We have one solvent regneration column which has 4 baffle trays and below which there is a stub-in reboiler at the bottom. Also at the bottom, steam sparger is provided(we think same might have been provided to reduce the boiling point of the column bottoms liquid). Column operates at vacuum (-0.2 kg/cm2g). Column bottom temperature is 187 deg c.Fresh solvent is taken out from top and heavies are removed from bottom intermittantly.The stub in reboiler utilises MP steam(16.5 kg/cm2g) while sparger steam enters at 127 deg C & 1.5 kg/cm2g pressure. The problem is, tubes of this bottom stub in reboiler fail every year and many times, tube bundle is replaced. In recent inspection, the bottom two trays were also found to be fallen & accumulated at bottom.Wanted to know, whether is it a good practice to push steam through sparger in the liquid pool over the bundle of stub in reboiler? And, column bottoms liquid is at 187 deg C & steam enters at 127 deg C. Will that cause steam getting superheated and exert forces on tube bundle & trays above? what could be the possible reasons for both failures and what should be done to avoid them in future?Also, would appreciate any good material or information on mechanical stregthening of trays and various calculations involved.