Pay more attention to the public account: environmental protection water treatment
The core technologies of RCC are "mechanical vapor recompression cycle evaporation technology", "seed method technology", and "mixed salt crystallization technology".
01
Mechanical vapor recompression cycle evaporation technology
1.1, Basic principle
The so-called mechanical vapor recompression cycle evaporation technology is based on the principle of physics, and the same amount of matter needs to absorb a certain amount of heat energy in the process of changing from a liquid state to a gaseous state. When a substance is converted from a gaseous state to a liquid state, an equal amount of heat energy is released. According to this principle, when treating wastewater with this evaporator, the heat energy required to evaporate the wastewater is provided by the release of heat energy when the steam condenses and the condensate cools.
During operation, there is no loss of latent heat. The only energy consumed during operation is the power consumed by the pumps, steam pumps and control systems that drive the circulation and flow of wastewater, steam, and condensate in the evaporator. In order to resist the corrosion of the evaporator by wastewater and ensure the service life of the equipment, the main body of the evaporator and the internal heat exchange tube are usually made of high-grade titanium alloy. Its service life is 30 years or more.
The wastewater treatment capacity of the evaporator starts from 27 tons/day to 3,800 tons/day. If the amount of wastewater to be treated is greater than the maximum capacity of a single machine, multiple evaporators can be installed for treatment. The evaporator, when operated with seed technology, is also known as a Brine Concentrator.
1.2. Brine concentrator structure and process
(1) The brine to be treated enters the storage box, and the pH value of the brine is adjusted to between 5.5-6.0 in the box to prepare for degassing and carbon removal. The brine enters the heat exchanger and raises the temperature to the boiling point.
(2) The heated brine passes through the degasser to remove insoluble gases such as oxygen and carbon dioxide from the water.
(3) The new brine enters the bottom tank of the deep shrinker, mixes with the brine circulating inside the concentrator, and then is pumped to the water tank at the top of the heat exchanger tube bundle.
(4) The brine passes through the device, and the brine distribution parts at the top of the heat exchange tube flow into the tube, evenly distributed on the inner wall of the tube, in the form of a film, and descends to the bottom groove by ground gravity. When part of the brine descends along the pipe wall, it absorbs the heat energy released by the steam outside the pipe and evaporates, and the steam and the unevaporated brine fall to the bottom tank together.
(5) The steam in the bottom tank enters the compressor through the mist eliminator, and the compressed steam enters the concentrator.
(6) The latent heat of the compressed steam is transmitted through the wall of the heat exchange tube, and the brine film with a lower temperature falling along the inner wall of the tube is heated to evaporate part of the brine, and when the latent heat of the compressed steam is released, it is condensed into distilled water on the outer wall of the heat exchange tube.
(7) The distilled water descends along the pipe wall, accumulates at the bottom of the concentrator, and is pumped through the heat exchanger into the storage tank for later use. As the distilled water flows through the heat exchanger, the new incoming brine is heated.
(8) Part of the brine in the bottom tank is discharged to control the concentration of brine in the concentrator.
02
Seeding technology
Seed technology: It can solve the problem of fouling of the heat exchanger tube of the evaporator, and the concentrated wastewater discharged after treatment is usually sent to the crystallizer or dryer, where it is crystallized or dried into a solid and transported to the landfill for burial. The cycle continues.
If the wastewater contains a large amount of salt or TDS, when the wastewater evaporates in the evaporator, the TDS in the water is easy to adhere to the surface of the heat exchanger tube and scale, which will affect the efficiency of the heat exchanger at least and block the heat exchanger tube in serious cases. Solving the fouling problem of the heat exchanger tube in the evaporator is the key to whether the evaporator can be used to treat industrial wastewater. Evaporators using "seeding" technology, also known as "Brine Concentrators". Concentrated wastewater discharged after brine concentrator treatment, with a TDS content of up to 300,000 pp, is typically sent to a crystallizer or dryer where it crystallizes or dries into a solid and is transported to landfill for burial.
The "seed method" is based on calcium sulfate. Before the concentrator starts to operate, if the natural calcium and sulfide ion content in the wastewater is insufficient, it can be manually supplemented, and calcium sulfate seeds are added to the wastewater to make the calcium and sulfide ion content in the wastewater reach an appropriate level.
When the wastewater begins to evaporate, the amount of calcium and calcium sulfate ions that begin to crystallize in the water reaches the appropriate levels. When the wastewater begins to evaporate, the calcium and calcium sulfate ions that begin to crystallize in the water adhere to these seeds and remain suspended in the water without fouling on the surface of the heat exchanger tubes. This phenomenon is called "selective crystallization". Brine concentrators usually last for up to a year or more before they need to be cleaned regularly. In general, there is no need to add a "seed" during normal operation, except for the possibility of adding "seeds" when the concentrator is started.
03
Mixed whole salt crystallization technology
3.1. Application of mixed whole salt crystallization technology
The brine concentrator can recover 95% to 98% of the water in the brine, and the remaining concentrated brine residue contains a large amount of soluble solids. In some areas, brine residues are sent to evaporation ponds for natural evaporation or for deep well pressure injection.
However, in many areas, in order to prevent the concentrated brine from being discharged into the evaporation pond or seeping out after deep well pressure injection treatment, causing secondary pollution to the water source, it must be treated with "zero discharge". If the flow rate of the residual liquid is very small, the residual liquid can be dried into a solid with a dryer, collected and sent to the landfill after collection;
The general productive chemical crystallization process, such as the production of sodium chloride, sodium sulfate and other chemical commodities, only needs to deal with the crystallization of one salt, this kind of single-salt brine crystallization process, it is relatively easy to master, but the salt contained in industrial sewage is varied, and even contains two kinds of salt composed of double salt. The brine with a variety of salts will produce foam and be extremely corrosive in the crystallizer, and the presence of a variety of different salts will cause the boiling point of the brine to rise. Different degrees of fouling have different degrees of influence on the heat transfer coefficient of the equipment.
3.2. Equipment and process flow of mixed whole salt crystallization technology
The crystallizer used for the crystallization of mixed salts can be either steam driven or an electric steam compressor, which is a more energy-efficient system.
Forced Circulation Compressed Steam Crystallizer: The forced circulation compressed steam crystallizer is the most thermally efficient crystallization system, and the thermal energy required by the system is provided by an electric steam compressor. Its main working procedures are as follows:
(1) The concentrated brine to be treated is pumped into the crystallizer.
(2) Mix with the circulating brine, and then enter the shell and tube heat exchanger. Because the heat exchanger tube is filled with water, the brine will not boil under pressure and inhibit the fouling in the tube.
(3) The circulating brine enters the vapor gas at a specific angle, resulting in a vortex, and a small part of the brine is evaporated.
(4) When the water is evaporated, crystals are formed in the brine.
(5) Most of the brine is circulated to the heater, and a small stream of water is pumped to a centrifuge or filter to separate the crystals.
(6) The steam passes through the mist eliminator to remove the attached particles.
(7) The steamer is pressurized by the compressor, and the compressed steam is condensed into distilled water on the heat exchange tube shell of the heater, and the latent heat is released to heat the brine in the tube.
(8) After the distilled water is collected, it is used in the process of high-quality distilled water in the factory, and under certain conditions, the crystals produced by the crystallizer are chemical products with high commercial value.