1000 Litre (250 Gallon) Autoclave

Introduction: 1000 Litre (250 Gallon) Autoclave

I made this large sterilizer for mushroom culture, but it could also be used for composite part layup.
It was a fast build and there is some danger, so read and use precautions where indicated.
I've sterilized 25 one gallon bags of media so far, but it could easily fit 60. You will also need a low pressure boiler in the 300,000 BTU range.
One could also heat the bottom with some kind of flame I suppose, couple of propane crab cookers? Around 100,00 BTU each.

Step 1: Cutting the Tank

I decided to buy a new propane tank, so I blew my budget right at the start. It was $ 1600 Canadian plus they wouldn't let me put it my van. Add $50 delivery. It did look kinda heavy, so whatever. There were lots of larger ones in stock too. 250 gallon US is a reasonable size for my plan.
If you start with a used propane tank there is some danger of exploding and bad smells. I would at least steam it out before cutting.
To cut, wrap some stiff tape near an end to act as a guide ( not on the weld) and cut the end off. I left enough room for welding on a straight area not on the dish.

Step 2: Leg Mounting System

I used 1/8" by 2" square tubing. The casters are 4" heavy duty solid polyurethane. The frame was TIG welded by myself. I'm only an ok welder so most people could do it and it won't explode. I shaped and reshaped the angle(curve) to attach the tank to the legs.

Step 3: Attaching the Flanges

A friend water cut the flanges out of 3/8 steel plate for $200. Originally I was going to get a piece of angle iron curled to make flanges, but they were $300 each. I was a bit nervous to weld the flanges, as they have to hold 11 tons of force, so another friend that is a certified pressure welder came over to help. I had to squeeze the tank a bit to get the flange in place, but when it was on there was a 1/16 " gap around it to allow a deep weld. Just kidding, that's just how it went.
I left the tank 1/4" proud to make the inside channel for the O-ring. Grind and sand the weld 'till smooth where it is against the O-ring
The tank side also had a piece of 1/16"X1/4" that I hand rolled round and tacked on to hold the O-ring from the outside.

For the amount of force on the O-ring and the door I used eight 5/8" high grade bolts. Totally overkill, but they are really easy to use over and over and don't dent from the door hitting them.
I bolted on the lid side flange and used a chain block to force the lid into position then welded it from the outside.
At this time I built the door hinge. It has to be a three point pivot to allow the door to move flat against the seal. I used some scrap heavy pipe and the lathe to make them. The door swings all the way out of the way for unloading the racks.

Step 4: Hydro Test

Put it all together. Pressure release, bottom drain(weld one in), air vent, steam inlet, temperature probe bulkhead, pressure gauge.
This is the only safe way to test a pressure tank;
Hook up a garden hose and fill it with water making sure to leave the air vent open. When it is full, shut everything and then SLOWLY add small shots of water from the hose.
I got to 12 psi before water started leaking from a badly ground section. I tightened a little bit and it stopped. I then brought the pressure up and let it leak. Noting the problem areas until it got to at least 32 psi (buried the gauge).
It runs at 15 psi so I figure it's ok.
This photo is from afterward. It really doesn't leak that much.
I did a trial run with steam and there were no leaks. I guess the heat let the Bunan O-ring form to shape.

Step 5: Operation

Bags of media contain air and so a few venting and vacuum cycles get all the air out and really let the steam transfer heat fast. Use steam tables to tell when the media temperature is high enough to vaporize water inside the bag at the current vacuum. I pulled it down to -12" Mercury, which corresponds to 85 Celcius.
I have to build rolling racks and a water spray( to create a vacuum inside) and an air filter to keep everything sterile during cool down.
I've installed 5 Teflon coated thermocouples for monitoring temperatures inside the bags.
I intend on sterilizing 500kg (1/2 ton) of media based on brewery waste each week.

Total cost is a bit over $2500 plus the thermocouple wire and reader $300 which took me plus some help around a week to put together.

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    18 Discussions

    0
    Thefunguys23
    Thefunguys23

    Question 7 months ago on Step 5

    Hey man what’s going on love the work you did an awesome job. I have a friend who is a licensed welder and he says he’s willing to help me build one of these bad boys. I somewhat have a good idea of what I need to do but I still have a few questions that would be awesome if you could help me out an answer. I’m going Monday to buy the propane tank. It would be huge if you could point me in the right direction and answer a few questions for me. I’m definitely willing to pay you for your advice. Much appreciated thanks a lot. Oh yeah and I’m really new to this so I’m not sure how to check my messages LOL if for some reason I can’t figure it out could you please send me an email. Highhorizons710@gmail.com Thanks a lot man hope to hear from you soon. Chad

    0
    vince9
    vince9

    Question 7 months ago on Step 5

    I am interested in getting an industrial autoclave of this sort. If you could make another one to sell, how much would you sell one for? As much as i love diy, this kind of project seems to be a bit more technical and would rather have someone of higher knowledge complete the build. If thats something you can help with please let me know as im looking to purchase one. Thanks.

    0
    Brewerjames
    Brewerjames

    Answer 7 months ago

    Sure. I’m in vancouver canada, and I have no idea what it costs to ship. Boilers are the per-view of the local governing body. The legality of firing it up might be a show stopper. But let me know how big you want and i can source the stuff. All the traps and piping will be mounted for turnkey start.

    1
    AugustJ
    AugustJ

    3 years ago

    So many questions. Are you maintaining 15lbs of pressure for 90 min? Are you using a condensate pump for the boiler, or is steam only going in then escaping? How with a low pressure boiler are you keeping pressure at 15 lbs? How much water would I need to boil(crab cooker) to steam at 15lbs for 90 min? Wish I could speak with you, we’re starting on the welding and realizing the boiler aspect is difficult to say the least. Needing a steam dynamics lesson please

    0
    Brewerjames
    Brewerjames

    Reply 8 months ago

    just buy a steam boiler. jury rigging one is too dangerous

    0
    Brewerjames
    Brewerjames

    Reply 10 months ago

    each pound of steam has 1000 btu in it. Thats enough heat to raise 5lbs of material from 50 F to 250 F. Dont forget that you are also adding a pound of water, so you don't want be close to the field capacity of the media

    0
    nicemushrrooms
    nicemushrrooms

    Question 9 months ago on Introduction

    Great build! I’m a bit confused with the low pressure boiler if I had A pressure cooker and just ran a pipe into the autoclave that would provide enough steam and pressure to get the autoclave up to temp? That’s basically what you did right?

    0
    Brewerjames
    Brewerjames

    Answer 8 months ago

    You would need a really big pressure cooker. My two Boilers are 300,000 BTU each, although it will run happily on one. probably. I have to push the pressure up a bit abouve 15 psi, but it might just be a problem from the 25 year old gauge. I broke it today, so i guess I'll be getting a new one. You should have one that measures vacuum as well because as it cools, the vacuum formed pulls some water out of the bags which evenly cools them. water spray only has to be on the outside.
    I do a half hour vac cycle to 2mm Hg and a slow half hour steam ramp up to 15-17 psi while measuring the bag centre. it takes a few hours to hit 121C (250 F) and to get 30 log kills takes a half hour more. but to play it safe i let it run longer to top out the entire cycle to 4 hrs. often getting 100 log kills.

    0
    RyanE87
    RyanE87

    Question 2 years ago

    Hey my man, could you give us some more details on your vacuum pump you used and the water spray? How necesarry is it vs just letting the steam flow for a long while before sealing it off to remove air?

    0
    Brewerjames
    Brewerjames

    Reply 10 months ago

    Hey Ryan. I forgot about this account. I bought a 300,000btu boiler for my brewery and ran an extra line for the sterilizer. i put a sand bag on the relief to get it up to 17 psi, which pushes the pressure up. i just dump the condensate out through the thermostatic condensation trap. the vacuum seems to work better than blasting steam through, but isn't necessary. I just let it cool under vacuum until morning and it seems to force cool the bags enough to do innoculations by morning. I quit using an oring and just lay in a silicon bead with plastic wrap stretched over it and push the lid against it

    0
    RyanE87
    RyanE87

    Question 2 years ago on Step 5

    Hi, great build. I was wondering if you could share any information on the boiler like how you hooked it up and how the boiler works, what model etc. Also where did you get the oring and do you have a model number for the oring?

    0
    LeMaraicher
    LeMaraicher

    3 years ago

    i was very exited about this project. Took a premium merbership, ans it is the same pictures/intructions has the freeview. Vry dissappointed for the lack of instruction with the «blueprints» How you run it with the low pressure boiler??? and more...

    0
    Brewerjames
    Brewerjames

    Reply 3 years ago

    I'll see if I can dig up more info if you want to build it

    0
    Brewerjames
    Brewerjames

    Reply 3 years ago

    Sorry about the lack of blueprints. I didn't record that part. Currently I'm running a vacuum cycle before steam starts to pull it down to 20" hg. Then slowly starting the steam to get to full pressure after about 1/2 hr. I'm doing 3kg polypropylene bags of media. It can fit around 80-90 in three shelves. Steam is travelling about 100ft in 1 1/4" steel lines, but it could be less. Graphing the log kills of the substrate, which looks cool.

    0
    memjr73
    memjr73

    5 years ago

    What kind of tank did you use? As in what it was designed/built for.

    0
    Brewerjames
    Brewerjames

    Reply 5 years ago

    Thanks for the comment. I didn't realize i forgot to say "propane tank".

    This is my first instructable, I'll change it

    0
    memjr73
    memjr73

    Reply 5 years ago

    Awesome! Thanks!

    0
    seamster
    seamster

    5 years ago

    Very cool. Thanks for sharing how you made this. I so need to learn to weld! :)