a difficuilt question

You are asking what happens to the driven system if you have a drop in the driving vapor with associated drop in speed of 12%? It will be driven at a speed 12% less. Actually, the speed drop is already the consequence of the drop of energy in the system.

Do you need a constant speed in it? Have considered using a pressure regulator and work with some supply pressure margin to minimize variations in vapor supply and speed fluctuations?

Based on experience in gas turbines, a 12% drop in speed without load fluctuation (thats what you have, load constant and drop in input energy) and without impact in the transmission shafts and gears should give you no problems. The client system (the process that is using the power) may observe some malfunction due to running out of specs. Except, of course, if this variation is cyclic, frequent, and occurs also in the speed increase. So you could observe some wear and fatigue in the gears and in the turbine blades due to power increase too fast.

But this is only my experience. Maybe some guy here with vapor driven turbines have another oppinion.

my dear if you have a experience of gear boxes then pl Tell me what will happen with gear box bearing especially with fix geometry taper land thrust bearing. if the exhaust pressure of blower reduced due decrease in speed. is there is no surging occur?

is there is no jerk load on gear box bearings?

Is the turbine only driving the ID through the gearbox, or is this only a tap off of the system? What is the main function of the Steam turbine? Various implications can be assosiated by a reduction in running frequency. The purpose of the turbine to only drive an ID Fan does not make any sense.

my dear

I d fan is sucking air from a furnace to mixing the air with methane in NH3 plant. id fan's(centrifugal blower) driver is turbine through-gear box which reduce the speed by 5 time.