A comprehensive stress analysis was conducted on an assembly comprising two burners and two interconnected chambers. Each burner generates a substantial flame, which combusts waste gas within the chambers. The top chamber is stacked atop the bottom chamber, with both chambers connected by piping that channels flue gas to the bottom burner for further processing. The design must accommodate temperatures up to 350˚C and internal pressures of 5 barg.
The analysis also considered the thermal interactions between the chambers, which could induce significant stresses in the interconnecting piping, particularly in the elbows and connecting nozzles. The assessment followed the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, and included finite element (FE) analyses to evaluate stresses at the nozzle junctions and in the saddles of the bottom chamber.
Stress Analysis
The analysis evaluated all critical components, and modifications to the preliminary design were proposed where necessary. The complexity of the analysis stemmed from the interaction between the top and bottom chambers. The saddles and interconnecting piping played a significant role in this interaction. Bolting created rigid connections between the chambers in both vertical and lateral directions, while friction forces contributed to longitudinal interactions.
These friction forces arose from differential thermal expansion and seismic accelerations. The interconnecting piping was responsible for transferring loads between the chambers. To understand this interaction, a comprehensive model was developed, incorporating all components along with weight loads, thermal conditions, wind loads, seismic loads, and friction on the saddles. This model provided data on pipe stress, saddle loads, nozzle loads, and flange loads, which were used to assess these components. Various temperature distributions were analyzed to account for all possible operational scenarios.
Results
The analysis led to the sizing of slotted holes for the bolting between the top and bottom chamber saddles based on the computed results. Several modifications to the preliminary design were made following consultations with the client. These changes included adjustments to flange ratings, flange materials, and nozzle reinforcements. Additionally, different design options for the saddles were evaluated, and the most suitable option was selected based on the analysis.
This stress assessment ensures the integrity and reliability of the double burner-chamber assembly under operational conditions, addressing potential thermal and mechanical stresses and optimizing the design for safety and performance.
