Determining Steam Generator Capcity

[Rajjil]

Hi,
we have a steam generator (>30 year old) for which I need to determin the capacity in order to verify the PSV sizes and check its relief capacity for the existing steam generator for reduced rating (PSV set pressure) conditions (de-rating is required due to reduced tube thickness found in recent inspection).
I only have the data for the heat tranfer surfaces for the Economiser and Radiant section. There is no capacity written in the manufacturer data book. The boiler is currently under shut down due to missing regulatory compliance (PSV de-rating) and historical data is of no use as the tubes were cleaned with extensive pigging.
how do I find the capacity of steam generator (I am asking for detail sample calculation or steps)? I guess its not simple heat transfer in a heat exchanger.

 

[rmw]

Sorry, I once knew the answer to that but can't remember and don't know if I can go dig it out. If you can get a book by Babcock and Wilcox titled "Steam", you might find the answer. If forced to give an answer off the top of my head, I think I remember that the figure is 5 lb./hr/ft^2 but don't go to the bank on that.

One thing you will have to do is calculate a decent estimate of your square footage which is as simple as counting your tubes and measuring lengths. Don't count surface like drum or header surfaces even if they do contribute to the steam generation.

BTW, what type of boiler is it? Straight tube, bent tube, fire tube, water tube?

rmw

 

[TD2K]

Is this a conventional steam boiler or is some other hot gas stream used as the heating side fluid? Do you have any control on the steam generation rate or is strictly based on the hot side fluid flow and heat transfer?

 

[Rajjil]

It is Once Through Steam Generator (OTSG), water tube.
I already have the surface area for the radiant and convection section. what could be the next step to calculate?
I am trying to understand the control exactly, there were modifications and don't know whether the drawing I have is reflecting the control.

 

[Rajjil]

RMW,
any idea on how much efficiency for OTSG can be considered. I have burner capacity and also got the "Steam" book, I can calculate amount of steam generated from heat input considering the available heat transfer area of convection and radiant section. thanks

 

[athomas236]

If I understand this correctly, you have a 30 year old OTSG that has been modified to some unknown extent and you want to calculate the boiler output at a reduced operating pressure and hence determine the required safety valve capacity.

I assume that you have no particular experience in boiler performance calculations. Although this assumption may be incorrect.

I first reaction is whether you should be proceeding in the manner described above.

Best regards,

athomas236