uncommon pump configuration

[ucfenveng]

I'm currently a part of a design for several components of an existing wastewater plant. Due to limited space, the pump stations for the RAS will be located adjacent to each clarifier (there are 3). I'm evaluating some pump selections we expect to install, however, I have not come across a system with this type of configuration. The pumps are so far apart that modeling the pump system as a parallel configuration would be inappropriate. The distances between the clarifiers are approximately 250' (b/w 1,2) and 50' (b/w 2,3). The distance between the closest clarifier and the aeration basin is about 200'. In order for the pump selection to work, the capacity of the pump with the closest clarifier out must be 1.5Q(design). Because of this constraint, I would like to get a relatively accurate model of the system when the pumps are at 100% (without having to invest in any software). I'm thinking that I should set up a system of equations from a point in the pipeline where all the flow has collected (intersection of the line from clarifier 1 and 2). Next, I write Bernoulli's equation from this point to clarifier 1, clarifier 2, and the aeration basin (3 equations). Based on the pump curves and the headlosses across each path corresponding to each pump, I should be about to find a unique solution for the Q of each pump. Has anyone dealt with a similar pump configuration where modeling as a parallel system wasn't the best assumption. If so, please help. Thanks.

 

[gerhardl]

I agree that you should check the theoretical minimum correct capacity of the pumps, in general as you suggest.

Question: How do you foresee the actual fine-regulation at site when built?

Isn't the purpose of the exercise to find the minimum capacity plus some additional safety factor, and then regulate by either regulate pump speed or by throttling the output (knifegate valves with v-port or pentagon type blinds)?

 

[bimr]

Would you provide the reason for modeling?

Why can't you model the clarifier and sludge pump as one component? Each of these parallel components will have the same or similiar hydraulic setup.

Typically, one would want to minimize the length of the suction piping, so it seems your system design is appropriate.

 

[ucfenveng]

Thanks for everyone's input. Sorry for the late response. I'll prepare a sketch of the system during the week and post it (I'd attach the drawing, but I think it may be inappropiate to post the company's work). I plan on modeling while using the approach I explained (hopefully within the next two weeks or as the project permits) as there doesn't seem to be any significant concerns. Once again, thanks and I'll make sure to post the results.