A method for calculating the maximum temperature rise of non-25℃ solution after dilution

Abstract

The present invention provides a method for calculating the maximum temperature rise of a non-25°C solution after dilution, comprising the following steps: according to engineering design conditions, the concentration of the solution before dilution and the concentration after dilution for which the temperature rise is pre-solved are set, and the solution and solvent temperatures before dilution are set to the design temperature; the solution is a solution with a known molar heat of solution at 25°C; the solute and solvent are set as the initial state according to the concentration of the solution after dilution, and the temperature of the initial state is 25°C; the diluted solution is the final state, and the temperature of the diluted solution is the design temperature; two thermodynamic paths from the initial state to the final state are designed, one of which contains the heat release △H from before dilution to after dilution of the solution at the design temperature; according to the principle of equal enthalpy change of the two thermodynamic paths, the heat release △H and the solution temperature rise are calculated. The present invention does not require chemical experiments, and can calculate the heat release and solution temperature rise of various solute solutions at other design temperatures based on the 25°C molar heat of solution data.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for calculating the maximum temperature rise of a non-25°C solution after dilution. Background Art

[0002] Water treatment systems often carry out chemical treatment, such as boiler feed water treatment systems in power plants and ion exchange systems for condensate polishing. When regenerating anion resins, high-concentration alkali solution is often added to the desalted water pipeline for regeneration, mixed into low-concentration alkali solution in the delivery pipeline, and delivered to the ion exchanger for anion resin regeneration. Alkali solution dilution is an exothermic process, and the solution temperature rises after dilution. The material selection of dilution mixing equipment and pipelines requires understanding the highest temperature of the delivery solution after dilution and exothermicity.

[0003] According to the existing data, we can only calculate the heat released by dilution of sodium hydroxide with different concentrations at 25°C. It is difficult to calculate the heat released by dilution of sodium hydroxide solution under actual operating temperature conditions, and it is difficult to further estimate the temperature rise of the sodium hydroxide solution after dilution. If we want to understand the temperature rise of the sodium hydroxide solution after dilution, we often have to use experiments to evaluate it. However, chemical experiments are rarely carried out for engineering design units, which often lack relevant equipment and professional operations.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for calculating the maximum temperature rise of a non-25°C solution after dilution. The method does not require chemical experiments and can calculate the heat release and solution temperature rise of various solute solutions at other design temperatures based on 25°C molar heat of solution data.

[0006] In a first aspect of the present invention, a method for calculating the maximum temperature rise of a non-25°C solution after dilution is provided, comprising the following steps:

[0007] According to the engineering design conditions, the concentration of the solution before dilution and the concentration after dilution for which the temperature rise is pre-solved are set, and the solution and solvent temperatures before dilution are set to the design temperature; the solution is a solution with a known molar heat of solution at 25°C;

[0008] The solute and solvent are set as the initial state according to the concentration of the diluted solution. The solute and solvent are used as a research system, and the temperature of the system in the initial state is set to 25°C; the diluted solution is used as the final state, and the temperature of the diluted solution is set to the design temperature;

[0009] Design two thermodynamic paths from the initial state to the final state, one of which contains the heat release △H before and after the solution is diluted at the design temperature, and the heat changes of other thermodynamic processes in the two paths can be solved;

[0010] The total enthalpy change of thermodynamic path 1 is △H n +△H, where △H n is the heat change of other thermodynamic processes in thermodynamic path 1; the total enthalpy change of thermodynamic path 2 is △H m ; According to the principle that the enthalpy changes of the two thermodynamic paths are equal, that is, △H n +△H=△H m , then △H=△H m -△H n ;

[0011] The temperature rise of the solution is calculated based on the heat released △H from before to after dilution at the design temperature.

[0012] Preferably, the design temperature is T 设 The concentration of the solution before dilution is C1, in which the solute content is n moles and the solvent content is n' moles; the concentration of the solution after dilution is C2, in which the solute content is n moles and the solvent content is n" moles. The two thermodynamic paths are designed as follows: Figure 1 shown.

[0013] Preferably, the total enthalpy change of thermodynamic path 1 is △H1+△H2+△H, and the total enthalpy change of thermodynamic path 2 is △H3+△H4. According to the principle that the enthalpy changes of the two thermodynamic paths are equal,

[0014] △H=△H4+△H3-△H2-△H1.

[0015] Preferably, in thermodynamic path 1, at 25°C, the molar heat of solution of C1 concentration is

[0016] △HΘsol1, then △H1=△HΘsol1;

[0017] △H2=(n×M×0.001 / C1)×Cp×△T+(n”-n’)×0.001×M’×Cp’×△T;

[0018] Where: n is the number of moles of solute in the C1 concentration solution;

[0019] n' is the number of moles of solvent in the C1 concentration solution;

[0020] n” is the number of moles of solvent in the C2 concentration solution;

[0021] M is the molecular weight of the solute;

[0022] M' is the molecular weight of the solvent;

[0023] Cp is the specific heat capacity of the solution with concentration C1;

[0024] Cp' is the specific heat capacity of the solvent;

[0025] △T is the temperature change of C1 concentration solution and solvent during the heat absorption process, △T=T 设 -25℃.

[0026] Preferably, in thermodynamic path 2, at 25°C, the molar heat of solution of C2 concentration is

[0027] △HΘsol2, then △H3=△HΘsol2;

[0028] △H4=(n×M×0.001 / C2)×Cp”×△T;

[0029] Where: n is the number of moles of solute in the C2 concentration solution;

[0030] M is the molecular weight of the solute;

[0031] Cp” is the specific heat capacity of the solution with concentration C2;

[0032] △T is the temperature change of C2 concentration solution and solvent during the heat absorption process, △T=T 设 -25℃.

[0033] Preferably, when the heat released △H is all used for the internal energy of the diluted solution, so that the temperature of the diluted solution increases, the increased temperature is △T1=-Q / (m'×Cp");

[0034] The highest temperature that the solution can reach after dilution is T = T 设 +△T1;

[0035] Where: Cp” is the specific heat capacity of the diluted solution;

[0036] Q is the heat released, Q = △H;

[0037] m' is the mass of the diluted solution;

[0038] Cp” is the specific heat capacity of the diluted solution.

[0039] Preferably, the solution is a sodium hydroxide solution, the solute is sodium hydroxide, and the solvent is water.

[0040] The second aspect of the present invention provides the application of the above-mentioned method for calculating the maximum temperature rise of a non-25°C solution after dilution in the field of water treatment.

[0041] A third aspect of the present invention provides a water treatment system, which adopts the above-mentioned method for calculating the maximum temperature rise after dilution of a non-25°C solution.

[0042] Preferably, the water treatment system is an ion exchange regeneration system.

[0043] Beneficial effects: The calculation method of the present invention does not require chemical experiments and can calculate the heat release and solution temperature rise of various solute solutions at other design temperatures through the known molar heat of solution of various solutions at 25°C, thereby providing a reference for engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Two schematic diagrams of thermodynamic path design provided by the present invention. Figure 2 Schematic diagrams of two thermodynamic pathways designed to study sodium hydroxide and water as a system. DETAILED DESCRIPTION

[0045] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0046] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0047] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example

[0049] In this embodiment, the liquid temperature is designed to be T 设 Taking 27℃ as an example, the regeneration of boiler feed water anion exchange resin uses 4% sodium hydroxide solution as an example. The drug concentration is assumed to be 30%. The regeneration process requires that the 30% sodium hydroxide solution in the storage tank be diluted to 4% concentration with regenerated demineralized water in the dosing pipeline and mixing equipment.

[0050] When the liquid temperature is 27°C, taking a 30% sodium hydroxide solution containing 1 mol of sodium hydroxide as an example, after the concentration C1 of 30% sodium hydroxide solution is diluted to the concentration C2 of 4%, the heat released is △H.

[0051] As a research system, sodium hydroxide and water have an initial state of 25°C, 1 mol of sodium hydroxide and 53.3 mol of water; the final state is a mixed solution of sodium hydroxide containing 1 mol of sodium hydroxide and a concentration of 4% at 27°C. The research system changes from the initial state to the following: Figure 2 Two thermodynamic paths are shown to reach the final state.

[0052] At 27°C, diluting a 30% sodium hydroxide solution into a 4% sodium hydroxide solution will produce heat of dilution.

[0053] The following solution containing 1 mol of NaOH solute is taken as the research object:

[0054] The ratio of the amount of NaOH (solute) to H2O (solvent) in a 30% NaOH solution containing 1 mol of NaOH solute is:

[0055] a30%=nNaOH / n'H20=(30 / 40) / (70 / 18)=1 / 5.18;

[0056] The molar ratio of NaOH to H2O in a 4% NaOH solution containing 1 mol of NaOH solute is:

[0057] a4%=nNaOH / n”H20=(4 / 40) / (96 / 18)=1 / 53.3;

[0058] At 27°C, to prepare a 4% NaOH solution from a 30% NaOH solution containing 1 mol of NaOH solute, the amount of H2O at 27°C required is n"-n'=53.3-5.18=48.1 mol.

[0059] Take 30% NaOH solution containing 1 mol NaOH solute and 48.1 mol H2O as a system, △H is the enthalpy change of the system before and after dilution.

[0060] According to the first law of thermodynamics and Hess's law, the enthalpy change caused by the system changing from the initial state to the final state depends only on the state of the system before and after the change, and has nothing to do with the specific change path. Assume that the initial state of the system is 1 mol NaOH at 25℃ + 53.3 mol H2O at 25℃, and the final state is 4% NaOH solution containing 1 mol NaOH solute at 27℃.

[0061] According to the principle that the enthalpy changes of the two thermodynamic paths are equal, that is:

[0062] △H1+△H2+△H=△H3+△H4;

[0063] △H=△H4+△H3-△H2-△H1.

[0064] At 25°C, take the molar heat of solution of sodium hydroxide solution at a30% = 1 / 5.18

[0065] △HΘsol=-37.75kJ / mol, then

[0066] △H1=△HΘsol=-37.75kJ=-9.02kcal

[0067] △H2=(n×M×0.001 / 30%)×Cp×△T+48.1×0.001×M'×Cp'×△T

[0068] =(40×0.001 / 0.3)×0.845×(27-25)+0.0481×18×0.997×2

[0069] =0.225+1.726

[0070] =1.951kcal

[0071] At 25°C, take the molar heat of solution of sodium hydroxide solution at a4% = 1 / 53.3

[0072] △HΘsol=-42.5kJ / mol, then

[0073] △H3=△HΘsol=-42.5kJ=-10.153kcal

[0074] △H4=(n×M×0.001 / 4%)×C p”×△T

[0075] =(40×0.001 / 0.04)×0.951×(27-25)

[0076] =1.902kcal

[0077] Where: a is the concentration of sodium hydroxide solution;

[0078] n is the number of moles of sodium hydroxide in the analyzed solution, n = 1;

[0079] M is the molecular weight of sodium hydroxide;

[0080] M' is the molecular weight of water;

[0081] Cp is the specific heat capacity of 30% sodium hydroxide solution, Cp = 0.845 kcalC (kgC℃) -1 ;

[0082] Cp' is the specific heat capacity of water, Cp' = 0.997 kcalC (kgC℃) -1 ;

[0083] Cp" is the specific heat capacity of 4% sodium hydroxide solution, take Cp" = 0.951kcalC (kgC℃) -1 ;

[0084] △T is the change in temperature during the heat absorption process of the solution and water, △T = 27-25 = 2°C;

[0085] △H=△H4+△H3-△H2-△H1

[0086] =1.902-10.153-1.951+9.02

[0087] =-1.182kcal

[0088] That is, at a liquid temperature of 27°C, dilute a 30% sodium hydroxide solution containing 1 mol of NaOH. If the concentration of the diluted solution is required to be 4%, the heat released during the dilution process is Q = △H = -1.182 kcal, and the negative sign indicates that the dilution process is an exothermic process.

[0089] If all the above heat release is converted into the internal energy of a sodium hydroxide solution containing 1 mol of NaOH with a concentration of 4%, so that the temperature of the diluted sodium hydroxide solution increases, the increased temperature △T1 is:

[0090] △T1=-Q / (m'×Cp")

[0091] =1.182 / ((40+53.3×18)×0.001×0.951)

[0092] =1.24℃

[0093] Where: Cp" is the specific heat capacity of 4% sodium hydroxide solution, Cp" = 0.951kcalC (kgC℃) -1 ;

[0094] The highest temperature that the solution system can reach is T = T 设 +△T1, that is, 27+1.24=28.24℃.

[0095] In actual engineering situations, the dilution process is a non-adiabatic process. The theoretically calculated heat -Q = 1.182 kcal cannot be completely converted into the internal energy of the dilute solution. The temperature of the 4% sodium hydroxide solution after dilution will be lower than 28.24°C and higher than 27°C.

[0096] This embodiment can calculate the heat release of sodium hydroxide dilution under different temperature conditions by finding the heat release of sodium hydroxide solutions with different concentrations at 25°C. In engineering design, the temperature rise range of the sodium hydroxide solution after dilution under the corresponding temperature conditions can be calculated without the help of chemical experiments. This can be used for calculating the temperature rise range of the solution after dilution in the sodium hydroxide dosing system, and can also be used for calculating the heat release and temperature rise of other drugs after dilution.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the maximum temperature rise of a non-25°C solution after dilution, characterized in that: The steps include: According to the engineering design conditions, the concentration of the solution before dilution and the concentration after dilution for which the temperature rise is pre-solved are set, and the solution and solvent temperatures before dilution are set to the design temperature; the solution is a solution with a known molar heat of solution at 25°C; The solute and solvent are set as the initial state according to the concentration of the diluted solution. The solute and solvent are used as a research system, and the temperature of the system in the initial state is set to 25°C. The diluted solution is used as the final state, and the temperature of the diluted solution is set to the design temperature. Design two thermodynamic paths from the initial state to the final state, one of which contains the heat release △H before and after the solution is diluted at the design temperature, and the heat changes of other thermodynamic processes in the two paths can be solved; The total enthalpy change of thermodynamic path 1 is △H n +△H, where △H n is the heat change of other thermodynamic processes in thermodynamic path 1; the total enthalpy change of thermodynamic path 2 is △H m ; According to the principle that the enthalpy changes of the two thermodynamic paths are equal, that is, △H n +△H=△H m , then △H=△H m -△H n ; The temperature rise of the solution is calculated based on the heat released △H from before to after dilution at the design temperature.

2. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 1, characterized in that: The design temperature is T 设 ; The concentration of the solution before dilution is C1, in which the solute content is n moles and the solvent content is n' moles; the concentration of the solution after dilution is C2, in which the solute content is n moles and the solvent content is n" moles. The two thermodynamic path designs are shown in Figure 1.

3. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 2, characterized in that: The total enthalpy change of thermodynamic path 1 is △H1+△H2+△H, and the total enthalpy change of thermodynamic path 2 is △H3+△H4. According to the principle that the enthalpy changes of the two thermodynamic paths are equal, △H=△H4+△H3-△H2-△H1.

4. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 3, characterized in that: In thermodynamic path 1, at 25°C, the molar heat of solution of the C1 concentration solution is △HΘsol1, so △H1=△HΘsol1; △H2=(n×M×0.001 / C1)×Cp×△T+(n”-n’)×0.001×M’×Cp’×△T; Where: n is the number of moles of solute in the C1 concentration solution; n' is the number of moles of solvent in the C1 concentration solution; n” is the number of moles of solvent in the C2 concentration solution; M is the molecular weight of the solute; M' is the molecular weight of the solvent; Cp is the specific heat capacity of the solution with concentration C1; Cp' is the specific heat capacity of the solvent; △T is the temperature change of C1 concentration solution and solvent during the heat absorption process, △T=T 设 -25℃.

5. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 3, characterized in that: In thermodynamic path 2, at 25°C, the molar heat of solution of the C2 concentration solution is △HΘsol2, so △H3=△HΘsol2; △H4=(n×M×0.001 / C2)×Cp”×△T; Where: n is the number of moles of solute in the C2 concentration solution; M is the molecular weight of the solute; Cp” is the specific heat capacity of the solution with concentration C2; △T is the temperature change of C2 concentration solution and solvent during the heat absorption process, △T = T 设 -25℃.

6. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 1, characterized in that: When the heat released △H is all used for the internal energy of the diluted solution, causing the temperature of the diluted solution to rise, the increased temperature is △T1=-Q / (m'×Cp”); The maximum temperature that the solution can reach after dilution is T = T 设 +△T1; Where: Cp” is the specific heat capacity of the diluted solution; Q is the heat released, Q = △H; m' is the mass of the diluted solution; Cp” is the specific heat capacity of the diluted solution.

7. The method for calculating the maximum temperature rise of a non-25°C solution after dilution according to claim 1, characterized in that: The solution is a sodium hydroxide solution, the solute is sodium hydroxide, and the solvent is water.

8. Application of the method for calculating the maximum temperature rise of a non-25°C solution after dilution as claimed in any one of claims 1 to 7 in the field of water treatment.

9. A water treatment system, characterized in that: The method for calculating the maximum temperature rise of a non-25°C solution after dilution as described in any one of claims 1 to 8 is adopted.

10. The water treatment system according to claim 9, characterized in that: The water treatment system is an ion exchange regeneration system.

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