the start up time of the micro-tubular cells is very short (minutes). 

---