CN101985382B - Advanced treatment method for urban reclaimed water used for power plant - Google Patents

Abstract

The invention relates to a treatment method of urban reclaimed water, in particular to an advanced treatment method of urban reclaimed water for cooling water of a power plant. The invention discloses an advanced treatment method of urban reclaimed water for a power plant, which comprises the following steps: carrying out aeration treatment and filtering; adding slaked lime, coagulant polyferric sulfate and high-efficiency coagulant aid; adding bactericide for sterilization; adding the composite scale and corrosion inhibitor, mixing uniformly, and adding the mixture into the circulating water of a power plant. The advanced treatment method solves the related technical problems of advanced treatment, sterilization, scale inhibition, corrosion prevention, ammonia nitrogen treatment and the like of the reclaimed water in the recycling of the power plant, provides technical support for the safe and economic use of the reclaimed water in the power station, and has remarkable economic, social and environmental benefits when the reclaimed water is recycled as the circulating water make-up water in the power station.

Description

Advanced treatment method for urban reclaimed water used in power plants

technical field

The present invention relates to a treatment method for urban reclaimed water, in particular to an advanced treatment method for urban reclaimed water used as cooling water for power plants.

Background technique

Cooling water consumes the most water in thermal power plants. Using urban reclaimed water as the supplementary water source for industrial circulation cooling is currently the first choice for countries around the world to solve the water shortage problem. The reuse of urban reclaimed water as circulating cooling water for thermal power plants can not only expand the scale of reclaimed water reuse, but also provide a long-term, stable and sufficient second water source for power plant cooling water. It has broad application prospects in alleviating the contradiction between supply and demand of water sources in power plants, reducing pollution, and reducing the amount of sewage discharged from cities to the environment. However, the reclaimed water of urban sewage treatment plants has the characteristics of high salt content, high organic matter content, high ammonia nitrogen content, complex bacterial population, and high corrosion and scaling tendency, resulting in scaling, corrosion and microbial growth of heat exchangers and other components.

The water quality of the circulating cooling water after treatment must meet the following conditions: (1) avoid fouling of the heat transfer surface; (2) avoid causing large-scale corrosion of the heat transfer surface, and pay special attention to preventing pitting corrosion; (3) avoid microorganisms in the circulation system Accumulation, growth of bacteria and algae; (4) The circulating water treatment system should be as simple as possible; (5) The operating cost of the circulating water treatment system is low; (6) The circulating water treatment system is reliable in operation, the effluent quality is stable, and meets the requirements of the equipment specification.

In order to meet the above requirements, urban reclaimed water must undergo advanced treatment in order to meet the requirements of power plants.

Contents of the invention

In order to overcome the deficiencies of the above technologies, the present invention provides a method for advanced treatment of urban reclaimed water used in power plants, so that the urban reclaimed water can meet the requirements of supplementary water for circulating cooling water in power plants.

The advanced treatment method for urban reclaimed water used in power plants of the present invention adopts the following steps:

(1) The reclaimed water of the urban sewage treatment plant is introduced into the reclaimed water tank, and the biological aerated filter treatment method is used for aeration treatment and filtration;

(2) Add slaked lime, coagulant polyferric sulfate and high-efficiency coagulant to the filtrate of step (1), stir, settle naturally, and extract the upper clarified liquid; the amount of hydrated lime added is 300-500mg/L, The addition amount is 6mg/L～15mg/L, and the addition amount of high-efficiency coagulant aid is 200mg/L～300mg/L; the high-efficiency coagulant aid is attapulgite clay of 150-200 mesh;

(3) Add bactericide to the clarified liquid in step (2) for sterilization, then add sulfuric acid to adjust the pH to 8.5~8.8;

(4) The reclaimed water in step (3) is added with a compound scale and corrosion inhibitor in an amount of 10mg/L, and after mixing evenly, add the circulating cooling water of the power plant; the weight ratio of the compound scale and corrosion inhibitor is 1 :0.8:0.4 cyclohexanol hexaphosphate, sodium lauryl sulfate and 2-phosphono-1,2,4-tricarboxylic butane.

Since circulating cooling water has strict requirements on ammonia nitrogen, COD, phosphorus and other nutrient elements, excessive nutrient elements will cause the growth of bacteria and cause slime corrosion problems, especially when the ammonia nitrogen content is high, the reproduction of nitrifying bacteria will consume alkalinity, Cause the pH value to drop, which seriously endangers the safe operation of the circulating water system. Therefore, the treatment method of the present invention first adopts biological aeration treatment, and after removing ammonia nitrogen, it is used to make up water for circulating cooling water.

Slaked lime, coagulant and high-efficiency coagulant are added to the reclaimed water after aeration treatment for sedimentation treatment. First add slaked lime for softening treatment to remove most of the carbonate hardness. Secondly, coagulant (polyferric sulfate) is added for coagulation treatment, so that the original suspended solids, colloids and calcium carbonate crystallites formed in the softening process in the water form a large-sized alum flower precipitation. Finally, a high-efficiency coagulant is added to further promote the growth and precipitation of flocs, and reduce the hardness and turbidity of reclaimed water. The tiny sediments formed during the coagulation process are adsorbed by the attapulgite clay to form larger particles, which are directly separated from the water by the natural sedimentation method, and the reclaimed water in the upper layer is directly used. The high-efficiency coagulant aid used in the present invention is attapulgite clay, whose crystal shape is rod-like, fibrous, and needle-like, and its molecular formula is: (Mg,Al,Fe) ₅ Si ₈ O ₂₀ (OH) ₂ (OH ₂ ) ₄ ??4H ₂ O. The attapulgite clay aggregate is a soil-like block structure, with a pH of about 8.5, internal porous channels, and a large specific surface area, which can reach more than 350m ² /g. It has the properties of nanomaterials, and macromolecules can be directly absorbed into the channels. Its electrochemical performance is stable, and it has good stability in high temperature and high salinity water.

The reclaimed water of the present invention is directly added to the composite scale and corrosion inhibitor, and is used for supplementary water of circulating cooling water in power plants. The composite scale and corrosion inhibitor of the present invention has low phosphorus content, can operate under high temperature (80°C) and high pH system for a long time, and has good anticorrosion performance.

In order to further improve the bactericidal effect of the above-mentioned urban reclaimed water advanced treatment method for power plants of the present invention, the bactericide is a composite bactericide composed of an oxidizing bactericide and a non-oxidizing bactericide, and the oxidizing bactericide is sodium hypochlorite or chlorine dioxide , the dosage (in terms of available chlorine) is 3-8 mg/L, and the non-oxidative bactericide is a quaternary ammonium salt fungicide, and the dosage is 80-120 mg/L. 

Through the advanced treatment method of the present invention, the technical problems related to the advanced treatment of reclaimed water involved in the reuse of reclaimed water in power plants, such as sterilization, scale inhibition, anti-corrosion, ammonia nitrogen treatment, etc. are solved, and the safe and economical use of reclaimed water in power plants is provided. With technical support, reclaimed water can be reused as circulating water supplementary water in power plants, and its economic, social and environmental benefits are very significant.

Detailed ways

2 × 1000MW expansion unit supporting reclaimed water advanced treatment project, to carry out specific experiments. The reclaimed water is taken from the secondary discharge water of the urban sewage treatment plant.

One: the raw material that the present invention adopts:

Slaked lime: solid powder, purity ≥ 94%, fineness: 325 mesh;

Coagulant: polyferric sulfate (PFS): liquid, total iron content ≥ 10%, density: ≥ 1.45g/cm ³ ;

High-efficiency coagulant: 150-200 mesh attapulgite clay;

The water sample is the reclaimed water effluent of the sewage treatment plant during normal operation, the main water quality indicators are shown in Table 1, and the test water temperature is 26.3°C.

Table 1 The main water quality indicators of the test water samples

pH 7.09 Total P mg/L 1.99 Turbidity (NTU) 4.95 Full hardness mmol/L 8.60 Suspended matter mg/L 10.0 Ca hard mmol/L 6.45 BOD _5mg /L 15.0 Temporary hardness mmol/L 6.5 CODcr mg/L 36.21 Total Alkalinity mmol/L 6.5 Free CO ₂ mg/L 28.75 Alkalinity of phenolphthalein mmol/L 0 Ammonia nitrogen mg/L 38 Alkalinity of methyl orange mmol/L 6.5

Two: Processing technology:

The above-mentioned urban reclaimed water is subjected to advanced treatment in the following steps:

The reclaimed water of the urban sewage treatment plant is introduced into the reclaimed water tank, aerated by the biological aerated filter treatment method, and filtered; the filtrate is respectively added with slaked lime, coagulant polyferric sulfate and high-efficiency coagulant aid, stirred, naturally settled, and the upper layer is extracted Clarified liquid; the addition of slaked lime is 400 mg/L, the addition of polyferric sulfate is 10 mg/L, and the addition of high-efficiency coagulant aid is 260 mg/L; described high-efficiency coagulant aid is 200 mesh attapulgite clay

After adding bactericide to the above-mentioned clarified liquid for sterilization, add sulfuric acid to adjust the pH to 8.7; the bactericide is a compound bactericide composed of an oxidizing bactericide and a non-oxidizing bactericide, and the oxidizing bactericide is a sodium hypochlorite bactericide, and the dosage (with Available chlorine) is 5 mg/L, and the non-oxidizing bactericide is a quaternary ammonium salt fungicide with a dosage of 100 mg/L.

Table 2 Reclaimed water quality indicators after sterilization treatment

project after treatment Total alkalinity, mmol/L ~1.3 Total hardness, mmol/L ~1.5 Calcium hardness, mmol/L ~1.1 Magnesium hardness, mmol/L ~0.4 Turbidity, NTU <0.5 Total phosphorus, mg/L ~0 COD _Cr ，mg/L ~8.7 _BOD5 ，mg/L ~2 NH ₃ -N, mg/L 0 Fe mg/L <0.1 Mn mg/L <0.001 Free residual chlorine mg/L ---- Total number of bacteria, pcs/mL <50

The reclaimed water after the above treatment is added with a compound scale and corrosion inhibitor in an amount of 10mg/L, and after mixing evenly, it is added to the circulating water of the power plant; the weight ratio of the compound scale and corrosion inhibitor is 1:0.8:0.4 Cyclohexanol hexaphosphate, sodium lauryl sulfate and butane-2-phosphono-1,2,4-tricarboxylate.

The above-mentioned circulating cooling water of the present invention is operated for 221 days under the control temperature of 80°C, pH value of 8.7, and concentration rate of 4.0, while replenishing the normal loss of water such as evaporation, wind blowing, leakage and sewage discharge of the system, and maintaining water balance. , open the condenser, no scale, no corrosion. the

Claims (2)

1. a power plant uses the municipal middle water deep treatment method, it is characterized in that adopting following steps:

(1) in the pond, adopts the BAF treatment process to carry out aeration and handle during water is introduced in the municipal sewage plant, filter;

(2) filtrating of step (1) adds slaked lime, coagulant polymeric ferric sulfate and high-efficient coagulant aide respectively, stirs, and natural subsidence extracts supernatant liquid; The add-on of slaked lime is 300-500mg/L, and the add-on of bodied ferric sulfate is 6mg/L～15 mg/L, and the add-on of high-efficient coagulant aide is 200mg/L～300mg/L; Described high-efficient coagulant aide is a 150-200 purpose attapulgite clay;

(3) after the clear liquor of step (2) adding sterilant carries out sterilization, add sulfuric acid and transfer pH to 8.5 ~ 8.8;

(4) the middle water of step (3) is pressed the adding composite scale-inhibiting corrosion inhibitor of 10mg/L, after mixing, is added to power plant's cycling use of water; Described composite scale-inhibiting corrosion inhibitor is that weight proportion is 1:0.8:0.4 ring pure six SULPHOSUCCINIC ACID ESTERs, Sodium Lauryl Sulphate BP/USP and a 2-phosphonate group-1,2, the 4-butane tricarboxylate.

2. power plant according to claim 1 uses the municipal middle water deep treatment method; It is characterized in that: described sterilant is the compound disinfectant that oxidation series bactericidal agent and non-oxide series bactericidal agent are formed; The sterilization of oxidation class is that Youxiaolin or dioxide peroxide are as sterilant; Consumption is counted 3-8 mg/L with available chlorine, and non-oxide type of sterilization is the quaternary ammonium salt sterilant, and consumption is 80-120 mg/L.