Zero wastewater discharge monitoring method and system

Abstract

Provided in the present invention are a zero wastewater discharge monitoring method and system. The zero wastewater discharge monitoring method of the present invention comprises the following steps: S1, atomizing wastewater and then feeding atomized wastewater droplets into a drying tower, introducing high-temperature flue gas into the drying tower to evaporate and dry the atomized wastewater droplets, and monitoring in real time a flue gas temperature T2 at an outlet of the drying tower; S2, respectively acquiring a motion time t1 of the flue gas in a constant-rate evaporation phase and a motion time t2 of the flue gas in a falling-rate evaporation phase, and on the basis of the motion time t1 and the motion time t2, acquiring a total residence time tall of the flue gas, wherein tall=t1+t2; and S3, on the basis of the total residence time tall of the flue gas, regulating and controlling the wastewater flow rate and the flue gas flow rate, and maintaining the flue gas temperature T2 at the outlet of the drying tower within the range of 428-448 K. The zero wastewater discharge monitoring method and system of the present invention fully consider the law of variation of the flue gas flow velocity with temperature in a drying tower, thereby improving the monitoring accuracy of the system, and ensuring the operational stability of the system.

Description

A wastewater zero-discharge monitoring method and system Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a wastewater zero-discharge monitoring method and system. Background Technology

[0002] High-salinity wastewater from thermal power plants (such as chemical regeneration wastewater and wet desulfurization wastewater) has a complex composition, and direct discharge would cause serious environmental pollution. Currently, rotary atomization drying technology is one of the mainstream technologies in the power industry to achieve zero discharge of high-salinity wastewater. This technology uses a drying tower, which atomizes the wastewater into droplets using high-speed rotation and sprays them into the drying tower. At the same time, high-temperature flue gas from the thermal power plant is drawn into the drying tower. The high-temperature flue gas and the wastewater droplets exchange heat fully 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 the gas-liquid two-phase fluid and is a key parameter affecting the zero-emission effect of wastewater evaporation. At present, the calculation method of residence time is relatively crude. Generally, the average flow velocity of flue gas in the drying tower can only be calculated by the average of the flue gas temperature at the inlet and outlet of the drying tower, and then the residence time of flue gas can be calculated by the height of the drying tower.

[0004] However, since the drying process of wastewater in the drying tower includes two stages—constant-rate evaporation and falling-rate evaporation—the temperature of the flue gas continuously decreases during its downward flow, and the rate of temperature decrease varies, leading to corresponding changes in its flow velocity. Existing methods for calculating residence time cannot reflect the variation of flow velocity with temperature. Calculating flue gas residence time using average temperature and average flow velocity can easily lead to unreasonable operation and control of the zero-discharge wastewater system, resulting in insufficient system output or poor zero-discharge performance, which in turn seriously affects the stable operation of the system.

[0005] In addition, the physical properties of high-temperature flue gas from thermal power plants are somewhat volatile. Since these parameters are unstable and cannot be controlled, when using this high-temperature flue gas to evaporate and dry wastewater, unstable evaporation effects and malfunctions such as wet ash, blockage, and corrosion may occur, which will have a serious adverse impact on the normal operation of the drying tower.

[0006] To ensure zero wastewater discharge, it is necessary to adopt a more reasonable method to calculate the flue gas residence time and adjust the system operating parameters accordingly.

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

[0008] Summary of the Invention

[0009] The purpose of this invention is to provide a wastewater zero-discharge monitoring method and system that fully considers the variation law of flue gas velocity in the drying tower with temperature, improves the operational stability of the drying tower, and ensures the wastewater drying effect.

[0010] This invention provides a method for monitoring zero wastewater discharge, comprising the following steps:

[0011] S1: The wastewater is atomized and sent into the drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The temperature of the flue gas at the outlet of the drying tower, T2, is monitored in real time.

[0012] S2: Obtain the travel time t1 of the flue gas during the constant-rate evaporation stage and the travel time t2 during the decreasing-rate evaporation stage, respectively, and obtain the total residence time t of the flue gas based on the travel time t1 and the travel time t2. all , t all =t1+t2;

[0013] S3: Based on the total residence time of flue gas t all The flow rates of wastewater and flue gas are regulated, and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K.

[0014] In step S1, the upper part of the drying tower is a hollow cylinder, which is the main site for wastewater evaporation and drying; 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 installed at the top of the drying tower to atomize the wastewater. The rotation speed of the rotary atomizer is controlled at 12000-18000 r / min, and the particle size of the atomized wastewater droplets is 10-60 μm.

[0015] In step S2, the evaporation process of wastewater droplets inside the drying tower includes two stages: constant-rate evaporation and decelerating evaporation. Constant-rate evaporation occurs in the upper part of the drying tower. In this stage, the moisture on the surface of the wastewater droplets rapidly exchanges heat with the high-temperature flue gas, causing the flue gas temperature to drop sharply and the wastewater to evaporate quickly. The dissolved salts and suspended solids in the wastewater form a solid shell, which slows down the evaporation rate. Decelerating evaporation occurs in the lower part of the drying tower. Due to the influence of the formed solid shell, the wastewater evaporates slowly, and the flue gas temperature drops slowly.

[0016] After the flue gas enters the drying tower, its vertical velocity can be calculated using the following formula:

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

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

[0019] From the top of the drying tower to the friction-measuring thermometer, the wastewater undergoes a constant-rate evaporation phase. Within this distance, the flue gas temperature drops sharply as it moves downwards. The following linear model simulates the variation of flue gas temperature with vertical distance traveled:

[0020] T = a1L + b1

[0021] Where: L is the vertical movement distance of the flue gas (starting from the top of the drying tower); a1 and b1 are model parameters.

[0022] Let T c T1 is the reading of the friction-feed thermometer (i.e., the critical temperature of the flue gas between the constant-rate evaporation stage and the falling-rate evaporation stage), T1 is the inlet flue gas temperature, and L1 is the distance of the friction-feed thermometer from the top of the drying tower (i.e., the vertical flow distance of the flue gas during the constant-rate evaporation stage, approximately 2.5-5.4m).

[0023] When L = 0, T = T1; when L = L1, T = T c Therefore, a1 and b1 can be obtained using the following formula:

[0024] b1 = T1

[0025] Wherein: T c T1 is the critical temperature of the flue gas between the constant-rate evaporation stage and the falling-rate evaporation stage; L1 is the inlet flue gas temperature; and L1 is the vertical flow distance of the flue gas during the constant-rate evaporation stage.

[0026] Since the vertical velocity of the flue gas is the derivative of the vertical distance traveled and the time of travel, that is:

[0027] The flue gas travel time t (starting from the top of the drying tower) is calculated using the following formula:

[0028] When L = 0, t = 0, we can obtain:

[0029] During the constant-rate evaporation stage, let L = L1, and the movement time of the flue gas during the constant-rate evaporation stage can be calculated and denoted as t1.

[0030] That is, the travel time t1 of the flue gas during the constant-rate evaporation stage can be obtained by the following formula:

[0031] Where: t1 is the travel time of flue gas during 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 during the constant-rate evaporation stage.

[0032] From the friction-measuring thermometer to the bottom outlet flue of the drying tower, the wastewater undergoes a slow evaporation phase. Within this distance, the flue gas temperature decreases slowly as it moves downwards. The variation of flue gas temperature with vertical distance traveled is simulated by the following linear function:

[0033] T = a²L + b²

[0034] Where: L is the vertical movement distance of the flue gas (taken as the starting point of the deceleration evaporation, denoted as L2); a2 and b2 are model parameters.

[0035] Let T2 be the outlet flue gas temperature, and h be the height of the hollow cylinder in the drying tower. When L = 0, we have T = T c When L = h - L1, T = T2. Therefore, a2 and b2 can be obtained using the following formulas:

[0036] b2 = T c

[0037] 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 falling-rate evaporation stage; h is the height of the hollow cylinder in the drying tower (i.e., the height of the upper hollow cylinder in the drying tower); L1 is the vertical flow distance of the flue gas during the constant-rate evaporation stage.

[0038] The vertical velocity of the flue gas is the derivative of the vertical distance traveled with respect to the time of travel, that is:

[0039] The flue gas travel time t (with the starting point of falling evaporation as the starting point, denoted as t2) is calculated using the following formula:

[0040] When L = 0, t = 0, we can obtain:

[0041] During the slow-evaporation stage, let L = h - L1 = L2, and we can calculate the time of the flue gas movement during the slow-evaporation stage, denoted as t2.

[0042] That is, the travel time t2 of the flue gas during the slowing evaporation stage can be obtained by the following formula:

[0043] Where: t2 is the travel time of flue gas during the falling-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; a2 and b2 are model parameters; L2 is the vertical flow distance of flue gas during the falling-rate evaporation stage.

[0044] The total residence time t of the flue gas is determined according to the solids content x of the wastewater as follows: all Control range:

[0045] When the solid content x of the wastewater is x≤10%, the total residence time t of the flue gas is... all The control interval is [30s, 35s), that is, 30s ≤ t all <35s;

[0046] When the solid content x of the wastewater is 10% < x ≤ 20%, the total residence time t of the flue gas is... all The control interval is [35s, 40s), that is, 35s ≤ t all <40s;

[0047] When the solid content x of the wastewater is 20% < x ≤ 30%, the total residence time t of the flue gas is... all The control interval is [40s, 45s], that is, 40s ≤ t all ≤45s.

[0048] In addition, the gas-liquid ratio is adjusted as follows:

[0049] When the total residence time of flue gas t all When the temperature of the flue gas at the outlet of the drying tower is maintained at 428K-448K within the control range, the wastewater flow rate and flue gas flow rate are kept constant.

[0050] When the total residence time of flue gas t all When the flow rate is below the lower limit of the control range, reduce the wastewater flow rate and flue gas flow rate until the total flue gas residence time t is reached. all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the reduction rate of gas flow rate is controlled to not exceed the reduction rate of wastewater flow rate.

[0051] When the total residence time of flue gas t all When the flow rates exceed the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate until the total flue gas residence time t is reached. all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the increase rate of wastewater flow rate is controlled not to exceed the increase rate of gas flow rate.

[0052] The above control method can obtain the corresponding total residence time t of flue gas based on the variable flow law of flue gas. all At the same time, based on the total residence time t of the flue gas allThe control range coordinates the flow rates of wastewater and flue gas during the operation of the drying tower, thereby effectively overcoming problems such as unstable temperature of the high-temperature flue gas entering the drying tower. This helps to avoid unstable evaporation effects and malfunctions such as wet ash, blockage, and corrosion caused by poor evaporation during the operation of the drying tower, ensuring its stable operation.

[0053] This 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. A rotary atomizer is installed at the top of the drying tower and connected to a wastewater pipeline. A wastewater regulating valve is installed on the wastewater pipeline. An inlet flue and an outlet flue are respectively installed at the upper and lower parts of the drying tower. A flue gas regulating valve, an inlet thermometer, and a flow meter are installed on the inlet flue. An outlet thermometer is installed on the outlet flue. A friction thermometer and a pressure gauge are installed on the drying tower. The controller includes a calculation module that can calculate the flue gas travel time t1 during the constant-rate evaporation stage, the travel time t2 during the decreasing-rate evaporation stage, and the total residence time t of the flue gas based on data fed back from the inlet thermometer, outlet thermometer, friction thermometer, flow meter, and pressure gauge. all The controller is based on the total residence time t of the flue gas. all The wastewater regulating valve and the flue gas regulating valve are controlled to regulate the wastewater flow and flue gas flow.

[0054] Specifically, the upper part of the drying tower is a hollow cylinder, and the bottom is a hollow cone. The inlet flue and outlet flue are respectively located at the upper and lower parts of the hollow cylinder. A rotary atomizer is used to atomize the wastewater, and the rotary atomizer can be located at the center of the top of the drying tower. A wastewater regulating valve is used to regulate the wastewater flow rate. A flue gas regulating valve is used to regulate the flue gas flow rate. An inlet thermometer is used to monitor the inlet flue gas temperature T1 in real time, and a flow meter is used to monitor the flue gas volumetric flow rate V in real time, which is converted to obtain the molar flow rate n. The inlet thermometer and flow meter can be installed at a depth of 1 / 2 diameter inside the inlet flue, with a spacing of 0.8-1.2m between them. An outlet thermometer is used to monitor the outlet flue gas temperature T2 in real time and can be installed at a depth of 1 / 2 diameter inside the outlet flue. A friction thermometer is used to monitor the critical temperature T between the constant-rate evaporation stage and the falling-rate evaporation stage of the flue gas in real time. c It 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 1 / 2 the height of the hollow cylinder and at a depth of 1 / 8 of the diameter inside the hollow cylinder.

[0055] Furthermore, based on the solids content x of the wastewater, the flow path thermometers are set up as follows:

[0056] When the solid content x of the wastewater is x≤10%, the friction temperature gauge should be set at a distance of 4.5-5.4m from the top of the drying tower.

[0057] The solids content x of the wastewater is: 10% < x ≤ 20%. The friction temperature gauge is set at a distance of 3.5-4.4m from the top of the drying tower.

[0058] The solids content x of the wastewater is 20% < x ≤ 30%. The flow temperature meter is set at a distance of 2.5-3.4m from the top of the drying tower.

[0059] This invention establishes a wastewater zero-discharge monitoring method and system based on the characteristics of wastewater during constant-rate evaporation and falling-rate evaporation stages. By monitoring key parameters, it provides a data foundation for establishing a kinetic model. The method and system fully consider the relationship between flue gas velocity and temperature in different evaporation stages, establishing linear models for flue gas movement time and distance, and deriving a kinetic model for calculating the total residence time of flue gas, thus improving the accuracy of the calculation. Furthermore, based on the calculation of the total residence time of flue gas using the kinetic model, corresponding intelligent control methods are formulated for different types of wastewater. This ensures both the wastewater treatment effect and capacity of the drying tower, while effectively overcoming various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower, improving the operational stability of the drying tower, and guaranteeing the wastewater drying effect. Attached Figure Description

[0060] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0061] Figure 1 is a schematic diagram of the structure of the drying tower of the present invention.

[0062] Explanation of reference numerals in the attached figures:

[0063] 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: Friction thermometer; 10: Pressure gauge; 11: Flow meter; 12: Wastewater regulating valve. Detailed Implementation

[0064] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0065] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0066] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Example 1

[0068] The wastewater zero-discharge monitoring method of this embodiment includes the following steps:

[0069] S1: The wastewater is atomized and sent into the drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The temperature of the flue gas at the outlet of the drying tower, T2, is monitored in real time.

[0070] S2: Obtain the travel time t1 of the flue gas during the constant-rate evaporation stage and the travel time t2 during the decreasing-rate evaporation stage, respectively, and obtain the total residence time t of the flue gas based on the travel time t1 and the travel time t2. all , t all =t1+t2;

[0071] S3: Based on the total residence time of flue gas t all The flow rates of wastewater and flue gas are regulated, and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K.

[0072] Specifically, a rotary atomizer is used to atomize the wastewater, with the atomizer speed controlled at 12000-18000 r / min, and the particle size of the wastewater droplets formed by atomization is 10-60 μm.

[0073] During the evaporation and drying process, the inlet flue gas temperature T1, the outlet flue gas temperature T2, and the critical temperature T between the constant-rate evaporation stage and the falling-rate evaporation stage are monitored. c Real-time monitoring of relevant parameters such as flue gas pressure P and flue gas volumetric flow rate V; calculation of the cross-sectional area of ​​the drying tower based on the tower diameter; and calculation of the molar flow rate n based on the flue gas volumetric flow rate V.

[0074] a1 and b1 can be obtained using the following formula:

[0075] b1 = T1

[0076] Wherein: T c T1 is the critical temperature of the flue gas between the constant-rate evaporation stage and the falling-rate evaporation stage; T2 is the inlet flue gas temperature.

[0077] The time t1 of the flue gas during the constant-rate evaporation stage can be obtained using the following formula:

[0078] Where: t1 is the travel time of flue gas during 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 during the constant-rate evaporation stage.

[0079] a2 and b2 can be obtained using the following formula:

[0080] b2 = T c

[0081] 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 falling-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 during the constant-rate evaporation stage.

[0082] The time t2 of the flue gas during the slowing evaporation stage can be obtained using the following formula:

[0083] Where: t2 is the travel time of flue gas during the falling-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; a2 and b2 are model parameters; L2 is the vertical flow distance of flue gas during the falling-rate evaporation stage.

[0084] After obtaining the travel time t1 of the flue gas during the constant-rate evaporation stage and the travel time t2 during the decreasing-rate evaporation stage, according to t all =t1+t2 to obtain the total residence time t of the flue gas all .

[0085] The total residence time t of the flue gas is determined as follows: all Control range:

[0086] When the solid content x of the wastewater is x≤10%, the total residence time t of the flue gas is... all The control interval is [30s, 35s);

[0087] When the solid content x of the wastewater is 10% < x ≤ 20%, the total residence time t of the flue gas is... all The control interval is [35s, 40s);

[0088] When the solid content x of the wastewater is 20% < x ≤ 30%, the total residence time t of the flue gas is... all The control range is [40s, 45s].

[0089] Based on the obtained total residence time t of the flue gas all And the total residence time t of the flue gas as described above all Within the control range, the wastewater flow rate and flue gas flow rate are regulated as follows:

[0090] When the total residence time of flue gas t all When the temperature of the flue gas at the outlet of the drying tower is maintained at 428K-448K within the control range, the wastewater flow rate and flue gas flow rate are kept constant.

[0091] When the total residence time of flue gas t all When the flow rate is below the lower limit of the control range, reduce the wastewater flow rate and flue gas flow rate until the total flue gas residence time t is reached. all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the reduction rate of gas flow rate is controlled to not exceed the reduction rate of wastewater flow rate.

[0092] When the total residence time of flue gas t all When the flow rates exceed the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate until the total flue gas residence time t is reached. all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the increase rate of wastewater flow rate is controlled not to exceed the increase rate of gas flow rate.

[0093] Example 2

[0094] Referring to Figure 1, 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 installed at the top of the drying tower 1, and the rotary atomizer 2 is connected to a wastewater pipe 5. A wastewater regulating valve 12 is installed on the wastewater pipe 5. An inlet flue duct 3 and an outlet flue duct 4 are respectively installed at the upper and lower parts of the drying tower 1. A flue gas regulating valve 7, an inlet thermometer 8, and a flow meter 11 are installed on the inlet flue duct 3. An outlet thermometer 6 is installed on the outlet flue duct 4. A friction thermometer 9 and a pressure gauge 10 are installed on the drying tower 1. The controller has a calculation module that can calculate the travel time t1 of the flue gas in the constant-rate evaporation stage, the travel time t2 in the decreasing-rate evaporation stage, and the total residence time t of the flue gas based on the data fed back from the inlet thermometer 8, outlet thermometer 6, friction thermometer 9, flow meter 11, and pressure gauge 10. all The controller is based on the total residence time t of the flue gas. all The wastewater regulating valve 12 and the flue gas regulating valve 7 are controlled to regulate the wastewater flow rate and the flue gas flow rate.

[0095] Specifically, the upper part of the drying tower 1 is a hollow cylinder, and the bottom is a hollow cone. The inlet flue 3 and the outlet flue 4 are respectively located at the upper and lower parts of the hollow cylinder. The rotary atomizer 2 is used to atomize the wastewater and can be located at the center of the top of the drying tower 1. The wastewater regulating valve 12 is used to regulate the wastewater flow rate. The flue gas regulating valve 7 is used to regulate the flue gas flow rate. The inlet thermometer 8 is used to monitor the inlet flue gas temperature T1 in real time, and the flow meter 11 is used to monitor the flue gas volumetric flow rate V in real time. The molar flow rate n is obtained after 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, with a spacing of 0.8-1.2m between them. The outlet thermometer 6 is used to monitor the outlet flue gas temperature T2 in real time and can be installed at a depth of 1 / 2 diameter inside the outlet flue 4. The friction thermometer 9 is used to monitor the critical temperature T between the constant-rate evaporation stage and the falling-rate evaporation stage of the flue gas in real time. c The pressure gauge 10 is used to monitor the flue gas pressure P in real time and can be installed at 1 / 2 the height of the hollow cylinder and at 1 / 8 the depth of the hollow cylinder.

[0096] Based on the solids content x of the wastewater, the friction-line thermometer 9 should be installed as follows:

[0097] When the solid content x of the wastewater is x≤10%, the friction thermometer 9 is set at a distance of 4.5-5.4m from the top of the drying tower 1;

[0098] The solid content x of the wastewater is: 10% < x ≤ 20%. The friction thermometer 9 is set at a distance of 3.5-4.4m from the top of the drying tower 1.

[0099] The solid content x of the wastewater is 20% < x ≤ 30%. The friction thermometer 9 is set at a distance of 2.5-3.4m from the top of the drying tower 1.

[0100] Example 3

[0101] The wastewater zero-discharge monitoring system of Example 2 was used for evaporative drying of wastewater; the parameters are as follows: wastewater solids content x is 5%, inlet flue gas temperature T1 is 633K, outlet flue gas temperature T2 is 448K, the diameter of the drying tower is 8.5m, the height h of the hollow cylinder in the drying tower is 15m, and the friction-measuring thermometer is set at a position 5m away from the top of the drying tower (i.e., L1 is 5m); the design value of the flue gas flow rate is 58100Nm³. 3 / h.

[0102] During the constant-rate evaporation stage, we have:

[0103] Flue gas temperature: T=a1L+b1=-34.6L+633.

[0104] The travel time of flue gas during the constant-rate evaporation stage:

[0105] During the slowing evaporation stage, we have:

[0106] Flue gas temperature: T=a2L+b2=-1.2L+460.

[0107] The travel time of flue gas during the slowing evaporation phase:

[0108] Total residence time of flue gas: t all =t1+t2≈8.9+21.2≈30.1s.

[0109] Based on the above parameters, actual operation was conducted, and the measured total residence time of the flue gas in the drying tower was 33.2 s. Therefore, the total residence time t calculated in this embodiment is... all The result is very close to the total residence time of flue gas obtained from actual operation, indicating that the above calculation method in this embodiment can obtain the total residence time of flue gas during the operation of the drying tower relatively accurately.

[0110] Example 4

[0111] The wastewater zero-discharge monitoring system of Example 2 was used for evaporative drying of wastewater. The parameters were as follows: wastewater solids content x was 17%, inlet flue gas temperature T1 was 611K, outlet flue gas temperature T2 was 438K, the diameter of the drying tower was 7.5m, the height h of the hollow cylinder in the drying tower was 11.5m, and the friction-measuring thermometer was set at a distance of 4m from the top of the drying tower (i.e., L1 was 4m); the design value of the flue gas flow rate was 30700 Nm³. 3 / h.

[0112] During the constant-rate evaporation stage, we have:

[0113] Flue gas temperature: T=a1L+b1=-41.3L+611.

[0114] The travel time of flue gas during the constant-rate evaporation stage:

[0115] During the slowing evaporation stage, we have:

[0116] Flue gas temperature: T=a2L+b2=-1.1L+446.

[0117] The travel time of flue gas during the slowing evaporation phase:

[0118] Total residence time of flue gas: t all =t1+t2≈10.9+24.2≈35.1s.

[0119] Based on the above parameters, the actual total residence time of the flue gas in the drying tower was measured to be 37.8 s. Therefore, the total residence time t calculated in this embodiment is... all The result is very close to the total residence time of flue gas obtained from actual operation, indicating that the above calculation method in this embodiment can obtain the total residence time of flue gas during the operation of the drying tower relatively accurately.

[0120] Example 5

[0121] The wastewater zero-discharge monitoring system of Example 2 was used for evaporative drying of wastewater; the parameters are as follows: wastewater solids content x is 25%, inlet flue gas temperature T1 is 645K, outlet flue gas temperature T2 is 428K, the diameter of the drying tower is 7m, the height h of the hollow cylinder in the drying tower is 14m, and the friction-meter is set at a position 3m away from the top of the drying tower (i.e., L1 is 3m); the design value of the flue gas flow rate is 29600Nm³. 3 / h.

[0122] During the constant-rate evaporation stage, we have:

[0123] Flue gas temperature: T=a1L+b1=-70L+645.

[0124] The travel time of flue gas during the constant-rate evaporation stage:

[0125] During the slowing evaporation stage, we have:

[0126] Flue gas temperature: T=a2L+b2=-0.6L+435.

[0127] The travel time of flue gas during the slowing evaporation phase:

[0128] Total residence time of flue gas: t all =t1+t2≈7.3+32.9≈40.2s.

[0129] Based on the above parameters, actual operation was conducted, and the measured total residence time of the flue gas in the drying tower was 42.8 s. Therefore, the total residence time t calculated in this embodiment is... all The result is very close to the total residence time of flue gas obtained from actual operation, indicating that the above calculation method in this embodiment can obtain the total residence time of flue gas during the operation of the drying tower relatively accurately.

[0130] Example 6

[0131] The wastewater zero-discharge monitoring method in this embodiment calculates the total residence time t of flue gas based on the method in Embodiment 3. all≈30.1s, the actual value of the adjusted flue gas flow rate is 63625 Nm. 3 / h (i.e., at 63625 Nm) 3 At the actual flue gas flow rate of / h, the corresponding total residence time of flue gas is 30.1s, and other parameters are the same as in Example 3.

[0132] The actual operation was carried out according to the adjusted flue gas flow rate described above; during the actual operation, the total flue gas residence time t was calculated according to the method in Example 3. all The wastewater flow rate and flue gas flow rate of the drying tower are controlled as follows:

[0133] When 30s≤t all When the time is less than 35s and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are kept constant.

[0134] When t all If the flow rate is less than 30 seconds, reduce the wastewater flow rate and flue gas flow rate until 30 seconds ≤ t. all <35s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K;

[0135] When t all If the flow rate is ≥35s, increase the wastewater flow rate and flue gas flow rate until 30s≤t all <35s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K.

[0136] Sampling was conducted after different operating times to test the ash moisture content at the outlet of the drying tower. The results are shown in Table 1. The results show that the ash moisture content at the outlet of the drying tower measured in the five samplings was within the range of 1-2%, and the average ash moisture content measured in the five samplings was 1.39%, which meets the industry standard requirement (ash moisture content at the outlet of the drying tower not exceeding 2%).

[0137] Example 7

[0138] The wastewater zero-discharge monitoring method in this embodiment calculates the total residence time t of flue gas based on the method in Example 4. all ≈35.1s, the actual value of the adjusted flue gas flow rate is 32760Nm. 3 / h (i.e., at 32760Nm) 3 At the actual flue gas flow rate of / h, the corresponding total residence time of flue gas is 35.1s, and other parameters are the same as in Example 4.

[0139] The actual operation was carried out according to the adjusted flue gas flow rate described above; during the actual operation, the total residence time t of the flue gas was calculated according to the method in Example 4. all The wastewater flow rate and flue gas flow rate of the drying tower are controlled as follows:

[0140] When 35s≤t all When the time is less than 40 seconds and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are kept constant.

[0141] When t all If the flow rate is less than 35 seconds, reduce the wastewater flow rate and flue gas flow rate until 35 seconds ≤ t. all <40s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K;

[0142] When t all If the flow rate is ≥40s, increase the wastewater flow rate and flue gas flow rate until 35s≤t. all <40s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K.

[0143] Samples were taken after different operating times to test the ash moisture content at the outlet of the drying tower. The results showed that the ash moisture content at the outlet of the drying tower measured in the five samples was within the range of 1-2%, and the average ash moisture content measured in the five samples was 1.15%, which meets the industry standard requirements.

[0144] Example 8

[0145] The wastewater zero-discharge monitoring method in this embodiment calculates the total residence time t of flue gas based on the method in Example 5. all ≈40.2s, the actual value of the adjusted flue gas flow rate is 31254 Nm. 3 / h (i.e., at 31254 Nm) 3 At the actual flue gas flow rate of / h, the corresponding total residence time of flue gas is 40.2s, and other parameters are the same as in Example 5.

[0146] The actual operation was conducted according to the adjusted flue gas flow rate described above; during the actual operation, the total flue gas residence time t was calculated according to the method in Example 5. all The wastewater flow rate and flue gas flow rate of the drying tower are controlled as follows:

[0147] When 40s≤t all When the time is ≤45s and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are kept constant.

[0148] When t all If the flow rate is less than 40 seconds, reduce the wastewater flow rate and flue gas flow rate until 40 seconds ≤ t. all ≤45s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K;

[0149] When t allIf the flow rate exceeds 45s, increase the wastewater flow rate and flue gas flow rate until 40s ≤ t. all ≤45s and the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K.

[0150] Sampling was conducted after different operating times 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 in the five samplings was within the range of 1-2%, and the average ash moisture content measured in the five samplings was 1.52%, which meets the industry standard requirements.

[0151] Compare with Example 1

[0152] Except for obtaining the total residence time of the flue gas using the average flow rate method, the other conditions are the same as in Example 3; the average flow rate is calculated as follows:

[0153] Average temperature

[0154] Average flow rate

[0155] The total residence time of the flue gas is:

[0156] Based on the above parameters, the actual total residence time of the flue gas in the drying tower was measured to be 33.2 s. Therefore, the total residence time t calculated in this comparative example is... all The significant difference between the actual total residence time of the flue gas and the calculation method described in this comparative example indicates that the above calculation method cannot accurately obtain the total residence time of the flue gas during the operation of the drying tower.

[0157] The total residence time t of the flue gas obtained from the above calculation all ≈26.7s, the actual value of the adjusted flue gas flow rate is 71536 Nm. 3 / h (i.e., when the actual flue gas flow rate is 71536 Nm) 3 When the flow rate is / h, the corresponding total residence time of the flue gas is 26.7s. The actual operation was carried out according to the adjusted flue gas flow rate. The results showed that the ash moisture content at the outlet of the drying tower was 2.81%, which could not meet the industry standard requirements.

[0158] Compare with Example 2

[0159] Except for obtaining the total residence time of the flue gas using the average flow rate method, the other conditions are the same as in Example 4; the average flow rate is calculated as follows:

[0160] Average temperature

[0161] Average flow rate

[0162] The total residence time of the flue gas is:

[0163] Based on the above parameters, actual operation was conducted, and the measured total residence time of the flue gas in the drying tower was 37.8 s. Therefore, the total residence time t calculated in this comparative example is... all The significant difference between the actual total residence time of the flue gas and the calculation method described in this comparative example indicates that the above calculation method cannot accurately obtain the total residence time of the flue gas during the operation of the drying tower.

[0164] The total residence time t of the flue gas obtained from the above calculation all ≈31.2s, the actual value of the adjusted flue gas flow rate is 36643 Nm. 3 / h (i.e., when the actual flue gas flow rate is 36643 Nm) 3 When the flow rate is / h, the corresponding total residence time of the flue gas is 31.2s. The actual operation was carried out according to the adjusted flue gas flow rate. The results showed that the ash moisture content at the outlet of the drying tower was 3.40%, which could not meet the industry standard requirements.

[0165] Compare with Example 3

[0166] Except for obtaining the total residence time of the flue gas using the average flow rate method, the other conditions are the same as in Example 5; the average flow rate is calculated as follows:

[0167] Average temperature

[0168] Average flow rate

[0169] The total residence time of the flue gas is:

[0170] Based on the above parameters, actual operation was conducted, and the measured total residence time of the flue gas in the drying tower was 42.8 s. Therefore, the total residence time t calculated in this comparative example is... all The significant difference between the actual total residence time of the flue gas and the calculation method described in this comparative example indicates that the above calculation method cannot accurately obtain the total residence time of the flue gas during the operation of the drying tower.

[0171] Furthermore, based on the total residence time t of the flue gas obtained from the above calculations... all ≈33.6s, the actual value of the adjusted flue gas flow rate is 37420Nm. 3 / h (i.e., when the actual flue gas flow rate is 37420 Nm) 3 When the flow rate is / h, the corresponding total residence time of the flue gas 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 outlet of the drying tower was 3.15%, which could not meet the industry standard requirements.

[0172] Compare with Example 4

[0173] Except for not adjusting the wastewater flow and flue gas flow during actual operation, it is the same as in Example 6.

[0174] Sampling and testing were performed according to the method in Example 6; the results are shown in Table 1.

[0175] Compare with Example 5

[0176] Except for the following method used to regulate wastewater flow and flue gas flow during actual operation, the other conditions are the same as in Example 6.

[0177] In this comparative example, the outlet flue gas temperature Tout of the drying tower is monitored during operation. Based on the outlet flue gas temperature Tout, the flow rates of wastewater and flue gas entering the drying tower are adjusted as follows:

[0178] If 150℃≤Tout≤160℃, maintain the wastewater and gas flow rates constant;

[0179] If Tout < 150℃, 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℃ ≤ Tout ≤ 160℃;

[0180] If Tout > 160℃, increase the wastewater flow rate entering the drying tower and / or decrease the flue gas flow rate entering the drying tower until Tout decreases to 150℃ ≤ Tout ≤ 160℃.

[0181] Sampling and testing were performed according to the method in Example 6; the results are shown in Table 1.

[0182] Table 1 Results of Ash Moisture Content Test at Drying Tower Outlet

[0183] The results show that:

[0184] 1. The method of Example 6 was used for operation. The wastewater drying effect was good. The ash moisture content at the outlet of the drying tower could be stably maintained at 1-2%. It could effectively overcome various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower. The ash moisture content at the outlet of the drying tower met the industry standard requirements and would not have an adverse effect on the resource utilization of ash (i.e., fly ash). The drying tower had good operational stability and no operational failures occurred.

[0185] 2. When operating using the method of Comparative Example 4, without adjusting the flue gas flow rate and wastewater flow rate, the wastewater drying effect is poor. It is impossible to overcome various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower. The ash moisture content at the outlet of the drying tower fluctuates greatly, and problems such as wet ash and blockage occur in the drying tower, which seriously affects the stable operation of the drying tower and the resource utilization of ash.

[0186] 3. Using the method of Comparative Example 5, the flow rates of wastewater and gas were adjusted with the outlet flue gas temperature of the drying tower as a reference value. The wastewater drying effect was unstable, and problems such as wet ash and blockage occurred during operation, which adversely affected the normal operation of the drying tower. At the same time, some ash agglomerated and caking, which affected the resource utilization of ash.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 wastewater discharge, characterized in that, Includes the following steps: S1: The wastewater is atomized and sent into the drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The temperature of the flue gas at the outlet of the drying tower, T2, is monitored in real time. S2: Obtain the travel time t1 of the flue gas during the constant-rate evaporation stage and the travel time t2 during the decreasing-rate evaporation stage, respectively, and obtain the total residence time t of the flue gas based on the travel time t1 and the travel time t2. all , t all =t1+t2; S3: Based on the total residence time of flue gas t all The flow rates of wastewater and flue gas are regulated, and the flue gas temperature T2 at the outlet of the drying tower is maintained at 428K-448K.

2. The wastewater zero-discharge monitoring method according to claim 1, characterized in that, The time t1 of the flue gas during the constant-rate evaporation stage can be obtained using the following formula: Where: t1 is the travel time of flue gas during 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 during the constant-rate evaporation stage.

3. The wastewater zero-discharge monitoring method according to claim 2, characterized in that, a1 and b1 can be obtained using the following formula: b1 = T1 Wherein: T c T1 is the critical temperature of the flue gas between the constant-rate evaporation stage and the falling-rate evaporation stage; T2 is the inlet flue gas temperature.

4. The wastewater zero-discharge monitoring method according to claim 1, characterized in that, The time t2 of the flue gas during the slowing evaporation stage can be obtained using the following formula: Where: t2 is the travel time of flue gas during the falling-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; a2 and b2 are model parameters; L2 is the vertical flow distance of flue gas during the falling-rate evaporation stage.

5. The wastewater zero-discharge monitoring method according to claim 4, characterized in that, a2 and b2 can be obtained 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 falling-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 during the constant-rate evaporation stage.

6. The wastewater zero-discharge monitoring method according to claim 1, characterized in that, The total residence time t of the flue gas is determined according to the solids content x of the wastewater as follows: all Control range: 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 wastewater zero-discharge monitoring method according to claim 6, characterized in that, Wastewater flow and flue gas flow shall be regulated in the following manner: When the total residence time of flue gas t all When the temperature of the flue gas at the outlet of the drying tower is maintained at 428K-448K within the control range, the wastewater flow rate and flue gas flow rate are kept constant. When the total residence time of flue gas t all When the flow rate is below the lower limit of the control range, reduce the wastewater flow rate and flue gas flow rate until the total flue gas residence time t is reached. all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the reduction rate of gas flow rate is controlled to not exceed the reduction rate of wastewater flow rate. When the total residence time of flue gas t all When the flow rates are above the upper limit of the control range, increase the wastewater flow rate and flue gas flow rate. Until the total residence time t of the flue gas all Within the control range, the outlet flue gas temperature T2 of the drying tower is maintained at 428K-448K, and the increase rate of wastewater flow rate is controlled not to exceed the increase rate of gas flow rate.

8. The wastewater zero-discharge monitoring method according to claim 1, characterized in that, Wastewater is atomized using a rotary atomizer, and the resulting wastewater droplets have a particle size of 10-60 μm.

9. A wastewater zero-discharge monitoring system for implementing the wastewater zero-discharge monitoring method according to any one of claims 1-8, characterized in that, The system includes a drying tower and a controller. A rotary atomizer is installed at the top of the drying tower and connected to a wastewater pipe. A wastewater regulating valve is installed on the wastewater pipe. Inlet and outlet flues are located at the upper and lower parts of the drying tower, respectively. A flue gas regulating valve, an inlet thermometer, and a flow meter are installed in the inlet flue. An outlet thermometer is installed in the outlet flue. A friction thermometer and a pressure gauge are installed on the drying tower. The controller has a calculation module that can calculate the flue gas's travel time t1 during the constant-rate evaporation stage, the travel time t2 during the falling-rate evaporation stage, and the total residence time t based on data from the inlet, outlet, friction thermometer, flow meter, and pressure gauge. all The controller is based on the total residence time t of the flue gas. all The wastewater regulating valve and the flue gas regulating valve are controlled to regulate the wastewater flow and flue gas flow.

10. The wastewater zero-discharge monitoring system according to claim 9, characterized in that, Based on the solids content x of the wastewater, the friction-line thermometers should be installed as follows: When x≤10%, the friction temperature gauge should be set at a distance of 4.5-5.4m from the top of the drying tower; When 10% < x ≤ 20%, the friction temperature gauge should be set at a distance of 3.5-4.4m from the top of the drying tower; When 20% < x ≤ 30%, the friction temperature gauge should be set at a distance of 2.5-3.4m from the top of the drying tower.

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