Method for determining alkali excess threshold value of ammonia distillation process based on conductivity second-order change rate

Abstract

The invention relates to the field of chemical engineering, in particular to a method for determining an excessive alkali threshold value based on a conductivity second-order change rate in an industrial ammonia distillation process, which mainly comprises the following steps: recording data of conductivity and alkali addition amount, calculating a change rate of the conductivity along with the liquid alkali addition amount and a second-order change rate, and drawing a curve graph; and judging the alkali excess threshold according to the curve graph. The method can accurately determine the threshold value of the amount of alkali added into the wastewater before ammonia distillation, and the excessive alkali exceeding the threshold value cannot continue to improve the ammonia distillation effect. Alkali addition is controlled by a threshold value, so that the condition that the alkali amount is insufficient or seriously excessive due to manual alkali addition through equal equivalent points or depending on experience in the prior art can be avoided, and the alkali consumption is reduced while the ammonia distillation effect is ensured. Two embodiments are described in the specification, and the alkali excess threshold value is determined through the conductivity second-order change rate for an NH4Cl solution and ammonia-containing industrial wastewater with certain unknown concentration.

Description

Technical Field The present invention relates to the field of chemical industry, and in particular to a method for determining an excess alkali threshold value of an ammonia distillation process based on a second-order conductivity change rate in industrial deammonification production. Background Art In the industrial stripping deamination process, adding alkali is a key step, and the appropriate amount of alkali added is of great significance to the deamination efficiency and economy. Traditional methods for determining the amount of alkali added generally rely on experience and manual operation, lacking a reliable basis for judgment, which may lead to insufficient or excessive alkali addition. In addition, traditional experience believes that the point where the reaction theory is complete, that is, the equivalence point, is the point of optimal alkali addition. It does not take into account the partial ionization of ammonia water as a weak electrolyte, resulting in insufficient alkali addition at the equivalence point, affecting the deamination effect. Generally, a relatively large excess of alkali is used in industrial production to ensure the deamination effect. However, when the excess of alkali exceeds a certain threshold, further increasing the amount of alkali will not improve the deamination effect. Therefore, there is a need for a method that can determine the alkali excess threshold in the ammonia steam process to avoid excessive alkali input and reduce economic losses. Summary of the Invention The purpose of the present invention is to propose a method for determining the alkali excess threshold of the ammonia distillation process based on the second-order change rate of conductivity, so as to solve the problem of excessive alkali consumption caused by the lack of accurate and effective judgment of the alkali addition threshold for steam stripping deamination in the prior art.

[0001] To achieve the above object, the present invention adopts the following technical solutions:

[0002] Step 1: Add liquid caustic soda to the ammonia solution until the conductivity increases continuously and uniformly, and record the amount of liquid caustic soda added and the corresponding solution conductivity during the addition process;

[0003] Step 2: Calculate the solution conductivity change rate (Δ conductivity / Δ amount of liquid caustic soda added) based on the recorded amount of liquid caustic soda added and its corresponding conductivity value;

[0004] Step 3: Based on the recorded amount of liquid alkali added and the calculated conductivity change rate, plot the conductivity second-order change rate (Δ 2 Conductivity / Δ amount of liquid alkali added 2 ) and the amount of liquid alkali added, such as Figure 1 ;

[0005] Step 4: From the relationship diagram between the second-order rate of change of conductivity and the amount of liquid alkali added, select the turning point of the curve where it rises significantly and then decreases to a stable state as the point corresponding to the alkali excess threshold.

[0006] Beneficial effects The present invention analyzes the second-order change rate of conductivity and finds that initially due to the NH4 + Relatively excessive, at this time with the addition of alkali solution, NH4 + Uniform speed and OH- Combined with the above, the conductivity decreases at a uniform rate, and the second-order rate of change of conductivity basically fluctuates around a certain stable value; as the alkali solution continues to increase, NH4 + The concentration decreases and free OH begins to be generated in the water - , the conductivity change rate has changed, and the second-order change rate has increased first and then decreased; when the alkali solution exceeds a certain value, the ionization of NH3·H2O is almost completely inhibited. With the addition of alkali solution, the conductivity increases at a uniform rate, and the second-order change rate of conductivity tends to be stable. This value is the alkali excess threshold point. Alkali exceeding this alkali excess threshold cannot promote the free NH4 + Conversion to NH3·H2O does not improve deammonification efficiency, so industrial production should avoid adding alkali above this threshold. The second-order conductivity rate curve has a clear trend, intuitively reflecting the transformation of ammonia forms in the ammonia-containing system during the continuous addition of liquid alkali. This allows for accurate determination of the alkali excess threshold, avoiding errors caused by empirical judgment, manual operation, and determination of the equivalence point in traditional methods, thereby improving deammonification efficiency and economic efficiency.

[0007] The present invention can accurately observe the solution environment changes during the addition of liquid alkali in the steam stripping deammonification process by analyzing the second-order change rate of electrical conductivity, and better implement related operations.

[0008] The method of the present invention has strong versatility and adaptability, and can be used in the deammoniation process of ammonia-containing wastewater with different sources and treatment requirements. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0009] Figure 1 Schematic diagram of the relationship between conductivity, second-order rate of change of conductivity and amount of alkali added

[0010] Figure 2 The conductivity and second-order change rate of conductivity when 0.2 mol / L NaOH solution is added to 5 mmol / L NH4Cl solution

[0011] Figure 3 The conductivity and second-order conductivity change rate diagram of ammonia-containing industrial wastewater with a mass concentration of about 10% liquid alkali added DETAILED DESCRIPTION The present invention is described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0012] Example 1

[0013] A certain amount of NaOH needs to be added to an NH4Cl solution with an NH4 concentration of 5 mmol / L and a pH of 6.17 before ammonia evaporation to determine the alkali excess threshold. A method based on the second-order rate of change of conductivity is used to determine the alkali excess threshold in the ammonia evaporation process, including the following steps:

[0014] In the first step, take 1L of 5mmol / L NH4Cl solution and gradually add 0.2mol / L NaOH solution until the conductivity increases continuously and uniformly (addition rate is 1mL / time). Record the conductivity of the solution during the addition process (DDS1, DDS2, DDS3…DDS x ), and the corresponding amount of liquid alkali added (V1, V2, V3,…, V x );

[0015] The second step is to convert the volume of the corresponding liquid alkali dosage into the amount of NaOH substance (n1, n2, n3, ..., n x )

[0016] The third step is to calculate the rate of change of conductivity with the amount of liquid caustic soda added (ΔDDS / Δn) based on the recorded amount of liquid caustic soda added and its corresponding conductivity, where ΔDDS=DDS x -DDS x-1 (x≥2), Δn=n x -n x-1 (x ≥ 2);

[0017] Step 4: According to the value of the change rate of solution conductivity with the amount of liquid alkali added, calculate the change rate of conductivity with the amount of liquid alkali added (Δ 2 DDS / Δn 2 );

[0018] Step 5: Draw a graph showing the relationship between the second-order change rate of solution conductivity and the amount of alkali added, such as Figure 2 ;

[0019] Step 6: From Figure 2 In the equation, the amount of alkali added corresponding to the turning point b where the concentration increases significantly and then decreases to a stable state is selected, that is, n = 7 mmol, so the alkali excess threshold is 7 mmol NaOH / liter solution.

[0020] Example 2

[0021] Ammonia-containing industrial wastewater, which also contains salts such as sodium chloride and sodium sulfate, and waste acid, has a pH of 4.22. A steam stripping process is proposed for removing ammonia. The concentration of the liquid caustic soda prepared in the workshop is approximately 10%. The excess alkali threshold for adding this liquid caustic soda to the industrial wastewater is determined.

[0022] In the first step, a 10% NaOH solution was added dropwise to 0.5 L of industrial ammonia wastewater until the conductivity continued to increase at a constant rate (titration rate was 1 mL / time). The conductivity of the solution during the addition process (DDS1, DDS2, DDS3…DDS x ), and the corresponding amount of liquid alkali added (V1, V2, V3…V x );

[0023] The second step is to calculate the corresponding liquid alkali dosage ratio (Ratio1, Ratio2, Ratio3, ..., Ratio x )

[0024] The third step is to calculate the rate of change of conductivity with the amount of liquid caustic soda added (ΔDDS / ΔRatio) based on the recorded amount of liquid caustic soda added and its corresponding conductivity, where ΔDDS=DDS x -DDS x-1 (x≥2), ΔRatio=Ratio x - Ratio x-1 (x ≥ 2);

[0025] Step 4: According to the value of the change rate of solution conductivity with the amount of liquid alkali added, calculate the change rate of conductivity with the amount of liquid alkali added (Δ 2 DDS / ΔRatio 2 );

[0026] Step 5: Draw a graph showing the relationship between the second-order change rate of solution conductivity and the amount of alkali added, such as Figure 3 ;

[0027] Step 6: From Figure 3 In the equation, the amount of alkali added corresponding to the turning point b where the value of the alkali increases significantly and then decreases to a stable value is selected, that is, Ratio 液碱 / 废水 =2.7%, so the alkali excess threshold for adding liquid alkali to industrial wastewater is 2.7% (calculated as the volume percentage of liquid alkali to industrial wastewater).

[0028] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining the alkali excess threshold value in an ammonia distillation process based on the second-order rate of change of conductivity, characterized in that: The following steps are involved: Step 1: Add liquid caustic soda to the ammonia solution until the conductivity increases continuously and evenly, and record the amount of liquid caustic soda added and the corresponding solution conductivity during the addition process; Step 2: Calculate the solution conductivity change rate (Δ conductivity / Δ amount of liquid caustic soda added) based on the recorded amount of liquid caustic soda added and its corresponding conductivity value; Step 3: Based on the recorded amount of liquid alkali added and the calculated conductivity change rate, plot the conductivity second-order change rate (Δ 2 Conductivity / Δ amount of liquid alkali added 2 ) and the relationship between the amount of liquid alkali added; Step 4: From the relationship diagram between the second-order rate of change of conductivity and the amount of liquid alkali added, select the turning point of the curve where it rises significantly and then decreases to a stable state as the point corresponding to the alkali excess threshold.

2. The method for determining the alkali excess threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The ammonia solution in the first step contains NH4 + organic or inorganic solutions.

3. The method for determining the alkali excess threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The liquid alkali in the first step is a strong alkaline solution, including NaOH, KOH, etc.

4. The method for determining the alkali excess threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The amount of liquid alkali added recorded in the second step can be a measurement unit that can be converted according to a certain relationship, such as solution volume (V), amount of substance (n), flow rate (Q), flow velocity (v), time (t), etc.

5. The method for determining the alkali excess threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The change rate in the second and third steps refers to the change rate calculated between a certain latter segment of data and a certain former segment of data, preferably between two adjacent recorded data.

6. The method for determining the excess alkali threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The alkali excess threshold in the fourth step refers to the point at which continuing to add alkali to the wastewater in the ammonia distillation process will no longer have an impact on the ammonia distillation efficiency.

7. The method for determining the excess alkali threshold value in an ammonia distillation process based on the second-order rate of change of conductivity according to claim 1, characterized in that: The point selected in the fourth step is not the equivalence point of the reaction between the solution and the liquid alkali, but after the equivalence point.

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