Wastewater zero discharge monitoring method and system

Abstract

The invention provides a wastewater zero discharge monitoring method and system. The wastewater zero discharge monitoring method comprises the following steps that S1, wastewater is atomized and then fed into a drying tower, high-temperature flue gas is introduced into the drying tower to evaporate and dry atomized wastewater liquid drops, and the temperature T2 of flue gas at an outlet of the drying tower is monitored in real time; s2, the movement time t1 of the flue gas in the constant-speed evaporation stage and the movement time t2 of the flue gas in the speed-reducing evaporation stage are obtained respectively, the total flue gas retention time tall is obtained according to the movement time t1 and the movement time t2, and tall = t1 + t2; and S3, the wastewater flow and the flue gas flow are regulated and controlled according to the flue gas total residence time all, and the flue gas temperature T2 of an outlet of the drying tower is maintained at 428-448 K. According to the waste water zero discharge monitoring method and system, the change rule of the flow speed of the flue gas in the drying tower along with the temperature is fully considered, the monitoring accuracy of the system is improved, and the operation stability of the system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a wastewater zero-discharge monitoring method and system. Background Art

[0002] The high-salt wastewater from thermal power plants (such as chemical regeneration wastewater, wet desulfurization wastewater, etc.) has complex components, and direct discharge will cause serious pollution to the environment. At present, rotary atomization drying technology is one of the mainstream technologies for the power industry to achieve zero discharge of high-salt wastewater. This technology sets up a drying tower, uses high-speed rotation to atomize the wastewater into droplets and then sprays it into the drying tower. At the same time, the high-temperature flue gas from the thermal power plant is extracted and sent to the drying tower. The high-temperature flue gas and wastewater droplets fully exchange heat in the drying tower, quickly achieving zero discharge of wastewater.

[0003] The residence time of high-temperature flue gas in the drying tower determines the heat exchange time of gas-liquid two-phase fluid, and is also a key parameter affecting the zero emission effect of wastewater evaporation. At present, the calculation method of residence time is relatively extensive. Generally, the average flow rate of flue gas in the drying tower can only be calculated by the average value of the inlet and outlet flue gas temperatures of the drying tower, and then the flue gas residence time is calculated by the tower height of the drying tower.

[0004] However, since the drying process of wastewater in the drying tower includes two stages: constant-rate evaporation and reduced-rate evaporation, the temperature of the flue gas will continue to decrease during the flow from top to bottom, and the decrease will vary, which will cause its flow rate to change accordingly. The existing method of calculating the residence time cannot reflect the law of flow rate changes with temperature. The method of calculating the flue gas residence time based on the average temperature and average flow rate is likely to lead to unreasonable operation and control of the wastewater zero emission system, resulting in insufficient system output or poor zero emission effect, which will seriously affect the stable operation of the system.

[0005] In addition, the physical properties of high-temperature flue gas from thermal power plants have certain fluctuations. Since these parameters are unstable and cannot be adjusted, when using the high-temperature flue gas to evaporate and dry wastewater, unstable evaporation effects and poor evaporation may cause wet ash, blockage, corrosion and other faults, which will have a serious adverse effect on the normal operation of the drying tower.

[0006] In order to ensure the zero discharge of wastewater, it is necessary to adopt a more reasonable method to calculate the flue gas residence time and make necessary adjustments to the system operating parameters based on the residence time.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The purpose of the present invention is to provide a wastewater zero discharge monitoring method and system, which fully considers the variation law of flue gas flow velocity with temperature in a drying tower, improves the operation stability of the drying tower, and ensures the wastewater drying effect.

[0009] The present invention provides a wastewater zero discharge monitoring method, comprising the following steps:

[0010] S1: The wastewater is atomized and sent to the drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The flue gas temperature T at the outlet of the drying tower is 2 Conduct real-time monitoring;

[0011] S2: Obtain the movement time t of the flue gas in the constant evaporation stage 1 and the movement time t in the falling evaporation stage 2 , according to the movement time t 1 and movement time t 2 Get the total residence time of flue gas t all , t all =t 1 +t 2 ;

[0012] S3: According to the total residence time of flue gas t all The wastewater flow and flue gas flow are regulated, and the flue gas temperature T at the drying tower outlet is 2 Maintain at 428K-448K.

[0013] In step S1, the upper part of the drying tower is a hollow cylinder, which is the main place for evaporation and drying of wastewater; the bottom of the drying tower is a hollow cone, which is mainly used for ash deposition; unless otherwise specified, the drying tower mainly refers to the hollow cylindrical part. A rotary atomizer is set at the top of the drying tower, and the rotary atomizer is used to atomize the wastewater. The speed of the rotary atomizer is controlled to be 12000-18000r / min, and the particle size of the wastewater droplets formed by atomization is 10-60μm.

[0014] In step S2, the evaporation process of the wastewater droplets inside the drying tower includes two stages: constant-rate evaporation and reduced-rate evaporation; wherein, the constant-rate evaporation occurs at the upper part of the drying tower, during which the moisture on the surface of the wastewater droplets quickly exchanges heat with the high-temperature flue gas, the flue gas temperature drops sharply, the wastewater evaporates rapidly, and the dissolved salts and suspended matter in the wastewater form a solid shell, slowing down the evaporation rate of the water; the reduced-rate evaporation occurs at the lower part of the drying tower, and affected by the formed solid shell, the wastewater evaporates slowly and the flue gas temperature drops slowly.

[0015] After the flue gas enters the drying tower, its vertical flow velocity can be calculated according to the following formula:

[0016]

[0017] Wherein: v is the vertical flow velocity of flue gas; V is the volume flow rate of flue gas (referred to as flue gas flow rate); n is the molar flow rate, which is calculated by the volume flow rate of flue gas; R is the gas constant; T is the Kelvin temperature of flue gas; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower, which is calculated by the diameter of the drying tower.

[0018] A thermometer is arranged in the middle of the drying tower, and the thermometer is arranged between the constant-rate evaporation stage and the decreasing-rate evaporation stage. The thermometer is used to detect the critical temperature of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage.

[0019] From the top of the drying tower to the thermometer along the way is the constant-rate evaporation stage of the wastewater. Within this distance, the flue gas temperature drops sharply as it moves downward. The following linear model is used to simulate the change of flue gas temperature with vertical movement distance:

[0020] T=a 1 L+b 1

[0021] Where: L is the vertical movement distance of the flue gas (starting from the top of the drying tower); a 1 , b 1 is the model parameter.

[0022] Assume T c is the reading of the thermometer along the process (i.e. the critical temperature of the flue gas between the constant evaporation stage and the decreasing evaporation stage), T 1 is the inlet flue gas temperature, L 1 It is the distance between the temperature meter along the way and the top of the drying tower (i.e. the vertical flow distance of the flue gas during the constant evaporation stage, which is about 2.5-5.4m).

[0023] When L = 0, T = T 1 ; When L = L 1 When T = T c Therefore, a is obtained by the following formula 1 , b 1 :

[0024]

[0025] b 1 =T 1

[0026] Where: T c T is the critical temperature of flue gas between the constant evaporation stage and the decreasing evaporation stage; 1 is the inlet flue gas temperature; L 1 It is the vertical flow distance of flue gas in the constant evaporation stage.

[0027] Since the vertical flow velocity of smoke is the derivative of the vertical movement distance and movement time, that is:

[0028]

[0029] The flue gas movement time t (starting from the top of the drying tower) is calculated by the following formula:

[0030]

[0031] When L = 0, t = 0, we can get:

[0032]

[0033] In the constant rate evaporation stage, let L = L 1 , the movement time of the flue gas in the constant evaporation stage can be calculated, recorded as t 1 .

[0034] That is, the movement time t of the flue gas in the constant evaporation stage is obtained by the following formula: 1 :

[0035]

[0036] Where: t 1 is the movement time of flue gas in the constant evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a 1 、b 1 is the model parameter; L 1 It is the vertical flow distance of flue gas in the constant evaporation stage.

[0037] From the thermometer along the way to the flue gas outlet at the bottom of the drying tower is the stage of slow evaporation of wastewater. Within this distance, the flue gas temperature slowly decreases as it moves downward. The following linear function is used to simulate the change of flue gas temperature with vertical movement distance:

[0038] T=a 2 L+b 2

[0039] Where: L is the vertical movement distance of the smoke (starting from the starting point of the speed reduction evaporation, denoted as L 2 );a 2 、b 2 is the model parameter.

[0040] Assume T 2 is the outlet flue gas temperature, and the height of the hollow cylinder in the drying tower is h. When L = 0, T = T c ; When L = hL 1 When T = T 2 Therefore, a is obtained by the following formula 2 、b 2 :

[0041]

[0042] Where: T 2 is the outlet flue gas temperature; T c is the critical temperature of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage; h is the height of the hollow cylinder in the drying tower (i.e., the height of the hollow cylinder in the upper part of the drying tower); L 1 It is the vertical flow distance of flue gas in the constant evaporation stage.

[0043] The vertical velocity of smoke is the derivative of the vertical movement distance and movement time, that is:

[0044]

[0045] The smoke movement time t (taking the starting point of the falling evaporation as the starting point, denoted as t) is calculated by the following formula 2 ):

[0046]

[0047] When L = 0, t = 0, we can get:

[0048]

[0049] In the stage of decreasing speed evaporation, let L = hL 1 =L 2 , the movement time of the flue gas in the deceleration evaporation stage can be calculated, which is recorded as t 2 .

[0050] That is, the movement time t of the flue gas in the deceleration evaporation stage is obtained by the following formula: 2 :

[0051]

[0052] Where: t 2 is the movement time of flue gas in the deceleration evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a 2 , b 2 is the model parameter; L 2 It is the vertical flow distance of flue gas during the deceleration evaporation stage.

[0053] According to the solid content x of the wastewater, the total residence time t of the flue gas is determined as follows all Control interval:

[0054] When the solid content of wastewater is x≤10%, the total residence time of flue gas is t all The control interval is [30s, 35s), that is, 30s≤t all <35s;

[0055] When the solid content of wastewater x is: 10%<x≤20%, the total residence time of flue gas is t all The control interval is [35s, 40s), that is, 35s≤t all <40s;

[0056] When the solid content of wastewater x is: 20%<x≤30%, the total residence time of flue gas is t all The control interval is [40s, 45s], that is, 40s≤t all ≤45s.

[0057] In addition, the gas-liquid ratio is regulated as follows:

[0058] When the total residence time of smoke is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 When maintained at 428K-448K, the wastewater flow and flue gas flow remain unchanged;

[0059] When the total residence time of smoke is t all When it is lower than the lower limit of the control interval, reduce the wastewater flow and flue gas flow until the total residence time of the flue gas is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 Maintain at 428K-448K, and control the gas flow rate reduction rate not to exceed the wastewater flow rate reduction rate;

[0060] When the total residence time of smoke is t all When it is higher than the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate until the total residence time of the flue gas is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 Maintain at 428K-448K, and control the increase rate of wastewater flow rate not to exceed the increase rate of gas flow rate.

[0061] The above control method can obtain the corresponding total smoke residence time t based on the smoke variable speed flow law all At the same time, according to the total residence time of flue gas t all The control range can coordinately adjust the wastewater flow and flue gas flow during the operation of the drying tower, so as to overcome the problem of unstable temperature of high-temperature flue gas entering the drying tower, thereby avoiding the unstable evaporation effect during the operation of the drying tower and the wet ash, blockage, corrosion and other faults caused by poor evaporation, thus ensuring the stable operation of the drying tower.

[0062] The present invention also provides a wastewater zero discharge monitoring system for implementing the above-mentioned wastewater zero discharge monitoring method, comprising a drying tower and a controller, wherein a rotary atomizer is arranged on the top of the drying tower, the rotary atomizer is connected to a wastewater pipe, a wastewater regulating valve is arranged on the wastewater pipe, an inlet flue and an outlet flue are arranged at the upper and lower parts of the drying tower respectively, a flue gas regulating valve, an inlet thermometer and a flow meter are arranged on the inlet flue, an outlet thermometer is arranged on the outlet flue, an along-the-way thermometer and a pressure gauge are arranged on the drying tower, and a calculation module is arranged on the controller, and the calculation module can calculate the movement time t of the flue gas in the constant-rate evaporation stage according to the data fed back by the inlet thermometer, the outlet thermometer, the along-the-way thermometer, the flow meter and the pressure gauge 1 , Movement time t in the deceleration evaporation stage 2 and total smoke residence time t all The controller is based on the total residence time of the flue gas t all The wastewater regulating valve and the flue gas regulating valve are controlled to regulate the wastewater flow and the flue gas flow.

[0063] Specifically, the upper part of the drying tower is a hollow cylinder, the bottom is a hollow cone, the inlet flue and the outlet flue are respectively arranged at the upper and lower parts of the hollow cylinder; the rotary atomizer is used to atomize the wastewater, and the rotary atomizer can be arranged at the top center of the drying tower; the wastewater regulating valve is used to adjust the wastewater flow; the flue gas regulating valve is used to adjust the flue gas flow; the inlet thermometer is used to monitor the inlet flue gas temperature T in real time 1 The flow meter is used to monitor the flue gas volume flow rate V in real time, and the molar flow rate n is obtained by conversion. The inlet thermometer and flow meter can be installed at a depth of 1 / 2 diameter inside the inlet flue. The inlet thermometer and flow meter are arranged at a distance of 0.8-1.2m; the outlet thermometer is used to monitor the outlet flue gas temperature T in real time. 2 , can be installed at a depth of 1 / 2 diameter inside the outlet flue; the along-the-way thermometer is used to monitor the critical temperature T of the flue gas between the constant evaporation stage and the reduced evaporation stage in real time c , which can be installed at a depth of 1 / 8 of the diameter inside the hollow cylinder; the pressure gauge is used to monitor the flue gas pressure P in real time, and can be installed at a height of 1 / 2 of the hollow cylinder and at a depth of 1 / 8 of the diameter inside the hollow cylinder.

[0064] Furthermore, according to the solid content x of the wastewater, the temperature measuring instruments along the process are set as follows:

[0065] When the solid content x of the wastewater is: x≤10%, the temperature meter along the process is set at a position 4.5-5.4m away from the top of the drying tower;

[0066] The solid content x of the wastewater is: 10%<x≤20%, and the temperature meter along the process is set at a distance of 3.5-4.4m from the top of the drying tower;

[0067] The solid content x of the wastewater is: 20%<x≤30%, and the along-the-way thermometer is set at a position 2.5-3.4m away from the top of the drying tower.

[0068] The present invention establishes a wastewater zero-discharge monitoring method and system based on the characteristics of wastewater in constant-rate evaporation and reduced-rate evaporation stages, and provides a data basis for establishing a kinetic model by monitoring key parameters; the method and system fully consider the relationship between flue gas flow rate and temperature in different evaporation stages, respectively establish linear models of flue gas movement time and movement distance, and derive a kinetic model for calculating the total residence time of flue gas, thereby improving the accuracy of calculating the total residence time of flue gas in a drying tower; in addition, according to the calculation of the total residence time of flue gas by the kinetic model, corresponding intelligent control methods are formulated for different types of wastewater, which not only ensures the wastewater treatment effect and treatment capacity of the drying tower, but also can well overcome various problems caused by the unstable temperature of high-temperature flue gas entering the drying tower, thereby improving the operating stability of the drying tower and ensuring the wastewater drying effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0070] Figure 1 It is a structural schematic diagram of the drying tower of the present invention.

[0071] Description of reference numerals:

[0072] 1: Drying tower; 2: Rotary atomizer; 3: Inlet flue; 4: Outlet flue; 5: Wastewater pipe; 6: Outlet thermometer; 7: Flue gas regulating valve; 8: Inlet thermometer; 9: Along-the-process thermometer; 10: Pressure gauge; 11: Flowmeter; 12: Wastewater regulating valve. DETAILED DESCRIPTION

[0073] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0074] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0075] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0076] Example 1

[0077] The wastewater zero discharge monitoring method of this embodiment includes the following steps:

[0078] S1: The wastewater is atomized and sent to the drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The flue gas temperature T at the outlet of the drying tower is 2 Conduct real-time monitoring;

[0079] S2: Obtain the movement time t of the flue gas in the constant evaporation stage 1 and the movement time t in the falling evaporation stage 2 , according to the movement time t 1 and movement time t 2 Get the total residence time of flue gas t all , t all =t 1 +t 2 ;

[0080] S3: According to the total residence time of flue gas t all The wastewater flow and flue gas flow are regulated, and the flue gas temperature T at the drying tower outlet is 2 Maintain at 428K-448K.

[0081] Specifically, a rotary atomizer is used to atomize the wastewater, the rotation speed of the atomizer is controlled to be 12000-18000 r / min, and the particle size of the wastewater droplets formed by atomization is 10-60 μm.

[0082] During the evaporative drying process, the inlet flue gas temperature T 1 , outlet flue gas temperature T 2 , the critical temperature T between the constant evaporation stage and the decreasing evaporation stage c, flue gas pressure P, flue gas volume flow rate V and other related parameters are monitored in real time, the cross-sectional area of ​​the drying tower is calculated according to the tower diameter of the drying tower, and the molar flow rate n is calculated according to the flue gas volume flow rate V.

[0083] Get a by the following formula 1 , b 1 :

[0084]

[0085] b 1 =T 1

[0086] Where: T c T is the critical temperature of flue gas between the constant evaporation stage and the decreasing evaporation stage; 1 is the inlet flue gas temperature.

[0087] The movement time t of the flue gas in the constant evaporation stage is obtained by the following formula 1 :

[0088]

[0089] Where: t 1 is the movement time of flue gas in the constant evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a 1 , b 1 is the model parameter; L 1 It is the vertical flow distance of flue gas in the constant evaporation stage.

[0090] Get a by the following formula 2 , b 2 :

[0091]

[0092] b 2 =T c

[0093] Where: T 2 is the outlet flue gas temperature; T c is the critical temperature of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage; h is the height of the hollow cylinder in the drying tower; L 1 It is the vertical flow distance of flue gas in the constant evaporation stage.

[0094] The movement time t of flue gas in the deceleration evaporation stage is obtained by the following formula 2 :

[0095]

[0096] Where: t2 is the movement time of flue gas in the deceleration evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a 2 , b 2 is the model parameter; L 2 It is the vertical flow distance of flue gas during the deceleration evaporation stage.

[0097] The movement time t of the flue gas in the constant evaporation stage is obtained. 1 and the movement time t in the slowing down evaporation stage 2 After that, according to t all =t 1 +t 2 Get the total residence time of flue gas t all .

[0098] The total flue gas residence time t is determined as follows all Control interval:

[0099] When the solid content of wastewater is x≤10%, the total residence time of flue gas is t all The control interval is [30s, 35s);

[0100] When the solid content of wastewater x is: 10%<x≤20%, the total residence time of flue gas is t all The control interval is [35s,40s);

[0101] When the solid content of wastewater x is: 20%<x≤30%, the total residence time of flue gas is t all The control interval is [40s,45s].

[0102] According to the total smoke residence time t all and the total residence time of flue gas as above t all The wastewater flow and flue gas flow are regulated in the following manner:

[0103] When the total residence time of smoke is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 When maintained at 428K-448K, the wastewater flow and flue gas flow remain unchanged;

[0104] When the total residence time of smoke is t all When it is lower than the lower limit of the control interval, reduce the wastewater flow and flue gas flow until the total residence time of the flue gas is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 Maintain at 428K-448K, and control the gas flow rate reduction rate not to exceed the wastewater flow rate reduction rate;

[0105] When the total residence time of smoke is t allWhen it is higher than the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate until the total residence time of the flue gas is t all The flue gas temperature at the drying tower outlet is within the control range and T 2 Maintain at 428K-448K, and control the increase rate of wastewater flow rate not to exceed the increase rate of gas flow rate.

[0106] Example 2

[0107] Combination Figure 1 As shown, the wastewater zero discharge monitoring system of this embodiment is used to implement the wastewater zero discharge monitoring method of embodiment 1. The wastewater zero discharge monitoring system includes a drying tower 1 and a controller (not shown). A rotary atomizer 2 is provided on the top of the drying tower 1. The rotary atomizer 2 is connected to a wastewater pipe 5. A wastewater regulating valve 12 is provided on the wastewater pipe 5. An inlet flue 3 and an outlet flue 4 are provided at the upper and lower parts of the drying tower 1, respectively. A flue gas regulating valve 7, an inlet thermometer 8 and a flowmeter 11 are provided on the inlet flue 3. An outlet thermometer 6 is provided on the outlet flue 4. A thermometer 9 and a pressure gauge 10 are provided along the drying tower 1. The controller is provided with a calculation module, which can calculate the movement time t of the flue gas in the constant rate evaporation stage according to the data fed back by the inlet thermometer 8, the outlet thermometer 6, the thermometer 9 along the process, the flowmeter 11 and the pressure gauge 10. 1 , Movement time t in the deceleration evaporation stage 2 and total smoke residence time t all The controller is based on the total residence time of the flue gas t all The wastewater regulating valve 12 and the flue gas regulating valve 7 are controlled to adjust the wastewater flow and the flue gas flow.

[0108] Specifically, the upper part of the drying tower 1 is a hollow cylinder, the bottom is a hollow cone, the inlet flue 3 and the outlet flue 4 are respectively arranged at the upper and lower parts of the hollow cylinder; the rotary atomizer 2 is used to atomize the wastewater, and the rotary atomizer 2 can be arranged at the top center of the drying tower 1; the wastewater regulating valve 12 is used to adjust the wastewater flow; the flue gas regulating valve 7 is used to adjust the flue gas flow; the inlet thermometer 8 is used to monitor the inlet flue gas temperature T in real time 1 The flow meter 11 is used to monitor the flue gas volume flow rate V in real time, and the molar flow rate n is obtained by conversion. The inlet thermometer 8 and the flow meter 11 can be installed at a depth of 1 / 2 diameter inside the inlet flue 3, and the inlet thermometer 8 and the flow meter 11 are arranged at a distance of 0.8-1.2m; the outlet thermometer 6 is used to monitor the outlet flue gas temperature T in real time. 2 , can be installed at a depth of 1 / 2 diameter inside the outlet flue 4; the along-the-way thermometer 9 is used to monitor the critical temperature T of the flue gas between the constant-speed evaporation stage and the reduced-speed evaporation stage in real time c, which can be installed at a depth of 1 / 8 of the diameter inside the hollow cylinder; the pressure gauge 10 is used to monitor the flue gas pressure P in real time, and can be installed at a height of 1 / 2 of the hollow cylinder and at a depth of 1 / 8 of the diameter inside the hollow cylinder.

[0109] According to the solid content x of the wastewater, the temperature measuring meter 9 along the process is set as follows:

[0110] When the solid content x of the wastewater is: x≤10%, the along-line thermometer 9 is set at a position 4.5-5.4m away from the top of the drying tower 1;

[0111] The solid content x of the wastewater is: 10%<x≤20%, and the along-line thermometer 9 is set at a position 3.5-4.4m away from the top of the drying tower 1;

[0112] The solid content x of the wastewater is: 20%<x≤30%, and the along-the-way temperature measuring meter 9 is set at a position 2.5-3.4m away from the top of the drying tower 1.

[0113] Example 3

[0114] The wastewater zero discharge monitoring system of Example 2 is used to evaporate and dry the wastewater; the parameters are as follows: the solid content x of the wastewater is 5%, the inlet flue gas temperature T 1 is 633K, and the outlet flue gas temperature is T 2 The temperature is 448K, the diameter of the drying tower is 8.5m, the height h of the hollow cylinder of the drying tower is 15m, and the temperature measuring instrument along the drying tower is set at a position 5m away from the top of the drying tower (i.e. L 1 5m); the design value of smoke flow is 58100Nm 3 / h.

[0115] In the constant rate evaporation stage, there are:

[0116] Flue gas temperature: T = a 1 L+b 1 =-34.6L+633.

[0117] Movement time of flue gas in the constant evaporation stage:

[0118] In the falling speed evaporation stage, there are:

[0119] Flue gas temperature: T = a 2 L+b 2 =-1.2L+460.

[0120] Movement time of flue gas in the deceleration evaporation stage:

[0121] Total smoke residence time: t all =t 1 +t2 ≈8.9+21.2≈30.1s.

[0122] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 33.2s. It can be seen that the total residence time of the flue gas calculated in this embodiment is t all This is very close to the total residence time of flue gas obtained during actual operation, indicating that the above calculation method of this embodiment can more accurately obtain the total residence time of flue gas during operation of the drying tower.

[0123] Example 4

[0124] The wastewater zero discharge monitoring system of Example 2 is used to evaporate and dry the wastewater; the parameters are as follows: the solid content x of the wastewater is 17%, the inlet flue gas temperature T 1 is 611K, and the outlet flue gas temperature is T 2 The temperature is 438K, the diameter of the drying tower is 7.5m, the height h of the hollow cylinder of the drying tower is 11.5m, and the temperature measuring instrument along the drying tower is set at a position 4m away from the top of the drying tower (i.e. L 1 4m); the design value of smoke flow is 30700Nm 3 / h.

[0125] In the constant rate evaporation stage, there are:

[0126] Flue gas temperature: T = a 1 L+b 1 =-41.3L+611.

[0127] Movement time of flue gas in the constant evaporation stage:

[0128] In the falling speed evaporation stage, there are:

[0129] Flue gas temperature: T = a 2 L+b 2 =-1.1L+446.

[0130] Movement time of flue gas in the deceleration evaporation stage:

[0131] Total smoke residence time: t all =t 1 +t 2 ≈10.9+24.2≈35.1s.

[0132] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 37.8s. allThis is very close to the total residence time of flue gas obtained during actual operation, indicating that the above calculation method of this embodiment can more accurately obtain the total residence time of flue gas during operation of the drying tower.

[0133] Example 5

[0134] The wastewater zero discharge monitoring system of Example 2 is used to evaporate and dry the wastewater; the parameters are as follows: the solid content x of the wastewater is 25%, the inlet flue gas temperature T 1 is 645K, and the outlet flue gas temperature is T 2 The temperature is 428K, the diameter of the drying tower is 7m, the height h of the hollow cylinder of the drying tower is 14m, and the temperature measuring instrument along the drying tower is set at a position 3m away from the top of the drying tower (i.e. L 1 3m); the design value of smoke flow is 29600Nm 3 / h.

[0135] In the constant rate evaporation stage, there are:

[0136] Flue gas temperature: T = a 1 L+b 1 =-70L+645.

[0137] Movement time of flue gas in the constant evaporation stage:

[0138] In the falling speed evaporation stage, there are:

[0139] Flue gas temperature: T = a 2 L+b 2 =-0.6L+435.

[0140] Movement time of flue gas in the deceleration evaporation stage:

[0141] Total smoke residence time: t all =t 1 +t 2 ≈7.3+32.9≈40.2s.

[0142] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 42.8s. It can be seen that the total residence time of the flue gas calculated in this embodiment is t all This is very close to the total residence time of flue gas obtained during actual operation, indicating that the above calculation method of this embodiment can more accurately obtain the total residence time of flue gas during operation of the drying tower.

[0143] Example 6

[0144] The wastewater zero discharge monitoring method of this embodiment is based on the total flue gas residence time t calculated by the method of Example 3. all≈30.1s, the actual value of adjusting the flue gas flow is 63625Nm 3 / h (ie: at 63625Nm 3 / h actual flue gas flow rate, the corresponding actual value of the total flue gas residence time is 30.1s), and other parameters are the same as those in Example 3.

[0145] The actual operation is performed according to the flue gas flow rate after the above adjustment. During the actual operation, the total residence time of the flue gas t is calculated according to the method of Example 3. all , and the wastewater flow and flue gas flow of the drying tower are regulated as follows:

[0146] When 30s≤t all <35s and the flue gas temperature at the drying tower outlet is T 2 When maintained at 428K-448K, the wastewater flow and flue gas flow remain unchanged;

[0147] When t all <30s, reduce the wastewater flow and flue gas flow until 30s≤t all <35s and the flue gas temperature at the drying tower outlet is T 2 Maintained at 428K-448K;

[0148] When t all ≥35s, increase the wastewater flow and flue gas flow until 30s≤t all <35s and the flue gas temperature at the drying tower outlet is T 2 Maintain at 428K-448K.

[0149] Sampling was carried out after running for different time periods, and the ash moisture content at the drying tower outlet was tested respectively. The results are shown in Table 1. The results show that the ash moisture content at the drying tower outlet measured by five samplings was within the range of 1-2%, and the average ash moisture content measured by five samplings was 1.39%, which met the industry standard requirements (the ash moisture content at the drying tower outlet does not exceed 2%).

[0150] Example 7

[0151] The wastewater zero discharge monitoring method of this embodiment is based on the total flue gas residence time t calculated by the method of Example 4. all ≈35.1s, the actual value of adjusting the flue gas flow is 32760Nm 3 / h (ie: at 32760Nm 3 / h actual flue gas flow rate, the corresponding actual value of the total flue gas residence time is 35.1s), and other parameters are the same as those in Example 4.

[0152] The actual operation is performed according to the flue gas flow rate adjusted as above; during the actual operation, the total residence time t of the flue gas is calculated according to the method of Example 4.all , and the wastewater flow and flue gas flow of the drying tower are regulated as follows:

[0153] When 35s≤t all <40s and the flue gas temperature at the drying tower outlet is T 2 When maintained at 428K-448K, the wastewater flow and flue gas flow remain unchanged;

[0154] When t all <35s, reduce the wastewater flow and flue gas flow until 35s≤t all <40s and the flue gas temperature at the drying tower outlet is T 2 Maintained at 428K-448K;

[0155] When t all ≥40s, increase the wastewater flow and flue gas flow until 35s≤t all <40s and the flue gas temperature at the drying tower outlet is T 2 Maintain at 428K-448K.

[0156] Sampling was carried out after running for different time periods to test the ash moisture content at the drying tower outlet. The results showed that the ash moisture content at the drying tower outlet measured by five samplings was within the range of 1-2%, and the average ash moisture content measured by five samplings was 1.15%, which met the industry standard requirements.

[0157] Example 8

[0158] The wastewater zero discharge monitoring method of this embodiment is based on the total flue gas residence time t calculated by the method of Example 5. all ≈40.2s, the actual value of adjusting the flue gas flow is 31254Nm 3 / h (ie: at 31254Nm 3 / h actual flue gas flow rate, the corresponding actual value of the total flue gas residence time is 40.2s), and other parameters are the same as those in Example 5.

[0159] The actual operation is performed according to the flue gas flow rate adjusted as above; during the actual operation, the total residence time t of the flue gas is calculated according to the method of Example 5. all , and the wastewater flow and flue gas flow of the drying tower are regulated as follows:

[0160] When 40s≤t all ≤45s and the flue gas temperature at the drying tower outlet is T 2 When maintained at 428K-448K, the wastewater flow and flue gas flow remain unchanged;

[0161] When t all <40s, reduce the wastewater flow and flue gas flow until 40s≤tall ≤45s and the flue gas temperature at the drying tower outlet is T 2 Maintained at 428K-448K;

[0162] When t all >45s, increase the wastewater flow and flue gas flow until 40s≤t all ≤45s and the flue gas temperature at the drying tower outlet is T 2 Maintain at 428K-448K.

[0163] Sampling was carried out after running for different time periods to test the ash moisture content at the drying tower outlet. The results showed that the ash moisture content at the drying tower outlet measured by five samplings was within the range of 1-2%, and the average ash moisture content measured by five samplings was 1.52%, which met the industry standard requirements.

[0164] Comparative Example 1

[0165] Except for using the average flow rate method to obtain the total residence time of the flue gas, the other conditions are the same as those in Example 3; the average flow rate is calculated as follows:

[0166] Average temperature

[0167] Average flow rate

[0168] The total residence time of flue gas is:

[0169] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 33.2s. It can be seen that the total residence time of the flue gas calculated in this comparative example is t all There is a big difference between the total residence time of flue gas obtained from actual operation and the total residence time of flue gas obtained from actual operation, which indicates that the above calculation method of this comparative example cannot accurately obtain the total residence time of flue gas during operation of the drying tower.

[0170] The total flue gas residence time t obtained from the above calculation all ≈26.7s, the actual value of adjusting the flue gas flow is 71536Nm 3 / h (ie: the actual flue gas flow rate is 71536Nm 3 / h, the actual value of the corresponding total residence time of flue gas is 26.7s); the actual operation was carried out according to the adjusted flue gas flow rate, and the results showed that the moisture content of ash at the outlet of the drying tower was 2.81%, which could not meet the industry standard requirements.

[0171] Comparative Example 2

[0172] Except for using the average flow rate method to obtain the total residence time of the flue gas, the other conditions are the same as those in Example 4; the average flow rate is calculated as follows:

[0173] Average temperature

[0174] Average flow rate

[0175] The total residence time of flue gas is:

[0176] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 37.8s. It can be seen that the total residence time of the flue gas calculated in this comparative example is t all There is a big difference between the total residence time of flue gas obtained from actual operation and the total residence time of flue gas obtained from actual operation, which indicates that the above calculation method of this comparative example cannot accurately obtain the total residence time of flue gas during operation of the drying tower.

[0177] The total flue gas residence time t obtained from the above calculation all ≈31.2s, the actual value of the adjusted flue gas flow is 36643Nm 3 / h (ie: the actual flue gas flow rate is 36643Nm 3 / h, the actual value of the corresponding total flue gas residence time is 31.2s); according to the actual operation of the adjusted flue gas flow rate, the results show that the moisture content of the ash at the drying tower outlet is 3.40%, which cannot meet the industry standard requirements.

[0178] Comparative Example 3

[0179] Except for using the average flow rate method to obtain the total residence time of the flue gas, the other conditions are the same as those in Example 5; the average flow rate is calculated as follows:

[0180] Average temperature

[0181] Average flow rate

[0182] The total residence time of flue gas is:

[0183] According to the above parameters, the actual value of the total residence time of the flue gas in the drying tower is 42.8s. It can be seen that the total residence time of the flue gas calculated in this comparative example is t all There is a big difference between the total residence time of flue gas obtained from actual operation and the total residence time of flue gas obtained from actual operation, which indicates that the above calculation method of this comparative example cannot accurately obtain the total residence time of flue gas during operation of the drying tower.

[0184] In addition, the total flue gas residence time t obtained from the above calculation is all ≈33.6s, the actual value of adjusting the flue gas flow is 37420Nm 3 / h (ie: the actual flue gas flow rate is 37420Nm 3 / h, the actual value of the corresponding total flue gas residence time is 33.6s); the actual operation was carried out according to the adjusted flue gas flow rate. The results showed that the ash moisture content at the drying tower outlet was 3.15%, which could not meet the industry standard requirements.

[0185] Comparative Example 4

[0186] Except that the wastewater flow rate and the flue gas flow rate are not regulated during the actual operation, the rest is the same as Example 6.

[0187] Sampling and testing were carried out according to the method of Example 6; the results are shown in Table 1.

[0188] Comparative Example 5

[0189] Except that the wastewater flow rate and flue gas flow rate are regulated in the following manner during the actual operation, the other conditions are the same as those in Example 6.

[0190] In this comparative example, the flue gas temperature Tout at the drying tower outlet is monitored during operation. According to the flue gas temperature Tout at the drying tower outlet, the wastewater and flue gas flow rates entering the drying tower are adjusted in the following manner:

[0191] If 150℃≤Tout≤160℃, maintain the wastewater and gas flow rates unchanged;

[0192] If Tout is less than 150°C, reduce the wastewater flow rate entering the drying tower and / or increase the flue gas flow rate entering the drying tower until Tout rises to 150°C ≤ Tout ≤ 160°C;

[0193] If Tout>160℃, increase the wastewater flow rate entering the drying tower and / or reduce the flue gas flow rate entering the drying tower until Tout decreases to 150℃≤Tout≤160℃.

[0194] Sampling and testing were carried out according to the method of Example 6; the results are shown in Table 1.

[0195] Table 1 Test results of moisture content of ash at the outlet of drying tower

[0196]

[0197]

[0198] The results show that:

[0199] 1. The method of Example 6 is adopted for operation, and the wastewater drying effect is good. The moisture content of the ash at the drying tower outlet can be stably maintained at 1-2%, which can effectively overcome various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower. The moisture content of the ash at the drying tower outlet meets the requirements of industry standards and will not have an adverse effect on the resource utilization of the ash (i.e., fly ash). The operating stability of the drying tower is good, and no operating failure occurs.

[0200] 2. When the method of Control Example 4 is adopted, without adjusting the flue gas flow rate and the wastewater flow rate, the wastewater drying effect is poor, and the various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower cannot be overcome. The moisture content of the ash at the outlet of the drying tower fluctuates greatly, and the drying tower has problems such as wet ash and blockage, which seriously affects the stable operation of the drying tower and the resource utilization of the ash.

[0201] 3. The method of Control Example 5 was adopted to adjust the wastewater and gas flow rates using the flue gas temperature at the drying tower outlet as a reference value. The wastewater drying effect was unstable, and problems such as wet ash and blockage occurred during operation, which had an adverse effect on the normal operation of the drying tower. At the same time, part of the ash agglomerated and compacted, affecting the resource utilization of the ash.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring zero discharge of wastewater, characterized in that: The steps include: S1: The wastewater is atomized and sent to a drying tower, high-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets, and the flue gas temperature T2 at the drying tower outlet is monitored in real time; S2: Obtain the movement time t1 of the flue gas in the constant speed evaporation stage and the movement time t2 of the flue gas in the decreasing speed evaporation stage respectively, and obtain the total residence time t of the flue gas according to the movement time t1 and the movement time t2 all , t all =t1+t2; S3: According to the total residence time of flue gas t all The wastewater flow and flue gas flow are regulated, and the flue gas temperature T2 at the drying tower outlet is maintained at 428K-448K.

2. The method for monitoring zero discharge of wastewater according to claim 1, characterized in that: The movement time t1 of the flue gas in the constant evaporation stage is obtained by the following formula: Among them: t1 is the movement time of flue gas in the constant rate evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a1 and b1 are model parameters; L1 is the vertical flow distance of flue gas in the constant rate evaporation stage.

3. The method for monitoring zero discharge of wastewater according to claim 2, characterized in that: Get a1 and b1 through the following formula: b1=T1 Where: T c It is the critical temperature of flue gas between the constant rate evaporation stage and the decreasing rate evaporation stage; T1 is the inlet flue gas temperature.

4. The method for monitoring zero discharge of wastewater according to claim 1, characterized in that: The movement time t2 of the flue gas in the deceleration evaporation stage is obtained by the following formula: Among them: t2 is the movement time of flue gas in the deceleration evaporation stage; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower; n is the molar flow rate; R is the gas constant; a2 and b2 are model parameters; L2 is the vertical flow distance of flue gas in the deceleration evaporation stage.

5. The method for monitoring zero discharge of wastewater according to claim 4, characterized in that: Get a2 and b2 using the following formula: b2=T c Where: T2 is the outlet flue gas temperature; T c is the critical temperature of the flue gas between the constant rate evaporation stage and the decreasing rate evaporation stage; h is the height of the hollow cylinder in the drying tower; L1 is the vertical flow distance of the flue gas in the constant rate evaporation stage.

6. The method for monitoring zero discharge of wastewater according to claim 1, characterized in that: According to the solid content x of the wastewater, the total residence time t of the flue gas is determined as follows all Control interval: When x≤10%, control 30s≤t all <35s; When 10%<x≤20%, control 35s≤t all <40s; When 20%<x≤30%, control 40s≤t all ≤45s.

7. The method for monitoring zero discharge of wastewater according to claim 6, characterized in that: The wastewater flow and flue gas flow are regulated as follows: When the total residence time of smoke is t all When the flue gas temperature T2 at the drying tower outlet is maintained at 428K-448K within the control range, the wastewater flow rate and flue gas flow rate are maintained unchanged; When the total residence time of smoke is t all When it is lower than the lower limit of the control interval, reduce the wastewater flow and flue gas flow until the total residence time of the flue gas is t all The flue gas temperature T2 at the drying tower outlet is maintained within the control range and is maintained at 428K-448K, and the gas flow rate reduction rate is controlled not to exceed the wastewater flow rate reduction rate; When the total residence time of smoke is t all When it is higher than the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate until the total residence time of the flue gas is t all The flue gas temperature T2 at the drying tower outlet is within the control range and is maintained at 428K-448K, and the increase rate of the wastewater flow rate is controlled not to exceed the increase rate of the gas flow rate.

8. The method for monitoring zero discharge of wastewater according to claim 1, characterized in that: The wastewater is atomized by a rotary atomizer, and the particle size of the wastewater droplets formed by atomization is 10-60μm.

9. A wastewater zero discharge monitoring system for implementing the wastewater zero discharge monitoring method according to any one of claims 1 to 8, characterized in that: The invention comprises a drying tower and a controller. A rotary atomizer is arranged on the top of the drying tower. The rotary atomizer is connected to a wastewater pipe. A wastewater regulating valve is arranged on the wastewater pipe. An inlet flue and an outlet flue are arranged at the upper and lower parts of the drying tower respectively. A flue gas regulating valve, an inlet thermometer and a flow meter are arranged on the inlet flue. An outlet thermometer is arranged on the outlet flue. A thermometer and a pressure gauge along the way are arranged on the drying tower. The controller is provided with a calculation module. The calculation module can calculate the movement time t1 of the flue gas in the constant speed evaporation stage, the movement time t2 in the speed reduction evaporation stage and the total residence time t of the flue gas according to the data fed back by the inlet thermometer, the outlet thermometer, the thermometer along the way, the flow meter and the pressure gauge. all The controller is based on the total residence time of the flue gas t all The wastewater regulating valve and the flue gas regulating valve are controlled to regulate the wastewater flow and the flue gas flow.

10. The wastewater zero discharge monitoring system according to claim 9, characterized in that: According to the solid content x of the wastewater, set the temperature meter along the process as follows: When x≤10%, set the along-the-way thermometer at a distance of 4.5-5.4m from the top of the drying tower; When 10%<x≤20%, set the temperature meter along the drying tower at a distance of 3.5-4.4m from the top of the drying tower; When 20%<x≤30%, set the along-the-way thermometer at a distance of 2.5-3.4m from the top of the drying tower.

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