Here, we report on the fabrication of flame retardant hydrophobic cotton fabrics based on the coating with two-dimensional hexagonal boron nitride (2D hBN) nanosheets. A simple one-step solution dipping process was used to coat the fabrics by taking advantage of the strong bonding between diethylenetriamine and hBN on the cotton surface. Exposure to direct flame confirmed the improvement of the flame retardant properties of the coated cotton fabrics. In turn, removal of the flame source revealed self-extinguishing properties. Molecular dynamics simulations indicate that hBN hinders combustion by reducing the rate at which oxygen molecules reach the cotton surface. This time-saving and one-step approach for the fabrication of flame-retardant cotton fabrics offers significant advantages over other, less efficient production methods.
One of the pulverized coal fired thermal power plants in India intended to find the root cause of frequent boiler tube failures in three 210 MW units. Operation & Maintenance history and feedback from plant O&M team revealed that economizer tube failure was a frequent cause of forced outage. The plant under study used CFS (continuous fin surface) economizer with staggered tube arrangement in the 210 MW units. CFS staggered tube economizers originally appealed to many plant designers because the tortuous path created for the flue gas, enhanced heat absorption and the fins could capture heat and transfer it to the tubing. This made the CFS economizer less costly and easy for installation in a relatively small space.
There is increasing use of lower quality high ash coals over the past few decades. Due to this fact an advantage of the CFS economizer design became a disadvantage. The narrow spacing in the tubes proved more susceptible to plugging and fly ash erosion. Literature study and the root cause analysis suggested that CFS staggered arrangement of economizer could be one of the prominent reason of failure of economizer tube bundle due to fly ash erosion. Flue gas flow simulation also highlighted that there is increase in velocity of flue gases across the economizer. A bare tube in-line configuration in place of existing CFS economizer was an alternative. To recommend an alternate economizer as solution, the merits of an in-line bare tube economizer were studied. Bare tubes arranged in-line are most conservative in hostile environments with high ash content, are least likely to plug, and have the lowest gas-side resistance per unit of heat transfer.
A bare tube in-line economizer that can replace the existing finned tube economizer in the available space while meeting the existing design & performance parameters is recommended. An attempt was made to model & analyze the new economizer using computational fluid dynamics (CFD) tools in order to get firsthand experience and validate the results obtained using manual calculations. With limited computational resources and not so fine meshing, the performed CFD model analysis showed the expected trend but did not completely match the results.
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