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Simple question for those of you with low pressure steam boilers:  How do you control how much heat is going to the still if the boiler has only on/off operation?  Can someone please describe their setup and how it works?  I've only been exposed to direct heating with electric elements and steam is a different animal.

Cheers,

VB

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Typically a globe valve that allows you to adjust steam flow, just like you would with electric.

Your low pressure boiler will have an upper and lower pressure controls that the burner will cycle around.

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We have a globe valve on our steam line that allows us to control the flow of steam to the still.

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Your boiler will cycle on and off based on pressure. You'll have a pressuretrol (normally two for safety) for which you'll set a pressure and offset. We set our pressure at 8 PSI with a band hysteresis of 3 PSI so it kicks on a 5 PSI and off at 11 PSI.

 

As for control, we have two valves piped in parallel, one 2" valve that open during heatup and then a smaller 3/4" valve used for fine control once the still has come up to temp.

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You can use two smaller boilers each with its own set point so only one will run when you are in the 'heart' or the low demand portion of the day and both will operate under startup conditions like the start of the day or a mash cook.   There are modulating burners (powerflame, etc.) that can be set to a given PSI and hold that PSI over the course of the day.  Honeywell has a boiler control that has high and low set points and a sensitivity band to control within a smaller (+,-) differential range so there is less of a steam impulse.  I set up a PSI meter that allowed the distillers to monitor the steam pressure and control the gate valves against their demand around the available PSI, this could be a simple low pressure steam gauge your plumber can add to the steam line.

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Thanks for the replies.  Can someone post / email me some pictures of their boiler setup / piping?  I'm trying to get my head around boilers.  I'm a mechanical engineer, so boilers are within my realm of understanding, I've just not been exposed to them much...yet. 

Cheers,

VB

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Thanks for all of the responses.

Brian, the website is quite helpful.

What is everyone's take on fire tube vs water tube boilers?  I've got quotes from two vendors, each with a different type?

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Steam is not a popular as it once was and it may be hard to find a local plumber or PE that can guide you through the layers to build a safe, inspected, code compliant and efficient system.

Probably could be looking at efficiency as the underlying factor.  How fast can you get to operating pressure?

Is your code compliant boiler room large enough to service the tubes?  Can they be changed out by a local company (or on site engineer) or would the re-tubing require fairly exotic tools and factory support and re-certification inspection?

Look at the used market.  We found a great boiler nearly new but it was 2500 miles away....

You could consider hiring a chemical treatment company to come in a add boiler/steam (buffering) chemicals  and perform monthly testing to reduce the corrosion of the tubes and steam lines with controlled blow down systems.  Boilers need combustion air supplied from the outside of the building and isolation from sources of fuel.

Are you going with low pressure steam or high pressure steam?  High pressure steam is quite a bit hotter and may allow you do do cool stuff like generate clean steam for direct injection or flash cooking but may require a higher hurdle for licensing, operation and inspection.

So what is your time line and expansion plan or are you just trying to get out of the dirt?

You might want to review the inspection/operating/pressure certification (AHJ) license requirements for what ever system you use.

 

 

 

 

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At your size, firetube vs watertube isn't a consideration. 

Once you're over 2 or 3 million btus, firetube are generally more efficient but need more maintenance cycles. The maintenance downtime is lower than a watertube, though. 

That is only of academic interest. 

The boiler will maintain steam in the line. Controlling it at the still is easy, and there are many ways (globe valve, needle valve..)

I prefer to use a PID controlled pneumo- or servo-actuated pilot valve, with an inline needle valve and a ballvalve shutoff. Unless your still is under 250 gal, and then it's not worth the expense. 

My first real job was as a boiler maintenance engineer :-D

 

Dan

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