Heavy water looks like ordinary water. Their chemical properties are the same, but some physical properties are different. The density of ordinary water is 1g/cm3, while that of heavy water is 1.056g/cm3. The boiling point of ordinary water is 100℃, and that of heavy water is 10 1.42℃. The freezing point of ordinary water is 0℃, and that of heavy water is 3.8℃. Besides, ordinary water can nourish life and cultivate everything, while heavy water can't germinate seeds. If people and animals drink a lot of water, it will also lead to death. However, the special value of heavy water is reflected in the application of atomic energy technology. In order to make powerful nuclear weapons, heavy water is needed as a moderator of nuclear fission reaction.
Heavy water, like ordinary water, is also a liquid compound formed by hydrogen and oxidation, but the hydrogen atoms of heavy water molecules are different from those of ordinary water molecules. As we know, hydrogen has three isotopes. One is true and contains only one proton. It can combine with an oxygen atom to form ordinary water molecules. The other is heavy hydrogen-deuterium. It contains a proton and a neutron. It can combine with an oxygen atom to form heavy water molecules. There is also an overweight hydrogen-tritium. It contains two neutrons and a proton.
Heavy water can be produced in many ways. The original method is electrolysis, because heavy water can't be electrolyzed, so it can be separated from ordinary water. Another simple method is to make use of the feature that heavy water has a higher boiling point than ordinary water through repeated distillation. Later, some other better methods were developed.
However, only two methods have been proved to be of commercial significance: water-hydrogen sulfide exchange method (GS method) and ammonia-hydrogen exchange method.
GS method is a method based on water and hydrogen sulfide to exchange hydrogen and deuterium in a series of towers (through top cooling and bottom heating operations). In this process, water flows to the bottom of the tower, and hydrogen sulfide gas circulates from the bottom to the top of the tower. A series of perforated plates are used to promote the mixing of hydrogen sulfide gas and water. Deuterium migrates to water at low temperature and to hydrogen sulfide at high temperature. Hydrogen sulfide gas or water containing concentrated deuterium is discharged from the junction of the hot section and the cold section of the first stage tower, and the process is repeated in the next stage tower. The product of the last stage (deuterium concentrated to 30% water) is sent to the distillation unit to prepare heavy water (99.75% deuterium oxide) in the reactor stage.
The ammonia-hydrogen exchange method can extract deuterium from synthesis gas by contacting with liquid ammonia in the presence of catalyst. The synthesis gas is sent to the exchange tower and then to the ammonia synthesis tower. In the exchange tower, gas flows from the bottom to the top, while liquid ammonia flows from the top to the bottom. Deuterium is eluted from hydrogen in synthesis gas and concentrated in liquid ammonia. Then the liquid ammonia flows into the ammonia cracker at the bottom of the tower, and the gas flows into the ammonia synthesis tower at the top of the tower. Further concentrating in the subsequent stage, and finally producing reactor-grade heavy water by distillation. Synthesis gas feed can be provided by synthetic ammonia plant, which can also be built together with ammonia-hydrogen exchange heavy water plant. Ammonia-hydrogen exchange method can also use ordinary water as deuterium supply source.
Many key equipment items used in factories producing heavy water by GS method or ammonia-hydrogen exchange method are the same as those used in several production processes in chemical industry and petroleum industry. This is especially true for small factories that use GS method. However, this kind of equipment is rarely "off the shelf". GS method and ammonia-hydrogen exchange method need to deal with a large number of flammable, corrosive and toxic fluids under high pressure. Therefore, when formulating the design and operation standards of factories and equipment using these methods, it is necessary to pay careful attention to the selection of materials and the specifications of materials to ensure high safety and reliability in long-term use. The choice of scale mainly depends on economy and demand. Therefore, most equipment items will be manufactured according to the requirements of users.
Finally, it should be pointed out that for GS method and ammonia-hydrogen exchange method, those equipment items that are not specially designed or manufactured for heavy water production can be assembled into systems specially designed or manufactured for heavy water production. The catalyst production system used in the ammonia-hydrogen exchange method and the water distillation system used in the above two methods to finally concentrate heavy water to the reactor level are examples of such systems.
Equipment items specially designed or manufactured for the production of heavy water by GS method or ammonia-hydrogen exchange method include:
6. 1. Water-hydrogen sulfide exchange tower
An exchange tower made of high-quality carbon steel (such as ASTM A5 16) specially designed or manufactured for the production of heavy water by GS method. The diameter of the tower is 6 meters (20 feet) to 9 meters (30 feet), and it can operate at a pressure greater than or equal to 2 MPa (300 psi) with a corrosion resistance of 6 mm or higher.
6.2. Blowers and compressors
A single-stage low-pressure head (i.e. 0.2 MPa or 30 psi) centrifugal blower or compressor specially designed or manufactured for circulating hydrogen sulfide gas (i.e. gas containing more than 70% H2S) is used to produce heavy water by GS method. The gas throughput of these blowers or compressors is greater than or equal to 56 m3/s (65 65,438+020,000 standard cubic feet/minute), and they can operate at a suction pressure greater than or equal to 65,438+0.8 MPa (260 psi), and they are designed to seal wet H2S media.
6.3. Ammonia-hydrogen exchange tower
An ammonia-hydrogen exchange tower specially designed or manufactured for producing heavy water by ammonia-hydrogen exchange method. The height of the tower is greater than or equal to 35 meters (1 14.3 feet), the diameter is 1.5 meters (4.9 feet) to 2.5 meters (8.2 feet), and it can operate at a pressure greater than15 MPa (2,225 psi). These towers have at least one axial hole connected by a flange, the diameter of which is equal to the diameter of the cylinder of the exchange tower, through which the internal components of the tower can be installed or removed.
6.4. Tower internals and multistage pumps
Tower internals and multistage pumps specially designed or manufactured for producing heavy water by ammonia-hydrogen exchange method. The inside of the tower includes a specially designed multistage contact device to promote the full contact of gas/liquid. Multistage pumps include underwater pumps specially designed to circulate liquid ammonia in one contact stage to other stages.
6.5. Ammonia Cracker
An ammonia cracker specially designed or manufactured for producing heavy water by ammonia-hydrogen exchange method. The device can operate at a pressure greater than or equal to 3 MPa (450 psi).
6.6. Infrared absorption analyzer
When the deuterium concentration is equal to or higher than 90%, the infrared absorption analyzer can analyze the hydrogen/deuterium ratio "online".
6.7. Catalytic burner
When producing heavy water by ammonia-hydrogen exchange method, a specially designed or manufactured catalytic burner is used to convert concentrated deuterium gas into heavy water.
hard water
The so-called "hard water" means that many mineral components are dissolved in water, especially calcium and magnesium. Hard water will not cause direct harm to health, but it will bring a lot of troubles to life, such as scaling on water appliances and reducing the washing efficiency of soap and detergent.
Water is a good solvent, which can effectively remove dirt and impurities. Pure water-colorless, tasteless and odorless, is called "universal solvent". When water is combined with carbon dioxide to produce trace carbonic acid, the dissolution effect of water is better. When water flows through land and rocks, it will dissolve a small amount of mineral components. Calcium and magnesium are the two most common components, that is, they make water hard. The more mineral components such as calcium and magnesium in water, the greater the hardness of water.
In Britain, the hardness of water is generally expressed by the following indicators:
Hardness range: soft light hardness, medium hardness, high hardness and super hardness.
Dissolved minerals (mg/liter of water) 0-17.17.1-60 60-120–180 & exceed
soft water
soft water
soft water
Natural water or softened hard water containing only a small amount of soluble calcium and magnesium salts. Natural soft water generally refers to rivers, rivers and lakes (freshwater lakes). Softening hard water refers to softened water obtained after the contents of calcium salt and magnesium salt are reduced to1.0 ~ 50 mg/L. Although temporary hard water can be turned into soft water by boiling, it is extremely uneconomical to treat a large amount of water in industry by this method. The methods of softening water are as follows: ① Lime-soda method. Firstly, the hardness of water is measured, and then a certain amount of calcium hydroxide and sodium carbonate are added to precipitate calcium and magnesium ions in hard water.
Ca(HCO3)2+Ca(OH)22CaCO3↓+2H2O
Mg(HCO 3)2+2Ca(OH)2Mg(OH)2↓+2Ca co 3 ↓+ 2H2O
CaSO4+Na2CO3CaO3 ↓+Na2SO4 ② phosphate soft water method. For boiler water, sodium hypophosphite (NaPO3) can be added as a water softener, which forms a complex with calcium and magnesium ions. When water is boiled, calcium and magnesium will not precipitate, so scale will not form. This method is not suitable for softening drinking water. ③ ion exchange method. Although zeolite and ion exchanger are insoluble in water, sodium ions and hydrogen ions in them can be exchanged with calcium and magnesium ions in hard water, so that calcium and magnesium ions are adsorbed and removed by zeolite, artificial zeolite and ion exchanger. Zeolite and ion exchanger that have failed for a long time can be reused through regeneration, so this method is an economical and advanced soft water method.
Free water
Free water
(Free water) Water in plant cells that is not adsorbed by colloidal particles or macromolecules can move freely and act as a solvent. Water exists in cells in two states: free water and bound water, and its characteristics are different due to different existing states. Therefore, it plays different roles in cells. Because of the different proportion between them, it will affect the physical properties of protoplasm and then affect the intensity of metabolism. The greater the ratio of free water to total water content, the smaller the viscosity of protoplasm and the more vigorous the metabolism.