Designing the optimal geometry of a membrane reactor for hydrogen production from a pre-reformed gas mixture based on the extent of the reaction boundary layer

Modeling Fixed Bed Membrane Reactors for Hydrogen Production through Steam Reforming Reactions: A Critical Analysis

“…Obviously, in some cases this loss of information may be insignificant, particularly when the membrane permeability is low or the mass dispersion is high; however, in other cases the error made on the concentration profiles by introducing this approximation translates into an error in the evaluation of integral quantities, such as the total hydrogen permeate flow rate and recovery, and consequently in the design of the reactors. In fact, a strict relationship between the behavior of local variables (i.e., concentration profiles) in proximity of the membrane and integral quantities has been shown in previous works [ 55 , 84 ] (see discussion of Figure 7 below).…”

“…Its upperbound is 1 if no hydrogen is present in the feed. Separator-based yield: This parameter has been introduced in [ 54 , 55 ] and is defined as the ratio between the hydrogen permeate flow rate and the inlet hydrogen flow rate. Naturally, this parameter can only be defined if hydrogen is already present in the feed and is particularly significant if the feed is the product of a pre-reactor in which equilibrium conditions have been reached.…”

“…A thorough discussion and review of the description of the rate of reaction for low temperature methane steam reforming may be found in [ 86 ], whereas reaction rate expressions proposed for methane steam reforming in a wider temperature range on Ni-based catalysts are summarized in [ 87 ]. It is worth mentioning that several authors have reported that in commonly used operating conditions and with the catalysts available the reaction rate is often high enough as to make it possible to consider local equilibrium in every point of the reactor [ 4 , 5 , 12 , 55 ].…”

“…The first two assumptions actually coincide with choices on the operating conditions. The first is equivalent to envisaging the presence of a traditional pre-reforming reactor before the membrane reactor and was motivated by the observation that the initial length of the membrane would be useless should the feed consist exclusively of methane and steam [ 53 , 55 , 138 ]. This is particularly important since the Pd-based membranes are often the most expensive component of membrane reactors.…”

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

“…Alternatively, a heat exchanger-type reactor may be envisaged, in which a heating medium receives the solar radiation and transfers it to the reactor wall, which in turn heats the process fluid [5]. The latter solution has been proposed, for example, for the solar-driven steam reforming of fossil fuels in membrane reactors [7][8][9][10]. The presence of a heat transfer fluid represents an additional resistance to heat transport, thereby lowering the maximum operating temperature in the reactor, but also introduces a heat storage medium, thus allowing a continuous operation of the system despite the intermittency of solar radiation.…”