Valve-Based Generation System Provides On-site Power
Having onsite power at a valve/vault site provides many advantages.
Having onsite power at a valve/vault site provides many advantages. With power, you can have lighting, add a security alarm, run a sump pump to keep the vault dry or even use a heater to keep the space from freezing in cold climates. Another significant advantage of onsite power is having the necessary means to operate SCADA equipment for monitoring and control.
Unfortunately, in many cases it is impractical to provide power to a remote valve vault because of location or cost. However, a new variation on a simple, established technology makes it possible to used a valve-based package that uses the energy in the piping system to generate power.
|Installation in an underground vault adjacent to an irrigation canal|
One such system is offered by Cla-Val. Its valve-based power generation package uses a standard automatic control valve, a small turbine, a control panel to manage output, a battery to store power, and a diversion load to burn off excess power after the battery is fully charged. The most common installation site is an underground valve vault where there is no existing power.
The optimum valve type to use in the power generation package is a pressure-reducing valve (PRV) because a PRV automatically produces a pressure drop, which is essential for the package to generate power. The primary valve in the package must have a minimum differential pressure to operate properly: some models will operate with as low as 15 psi pressure drop. The amount of power the package can generate is directly related to the pressure drop, i.e. the greater the differential, the more power can be generated. When considering using this type of generation package, a basic calculation can determine what can be expected in terms of output based on the valve's inherent pressure drop.
How It Works
Simply put, a valve-based generation system uses the energy from the pressure drop that occurs in a pressure reducing valve to operate a turbine and generate power. In this scenario, a turbine assembly is installed in bypass piping in parallel with a PRV. A control panel with integral display manages the output by sending the power generated by the turbine to one or more batteries. The batteries, in turn, provide power for the site equipment such as lighting, sump pumps and communications equipment. When the battery is fully charged, a diversion load burns off the excess power.
It is important to note that a valve-based power generation package is not intended for connection to an electric company's grid.
Valve-based power packages are typically compact and can be installed in a vault or enclosure that protects them from vandalism, tampering, theft and the environment. They can be less expensive than other onsite power options and generate power reliably regardless of the time of day or weather conditions.
|Electric heat tape provides protection from cold Canadian winters.|
Valve-based power generation packages can be retrofitted to an existing valve, as shown in Figure 1 at a job site located in the Pacific Northwest. In this installation, the power generation package was installed in an existing vault with 6-inch Pressure Sustaining Valve serving an irrigation canal.
Because there was no power at the site, maintenance personnel had to drive 12 miles each way every time they needed to operate the valve. The water company wanted to control the valve electronically using their SCADA system but there was no available power and the locale was not well suited for a solar panel system. To meet this challenge, the existing hydraulic control valve was retrofitted with an electronic pilot control system. The installation was then fitted with two 12 volt batteries - enough to operate the equipment at the valve site which included an RTU, in addition to the electronic valve.
|An above-ground control panel and display controls the valve-based generation system in the vault below.|
This power generation package has been in operation since early 2009 with no interruption of power and no maintenance issues.
In many climates, valve sites are subjected to very cold weather, causing operational issues from freezing, water quality challenges and difficult access to unheated, confined spaces with no lighting or communications. In Figures 2 and 3, the valve-based power generation package was installed in an aboveground enclosure at a new underground vault/pressure reducing station in Canada. There was no power at this particular station to run a heater or other device to prevent the site equipment from freezing in the winter.
The option was considered a good alternative to conventional power sources because average cost to heat a vault in this area was approximately $3,500 annually, in addition to the cost of bringing power to the site by tying into the local power grid. In this installation, two standard PRVs were used: one 4-inch and one 1.25-inch. The generator provides power to operate a meter and electric heat tape that is used to protect the valve tubing from freezing. The power requirement for the heat tape is 101Watts/1 Amps 12vDC with the tape operating 24 hours per day. Since the generator was already producing more than enough power for the heat tape and meter, the water company also had the option of installing a heater to further protect vault equipment from freezing.
It is typical that over time, water distribution system requirements change and supplementary equipment must be installed to meet the new needs. If the upgrade includes an electronic component, onsite power must also be available. Using a valve-based power generation package is a good alternative in such a situation. Figures 4, 5, and 7 show the generation package installed at an existing pressure reducing valve station/vault (with one 2-inch and one 4-inch PRV) to provide power to operate a chlorine analyzer.
|The system provided enough power to operate a chlorine analyzer and sump pump to keep this vault dry.|
This underground vault was chosen as the installation site for the chlorine analyzer because operators felt they would be able to get the most accurate readings there. Because the vault has a tendency to flood during heavy rains, a sump pump was also needed to keep it dry enough for the analyzer to work properly.
The power generation package replaced a solar panel system from which panels had been stolen less than 24 hours after installation. The valve-based package was seen as a good alternative because the cost to tie into the nearby electric company power source was estimated to be $10,000 plus the ongoing monthly usage charges.
Within 10 minutes of start-up, the generator was producing enough power (150 watts) to run the analyzer and sump pump as well as completely recharging the battery. The control panel/display was installed in the existing, locked solar panel system enclosure aboveground, thus providing a secure location for the new equipment, while the remainder of the power generation system was located below ground in the existing, now dry, vault.