That is a good start but the table referenced leaves out an important footnote. That the numbers are based on a steam silica concentration of 0.1 ppm. Most STG manufacturers want to see silica in the 0.010 - 0.005 ppm range.
Silica volatility is part of the equation but so is the efficiency of your cyclone separators and your mist eliminators.
Several EPRI publications have the requested information in them if you have access.
in my utilities plant the BFW pumps are run by steam turbines and motors.sometime the turbine driven pump is kept as auto standby and the motor driven pump is kept in service. while the turbine driven pump is kept as auto standby, its auxiliary lube oil pump(motor driven) is running. During the power failure the running motor driven pump trips and the turbine driven pump governor also trips as the auxiliary lube oil pump also tripped due to power failure. eventhough the auxiliary lube oil pump is equipped with emergecy power supply from diesel generator it took minimum 45 seconds to 1 minute to come online with all emergency breaker closing and resuming emergency power supply for this auxilairay lube oil pump. once the governor is tripped, it takes 5 minutes to reset by approaching the governor. during this time the boiler looses BFW and trips due to low low level in drum. can any one suggest a suitable remedy.( we are in the process of arranging steam tubine driven auxilairy lube oil pump)any other easy method please specifiy.
There is another avenue for silica to enter the steam turbine. The superheater spray attemporator directly adds silica from boiler feedwater into the steam; if you have a 5% spray water flow in the attemporator, thenthe silica content of the turbine inlet steam will be increased by about 5% of tehfeedwater silica content.
For HRSG's there is a growing tendency to not use chevron driers ( in the drum steam space) and instead use demister pads- these may provide an improvement on initial steam quality leaving the drum, but of course have no impact on the silica added in the spray attemporator.
Other causes of spikes in silica include drum water level "humping" caused by uneven steam liberation along the length of the drum ( related to the steam riser distribution form diffferent waterwall zones ), incorrect hole drilling pattern in the drum feedwater pipe, incorrect pressure compensation in the drum water level indicator, and the need to raise drum water lvel due to excess steam entrainment in the downcomer inlet vortex..
