Ovelap Backup Design

[jeap]

Hi All!

Recently I found a conceptual description of a Wastewater treatment plant where "Overlap Backup Design" is mentioned as a philosophy of design. From that philosophy it is proposed to install two parallel separation trains wich includes: coalescer, flotation unit and filter. Each train normally would receive fluids from different sources.

I really don't understand the exact meaning of that philosophy. I assume both trains operate simultaneously but (here my question):

a)Should the capacity of the equipments include a overdesign in order serve as backup for the other in case of maintainance? Thus keeping the process continuosly working.

b)Should I consider some adittional equipment to be a backup for both trains?

I thank you in advance for your help.

jeap

 

[MikeHalloran]

Speaking of factories in general, and not wastewater plants specifically, of which I know, uh, "used food":

A lot of factories are at risk because of Single Points of Failure, e.g. one major piece of capital equipment through which all work flows. When that machine is down, you're out of business.

... and your competitor takes up the slack.

;---

It seems that wastewater is different, because it just keeps coming, and there's no competitor there to take up the slack when you go offline, so you can't afford to go offline.

It would therefore make sense to provide some kind of onsite backup. Logically, each should be sized to at least take care of the full normal flow somehow, to cover the case when one line is down. Which happens when any one unit is down.

The word 'overlap' suggests a relatively simple enhancement; providing cross- connects, normally closed, so that, e.g. coalescer A could feed flotation unit B, etc., so that the plant could run at full capacity even if two non- corresponding units are down. You've still got a problem if, e.g., both coalescers are down.





Mike Halloran
Pembroke Pines, FL, USA

 

[jeap]

Mike, thanks for your answer. Really useful.

 

[dcasto]

This may be a definition for what you described. We would install two 66% to 75% capacity trains. Normally each train was partially loaded. During an upset, one train would run and we could handle 66% to 75% of the load. With some scheduling for downtime that load would be sufficient. This arrangement also allows for some off peak times at 130% to 150% of the original design. It saves on capital if you required 2 - 100% trains.