Why? (1) Condensate water (condensed steam) is of too high value to waste. (2) Condensate can contain up to 20% of the energy required to make the steam in the boiler. (3) Maximizing the amount of condensate that is returned to the boiler can help save both energy and water treatment chemicals.
The value of the condensate varies with its pressure and temperature which depends on the operating pressure of the steam system. If boiler feedwater is 60F, and the condensate is 212F, then each pound of condensate contains at least 162 BTUs (212-60=152); if the boiler is operating at 80% efficiency, then it represents 190 BTUs (122/80%)
RECOVER YOUR FLASH
Flash steam is formed when high pressure/temperature condensate is suddenly decreased in pressure. A facility may have two steam operating pressures, such as a high pressure for process loads, and a low pressure for heating water and space heating equipment. If there is enough differential in the steam pressures, about 75 psi, flash steam from the high pressure condensate can be recovered to supply steam to the low pressure steam header. If not recovered in a flash steam generator, high pressure condensate is either flashed to steam and vented (lost), or may be used in the deaerator to pre-heat boiler feed water. The economics of a flash steam recovery system will depend on the amount of flash steam available and how much can be used in applications such as the deaerator.
Typical operation involves passing the high pressure steam through a pressure reducing valve to form low pressure steam. (Example: 100psi high pressure to 25 psi low pressure.) High pressure condensate enters the flash steam generator, a rapid drop in pressure flashes some of the condensate to steam that goes up into the low pressure steam header, and the rest becomes low pressure condensate that flows into a pumping steam trap that returns it to the low pressure condensate return line.
STEAM ECONOMICS 101
As an example: Assume an 80% boiler efficiency and a steam recovery rate of 1,060 lbs of steam per hour. On a BTU basis, this steam is worth at least 1,200 BTUs, per pound. Assume for the sake of this example that natural gas is $6.00 per million BTUs, the value is at least (1,060 lbs x 1,200 BTUs) / (1,000,000 BTUs x 80% Boiler Efficiency) x $6.00=$9.54 per hour. That’s a lot of spare change available to SAVE. Additionally, steam “gained” is in effect “treated” steam recovered. The ability to maximize steam usage and minimize condensate “lost” results in a lower make-up water rates and as a result a reduction in chemical treatment costs.