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Treatment methods of different boiler water
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Treatment methods of different boiler water

Views: 0     Author: Site Editor     Publish Time: 2022-10-17      Origin: Site

1Make up water treatment

1. Pretreatment

If the source water is surface water, the purpose of pretreatment is to remove suspended solids, colloidal substances and organic substances in the water. Generally, flocculants (such as aluminum sulfate) are added to the raw water to flocculate the above impurities into large particles, which are settled by their own weight and filtered into clean water.

When groundwater or urban water is used as make-up water, the pretreatment of raw water can be omitted and only filtration can be carried out. Common clarifiers include pulse clarifiers, hydraulic accelerators and mechanical agitation clarifiers, and filtering devices include siphon filters, valveless filters, single flow or double flow mechanical filters. An activated carbon filter can also be added to further remove organics from the water.

2. Softening

Use natural or artificial ion exchanger to convert calcium magnesium hard salt into non hard scale to form salt to prevent calcium magnesium hard scale from forming on the inner wall of boiler tube. Strong alkaline water containing calcium bicarbonate or magnesium bicarbonate can also be solved by sodium hydrogen ion exchange or pretreatment (such as adding lime). In some industrial boilers, the feed water salinity may not be significantly reduced, but this treatment is usually sufficient.

3. Seawater desalination

With the continuous improvement of boiler parameters and the emergence of once through boiler, it is even necessary to remove all the salt in the boiler feed water. In this case, the method of dilution shall be adopted. There are many kinds of ion exchangers used in chemical desalination, but the most commonly used ones are cation exchange resin and anion exchange resin, also known as "cation resin" and "anion exchange resin". In the ion exchanger, when the brine passes through the resin, the cations and anions of the salt are removed by exchanging with the cations (H+) and anions (OH -) of the resin respectively.

If the alkalinity of water is high, it is usually necessary to add a series of decarburizers after the cation exchanger to remove carbon dioxide, so as to reduce the burden of the anion exchanger and improve the economy of system operation. For particularly salty water, reverse osmosis or electrodialysis can also be used to desalt the water first, and then put it into the ion exchanger for deep desalination. For high pressure or higher pressure drum boiler and once through boiler, it is necessary to remove trace silicon in feed water, and for medium and low pressure boiler, it is necessary to treat according to the content.

2Condensate treatment

During the circulation of condensate water, the cooling water leakage of the turbine condenser and the corrosion products of the system will pollute and may need to be treated. The treated condensate quantity is related to boiler parameters, furnace type (without steam drum or separator) and condensate pollution. With the increase of boiler parameters, the condensate treatment capacity generally increases gradually. All supercritical boilers shall be treated; For ultrahigh pressure and subcritical boilers, the capacity is 25-100%; Drum boilers under high pressure generally do not need to be treated. Common condensate treatment equipment includes cellulose coated filter and electromagnetic filter. After removing corrosion products (such as copper and iron oxides), the condensate enters the mixed bed or the filter covered with powdered resin for deep desalination.

3Boiler feed water treatment

The dissolved oxygen in the boiler feed water will corrode the metals in the thermal system, and the corrosion products will form copper and iron scales under the high heat load of the boiler. It conducts heat in the high pressure cylinder of the steam turbine, causes pipe rupture and deposits, thus reducing the efficiency of the steam turbine. Therefore, softened or demineralized make-up water and condensate are generally deoxidized before entering the boiler. Common deoxidation methods include thermal deoxidation, vacuum deoxidation, and sometimes chemical deoxidation. The so-called thermal degassing means that when the raw water is heated to boiling in the deaerator, the solubility of the gas in the water decreases, and the gas escapes from the water and releases into the atmosphere. According to the working pressure, the most widely used thermal deaerator is 0.12 MPa and 0.6 MPa. During thermal deoxidation, the water shall be heated to the saturation temperature, and the surface area of deoxidized water shall be large (for example, using water spray or atomizing diffusion device). This allows rapid venting of escaping gases Vacuum degassing is usually carried out in the turbine condenser. Chemical deoxidation is to add hydrazine or sodium sulfite in water to further reduce the oxygen content in water.

 


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