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Steam boilers in food-processing applications

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Author
Dan Holohan
Published
July 16, 2009
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Billy was having a bad day. Mario the Baker had called him first thing that morning to say he was going to drive to Billy’s office and punch him in the face. It seems that Mario the Baker’s steam boiler had just spit about ten gallons of dirty boiler water into the oven along with the steam. That, of course, ruined the rolls, and since Billy’s company serviced this particular boiler, Mario felt that he needed to hit Billy. "You ruina my rolls!" Mario the Baker had screamed into the telephone, so Billy was now on his way to the job. As he drove, he thought about what he would do once he arrived. He wasn’t sure what he would do once he arrived. He was having a very bad day.

Bakers use steam boilers to make their rolls crusty. They have to hit the rolls with the right amount of steam at just the right time, and they have to make sure that the steam isn’t too wet or it will make the rolls mushy rather than crusty. Nobody wants to buy mushy rolls. Mario the Baker had, on this day, cornered the market on mushy because the steam leaving his boiler was way too wet. This, he firmly believed, was Billy’s fault. And, in this, he was partially correct.

On the day he installed the boiler, Billy had told Mario the Baker that these jobs were tricky, and that they had to be piped just so. At the time, however, Mario the Baker was only interested in price. He wanted the job done quickly and cheaply, so that’s what Billy gave him - quick and cheap – because Billy didn’t want to lose the oil account. Billy ran a 1" copper line directly from the steam boiler into the oven. He installed a *" solenoid valve in that 1" line and showed Mario the Baker how to hit the switch for the solenoid valve whenever he desired steam. Billy set the boiler to maintain seven pounds per square inch of pressure so that Mario would not have to wait – and so that he would also burn lots of oil.

When Mario the Baker hit the solenoid’s switch on that first day, it was like pulling the pin on a grenade. The dirty boiler water, driven by the high-velocity steam, rocketed out of the boiler and flew down the 1" copper line. That which would be crusty turned to mush. This is what you get what when you insist on quick and cheap.

Can you can see what’s going on here? You will if you use your imagination. Just think about steam for a minute. At zero psi, it takes up about 1,700 times the space of the water from that produced it. That means that if you turn a pint of water into steam, you’ll need 1,700 pint-size glasses to catch it all. As you raise the pressure, you’ll compress the steam so it will take up less space, but it still takes up a lot more space than the water did. Can you see that in your mind’s eye? Good. Now, confine all that steam under about seven pounds per square inch pressure inside a boiler. Can you imagine how that must feel? The steam wants to get out, right?

What do you suppose happens when you pop that solenoid valve and let that pent-up steam fly down that relatively small copper pipe? Is it any wonder that the dirty boiler water goes with it?

This is why boiler manufacturers want you to use headers and the rest of that semi-elaborate near-boiler piping they specify in their installation-and-operating manuals. They’ve laid out very specific ways for you to pipe their boilers, the idea being that the water should stay in the boiler while the steam is leaving.

This is especially important when you’re using a steam boiler for process work, such as when you want to make rolls crusty. There’s a difference between a steam boiler that’s going to heat a building and a steam boiler that’s going to put steam into an oven. The boiler itself will be the same, but in a bakery, none of the condensate will be coming back to the boiler, and that makes a big difference. You’ll have to feed fresh water into the boiler all day long. Fresh water is murder on cast-iron and steel, and that’s why steam boilers that are used for this sort of commercial process don’t last very long. They wind up with holes in the metal – right there at the water line. It’s oxygen corrosion at its worse. And depending on the quality of the water, this can happen in less than a year.

There are FDA-approved chemicals that are designed specifically for process boilers that provide steam for direct contact with food. These are available from Rochester Midland Co., 333 Hollandbeck St. Rochester, NY 14621, Telephone: (716) 336-2200. These chemicals will add years of life to a process boiler, but you can’t let them leave the boiler because they’re not allowed to touch the food. If the near-boiler and system piping aren’t just right, the chemical can wind up out there with the carry-over water, so be careful.

A good way to protect a process boiler from oxygen corrosion and liming is to feed it through an ordinary water heater. Set the water heater temperature on maximum. Most of the lime that drops out of solution when you heat the water will settle inside the heater instead of the boiler (water heaters are cheaper than boilers, right?).

Install a microbubble air separator on the supply line between the water heater and the automatic water feeder. It will catch the air that comes out of the heated water before it can enter the boiler and cause oxygen-corrosion damage at the water line.

And there you have it – a homemade deaerator that works wonders. The one drawback is that automatic-water-feeder manufacturers recommend you use their feeders only with cold water. This is because lime can settle out on the feeder’s valve seat and keep it from closing tightly. That can lead to a flooded boiler – or in the case of a steam heating system, a flooded house. But this is less of a concern in a process situation where the boiler is losing water to steam all day long. Someone is there to watch what’s going on. And even if you have to replace the automatic water feeder from time to time, it’s still cheaper than replacing the boiler.

So, when you’re selling a boiler to a bakery, resist the quick-and-cheap request. Show Mario the Baker this story, and then sell him a boiler, a water heater, an automatic water feeder and a microbubble air separator.

He’ll be happier in the long run. And so will you.