A wastewater zero discharge monitoring method and system

Abstract

The application provides a wastewater zero discharge monitoring method and system. The wastewater zero discharge monitoring method of the application comprises the following steps: S1: sending the atomized wastewater into a drying tower, introducing high-temperature flue gas into the drying tower to evaporate and dry the atomized wastewater droplets, and monitoring the flue gas temperature T2 at the outlet of the drying tower in real time; S2: obtaining 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 respectively, and obtaining 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: controlling the wastewater flow and the flue gas flow according to the total residence time t all of the flue gas, and maintaining the flue gas temperature T2 at the outlet of the drying tower at 428K-448K. The wastewater zero discharge monitoring method and system of the application fully considers the change rule of the flue gas flow rate in the drying tower with temperature, improves the accuracy of system monitoring, and ensures the operation stability of the system.

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] High-salinity wastewater from thermal power plants (such as chemical regeneration wastewater and wet desulfurization wastewater) has complex composition, and direct discharge can cause serious environmental pollution. Currently, rotary atomization drying technology is one of the mainstream technologies for achieving zero discharge of high-salinity wastewater in the power industry. This technology uses a drying tower that uses high-speed rotation to atomize the wastewater into droplets, which are then sprayed into the drying tower. At the same time, high-temperature flue gas from the thermal power plant is drawn into the drying tower, where it fully exchanges heat with the wastewater droplets, quickly achieving zero discharge of wastewater.

[0003] The residence time of high-temperature flue gas within the drying tower determines the heat exchange time between the gas and liquid phases and is a key parameter influencing the effectiveness of zero-emission wastewater evaporation. Currently, the calculation of residence time is relatively crude, typically using the average of the inlet and outlet flue gas temperatures to calculate the average flow rate within the drying tower, and then calculating the residence time based on the tower height.

[0004] However, because the wastewater drying process in the drying tower involves two stages: constant-rate evaporation and decreasing-rate evaporation. The flue gas temperature decreases continuously and unevenly as it flows from top to bottom, causing a corresponding change in its flow rate. Existing methods for calculating residence time fail to reflect how flow rate changes with temperature. Calculating flue gas residence time based on average temperature and average flow rate can easily lead to irrational control of the zero-discharge wastewater system, resulting in insufficient system output or poor zero-discharge performance, which can seriously impact the system's stable operation.

[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 controlled, when using this high-temperature flue gas to evaporate and dry wastewater, unstable evaporation effects and poor evaporation may cause faults such as wet ash, blockage, and corrosion, which will have a serious adverse impact on the normal operation of the drying tower.

[0006] In order to ensure 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 of flue gas flow velocity with temperature in a drying tower, improves the operating 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 a drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The flue gas temperature T2 at the drying tower outlet is monitored in real time.

[0011] S2: Obtain the flue gas movement time t1 in the constant speed evaporation stage and the movement time t2 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;

[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 T2 at the drying tower outlet is maintained at 428K-448K.

[0013] In step S1, the upper portion of the drying tower is a hollow cylinder, which is the primary location for wastewater evaporation and drying. The lower portion of the drying tower is a hollow cone, which is primarily used for ash deposition. Unless otherwise specified, the drying tower primarily refers to the hollow cylindrical portion. A rotary atomizer is installed at the top of the drying tower to atomize the wastewater. The rotary atomizer speed is controlled to 12,000-18,000 rpm, and the particle size of the atomized wastewater droplets is 10-60 μm.

[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. Among them, the constant-rate evaporation occurs at the upper part of the drying tower. In this stage, 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 water. The reduced-rate evaporation occurs at the lower part of the drying tower. 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] Where: v is the vertical flow velocity of the flue gas; V is the flue gas volume flow rate (referred to as flue gas flow rate); n is the molar flow rate, which is calculated from the flue gas volume flow rate; R is the gas constant; T is the flue gas Kelvin temperature; P is the flue gas pressure; S is the cross-sectional area of ​​the drying tower, which is calculated from the drying tower diameter.

[0018] A thermometer is set along the way in the middle of the drying tower. The thermometer is set 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] The distance 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=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] Assume T c is the reading of the along-line thermometer (i.e. the critical temperature of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage), T1 is the inlet flue gas temperature, and L1 is the distance between the along-line thermometer and the top of the drying tower (i.e. the vertical flow distance of the flue gas in the constant-rate evaporation stage, which is about 2.5-5.4m).

[0023] When L = 0, T = T1; when L = L1, T = T c , therefore, a1 and b1 are obtained by the following formula:

[0024]

[0025] b1=T1

[0026] Where: T c is the critical temperature of the flue gas between the constant rate evaporation stage and the decreasing rate evaporation stage; T1 is the inlet flue gas temperature; L1 is the vertical flow distance of the flue gas in the constant rate 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 using the following formula:

[0030]

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

[0032]

[0033] In the constant-rate evaporation stage, let L=L1, and the movement time of the flue gas in the constant-rate evaporation stage can be calculated, which is recorded as t1.

[0034] That is, the movement time t1 of the flue gas in the constant evaporation stage is obtained by the following formula:

[0035]

[0036] Where: t1 is the movement time of the 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 the flue gas in the constant-rate evaporation stage.

[0037] The distance from the temperature meter along the drying tower to the flue 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=a2L+b2

[0039] Where: L is the vertical movement distance of the smoke (starting from the starting point of the speed reduction evaporation, denoted as L2); a2 and b2 are model parameters.

[0040] Assume T2 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 = h - L1, T = T2, so a2 and b2 are obtained by the following formula:

[0041]

[0042] 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 (i.e. the height of the hollow cylinder at the top of the drying tower); L1 is the vertical flow distance of the flue gas in the constant rate evaporation stage.

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

[0044]

[0045] The smoke movement time t (starting from the starting point of the evaporation rate decrease, recorded as t2) is calculated using the following formula:

[0046]

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

[0048]

[0049] In the falling speed evaporation stage, let L = h - L1 = L2, and the movement time of the flue gas in the falling speed evaporation stage can be calculated, which is recorded as t2.

[0050] That is, the movement time t2 of the flue gas in the deceleration evaporation stage is obtained by the following formula:

[0051]

[0052] Where: t2 is the movement time of the 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 the flue gas in 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 The control interval is:

[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 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 flue gas is t all When the temperature of flue gas at the drying tower outlet is within the control range and T2 is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged;

[0059] When the total residence time of flue gas is t all When the flow rate is lower than the lower limit of the control range, reduce 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 maintained within the control range and is maintained at 428K-448K, and the reduction rate of the gas flow is controlled not to exceed the reduction rate of the wastewater flow;

[0060] When the total residence time of flue gas is t all When the flow rate 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 allThe flue gas temperature T2 at the drying tower outlet is maintained within the control range and is maintained at 428K-448K, and the increase rate of the wastewater flow is controlled not to exceed the increase rate of the gas flow.

[0061] The above control method can obtain the corresponding total residence time t of flue gas based on the flue gas variable speed flow law. all At the same time, according to the total residence time of flue gas t all The control range coordinates the wastewater flow and flue gas flow during the operation of the drying tower, thereby effectively overcoming problems such as the unstable temperature of the high-temperature flue gas entering the drying tower, thereby avoiding unstable evaporation effect during the operation of the drying tower and faults such as wet ash, blockage, corrosion caused by poor evaporation, thereby 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 provided on the top of the drying tower, the rotary atomizer is connected to a wastewater pipe, a wastewater regulating valve is provided on the wastewater pipe, an inlet flue and an outlet flue are respectively provided at the upper and lower parts of the drying tower, a flue gas regulating valve, an inlet thermometer and a flow meter are provided on the inlet flue, an outlet thermometer is provided on the outlet flue, and an along-line thermometer and a pressure gauge are provided on the drying tower, and the controller is provided with a calculation module, which can calculate the movement time t1 of the flue gas in the constant-rate evaporation stage, the movement time t2 in the decreasing-rate evaporation stage and the total residence time t of the flue gas based on the data fed back by the inlet thermometer, the outlet thermometer, the along-line thermometer, 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 flue gas regulating valve are controlled to regulate the wastewater flow and flue gas flow.

[0063] Specifically, the upper part of the drying tower is a hollow cylinder, and 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 in the center of the top 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 T1 in real time, and the flowmeter is used to monitor the flue gas volume flow V in real time, and the molar flow n is obtained by conversion. The inlet thermometer and the flowmeter can be installed at a depth of 1 / 2 diameter inside the inlet flue, and the inlet thermometer and the flowmeter are arranged at a distance of 0.8-1.2m; the 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; the along-line thermometer is used to monitor the critical temperature T1 of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage in real time c, can be installed at a depth of 1 / 8 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 height position of the hollow cylinder and at a depth of 1 / 8 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%, set the temperature meter along the drying tower at a distance of 4.5-5.4m 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 position 3.5-4.4m away from the top of the drying tower;

[0067] The solid content x of the wastewater is: 20%<x≤30%, and the along-process 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 the constant-rate evaporation and reduced-rate evaporation stages, and provides a data basis for the establishment of a kinetic model by monitoring key parameters; the method and system fully consider the relationship between the flue gas flow rate and temperature in different evaporation stages, establish linear models of flue gas movement time and movement distance respectively, and derive a kinetic model for calculating the total residence time of flue gas, thereby improving the accuracy of the calculation of the total residence time of flue gas in the 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 effectively 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 embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any 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-process thermometer; 10: Pressure gauge; 11: Flow meter; 12: Wastewater regulating valve. DETAILED DESCRIPTION

[0073] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as 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 also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0075] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts 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 a drying tower. High-temperature flue gas is introduced into the drying tower to evaporate and dry the atomized wastewater droplets. The flue gas temperature T2 at the drying tower outlet is monitored in real time.

[0079] S2: Obtain the flue gas movement time t1 in the constant speed evaporation stage and the movement time t2 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;

[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 T2 at the drying tower outlet is maintained 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 evaporation drying process, the inlet flue gas temperature T1, the outlet flue gas temperature T2, the critical temperature T between the constant speed evaporation stage and the speed reduction evaporation stage c , flue gas pressure P, flue gas volume flow 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 a1 and b1 using the following formula:

[0084]

[0085] b1=T1

[0086] 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.

[0087] The movement time t1 of the flue gas in the constant evaporation stage is obtained by the following formula:

[0088]

[0089] Where: t1 is the movement time of the 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 the flue gas in the constant-rate evaporation stage.

[0090] Get a2 and b2 using the following formula:

[0091]

[0092] b2=T c

[0093] 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.

[0094] The movement time t2 of the flue gas in the deceleration evaporation stage is obtained by the following formula:

[0095]

[0096] Where: t2 is the movement time of the 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 the flue gas in the deceleration evaporation stage.

[0097] After obtaining the flue gas movement time t1 in the constant speed evaporation stage and the flue gas movement time t2 in the decreasing speed evaporation stage, according to t all =t1+t2 to obtain the total residence time of flue gas t all .

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

[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 t all The control interval is [40s,45s].

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

[0103] When the total residence time of flue gas is t all When the temperature of flue gas at the drying tower outlet is within the control range and T2 is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged;

[0104] When the total residence time of flue gas is t all When the flow rate is lower than the lower limit of the control range, reduce 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 maintained within the control range and is maintained at 428K-448K, and the reduction rate of the gas flow is controlled not to exceed the reduction rate of the wastewater flow;

[0105] When the total residence time of flue gas is t all When the flow rate 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 maintained within the control range and is maintained at 428K-448K, and the increase rate of the wastewater flow is controlled not to exceed the increase rate of the gas flow.

[0106] Example 2

[0107] Combine Figure 1 As shown, the wastewater zero discharge monitoring system of this embodiment is used to implement the wastewater zero discharge monitoring method of Example 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 the 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 flow meter 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. The calculation module can calculate the movement time t1 of the flue gas in the constant rate evaporation stage, the movement time t2 in the decreasing rate evaporation stage and the total residence time t of the flue gas based on the data fed back by the inlet thermometer 8, the outlet thermometer 6, the along-the-line thermometer 9, the flow meter 11 and the pressure gauge 10. 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 regulate the wastewater flow and the flue gas flow.

[0108] 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 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 in the center of the top 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 T1 in real time, and the flowmeter 11 is used to monitor the flue gas volume flow V in real time, and the molar flow n is obtained by conversion. The inlet thermometer 8 and the flowmeter 11 can be installed at a depth of 1 / 2 diameter inside the inlet flue 3, and the inlet thermometer 8 and the flowmeter 11 are arranged at a distance of 0.8-1.2m; 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 along-line thermometer 9 is used to monitor the critical temperature T1 of the flue gas between the constant-rate evaporation stage and the decreasing-rate evaporation stage in real time c , which can be installed at a depth of 1 / 8 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 diameter inside the hollow cylinder.

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

[0110] When the solid content x of the wastewater is: x≤10%, the temperature measuring instrument 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 temperature measuring instrument 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-line thermometer 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 was used to evaporate and dry the wastewater; the parameters were as follows: the solid content x of the wastewater was 5%, the inlet flue gas temperature T1 was 633K, the outlet flue gas temperature T2 was 448K, the tower diameter of the drying tower was 8.5m, the height h of the hollow cylinder of the drying tower was 15m, and the temperature meter along the drying tower was set at a position 5m from the top of the drying tower (i.e., L1 was 5m); the design value of the flue gas flow rate was 58100Nm 3 / h.

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

[0116] Flue gas temperature: T = a1L + b1 = -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 = a2L + b2 = -1.2L + 460.

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

[0121] Total residence time of flue gas: t all =t1+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 was used to evaporate and dry the wastewater; the parameters were as follows: the solid content x of the wastewater was 17%, the inlet flue gas temperature T1 was 611K, the outlet flue gas temperature T2 was 438K, the tower diameter of the drying tower was 7.5m, the height h of the hollow cylinder of the drying tower was 11.5m, and the temperature meter along the drying tower was set at a position 4m from the top of the drying tower (i.e., L1 was 4m); the design value of the flue gas flow rate was 30700Nm 3 / h.

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

[0126] Flue gas temperature: T = a1L + b1 = -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 = a2L + b2 = -1.1L + 446.

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

[0131] Total residence time of flue gas: t all =t1+t2≈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. 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.

[0133] Example 5

[0134] The wastewater zero-discharge monitoring system of Example 2 was used to evaporate and dry the wastewater; the parameters were as follows: the solid content x of the wastewater was 25%, the inlet flue gas temperature T1 was 645K, the outlet flue gas temperature T2 was 428K, the tower diameter of the drying tower was 7m, the height h of the hollow cylinder of the drying tower was 14m, and the temperature meter along the drying tower was set at a position 3m from the top of the drying tower (i.e., L1 was 3m); the design value of the flue gas flow rate was 29600Nm 3 / h.

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

[0136] Flue gas temperature: T=a1L+b1=-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 = a2L + b2 = -0.6L + 435.

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

[0141] Total residence time of flue gas: t all =t1+t2≈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. 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 the flue gas flow is 63625Nm 3 / h (ie: at 63625Nm 3 / h, the corresponding actual value of the total residence time of the flue gas is 30.1s), and other parameters are the same as those in Example 3.

[0145] The actual operation is carried out 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 When the s is less than 35s and the flue gas temperature T2 at the drying tower outlet is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged;

[0147] When t all When t<30s, reduce the wastewater flow and flue gas flow until 30s≤t all <35s and the flue gas temperature T2 at the drying tower outlet is 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 T2 at the drying tower outlet is maintained 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 all 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 the adjusted flue gas flow is 32760Nm 3 / h (ie: at 32760Nm 3 At an actual flue gas flow rate of 1 / h, 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 was carried out according to the flue gas flow rate after the above adjustment; during the actual operation, the total residence time of the flue gas t was 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 When the time is less than 40s and the flue gas temperature T2 at the drying tower outlet is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged;

[0154] When t all When t<35s, reduce the wastewater flow and flue gas flow until 35s≤t all <40s and the flue gas temperature T2 at the drying tower outlet is 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 T2 at the drying tower outlet is maintained at 428K-448K.

[0156] Sampling was performed 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 was within the range of 1-2% for all five sampling measurements, and the average ash moisture content for the five sampling measurements was 1.15%, meeting industry standards.

[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 the adjusted flue gas flow is 31254Nm 3 / h (ie: at 31254Nm 3 At an actual flue gas flow rate of 1 / h, 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 carried out 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 5. all , and the wastewater flow and flue gas flow of the drying tower are regulated as follows:

[0160] When 40s≤t all When the time is ≤45s and the flue gas temperature T2 at the drying tower outlet is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged;

[0161] When t all When t<40s, reduce the wastewater flow and flue gas flow until 40s≤t all ≤45s and the flue gas temperature T2 at the drying tower outlet is 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 T2 at the drying tower outlet is maintained at 428K-448K.

[0163] Sampling was performed 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 was within the range of 1-2% for all five sampling measurements, and the average ash moisture content for the five sampling measurements was 1.52%, meeting industry standards.

[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 and that obtained during 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 residence time of flue gas t obtained by the above calculation all ≈26.7s, the actual value of the adjusted flue gas flow is 71536Nm 3 / h (ie: the actual flue gas flow rate is 71536Nm 3 / h, the corresponding total residence time of flue gas is actually 26.7s); 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 2.81%, which cannot 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 and that obtained during 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 residence time of flue gas t obtained by 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 total residence time of the flue gas 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 and that obtained during 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 the adjusted flue gas flow is 37420Nm 3 / h (ie: the actual flue gas flow rate is 37420Nm 3 / h, the actual value of the total residence time of the flue gas is 33.6s); 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 3.15%, which cannot meet the industry standard requirements.

[0185] Comparative Example 4

[0186] Except that the wastewater flow rate and 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. Based on 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°C, 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°C≤Tout≤160°C.

[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 drying tower outlet

[0196]

[0197]

[0198] The results show that:

[0199] 1. The method of Example 6 was used to dry the wastewater effectively. The moisture content of the ash at the drying tower outlet was stably maintained at 1-2%. This method effectively overcomes 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 met the industry standard requirements and did not adversely affect the resource utilization of the ash (i.e., fly ash). The drying tower had good operational stability and no operational failures occurred.

[0200] 2. When the method of Control Example 4 was used, without adjusting the flue gas flow and wastewater flow, the wastewater drying effect was poor, and the various problems caused by the unstable temperature of the high-temperature flue gas entering the drying tower could not be overcome. The moisture content of the ash at the outlet of the drying tower fluctuated greatly, and the drying tower suffered from wet ash and blockage, which seriously affected the stable operation of the drying tower and the resource utilization of the ash.

[0201] 3. The method of Control Example 5 was adopted, and the wastewater and gas flow rates were adjusted with 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, some 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 wastewater zero discharge monitoring method, 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. The flue gas temperature T2 at the drying tower outlet is monitored in real time. S2: Obtain the flue gas movement time t1 in the constant speed evaporation stage and the movement time t2 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 Regulate the wastewater flow and flue gas flow, and maintain the flue gas temperature T2 at the drying tower outlet at 428K-448K; The movement time t1 of the flue gas in the constant evaporation stage is obtained by the following formula: Where: t1 is the movement time of the 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; a1 and b1 are model parameters; L1 is the vertical flow distance of the flue gas in the constant evaporation stage; Get a1 and b1 using the following formula: b1=T1 Where: T c is the critical temperature of the flue gas between the constant rate evaporation stage and the decreasing rate evaporation stage; T1 is the inlet flue gas temperature; The movement time t2 of the flue gas in the deceleration evaporation stage is obtained by the following formula: Where: t2 is the movement time of the 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 the flue gas in the deceleration evaporation stage; 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.

2. The wastewater zero discharge monitoring method 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 The control interval is: 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.

3. The wastewater zero discharge monitoring method according to claim 2, characterized in that: The wastewater flow and flue gas flow are regulated as follows: When the total residence time of flue gas is t all When the temperature of flue gas at the drying tower outlet is within the control range and T2 is maintained at 428K-448K, the wastewater flow rate and flue gas flow rate are maintained unchanged; When the total residence time of flue gas is t all When the flow rate is lower than the lower limit of the control range, reduce 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 maintained within the control range and is maintained at 428K-448K, and the reduction rate of the gas flow is controlled not to exceed the reduction rate of the wastewater flow; When the total residence time of flue gas is t all When the flow rate 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 maintained within the control range and is maintained at 428K-448K, and the increase rate of the wastewater flow is controlled not to exceed the increase rate of the gas flow.

4. The wastewater zero discharge monitoring method 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.

5. The wastewater zero discharge monitoring method according to claim 1, characterized in that: The wastewater zero discharge monitoring system is adopted. The wastewater zero discharge monitoring system includes a drying tower and a controller. A rotary atomizer is provided on the top of the drying tower. The rotary atomizer is connected to the wastewater pipe. A wastewater regulating valve is provided on the wastewater pipe. An inlet flue and an outlet flue are provided at the upper and lower parts of the drying tower respectively. A flue gas regulating valve, an inlet thermometer and a flow meter are provided on the inlet flue, an outlet thermometer is provided on the outlet flue, and an along-process thermometer and a pressure gauge are provided 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-rate evaporation stage, the movement time t2 in the decreasing-rate 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 along-process thermometer, 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 flue gas regulating valve are controlled to regulate the wastewater flow and flue gas flow.

6. The wastewater zero discharge monitoring method according to claim 5, characterized in that: According to the solid content x of the wastewater, set the temperature measuring instruments along the process as follows: When x≤10%, set the temperature meter along the drying tower 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-line thermometer at a distance of 2.5-3.4m from the top of the drying tower.

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