Testing of DanfossAPP1.0-2.2 with APP pumps as water hydraulic motors for energy recovery

A high pressure system, using Danfoss APP pumps both as high pressure pumps and also as reverse running water hydraulic motors for energy recovery has been tested. The pumps were built together on a transmission, built by Balder Water Technology A/S. So that the speed of the pumps, waterhydraulic motors and the electrical motor was linked together in a fixed relation. Four different configurations/combinations of pumps/waterhydraulic motors were tested to get results of production rate, recovery and energy consumption per m3 of water produced. The combinations tested covered the area from 8 to 23 m3/day with recoveries from 31 to 46%. However all possible combinations of the smaller range of the Danfoss APP pumps on such a transmission can cover the area from 8 to 60 m3/day. The result shows that energy consumptions between 3 and 4 kWh/m3 is very well achievable with pressure units using APP2.2 and 1.8, also in combination with APP1.0. For some combinations an energy consumption between 3.0 and 3.5 kWh/m3 is achievable. For pressure units using APP1.0 and 0.6 the energy consumption will be from 4.4-4.8 kWh/m3. The results show that the energy consumption is reduced with 6-9% after a run-in period of 12-16 h. For combinations with APP2.2/1.8 and 1.0 the results show that the energy consumption is reduced with reduced speed. For the combination with APP1.0/0.6 the energy consumption had a minimum point at 3100 rpm. It is believed that the other combinations also have minimum points, but at lower speed than 2500 rpm. There is an indication that lower recovery leads to higher energy consumption with this system. However, for small plants like this it is very unpractical to have very high recovery. The operation of the system is very smooth and stable and the result shows that this system can be an interesting alternative for small desalination plants, especially where low energy consumption is important.