What is Streams in Superheater or Economizer?

Sad Dragon,

Calculating massflow for a particular economizer or superheater is done by the boiler vendor and is recorded in the contract documents. This specific document is called a mass/energy balance.

Because most boiler owners discard all important documentation, this is a near impossible question for a new engineer to answer.

Suggest that you contact the original boiler vendor and ask if they will give you what you desire from their records.

It is nearly impossible to empirically measure massflow rates on hot high temperature piping systems using temporary instruments and devices