BTU Capacity of Steam Pipes

[HedgeBird]

Howdy all,

I am working on installing my boiler and ran into a potential issue I did not expect. My plan is to install a 320,000 BTU (output capacity) atmospheric steam boiler to power my 300 gallon mash tun. My heating/cooling contractor has expressed concern that the 1" steam supply line leading into the mash tun may not have the capacity to carry that much steam/BTUs. The over pressure valve on the mash tun inlet is set to 0.5 Bar / 7 PSI. If I recall the previous owner of this mash tun mentioned that he did trip this release on occasion. I tried to do the steam/BTU capacity of various pipe dimension myself but I don't think I am doing it right. Anyone have any insight?

Thanks!

[nick jones]

I'd tend to agree with your contractor. I'd probably run 1.5" minimum myself, but maybe you should make your contractor do the calcs. That's what he's paid for, right?

Nick

[Jedd Haas]

Bigger pipes act like a "shock absorber" on the system, storing additional steam, which is handy when you crank the steam wide open. Or so I'm told by various contractors. If you go up a few sizes you could also accommodate a future boiler upgrade.

[meerkat]

In round numbers the latent heat of steam is 1,000 BTU per pound. This gives a flow of 320 lb/h. The density of 7 psig steam is about 0.052 lb/ft³ and the ID of a 1" pipe (Sched 40) is 1.05". This gives a steam velocity of close to 300 ft/second, which I would regard as too fast. It will be noisy and if there are water droplets present you will get erosion.

A 1.5" pipe will bring the velocity down to 120 ft/second. This is on the upper end of acceptable, but if you don't have people working close by who will be troubled by the noise it would be OK.

[HedgeBird]

Thanks for the responses everyone!

So it seems I did not do a great job of describing the situation! I have not yet ran the steam delivery pipes, and will certainly run that larger than 1". Its the actual inlet on the mash tun itself that is only 1" and I am/was concerned that this would be a restriction for the boiler I sized.

Nick; Yeah, thats part of what they are being paid for, but honestly steam work is just not that common anymore and I do not want to rely exclusively on any one opinion. The first HVAC company to look at my project recommended that I purchase a process boiler. A bit of studying on my own and talking to others and I realized this was totally inappropriate.

Meekat, thanks for doing the maths!

I was thinking I would run a 2" main off the boiler header with 1.5" branches going to this mash tun and to the still.. I could jump it up to a 2.5" main coming off the header, and 2" branches going to the equipment..

I guess to summarize, my concern is that I am looking at buying a boiler with a 3" header; and need to send that steam to tanks with 1" openings.

[Beach Time]

Hedgebird, If you supply the boiler operating pressure I can size the proper steam header diameter. Typically when there are low steam pressure at the point of use you would operate the boiler at say 30-45 psi 2-3 bar and use a pressure reducing valve to precisely trim the operating pressure to 3-5 psi .2 to .3 bar. Your HVAC guy might be on the current path with that recommendation. Good luck!

[MG Thermal Consulting]

Just a word to the wise...contractors do the building and not he consulting (for size purposes) unless they have a PE onboard or someone to sign off if situations become marginal.

Liability becomes an issue and when someone tells me they are "popping" reliefs whether it be steam, refrigerant, etc...I wonder why and who sized the system if something bad happens (like the relief sticking).