One of the ways with which to reduce carbon dioxide emissions is through energy efficiency which is one of the useful benefits derived from the integration of variable frequency drives. In pump and fan applications onboard marine vessels, ABB VFD’s from techniconiec.com/ reduces energy consumption for the applications by as much as 60%. Until recently, energy efficiency was not a major consideration in the design of existing ships and if shipbuilders will continue to ignore energy efficient solutions, the ship’s capabilities will be limited. In most marine environments, any changes are mitigated through inefficient methods like throttling and by-pass loops.
Variable frequency drives for ship’s pumps and fans
Pumps and fans onboard ships have critical applications. If they are not working properly, the ship will not sail. Onboard the vessel are different pumps applications that include sea water cooling pumps, boiler feed pumps, HVAC pumps, bilge water pumps, waste water pumps, fire pumps and many more. Pump design criteria is set to meet extreme conditions to which the vessel may operate but daily operations rarely come close to such conditions. When pumps and fans are controlled through variable frequency drives, power demand is adjusted to normal operational conditions to optimize the shipboard systems.
The most frequently used antiquated methods of control like throttling controls and by-pass loops in order to adjust temperature makes the pumps run continuously at 100% loads which is very ineffective in terms of energy efficiency and can also exacerbate equipment wear. The least efficient of the control methods is by-pass control where superfluous flow is redirected back to the pump through a by-pass valve. Variable frequency drive is the only optimal energy efficient method of control because it ensures that only the energy required is consumed and results into a payback time of 1.5 to 4 years for the VFD investment.
Reducing the risks of cavitations through VFD
A fluid flow system is characterized by a system curve that is totally independent from the pump. The system head which is visualized by the curve is a combination of the elevation and the friction of pipe bends and valves within the system. On the other hand, the pump curve is a graphical description of flow and pressure relation for one specific pump. The duty point of a pump in a vessel is always at the intersection between the pump curve and system curve but it can be changed through blinds, semi-closed valves and by-passes which are generally inefficient. When a VFD is installed in the pump, it provides for more flexible pump control and reduces the risks of cavitations in the most efficient way. Cavitations are significant sources of wear since they cause surface fatigue on metals resulting into wear.
When vessels are retrofitted with variable frequency drives, it is critical to have extensive knowledge of the ABB drives including the motor’s fans and pumps. In some instances, the motor has to be replaced with a new one that is compatible with VFD’s. As a rule of thumb, motors with voltage levels not exceeding 500V are great for VFD retrofitting while others have to be checked carefully for suitability.