Adding chemical treatment to boilers

Volume 2/ Issue 5/ September 2015

An engineer planning to specify a Domestic 75CBM22-85 BFU recently asked us if it’s feasible to have a chemical feed pump come on at the same time as the make-up to the BFU. The chemicals wouldn’t be pumped into the receiver, but instead added to the make-up water.

We advised the customer that adding chemicals to the boiler feed receiver or through the make-up water will void warranties. This is noted in every Domestic Pump Series operations manual:

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But let’s talk about when and how to add treatment chemicals.

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The drawing below shows the standard industry practice which has remained consistent for many years: by means of the funnel and receptacle between the pumps and boiler. That way you can periodically check treatment chemicals and add what’s needed to the boiler.

Some people have tried to automate this process (in other words, skipping service and maintenance contracts, leaving everything to the magic black box, and not knowing what’s really going on). They replace isolation valves on the discharge piping with a series of solenoid or similar control valves that open every time the pump comes on. The goal is to use the pump to mix and inject the chemicals.

This setup is often linked to a building management system via an auxiliary contact on the pump starter. Each and every time the pump comes on, the BMS is notified and performs a specified action. I’m sure the M&M guys can tell you more about the effects of this action on probes and other components. But our experience with pumps is that this approach simply doesn’t work.

So let’s cut to the chase. Please don’t let your customers inject chemicals in any form into the boiler feed receiver. At the very least they’ll create the following issues:

1. Solid or powdered chemicals injected into the boiler feed receiver won’t fully dissolve. There’s just not enough mixing. The result is rapid seal failure, a consequence of pumping high concentrations of abrasive solids—which also skew the pH beyond the seal’s rating (typically a pH of 7-9). Less-abrasive liquid compounds still raise the pH issue and can be equally dangerous.

2. The skewing of the pH also accelerates corrosion in the pumps / floats switches and other areas, increasing failures. Add the air from the vented receiver, plus a steam system’s high temperatures, and the potential for failure is doubled.

3. Using the make-up water as the mixing agent, then piping into the solenoid make up piping, is likely to compound the dissolving issues. The typical make-up water temperature is too low. Using liquid agents still leaves the other issues in the receiver. We continue to recommend a slightly more hands-on approach that includes regular checks and periodic reviews of the system as a whole. It’s like changing the oil in your car and doing other scheduled maintenance, rather than waiting for the engine to seize up and self-destruct.

If you rely on the chemical guy for answers, you may hear “if a little is good, a lot is better” (mainly for the chemical guy’s sales numbers). Have the customer look at what the boiler guy recommends for treating the boiler and how to handle its introduction. Then talk to the trap people and controls guys to make sure what you’re doing won’t contradict their products. Now factor in what I’ve said, and you should reach a happy medium that gets the best results for everybody.

Ultimately, as with any system, it’s not about what’s right for one part. It’s about what’s right for the system as a whole to keep it in proper balance, providing many years of efficient service.