A novel dehumidification system developed by Danish company Cotes A/S could prevent corrosion and electrical problems in transition pieces in especially humid environments
The prototype of an innovative way of protecting transition pieces (TPs) while an offshore windfarm is under construction is being tested on a nearshore windfarm in Denmark.
The developer of the concept believes it could protect TPs from the adverse effects of humidity and the salt-laden environment offshore. Without protection, problems such as condensation, corrosion and mould and fungus growth in TPs can arise after they have been installed, but before a turbine is operational and a permanent dehumidification system activated. In the worst case, high levels of humidity can lead to the failure of electrical equipment and a potentially dangerous working environment.
Cotes chief commercial officer Michael Holm tells OWJ the company had developed the temporary dehumidification concept after feedback from the market. It is already well known for dehumidification systems that are installed in TPs once a turbine has been completed.
Mr Holm explains the prototype the company is testing in Denmark is designed to protect a TP from day one, drying the air in it, preventing condensation and removing potentially corrosive salts. The challenge Cotes faced was to find a way to provide power to a dehumidification system that could create an over-pressure within a TP, that would keep out salt-laden air, without access to an external power supply.
The innovative solution it arrived at combines using a 24-volt battery pack and small-scale wind turbine attached to the TP that is used to recharge the batteries. The only maintenance required by the system is refilling a tank for a small diesel burner that heats the air in the tower. A 1,000 litre tank need only be replenished once every 12 months, Mr Holm explained. In the unlikely event of a windless period, a 24-volt battery pack can provide sufficient charge to the system for 36-48 hours.
“Moisture in the air is one of the leading sources of operational problems, damage to equipment and structures, and a range of practical problems in the nacelles and towers of wind turbines, especially those offshore,” Mr Holm explains. “A lot of the problems offshore wind turbines experience are directly or indirectly related to moisture and corrosion.
“Conventional filtration is not enough to remove corrosive salts from the air. The warmer and more humid the location where the wind turbine is installed, the greater the potential problem with corrosion and the greater the difficulty with conventional filtration.
“As a rule of thumb, the rate of corrosion doubles with every 10°C temperature increase. That makes solutions relying on filtering air potentially risky in turbines in warm, humid climates of the type found in countries such as Taiwan, China, Japan and Korea and others where offshore wind is growing quickly. In a country like Taiwan, a turbine can be exposed to 90% humidity much of the year.
“If a TP stands idle for several months before it is transported offshore and remains unprotected for weeks after it has been installed, before the turbines is completed, there is a real risk of problems with moisture, mould and corrosion. That is the challenge we hope we have addressed with our temporary dehumidification system.
“Creating a small over-pressure inside it seals it and prevents humid air getting into it. In this way, we can reduce condensation, keep electrical circuits dry and prevent corrosion. By the end of 2020, we should know exactly how effective the system is,” he concludes.
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