How to calculate the cost of wasted steam?

[bigdog50]

I would like to know if anybody could tell me how to calculate what the cost is to replace 200 psig of steam. What I'm trying to do is fiqure out what it's costing us in burning natural gas in the 501F dln gas turbine to reproduce 200 psig of steam. This 200 psig of steam is sent to HP dump and to the condenser, Start up vent and superheater drains on start up. This steam is being wasted before we even have flame in are turbine and at this point, flow for cooling and condensate removal should not be an issue, but I'm trying to convence those higher powers above me! Can anybody help? This steam that is wasted is not measured in kpph(flow) All I have for a reference is HP drum pressure and 200 psig is about what we throw away before pressure start gaining again. Thanks for any infor you may provide. Note, Equipment info, Siemens 501fg Gas turbine, N.E. 3 pressure hrsg. HP steam 2400 psig rated. Normal op. is 1700 psig with out duct burners.

FLORIDA,
BIGDOG50

 

[yogibear1]

If you can equate the cost of the gas per BTU or some other unit to the BTU's of wasted steam you would have the beginning of a comparison for your argument. After that you would want to perhaps figure a time based argument e.g. so many time units of wasted steam equates to $$$ wasted.
A few more pieces of data would be helpful: The steam temperature and pressure, and the pipe size (diameter and schedule).

 

[EdStainless]

Why do you start in this sequence? Per mfg instructions? Who designed the plant?

There are a lot of reasons to have steam in the system before you fire. Pre-heat and de-airiation are two that come to mind.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[metengr]

Fuel used during start-up to provide steam for turbine seals, and the feedwater cycle processes is part of the embedded cost of doing business. I suppose you could calculate this cost based on the time for start-up to provide aux steam at 200 psig. You should know or be able to calculate the fuel consumption per minute during start-up X amount of time for the start-up X cost of the fuel, as a rough estimate.

 

[bigdog50]

Metengr, We already have seals established we have up to 1100 psi of main steam on the HP drum. But on are start procedures they require us to place all dumps valves to the steam condenser to cascade which when a CTG is not running it defaults to a value of 877 psig. So on start up you have 1100 psig and You issue a start on the CTG. and you HP dump opens 25 % to meet 877 psig and there goes you HP steam. and for the next 35 min. before psig turns around.

thanks

FLORIDA,
BIGDOG50

 

[chicopee]

Figure out the percentage of steam wasted on a mass basis. First calculate the actual operating cost for lets say 24hrs,or 48hrs. The longer the operating hours the better the accuracy. During these operating hours you will have produced a certain amount of steam from which a percentage will be wasted. That percentage can be applied to the operating cost.