The Problem of Fuel Recirculation in Diesel Generators Part 3

This article continues to introduce the issue of fuel recycling and its impact on on-site power generation design.

Solution 3:

A separate fuel cooler can be specified to provide specific cooling performance for upcoming applications. A typical unit includes a fan/motor component for vertical or horizontal exhaust. Installed between the fuel return connector of the engine and the day tank, it will cool the fuel before it re-enters the day tank. Working together with the fuel temperature sensor, the fan/motor of the cooler starts as needed. It is important to note that although many common tank manufacturers offer optional fuel coolers pre installed on common tanks, these coolers are often not selected for specific engines and may result in only a small portion of the required heat load being removed from the fuel.

Solution 4:

It is possible to specify an automatic fuel recirculation function from the daily metering tank to the main metering tank for the daily metering tank. When the fuel in the metering tank reaches the critical high temperature on that day, the reflux pump/motor is activated to return the heated fuel to the large capacity storage tank. Once activated, the return function will remain active until the fuel tank is drawn to 50% liquid level, at which point the filling pump of the tank will open, extracting fresh (possibly cooler) fuel from the large capacity storage tank. If the size of the large capacity storage tank is sufficient to dissipate the heat of the return oil during long-term operation, the tank will be able to maintain an acceptable range of fuel temperatures for the engine. This solution requires the daily metering tank to be equipped with a temperature sensor, a reflux pump/motor connected to a suction pipe of sufficient depth to achieve a 50% liquid level in the daily metering tank, and a control logic to perform this function.

Conclusion:

During brief power outages, or on devices with light loads in the emergency power supply system (EPSS), the effect of heating fuel recirculation may not be significant. Depending on the performance of the installed fuel cooler and other factors such as the size of the metering tank, the size of the generator, and the load level of its application, it may take several hours to recirculate the fuel to raise the temperature of fresh fuel to a level harmful to the EPSS. However, considering that many instances of natural disasters require many EPSSs to operate for many days, as well as the practical and serious issues that generators may face when unable to maintain building loads during prolonged power outages, design engineers should be cautious in designing critical on-site generator systems in this regard.

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