Conformation of Turbines installed within a pressurized water main

It is with exciting news that energy recovery within an existing water supply system is a technology that is being applied around the world. Fred Howe from Thompson and Howe Energy Systems Incorporated said to me through email that they have supplied equipment for over 1180 Small Hydro Systems all around the World, and have been operating six pumps as turbines since 1975. They did a lot of research in the early 1970 and developed their own computer software which allows them to convert any pump curve to a turbine output. Fred was kind enough to continue our conversation and let me know that “the pump turbines actually work better with a positive discharge pressure”. Fred explained “We have installed many Pump-Turbines on isolated (non grid) systems that have been very successful. A Pump-Turbine is designed for a fixed flow. Usually these sites have flows available that exceed the flow required for each turbine all the time. Some sites use multiple Pump-Turbines that can operate with variable flow.
Municipal Pressure Reducing Stations usually have a large variation in flow and it is not generally economical to install turbines when they cannot run 24/7 especially when they are tied to a Utility grid because the payback at only $0.085 per kilowatt hour is much too long. On Stand-A-Lone systems that offset diesel generation the value of a kilowatt hour may be as high as $0.30 to $0.40 per kilowatt hour.

Over the past 12 years we have done design proposals for many Municipal Pressure Reducing Stations throughout Canada and the USA but only a few of these have actually been built.”

Below is a description sent to me from Len Howe from Thompson and Howe Energy Systems Incorporated
Here is PRV station installed May 2010 for the District of North Vancouver with an energy recovery turbine (PAT) (pump-as-turbine).






This turbine (Francis type, double-suction) has a net delta P. of 50 PSI across it and produces approximately 23kW passing while 80 litres per second. This flow is relatively constant because the primary user is a Chlorine plant which consumes the 80lps constantly 24/7. We have installed turbines recently for Nevada City California on a sewage treatment plant out-flow, as well, a PRV turbine for Grand Junction, Colorado.

Since most of these installations are usually induction generator type, intertied to the local public utility as the only practical means of recovering the energy, it is not very profitable, since it can take months of sending emails and hoops that you have to go through to get permits to do it. Most residential PRV stations have a very wide range of daily flows, therefore it is difficult to install just one turbine which can generate efficiently. If the flow drops below what the fixed flow turbine requires then the efficiency falls off dramatically.

I am great full for this information and appreciate the efforts made by Fred Howe and Len Howe thank you very much.