Seawater in the Persian Gulf contains up to 45 grams of salt per liter. When freshwater is produced from this seawater, it is generally done in plants that work according to the evaporation principle. Bilfinger has developed a process where seawater is heated up to the boiling point and then channeled into chambers that are 20 meters long and four meters wide. Water vaporizes as a result of the negative pressure in the chambers. Steam condenses on bundles made up of thousands of thin cooling tubes and drops of fresh water are the treasure that is withdrawn and collected. 15 to 20 such chambers with ever-increasing levels of negative pressure are chained together to produce as much fresh water as possible.
Saltwater also runs through the cooling tubes: Initially, seawater in the tubes serves as a cooling medium which ensures that the steam in the chambers condenses. Then the saltwater is brought to a boil outside the chambers before it is funneled back inside to evaporize.
About 10,000 cubic meters of seawater is sent through each of these production units per hour and, from that, 1,000 cubic meters of freshwater is produced. Dozens of these units make up large desalination plants.
“In order to make the process more efficient, you have to increase the speed of the saltwater that runs through the cooling tubes and the vaporizing chambers,” explains Clemens Wolters. This, however, leads to problems: “When the water is pushed through many thousands of small cooling water tubes, frictional resistance increases dramatically. It wouldn’t be possible for tubes or pumps to hold out for very long.”
The solution, therefore: “We set up bypasses.” The water boxes are directly connected with high-caliber pipes so that not all of the process water needs to be pumped through the delicate cooling tubes. As a result, tubes and pumps are spared while the water and steam flow rate is increased.