Reverse Osmosis Energy Recovery

"If its possible, how it works?"

That's what you are supposed to tell us.

What's a "pressure exchanger"?

Could you supply a detailed drawing for analysis?

Please go through the following link.

http://www.slideshare.net/dhinesht88/1-16197873

note the inlet & outlet parameter of energy recovery turbine. I want to know, how is it possible to lower the pressure at point 5 below the pressure at point 2.

Does anyone knows the internal arrangement of the same?

kindly help me to understand.

Maybe this will help:The turbo takes energy from the inlet (Brine) (red)side to drive the compressor wheel (blue side) It is conceivable that you could achieve the type of pressure drop you desire, but you'd need to have real numbers to work with.

It seems to me that the advantage would be the high SG fluid on the drive side, and not much else.

Pressure exchangers are an integral part of larger RO plants, where the cost of energy is an important parameter in the plant's operation. So, yes, it is both possible and works. In fact, it could be described as "routine".

Google "Reverse Osmosis pressure exchanger" for chapter-and-verse on the topic.

Look up Spectra watermakers. They make a high-efficiency watermaker for small boats that recover the seawater discharge pressure energy.

bandership

The equipment already exists, and yes, on seawater RO is very useful. It is not entirely necessary to use this with a pressure exchanger to pressurize some of the feed water, one can simply use a hydraulic turbine to drive a generator to recover energy, etc.

By the way with most larger RO systems, the feed is staged in such a way that the brine outlet pressure is in fact lower than the inlet pressure due to hydraulic losses as water passes by the membranes. This is a diagnostic as to the degree of fouling of the membranes, along with net driving pressure. NDP is the difference between inlet pressure, osmotic pressure, and hydraulic loss in a given vessel or stage, or this can be calculated across an entire array (system) to arrive at average NDP.

Pressure exchangers work by taking water from one stream at a given supply and discharge pressure and flow rate, driving a turbine which operates a pump to raise a smaller flow rate from a lower pressure to a much higher pressure. Hydraulic seal concepts are used in some designs to prevent much ingress of a saltier water into a water containing less salt. Other designs simply use "normal" mechanical seals between the turbine compartment and the pump compartment.