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Re: effieciency help

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Posted by response on October 23, 2006 at 14:04:46:

In Reply to: effieciency help posted by Jo on October 23, 2006 at 13:21:55:

If I understand you are asking a few questions. As for what is the improvement in boiler efficiency if operating pressure is reduced from 250 psig to 200 psig, the answer is almost nothing.

You would need to describe the use of the steam a little better as well to answer a consumption question. The enthalpy of 250 psig steam is 1,203 btu/lb and has a saturated temperature of 406 deg F. 200 psig steam is 1,201 btu/lb with a saturated temp of 388 deg F. Depending on how the steam is being utilized will answer the questions. The enthalpy is almost the same so if the steam is direct injected into a liquid there is almost no difference in total energy transferred. The slightly lower saturated steam temperature however may have a slight impact as the Log Mean Temperature Differential (LMTD) of the heat exchange model would be reduced. Simply put reduced LMTD with no other changes to the system will result in a reduction in total btu transfer, again without knowing the system details it could be negligible but could be something (it's probably nothing).

There are other considerations such as the slightly greater volume of lower pressure steam may have a slightly higher pressure loss when traveling through the same size steam piping resulting in higher losses than at the higher operating pressure, again would probably be extremely minor differences. Lower pressure operation may have maintenance advantages although I am not experienced with that aspect to comment as an expert. Might even be other considerations that are not coming to mind as I type fast to leave for lunch.

I guess to sum it up the efficiency improvement would be negligible. As for the impact to the rest of the system, that is a function of what the rest of the system.

You want to make a big and easy increase in efficiency: install a stainless steel economizer to preheat the 100% make-up water, that should buy you somewhere around a 6% increase in efficiency. Install it between the softener and feedwater tank so you don't have to change your feedwater system. The hotter the water entering the boiler the less energy required to heat it to saturated temperature.

I hope I have answered your question.

: boiler operates at 250 psi and 10 000#/hr of steam production. If pressure is reduced to 200 psi would the steam consumption increase and what would be the savingss. boiler feeds a consumer that is a saturated steam digester and 100% makeup.

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