All the typical ChemE books cover this tpoic. Simply, the chimney tray is a seal tray in the column with a hole in the bottom that has a piece of pipr going upward. As the liquids fall down the coulmn, they stack up on the sealed tray, they then leave out a nozzel just above the tray. Since the liquids are being captured to be routed to a reboiler, it is evedent that it will take some pressure to force the liquids over to the reboiler and back to the column as a vapor or as a two-phase mixture. In order to achieve this presure, the liquid will rise until the liquid head pressure over comes the pressure drop through the rebolier. The height of the liquid needed is basically the pressure drop expressed as feet of the fluid. For example, if the pressure drop is calculated as 1 psi, then it would take about .43 inches of water height on the chimey tray, furthermore if the liquid has a density of 1/2 that of water, then it will take .86 feet of that liquid. The tube that rises above the chimney tray will have to be about 1 foot high to make sure any liquid that falls on the tray will stack up and flow out the nozzel and not overfill and run down the pipe and by-pass the heater.
The tough part is calculating the pressure drop through the reboiler. The drop is the sum of the fluid flowing to the reboiler, the drop through the heater, and finally the drop on the two-phase flow back to the column.
Good Luck
