CN102173526B - Method for using brine generated after seawater desalination as circulating cooling water for cooling tower of power plant - Google Patents

Abstract

The invention relates to a method for using desalinated brine from seawater to circulate cooling water in a cooling tower of a power station. Seawater or conventional seawater desalinated concentrated brine is dehardened and pretreated, and fresh water is produced after desalination by various desalination technologies. At the same time, the desalinated concentrated brine enters the open circulation cooling system of the power station to replace seawater as cooling circulating water, and the cycle concentration ratio It is 1.5~2. After circulating cooling, the more concentrated brine after desalination is continuously added to the system, and the high-concentration brine after cooling is discharged for comprehensive utilization. Replacing seawater with more concentrated desalinated brine as the cooling medium not only solves the problem of repeated water intake of desalination and cooling medium seawater, but also solves the problem of discharge of desalinated concentrated brine and seawater after cooling cycle. It is a typical low-carbon and environmentally friendly project.

Description

Method for using seawater desalination concentrated brine to circulate cooling water in power station cooling towers

technical field

The present invention relates to seawater desalination technology and its application, in particular to a method for using desalinated seawater brine to circulate cooling water in cooling towers of power stations. Specifically, concentrated brine produced after dehardening pretreatment and desalination of seawater to produce fresh water is used to enter The open circulating cooling system of the power station replaces the current seawater as the method of cooling circulating water. Through the combination of desalination of seawater, the cooling cycle system of the power station and the new salt chemical technology, the present invention solves the scaling problem of equipment in the cooling cycle system of the power station, solves the problem of excessive COD of the desalinated concentrated brine and the concentrated seawater in the cooling cycle of the power station, and fails to meet the discharge standards, and solves the problem of desalination The problem of high energy consumption in concentrated brine factory salt production is a typical low-carbon, green and circular economic technology. This method is applicable to industrial circulating cooling water processes in all industries.

Background technique

Seawater desalination has become an important way to solve the global water shortage. With the maturation of seawater desalination technology and the healthy development of seawater desalination industry, the desalination scale of seawater desalination plants continues to expand. The bottleneck of scale development, the development of comprehensive utilization technology of desalinated concentrated brine has become an important topic in the field of seawater desalination in recent years. However, the high energy consumption of concentrating the desalinated brine into a nearly saturated solution that can be vacuum-salted has become a technical bottleneck restricting the comprehensive utilization of the desalinated brine.

There are quite a lot of patents on seawater desalination, and there are relatively few documents and patents on the combination of seawater desalination and comprehensive utilization. Chinese patent CN 200610046624 is a combined production process technology for low-cost and zero-emission seawater desalination and comprehensive utilization. Seawater is purified through seawater pretreatment. Electrodialysis (ED) concentration equipment and vacuum low-temperature evaporation concentration equipment concentrate seawater into saturated brine, and then use saturated brine as raw material to extract various salt chemical products.

CN02111670.9 Method for producing deep-sea drinking water and deep-sea additives by desalination and concentration of deep seawater For testing and testing, the deep sea water is filled into the container on board and transported back to the port. The testing, testing, and tempering are carried out on land. The deep sea water that passes the test is desalinated by reverse osmosis technology. 30%-40% of the desalinated deep-sea water obtained after desalination is made into bottled deep-sea drinking water, and the remaining 60%-70% of the preliminary concentrated liquid is distilled, and the deep-sea desalinated water obtained through distillation is made into bottled canned water The remaining concentrated part of the deep-sea drinking water after distillation is deep-sea saturated brine as an additive for deep-sea saturated brine.

CN200710057303.7 discloses a method for utilizing concentrated seawater with high hardness and high salinity as industrial circulating cooling water. The steps include passivation pretreatment; water collection and sedimentation; active treatment; filtration; heat exchange; Reagents and equipment are expensive and difficult to realize industrialization. At present, it has not been seen that seawater or conventional seawater desalinated concentrated brine is used as raw material. In the pretreatment process, calcium and magnesium are extracted to deharden, and then desalination technology is used. related technologies used.

We have developed a new technology for low-carbon seawater desalination in combination with power plant research, that is, seawater or conventional seawater desalination concentrated brine is pretreated by calcium and magnesium extraction in the pretreatment process, and then desalination technology (CN201010507614.0 seawater dehardening Pretreatment and desalination production method), and then the desalinated concentrated brine replaces seawater as cooling circulating water, which is circulated and concentrated through the cooling tower of the power station, and then comprehensively utilized (bromine extraction, potassium extraction, vacuum salt production). Due to the removal of calcium and magnesium ions and the purification of seawater, the cooling circulation system is fully guaranteed to be free of scaling, and part of the fresh water is evaporated through the cooling circulation tower, so that the concentrated brine after desalination is more than doubled, and it is concentrated without energy consumption, breaking the desalination The bottleneck of high cost of evaporation and concentration of post-concentrated brine using heat energy is too high for comprehensive utilization, which solves the problem of COD discharge of concentrated brine from desalination and power plant cooling circulation system exceeding the standard and failing to meet the discharge standard.

Contents of the invention

The object of the present invention is to provide a method for using desalinated brine from seawater to circulate cooling water in a cooling tower of a power station, which is a method for concentrating desalinated concentrated brine without energy consumption. After desalination of seawater or conventional seawater, concentrated brine is dehardened by extracting calcium and magnesium in the pretreatment process, and then using desalination technology to obtain fresh water and higher concentration brine at the same time. High concentration brine replaces seawater as the cooling cycle of power plants The water is re-concentrated through the cooling tower cycle, which realizes the re-concentration of the desalinated brine without energy consumption, and then comprehensive utilization, which has great economic and social benefits.

The present invention adopts dehardened pretreatment desalinated concentrated brine, and the circulating cooling system of the power supply station replaces seawater as cooling circulating water. The fresh water is continuously evaporated in the cooling tower. The salt content in the cooling water is maintained at a certain concentration to keep the total amount of circulating water unchanged, a part of the concentrated water is discharged for salt production and comprehensive utilization, and a part of the desalinated concentrated brine is added to the cooling circulation system. Due to the cooling tower's cyclic concentration, the concentration ratio can be more than doubled, so that the concentrated brine concentration after desalination can be more than doubled without energy consumption, which greatly reduces the cost of comprehensive utilization and provides a reliable technical guarantee for zero discharge of seawater desalination.

The method that a kind of seawater desalination brine provided by the present invention is used for circulating cooling water of power station cooling tower comprises the following steps:

1) Dehardening pretreatment of seawater: use chemical, physical, biological and other methods to remove the hardness in seawater, and the calcium and magnesium ion contents are all less than 50mg/L;

2) Seawater desalination: dehardened pre-treated seawater for seawater desalination (conventional seawater desalination technology is acceptable), and the TDS in the desalinated concentrated brine is 50000-125000mg/L;

3) Cooling tower circulation concentration: the desalinated concentrated brine is pumped to the open circulation cooling system of the power station as supplementary water for the power station circulation cooling system. After being cooled by the cooling circulation tower, the water temperature is reduced by 8-10°C, and part of the fresh water is evaporated at the same time The TDS is doubled, and the concentrated brine can be used for the preparation of salt chemical products, etc.

The dehardening pretreatment refers to the method of extracting calcium and magnesium described in patent CN201010507614.0 and CN200710059831.6 in the seawater pretreatment process, and other physical, chemical and biological methods can also be used to remove calcium in seawater ,Magnesium ions.

The conventional seawater desalination refers to the pretreatment of seawater by one process or a combination of several processes (such as CN200710059831. Make a fade.

The calcium and magnesium ion content of the seawater after dehardening pretreatment is 15-20 mg/L.

The desalinated seawater is concentrated brine with a TDS of 50000mg/L-120000mg/L.

The concentrated brine amount after supplementing desalination of described cooling tower can be calculated as follows:

Q _e =KΔtQ

In the formula, Q _e ——water loss by evaporation (m ³ /h);

Δt——the temperature difference between the inlet and outlet water of the cooling tower (°C);

Q——circulating water volume (m ³ /h);

K—coefficient (1/℃), see Table 1

The amount of evaporated fresh water can be calculated as follows:

Q _e ＝G(X ₂ -X ₁ )

In the formula, G—the amount of dry air entering the cooling tower (kg/h);

X ₂ , X ₁ - respectively the moisture content of the air entering and leaving the tower (kg/kg).

The present invention provides a method of desalinating concentrated brine from seawater for circulating cooling water in a cooling tower of a power station, which has the following advantages:

1) Calcium and magnesium ions are removed during the pretreatment process to increase the concentration of the desalinated concentrated brine, which is then concentrated by the cooling circulation system of the power station, providing high-quality salt for factory production and comprehensive utilization, and the cost is close to that of sun-dried salt. saturated brine.

2) Due to the removal and purification of calcium and magnesium ions, the cooling circulation system is fully guaranteed to be free of scaling, and the heat transfer coefficient of the cooling tower is improved, making it possible to replace seawater with concentrated brine after desalination as cooling circulation water, which solves the problem of desalination and power station cooling. Circulating seawater COD exceeds the standard and cannot meet the standard discharge problem.

3) Since the desalinated concentrated brine is used instead of seawater as the cooling medium, the investment and operation cost of seawater desalination water intake are saved.

4) Since the desalinated concentrated brine is used instead of seawater as the cooling medium, the concentration of the desalinated concentrated brine borrows the power and facilities of the cooling cycle system of the power station, which is equivalent to concentration without energy consumption. The bottleneck of comprehensive utilization provides low-cost and high-concentration raw materials for the comprehensive utilization of concentrated brine, making industrial salt production combined with seawater desalination possible, and the cost of the produced salt is even close to the cost of sun-dried salt.

5) Due to the removal of calcium and magnesium ions, the purity of sodium chloride produced by industrial salt production is high, which saves the investment and operating costs of refining crude salt in two alkali enterprises.

6) Since industrialized salt production can be realized, a large amount of valuable land resources occupied by beach sun-dried salt can be saved.

Description of drawings

Figure 1 Schematic diagram of the process flow of the circulating cooling water system of the power station.

Fig. 2 Process flow chart of using desalinated concentrated brine for circulating cooling water in power station cooling towers.

Detailed ways

As shown in Figure 1, 1 _a - water pump room; 2 - cold water pump; 3 - cold water pool; 4 - hot water pump; 5 - hot water pool, 6 - cooling tower.

In the open circulating cooling water system (conventional) of the power station, the cooling water circulates. The cooling tower is a kind of heat exchange equipment open to the atmosphere. water is concentrated. The cooling medium for the open circulating cooling water system can be tap water or sea water. The circulating cooling water system consists of cold and hot water pools, pump stations, cooling towers, cooled equipment or products, and piping systems.

After cooling the equipment or power station products, the hot water with increased temperature flows into the hot water pool 5, and after being lifted by the hot water pump 4, it flows into the cooling tower 6 for cooling. The equipment or product of cooling, the hot water that water temperature raises flows into hot water pool 5 again, and so continuously reciprocates. At the same time, due to the loss of water caused by evaporative heat dissipation and conduction heat dissipation, leakage, sewage discharge, and drifting, it is necessary to add a certain amount of cooling water to the cold water pool.

The present invention can use the production method of seawater dehardening pretreatment desalination disclosed in CN201010507614.0:

1) Use desalinated seawater as raw material, add precipitant carbonate to extract calcium, react under stirring, form calcium carbonate precipitation, stand still, settle, clarify, supernatant is filtered with ultrafiltration membrane;

2) The ultrafiltration membrane permeate seawater after calcium carbonate is mixed with sodium hydroxide solution to further extract magnesium or desalinate;

3) The seawater after extracting magnesium is filtered by ultrafiltration membrane, concentrated, and nano-scale calcium carbonate is recovered;

4) Add hydrochloric acid to the ultrafiltration membrane permeate to adjust the pH value, and then desalinate through the desalination device to produce fresh water and concentrated brine.

The conditions for extracting magnesium: after calcium removal, seawater is added with precipitating agent sodium hydroxide, and the rotation speed is 50-200r/min under stirring to react for 0.1-5h to form magnesium hydroxide precipitation, stand still for 3-24h, settle, clarify, The supernatant enters the ultrafiltration membrane for separation, and the ceramic ultrafiltration membrane permeate is used for desalination. The desalination method is reverse osmosis membrane desalination or distillation desalination.

For the power station where desalinated concentrated brine replaces seawater as the cooling medium, as shown in Figure 2, 1-heat exchange system, 2-cold water pump, 3-cold water pool, 4-hot water pump, 5-hot water pool, 6-cooling tower, 7- Seawater desalination device.

The seawater desalination device 7 desalinated concentrated brine instead of seawater as a cooling medium to circulate and cool in the system. The cold water pump 2 sends the desalinated concentrated brine to the heat exchange system 1. Sent to cooling tower 6, after being cooled by cooling tower, put into cold water pool 3 and mix with concentrated brine after seawater desalination device 7 (conventional) desalination, then send to heat exchange system 1 through cold water pump 2, so continuously reciprocating cycle.

During the circulation process, due to the circulation and cooling process of the desalinated concentrated brine, the fresh water is continuously evaporated, the salt content in the seawater is continuously concentrated and the concentration will double, and the concentrated brine is partly drawn out for comprehensive utilization. The desalinated concentrated brine is continuously replenished to the circulating cooling water system. The replenishment amount is the sum of the losses caused by evaporation heat dissipation, conduction heat dissipation, leakage, water drift, and external transportation of more concentrated brine.

Application Example 1

The dehardened pretreated seawater (the content of calcium and magnesium ions are all less than 20mg/L specifically refer to the production method of CN201010507614.0 seawater dehardened pretreatment desalination) is subjected to reverse osmosis desalination, and the desalinated concentrated brine TDS (Total dissolved solids, referred to as TDS ) 75000mg/L, the water temperature is 15℃ at room temperature, and pumped to the open cooling circulation system of the simulated power station. The circulating water volume of the cooling circulation tower is 2.8m ³ /h. After the tower is cooled, the water temperature is 15°C at normal temperature. Due to the continuous loss of evaporative fresh water, the volume of desalinated concentrated brine needs to be supplemented to the cooling circulation system at 60L/h. The TDS of the brine is 15000mg/L. In order to maintain the balance of the system, it is necessary to continuously extract 30L/h of the cooled concentrated brine for comprehensive utilization. The whole process is a continuous cycle.

Application Example 2

In the workshop of Tianjin No. 1 Salt Chemical Plant, the dehardened pretreated seawater (both calcium and magnesium ion contents are less than 50mg/L) is desalinated by reverse osmosis. The TDS of the desalinated concentrated brine is 70000mg/L, and the flow rate is 300m ³ /h , the water temperature is 20°C, put it directly into the cold water pool of the open cooling circulation system of the power station, and transport it to the heat exchange system with a cold water pump. Cooling circulation tower, the circulating water volume of the cooling circulation tower is 14000m ³ /h, and the water temperature after cooling by the cooling tower is 20°C at room temperature. Due to the continuous loss of fresh water evaporated by the cooling tower, it is necessary to replenish the desalinated concentrated brine to the cooling circulation system. The volume is 300m ³ / h, the concentration ratio of the desalinated concentrated brine is 1.8, that is, the TDS of the concentrated brine after cooling by the circulating cooling tower is 126000mg/L. In order to maintain the balance of the system, it is necessary to continuously draw 150m ³ /h of the concentrated brine cooled by the cooling tower for comprehensive Using (conventional methods to extract bromine, potassium, salt chemical products such as vacuum salt production), the whole process is continuously circulated.

The technology disclosed and proposed by the present invention for the use of seawater desalination concentrated brine in circulating cooling water of power station cooling towers can be realized by those skilled in the art by referring to the content of this article and appropriately changing the process route, etc., although the method of the present invention has passed the preferred implementation example Having described it, it is obvious for those skilled in the art to make changes or recombine the methods described herein without departing from the content, spirit and scope of the present invention to achieve the final result. In particular, it should be pointed out that all similar substitutions and modifications will be obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims (6)

1. sea water desaltination salt solution, for a method for Cooling Tower of Power Station recirculated cooling water, is characterized in that comprising the following steps:

1) hard-off pre-treating seawater: adopt chemistry, physics, biological method to remove calcium, magnesium ion in seawater, the content of calcium, magnesium ion is all less than 50mg/L;

2) sea water desaltination: the pretreated seawater of hard-off carries out conventional sea water desaltination and obtains strong brine; TDS50000～125000mg/L in strong brine after desalination;

3) cooling tower circulation is concentrated: the strong brine after desalination through pump delivery to power station the circulation cooling water system of open pattern, make up water as power station circulating cooling system, after refrigeration cycle tower cooler, water temperature reduces by 8～10 ℃, part fresh water is evaporated simultaneously, TDS doubles, and this strong brine is for the comprehensive utilization of seawater.

2. in accordance with the method for claim 1, it is characterized in that described conventional sea water desaltination refers to that seawater array mode pre-treatment of a kind of technique or several techniques in dosing coagulation, clarification, filter method desalinates again.

3. in accordance with the method for claim 1, it is characterized in that the described pretreated seawater calcic of hard-off, magnesium ion content are 15～20mg/L.

4. in accordance with the method for claim 1, it is characterized in that the strong brine that the seawater after described sea water desaltination is TDS50000mg/L～120000mg/L.

5. in accordance with the method for claim 1, strong brine amount after the desalination of the make up water of the cooling tower described in it is characterized in that, can be calculated as follows:

Q _e＝K△tQ

Q in formula _efor the vaporization losses water yield;

△ t is the temperature head of cooling tower Inlet and outlet water;

Q is the recirculated water water yield;

K is the coefficient value shown in table 1

Described evaporation fresh water amount can be calculated as follows:

Q _e＝G(X ₂-X ₁)

In formula, G is the dry air amount into cooling tower;

X ₁, X ₂be respectively the water capacity of turnover tower air.

6. in accordance with the method for claim 2, it is characterized in that described filtration is multi-medium filtering, micro-filtration or ultrafiltration.