Return to Economizer Information Main Page Most economizers have been manufactured out of standard carbon steel boiler tubing for the last 75 years. For many industrial applications this is sufficient, however with the rise of energy prices and the pressures of conservation, strides must be made to recover wasted energy in applications that typically would be looked over.
There are times when a cold water economizer is desireable even if the plant is equipped with a de-areator. One of the components of the heat transfer equation is the temperature differential between the inlet water and the inlet flue gas. A boiler with high amounts of make-up water can realize possibly 100% gains in heat recovery using 60 F water as opposed to 227 F water. The additional cost of the stainless alloys required is incremental to the additional recovery.
Most plants, however, have a modest condenate return. unfortunately many lower horsepower boiler plants (under 500 HP) have only an atmospheric condensate return system. These boilers can now also realize an energy recovery.
The main problem with non de-areated water is the dissolved gases (oxygen and carbon dioxide) in the water. When heated, these gases become extremely aggressive and with pit a carbon steel economizer in a matter of days. The correct solution for these applications is to install an economizer manufactured out of stainless steel. Some economizers have been manufactured with copper tubes, however the copper and the steel of the boiler induces a voltaic charge. Unfortunatley, it is the boiler that is plated in this reaction. A dielectric breaker could be installed, but the reality of these is that they often are not up to the task required. The correct solution is to install an economizer manufactured with stainless steel or other alloy tubes. These tubes are resistant to the kinds of corrosion caused by liberated dissolved gases.
Unfortunately, stainless steel is not the wonder cure for economizers. Stainless steel does have its place, however it is not indestructable. The biggest problem with 300 series stainless steel tubes is that they are prone to chloride stress corrosion cracking. High amounts of chlorides in municipal water supplies or improper water softener operation can expose an economizer with enough chloride to destroy it in a matter of days. There is a solution, the use of duplex stainless steels. Duplex is a reference to an alloy of stainless, not two seperate tubes. Typical duplex stainless steels are a combination of 300 and 400 series stainless steels. Duplex stainless steels provide all of the features of standard stainless steel plus the resistance to chlorides that most plants require.
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