Freshwater generators convert saltwater into potable water using heat and pressure. They are important for long sea voyages and are increasingly used in desalination plants. However, they are expensive and require maintenance. Generators are not a solution for widespread water shortages, as they are not powerful enough to meet the scale of the need.
A freshwater generator is a machine, usually aboard ship but also in some industrial settings ashore, that converts salt water from the seas and oceans into potable freshwater. The machines tend to be quite complex and rely on an array of pumps and pressure chambers as well as high temperatures to require both boiling and evaporation. They are usually quite sensitive and often require a lot of maintenance to keep them running efficiently; salts that are removed from the water can cause buildup, and if the sensors that measure relative salinity lose their accuracy, the water you dispense will not be fresh at all. These generators are a very important part of long sea voyages, as it is usually not practical for crews to load as much water as they need. Some communities have also begun building desalination plants to convert seawater into water that can be used instead of municipal water, but the costs here tend to be very high. Researchers have long been looking for inexpensive ways to convert saltwater into water that can be readily consumed by people, particularly in drought-affected parts of the world, but for now at least the practice is so expensive that it’s only used in wealthy areas that can both pay for the initial plant construction and perform the necessary maintenance.
Basic concept
The general concept of a freshwater generator is usually quite simple. First, seawater is evaporated using a heat source, separating the pure water from salt, sediment and other elements. Generators often use the jacket of the diesel engine as the heat source, although steam can also be used for this purpose. The practical aspects are often more complicated. The initial cost also tends to be very high, but, mainly because freshwater generators tend to use existing heat to operate, realized operating costs tend to be low, at least on ships. Depending on how much water they need to convert, they also tend to be quite small and can usually fit in a mechanical closet or small room.
Importance of fresh water
Ships and ocean liners often take weeks if not months to complete their voyages and a lot of fresh water is usually needed to sustain operations for that long. Crew and passengers need water to drink, of course, and water is also needed for things like cooking and cleaning. Many mechanical operations, particularly those involving the engine, also require steam and connection to a water supply to maintain optimum operation. Seawater is not suitable for drinking and cooking and the sediments it usually contains make it unacceptable for most other uses as well.
Long ago, sea travelers carried barrels of water which they rationed for the duration of their voyage. While this is usually still an option, packing enough clean water at the start often adds a lot of weight that modern sailors consider unnecessary, and the risks of spoilage are usually not even worth the costs. Investing in a freshwater generator is widely considered an industry standard and is required by most governments and regulatory agencies for business operations.
Primary components
There are two main elements in most generators. One heat exchanger evaporates seawater and another condenses fresh water vapor into potable water. In the condenser element, the vapor is condensed by cooling, often simply by using cold seawater to cool the exterior of the unit.
From a practicality point of view, the generator should also include a function to monitor the salinity of the treated water. If the salinity exceeds a specified level, usually between one and ten parts per million (ppm), the generator will automatically return the water to the supply line and cycle it back. Substantial problems may be a sign that repairs are needed.
Use in desalination plants
Generators are increasingly used as a core component of large-scale desalination plants, typically located in coastal areas; these systems are usually designed to provide small amounts of fresh drinking water and crop irrigation to the local community. These have become very common in the Middle East and are also in use in some California communities. More desalination plants are likely to be built in response to the drought and as concerns about water availability in growing cities continue to grow. However, the costs of desalination plants tend to be very high. As such, they are usually only considered when affluent communities face water shortages from traditional sources and usually only in places that already have a natural source of salt water.
Practical restrictions for daily use
Researchers and environmental experts have long questioned the sustainability of fresh water sources on earth, and many are looking for an affordable and reliable way to convert salt water for human use. In most cases, the generators aren’t powerful enough to meet the scale of the need, even if they weren’t expensive enough to run on land.
Many of the most desperate and water-poor communities are found inland, often in war-torn or developing countries; many of the central African regions are good examples. Building desalination plants here is not feasible because there is no ready source of salt water and trucking it from the coast is often cost prohibitive. As such, generators are a means of converting water, but are not usually considered a solution to widespread water shortages.
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