Channel flow catalytic combustion

J. Mantzaras, C. Appel, P. Benz, and U. Dogwiler. Numerical Modelling of Turbulent Catalytically Stabilized Channel Flow Combustion. Catalysis Today, 59 3-17,2000. 

Mantzaras J, Appel C Effects of finite rate heterogeneous kinetics on homogeneous ignition in catalytically stabilized channel-flow combustion. Combust Flame 130 336—351, 2002. 

Mantzaras J, Benz P An asymptotic and numerical investigation of homogeneous ignition in catalytically stabihzed channel flow combustion. Combust Flame 119 455—472, 1999. 

Mantzaras J, Appel C, Benz P, Dogwiler U Numerical modelling of turbulent catalytically stabilized channel flow combustion, Catal Today 53 3—17, 2000b. 

In Chap. 7, the investigation on combustion stabihty is extended to propane-fueled catalytic microreactors, using the catalytic and gas-phase chemical reaction schemes of propane combustion on platinum proposed and validated in Chap. 4. The steady hetero-Zhomogeneous combustion of lean propaneZair and methaneZair mixtures in a platinum-coated, catalytic plane channel-flow microreactor were investigated at pressures of 1 and 5 bar, channel heights of 1.0 and 0.3 mm, and wall thermal conductivities of 2 and 16 WZmK. Stability limits were assessed as a function of fuel type, inlet velocity, and imposed external heat losses. Parametric studies were performed with a full-eUiptic, two-dimensional numerical model employing detailed gas-phase (homogeneous) reaction schemes for both fuels. 

Fig. 1.4 Illustration of the chemically reacting boundary-layer flow in a single channel of a catalytic-combustion monolith.

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

Catalytic combustion in a monolith channel provides an illustration of boundary-layer flow in a channel [322], Figure 17.18 shows a typical monolith structure and the particular single-channel geometry used in this example. Since every channel within the monolith structure behaves essentially alike, only one channel needs to be analyzed. Also a cylindrical channel is used to approximate the actual shape of the channels. 

Catalysts are often implemented in the walls of monolith channels, with overall performance depending on a balance between surface reactivity and flow conditions. Consider a situation that represents a catalytic-combustion monolith such as in a gas-turbine system (e.g., Fig. 17.17), where an individual channel diameter of d = 2 mm and a length of L = 5 cm. The channel walls may be assumed to be isothermal at Tw = 800°C. A CH4-air mixture enters the monolith with a equivalence ratio of(p = 0.3, inlet temperature of Tm — 400°C, and pressure of p = 1 atm. 

An incremental improvement in the path to practical applications of catalytic combustion was disclosed by Yasuyoshi et al., who recognized the important applications of manipulating the heat balance in Eq. (5). These authors coated the walls of alternate channels to have only half of the reactant flow passing through catalytic channels. For similar heat transfer coefficients in coated and uncoated channels, and assuming that there is no temperature gradient in the channel wall, the heat removal term in the heat balance is given by Eq. (7). 

Tonkovich et al. [182] succeeded in obtaining a very thick washcoat on a MSR for the catalytic steam reforming of methane. The reactor was built from Inconel , a NiCrMo alloy, and consisted of a slit-like reaction channel with cross-flow combustion channels for autothermal operation... 

A honeycomb shape has been considered as the most desirable structure for the combustion catalyst due to a small pressure drop across the channel and a large surface-to-volume ratio. Stable combustion can be attained with laminar flow of gas mixture along the channel of the honeycomb, whereas turbulent flow and back-mixing are operative for the conventional flame combustion. The temperature at the honeycomb wall rises rapidly with fuel contact. The rate of homogeneous reaction depends on the fuel concentration and temperature therefore, the non-catalytic gas-phase reaction initiates from this hot wall where the temperature is raised by catalytic combustion. Once this catalytically initiated gas-phase reaction started, the reaction propagates rapidly toward the center of the channel. Then the high combustion efficiency can be attained. ... 

Another intricate coupling between transport and hetero-Z homogeneous chemistry occurs in turbulent catalytic combustion. In catalytic reactoK of large turbines operating at fuU load, the inlet Reynolds numbers in each individual honeycomb channel can exceed 30,000. In entry channel flows with heat transfer from the hot wall to the flowing gas, which... 

Lucci P, Prouzakis CE, Mantzaras J Three-dimensional direct numerical simulation of turbulent channel flow catalytic combustion of hydrogen over platinum, Proc Combust Inst... 

MantzarasJ, Appel C, Benz P Catalytic combustion of methane/air mixtures over platinum homogeneous ignition distances in channel flow configurations, Proc Combust Inst 28 1349-1357, 2000a. 

Use detailed numerical models and chemical schemes to investigate the combustion stabihty and hetero-Zhomogeneous chemistry coupling in methane- and propane-fueled catalytic, channel-flow microreactors while accounting for all relevant heat transfer mechanisms, for both transient and steady-state reactor conditions. 

Chapter 2 introduces the experimental methodology of in situ Raman spectroscopy of major gas-phase combustion species and laser induced fluorescence (LIF) of the OH radical, which were employed in an optically accessible, channel-flow, catalytic reactor to study the hetero-Zhomogeneous combustion of propane on platinum imder conditions pertinent to micro-gas-turbines. Moreover, a high-pressme test rig used in evaluating the thermal power output of a mesoscale catalytic honeycomb bmner is presented. 

By choosing a time step for the transient solid temperature equation long enough for gas-phase equilibration, the discretized, time-independent set of the Navier-Stokes equations under the boundary layer approximation can be solved for the flow field inside the catalytic channels [12] (quasisteady assumption for the gas-phase) using the CRESLAF package [13]. The applicability of the boundary layer approach in catalytic combustion at sufficiently large Reynolds numbers (Re > 20) has already been demonstrated [14]. The simplified equations thus become ... 

Appel C, Mantzaras J, Schaeren R, Bombach R, Inauen A (2005) Turbulent catalytically stabilized combustion of hydrogen/air mixtures in entry channel flows. Combust Flame 140 70-92... 

Dr. Karagiannidis doctoral thesis investigates combustion characteristics in channel-flow catalytic microcombustors/microreactors, with emphasis placed on microturbine concepts for portable power generation (an initiative within the Swiss Federal Institute of Technology Zurich) which employ reheat and have operational pressures up to 5 bar. 

Development of models that descnbe the flow in monolith channels in catalytic converters has received great attention [68,69]. See also Ref. 58 and references therein. As with channel interaction, the models applicable to monolith combustion catalysts are similar to those for catalytic converters... 

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