For the seawater reverse osmosis system, due to the high pressure of the concentrated water discharged, if it is recycled, it can greatly reduce the energy consumption of the system and reduce the operating cost.
At present, the commonly used energy recovery technologies are mainly divided into two types: turbine type and pressure type.
01 Turbine Energy Recovery
A turbo recuperator is an integral turbo pump, similar to a reversing single stage centrifugal pump.
The device is connected in series with the high-pressure pump on the reverse osmosis water inlet side, and transfers the pressure of the reverse osmosis concentrated water to all the influent water, and the energy recovery efficiency reaches about 60-80%, which can reduce the head of the high-pressure pump.
The process is as follows:
02 Pressure energy recovery device
The pressure exchanger energy recovery device is abbreviated as PX. It adopts an ingenious design to convert energy using the principle of positive displacement, and transfers the pressure of the reverse osmosis concentrated water to the same amount of influent water.
That is to say, the raw water is divided into two paths after passing through the security filter, one goes to the energy recovery device, and the other goes to the high pressure pump.
The device is connected in parallel with the high-pressure pump, which can reduce the flow rate of the high-pressure pump, and the energy recovery efficiency can reach more than 95%.
Since the PX high-pressure effluent goes to the high-pressure pump outlet, a booster pump needs to be set up to overcome the loss pressure drop and resistance loss.
The process is as follows:
03 Comparison of the two methods
Turbine energy recovery is characterized by high pressure pump, large flow, low head, low investment, small footprint and high operating cost;
The pressure type energy high pressure pump has small flow and high lift, high investment, large land occupation and low operating cost.
Take a seawater reverse osmosis device with a production water of 100t/h and a recovery rate of 45% as an example:
| Item | Turbine | Pressure |
| High pressure pump parameters | Q=222m3/h, H=402m, N=355kW | Q=100m3/h, H=557m, N=220kW |
| Booster pump | W/T | Q=122m3/h, H=40m, N=30kW |
| Investment | 3.85 million | 4.9 million |
| Energy consumption per ton of water | 3.55 kW | 2.5 KW |
It can be seen that, compared with turbine-type energy recovery, pressure-type can effectively reduce energy consumption. From the perspective of long-term energy saving and consumption reduction, pressure-type can be selected. If one-time investment is concerned, turbine-type can be selected.
