Centrifuge D.O. Spike

[blackbelly]

About 6 months ago, we purchased a ca.1964 Westfalia separator. Everything is manual. Everything.

I did a breakdown/rebuild of the bowl components down to the spindle shaft, replacing all of the gaskets and looking for gouges in the stainless. I've ran a water/yeast mixture through it three times before moving to beer. Yesterday I moved 3bbls out of a 90bbl FV to a small 4bbl holding tank. Reasoning for this was to check D.O. levels before committing to an entire 90bbl transfer.

Attempted a C02 flush on the bowl before moving beer (we don't have D-water yet). I purposefully discharged 3 times during the 3bbl run. Beer is clear and bright, looks great. Stuck the DO meter on the receiving tank, was reading aprx 6.7ppm. FV was reading <10ppb. I know discharging 3 times during a 3bbl run is not the norm, and will cause elevated DO levels regardless of the centrifuge but 6.7ppm seems insanely high.

Anyone know of any other problem areas for oxygen pickup? We are working on getting a progressive cavity pump for the discharge offshoot, currently it is just connected via a flange to a big SS reservoir. I believe the brewery we bought it from used it as mentioned. It's not airtight. Could this be the obvious source?

[brewtrain]

You have several variables that may be causing elevated DO's. The first is the low volume of beer. If your 4bbl holding tank did not have a full CO2 purge you will get higher DO's, as opposed to a larger tank that fills slower and thus allows CO2 to settle on the beer and the remaining air to push out the top as you fill. Also how much beer did you send to the floor before filling the tank? Without DA water your first barrel of beer will have high DO as a CO2 purge on the bowl is not as effective at removing air. After that doing three discharges on three barrels could let in quite a bit of air, especially on an older centrifuge. I assume you can only do full discharges instead of a partial discharge that evacuates solids without opening up the entire bowl. Also if you have mechanical feed and discharge seals instead of hydrohermetic you have a greater uptake of O2 with each discharge. Basically with an older centrifuge you want to run as much volume as possible without discharging, to keep DO's low. Outside of centrifuge theory I would also check the calibration on your DO meter. If you still have high DO's after larger runs it might be worth contacting GEA to get a tech to check it out. It will cost you, but not as much as oxidation on your beer. Good luck.

[blackbelly]

brewtrain,

The 4bbl tank was purged to the point of overkill. We sent roughly 1bbl to the drain before filling the tank. I agree, I think the bulk of the pickup was still from the lack of a good initial purge and the number of shots throughout such a small transfer.

We had the centripetal pump head modified to hydrohermetic. We can also do partial shots but it varies, as we're manually flipping a switch. We're planning on doing 3-4 timed discharges throughout a 90bbl, just dialing it in via our turbidity sensor.

Is the main O2 pickup during a discharge from the pump head/bad seals or is it entering via the discharge shoot? With a hydrohermetic head I would think its probably coming from the discharge shoot to relieve the vacuum during that half-second the bowl is down.

Thanks for the input!

[Inthelab]

How are you measuring DO? When numbers seems absurd, best to look at the method first. Does the beer taste like wet cardboard? That much 02 will taste terrible within a day or two.

[brewtrain]

Do you have a constant CO2 blanket on the bowl? Without deaerated water you could be getting slight pickup despite the hydrohermetic seal. The discharge port in theory should be sending solids out without allowing too much back in, but if your reservoir is not CO2 blanketed, there could be a point of entry there. Even with these small process flaws I wouldn't expect to see the DO numbers you got. I would make sure your DO meter is working and calibrated and then run a larger amount and see what you get in the brite tank. If the numbers are still very high I would assume a seal failure, or something mechanically wrong.

[blackbelly]

How are you measuring DO? When numbers seems absurd, best to look at the method first. Does the beer taste like wet cardboard? That much 02 will taste terrible within a day or two.

Inthelab,

We are using an orbisphere d.o. meter which we've tested against another brewery's do meter. Test beer tasted oxidized the next day.

[blackbelly]

Do you have a constant CO2 blanket on the bowl? Without deaerated water you could be getting slight pickup despite the hydrohermetic seal. The discharge port in theory should be sending solids out without allowing too much back in, but if your reservoir is not CO2 blanketed, there could be a point of entry there. Even with these small process flaws I wouldn't expect to see the DO numbers you got. I would make sure your DO meter is working and calibrated and then run a larger amount and see what you get in the brite tank. If the numbers are still very high I would assume a seal failure, or something mechanically wrong.

We don't have a constant blanket on the bowl, just doing the initial DA water flush. I added a p-trap to the discharge and bowl case drain. We just ran a few bbls of DA water through it after a good DA flush, measured our baseline, measured at the receiving tank and gained aprx 150ppb. We aren't carbing inline yet. I'm going to keep the reservoir blanketed and see if that helps.

Where would you push gas to keep the bowl blanketed? Inlet or outlet hard-piping? Or were you just referring to the discharge reservoir?

[brewtrain]

Usually the centrifuge will have a specific CO2 port for blanketing the bowl. If you have hydrohermetic with DA water then it isnt as important. Hopefully blanketing the reservoir does the trick.

[blackbelly]

Usually the centrifuge will have a specific CO2 port for blanketing the bowl. If you have hydrohermetic with DA water then it isnt as important. Hopefully blanketing the reservoir does the trick.

Ours doesn't unfortunately -- the perks of having 1960's machinery. Thanks for the input, hopefully this will do the trick

[dick murton]

If the delivery pump is not big enough to ensure a positive pressure in the centrifuge bowl whilst it discharges, then the system is liable to suck in tiny, but sufficient amounts of air to give high DO2 results. Similarly, if the tank you are filtering into does not have sufficient back pressure to maintain a positive bowl pressure, you are liable to get O2 pickup. I assume you have a back pressure control valve after the cf, in addition to the other comments made by myself and others. It takes quite a bit of good quality dearated water to flush through the cf and associated mains properly - aim for 2 metres (6.5 - 7ft) / second when carrying out the DA water pre-flush.

[blackbelly]

If the delivery pump is not big enough to ensure a positive pressure in the centrifuge bowl whilst it discharges, then the system is liable to suck in tiny, but sufficient amounts of air to give high DO2 results. Similarly, if the tank you are filtering into does not have sufficient back pressure to maintain a positive bowl pressure, you are liable to get O2 pickup. I assume you have a back pressure control valve after the cf, in addition to the other comments made by myself and others. It takes quite a bit of good quality dearated water to flush through the cf and associated mains properly - aim for 2 metres (6.5 - 7ft) / second when carrying out the DA water pre-flush.

We are regulating back pressure via a manual stuffing box and another manual valve, both on the outlet. Running 25bbl of DA water today to try to isolate where our pickup is. I think we may not have been flushing with deaerated as vigorously as we should, I'll give that a go today.

All good ideas, thanks guys