Helium Liquefier Cooling Work Done 14,15-March-2022 ------------------------------------------------------ Original Rev. 15-Mar-2022 Current Rev. 17-Mar-2022 Summary: this note describes work done on the water cooling system for the main compressor for the Helium Liquefier. - Recall IPF's un-announced shutoff of the Process Water system on about 22-Dec-2021 - they even left the building with the process water still turned Off. - The status of the system on Saturday 12-Mar-22 before any work was done is noted. - On 14-Mar-2022 the main compressor was stopped for about 30 minutes and its cooling water flow was turned off so that the pressure gauges in the sub-basement could be connected. When things were turned back On it was clear that the cooling water flow rate had fallen, and that the compressor temperatures had risen. - On 15-Mar-2022 measurement of various pressures made it clear that: there was a restriction in the Supply flow of water to this cooling circuit in the sub-basement that the Return flow of water appeared to be un-obstructed, at least at low flow rates and that the pressure boost from the booster pump appeared to approximately match what we should expect based on its specifications. - Also on 15-Mar-2022 two steps were taken to improve the flow of cooling water to the main compressor and an approximate doubling of that flow rate was noted along with a significant drop in main compressor temperatures. Details follow: 22-Dec-2021: ------------ On about 22-Dec-2021 during the afternoon IPF shut down the Process Water system and then left the building with it still turned Off. The liquefier system and many other systems tripped off on over temperature alarms. Reza had to call IPF to get them to come back to BPS and turn the Process Water system back On. Once it was turned back On the cooling water flow rate through the liquefier's main compressor appeared to have fallen below what it had been before this shutdown. Compressor temperatures were up compared to their value before this shutdown and were near the 70 deg C trip off point for the Gas temperature. Other systems, e.g. Johannes's Cryo-Mech compressors, appeared to have their cooling water flow rate return to its value from before this unannounced shutdown. To keep the liquefier main compressor running on about 29-Dec-2021 Reza ended up removing its side panels and installing a window fan to blow air through the main compressor. 12-March-2022: -------------- This entry is just a record of the typical running conditions before anything was touched on the 14th and 15th of March. These values were recorded after the compressor had been running for some days and its side panels are off with a window fan blowing air through it. These temperatures are the average of 3 readings taken over about 3 hours on the afternoon of 12-Mar-22. The 3 readings were all within a few 0.1 C of each other. Indicated Gas Oil Inlet Outlet Flow Rate ------ ------ ------ ------ --------- 60.0 C 41.4 C 23.0 C 43.2 C 5.5 LPM 14-March-2022: -------------- The work today was to: turn Off the compressor, turn Off the booster pump, turn Off the cooling water flow to the compressor, connect the 3 water pressure gauges for the compressor to its water cooling circuit, and then turn everything back On. Things were turned Off for about 30 minutes. As part of this plumbing work the male side of the water quick disconnects that plug into the front of the main compressor were also replaced. All plumbing components that were installed today have at least as big of an inside diameter as the components that they replaced. Nothing was done today that should have restricted the water flow in any way. It is noted that when the quick disconnect on even the Outlet side of the compressor was unplugged that the water that dripped out had a lot of sludge in it. When things were turned back On it was clear that the cooling water flow through the main compressor was less than it had been before this work was done and that the compressor temperatures were higher. To slightly complicate understanding what is going on, today was the first warm day (low 60s) of the year so you can see a warmer Inlet water temperature in the table below. It was still in the 30s when the reference temperatures were noted above on 12-March-2022. Stable readings after the system had been running for about 3 hours - the Fan is running just as it was before today's work: Indicated Gas Oil Inlet Outlet Flow Rate ------ ------ ------ ------ --------- 62.7 C 45.5 C 26.2 C 48.3 C 4.9 LPM or somewhat less Today for the first time we can also record the pressure at various points in the main compressor cooling circuit. Supply aka Pump Outlet Return aka Pump Inlet Compressor Inlet Compressor Outlet ---------- ---------------- ----------------- 82 psi 98 psi 94 psi This shows about a 4 psi drop going through the compressor cooling circuit. From Cryo-Mech's chart a 4 psi drop corresponds to about a 4.5 LPM flow rate. The Inlet to Outlet temperature rise is now about 22 C were as before today's work the rise had been about 20 C. 15-March-2022: -------------- Today we investigated why having the water flow turned Off for about 30 minutes yesterday resulted in a decrease of flow rate. This is very similar to what happened on about 22-Dec-2021 when IPF turned Off the process water flow without telling anyone. That time too, when the water flow was turned back On the flow through the main compressor was less than it had been before the interruption. First look at the static Supply and Return pressures in room B111 and B112. Measure these pressures at the taps in B111 behind the screened room and in B112 along its south wall: B111 B112 ------- -------- Supply 100 psi 100 psi Return 90 psi --- These are static pressures - there was no water flow from these process water circuit taps. This is a pressure difference of only 10 psi. These numbers are the pressures in the basement. Assume that the sub-basement is 12 feet lower and knowing that 2.31 feet of head is 1 psi this gives the expected pressures in the sub-basement of: Expected Pressure in the sub-basement ------------------- Supply 105 psi Return 95 psi Look again at the new pressure gauges in the sub-basement for the main compressor cooling circuit and see today: Supply aka Pump Outlet Return aka Pump Inlet Compressor Inlet Compressor Outlet ---------- ---------------- ----------------- 84 psi 99 psi 95 psi The most obvious problem is the low pressure at the input to the booster pump. There must be a restriction in the Supply line to the main compressor cooling setup. The Return pressure looks OK but recall that right now we have a very low flow rate compared to what we really need. Work on the restriction in the Supply line. My main point of concern is the rusty quick disconnect taps to the process water system up in B111. Looking at these QD connectors they look easy to plug up and recall that the Supply connector is before the filter in B111. Decide to replace the sketchy QD connectors in B111 for both the Supply and Return lines for the main compressor circuit. Replace them with straight brass barbs. Decide to also replace the filter element. Shut things down to do this work which all went rather quickly considering that pipe wrenches were involved. The system was only Off for about 20 minutes. Now we see: Supply aka Pump Outlet Return aka Pump Inlet Compressor Inlet Compressor Outlet ---------- ---------------- ----------------- 98 psi > 108 psi 94 psi The pressure gauges peg at about 108 psi. Without the Fan running the temperature measurements: Indicated Gas Oil Inlet Outlet Flow Rate ------ ------ ------ ------ --------- 64.4 C 37.3 C 22.6 C 35.5 C 10 LPM With the Fan Running temperature measurements: Indicated Gas Oil Inlet Outlet Flow Rate ------ ------ ------ ------ --------- 55.8 C 34.7 C 23.9 C 34.1 C 10 LPM Note: the Fan NOT Running temperature measurements were taken earlier in the afternoon than the Fan Running measurements - that is why you see an increase in the Inlet water temperature. Today again it got up to about the very low 60s. Summary Calculations and Cross Checks: -------------------------------------- 1. Before the work on March 15th the cooling water flow rate was about 5 LPM and the temperature rise, Inlet water temp to Outlet water temperature was about 20 deg C. After the work on March 15th the flow rate was about 10 LPM and the temperature rise is about 10 deg C. So we about doubled the flow rate and that cut the temperature rise about in half as one would expect. These are both measurements with the Fan running so this is an apples to apples comparison. 2. The booster pump Inlet to Outlet pressure difference noted on 14 and 15 March is about 15 to 16 psi. From the specifications for the Bell & Gossett model PL-36B pump (now on this web site) we should expect a head boost of 37 to 38 feet if this pump is working perfectly. At 2.31 feet per psi this is equal to a boost of about 16 psi - i.e. just what we see. 3. To push 10 LPM of cooling water through the main compressor the Cryo-Mech chart shows that it would require a pressure drop of about 19 psi. In this cooling circuit we have a Supply pressure that is 4 psi above the Return pressure. At this increased flow rate we expect a little less than 16 psi boost from the pump. So this estimate also looks OK. Recall that as the flow through the pump increases that the boost it can provide decreases. It can provide a maximum boost of about 16.8 psi at zero LPM flow rate. At 20 LPM flow rate the boost is down to 15.1 psi if the pump is working perfectly. 4. The Cryo-Mech specifications say that the compressor uses 9.9 k Watts of power. So if the cooling water flow really is 10 LPM what temperature raise should be expect ? Recall: 1 k Watt is 14.34 L per minute - degrees C So we should expect about a 14.2 C rise in water temperature with a 10 LPM flow rate. When the Fan is not running and thus most of the heat goes into the cooling water we see a raise of about 13 C so this looks OK. 5. Estimate how much heat is being blown away by the Fan into the enclosed air space of the sub-basement. With the Fan running the temperature rise of the cooling water is about 10 C and with the Fan NOT running it is about 13 C. So the Fan blows away into the sub-basement the heat in about 3 C of 10 LPM waters. From the equivalence just above this is about 915 Watts. 6. For reference recall what we really need to safely run this system with the 30 C Inlet water temperature that we saw last summer. We need at least 14.2 LPM which will require about 35 psi drop across the compressor.