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Re: stack economizers

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Posted by ex-Economizer Guy on August 06, 2002 at 15:52:54:

In Reply to: Re: stack economizers posted by Tom Stanton on July 30, 2002 at 12:37:42:

: For a 100 horsepower firetube boiler, don't bother with an economizer. You will end up with more headaches than you need.

Having designed and sold small economizers in the past that's not a fair statement. You can realize a nice energy recovery from a 100 HP boiler provided you understand the unique operational aspects of these smaller applications. Reguardless of boiler size I'm sure any operator would like to see a 3% to 5% or more reduction in their fuel bill. Converting 100,000 pph industrial watertube boiler economizer rules to a 100 HP commercial firetube boiler doesn't always work, that's where a lot of problems come from. Some of the differences that need to be accommodated are as follows: Feedwater is not typically deaerated so you need a unit with a stainless steel tubes and fins. Carbon steel tubes will be destroyed by condensation or oxygen pitting if there is no DA. Provisions for on-off feedwater systems must be incorporated since modulating systems are not common on these smaller boilers. Again no big deal just add a feedwater recirculation loop and recirc pump, we're not talking expensive items. Some kind of positive circulation must be built into the system. Failure to compensate for the periodic stop in flow of an on/off system will lift the economizer safety as the water stagnates in the economizer tubes and steams. The economizer is doing it's job, it is not it's fault that the installation is incorrect. Units with removable tubes like a Cain RTR or Cannon Feedwater Heater allow for fast and inexpensive repair of failed tubes. Remember, some of the damage the economizer is taking is damage your boiler is shielded from like oxygen pitting of the tubes. It's a lot cheaper to repair an economizer than it is to retube your boiler. Make sure the economizer also has provisions to keep condensation out of the boiler. One of the biggest failure modes I had seen was freezing tubes, that's not the economizers fault. Again if you go with a replaceable tube unit the fix is cheap and easy. Stay away from any design that cannot be repaired in place. The biggest drawback with these small units is operational hours. These smaller boilers often do not have the annual hours to justify the investment of an economizer. While the recovery per hour is good, there is often not enough hours to justify the expense. I'm sure you can get a lot more support from a sales engineer at Cain or Cannon.

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