CN104569281B - Method for Judging Limestone Slurry Poisoning Caused by Al3+ - Google Patents

Abstract

Disclosure one judges Al³⁺The method that the lime stone slurry that causes is poisoning, it is characterised in that the method step comprises: (1) first measures the pH value of lime stone slurry; (2) temperature of lime stone slurry is then measured; (3) calculate obtain [HCO in serosity according to the chemical equilibrium in serosity, charge balance relational expression^- ₃] and [CO^2- ₃] concentration; (4) according to [HCO drawn in step (3)^- ₃] and [CO^2- ₃] concentration result of calculation, calculate the Al causing lime stone slurry poisoning³⁺Concentration range. The present invention has can accurately detect Al³⁺The concentration limit that the lime stone slurry that causes is poisoning, thus the advantage that forewarning function is successfully provided.

Description

Method for Judging Limestone Slurry Poisoning Caused by Al3+

technical field

The invention discloses a method for judging limestone slurry poisoning caused by Al ³⁺ , and calculates the concentration of HCO ^- ₃ and CO ^2- ₃ in the slurry through chemical balance and charge balance, thereby calculating the Al ³ that causes limestone slurry poisoning The lower limit of the concentration of ⁺ . This judgment method is mainly used in the limestone-gypsum wet flue gas desulfurization process of thermal power plants.

Background technique

Coal occupies an absolutely important position in my country's primary energy consumption and is also the main fuel for my country's thermal power plants. With the development of the electric power industry, the SO ₂ pollution produced by coal burning is becoming more and more serious. In order to control SO ₂ pollution, in 2011, the Ministry of Environmental Protection and the General Administration of Quality Supervision, Inspection and Quarantine jointly issued the "Emission Standards of Air Pollutants for Thermal Power Plants" (GB11223-2011), which stipulated the corresponding air pollution levels for thermal power plant construction projects in different periods. Under such circumstances, thermal power plants all over the country have carried out the construction of flue gas desulfurization projects, which has greatly alleviated the pollution caused by sulfur dioxide emissions to the environment.

Among various flue gas desulfurization processes, the limestone-gypsum wet flue gas desulfurization process has become the most widely used flue gas desulfurization process due to its many advantages. During this process, the dissolution of limestone is one of the important rate-controlling steps. However, the Al ³⁺ dissolved in the fly ash from the flue gas tends to inhibit the dissolution of the limestone, which reduces the concentration of alkaline substances in the limestone slurry and reduces the ability to absorb SO ₂ , that is, the limestone slurry is poisoned, thereby greatly reducing the concentration of the flue gas. Desulfurization efficiency. And how to detect the lower limit of the concentration of limestone slurry poisoning caused by Al ³⁺ , so as to facilitate the establishment of concentration warning values for power plants and other units, and provide important reference significance for successfully solving limestone slurry poisoning.

Invention content:

The present invention aims at the above-mentioned deficiencies of the prior art, and provides a method that can accurately detect the concentration lower limit of limestone slurry poisoning caused by Al ³⁺ , thereby successfully providing an early warning function for judging the limestone slurry poisoning caused by Al ³⁺ .

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is: a method for judging the limestone slurry poisoning caused by ^Al , the method steps comprising:

(1) at first measure the pH value of limestone slurry;

(2) measure the temperature of limestone slurry then;

(3) Calculate the concentration of ^{HCO -} ₃ and CO _2-3 in the slurry according to the chemical balance in the slurry and the charge balance relational formula;

(4) According to the concentration calculation results of HCO ^- ₃ and ^CO2-3 in step ( ₃ ), determine the concentration range of Al ³⁺ that causes limestone slurry poisoning.

The chemical principle of Al ³⁺ causing limestone slurry poisoning is that, on the one hand, a double hydrolysis reaction occurs between Al ³⁺ and HCO ^- ₃ , CO ^2- ₃ , and Al(OH) ₃ is formed to precipitate and cover the surface of limestone particles, which seriously inhibits the On the other hand, because limestone cannot dissolve and cannot provide alkaline HCO ^- ₃ and CO ^2- ₃ , the absorption capacity for SO ₂ is greatly reduced, and the desulfurization efficiency is significantly reduced. The overall manifestation is limestone slurry poisoning. The chemical equation of this double hydrolysis reaction is as follows:

Al ³⁺ +3HCO ^- ₃ ＝Al(OH) ₃ +3CO ₂ (1)

2Al ³⁺ +3CO ^2- ₃ +3H ₂ O＝2Al(OH) ₃ +3CO ₂ (2)

In this way, the equilibrium concentration of various ions can be calculated according to the chemical balance and charge balance relationship between various ions in the limestone slurry, and thus the lower limit of the concentration of Al ³⁺ that causes limestone slurry poisoning can be calculated.

In limestone slurry, the following chemical reactions exist:

Dissolution of limestone:

CaCO ₃ ＝Ca ²⁺ +CO ₃ ^2- (3)

First order ionization _{of H2CO3} :

CO ₂ (aq)+H ₂ O=H ⁺ +HCO ₃ ^- (4)

_Second order ionization _of H2CO3:

HCO ^- ₃ ＝H ⁺ +CO ₃ ^2- (5)

The ionization balance of water:

H ₂ O = H ⁺ +OH ^- (6)

Charge balance:

2[Ca ²⁺ ]+[H ⁺ ]＝[OH ^- ]+[HCO ^- ₃ ]+2[CO ₃ ^2- ](7)

In this way, there is the following relationship between the various ion concentrations in the slurry:

[H ⁺ ]*[OH-]＝ _Kw (8)

where _Kw is the ion product of water as a function of temperature.

[Ca ²⁺ ]*[CO ₃ ² -]=K _cp (9)

where _Kcp is the solubility product _of CaCO3 as a function of temperature.

$\frac{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{<span\; class="notranslate">\; +</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; HCO</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; CO</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; aq</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

In the _formula , K _c1 is the first _- order ionization constant of H2CO3, which is a function of temperature.

$\frac{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{<span\; class="notranslate">\; +</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; CO</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; C</span>}{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

In the formula, K _c2 is the _{second -} order ionization constant of H2CO3, which is a function of temperature;

$\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; Ca</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{<span\; class="notranslate">\; +</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; Oh</span>}}^{<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; HCO</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; CO</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

[H ⁺ ]＝ ^10-5.5 (13)

Solving the equations formed by the combination of formula (8) and formula (13), the concentration of HCO ^- ₃ and CO ² _-3 ions in the slurry can be obtained, and then according to formula (1) and formula (2) According to the stoichiometric relationship, the theoretical value of the lower limit of the concentration of Al ³⁺ that causes limestone slurry poisoning can be obtained, which is 3.83mmol/L.

The correlation constant values at different temperatures can be calculated according to the following formula:

K _cp ＝10^(-171.9065-0.077993*T+2839.319/T+71.595*log10(T))

(14)

K _c1 =exp(-12092.1/T-36.7816*log(T)+235.482)(15)

K _c2 =exp(-12431.7/T-35.4819*log(T)+220.067)(16)

K _w =exp(-13445.9/T-22.4773*log(T)+140.932) (17).

According to the above formula, it can be calculated that pH=5.5, and the lower limit of concentration of Al ³⁺ that causes slurry poisoning at a temperature of 55° C. is 3.83 mmol/L.

Judgment method of limestone slurry poisoning caused by Al ³⁺ : on the basis of the above theoretical calculation, through the increase rate and decrease rate of Al ³⁺ concentration in the slurry tank of the wet flue gas desulfurization system, it can be judged whether Al ³⁺ may Limestone slurry poisoning.

Growth rate of Al ³⁺ in the slurry pool:

M ₁ =V _fg *F _fa *F _al *F _d *54/102*/27(18)

In formula (18), M ₁ is the concentration growth rate of ^Al in the slurry tank, mmol/h;

V _fa is the fly ash content in the flue gas, mg/m ³ ,

F _al is the alumina content in the fly ash,

F _d is the dissolved fraction of aluminum in fly ash,

_54/102 , Al content in _Al2O3 ,

27 is the atomic weight of Al;

The discharge rate of Al ³⁺ in the slurry pool:

M ₂ =3.83*V _ww *1000(19)

In the formula, 3.83 (the lower limit value at 55°C should be 3.83mmol/L) is the lower limit value of the Al ³⁺ concentration that causes limestone slurry poisoning, and V _ww is the wastewater discharge rate of the desulfurization system, in m ³ /h.

Using formulas (18) and (19), the values of M ₁ and M ₂ can be calculated. If M ₁ <M ₂ , the slurry will not be poisoned. If M ₁ >M ₂ , the slurry may be poisoned.

* involved in the present invention represents the multiplication sign "x" in multiplication and division.

Description of drawings

Fig. 1 is a curve diagram of the lower limit of the concentration of Al ^{3 +} corresponding to the equilibrium concentration of [HCO ^- ₃ ] and [CO ^2- ₃ ] in the slurry at different pH values when the slurry temperature is 55°C.

detailed description

The present invention is described in further detail below through the examples, but the present invention is not limited only to the following examples.

Example 1:

According to formula (8) - formula (13) when the slurry temperature is 25 ℃, calculate the [HCO ^- ₃ ] and [CO ^2- ₃ ] equilibrium concentrations in the slurry at different pH values, the lower limit of the concentration of Al ³⁺ is given by the formula ( 1) and the stoichiometric relationship of formula (2) are calculated, and the results are shown in Table 1.

Table 1. Equilibrium concentrations of [HCO ^- ₃ ] and [CO ^2- ₃ ] in slurry at 25°C

pH value [HCO ^- ₃ ](mmol/L) [CO ^2- ₃ ](mmol/L) [Al ³⁺ ](mmol/L) 3.5 194.5 2.88×10 ^-5 64.83 4 109.3 5.13×10 ^-5 36.43 4.5 61.47 9.11×10 ^-5 20.49 5 34.56 1.62×10 ^-4 11.52 5.5 19.43 2.88×10 ^-4 6.48 6 10.92 5.12×10 ^-4 3.64 6.5 6.14 9.11×10 ^-4 2.05

It can be seen from Table 1 that, compared with HCO ^- ₃ , the concentration of CO ^2- ₃ is very small and can be ignored, so the concentration of Al ³⁺ is only considered when calculating the concentration of Al 3+ , and the calculated concentration of Al ³⁺ The lower limit is shown in Table 1. It can be seen from Table 1 that when the temperature is constant, the lower limit of the concentration of Al ³⁺ decreases gradually with the increase of pH value. That is to say, the inhibitory effect of Al ³⁺ on the dissolution of limestone is more significant when the pH value is higher. This is consistent with the test results, which proves the correctness of the calculation method.

When the slurry temperature is 55°C, calculate the sum equilibrium concentration in the slurry at different pH values, and the lower limit of Al ³⁺ concentration is calculated from the stoichiometric relationship of formula (1) and formula (2). The results are shown in Figure 1. It can be seen from Figure 1 that with the increase of the pH value of the slurry, the concentration of Al3+ that inhibits the dissolution of limestone gradually decreases, which is consistent with the rule in Example 1. In addition, take a single pH value as an example: at pH=5.5, as the slurry temperature increases from 25°C to 55°C, the lower limit of Al ³⁺ concentration decreases from 6.48mmol/L to 3.83mmol/L, which is mainly due to Since the increase of temperature promotes the release of _CO from the liquid phase to the gas phase, resulting in a decrease in the concentration in the slurry, the constant pH titration test results also show that when the reaction temperature is 55 ° C, adding 3.83mmol/ The Al ³⁺ of L and the dissolution of limestone cannot be carried out at all, which shows the correctness of this method.

For a desulfurization system, the relevant parameters are shown in Table 2:

Table 2. Relevant parameters of desulfurization system 1

Calculated according to formulas (18) and (19), M ₁ =10165.27mmol/h, M ₂ =22980mmol/h, M ₁ <M ₂ , so the slurry will not be poisoned.

Example 2:

For another desulfurization system, relevant parameters are shown in Table 3.

Table 3. Relevant parameters of desulfurization system 3

Calculated according to formulas (18) and (19), M ₁ =23916.3mmol/h, M ₂ =22980mmol/h, M ₁ >M ₂ , the slurry will be poisoned.

Claims (1)

1. one kind judges Al³⁺The method that the lime stone slurry that causes is poisoning, it is characterised in that the method step comprises:

(1) pH value of lime stone slurry is first measured;

(2) temperature of lime stone slurry is then measured;

(3) calculate obtain [HCO in serosity according to the chemical equilibrium in serosity, charge balance relational expression^- ₃] and [CO^2- ₃] concentration;

(4) according to [HCO drawn in step (3)^- ₃] and [CO^2- ₃] concentration result of calculation, calculate the Al causing lime stone slurry poisoning³⁺Concentration range;

Al³⁺The principles of chemistry causing lime stone slurry poisoning are in that, on the one hand, Al³⁺With HCO^- ₃��CO^2- ₃Between there is double; two hydrolysis, generate Al (OH)₃Precipitation covers limestone particle surface, the serious dissolving suppressing limestone; On the other hand, owing to limestone cannot dissolve, it is impossible to provide the HCO with alkalescence^- ₃��CO^2- ₃, therefore to SO₂Absorbability decline to a great extent, desulfuration efficiency significantly reduces, and aggregate performance is that lime stone slurry is poisoning;The chemical equation of this pair of hydrolysis is as follows:

Al³⁺+3HCO^- ₃=Al (OH)₃+3CO₂(1)

2Al³⁺+3CO^2- ₃+3H₂O=2Al (OH)₃+3CO₂(2);

In described lime stone slurry, there is following chemical reaction:

The dissolving of limestone:

CaCO₃=Ca²⁺+CO₃ ^2-(3)

H₂CO₃Single order ionization:

CO₂(aq)+H₂O=H⁺+HCO₃ ^-(4)

H₂CO₃Second order ionization:

HCO^- ₃=H⁺+CO₃ ^2-(5)

The ionization equilibrium of water:

H₂O=H⁺+OH^-(6)

Charge balance:

2[Ca²⁺]+[H⁺]=[OH^-]+[HCO^- ₃]+2[CO₃ ^2-] (7);

Following relational expression is there is between various ion concentrations in serosity:

[H⁺]*[OH^-]=K_w(8)

In formula, K_wIt is the ionic product of water, is the function of temperature;

[Ca²⁺]*[CO₃ ^2-]=K_cp(9)

In formula, Kc_pIt is the solubility product of CaCO3, is the function of temperature;

$\frac{\&lsqb;H^{+}\&rsqb;*\&lsqb;{\mathrm{HCO}}_3^{-}\&rsqb;}{\&lsqb;{\mathrm{CO}}_2\left(aq\right)\&rsqb;}=K_{c1}---\left(10\right)$

In formula, K_c1It is H₂CO₃Single order ionization constant, be the function of temperature;

$\frac{\&lsqb;H^{+}\&rsqb;*\&lsqb;{\mathrm{CO}}_3^{2-}\&rsqb;}{\&lsqb;{\mathrm{HCO}}_3^{-}\&rsqb;}=K_{c2}---\left(11\right)$

In formula, K_c2It is H₂CO₃Second order ionization constant, be the function of temperature;

$2\&lsqb;{\mathrm{Ca}}^{2+}\&rsqb;+\&lsqb;H^{+}\&rsqb;=\&lsqb;{\mathrm{OH}}^{-}\&rsqb;+\&lsqb;{\mathrm{HCO}}_3^{-}\&rsqb;+2\&lsqb;{\mathrm{CO}}_3^{2-}\&rsqb;---\left(12\right)$

[H⁺]=10^-5.5(13)

Solve by the equation group of formula (8)-Shi (13) simultaneous, obtain HCO in serosity^- ₃��CO² _-3The concentration of two kinds of ions, further according to the stoichiometric relationship of formula (1) and formula (2), draws the Al causing lime stone slurry poisoning³⁺The theoretical value of concentration limit;

Dependent constant value under different temperatures is calculated according to the following formula:

Kc_p=10^ (-171.9065-0.077993*T+2839.319/T+71.595*log10 (T)) (14)

K_c1=exp (-12092.1/T-36.7816*log (T)+235.482) (15)

K_c2=exp (-12431.7/T-35.4819*log (T)+220.067) (16)

K_w=exp (-13445.9/T-22.4773*log (T)+140.932) (17);

By Al in wet method fume desulfurizing system slurry pool³⁺The rate of rise of concentration and minimizing speed, just can judge Al³⁺Whether it is likely to result in lime stone slurry poisoning, particularly as follows:

Al in slurry pool³⁺Rate of rise:

M1=Vf_g*Ffa*Fal*Fd*54/102*/27(18)

In formula (18), M₁It is Al in slurry pool³⁺Concentration rate of rise, mmol/h;

V_faIt is the fly ash content in flue gas, mg/m³;

Fal is the alumina content in flying dust;

Fd is the dissolution number of aluminum in flying dust

54/102, Al₂O₃In Al content;

27 is the atomic weight of Al

Al in slurry pool³⁺Rate of discharge:

M₂=3.83*V_ww*1000(19)

In formula, 3.83 is the Al causing lime stone slurry poisoning³⁺Concentration limit value, Vww is desulphurization system discharge of wastewater speed, m³/ h;

Utilize formula (18) and formula (19), calculate M₁And M₂Numerical value, if M₁<M₂, serosity will not be poisoning, if M₁>M₂, serosity exists poisoning.