The combination of vacuum enhanced distillation and waste heat recovery is a proven concept that has been used for over 60 years. Advances in technology have resulted in evaporators that are more efficient and reliable than ever before and offer a clear green advantage.
We want you to be able to make an informed decision about the technological, operational, and financial investment that comes with the purchase of a fresh water maker. This section has been designed to clarify the similarities and differences between a MAXIM Heat Recovery Evaporator and other desalination technologies.
Q: How does the upfront cost of a MAXIM heat recovery evaporator compare to other desalination technologies available on the market today?
A: When comparing one of our units to an RO unit of similar high quality, the upfront capital costs are comparable. The same is true when comparing a Maxim evaporator to waste heat units offered by other manufacturers. When considering long term economics, significantly longer equipment life and low operating costs yield an excellent return-on-investment.
Q: How does the installation costs of a heat recovery evaporator compare to that of a reverse osmosis watermaker?
A: Installation costs of an evaporator versus RO are only slightly higher. Both systems require connections to seawater feed, brine reject overboard and a connection to a fresh water holding tank. The only additional connection required by an evaporator is to the hot water loop coming from the engine and prior to the radiator or keel cooler. This connection is simple to perform and Maxim provides the technical support to assure it is done properly.
Q: What is involved in the routine maintenance of a heat recovery evaporator?
A: Maintenance involves prevention or removal of scale formation on the seawater heater tubes and the evaporator boiling chamber.
Scale prevention includes the use of a chemical feed system with an effective scale prevention chemical. Very small doses of a chemical are introduced into the incoming feed water on a continuous basis to prevent minerals dissolved in the feed water from forming on the tube surfaces. Maxim can provide such a chemical known as MAX-Defense.
Scale removal is another method of maintenance. Scale can be removed periodically using a low pH cleaner. This is accomplished while the system is still in operation and only requires about 15 minutes. Cleaning frequency is dependent on the amount of time the evaporator is in operation and the chemistry of the incoming feed water.
Maxim equipment is designed to minimize scale formation to keep maintenance time and costs to a minimum. Scale is minimized by boiling water at low temperatures under a vacuum along with the turbulent flow of water at critical points in the evaporator.
Q: How well does a heat recovery evaporator function in varying feed waters and fluctuations in feed water temperatures?
A: Heat recovery evaporators operate consistently across all types of feed water and can handle wide ranges of feed water temperatures. Evaporators can function well in river water, brackish bay water, or seawater and yield the same high quality water. The water quality is consistently good even when feed water contains silt, sand, oil and other contaminants found in coastal waters. The feed water pretreatment consists of only a screen strainer.
Q: When is it advantageous to use a heat recovery evaporator over a reverse osmosis watermaker?
A: Heat recovery evaporation is the most energy efficient desalination technology when waste heat is available. Waste heat from engine jacket water, exhuast gas, or other heat sources is utilized which provides the bulk of the energy requirement and reduces operating costs.
There are no consumables such as filters and membranes required on evaporators which reduces maintenance time and costs. An evaporator operates under low pressure and has few moving parts thus making this system highly reliable.
Water produced is high quality, containing less than 4ppm of total dissolved solids, compared to the water quality produced by an RO unit which contains 200 to 500ppm of total dissolved solids. The water produced by an evaporator is less corrosive and aggressive than that produced by an RO unit.
Heat recovery evaporators also do not require the use of membranes or filters. Membranes and filters foul in the presence of certain types of feed water and do not react well to changes in the feed water. Evaporators are very effective in all environments from bay water to offshore and all points in between. A heat recovery evaporator typically weighs less and has a smaller footprint compared to an RO unit.
A heat recovery evaporator is friendly to the environment. There are no filters or membranes that ultimately end up in landfills. The use of waste heat also reduces carbon emissions.
Q: How well does a heat recovery evaporator function in varying feed waters and fluctuations in feed water termperature?
A: Heat recovery evaporators operate consistently across all types of feed water and can handle wide ranges of feed water temperatures. Evaporators can function well in river water, brackish bay water or sea water and yield the same high quality water. The water quality is consistently good even when feed water contains silt, sand, oil or other contaminants. The feed water pretreatment generally consists of only a screen strainer.
Q: Is the fresh water made through desalination of sea water corrosive?
A: Fresh water made from sea water tends to have a lower pH and can be aggressive towards metal piping and storage tanks. The reason is that the desalination process liberates carbon dioxide which ends up dissolved in the clean water which lowers pH. The water made with reverse osmosis equipment tends to be more acidic since all of the carbon dioxide liberated easily passes through the RO membrane and ends up in the fresh water. In an evaporator, a large portion of the carbon dioxide is removed along with other non condensable gases because of the vacuum that is created. With less carbon dioxide in the water, fresh water made by an evaporator is less aggressive toward metal piping and storage tanks.