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brewman ! · 12-19-2006, 05:58 PM

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Ahh, k so basically an i/o board that is easily integrated with a pc. Most controllers I have seen are PID. Sounds like you've got lots of work ahead hehe (fun project btw).

Shouldn't take long at all.

I just ordered the McMasterCarr parts, btw.

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The step response is probably a good place to begin, and hopefully you won't have to get terribly complicated, although to hit your mashes without overshoot will be interesting because your amount of grain will usually be different.

I don't think there is much system inertia. I don't think overshoot will be an issue. It will be interesting to see. Hopefully I can just open the valve and watch the temp. When the temp gets to the setpoint, shut the valve.

Unlike other systems, the thermal capacitance of the heating components in the mash is just about zero. I guess we will see.

Here is an email I sent a guy on this topic.

So here is my attempt at mash boiler thermodynamics. Be kind... I am really rusty with my steam calcs.

My data source is http://www.chesterton.com/interactive/tables/steam/

Water and steam at 1atm, 212F. The liquid has an enthalpy of 180 btu/lb and the steam portion has energy of 1150 btu/lb

Water and steam at 25 PSIA (10 PSI), the temp will be 240F. The liquid has an enthalpy of 208 btu/lb and the steam portion is 1160 btu/lb

Straight liquid at 126F at 2PSI has an enthalpy of 94 btu per pound. Straight liquid at 170F at 6 psia has 138 btu per pound. For now we will ignore the energy due to pressure because water is nearly incompressible and that energy change is near nothing.

So to heat water (our mash) from 126 to 170F takes 138-94 = 44 btu per pound. Which makes sense because the temp spread is 44F and water has a specific heat of 1btu/lb.

Lets say we are brewing a beer that uses 10 pounds of grains. Using this page http://www.rackers.org/calcs.shtml and a water ratio of 1.25 q/lb, it will take 3.93 gallons of volume. Lets say that is all water at 8.33 pounds per gallon, we'd have 32.7 pounds of "water". In reality, it will be both lighter than that and have a lower heat capacity. But using these numbers, the total energy to raise our mash from 126 to 170 would be 32.7 x 44 btu = 1440 btu.

If we were direct heating, a 4.5KW element puts out 15,354 btu/hour or 256 btu/minute. Our water weighs 32.7 pounds so we would get 256/32.7 = 7.8F per minute. That is a pretty good heating rate as far as these systems go. Most are 3F or less per minute.

Now cooling steam from 240F to water at 170F will release 1160-138 = 1022 btu/lb. We need 1440 btu, so that is 1440/1022 = 1.4 pounds of steam = 0.17 gallons = 0.676 quarts. A little over 2 cups of water. Pretty incredible, isn't it !

Now how much energy is stored in the corny ? Assume we have 10L of water (22 pounds) and 9L of steam.

First the water part. When the valve is opened, the pressure will drop to 1 atm and any water over 212F will boil away as steam. And all that will be left is hot water at 212F. Neglecting the change in mass, we go from hot water at 240F to 212F, so that is 28btu/lb x 22 pounds = 616 btu.

Now the steam part. We have 9 L of steam at 16.31 ft^ per pound. 16.31 ft^3 x 1728 in^3/ft^3 /61 in^3/litre = 462 litres per lb. 9L/462L/lb = 1.94 x 10e-2 pounds. That steam has an energy of 1160 btu/lb so 1162 btu/lb x 1.94 x10e-2 lbs = 22.6 btu. Not nearly as much as the hot water because there is little mass.

The boiler energy storage will best work on the principle of heating the water up to a temperature higher than boiling at atmospheric pressure. Like 240F at 25psia. Then when the valve is opened, the pressure drops in the boiler and the water boils, making steam. Just like if you open the radiator cap on a hot car engine.

That is much different than a pressure cooker principle, where one is just capturing what the stove is boiling off as it boils.

Now... if one had the whole corny full of 240F water, then we'd have 19L x 2.2 lbs/litre x 28 btu/lb = 1170 btu stored up ready to go. Almost enough to do our whole batch. We need 1440 btu to go from 128 to 170F.

One could probably release the 1170 btu in about 2 minutes. That would give us a heating power of 1170 btu x 60 minutes/2minutes = 35,100 btu per hour from the hot water alone. 1 KW = 3412 btu/hr so 35100/3412 = 10.2KW. Plus the 4.5 kw element will cut in and add to that, so we have about 14.8 KW of of steam power going to the mash ! That is 50,453 btu/hr or 840 btu per minute. Our mash weighs 32.7 pounds, so the temp rise would be 25.7F per minute !

So a mash temp rise from 128 to 154F would be 32.7lbs x 26 btu = 850 btu, which is almost exacly 1 minute. One would have to throttle the steam flow so that you didn't overshoot on the temp. But on the other hand, you know how many btus is going into the mash from the boiler temp change if you wanted to get fancy ! The computer could measure the temp before and then watch it until it drops the right amount.

Now... how much energy are we putting into heating the water ?

19L x 2.2 = 41.8 pounds. The temp rise will be 240-60F = 180 btu/lb. So 41.8 x 180 = 7524 btu. 1 KWhr is 3412 btu/hr so 2.2 KW Hr of power or about 20 cents worth to get the water ready in the boiler. WIth a 4.5KW element, that should take 7524 btu/256 btu per minute = 29 minutes. If one started the element when the mash started, it would be ready before the first step. Cool ! At the end of the run, one will have 42 pounds of water at 212F for washing ! The energy in that water is 212F - 70F x 42 = 6000 btus. One could do a good job of sterilizing a counter flow chiller by pumping that water through it. I also capture the water that goes through the counterflow chiller in the HLT for washing purposes, so neither of that energy is totally wasted.

So... did I get my math and thermodynamics right ?

What do you think of the boiler operation ?

I like how fast it would raise the temp of the mash ! No more sitting around waiting for the temps to rise. If they are going to rise that quickly, I think I want to manually control the valve and stir at the same time. I think I am going to make a floating thermometer for my mash vessel, with multiple thermistors to get the bed temp at various depths automatically.

**DrewsBrews** · 12-19-2006, 10:25 PM

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Originally Posted by fifelee

I have yet to brew an all grain, so I may show my ignorance. I understand that when the mash reaches 170F, something happens to the enzymes. Will injecting 240F steam be bad for the areas right by the steam injectors?

Stirring the mash should alleviate any issues of directing hi temp steam into the mash. A motor operated stirring machine would be best (for consistent churn) but stirring by hand while introducing the steam works too. I've communicated with a handful of people that say the steam has no notable effect on their mash efficiency.

HERMS systems put the runnings through quite a bit of temperature differential as it passes through the tubing and heat exchanger and back into the mash. It seems that gently introducing steam would be less detrimental. Of course, I'm relying on others' experience until I get my system built...

psymn · 12-20-2006, 12:55 AM

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Originally Posted by fifelee

Will injecting 240F steam be bad for the areas right by the steam injectors?

In theory yes, any enzymes that are heated above 170f will be denatured. They do not simply pause above 170f and then restart once the temp comes down.

As I understand mashing, it should not effect the overall mash if a small area is superheated with steam.

Don't decoction mashes involve boiling some of the wort to raise the temps?

If so, this volume of wort has no enzyme activity, but it doesn't impact the overall conversion much.

How many steam injectors are you talking about here? Is this going to be a steam jacketed kettle, or direct injection?

Since you're already automating most of this system, why not build a grain stirrer as well?

Matt

brewman ! · 12-20-2006, 02:15 AM

I think this will be much gentler on the mash than heating over a stove burner or infusion of boiling water or even decotation. And for sure, RIMS, where a hot element directly contacts the wort. HERMs might be be gentler.

The steam will probably come out of a C shaped manifold at the bottom of the mash vessel.

zoebisch01 · 12-20-2006, 12:02 PM

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Originally Posted by brewman !

Shouldn't take long at all.

Not for simple do this, do that software no. You can easily set up the computer to throttle the valve etc, vary the duty cycle or some other method to get your setpoint. But to have a closed loop feedback control system specifically designed to do what you are doing could take a bit of time. I guess I'm overcomplicating it, but it seems to me that you really want to be accurate within a degree and that seems like it would be a bit of work to get your system tuned properly. It's all a process though, as I am sure you're aware. Not sure if I am understanding what the vessel that actually contains the mash is. The less lossy it is probably the better for you (I would not rule out heat flow from the vessel, this could really put you in a spin), as long as you can very accurately control that throttle valve. Sorry I don't mean to come across wierd or anything, you've just got the gears turning lol.

brewman ! · 12-21-2006, 11:14 PM

The parts arrived for converting the corny into a boiler. Bulk head fittings, element, valve, relief valve, etc. The microcontroller isn't here yet though. It will be a few days until I can find time to work on this. But I will.

**Orfy** · 12-22-2006, 07:10 AM

Get the camera man.

I think you should start a blog as well.

brewman ! · 12-22-2006, 07:13 AM

"Get the camera man."

Got one... actually two.

"I think you should start a blog as well"

Nah. I'll just post here. Blogs aren't interactive enough. I like it when you guys comment. Lots of good ideas here.

JonS · 12-27-2006, 04:22 PM

You should look into makeing a steam kettle now. Seeing you have a boiler.

brewman ! · 12-28-2006, 06:08 AM

Hmmm... very interesting. A pressure cooker would work as well.

Expensive ? $50 !
http://www.amazon.co.uk/Wagner-W14-240V-Wallpaper-Steamer/dp/B0001P16YS

This one is a plastic tank with a heating element. 2KW isn't a lot of power, but then again, a lot of the RIM systems are running with 1-1.5KW to avoid scorching the wort. This thing would be very easy to build.

Not to brag, but my element is 4.5KW.

Then there is the matter of storing superheated water. The wallpapers steamers will work, no doubt about it. But they aren't a pressure vessel. They make steam at atmospheric pressure and that is fine. It will work for heating the mash.

When done, my boiler will store hot water at 240F at a pressure of about 10PSI. When the steam line valve is cracked the pressure in the boiler will drop to atmosphere and all that hot water will boil, making steam. So my boiler actually stores heat energy ready to use. That is how I can get mash temp rises of 20F per minute if I want them.

Here is a more robust wallpaper steamer. It appears to have a metal tank and it probably runs at a higher pressure.
http://www.taylorrental.com/item_detail.asp?id=33

I didn't get to work on my steam stuff today and probably won't for a week.