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# Max Steam Power

edited October 2016 in General

I figure there is a definite limit to how much power you can get into a boiler with steam.
The governing factors being temp of steam, temp of wash, contact area, heat conduction of the metal and perhaps its thickness?
Has someone worked it out? (So I don't need too :D )
@grim, how much power can you put in to your boiler? I'm guessing it varies a lot depending whether its on startup at 20° or the end of the run at 100°.

What I'm ultimately after is a W/cm² figure to work off for 304SS @ Δt of 20° (so wash @ 100°C & using LP steam?)
How squat does a jacketed 1000l boiler need to be to get 70kW into it?

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## Comments

• edited October 2016

The Spirax website has everything you'd ever want to know about steam and much, much more. Enough to keep you reading for decades.

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• edited October 2016

I just had a bit of a play but it only has steam coils not jackets.

``````Coil   Diameter   Coil      Length     Steam      Velocity
mm     in         m         ft         m/s        ft/s
65    2 1/2      5.60938   18.4035    15.7799    51.7714
80    3          4.80517   15.7650    10.4172    34.1772
100    4          3.74481   12.2861     6.66702   21.8734
125    5          3.01946    9.90637    4.26689   13.9990
150    6          2.53525    8.31776    2.96312    9.72152
200    8          1.94747    6.38935    1.66675    5.46835
``````

The difference in total surface area required for a 2 1/2" coil compared to an 8" is three fold??
186cm² vs 612cm². I guess from pressure drop down the coil??
It doesn't really tell about jackets though. I think I'd need about 115kg/h of steam but does the boiler have enough surface area to condense it? My gut feeling it it would shit it in but recall grim talking about having his steam valve wide open and not being able to get any more steam in there, also about the agitator to get delta t back up.

I've got a heap of books sitting on the shelf here (even the Spirax one somewhere) so I could probably work it out but I was just wondering if someone already had?

• edited October 2016

Punkin, what pressure are your jacket boilers rated too and they come with any pressure vessel certification?

• Come with CE certification only i think mate. Rated to 15 psi from memory. Larry will be able to tell you more as he stocks them and i don't.

I'd be surprised if there's information you need that's not somewhere on that spirax site.

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• What size boiler are planning on using @jacksonbrown ? 115kg/h is a fair whack of steam. For a start you're going to need one heck of a condenser to knock the distillate vapour down to temp.

115kg/h is enough for a 2,000L charge! At least that's what I get when I calculate it.

• Heat up 1000 litres in an hour?
Was just ballparking, a realistic W/cm^2 figure is really all I was after. To work out the limit of a jacket system.

• Our boiler outputs 521 pounds of steam an hour.

The 1000 liter boiler can consume every single ounce of that on heat up.

If the boiler is at temp, it takes about an hour or hour 15 to get to boiling.

It's rated 15.6hp. It would have no problem consuming 20hp for an even faster startup.

• Cheers. Very roughly what is contact area between wash and steam (diameter/height)?

• 5' hemisphere, give or take?

• so roughly...

15.6hp=0.33W/cm²

20hp=0.42W/cm²

Thanks, that's something to go off.

• hmm? something don't seem right in those numbers.
I think I need to do it the hard way.

• Your biggest heat demand is at start-up. If you can afford the patience and let the heat up to boil take 90-120mins you're in for a much smaller boiler. In some cases it doesn't really impact much on the price but in others it seriously can.

• With the process plans I'm running at the moment, continuous operation will have the outgoing, spent wash at 100° heating the next batch (BP 95'ish) through a shell and tube as it's pumped into the boiler. It'll already be boiling as soon as it's full.

I'm just tossing ideas around and nutting out limits in the system.

• @jacksonbrown said: so roughly...

15.6hp=0.33W/cm²

20hp=0.42W/cm²

Thanks, that's something to go off. @jacksonbrown said: hmm? something don't seem right in those numbers.
I think I need to do it the hard way.

I think you're right if you're calculating a 1/2 sphere

• edited October 2016

Compared to immersion heaters, those watt densities look so low you would think they were errors. That's like 15x lower than ULWD elements.

• Our primary and cheapest source of energy (aside from wood burning) in Fiji is electricity. is it cheaper for me to run a boiler on steam generated from an electrically heated boiler, or heat the boiler directly on steam?

I'm confused on this point. been reading a lot and it seems like it's about the same energy requirement either way.

• Steam is only the energy transfer mechanism, make it however is most economical to make it.

• How do they make the electrickery in fiji?

• @jacksonbrown said: How do they make the electrickery in fiji?

Here lies the moral question. The personal answer could be different.

Its the same with hydrogen cars - sounds great until you figure in the 6 to 15 times energy inefficiency or conversion factor that the real answer is seen.

• edited December 2016

Not to mention the smug pollution.

https://www.youtube.com/watch?v=TMTkedIUX8U

Most small island power stations that I know about just burn diesel anyway which is pretty expensive to ship in.
What are you going to burn in your boiler?

• edited December 2016

@jacksonbrown said: How do they make the electrickery in fiji?

Half diesel and half hydro I beleive. ouer islands are mostly diesel.

Costs me about \$.23 USD per KWH so it's not to be taken lightly.

Transportation and energy are our greatest costs. Labor is cheap.

So, I might as well use electricity then and keep capex down I guess.

I do note with some interest that the neighborin the industrial subdivision runs a wood fired boiler for thier process. I wonder if some might be gotten from them?

• edited December 2016

We still talking fuel/industrial ethanol?

Electrical efficiency with immersion elements is going to give you the highest energy efficiency, especially compared to burning things directly (wood/coal fire), or indirectly (steam), where you are talking 80%. Whether or not it's cheaper is going to be based on the cost of your burny things.

Sugar is the fermentation material? I think its going to be hard to beat a continuous process with wash-preheaters for stripping. Why just stripping? Mainly because a continuous stripper is a whole lot more simple than a full continuous rig. It'll take a sugar wash no problem, even with an element-heated reboiler. Might even be worth running an old style doubler on the output of the continuous rig, and keeping distillate temps on the warmer side (as to not lose heat).

Would also imagine finishing on a plated or packed column still, insulated boiler, with the wash loaded at full strength from the strip (no dilution). Loading a batch rig with water-laden wash is wasting incredible amounts of energy if your goal is fuel/industrial. Insulated kettles should be a given.

Of course kettles/reboilers need to be designed in such a way to ensure elements are immersed and protected, otherwise you'll probably blow up.

Also recycle every drop of heads and tails - tails cut being determined purely by cost/benefit.

• edited December 2016

@grim said: We still talking fuel/industrial ethanol?

I might be pivoting. lol. plan in the works to be Fiji's first craft distillery.

I was thinking about adding a stripping still to my 4" column to increase output. I've been reading about a solid continuous stripper design to strip 1000l/9hr day that I can just build and put into production, but plans for an actual proven design seem to be eluding me.

What are the safety concerns with running a full strength strip without dilution over direct element heating tho?

• edited December 2016

Safety? No difference that is actually based in fact. Other than exposing the element, like I said, which is equally as dangerous.

• A level switch can easily fix that though.

• edited December 2016

Problem with proven designs on a continuous stripper is most of them are commercial, and guarded. Nobody is playing with them on the hobby scale, because they would be useless (or tiny).

The other factor is that to hit max efficiency, they are going to need to be run with extremely narrow operating conditions. They need to be designed for a specific feed rate at a specific feed temperature at a specific wash abv. However, once you are there, just keep feeding the beast.

The column design is simplistic (probably 6" x 12-15' packed for a 1000l a day). It's the condenser sizing thats the tough part in my book, especially if you are using only wash for condensing. It's going to be pure luck if an off-the-shelf condenser just so happens to be correctly sized. The worst case scenario is probably going to require a supplemental water-based product condenser.

You know, the SD guys just happen to have all the parts needed, the problem is the tons of trial-and-error that would be required to size it up and tune it.

Still seems like a complex trial-and-error setup to manage feed rate, reflux ratio, reboiler power, bottoms abv.

But, once it's done, it's done.

• edited December 2016

@grim said: You know, the SD guys just happen to have all the parts needed, the problem is the tons of trial-and-error that would be required to size it up and tune it.

This^

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• Well there are a group of hobby guys here in Aus playing with a 4 inch Dash as a continuous stripper. Most of them members here. Look for posts by @ElectricEd .

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• I have done it too. There are a few key parameters you need to control but it's not hard.
Just throw enough money at it.

• edited December 2016

What is the issue with condenser sizes? The bigger it is the more efficient.
One issue I had (which might not even be an issue) was, when using regen heat out of the bottoms (which should be closer to 100°) you can boil the feed in the preheater HEX which will have a BP around 10° less.

Key points are:

1. get exact control over the feed flow rate.
2. measure the vapour temp at the top of the analyser column (different feeds will change this set point).
3. use that temp to control the heat input.

By doing this you should be able to open up the operation window a bit.

You can add a rectification section as well, regen on the product condenser and bottoms to preheat the feed.
The great thing about utilizing SD sections is you can just add more plates to tune it rather than dick around trying to math the shit out of it. Measure the bottoms temp too so you know if you need to add a few more plates (the target should be at least 99.8°C).

Your feed type may not be suited to packing, sieve plates with dropper tubes for downcomers will be a bit more forgiving wrt fouling. foaming was an issue for me so degassing and a bit of a chamber at the injection point to prevent entrainment is a good idea.

A stripper column typically has about 15-30 plates and will take feed 7% to 14% ABV and put out 30% to 40%.
A rectification column typically has around 20-65 plates. The lot can be built as one column but due to height issues they are usually split in to two or more columns which means more pumps and piping.

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