A drying tower design method and wastewater drying method based on variable-speed gas flow

Abstract

The present invention provides a drying tower design method and a wastewater drying method based on variable-speed gas flow. The drying tower design method based on variable-speed gas flow of the present invention comprises the following steps: S1: A drying tower with a hollow cylinder is provided, a rotary atomizer is arranged at the top of the drying tower, a gas inlet and a gas outlet are respectively arranged at the upper and lower parts of the drying tower, and a constant-rate evaporation zone and a falling-rate evaporation zone are sequentially arranged in the drying tower from top to bottom; S2: The height H of the hollow cylinder of the drying tower is obtained by formulas (1)-(3). The drying tower design method of the present invention fully considers the variation law of the gas flow rate inside the drying tower with temperature, improves the rationality of the drying tower design, and ensures the drying capacity of the drying tower; in addition, the wastewater drying method of the present invention can reduce the operating energy consumption of the drying tower and ensure the drying effect and stable operation of the drying tower.

Description

Technical Field

[0001] The present invention relates to the technical field of power environmental protection, and particularly relates to a drying tower design method based on variable-speed gas flow and a wastewater drying method. Background Art

[0002] In recent years, with the upgrading of the control of industrial wastewater containing salt by the state and local governments, the zero discharge of high-salt wastewater from thermal power plants has become a hot topic in the industry. Among many wastewater zero-discharge technologies, the rotary atomization drying technology has advantages such as a simple process flow, low cost, and stable operation, and has become one of the mainstream technologies in the industry. This technology sets up a drying tower with a hollow cylinder, atomizes wastewater into droplets by a high-speed rotation method and sprays them into the top of the drying tower, and extracts high-temperature gas from the thermal power plant into the top of the drying tower; in the drying tower, the high-temperature gas exchanges heat fully with the wastewater droplets to achieve rapid drying of the wastewater, and finally the gas is discharged from the bottom of the drying tower.

[0003] The flow rate of the high-temperature gas in the drying tower determines the heat exchange time of the gas-liquid two-phase and is also a key parameter for calculating the height of the drying tower. At present, the calculation methods for the gas flow rate and the height of the drying tower are relatively rough. Generally, the average flow rate of the gas in the tower is calculated by the average value of the inlet gas temperature and the outlet gas temperature of the drying tower, and then the height of the tower is calculated by the drying time. However, since the temperature of the gas will continuously decrease and the change law is inconsistent when the gas flows in the drying tower, its flow rate will also change accordingly. The existing calculation methods cannot reflect the change law of the flow rate with temperature, which easily leads to unreasonable design of the drying tower, and then reduces the efficiency and effect of wastewater evaporation and drying.

[0004] In addition, when using the high-temperature gas from the thermal power plant to dry the wastewater, due to certain fluctuations in the temperature of the high-temperature gas, the temperature of the high-temperature gas entering the drying tower is unstable and not easy to control. There are problems such as unstable evaporation effect and faults such as wet ash, blockage, and corrosion caused by poor evaporation when using this high-temperature gas to evaporate and dry the wastewater, which not only has a serious adverse impact on the normal operation of the drying tower, but also may have problems such as excessive energy consumption waste.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a drying tower design method and a wastewater drying method based on variable-speed gas flow, which fully consider the change law of the gas flow rate in the drying tower with temperature, and improve the rationality of the drying tower design and the drying capacity of the drying tower.

[0007] The present invention provides a drying tower design method based on variable-speed gas flow, including the following steps:

[0008] S1: Set up a drying tower with a hollow cylinder. Install a rotary atomizer at the top of the drying tower, and set up a gas inlet and a gas outlet at the upper and lower parts of the drying tower respectively. Inside the drying tower, there are a constant-rate evaporation zone and a falling-rate evaporation zone arranged successively from top to bottom;

[0009] S2: Obtain the height H of the hollow cylinder of the drying tower through the following formulas (1)-(3);

[0010]

[0011] H = L1 + L2 (3)

[0012] Where: t1 is the residence time of the gas in the constant-rate evaporation zone; P is the gas pressure, taking the value of the inlet gas pressure (obtained from the preliminary design research); S is the cross-sectional area of the drying tower, calculated from the tower diameter of the drying tower. The tower diameter of the drying tower is determined by technical indicators such as the atomizing distance of the atomizer. The tower diameter of the drying tower is generally 6.5 - 10.0 m; n is the molar flow rate, converted from the gas volume flow rate. The gas volume flow rate is determined by the law of conservation of energy and is a known parameter for designing the drying tower; R is the gas constant, taking 8.314 J / (mol˙K); a1, b1, a2, b2 are model parameters; L1 is the vertical flow distance of the gas in the constant-rate evaporation zone; L x2 is the calculated value of the vertical flow distance of the gas in the falling-rate evaporation zone; t2 is the residence time of the gas in the falling-rate evaporation zone; H is the height of the hollow cylinder of the drying tower; L2 is the vertical flow distance of the gas in the constant-rate evaporation zone.

[0013] The upper part of the drying tower is a hollow cylinder, which is the main place 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 cylinder part. Inside the hollow cylinder of the drying tower, there are a constant-rate evaporation zone and a falling-rate evaporation zone arranged successively from top to bottom. A rotary atomizer is installed at the top of the drying tower, and a gas inlet and a gas outlet are set at the upper and lower parts of the drying tower respectively. The rotary atomizer is used to atomize the wastewater into droplets. The high-temperature gas enters the drying tower through the gas inlet, exchanges heat fully with the wastewater droplets inside the drying tower, the wastewater is evaporated and dried, and the gas is discharged through the gas outlet.

[0014] The evaporation and drying of wastewater droplets inside the drying tower are divided into a constant-rate evaporation stage and a falling-rate evaporation stage. The constant-rate evaporation stage occurs in the constant-rate evaporation zone, and the falling-rate evaporation stage occurs in the falling-rate evaporation zone. In the constant-rate evaporation stage, the water on the surface of the wastewater droplets absorbs the heat of the high-temperature gas and evaporates rapidly. The gas temperature drops sharply with the flow, and a solid shell (composed of soluble salts and suspended solids in the wastewater) forms on the surface of the droplets. In the falling-rate evaporation stage, the water inside the solid shell slowly transfers to the surface and evaporates, and the gas temperature drops slowly with the flow. During the rotary atomization drying process of high-salt wastewater in thermal power plants, the constant-rate evaporation stage generally occurs within 3 - 5 m from the top of the drying tower where the gas enters. The gas temperature drops sharply as the vertical flow distance increases. The falling-rate evaporation occurs after the constant-rate evaporation, and the gas temperature drops slowly as the vertical flow distance increases.

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

[0016]

[0017] Where: v is the vertical flow velocity of the gas; V is the gas volume flow rate; n is the molar flow rate; R is the gas constant; T is the gas temperature in Kelvin; P is the gas pressure; S is the cross-sectional area of the drying tower.

[0018] In step S2, the height H of the hollow cylinder in the drying tower is obtained through the following steps:

[0019] Step 1: Obtain the residence time t1 of the gas in the constant-rate evaporation zone.

[0020] In the constant-rate evaporation stage, the variation law of the gas temperature with the vertical flow distance is simulated by the following linear model:

[0021] T = a1L + b1

[0022] In the formula: L is the vertical flow distance of the gas (starting from the top of the drying tower); a1 and b1 are model parameters.

[0023] Let T c be the critical temperature between the constant-rate evaporation zone and the falling-rate evaporation zone of the gas, which can be obtained through the heat balance calculation of the wastewater drying process or by querying the "enthalpy-humidity diagram of air-water system"; T1 is the gas inlet temperature; L1 is the vertical flow distance of the gas in the constant-rate evaporation zone (about 3 - 5 m).

[0024] When L = 0, T = T1; when L = L1, T = T c ; Therefore, a1 and b1 are obtained through the following formula:

[0025]

[0026] b1 = T1

[0027] Since the vertical flow velocity of the gas is the derivative of the vertical flow distance with respect to the residence time, i.e.:

[0028]

[0029] The residence time t (starting from the top of the drying tower) is obtained through the following formula:

[0030]

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

[0032]

[0033] In the constant-rate evaporation stage, L = L1, and the residence time t1 of the gas in the constant-rate evaporation zone is calculated through the above formula, i.e.:

[0034]

[0035] Step 2: Obtain the calculated value L of the vertical flow distance of the gas in the falling-rate evaporation zone x2 .

[0036] In the falling-rate evaporation stage, the variation law of the gas temperature with the vertical flow distance is simulated by the following linear function:

[0037] T = a2L + b2

[0038] Where: L is the vertical flow distance of the gas (starting from the falling-rate evaporation starting point, denoted as L2); a2 and b2 are model parameters.

[0039] Let T2 be the gas outlet temperature, and assume L x1 is the initial value of the vertical flow distance of the gas in the falling-rate evaporation zone, which is initially set to 1.8 - 2.2 times the tower diameter of the drying tower (e.g., 2 times); therefore, a2 and b2 are obtained through the following formula:

[0040]

[0041] b2 = T c

[0042] The vertical flow velocity of the gas is the derivative of the vertical flow distance with respect to the residence time, i.e.:

[0043]

[0044] The residence time t (starting from the falling-rate evaporation starting point, denoted as t2) is obtained through the following formula:

[0045]

[0046] When L = 0, t = 0, we can obtain:

[0047]

[0048] Let the total evaporation and drying time of the wastewater be t all , then the residence time t2 of the gas in the falling-rate evaporation zone is:

[0049] t2 = t all - t1

[0050] Let t = t2, and the calculated value L of the vertical flow distance of the gas in the falling-rate evaporation zone can be obtained according to the above formula x2 ; that is:

[0051]

[0052] Step 3: Obtain the height H of the hollow cylinder in the drying tower.

[0053] In Step 2, the initial value of the vertical flow distance of the gas in the falling-rate evaporation zone was first assumed to be L x1 , and through L x1 the model parameter a2 was calculated, and then through a2 the calculated value L of the vertical flow distance of the gas in the falling-rate evaporation zone was calculated x2 . L x2 and L x1 are often not equal.

[0054] Reset the value of L x1 to make it gradually tend to the calculated value of L x2 , and repeat the calculation of L x2 . Perform iterative calculation in this way until the following conditions are met:

[0055]

[0056] When the above conditions are met, the vertical flow distance L2 of the gas in the constant-rate evaporation zone is obtained:

[0057] L2 ≈ L x2 ≈ L x1

[0058] The height H of the hollow cylinder in the drying tower is:

[0059] H = L1 + L2

[0060] For wastewaters with different solid contents, determine the vertical flow distance L1 of the gas in the constant-rate evaporation zone and the total evaporation and drying time t of the wastewater in the following way all :

[0061] If the solid content rate x of the wastewater is: x ≤ 10%, then the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 4.5 - 5.2 m, for example 5 m, and the total evaporation and drying time t of the wastewater all is 28 - 32 s, for example 30 s.

[0062] If the solid content rate x of the wastewater is: 10% < x ≤ 20%, then the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 3.8 - 4.4 m, for example 4 m, and the total evaporation and drying time t of the wastewater all is 33 - 37 s, for example 35 s.

[0063] If the solid content rate x of the wastewater is: 20% < x ≤ 30%, then the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 2.8 - 3.5 m, for example 3 m, and the total evaporation and drying time t of the wastewater all is 38 - 42 s, for example 40 s.

[0064] The present invention also provides a wastewater drying method based on variable-speed gas flow, comprising the following steps:

[0065] A) Design and manufacture a drying tower by using the above drying tower design method;

[0066] B) Use the above-designed and manufactured drying tower to evaporate and dry the wastewater with high-temperature gas, and discharge the ash formed by evaporation and drying from the drying tower.

[0067] Calculate the ash moisture content X at the outlet of the drying tower through the following formula:

[0068]

[0069] Wherein: X is the ash moisture content; Q1 is the inlet gas flow rate; W1 is the inlet gas moisture content; h1 is the inlet gas dust content; Q is the wastewater flow rate; W is the wastewater solid content rate; Q2 is the outlet gas flow rate; W2 is the outlet gas moisture content. Q, Q1, and Q2 can be measured by a flow meter, and h1, W1, and W2 can be measured by an on-line gas monitoring system. A flow meter and an on-line gas monitoring instrument can be respectively set on the inlet flue and the outlet flue of the drying tower to measure Q1, Q2, h1, W1, and W2, and a flow meter can be set on the wastewater pipeline to measure Q. The wastewater solid content rate W changes little and can be measured by a conventional method.

[0070] The drying tower first operates at a preset gas-liquid ratio. The gas-liquid ratio refers to the ratio of the gas flow rate to the water flow rate, and the water flow rate is calculated based on the water contained in the wastewater without other impurity components; the temperature T of the high-temperature gas is 550 - 680 K, and the preset gas-liquid ratio is set in the following manner:

[0071] If 550K ≤ T ≤ 600K, set the preset gas-liquid ratio to 11000 - 15500 Nm 3 / t;

[0072] If 600K < T ≤ 640K, set the preset gas-liquid ratio to 9000 - 12500 Nm 3 / t;

[0073] If 640K < T ≤ 680K, set the preset gas-liquid ratio to 7500 - 11500 Nm 3 / t.

[0074] During the evaporation drying process, the gas-liquid ratio of the drying tower is adjusted as follows according to the ash moisture content X:

[0075] If X ≤ 1.0%, reduce the gas-liquid ratio by 5 - 10% relative to the preset gas-liquid ratio;

[0076] If 1.0% < X ≤ 2.0%, keep the preset gas-liquid ratio unchanged;

[0077] If 2.0% < X ≤ 3.0%, increase the gas-liquid ratio by 5 - 15% relative to the preset gas-liquid ratio;

[0078] If 3.0% < X ≤ 5.0%, increase the gas-liquid ratio by 20 - 30% relative to the preset gas-liquid ratio;

[0079] If X > 5.0%, the drying tower stops running.

[0080] The drying tower can be controlled by a control system. The control system is provided with a calculation module for calculating the ash moisture content X in the above manner; a waste water regulating valve is provided on the waste water pipeline, and a gas regulating valve is provided on the inlet flue. The controller is electrically connected to the waste water regulating valve and the gas regulating valve. The controller can control the waste water regulating valve and the gas regulating valve, thereby adjusting the gas-liquid ratio of the drying tower according to the ash moisture content X as described above.

[0081] The present invention fully considers the relationship between the gas flow velocity and temperature inside the drying tower, establishes a model of gas flow time and flow distance, and improves the rationality of the drying tower design; based on the characteristics of wastewater in different evaporation drying stages, calculation methods for gas flow time in the constant rate evaporation stage and gas flow distance in the falling rate evaporation stage are respectively established. At the same time, for wastewater with different solid contents, methods for determining the distance in the constant rate evaporation stage and the total evaporation time of wastewater are formulated, which improves the rationality of the drying tower design and ensures the drying capacity of the drying tower. In addition, the present invention also adjusts the gas-liquid ratio of the drying tower in a specific manner, which can well overcome the adverse effects caused by the temperature fluctuation of high-temperature gas, stably maintain the ash moisture content at the outlet of the drying tower within 2%, reduce the energy consumption of the drying tower while ensuring the evaporation drying effect of wastewater, and ensure the operation stability of the drying tower. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0083] Figure 1 It is a schematic structural diagram of the drying tower of the present invention;

[0084] Figure 2 It is a flowchart for obtaining the height of the hollow cylinder of the drying tower of the present invention.

[0085] DESCRIPTION OF REFERENCE NUMERALS:

[0086] 1: Drying tower; 2: Wastewater pipeline; 3: Inlet flue; 4: Outlet flue; 5: Ash discharge pipeline. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0087] It should be noted that the following detailed description is exemplary and is 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 of ordinary skill in the technical field to which the present application belongs.

[0088] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0089] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0090] Embodiment 1

[0091] Combined with Figure 1 、 Figure 2 As shown, this embodiment provides a design method for a drying tower based on variable-speed gas flow, including the following steps:

[0092] S1: Set up a drying tower 1 with a hollow cylinder, install a rotary atomizer at the top of the drying tower 1, connect the rotary atomizer to the wastewater pipeline 2, set up an inlet flue 3 and an outlet flue 4 at the upper and lower parts of the drying tower 1 respectively. The inside of the drying tower 1 is successively provided with a constant-rate evaporation zone and a falling-rate evaporation zone from top to bottom. A dust discharge pipeline 5 is provided at the bottom of the drying tower 1;

[0093] S2: Obtain the height H of the hollow cylinder of the drying tower 1 through the following steps:

[0094] Step 1: Obtain the residence time t1 of the gas in the constant-rate evaporation zone through the following formula.

[0095]

[0096] b1 = T1

[0097] Where: t1 is the residence time of the gas in the constant-rate evaporation zone; P is the gas pressure; S is the cross-sectional area of the drying tower 1, which is obtained according to the tower diameter of the drying tower 1. The tower diameter of the drying tower 1 is generally 6.5 - 10.0 m; n is the molar flow rate; R is the gas constant; a1, b1 are model parameters; T c is the critical temperature between the constant-rate evaporation zone and the falling-rate evaporation zone of the gas; T1 is the gas inlet temperature; L1 is the vertical flow distance of the gas in the constant-rate evaporation zone.

[0098] Step 2: Obtain the calculated value L of the vertical flow distance of the gas in the falling-rate evaporation zone through the following formula x2 .

[0099]

[0100] b2 = T c

[0101] t2 = t all -t1

[0102] Where: L x1 is the initial value of the vertical flow distance of the gas in the falling-rate evaporation zone, which is set to 2 times the tower diameter of the drying tower 1; L x2 is the calculated value of the vertical flow distance of the gas in the falling-rate evaporation zone; T2 is the gas outlet temperature; t2 is the residence time of the gas in the falling-rate evaporation zone; t all is the total evaporation and drying time of the wastewater.

[0103] Step 3: Obtain the height H of the cylinder of the drying tower 1 through the following formula.

[0104] H = L1 + L2

[0105] Where: L2 is the vertical flow distance of the gas in the constant-rate evaporation zone, which is obtained through iterative calculation until the following conditions are met:

[0106]

[0107] At this time, L2 ≈ L x2 ≈ L x1 。

[0108] For wastewaters with different solid contents, the vertical flow distance L1 of the gas in the constant-rate evaporation zone and the total evaporation drying time t of the wastewater are determined as follows all :

[0109] If the solid content x of the wastewater is: x ≤ 10%, then the value of the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 4.5 - 5.2 m, such as 5 m, and the total evaporation drying time t of the wastewater all takes a value of 28 - 32 s, such as 30 s.

[0110] If the solid content x of the wastewater is: 10% < x ≤ 20%, then the value of the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 3.8 - 4.4 m, such as 4 m, and the total evaporation drying time t of the wastewater all takes a value of 33 - 37 s, such as 35 s.

[0111] If the solid content x of the wastewater is: 20% < x ≤ 30%, then the value of the vertical flow distance L1 of the gas in the constant-rate evaporation zone is 2.8 - 3.5 m, such as 3 m, and the total evaporation drying time t of the wastewater all takes a value of 38 - 42 s, such as 40 s.

[0112] After designing and manufacturing the drying tower in the above manner, the designed and manufactured drying tower can be used to evaporate and dry the wastewater; specifically, the wastewater is atomized into droplets by a rotary atomizer and enters the drying tower 1, while the high-temperature gas enters the drying tower 1 through the inlet flue 3. In the drying tower 1, the wastewater droplets are fully heat-exchanged with the high-temperature gas, the wastewater is evaporated and dried, the gas is discharged through the outlet flue 4, and the ash is discharged through the ash discharge pipeline 5.

[0113] Example 2

[0114] In this example, the method of Example 1 is used to evaporate and dry the wastewater; the parameter settings are as follows: the solid content of the wastewater is 4%, the high-temperature gas flow rate is 55064 m 3 / h (standard condition), the gas inlet temperature is 623 K, the gas outlet temperature is 413 K, the drying tower diameter D is 8.5 m, the value of L1 is 5 m, and t all takes a value of 30 s.

[0115] Step 1: Obtain the residence time t1 of the gas in the constant-rate evaporation zone according to the following formula.

[0116]

[0117] b1 = T1

[0118] According to T c = 426K, T1 = 623K, L1 = 5m; we get: a1 = -39.4, b1 = 623.

[0119] According to P = 1.0×10 5 Pa, S = 56.8m 2 , n = 682.8mol / s, R = 8.314J / (mol˙K), L1 = 5m; we get: t1 ≈ 9.8s.

[0120] Step 2: Obtain the calculated value of the vertical flow distance L of the gas in the falling-rate evaporation zone according to the following formula x2 .

[0121]

[0122] b2 = T c

[0123] t2 = t all - t1

[0124] According to T c = 426K, T2 = 413K, assuming L x1 = 17m; we get: a2 = -0.765, b2 = 426.

[0125] Let t = t2 = t all - t1 = 20.2s, we get: L x2 = 8.5m.

[0126] Step 3: Obtain the height H of the hollow cylinder in the drying tower according to the following formula.

[0127] Reset the value of L x1 to gradually approach the calculated value of L x2 and repeat the calculation of L x2 . Perform iterative calculations in this way until the following conditions are met:

[0128]

[0129] We get: L2 ≈ 8.4m.

[0130] The height H of the hollow cylinder in the drying tower = L1 + L2 = 13.4m.

[0131] Using the drying tower designed and manufactured above to evaporate and dry the wastewater, the zero discharge of the wastewater can be stably achieved, and the wastewater treatment capacity W = 5995kg / h.

[0132] The drying intensity of the drying tower: That is, every m 3 The amount of wastewater treated by the drying tower per hour is 7.90 kg.

[0133] Example 3

[0134] In this example, the method of Example 1 is used to dry the wastewater; the parameters are as follows: the solid content of the wastewater is 15.6%, the high-temperature gas flow rate is 93626 m 3 / h (standard condition), the gas inlet temperature is 613 K, the gas outlet temperature is 438 K, the diameter of the drying tower is 10.0 m, the value of L1 is 4 m, and t all The value is 35 s.

[0135] Step 1: Obtain the residence time t1 of the gas in the constant-rate evaporation zone according to the following formula.

[0136]

[0137] b1 = T1

[0138] According to T c = 451 K, T1 = 613 K, L1 = 4 m; it is obtained that: a1 = -40.5, b1 = 613.

[0139] According to P = 1.0×10 5 Pa, S = 78.5 m 2 , n = 1161 mol / s, R = 8.314 J / (mol˙K), L1 = 4 m; it is obtained that: t1 = 6.2 s.

[0140] Step 2: Obtain the calculated value L of the vertical flow distance of the gas in the falling-rate evaporation zone according to the following formula x2 .

[0141]

[0142] b2 = T c

[0143] t2 = t all -t1

[0144] According to T c = 451 K, T2 = 438 K, assuming L x1 = 20 m; it is obtained that: a2 = -0.65, b2 = 451.

[0145] Let t = t2 = t all -t1 = 28.8 s, it is obtained that: L x2 = 15.6 m.

[0146] Step 3: Obtain the height H of the hollow cylinder in the drying tower according to the following formula.

[0147] Reset the value of L x1 so that it gradually approaches the calculated value of L x2 and repeat the calculation of L x2 . Perform cyclic iterative calculations in this way until the following conditions are met:

[0148]

[0149] Obtain: L2≈15.5m.

[0150] The height H of the hollow cylinder in the drying tower is H = L1 + L2 = 19.5m.

[0151] Using the drying tower designed and manufactured as described above to evaporate and dry the wastewater can stably achieve zero discharge of the wastewater, and the wastewater treatment capacity W = 9240 kg / h.

[0152] The drying intensity of the drying tower: That is, the amount of wastewater treated per hour by each m 3 of the drying tower is 6.03 kg.

[0153] Example 4

[0154] In this example, the method of Example 1 is used to dry the wastewater; the parameters are as follows: the solid content of the wastewater is 27.5%, the high-temperature gas flow rate is 19294 m 3 / h (standard condition), the gas inlet temperature is 645 K, the gas outlet temperature is 438 K, the drying tower diameter is 6.5 m, the value of L1 is 3 m, and t all takes a value of 40 s.

[0155] Step 1: Obtain the residence time t1 of the gas in the constant-rate evaporation zone according to the following formula.

[0156]

[0157] b1 = T1

[0158] According to T c = 458 K, T1 = 645 K, L1 = 3 m; obtain: a1 = -62.3, b1 = 645.

[0159] According to P = 1.0×10 5 Pa, S = 33.2 m 2 , n = 239.3 mol / s, R = 8.314 J / (mol·K), L1 = 3 m; obtain: t1 = 9.3 s.

[0160] Step 2: Obtain the calculated value of the vertical flow distance L of the gas in the falling-rate evaporation zone according to the following formula. x2 .

[0161]

[0162] b2 = T c

[0163] t2 = t all -t1

[0164] According to T c = 458K, T2 = 438K, assuming L x1 = 13m; we get: a2 = -1.5, b2 = 458.

[0165] Let t = t2 = t all -t1 = 30.7s, we get: L x2 = 8.2m.

[0166] Step 3: Obtain the height H of the hollow cylinder in the drying tower according to the following formula.

[0167] Reset the value of L x1 to gradually approach the calculated value of L x2 and repeat the calculation of L x2 . Perform cyclic iterative calculation in this way until the following conditions are met:

[0168]

[0169] We get: L2 ≈ 8.1m.

[0170] The height H of the hollow cylinder in the drying tower = L1 + L2 = 11.1m.

[0171] Using the drying tower designed and manufactured as above to evaporate and dry the wastewater, zero discharge of the wastewater can be stably achieved, and the wastewater treatment capacity W = 2415 kg / h.

[0172] The drying intensity of the drying tower: That is, the amount of wastewater treated per m 3 of the drying tower per hour is 6.53 kg.

[0173] Example 5

[0174] Using the drying tower designed in Example 2 to evaporate and dry the wastewater, the drying tower first operates at a preset gas-liquid ratio of 9568 Nm 3 / t, and during the operation, calculate the ash moisture content X at the outlet of the drying tower through the following formula:

[0175]

[0176] Adjust the gas-liquid ratio of the drying tower according to the ash moisture content X as follows:

[0177] If X ≤ 1.0%, reduce the gas-liquid ratio by 10% relative to the preset gas-liquid ratio;

[0178] If 1.0% < X ≤ 2.0%, maintain the preset gas-liquid ratio unchanged;

[0179] If 2.0% < X ≤ 3.0%, increase the gas-liquid ratio by 15% relative to the preset gas-liquid ratio;

[0180] If 3.0% < X ≤ 5.0%, increase the gas-liquid ratio by 30% relative to the preset gas-liquid ratio;

[0181] If X > 5.0%, stop the operation of the drying tower.

[0182] The ash moisture content X of the drying tower every 10 days of operation, as well as the average energy consumption and operation effect during the operation of the drying tower, are shown in Table 1; among them, the average energy consumption refers to the additional energy that needs to be supplemented to the thermal power unit due to the evaporation and drying of wastewater, which is the average value during the test period.

[0183] Control Example 1

[0184] Except for calculating the height of the hollow cylinder in the drying tower by the average flow rate method, the other conditions are the same as those in Example 2; the average flow rate calculation method is as follows:

[0185] Average temperature

[0186] Average flow rate

[0187] The height H of the hollow cylinder in the drying tower = v × t all ≈15.4m.

[0188] Compared with Example 2, the height of the hollow cylinder in the drying tower calculated by the method of this control example is 2m more, and it needs to occupy about 15% more space in the vertical direction, consume about 8240 kg more steel, and need to configure mechanical supports with corresponding loads.

[0189] The drying tower designed and manufactured as above is used to evaporate and dry wastewater, and the process conditions are the same as those in Example 2. The drying intensity of the drying tower in this control example: That is, per m 3 The amount of wastewater treated by the drying tower per hour is 6.89 kg.

[0190] Compared with Example 2, the drying intensity of the drying tower in this control example is reduced by 12.8%; that is, the amount of wastewater treated by the drying tower per hour in this control example is 1.01 kg less than that in Example 2, and the drying capacity is significantly weakened. 3 The amount of wastewater treated by the drying tower per hour is 1.01 kg less than that in Example 2, and the drying capacity is significantly weakened.

[0191] Control Example 2

[0192] Except for calculating the height of the hollow cylinder in the drying tower by the average flow velocity method, the other conditions are the same as those in Example 3; the average flow velocity calculation method is as follows:

[0193] Average temperature

[0194] Average flow velocity

[0195] The height H of the hollow cylinder in the drying tower = v × t all ≈22.3 m.

[0196] Compared with Example 3, the height of the hollow cylinder in the drying tower calculated by the method of this comparative example is 2.8 m more, and it needs to occupy about 14.4% more space in the vertical direction, consume about 13,850 kg more steel, and need to configure mechanical supports with corresponding loads.

[0197] The drying tower designed and manufactured as above is used to evaporate and dry the wastewater, and the process conditions are the same as those in Example 3; the drying intensity of the drying tower in this comparative example: That is, per m 3 The amount of wastewater treated by the drying tower per hour is 5.27 kg.

[0198] Compared with Example 3, the drying intensity of the drying tower in this comparative example is reduced by 12.6%; that is, the amount of wastewater treated by the drying tower per hour per m 3 is 0.76 kg less than that in Example 3, and the drying capacity is significantly weakened.

[0199] Comparative Example 3

[0200] Except for calculating the height of the hollow cylinder in the drying tower by the average flow velocity method, the other conditions are the same as those in Example 4; the average flow velocity calculation method is as follows:

[0201] Average temperature

[0202] Average flow velocity

[0203] The height of the hollow cylinder in the drying tower

[0204] Compared with Example 4, the height of the hollow cylinder in the drying tower calculated by the method of this comparative example is 1.8 m more, and it needs to occupy about 16.2% more space in the vertical direction, consume about 5,400 kg more steel, and need to configure mechanical supports with corresponding loads.

[0205] The drying tower designed and manufactured as above is used to evaporate and dry the wastewater, and the process conditions are the same as those in Example 4; the drying intensity of the drying tower in this comparative example: That is, per m 3The amount of wastewater treated by the drying tower per hour is 5.68 kg.

[0206] Compared with Example 4, the drying intensity of the drying tower in this comparative example is reduced by 13.0%; that is, the amount of wastewater treated by the drying tower per cubic meter in this comparative example is 3 0.85 kg less than that in Example 4 per hour, and the drying capacity is significantly weakened.

[0207] Comparative Example 4

[0208] The drying tower designed in Example 2 is used to evaporate and dry the wastewater. Except that the drying tower always operates at a preset gas-liquid ratio of 9568 Nm 3 / t (that is, the gas-liquid ratio of the drying tower is not adjusted during operation), the remaining operating parameters are the same as those in Example 5.

[0209] The ash moisture content X of the drying tower every 10 days of operation, as well as the average energy consumption and operation effect during the operation of the drying tower, are shown in Table 1.

[0210] Comparative Example 5

[0211] The drying tower designed in Example 2 is used to evaporate and dry the wastewater. The drying tower operates at a preset gas-liquid ratio of 9568 Nm 3 / t. Except that the wastewater and gas flow rates entering the drying tower are adjusted in the following manner during operation, the remaining operating parameters are the same as those in Example 5.

[0212] In this comparative example, the wastewater and gas flow rates are adjusted according to the flue gas temperature Tout at the outlet of the drying tower:

[0213] If 150°C ≤ Tout ≤ 160°C, keep the wastewater and gas flow rates unchanged;

[0214] If 140°C ≤ Tout < 150°C, reduce the wastewater flow rate entering the drying tower and / or increase the gas flow rate entering the drying tower until Tout rises to 150°C ≤ Tout ≤ 160°C;

[0215] If 160°C < Tout ≤ 170°C, increase the wastewater flow rate entering the drying tower and / or reduce the gas flow rate entering the drying tower until Tout drops to 150°C ≤ Tout ≤ 160°C;

[0216] If Tout < 140°C, increase the gas flow rate entering the drying tower and / or reduce the wastewater flow rate entering the drying tower until Tout rises to 140°C ≤ Tout < 150°C;

[0217] If Tout > 170°C, reduce the gas flow rate entering the drying tower and / or increase the wastewater flow rate entering the drying tower until Tout drops to 160°C < Tout ≤ 170°C.

[0218] During operation, the ash moisture content X at the outlet of the drying tower is calculated by the following formula:

[0219]

[0220] The ash moisture content X of the drying tower every 10 days of operation, as well as the average energy consumption and operation effect during the operation of the drying tower, are shown in Table 1.

[0221] Table 1 Comparison of ash moisture content, average energy consumption and operation effect of each wastewater drying method

[0222]

[0223] The results in Table 1 show that:

[0224] 1. The method of Comparative Example 4 did not adjust the gas-liquid ratio of the drying tower, resulting in extremely unstable wastewater drying effect. Problems such as wet ash, blockage, and corrosion occurred during operation, which had a serious adverse impact on the normal operation of the drying tower; at the same time, some ash agglomerated and caked, thus affecting the subsequent resource utilization of the ash; in addition, the operation energy consumption of the drying tower was high, and there was a problem of heat waste.

[0225] 2. The method of Comparative Example 5 adjusted the wastewater and gas flow rates of the drying tower in a conventional manner, and the wastewater drying effect was unstable. Problems such as wet ash, blockage, and corrosion occurred during operation, which had an adverse impact on the normal operation of the drying tower; at the same time, some ash agglomerated and caked, thus affecting the subsequent resource utilization of the ash.

[0226] 3. The method of Example 5 detected the ash moisture content in a specific manner, which was beneficial to accurately judge the evaporation and drying effect of the wastewater in the drying tower; at the same time, based on the ash moisture content, the operation parameters of the drying tower were adjusted in a specific manner, and the ash moisture content could be stably maintained within 2%. It well overcame the adverse impact brought by the temperature fluctuation of the high-temperature gas in the drying tower. It could not only meet the requirements of industry standards, but also reduce the energy consumption of the drying tower, ensure the wastewater drying effect of the drying tower, and guarantee the safe and stable operation of the drying tower.

[0227] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for a drying tower based on variable-speed gas flow, characterized in that, It includes the following steps: S1: Set up a drying tower with a hollow cylinder, install a rotary atomizer at the top of the drying tower, set a gas inlet and a gas outlet at the upper and lower parts of the drying tower respectively, and successively arrange a constant-rate evaporation zone and a falling-rate evaporation zone from top to bottom inside the drying tower; S2: Obtain the height of the hollow cylinder in the drying tower through the following formulas (1)-(3) H ; Wherein: t 1 is the residence time of the gas in the constant-rate evaporation zone, with the unit of s; P is the gas pressure, with the unit of Pa; S is the cross-sectional area of the drying tower, with the unit of m 2 ; n is the molar flow rate, with the unit of mol / s; R is the gas constant; a 1, b 1, a 2, b 2 are model parameters; L 1 is the vertical flow distance of the gas in the constant-rate evaporation zone, with the unit of m; L x2 is the calculated value of the vertical flow distance of the gas in the falling-rate evaporation zone, with the unit of m; t 2 is the residence time of the gas in the falling-rate evaporation zone, with the unit of s; H is the height of the hollow cylinder in the drying tower, with the unit of m; L 2 is the vertical flow distance of the gas in the constant-rate evaporation zone, with the unit of m; Obtained through the following formula a 1、 b 1: Wherein: T c is the critical temperature between the constant-rate evaporation zone and the falling-rate evaporation zone of the gas, with the unit of K; T 1 is the gas inlet temperature, with the unit of K; Obtained through the following formula a 2、 b 2: Wherein: T 2 is the gas outlet temperature, with the unit of K; T c is the critical temperature between the constant-rate evaporation zone and the falling-rate evaporation zone of the gas, with the unit of K; L x1 is the initial value of the vertical flow distance of the gas in the falling-rate evaporation zone, with the unit of m, and it is initially set to be 1.8 - 2.2 times the diameter of the drying tower; Adjust L x1 the value of, so that it gradually approaches L x2 the calculated value of, and repeat the calculation L x2 , and perform iterative calculations in this cycle until the following conditions are met: When the above conditions are satisfied, the vertical flow distance of the gas in the constant velocity evaporation zone is obtained L 2: The residence time of the gas in the falling-rate evaporation zone is obtained through the following formula t 2: Wherein: t all is the total evaporation and drying time of the wastewater, in s; Determine the vertical flow distance of the gas in the constant-rate evaporation zone according to the solid content x of the wastewater L 1 and the total evaporation and drying time of the wastewater t all Value range: If x ≤ 10%, then L The value of 1 is 4.5 - 5.2 m, t all The value is 28 - 32 s; If 10% < x ≤ 20%, then L The value of 1 ranges from 3.8 to 4.4 m, t all The value ranges from 33 to 37 s; If 20% < x ≤ 30%, then L 1 takes a value of 2.8 - 3.5 m, t all takes a value of 38 - 42 s.

2. A wastewater drying method based on variable-speed gas flow, characterized in that, It includes the following steps: A) Design and manufacture a drying tower by using the drying tower design method described in Claim 1; B) Use the above-designed and manufactured drying tower to evaporate and dry the wastewater with high-temperature gas, and discharge the ash formed by evaporation and drying from the drying tower.

3. The wastewater drying method according to claim 2, wherein, Calculate the ash moisture content X at the outlet of the drying tower through the following formula: Wherein: X is the ash moisture content; Q 1 is the inlet gas flow rate; W 1 is the inlet gas moisture content; Q is the wastewater flow rate; W is the wastewater solid content; Q 2 is the outlet gas flow rate; W 2 is the outlet gas moisture content; h 1 is the inlet gas dust content.

4. The wastewater drying method according to claim 3, characterized in that, The drying tower first operates at a preset gas-liquid ratio; the temperature T of the high-temperature gas is 550 - 680 K, and the preset gas-liquid ratio is set in the following way: If 550 K ≤ T ≤ 600 K, set the preset gas-liquid ratio to 11000 - 15500 Nm 3 / t; If 600 K < T ≤ 640 K, set the preset gas-liquid ratio to 9000 - 12500 Nm 3 / t; If 640 K < T ≤ 680 K, set the preset gas-liquid ratio to 7500 - 11500 Nm 3 / t.

5. The wastewater drying method according to claim 4, characterized in that, During the evaporation and drying process, adjust the gas-liquid ratio of the drying tower according to the ash moisture content X as follows: If X ≤ 1.0%, reduce the gas-liquid ratio by 5 - 10% relative to the preset gas-liquid ratio; If 1.0% < X ≤ 2.0%, keep the preset gas-liquid ratio unchanged; If 2.0% < X ≤ 3.0%, increase the gas-liquid ratio by 5 - 15% relative to the preset gas-liquid ratio; If 3.0% < X ≤ 5.0%, increase the gas-liquid ratio by 20 - 30% relative to the preset gas-liquid ratio; If X > 5.0%, stop the operation of the drying tower.

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