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• 1. [Article] Pressure effects on density-difference driven stratified flow : CFD model of DCC event in the HTGR

  In a Modular High Temperature Gas Reactor (MHTGR), the Depressurized Conduction Cooldown (DCC) event can be separated into three distinct stages: 1) depressurization, 2) air ingress and, 3) natural circulation. ...

  Citation × Citation Citation Abstract Copy Title: Pressure effects on density-difference driven stratified flow : CFD model of DCC event in the HTGR Author: Magnusson, Jill E. In a Modular High Temperature Gas Reactor (MHTGR), the Depressurized Conduction Cooldown (DCC) event can be separated into three distinct stages: 1) depressurization, 2) air ingress and, 3) natural circulation. During normal operations, the HTGR utilizes forced convection to move the helium coolant through the reactor core. Thus, during normal operations the helium is pressurized to about 7 MPa. As a result of the high pressure system, when a DCC event is initialized, there exists a pressure difference between the helium coolant inside the vessel and the ambient air outside the vessel. After depressurization there exist an air-helium mixture of higher density than the helium in the reactor vessel. This results in the air-helium mixture ingressing into the reactor vessel through stratified flow. The High Temperature Test Facility (HTTF), under construction at Oregon State University, is a scaled model of the MHTGR. The HTTF is being built for code validation purposes. This study is to utilize CFD methods to simulate a DCC event in the HTTF. With this CFD simulation the effects of the depressurization stage on the rest of the model will be quantified. Title: Pressure effects on density-difference driven stratified flow : CFD model of DCC event in the HTGR Author: Magnusson, Jill E. In a Modular High Temperature Gas Reactor (MHTGR), the Depressurized Conduction Cooldown (DCC) event can be separated into three distinct stages: 1) depressurization, 2) air ingress and, 3) natural circulation. During normal operations, the HTGR utilizes forced convection to move the helium coolant through the reactor core. Thus, during normal operations the helium is pressurized to about 7 MPa. As a result of the high pressure system, when a DCC event is initialized, there exists a pressure difference between the helium coolant inside the vessel and the ambient air outside the vessel. After depressurization there exist an air-helium mixture of higher density than the helium in the reactor vessel. This results in the air-helium mixture ingressing into the reactor vessel through stratified flow. The High Temperature Test Facility (HTTF), under construction at Oregon State University, is a scaled model of the MHTGR. The HTTF is being built for code validation purposes. This study is to utilize CFD methods to simulate a DCC event in the HTTF. With this CFD simulation the effects of the depressurization stage on the rest of the model will be quantified. Close

• 2. [Article] Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor

  Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were ...

  Citation × Citation Citation Abstract Copy Title: Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor Author: Goodwin, Aaron K. Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were used to gasify biomass constituents in supercritical water. The first reactor configuration was a micro diameter stainless steel or Hastelloy tube (508 µm – 762 µm) imbedded into a reactor block. The reactor provided high rates of heat transfer to the reacting fluid to sustain an isothermal reaction temperature and was used to elucidate interactions between phenol, a lignin model compound, and xylose, a hemicellulose model compound, during co-gasification. In addition, a reaction mechanism and kinetics for phenol and xylose gasification by supercritical were estimated. The second microreactor configuration studied was a parallel channel Hastelloy microreactor. The reactor consisted of 14 parallel rectangular microchannels (1000 µm by 127 µm) integrated into a single contiguous reactor block by diffusion bonding a series of shims between two header plates. Fabrication of the reactor from Hastelloy C-276, a high nickel content alloy, substantially intensified biomass gasification reactions and promoted the water gas shift and methanation reactions due to its high catalytic activity and the large surface area to volume ratio in the microchannel. The dispersion and channel flow distribution in the microchannel reactor was characterized experimentally and modeled using computational fluid dynamics by a tracer pulse study. Furthermore, computational fluid dynamics were used to investigate the effect of endothermic biomass reforming reactions and the average fluid Reynolds number on the reaction temperature. Lastly, xylose was completely gasified to hydrogen and carbon dioxide in the parallel channel microreactor at 650°C and 250 bar within a 1.4 second residence time. Title: Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor Author: Goodwin, Aaron K. Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were used to gasify biomass constituents in supercritical water. The first reactor configuration was a micro diameter stainless steel or Hastelloy tube (508 µm – 762 µm) imbedded into a reactor block. The reactor provided high rates of heat transfer to the reacting fluid to sustain an isothermal reaction temperature and was used to elucidate interactions between phenol, a lignin model compound, and xylose, a hemicellulose model compound, during co-gasification. In addition, a reaction mechanism and kinetics for phenol and xylose gasification by supercritical were estimated. The second microreactor configuration studied was a parallel channel Hastelloy microreactor. The reactor consisted of 14 parallel rectangular microchannels (1000 µm by 127 µm) integrated into a single contiguous reactor block by diffusion bonding a series of shims between two header plates. Fabrication of the reactor from Hastelloy C-276, a high nickel content alloy, substantially intensified biomass gasification reactions and promoted the water gas shift and methanation reactions due to its high catalytic activity and the large surface area to volume ratio in the microchannel. The dispersion and channel flow distribution in the microchannel reactor was characterized experimentally and modeled using computational fluid dynamics by a tracer pulse study. Furthermore, computational fluid dynamics were used to investigate the effect of endothermic biomass reforming reactions and the average fluid Reynolds number on the reaction temperature. Lastly, xylose was completely gasified to hydrogen and carbon dioxide in the parallel channel microreactor at 650°C and 250 bar within a 1.4 second residence time. Close