by Jim Albright, National Sales Manager, Clayton Industries

An effective boiler feedwater treatment program is not only easy to implement, but is also fundamentally important to proper boiler operation, whether the boiler is a conventional firetube or a coil tube type.

Benefits
An effective water treatment program has many benefits. First, it results in efficient operation. Improperly treated water can result in scale build-up that greatly reduces fuel efficiency. Second, proper water treatment reduces the risk of unscheduled down times due to problems resulting from improper water treatment. This results in a more reliable operation.

An effective water treatment program also lowers maintenance costs. Improperly treated water can lead to failures from scale build-up or oxygen corrosion, either of which can mean costly repairs or coil replacement. Finally, a treatment program leads to consistent product quality. Inconsistent water quality can result in inconsistent steam quality. This in turn can affect the quality of the feed.

Elements of an effective feedwater treatment program include treatment, testing and control limits, frequency of testing and record keeping.

Treatment
In most animal feed boiler applications, treatment comprises four steps:

Softening involves treating the boiler water with a resin based (Zeolite) water softener. Water softening is essential to prevent the accumulation of scale on the tubes, which in turn impedes heat transfer and increases fuel consumption. For example, only 1/16-inch of scale build-up increases fuel consumption by 10 percent to 15percent. For a boiler operating at 300 BHP, 16 hours per day, 300 days per year, with a gas cost of $4.00 per MMBTU, this translates to an annual increase in fuel cost of between about $24,000 and $36,000!

In extreme cases, the continued use of un-softened water can lead to scale build-up sufficient to necessitate blocking or replacing a coil. Either fix is time-consuming and costly.

Deaeration removes excess oxygen in the feedwater, which causes corrosion and can necessitate tube replacement. Deaeration is typically accomplished by mechanical agitation aided by chemical treatment. (Sulfites are added to react with oxygen that remains after mechanical deaeration.) Pre-heating the water with steam in the feedwater receiver in an atmospheric or pressurized deaerator assists in stripping oxygen from the feedwater and reduces the amount of sulfites needed.

Addition of chemicals to help eliminate oxygen, control alkalinity (pH), and control sludge. In addition to the sulfites discussed above, other chemicals may be required, depending upon the make-up water analysis and the requirements of the boiler. In cases where condensate is returned to the boiler, a condensate treatment chemical is usually added to neutralize the acidic condensate that would otherwise tend to corrode steam and water piping.

Boiler blow-down controls the level of Total Dissolved Solids (TDS) in the feedwater. Make-up water always contains Total Dissolved Solids (TDS) that are introduced into the boiler water system. Over time, the level of TDS that is in the boiler water system elevates. For every boiler there is a limit to the level of these solids. Exceeding that limit can cause problems with boiler performance, including carry over (excessive water in the steam) or the formation of sludge at the bottom of a firetube boiler.

TDS levels are controlled by "blowing down" (removing) some of the concentrated water and diluting it with additional make-up water. In most cases, this can be done with automatic devices.

Testing
Each boiler manufacturer provides information on the control limits for each of the items that must be controlled in the water. Although the items that must be controlled are similar from one boiler type to another, the point of testing and the limits may vary. For instance, with a firetube boiler, the manufacturer may recommend testing the deaerator water, the boiler water and make-up water. By contract, a steam generator manufacturer requires testing only the feedwater and make-up water. In any case with condensate return, the condensate should be tested.

Testing usually involves simple chemical tests that take only 10 to 15 minutes total and involves checking for:

Hardness. - should be zero.
Dissolved Oxygen - should be zero.
PH, or alkalinity - limits vary with the type of boiler.
TDS - limits vary with the type of boiler.

Frequency of Testing
The frequency of testing depends upon the degree to which the operating conditions vary. In cases of relatively constant operation, testing once per day may be sufficient. On the other hand, in cases of varying conditions - such as steam load, amount of make-up water, and hours of operation - testing once per shift may be advisable.

Record Keeping
Water tests reveal a great deal about the health of a boiler system. As such, it is important to keep accurate logs of all test results. Such logs can be a valuable tool in analyzing boiler problems, in determining possible causes and solutions, and in providing a basis for changes in the water treatment program.

Summary
Implementing and maintaining a good feedwater treatment program is the basis for providing reliable and efficient operation of a boiler, regardless of the boiler type. Feedwater treatment programs are simple and inexpensive, and are essential to help ensure good product quality. This added assurance is especially critical in cases, such as typical animal feedmills, where the steam is added directly to the product. ©