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Boiler Sizing...Is Bigger Better


brandon8198

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Does anyone have any experience with oversizing a boiler for their application. We sourced a boiler for our distillery which is about 3 times the minimum size requirement from the manufacturer. I was told that the application you are using it for (ie: running the still or heating a mash vessel) would only use as much as it needs. So is it correct that if we have an oversized boiler, the energy it uses and the cost for running it would be the same as a smaller boiler? It seemes to be basic physics, but I'm not sure?

Thanks,

Brandon

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Brandon,

in my experience, it depends a lot on the boiler.

For instance, I had a Bryan electric boiler that was capable of generating far more steam than we needed. Although electric boilers are efficient by nature, because of the large size, it used more energy than a smaller boiler to get up to operating temps (we used it on demand) but once running, efficiencies were great. I suspect it would have worked better if we had used it often enough to justify continuous operation.

Currently, the place I'm with has an oversized Fulton boiler, which is rated for 100 psi. However, because we run it at low pressure (30 psi, valved down to 11-17 for process) it uses a fraction of the natural gas that it would at "full steam."

Generally, I advise people to oversize their boilers a bit...that way you have enough steam VOLUME to heat up a jacket quickly, recycle condensate, and excess capacity if you need to upsize or add more equipment (like, say, a shrink tunnel for plastic shrinks over your bartops) without the cost of removing and replacing a boiler, or adding another one (which can be especially costly in states with excessive regulation, or in Canada). Additional piping is costly enough as it is!

Boiler design is quite complex, and some boilers reach their peak efficiencies near max, where others are most efficient running 30% or 60%. However, even if your boiler costs you extra fuel for a year or two before you upsize, it will be far less money than the cost of replacement! The last time I did a boiler replacement (upgraded from 750000 BTU to 1.35 million BTU) it cost well north of 100G. That, my friend, is a LOT of natural gas!

One thing you might consider is buying a smaller boiler and having your engineer install it in such a way that you can twin it at a later date. That means offsetting the boiler in the original room to allow for a second, and having a pretty good boiler engineer design your system so that a second steam generator can go in with a minimum of fuss. It would probably add $10000 to your install, but it IS a middle ground. Bear in mind that the condensate return will have to be sized to run both boilers, and that might upsize your return piping.

Also, the shorter the run, the more money you save! Don't skimp on condensate return...that's where the efficiencies are, and I prefer a pump system to gravity.

One last thing...if you plan to do direct steam injection for your mash, I'd recommend a second small unit, such as a small Reimer steam generator. That way you can produce sanitary steam for cooking your mash (I tried it with our steam with the conditioners in it, and it took me days to get the smell out of the still). Those small Reimer units are less than ten thousand dollars, and work great for that.

Which is your last option...just buy a small, properly sized boiler that skid mounts for each piece of equipment. Not the most efficient, but VERY scalable...and you only burn as much fuel as you NEED. Only works in states that don't require dedicated boiler rooms, though. Sometimes you can get around that by calling it a "steam generator" instead of a "boiler."

Hope all that rambling helps :-)

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You can also get modulation and go bigger with the boiler. In the short run you still lose some energy efficiency from greater evaporation and so forth, but that can offset some of the natural gas waste. Modulation from most of the manufacturers I got quotes from added about $3500 to the cost of the boiler.

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Jedd,

I don't actually have a Reimers right now, and I know there are a lot of models! The best thing to do is call them, explain what you want it for, and let them go from there. I've no idea which one it was that i worked with...I think it was an SRH 20 or similar. I know of one guy who is using an RH-80 for cooking his bourbon mash.

But there was no sanitary steam filter on it...not for cooking mash. As long as you aren't injecting something objectionable, I think it's ok. If you are using steam to clean kegs for a brewery, that's a different matter!

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Thanks for the info, Natrat. What size mash tun did you use the SR 20 on, and how was the performance? Likewise, do you know the mash tun size for your associate with the 80kW model? According to the Reimers specs, both of those boilers are stainless and make "clean steam" by default, so apparently no filter is needed. Did you need to use any cleaning chemicals with that boiler, or did you just do a blowdown every so often?

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I don't think the Reimers needs to be aggressively cleaned. It depends on your input water. If it is excessively hard, then I imagine descaling the boiler occasionally will help, but since it stays wet or half wet all the time, scaling is a minor issue. If you DID need to clean it, I'm sure a quick acid passivation would be all it needed :-) Steam tends to keep stainless pretty clean, and if I remember correctly, even the elements are cladded in 316. Usually, I spring for an automatic blowdown cycle with my boilers, and just run a manual once a month to make sure.

The 20 Kw was on a 5 bbl mash tun, and it made plenty lots of steam. Overkill, probably, but I like having extra capacity. It was run at about 75% and cooked corn like wow. I'm going to guess the tun on the big one is about...20 bbl? Maybe bigger. I'll see if I can dig up the info from him, or if I have a picture of it on my phone. I can't comment on the performance, since I've never actually seen him using it for direct injection, but it seemed to keep a nice rolling boil going when it was being run in the jacket.

One thing to note, if you're going to use a stainless boiler, you need to use stainless pipe...well, you can use brass or copper. But not black iron pipe, which will introduce contaminants to your boiler. That's the reason these babies are often placed in situ, or skid mounted close to the equipment. I'll shoot an email to Florian and see what he recommends for cooking corn mashes with injected steam. He may have some tidbits.

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I spoke to Reimers today. Their man indicated that these boiler require a de-ionized water supply. He seemed to suggest that filtered city water; or even RO water, wouldn't be good enough and might cause the welds in the boiler to fail. For anyone else interested, the 20kW version goes for $15,500. There are various options which can increase the price, one of which is an upgrade from a mix of 304/316 to all 316.

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