Transport Characteristic Study On Methanol Steam Reforming For Hydrogen Production In Micochannel Reactor

Proton exchange membrane fuel cell (PEMFC) is generally accepted that it is a high-efficiency,energy-efficient and pro-environment type of power generation in the 21 century. It has a widely application future in both fixed power generating plant and mobile electric power sources. But PEMFC's commercialization needs hydrogen source. Methanol reforming for hydrogen production is one way to solve the problem. In the three types of methanol reforming, namely methanol partial oxidation (POX),methanol steam reforming (MSR) and methanol autothermal reforming (ATR), MSR has the advantage of low reaction temperature,high hydrogen and low carbon monoxide content in the reforming products.Currently, the study of MSR is mainly focus on the development of highly active catalyst. However, the process of MSR is a strongly endothermal reaction, it is usually limited by heat and mass transfer and shows a low dynamic responds and cold spot in the catalyst bed. But there is little reseach pay attention to this question. The only method to intensify and optimize the process of MSR is the adoption of microreactor and coating catalyst which is recently developed in laboratory. Through the minimization of the reactor channel and application of coating catalyst one can improve the transport characteristic in the reactor. Therefore, the study of transport characteristic on MSR for hydrogen production in micochannel reactor is beneficial to this technology's industry application and spread.So in this thesis, through the analysis of MSR literature at home and abroad, we designed and fabricated a innovative stainless steel microreactor which can adopt both kernel catalyst and coating catalyst. We also proposed a catalytic coating fabrication method by cold gas dynamic spray technology. Experiment and simulation study were carried out on MSR reaction in the microreactor and coating catalyst fabrication. The main research work of this thesis includes:(1) In order to intensify the transport process of MSR for hydrogen production, a microreactor which includes the function of preheating,evaperation,superheating and reaction is innovatively designed and fabricated. Effects of reaction temperature,water and methanol molar ratio,liquid space velocity on the reactor outlet parameters such as methanol conversion are studied through experiment. A 3-D model is established for the reactor as to describe the performance of the reactor. On basis of this, by means of optimize the process of heat transfer in the microchannel, for the fist time effect of unequally distributed catalytic bed were studied on methanol conversion and hydrogen content at reactor outlet. The optimum condition of the reactor was obtained; The 3-D model can reflect performance of the microreactor to a certain extent. Methanol conversion and outlet H2 content can be increased through catalytic bed unequal distribution of sparsely at inlet and dense at outlet. Compare unequally distributed with equally catalytic bed, the cold spot temperature difference reduced, experiment results proved that H2 content at outlet increases and CO decreases.(2) In order to further optimize the transport charactor of MSR in microchanel reactor, the effects of catalytic surface distribution,catalytic activity distribution,type of catalyst distribution on this reaction were innovately investigated by numerical simulation. Results show that, at the same conditions, through interrupted distribution of catalytic surface, one can improve methanol conversion although the temperature in reaction channel becomes uneven. So in microreators which utilize coating catalyst, this interrupted distribution of surface can improve the efficiency of catalyst and thus reduce the cost of catalyst. One can also improve methanol conversion through reasonable catalytic surface activity distribution; The optimal activity distribution is that the activity should be low at inlet, along with the reactor channel, the activity gradually go up; This kind of activity distribution can also be used to decrease the cold spot temperature difference in the reactor. Methanol conversion can also be increased through interrupted distribution of catalyst coating types.(3) Copper coating was fabricated by cold gas dynamic spray (CGDS) on aluminum substrate. For the fist time Cu-Al2O3 composite power,CuO/ZnO/Al2O3 and NiO/Al2O3 catalyst powers were used as feedstock for coating fabrication this technology. MSR experiment was carried out on the fist three type of coating for hydrogen production; The microstructure,micro-region and phase composition of the coating before and after the reaction were analyzed by SEM,EDX and XRD. Results show that, four kinds of coating were effectively deposited on the substrate, among which the copper coating has a better bonding with aluminum substrate. For the catalytic coating, the carrying gas heating temperature and impacting angle of the powder with the substrate in spraying has large influence on it's morphology. As to the composite coating, different power property has important effects on the quality of Cu-Al2O3 coating. MSR experiment results show that all the cold sprayed coating which contains copper has activity to this reaction, among which the copper coating has a low activity and stability, Cu-Al2O3 has a higher stability compared to copper coating, CuO/ZnO/Al2O3 has the highest activity.(4) Finally we investigate the possibility of reactor integration,scale-up and function integration in one channel. The 3-D simulation results of MSR for hydrogen production in self-designed plate microreactor show that in microreactor it can maintain high hydrogen molar fraction and methanol conversion at high reactant flow rate. After fuction integration of MSR reaction,water gas shift (WGS) reaction and partial oxidation of CO (PrOX) reaction in one channel, reactor outlet parameters such as methanol conversion,hydrogen and carbon monoxide mole fraction under optimum condition can completely satisfy the request of PEMFC.