CN108002500B

CN108002500B - Rotational flow flocculation device, high-salinity high-turbidity wastewater treatment system of coal-fired power plant and application

Info

Publication number: CN108002500B
Application number: CN201711385164.0A
Authority: CN
Inventors: 段翠佳; 李宗慧; 王珍; 邹重恩
Original assignee: China Huadian Science And Technology Institute Co ltd
Current assignee: China Huadian Science And Technology Institute Co ltd
Priority date: 2017-12-20
Filing date: 2017-12-20
Publication date: 2020-07-14
Anticipated expiration: 2037-12-20
Also published as: CN108002500A

Abstract

The invention provides a rotational flow flocculation device, a high-salinity high-turbidity wastewater treatment system of a coal-fired power plant and application. The device comprises a box body (1), wherein a rotational flow coagulation pipe (2) and an inner cylinder (3) are arranged in the middle of the interior of the box body, the rotational flow coagulation pipe is arranged at the bottom of the box body, extends upwards to the top edge of the rotational flow coagulation pipe, is positioned in the inner cylinder and is not contacted with the top of the box body, the inner cylinder is arranged at the top of the box body, extends downwards, and the bottom edge of the inner cylinder is not contacted with the box body; a rotational flow guide plate (4) is arranged on the outer wall of the part of the rotational flow coagulation pipe extending into the inner cylinder, and rotational flow blades (5) are arranged in the rotational flow coagulation pipe; the bottom of the box body is outwards provided with a water inlet pipe (6), and the water inlet pipe is communicated with the rotational flow coagulation pipe; the edge of the top of the box body is provided with an overflow groove (8). The system comprises: a water softening device (101), a cyclone flocculation device (102), a filter (103), a pre-concentrator (104), a preheater (105), a membrane distiller (106) and an evaporation tower (107) which are connected in sequence by pipelines.

Description

Rotational flow flocculation device, high-salinity high-turbidity wastewater treatment system of coal-fired power plant and application

Technical Field

The invention relates to the field of power plant wastewater treatment, in particular to a rotational flow flocculation device, a high-salinity high-turbidity wastewater treatment system for a coal-fired power plant and application of the rotational flow flocculation device.

Background

Along with the coming of a series of wastewater discharge management policies such as ten water discharge policies, the coal-fired power plant wastewater zero discharge related technology is more and more concerned and emphasized, and the coal-fired power plant wastewater zero discharge is a necessary trend. Under the existing conditions, partial high-salt-content wastewater in a coal-fired power plant still has difficulty in realizing near zero emission, wherein the most difficult to treat is desulfurization wastewater generated in a limestone-gypsum wet desulfurization operation process. The desulfurization waste water not only contains solid and the aquatic contains a large amount of calcium, magnesium, sulfate radical, chloridion etc. greatly, and most granule and trace heavy metal of aquatic are got rid of to the current traditional triple box processing technology branch of academic or vocational study of power plant, but can't get rid of the salinity of aquatic, and the desulfurization waste water through triple box processing still is the high salt waste water that does not reach standard. In addition, in northern water-deficient areas, the water quality is poor, the salt content in water is high, and the salt content in the water discharged by the circulating cooling tower is high. In order to recover fresh water resources and reduce the discharge amount of strong brine, the coal-fired power plant mostly adopts a method of concentrated circulating cooling water followed by concentrated water discharge and fresh water reuse for treatment, and the treatment of the concentrated circulating cooling water is also a difficult problem.

At present, two main technical schemes about zero discharge of salt-containing wastewater of a coal-fired power plant are provided: firstly, pretreatment, concentration and evaporative crystallization; second, pretreatment, concentration (or not concentration), and flue evaporation. In the whole, the pretreatment process of the first two schemes mostly adopts the traditional triple box treatment technology, and although the effect of removing the heavy metal flocculation particles can be achieved, the flocculation dosage and the equipment volume are large. Secondly, modes such as reverse osmosis, high-pressure reverse osmosis and multi-effect evaporation are usually adopted in the wastewater concentration process, the reverse osmosis is limited by application conditions, the wastewater can be concentrated to about 5%, the high-pressure reverse osmosis can only reach about 13% at most, and the energy consumption of the high-pressure reverse osmosis is obviously increased. In terms of the whole treatment process, the scheme I is adopted for zero discharge of waste water of the power plant at present, the operation is relatively mature and stable, but the whole evaporation crystallization equipment is complex and large in investment, a high-temperature heat source needs to be additionally introduced in the evaporation process, and the energy consumption is very high. The flue evaporation technology is a hotspot of the current research, has the advantages of simple equipment, low investment, low energy consumption and the like, has application in some power plants, and has some problems which need to be solved urgently at present: how to prevent the corrosion and scaling of the flue wall in the spray evaporation process and the potential safety hazard possibly brought to electric precipitation.

Disclosure of Invention

One object of the present invention is to provide a cyclone flocculation apparatus;

the invention also aims to provide a high-salinity high-turbidity wastewater treatment system for a coal-fired power plant;

the invention further aims to provide a method for treating high-salinity high-turbidity wastewater of a coal-fired power plant.

In order to achieve the above objects, in one aspect, the present invention provides a cyclone flocculation apparatus, wherein the apparatus comprises a closed tank 1, a cyclone coagulation pipe 2 and an inner cylinder 3 arranged in the middle of the interior of the tank, the cyclone coagulation pipe being arranged at the bottom of the tank and extending upward until the top edge thereof is positioned in the interior of the inner cylinder, and being out of contact with the top of the tank to form a water flow channel between the top edge thereof and the top of the tank, the inner cylinder being arranged at the top of the tank and extending downward, and the bottom edge thereof being out of contact with the tank to form a water flow channel between the bottom edge thereof and the inner wall of the tank; a rotational flow guide plate 4 is arranged on the outer wall of the part of the rotational flow coagulation pipe extending into the inner cylinder, and rotational flow blades 5 are arranged in the rotational flow coagulation pipe; a water inlet pipe 6 is arranged outwards at the bottom of the box body, and a water outlet pipe is communicated with the rotational flow coagulation pipe; the edge of the top of the box body is provided with an overflow groove 8.

According to some embodiments of the invention, the number of the swirl flow guide plates is 6 to 8.

According to some embodiments of the invention, the height of the cyclone guide plate is 1/6-1/3 of the height of the part of the cyclone coagulation tube extending into the inner cylinder.

According to some embodiments of the present invention, the overflow weir 81 is formed outside the overflow trough.

According to some embodiments of the present invention, the number of the overflow grooves is 1 to 3, and each length is 1/4-1 of the circumference of the top of the tank.

According to some embodiments of the invention, wherein the weir height is 1/2-1/5 of the width of the trough.

According to some specific embodiments of the invention, the height of the cyclone coagulation pipe 2 is 2/3-9/10 of the height of a box body, and the cyclone coagulation pipe 2 comprises a first straight pipe section 21 and an inverted cone-shaped expanding section 22; the diameter of the upper edge of the first straight pipe section is equal to that of the lower edge of the diameter expanding section, the upper edge of the diameter expanding section is connected with the lower edge of the diameter expanding section, and the diameter ratio of the upper edge of the diameter expanding section to the lower edge of the diameter expanding section is (1.5-3): 1, the diameter ratio of the height of the expanding section to the upper edge of the expanding section is 2/1-4/1.

According to some specific embodiments of the invention, the height of the part of the cyclone coagulation pipe 2 extending into the inner cylinder is 1/5-1/2 of the total height of the cyclone coagulation pipe.

According to some specific embodiments of the invention, the swirl mixing pipe 2 further comprises a second straight pipe section 23, wherein the lower edge of the second straight pipe section and the upper edge of the expanding diameter section have the same diameter and are connected with each other.

According to some embodiments of the invention, the height of the second straight tube section is 1/3-1/8 of the height of the expanded diameter section.

According to some embodiments of the present invention, at least the upper end of the box body 1 is cylindrical, and the height of the cylindrical box body accounts for 1/3-2/3 of the total height of the box body; the diameter ratio of the inner cylinder 3 to the cylindrical box body is 2/5-2/3; the height ratio of the inner cylinder to the cylindrical box body is 1/4-1/2.

According to some embodiments of the present invention, at least the upper end of the case 1 is cylindrical, and the ratio of the height to the diameter of the cylinder is 1/4 to 1/1.

According to some embodiments of the invention, the lower end of the tank 1 is in the shape of an inverted truncated cone, the upper edge of which is connected to the lower edge of the cylinder.

According to some embodiments of the invention, the diameter ratio of the upper bottom surface and the lower bottom surface of the circular truncated cone is 1/10-1/4.

According to some embodiments of the present invention, a flocculant adding port 7 is further provided on the water inlet pipe.

In another aspect, the present invention further provides a coal-fired power plant saline wastewater treatment system, wherein the system comprises: a softened water device 101, a cyclone flocculation device 102, a filter 103, a pre-concentrator 104, a preheater 105, a membrane distiller 106 and an evaporation tower 107 which are connected in sequence by pipelines.

According to some embodiments of the present invention, the system further comprises a flue gas mixer 108, wherein the flue gas mixer is used for mixing flue gas entering the air preheater 109 of the flue gas treatment system of the coal-fired power plant and flue gas exiting the dust remover 110 of the flue gas treatment system of the coal-fired power plant, and conveying the mixed flue gas to the evaporation tower 107 for heating the evaporation tower (spray drying tower), and conveying the heat-exchanged flue gas to a pipeline between the air preheater and the dust remover through a pipeline.

The water softening device 101, the filter 103, the pre-concentrator 104, the pre-heater 105, the membrane distiller 106, the evaporation tower 107, the flue gas mixer 108, the air pre-heater 109 and the dust remover 110 according to the present invention can be conventional devices in the field.

According to some embodiments of the present invention, the system further comprises a pipeline connecting the preheater 105 with the dust remover 110 and the desulfurization tower 111, so as to heat the preheater by using the flue gas from the dust remover and send the heat-exchanged flue gas to the desulfurization tower.

According to some embodiments of the present invention, the water softener 101 is provided with a desulfurized waste water inlet 1011 and a recirculated cooling water inlet 1012.

In still another aspect, the invention further provides a method for treating salt-containing wastewater of a coal-fired power plant, wherein the method comprises the step of performing flocculation separation treatment on desulfurization wastewater of the power plant and/or recirculated cooling water of the power plant by using the cyclone flocculation device of any one of the aspects of the invention instead of a triple box.

The independently researched and developed cyclone flocculation device replaces the traditional triple box, realizes quick flocculation and flocculation particle separation, shortens flocculation clarification time, and reduces equipment floor area

According to some specific embodiments of the invention, the method comprises softening the power plant desulfurization wastewater and/or power plant circulating cooling water, performing flocculation separation treatment by using the cyclone flocculation device, filtering, performing pre-concentration, preheating the liquid obtained after the pre-concentration, performing membrane distillation, and evaporating concentrated brine obtained after the membrane distillation.

In the membrane distillation process, the strong brine is heated by adopting low-temperature waste heat of a power plant, so that the extra energy consumption is little;

after membrane distillation, strong brine enters an evaporation tower in a spraying mode for evaporation and drying, mixed flue gas from high-temperature flue gas between the SCR and the air preheater and flue gas between the dust remover and the desulfurization island is used as an evaporation heat source, and the flue gas returns to a front flue of the dust remover after passing through the evaporation tower, so that zero emission of wastewater is realized.

The water softening device is used for reducing the hardness of the wastewater, and can adopt one or more of a tubular softener dosing device, a softening water tank and a swirler.

The filter can adopt one or more of multi-medium filtration, microfiltration and ultrafiltration.

The pre-concentration process can be one or more of nanofiltration, primary reverse osmosis or multi-stage reverse osmosis.

The preheater is used for heating the wastewater before membrane distillation, and the heating heat source can be one or two of hot flue gas from a dust remover to a desulfurizing tower and boiler steam preheating. If the hot flue gas after the dust remover is adopted as a heat source, the low-temperature flue gas discharged from the membrane distillation device returns to the original flue gas channel.

According to some embodiments of the invention, the liquid obtained after pre-concentration is preheated to 50-95 ℃.

According to some embodiments of the present invention, the membrane distillation may be atmospheric distillation or low-pressure distillation.

According to some embodiments of the invention, the membrane distillation effluent contains no less than 15% salt.

According to some embodiments of the present invention, the flue gas pipeline section entering the evaporation tower can be provided with a cyclone ash removal device.

The solid salt particles formed by the spray evaporation of the salt-containing wastewater can be returned to the front flue of the dust remover along with the flue gas or collected by an additional dust removal structure.

According to some embodiments of the invention, the treatment method is treatment using any one of the treatment systems of the invention.

According to some embodiments of the present invention, the system comprises a flue gas mixer 108, and the flue gas to be introduced into the coal fired power plant flue gas treatment system air preheater 109 and the flue gas from the coal fired power plant flue gas treatment system dust remover 110 are mixed in a ratio of 10: 0-5: 5, and then sent to the evaporation tower 107 for heating of the evaporation tower.

In conclusion, the invention provides a rotational flow flocculation device, a high-salinity high-turbidity wastewater treatment system of a coal-fired power plant and application. The scheme of the invention has the following advantages:

the invention aims to develop a zero-discharge treatment system for salt-containing wastewater of a coal-fired power plant, which can realize zero discharge of wastewater of the power plant, has the advantages of small dosage, small occupied area, low energy consumption and adjustable wastewater treatment capacity by taking flue gas as a heat source in the concentration and evaporation processes, and cannot cause scaling corrosion of flue walls and harm of electric precipitation.

The whole process almost does not need additional energy consumption, is completed by utilizing the waste heat of the boiler flue gas, and can concentrate the salt-containing wastewater to more than 15% by adopting membrane distillation, and the membrane distillation has higher concentration ratio than two-stage reverse osmosis concentration, so that the flue gas volume in the process of evaporating and drying the wastewater can be effectively saved; solid salt particles formed by evaporating and drying the wastewater in the evaporation tower can enter a subsequent dust remover along with the flue gas and are captured, or a high-efficiency cyclone separator is adopted to collect and recycle most of the solid particles, and the residual flue gas enters the dust remover for further dust removal and purification, and the two schemes can be selected according to the specific ash sample requirement of the power plant. The humidity of the flue gas entering the dust remover can be improved, and the improvement of the dust removal efficiency of electric dust removal is facilitated. The whole process is finished outside the flue, the operation of the boiler, the air preheater, the dust remover and the desulfurization process are not affected, and the maintenance and the overhaul are convenient. Solid salt particles formed by spray drying the salt-containing wastewater can not enter a dust remover, and the quality of the original fly ash is not influenced.

Drawings

FIG. 1 is a cyclone flocculation apparatus of example 1.

FIG. 2 is the salt-containing wastewater treatment system of the coal fired power plant of example 1.

Detailed Description

The following detailed description is provided for the purpose of illustrating the embodiments and the advantageous effects thereof, and is not intended to limit the scope of the present disclosure.

Example 1

The wastewater treatment system shown in figure 2 is used, and the wastewater (indexes before treatment are shown in table 1) treatment process comprises (1) adding soda into a softening water device for softening, then entering a cyclone flocculation device (shown in figure 1), sequentially adding a polyferric chloride coagulant aid and a polyacrylamide flocculant, wherein the SS content in the wastewater at the outlet of the cyclone flocculation device is up to 12 mg/L, the copper ion content is 5 mg/L, and other components are basically unchanged, (2) adopting a multi-media filter in the filtration process, wherein the suspended matter content is at the moment<3 mg/L, calcium ion (Ca)²⁺)657 Mg/L, magnesium ion (Mg)²⁺)366 mg/L, (3) pre-shrinking by adopting two-stage reverse osmosis treatment, the waste water TDS is concentrated to about 60000 mg/L from 25000 mg/L, fresh water is recycled, strong brine enters a membrane distillation treatment unit, (4) the membrane distillation process takes low-grade steam as a heat source, the membrane distillation temperature is 75oC, the condensed fresh water is recycled, the salt content of the waste water is further concentrated to more than 150000mg/l, and the strong brine amount is about 20-30% of the original waste water amount at the moment, (5) the strong brine enters an evaporation tower outside a flue in a form of 100-200 micron fog drops through a double-fluid nozzle, spray evaporation is carried out by taking high-temperature flue gas of more than 300oC as a heat source, salt particles after evaporation enter an electrostatic dust collector along with the flue gas and are captured, and evaporated water is condensed in a desulfurization tower.

The operation process of the wastewater in the rotational flow flocculation device shown in figure 1 is as follows: wastewater enters the equipment from a water inlet pipe 6 at the bottom of the self-current device, and meanwhile, a flocculating agent is added into a flocculating agent adding port 7 at the rear side of the pipeline; the wastewater and the flocculating agent form strong rotational flow after passing through the rotational flow blades 5, so that the wastewater and the flocculating agent are quickly and fully mixed; the water flow speed is gradually reduced at the diameter expansion section 22 of the rotational flow coagulation pipe, which is helpful for the formation of small flocs and is the initial stage of coagulation; the primarily coagulated wastewater enters the inner cylinder 3, the cross section of the inner cylinder is far larger than the expansion section, the water flow speed is obviously reduced, the growth of small flocs is facilitated, and the large flocs are prevented from being broken. The cyclone guide plate 4 is additionally arranged at the middle and lower reaches of the inner cylinder, so that mutual collision of flocs is facilitated to form large flocs on one hand, and large and stable cyclone is further formed in the wastewater on the other hand, and the cyclone sedimentation of the subsequent large flocs is facilitated; and (3) enabling the flocculated bodies to downwards enter the conical section to realize cyclone sedimentation and discharge from the bottom of the waste water flowing out of the inner cylinder, and enabling clear water to upwards enter the water outlet pipeline from the water outlet section through the overflow groove to obtain clear water without suspended matters. The wastewater indexes before and after the treatment are shown in the following tables 1 and 2, respectively.

TABLE 1 wastewater index before treatment

Serial number	Item	Unit of	Parameters of wastewater
				1	pH		6.67
2	Suspended Substance (SS)	mg/L	310
				3	Ammonia nitrogen	mg/L	～10
4	Chloride ion (Cl-)	mg/L	18123
				5	Sulfate ion (SO)₄ ^2-)	mg/L	997
6	all-Silicon (SiO)₂)	mg/L	84
				7	Calcium ion (Ca)²⁺)	mg/L	8334
8	Magnesium ion (Mg)²⁺)	mg/L	1314
				9	Copper ion (Cu)²⁺)	mg/L	64
10	TDS	mg/L	29455

TABLE 2 wastewater index after treatment by cyclone flocculation device

Claims

1. A rotational flow flocculation device comprises a box body (1), a rotational flow coagulation pipe (2) and an inner cylinder (3) are arranged in the middle of the interior of the box body, the rotational flow coagulation pipe is arranged at the bottom of the box body, extends upwards to the top edge of the rotational flow coagulation pipe, is positioned in the inner cylinder, is not in contact with the top of the box body so as to form a water flow channel between the top edge of the rotational flow coagulation pipe and the top of the box body, is arranged at the top of the box body, extends downwards, and is not in contact with the box body so as to form a water flow channel between the bottom edge of the inner cylinder and; a rotational flow guide plate (4) is arranged on the outer wall of the part of the rotational flow coagulation pipe extending into the inner cylinder; the number of the rotational flow guide plates is 6-8; the height of the rotational flow guide plate is 1/6-1/3 of the height of the part of the rotational flow coagulation pipe extending into the inner cylinder, and rotational flow blades (5) are arranged in the rotational flow coagulation pipe; a water inlet pipe (6) is arranged outwards at the bottom of the box body; the water inlet pipe is also provided with a flocculating agent adding port (7), and the water inlet pipe is communicated with the rotational flow coagulation pipe; the edge of the top of the box body is provided with an overflow groove (8); the height of the cyclone coagulation pipe (2) is 2/3-9/10 of the height of the box body, and the cyclone coagulation pipe (2) comprises a first straight pipe section (21) and an inverted-cone-shaped expanding section (22); the diameter of the upper edge of the first straight pipe section is equal to that of the lower edge of the diameter expanding section, the upper edge of the diameter expanding section is connected with the lower edge of the diameter expanding section, and the diameter ratio of the upper edge of the diameter expanding section to the lower edge of the diameter expanding section is (1.5-3): 1, the diameter ratio of the height of the diameter expanding section to the upper edge of the diameter expanding section is 2/1-4/1; the height of the part of the cyclone coagulation pipe (2) extending into the inner cylinder is 1/5-1/2 of the total height of the cyclone coagulation pipe.

2. A rotational flow flocculation apparatus according to claim 1, wherein the rotational flow coagulation tube (2) further comprises a second straight tube section (23) having a lower edge of the same diameter as the upper edge of the expanded diameter section and being interconnected.

3. A spiral-flow flocculation apparatus according to claim 2 wherein the second straight tube section has a height which is 1/3-1/8 of the height of the expanded diameter section.

4. A spiral-flow flocculation apparatus according to claim 1, wherein the tank (1) is cylindrical at least at its upper end, the height of the cylindrical tank being 1/3-2/3 of the total height of the tank; the diameter ratio of the inner cylinder (3) to the cylindrical box body is 2/5-2/3; the height ratio of the inner cylinder to the cylindrical box body is 1/4-1/2.

5. A spiral-flow flocculation apparatus according to claim 4, wherein the cylindrical tank (1) has a ratio of height to diameter of 1/4-1/1.

6. A spiral-flow flocculation apparatus according to claim 4, wherein the lower end of the tank (1) is inverted truncated cone shaped, the upper edge of the truncated cone of the tank being connected to the lower edge of the cylinder.

7. A spiral-flow flocculation apparatus according to claim 4, wherein the ratio of the diameter of the upper and lower bottom surfaces of the truncated cone shaped tank (1) is 1/10-1/4.

8. A spiral-flow flocculation apparatus according to claim 1, wherein an overflow weir (81) is formed outside the overflow launder.

9. The cyclone flocculation apparatus of claim 8, wherein the number of overflow launders is 1-3, and each length is 1/4-1 of the perimeter of the top of the tank.

10. A spiral-flow flocculation apparatus as claimed in claim 8 wherein the weir height is 1/2-1/5 of the width of the overflow trough.

11. A coal fired power plant high salinity high turbidity wastewater treatment system, wherein, the system includes: a water softening device (101), a cyclone flocculation device (102) as claimed in any one of claims 1 to 10, a filter (103), a pre-concentrator (104), a pre-heater (105), a membrane distiller (106) and an evaporation tower (107) connected in series by a pipeline.

12. The high-salinity high-turbidity wastewater treatment system for the coal-fired power plant according to claim 11, further comprising a flue gas mixer (108) for mixing flue gas to be introduced into the air preheater (109) of the flue gas treatment system of the coal-fired power plant and flue gas discharged from the dust remover (110) of the flue gas treatment system of the coal-fired power plant, and delivering the mixed flue gas to the evaporation tower (107) for heating the evaporation tower, wherein the heat-exchanged flue gas is delivered to a pipeline between the air preheater and the dust remover through a pipeline.

13. The high salinity and high turbidity wastewater treatment system of claim 12, wherein the system further comprises a pipeline connecting the preheater (105) with the dust remover (110) and the desulfurizing tower (111) to heat the preheater with the flue gas from the dust remover and to send the heat exchanged flue gas to the desulfurizing tower.

14. The high-salinity high-turbidity wastewater treatment system for the coal-fired power plant according to any one of claims 11 to 13, wherein the water softening device (101) is provided with a desulfurization wastewater inlet (1011) and a circulating cooling water inlet (1012).

15. A method for treating high-salinity high-turbidity wastewater of a coal-fired power plant, wherein the method comprises the step of performing flocculation separation treatment on desulfurization wastewater of the power plant and/or recirculated cooling water of the power plant by using the cyclone flocculation device of any one of claims 1 to 10 instead of a triple box.

16. The treatment method according to claim 15, wherein the method comprises softening the power plant desulfurization wastewater and/or the power plant circulating cooling water, performing flocculation separation treatment by using the cyclone flocculation device of any one of claims 1 to 10, performing pre-concentration after filtration, preheating the liquid obtained after pre-concentration, performing membrane distillation, and evaporating concentrated brine obtained after membrane distillation.

17. The process of claim 16, wherein the preheating is heating to 50-95 ℃.

18. The treatment method according to claim 16, wherein the treatment method is used for treating high-salinity and high-turbidity wastewater of a coal-fired power plant by using the treatment system of any one of claims 11 to 14.

19. The treatment method according to claim 18, wherein the system comprises a flue gas mixer (108) and the flue gas to be fed into the coal fired power plant flue gas treatment system air preheater (109) and the flue gas from the coal fired power plant flue gas treatment system dust remover (110) are mixed in a ratio of 10: 0-5: 5, and then sent to the evaporation tower (107) for heating of the evaporation tower.