Our client had developed a proprietary biomass thermal reactor designed for large scale production of renewable pipeline grade natural gas. Forestry waste product is used as the primary fuel and converted to natural gas through a thermochemical process. In order to be deemed fit for service, the design was required to be analysed per Section XIII Div 2 of the ASME Boiler Pressure Vessel Code (BPVC). The analysis is used in order to determine the maximum number of thermal cycles that the reactor vessel could safely withstand and was an important project for our client as the results supported the registration of the vessel within the jurisdiction of its intended location.
To fulfill code obligations, the BPVC code specifies the use of an FEA thermal simulation and a specific calculation technique that, when combined, determine the maximum metal temperature differences during ramp-up and steady state operation. These areas of maximum metal temperature differences indicate the highest thermally induced stresses in the design and therefore the areas likely to fail first due to thermal stress cycling (fatigue).
Innovex first imported a 3D CAD model developed by the client into our FEA environment. All mechanical and thermal material properties of the various assembly components were accurately defined. A custom material was created to define the insulation jacket which shrouds a significant portion of the reactor. Ambient environment conditions were specified in order to model convective heat loss which occurred mostly from the uninsulated areas. Although a relatively minor contributor to the thermal flow in this case, radiative heat transfer was also included in the model. After several preparatory runs to ensure accurate FEA meshing and suitable boundary conditions, a transient simulation was run which generated a temperature profile that changed during the initial heating phase as it increased to a steady state condition. These results were tabulated and later analysed to determine the maximum metal temperature differences per the BPVC method. The maximum permissible number of cycles was determined and subsequently provided to the client.