Chemical processes for water quality treatment
1. Problems in the selection of water quality treatment methods
Heating and heating water treatment methods are divided into four kinds:
The first: simple sodium ion exchange softening method
Is the use of ion exchange agent to reduce the hardness of water water treatment method. Commonly used ion exchange agents are sodium type resin (RNa), strong acidic H (RH) type resin and weak acidic H resin. Ion exchange softening system using Na ion exchange softening system and H-Na ion exchange dealkalisation softening system. Ion exchange softening is mainly the use of resin adsorption and exchange function, the main calcium and magnesium ions in the water to remove the process, sodium ion exchanger in the softening reaction is as follows:
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From the above reaction can be seen to replace the Ca2+Mg2+ in the original water, so the water can be softened, the treatment makes the salt content of the water slightly increased, the alkalinity remains unchanged.
However, this method only prevents the scale, but cannot achieve the fundamental scale prevention. And softened water is more corrosive than tap water, resulting in increased corrosion of the entire water system.
The British Standard: Water Treatment in Domestic Hot Water Central Heating Regulations (British Standard-BS7593:1992) states in the General Regulations that "water supplied through a softener should not be used in any central heating system unless it is specifically and explicitly stated that a corrosion inhibitor has been added for this purpose. ". From the British standard regulations can be seen in the central heating water supply should not be used in softened water, if you have to use softened water, must be in the softened water with corrosion inhibitors.
The second: softened water supplemented with drug delivery method
This method solves the corrosion problem of softened water, as well as additional anti-scaling, to prevent unqualified softened water and lead to equipment scaling. At present, large-scale centralised heating and district heating are generally chosen to soften water dosing this water treatment method.
The third: tap water dosing method, that is, the pot water treatment method
Tap water dosing directly, due to the cancellation of the softened water, reducing equipment investment, saving manpower, but only in the selection of chemicals to be very careful. This method is suitable for direct hot water boilers below 7MW and any secondary heat transfer heating system with heat transfer.
In the country more than 400 million square metres of heating area of the secondary network system and cogeneration heating of the primary network system are basically used in tap water plus YZ-101 anticorrosive scale inhibitor water treatment method.
The fourth: physical methods
This type of method generally refers to the field treatment, the choice of this method should be very careful, because so far the effect of better physical treatment methods are very few.
The above four water treatment methods, from the long-term development trend, method one is to gradually fade, method two and method three should be advocated, in method two and method three, the key is to select high-quality anticorrosion and scale inhibitor according to three criteria.
2. Oxygen removal method of choice
Heating heating water system in operation is not mainly oxygen corrosion, is mainly CO2 corrosion and corrosion under the scale, CO2 comes from the alkalinity of raw water (HCO3-) thermal decomposition. Dissolved oxygen content in raw water in winter is only about 11mg / L, and the dissolved oxygen in the circulating water mainly from the negative pressure side of the circulating water pump suction and water system leakage when running the wind (forming a negative pressure) of the suction. These two places of air intake leads to circulating water oxygen is tens of times, hundreds of times or more of the dissolved oxygen in the make-up water. The use of solid anticorrosion scale inhibitor is generally no longer deoxidised can be effective corrosion prevention, because it has the following three functions: one, is due to scale and rust removal, it is equal to remove the cathode of electrochemical corrosion, thus preventing the electrochemical corrosion; the second, contains several kinds of Yuk film agent, in the surface of iron to generate a layer of black glossy protective film, which can block the oxygen and carbon dioxide corrosion; the third, which is an alkaline agent, it can rapidly improve the water The third is that it is an alkaline agent, which can rapidly increase the pH value of water. When the pH value is ≥10, the iron is in the passivation zone, and the corrosion is minimum. Anti-corrosion and scale inhibitor has been proved to be a simple and effective water treatment method for central heating system in practice.
Monitoring technology and description of water quality treatment and anti-corrosion
1, the system adopts full-automatic control to run and stop; the system is designed with automatic and manual control modes, which can be switched according to different conditions; the system is equipped with perfect protection devices and monitoring equipment, and the control system is controlled by a computer programme to achieve positive and negative washing and regeneration functions, fully automatic control and real-time status display, and contains a remote control function.
2,Piping and valve parts in the system: the pipeline is made of UPVC, the pipe fittings are required to be made of the same material and brand, and the valves are made of pipeline materials, and the valve materials must meet the national drinking water hygiene standards;
3, softened water system dosing barrel tank can store at least 1 week of dosage, by the liquid level control system;
4, the system of each treatment stage outlet installation pressure gauge;
5, all the equipment of the system in addition to the control room set up control cabinets, are required to set up on-site control cabinets, easy maintenance, and emergency treatment;
6, boiler room softened water system are required to use a standby design to ensure safe and continuous operation.
7, the valve installation location can not be too high, must be convenient for maintenance;
8, the pipeline can not be bent.
9, pump start and stop level control by the tank high and low level sensor control;
10,Full automatic control of operation and flushing function.
Characteristics of water softening equipment for heat exchange station
1. High degree of automation Fully automatic water softening device according to the pre-set procedures, automatically complete the softening regeneration cycle process, in addition to manually add regeneration salt regularly without any manual operation, saving a lot of manpower and material resources. The automatic controller or computer automatic controller can easily adjust the operation of the system according to the change of water quality.
2. Stable water quality.
3. High efficiency, low energy consumption, low operating costs Due to the overall design of the water softener is reasonable, and the implementation of strict automatic control, so that the exchange capacity of the resin to ensure that give full play to the salt consumption of the equipment, water consumption and other indicators are significantly lower than the general water softening device compared to the power consumption is significantly reduced.
4. Reliable operation and long service life.
5. Small footprint Advanced process design makes the water softening device compact, covers an area of significantly reduced, saving the building investment.
