Adding a proportional control valve to an LP gas valve train 1

[probrewer]

Hi!

I'm building a 200-L fully automated, gas-fired pilot brewery. Here's the problem: I need to be able to remotely modulate the flame from a ~50,000-Btu/hr impinged jet gas burner via a potentiometer mounted on the control panel. The only valves I've been able to find that meet my criteria are the Asco 8202/3 Proportional solenoid valves, but they don't appear to be compataible with combustable gas; and the Asco AH8D series actuators/V710 body, which seem to be too big.

Basically, I need to be able to throttle down the burner as the temperature in the kettle approaches 100*C, because of the instability of the wort as it comes to a boil. (Wort is what beer is called prior to fermentation).

Wort coming to an initial boil has a nasty tendency to violently boil over the top of the kettle if the firing rate is too high at boiling point, until the proteins in the wort have had time to coagulate, and then it settles down for the remainder of the 1-hr boil.

Does anyone have any ideas on how to safely and reliably perform this task, or better yet, a good book? Ultimately, I have to thoroughly understand this system because I am the one who is going to have to build and maintain it.

Thank you for any insight,

harlan.

 

[lownox]

Could you not use a two-stage gas valve? and cycle it?

Otherwise...
Check out Maxitrol.

http://www.maxitrol.com/SelectraMod/modulator.html

You would need the positive pressure valves. These things use a 0-20VDC signal, so that is not readily available. You could build a simple voltage source for it that you could control with a potentiometer.

If you are contolling this thing manually, you could always figure out the rate reduction you need and add a manual valve with a fixed stop so you don't go below the "minimum" you require.

From a safety standpoint, make sure you stay within the operating limits of the burner with regard to CO, flame stability, etc. Good Luck with it.

Milwaukee valve makes an inexpensive valve they call the butterball. It is a tight, shutoff butterfly valve that you could retro-fit with an direct coupled actuator.

 

[probrewer]

Thanks lownox!

The Milwaukee valves are beautiful--Grainger had them in stock and I've got one in front of me right now. This was exactly what I was looking for but I had no idea they even existed in this small of a package.

A couple more questions, if I may:

1. The placement of this valve should be downstream of my valve train/flame safeguard controls but before the manual shutoff valve I'm placing just before the burner, correct?

2. You suggest retro-fitting a direct coupled actuator to this valve--can you suggest any that are reasonably priced? I know how to attach it and get it to work, I just don't know which one to get. Milwaukee Valve makes one but it looks expensive (model MCR100I, according to their "Actuation Sizing Charts") and is probably overkill.

3. Is there an advantage to using a 3/4-in. butterfly valve vs. a 1/2-in. valve insofar as my ability to make finer adjustments? These burners have a pretty poor turn-down ratio, and being able to "expand the scale" would be beneficial.

4. I'm with you on the CO question and safety--my design plan is to work backwards from the burner adding additional components only after I've proven the previous component. My plan is to hook up the valve to the burner and manually "play" with it to determine the *actual* usage range, then add the actuator controlled by a potentiometer to replicate my manual actions and make it impossible to fire the burner below those limits. Clearly, it has to function perfectly every time since I will be using it while I'm looking into the boiling kettle, not looking into the combustion chamber watching the flame. Does this sound like a prudent approach?

I think that's it on this topic, and again, thank you so much for generously sharing your knowlege.

harlan.

 

[lownox]

Check Belimo for an actuator. they have some small ones... you may have to make a small bracket to hold the actuator from rotating and you can use a coupler/set screw to extend the shaft of the butterball valve if needed. Powerflame uses this setup on their X4 modulating burner, but with a honeywell actuator. The belimo is smaller though. I will look tomorrow and let you know which one I used before.

You can put this valve after everything in the gas train.

At 50MBH, I would use the 1/2" valve. You aren't going to have "great" control, but the Belimo actuators have "stops" you can use to limit the stroke. That shouldn't be an issue. You probably end up around 50-70% of full rate??? Is that your target?

Hopefully you have access to a combustion analyzer so you can check the CO.

Also, I don't have a problem helping you. If you are making beer... that is a good thing.

 

[probrewer]

lownox,

Thanks for the tip on the Belimo actuator!

I don't need *great* control, just enough to prevent a boil-over which can occur in the first 15-min. of boil if the burner is set too high...which brings to light another question: right now, I'm looking at Solarflo impinged jet and slotted cap jet burners as the heat source. Do you know off hand which type will give a larger turn-down ratio? Do you have a better suggestion?

Assuming I've sized the burner correctly, 50-75% should be just fine. In fact, the only reason for oversizing the burner at all would be to reduce the time it takes to just heat the wort up to the boiling point. Once the wort has calmed down, I can raise the firing rate again, if necessary, since I'm only interested in maintaining a vigorous enough boil to flocculate the proteins and extract the bittering compounds from the hops--which require the mechanical action of the rolling boil--but not so high that I get excessive evaporation because it decreases yield (read: less beer!).

Is combustion analysis a one time deal or is this something that should be part of routine maintenence? Could I get away with using a Kidde Nighthawk CO/Gas alarm to do the testing?

Thank you again for your help,

harlan.

 

[lownox]

I assume you are just putting this burner under the boiling pot, right? If this is the case, it would be difficult to get a proper CO measurement. Definitely have some sort of CO alarm in the area though. Most of them will sound off at 200ppm or so. That standard changed within the last few years and I don't remember the exact point at which they sound off.

Will you be using natural gas or LP? Regardless, the burner appears to operate at 3.5"WC on Natural and 11" on LP. These manifold pressure will yeild full input of the burner. Will you have a gas flow meter in line that you can clock?

Turndown ratios are listed on the Solarflo website. Don't exceed those and you should be OK. Rate can be calculated based on manifold pressure. for example...

SQRT(p2/p1)* q1 = q2

Say you reduced the manifold pressure with your valve by half, so... the square root of .5 is .707, so .707 times 50MBH gets you down to 35.36MBH. Make sense? Maybe you already know how to do this, so no offence if I am stating the obvious to you. This is a basic calculation and will work for what you are doing.

Let me know how the beer tastes.

BTW, are you doing this indoors? May get hot in that room.

 

[probrewer]

No, the burner is going to go inside a combustion chamber with all primary and secondary combustion air piped in from below the burner with outdoor air. A properly sized flue will be installed as well to exhaust combustion gasses. The kettle, a 55-gal SS drum, will sit atop the combustion chamber.

The kettle is to be a permanantly mounted structure, insulated with 2-in. rigid fiberglass and probably encased in brick or tile to facilitate cleaning.

I'm going to be using LP from one or two 100-lb tanks--no gas flow meter, but I can get the same data by accurately weighing the tanks before and after a given period of time, no?

The room will get hot AND steamy. There's a possiblity that I'm going to be forced to have a dome welded to the top of the kettle with a vent pipe--175-L with a 7.5% evaporation rate is 13-14-L water vapor released to the room every hour.

I take offense at nothing--I spend all my free time reading manuals in an attempt to understand something that is way outside my comfort zone.

I went to Belimo's web site and downloaded a bunch of info--I'm filtering through it now. I'll let you know which actuator I think will work and run it past you to verify that I know what I'm doing :-D BTW, the Milwaukee valves have the following specs:
1/2-in. valve = 18-in/lbs torque; 13 Cv
3/8-in. valve = 18-in/lbs torque; 10 Cv

Does this mean that I will get slightly more modulation control from the 3/8-in. valve vs the 1/2-in? All the Solarflo burners in the Btu range I'm looking at have a 3/8-in. pipe size.

By the time you're done with me you're going to want to build a brewery for yourself!

harlan.

 

[lownox]

I would use the 3/8 valve. The actuator I used before was the LM series. You should be able to order one for 0-135 Ohms, but I was wondering if it would make sense to just use a 2 position actuator. Once you dial in the rate reduction you want you could cycle it between the two rates. Full modulation seems a bit overkill.

I wouldn't bother weighing the tanks. The pressure method I mentioned will be much easier for you. With regard to weight... the tanks won't become lighter at a very significant rate, so that method may prove to be ineffective.

Another option I was thinking about for this... if you only need to reduce the rate at the beginning of the boiling cycle, you could manifold two regulators in parallel with one set for 11" and the other set for 5"-ish and switch the higher pressure on and off to take the rate up and down. Just a thought. Nevermind, you could use a 2 stage gas valve like a White-Rogers 36G54. Here is a link.

http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-6464.pdf

Then just switch between high and low fire.

 

[probrewer]

OK, things are starting to make a little sense here. It looks like the actuator I want is Belimo LMB24-SR, proportional control actuator. Is this the right one? Is the blank (or conduit) option the one that I want?

http://www.belimo.us/bellib/Damper_Actuators/LMB24_SR_T.pdf

Question: you said I should use the 3/8" valve with a 3/8" pipe to the burner; what should I use with a burner with a 1/2" pipe?

I'm assuming I should still use the 3/8" valve because at the low pressures I'm running, I'm getting full flow before the valve is fully opened, but that more of the valve stem motion is available for modulation. Is that correct?

Again, I can't thank you enough for walking me through this.

harlan.

 

[lownox]

You are correct. The size of the valve is depends on the flow you will be operating at. 20cfh of LP gas is not a lot. Even with the 1/2" valve the amount of control will be small. You will have full flow before the valve is completely open and the effective stroke will be small. This is why I have been asking about 2 stage control. The butterball valve will work and won't cost a fortune, so no worries.

That actuator will work, but keep in mind it uses a 0-10VDC control signal.

 

[probrewer]

Perfect! I found this for $110 after shipping, does that seem about right to you?

http://www.controldepot.net/index.asp?PageAction=VIEWPROD&ProdID=2869

So, I'll have the valve and the actuator; now I need a control signal. This is where I always have problems: I can put anything together properly if I have the right parts, but like I've said, I'm way outside my comfort zone here. What would be a good choice to place on the control panel to control the actuator? I would prefer a dial rather than buttons.

Once I get this together, I'll be able to control a burner with just an adjustable regulator upstream from the valve/actuator, followed by the burner downstream. In this way, I can experiment on sizing the burner such that the burner is powerful enough to perform the task, but not so powerful that it needs a large degree of modulation. I'm assuming that impinged jet burners function most efficiently when they are run at the higher end of their usable range. If that's the case, then, if I get the right sized burner for the job I'll be able to tweak it a bit from the control panel and I'll still be well within the usable range/limitations of the valve. IOW, if a 50,000-Btu burner will perform the task with just a bit to spare then anything with a higher Btu rating would require excessive modulation and be less efficient. Am I being clear?

harlan.

 

[lownox]

If you are going to control this thing manually with a pot... I would use a plug in type DC power supply with a voltage divider circuit to give you the 0-10VDC. Something from radio shack should work fine.

I assume that price is OK. I have never bought just one and my company was buying them in volume. Can't remember the price since it was like 6 years ago or so at a different company.

Maybe you want to get a temperature controller and directly control the brew to a specific temperature? Thus modulate the burner using this signal?

 

[probrewer]

Actually, I'd already figured it out. By reading the Belimo documentation a little more carefully (RTFM), I realized that their SGF24 positioner is perfect--for one thing it's a NEMA 4 panel mount package and the control panel WILL get wet--and was only $44 from the same place I ordered the actuator from; and for good measure, I got the Belimo transformer too. That should pretty much guarantee that they will all play nice together.

As for the temperature controller, I always intended to have one on the control panel for the kettle and another for the 5.5kW electric heating element in the "hot liquor tank" (brewerese for brewing water tank).

For the kettle, a temperature controller is a safety device. You need to be able to set the temperature to ~208*F while the kettle is filling from the Mash Tun--the burner gets turned on when there's enough wort in the kettle that it won't scorch. What you don't want to happen it to be distracted by some kind of problem with the mash tun and not be paying attention to the kettle temperature--like having the kettle come to a boil while your back is turned.

The start of boil is so inherently dangerous that you don't want to ramp up the temp controller to 213*F until the kettle is completly full and you can stand over the kettle ready with a hose to spray back the initial explosion at first boiling point. This is really the only point it the whole process where you must give your undivided attention to the kettle. I've heard of pro brewers who where distracted, turned their back for just a second and their boots were filled with boiling wort...

No matter how much money I throw at this project for redundant safety devices, it's still cheaper than the deductable on my insurance and a trip to the hospital.

I'd really like to thank you again for helping me with this. This part of the puzzle is solved and I couldn't have done it without you.

harlan.

 

[lownox]

Don't forget to let me know how the beer turns out. I enjoyed this thread.

Steve

 

[probrewer]

Not to worry, Steve, I'm certain I will be back with another problem...and I'm quite pleased that you've enjoyed this thread. So have I.

Understand that this is a long term project--at least a year. I know another brewer whose homebrewery took 3 years to build--his is steam-powered. Lots of details to work out, and then there's the welding that still needs to be done. Finding a welder that can make sanitary welds in 304 stainless is difficult and it ain't cheap... A lot also depends on how far I get this summer in building my house--then I can start on the tower that is to house the brewery. Gravity feed.

At some point, I'll be putting up a web site to chronicle the progress, so I'll post that when I get around to it.

You might enjoy another group I belong to, Homebrew Digest (hbd.org). We're all crazy over there. You'd certainly be a welcome addition and who knows, you might get the bug yourself. As we're all fond of saying: If you give a man a beer, he'll waste an hour, but if you teach a man to brew, he'll waste a lifetime...

Good luck, and again, thank you!

harlan.