API Publ 935:1999 pdf download.Thermal Conductivity Measurement Study of Refractory Castables
Thermal conductivity is a physical property that provides guidance in designing refractory systems for equipment in which heat loss and/or thermal behavior are important. The accuracy of reporting and understanding thermal conductivity is vital to developing the most cost effective, efficient, and reliable equipment. The refractory industry uses various methods for measur- ing and reporting thermal conductivity that contribute to con- fusion in interpreting thermal conductivity data. The presence of chemically combined moisture in unfired castable masses complicates the measurement of thermal conductivity. The moisture contributes to higher thermal conductivity values until it is removed. Improper removal of the moisture during initial heat-up can also contribute to incorrect thermal con- ductivity data. Temperatures associated with refining of petroleum prod- ucts are considerably lower than other industries such as steel, foundries, aluminum, etc. At low operating temperatures (1000°F — 1400°F), removal of chemically combined water from refractory castable linings is incomplete, and castable products do not achieve the optimum thermal characteristics. Removal of chemically combined water is a function of tem- perature. The majority of chemically combined water— approximately 70%—is removed between 500°F and 850°F, with the remainder dissociating up to 1250°F. This is illus- trated in a Thermo-Gravimetric Analysis (TGA), shown in Appendix A. Historically, thermal conductivity of castables was represented as a single value. More representative multi- point curves were later introduced as heat loss became more important but captured data while cooling a specimen fired to within 100°F of its use limit. Data collected during cooling of specimens is classified as descending data.
The study concluded that the different thermal conductivity procedures/apparatuses yield very different results. Thermal conductivity of lightweight and medium weight insulating castables varied by 100%, depending on the measuring tech- nique. As density increased, differences in thermal conductiv- ity values attributed to measuring technique decreased but were still significant. Test results also indicate that differences in ascending and descending thermal conductivity data, for the castables studies, are considerable and worthy of design consideration. It is recommended that users and designers utilize ascend- ing thermal conductivity curves (data) in designing refractory lining systems, where heat transfer is a major consideration for applications below 1500°F. It is also recommended that users and designers evaluate thermal conductivity data and the method of measuring the data before using the data in designs when heat transfer and skin temperatures are impor- tant to successful equipment operation.
API Publ 935:1999 pdf download
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