Found out yesterday that one of my favourite projects didn't work very well in practice. I had designed a fantastic combined diversion/bypass/air release chamber downstream of a new BAFF plant in a sewage works. One of my best bits of work.
When used in practice, it generated a huge quantity of foam (foam gets worse as you pass through a sewage works: there is less muck for detergents in the flow to work on so it just foams). Being an air release chamber, that was where the bubbles came up. And stayed!
So the commisioning team added a penstock to restict the flow so that it would back up and submerge the drop at which I had correctly interpreted that air entrainment woudl occur, and succesfully stopped the foaming. They also removed a very expensive perforated baffle plate taht I had designed. But now they had a supercritical flow shooting under the penstock, which blasted through the air release chamber and made a huge wave against the opposite wall, which of course entrained air here instead.
I said 'Why didn't you put the baffle plate back in?'
The reply 'Oh, that had already been weighed in [at the scrap yard]'.
So the dropped a lump of concrete in instead.
Also, although we had looked at the theoretical Dry weather Flow, nobody had checked the lowest diurnal flow (in the middle of the night), which wasn't enough to keep the pumps running continuously so the UV plant downstream (which needs a steady flow because you can't keep switching the bulbs on and off) failed. Now they have had to introduce a new recirculation flow at these times.
No comments:
Post a Comment