Application of the boiling model to a steam drum and recirculation loop

Because the boiling model described above is fully explicit, it is rapid and easy to apply. It has been used with success in modelling steam drums and boiler recirculation loops, direct-contact feedwater heaters, high-pressure feedwater heaters, deaerator towers and vessels, condensers and refrigeration loops. The application of the boiling model to a steam drum and recirculation loop will be discussed in the next section because of its importance for the modelling of power stations. 

4 Application of the boiling modei to a steam drum and recirculation loop 

It is possible to obtain a very good representation for control engineering purposes by decomposing the boiler recirculation loop, into four notional lumped sections  

To a good approximation, we may treat the subcooled region as having a constant volume of the order of 10% of the liquid volume in the drum. It may be treated as separate from the equilibrium thermodynamics of the steam drum. It may be regarded as an extension of the downcomer, with its volume added to that of the downcomer pipework in order to work out a downcomer time delay. 

The downcomer flow, Wj, will be determined by the pump characteristic, as it pumps from the drum at 

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