3 replies to this topic

[art_has]

Dear All,

Now I'm working at engineering design stage which dealt with steam system.
Referring to steam system, there might be any steam let-down from higher to lower steam pressure for balancing the overall steam/mass balance.

I would like to know the principle of Steam Let-Down, especially how can we determine the amount of steam that will be passed through Let-Down System, because this information will be useful to determine the capacity of Desuperheater.

Thank you for your help and if anyone here have references or link which may be useful, your info will be higly appreciated.

Regards,
Hastings

[fallah]

Steam let down would be done when you need low pressure steam and have in hand medium/high pressure steam.The applications would be such as inlet of steam to steam reboiler where you need low pressure steam.

If you are specifying the desuperheater for purchasing you need to determine its capacity as steam flowrate to be passed through it for vendor.

[chemsac2]

Your query is not clear. Still I would give a preliminary method to decide steam flow for let down system.

If you are designing entire steam distribution system, you need to know total steam consumption of all levels i.e. HP plus MP plus LP steam. This will be your boiler capacity.

Typically boilers generate high pressure steam (efficient to generate HP steam than LP steam).

Boiler capacity minus HP steam consumption would be let down to MP steam header. MP steam generated thus would be let down to LP after all MP steam users get their requirement.

Corrections need to be made due to BFW used for superheat.

Regards,

Sachin

[Padmakar Katre]

Dear,
The design of the steam boiler steam flow as per requirement of the total steam load of the unit will be less. As the users like reboilers which will use the saturated steam at different pressure levels. The saturation steam is achieved through a PRDS where the degree of superheat(If boiler generates superheated steam + degree of superheat due to let-down) will be removed by injection of boiler feed water. So when you calculate the steam load at reboilers then it will be the sum of the superheated steam plus the boiler feed water injected.