Recovering Pump Power

What type of pumps do you have?

What type of flow?

Duration and frequency of surplus?

Generating electricity will be easy but finding a use or a buyer for an intermittent supply may be hard.

Can you not rather schedule the use to allow you to use a smaller pump unit(s) continues?

Beats me as to the type of pump or the flow level, I just know that they deliver water at 2300psi.

We have enough load capacity that we could use the recovered power ourselves (we're a steel mill). The whole idea is to minimize wastage during production delays when we still have high fixed loads.

Goooosssshh! That's a lot of juice there. Good to check-up 'Strainers or Filters' for clog-ups condition and also I will try to check-up diverting valve operation (Open-Close Travel) and assuming there is a loop back to the reservoir (Stand-By) tank, I Guess. Most of such industrial pumps also have a safety by-pass wrigth at front which is spring actuated flapper feature in order to protect it from maximum limits as well. Good to check it out just in case however that thing are factory pre-set for operating conditions. Will be good to check-up manufacturer literature by the way. Nice Saturday Job I Believe. Hang in There and bring some good 'Lunch and Tools Boxs'.

Overtime Rate,

MC

And the reason they can't just be switched off is what, please?

The system is for removal of oxide from hot steel so it has multiple headers throughout the mill. These can't be left open when there's no steel there as they act in opposition and will erode themselves. The system has to be left partially pressurized to avoid shock loads so when there's no steel being run the excess pressure gets dumped to a bypass line into the mill waste water stream (it's treated before release).

Periods when the bypass is open can be as short as a couple of minutes to a couple of hours but with little predictability. The idea was to recapture some of the energy and service our other fixed loads across the plant. It would be very unlikely that we'd ever generate back to the grid but the meter wouldn't be going forward quite as fast.

Could you use this idea to store excess water t a higer elevation and use the stored water to feed the working pumps.

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

Good suggestion. The OP might also want to google "Dinorwig pumped storage scheme".

Suggest that you Google Pumps as turbines, you may get some ideas.

At this head, a Pelton wheel would be a possible choice, but you would need to know the flow available at that head.

These normally have a hydraulic efficiency better than 85%, depending on size, and can often be switched on and off fairly rapidly.

There could be some fun synchronizing this short term, intermittent power to your plant grid.

I assume the pumps can't be turned off because of the restrictions on number of starts (especially hot starts) which apply to large electric motors?

Another option is to get a pump the same as your main pumps, but with special screwing so they can be run in reverse as a turbine. This gives an efficiency similar (although usually a little lower) than the pump running normally.

If this happens often, I can understand the interest in reclaiming at least some of the energy.

if they nare positive displacement pumps and you have syncronous motors, opening a discharge valve will drop the amps significantly.

Have you considered a solid state variable voltage control system? 4200 volts is well within the capacity of solid state devices now a days. Simply do what ever reduces system back pressure the most and then use a simple but big SCR type voltage control system to drop the unloaded motor voltage down while not in use. I have seen articles relating to mines using that form of system for massive crusher drives running 4200 volts at 3000+ hp. I think they had something like 5 -10% no load power consuption when compaired to full load.

There was information on the internet one time about how its done.