Green chemicals are a class of compounds that are biodegradable. In boiler applications, usually that will be the oxygen scavenger, and perhaps a corrosion inhibitor or two. There is no definition for "green," unless you are Kermit the Frog, and even then it's not easy.

For most boiler water treatment applications, the majority of the chemical compounds used tend to be inorganic and non-biodegradable. This is primarily because the boiler needs a strongly alkaline source to prevent corrosion. As a result, most of the boilers have a pH of 8.5 or above depending upon the pressure in the boiler. The other thing most boilers need is "soft" water, free of calcium and magnesium ions, and that process is usually performed by ion exchange or sometimes chemical softening.

Each of those processes has their advantages and disadvantages. The chemical softening produces a chemical sludge which can be stabilized and sent off for inert landfilling. The ion exchange generally uses a sodium chloride as a regenerant, and that gives a volume of liquid brine which is contaminated with calcium and magnesium. If you have some place to put the spent regnerant, that's fine. Most often, it is diluted and sent into the wastewater treatment plant where it passes harmlessly through the treatment system. Boiler blowdown should be sent to the facility waste water treatment plant, as it contains whatever was in the boiler. The key there is the chemicals added to the system. Boiler acid cleaning and other chemicals should be contained and neutralized where appropriate.

You will be able to find some additional information on specific brands of chemicals in the "green pages," at www.eco-web.com/index/category/2.6.html, or you may want to talk to your local boiler chemicals representative to insure that the compounds he is selling are biodegradable. In order to do that, you will want to inspect the MSDS for the boiler chemicals. Toxicity and biodegradability are listed on the sheets. Most boiler suppliers, including NALCO, BETZ and others have a line of "green compounds" for boilers.

One final thing is the attempt to be green is more of an attitude and application of existing technology. For example, take a look at your cooling towers and investigate the chemicals. If you are using phosphates, that's one thing, but untreated blowdown can cause algal blooms unless you reduce the phosphates. If you are using chromates, (there is a general prohibition against chromates unless you have a process system for manufacturing connected to the cooling tower. The prohibition is in using chromates for comfort cooling) the chromates have high toxicity and good corrosions resistance, but they have been largely replaced by antimony and other compounds of slightly less toxicity. Although Antimony is not necessarily a good choice because it too has a degree of toxicity- just lower than chromate. Talk to your chemical suppliers, and for heaven's sake, watch your solvent usages and control the use of degreasing chemicals on the base. Those are critical to being green.