阅读说明：本技术 一种灵敏且经济的湿法脱硫喷淋浆液pH值控制方法 (Sensitive and economical wet desulphurization spraying slurry pH value control method ) 是由 张启玖 于 2021-07-05 设计创作，主要内容包括：本发明涉及半液相方法净化废气技术领域,公开了一种灵敏且经济的湿法脱硫喷淋浆液pH值控制方法,用于采用石膏法进行脱硫时浆液循环回路中喷淋浆液pH值的控制,通过预测控制器控制喷淋浆液的pH值；预测控制器中,给定值为浆液循环回路中,单位时间内应当脱除的SO-(X)的量；被控变量为该浆液循环回路在被控变量被测量时的瞬态工况下,单位时间内能够脱除的SO-(X)的量；操纵变量为供浆流量。本发明中,通过采用预测控制器,并将烟气状况计入给定值,实现全自动控制；供浆流量由传递函数模型给出,符合脱硫装置实际需求,避免供浆流量过大而浪费；被控变量为浆液循环回路单位时间内能够脱除的SO-(X)的量,对被控变量的影响更直接,控制的灵敏度更高。(The invention relates to the technical field of waste gas purification by a semi-liquid phase method, and discloses a sensitive and economic wet desulphurization spraying slurry pH value control method, which is used for controlling the pH value of spraying slurry in a slurry circulation loop during desulphurization by adopting a gypsum method, and controlling the pH value of the spraying slurry by a prediction controller; in the prediction controller, the given value is SO which should be removed in the slurry circulation loop in unit time X The amount of (c); the controlled variable is SO which can be removed in unit time under the transient working condition of the slurry circulation loop when the controlled variable is measured X The amount of (c); the manipulated variable is the feed stock flow. In the invention, full-automatic control is realized by adopting a predictive controller and counting the smoke condition into a given value; the slurry supply flow is given by a transfer function model, the actual requirement of the desulfurization device is met, and the waste caused by overlarge slurry supply flow is avoided; the controlled variable is SO which can be removed in the slurry circulation loop in unit time X The quantity of (2) has more direct influence on the controlled variable and has higher control sensitivity.)

1. The utility model provides a sensitive and economic wet flue gas desulfurization sprays thick liquid pH value control method for spray thick liquid pH value's control in the thick liquid circulation circuit when adopting the gypsum method to carry out the desulfurization, its characterized in that: controlling the pH value of the spraying slurry through a predictive controller;

in the predictive controller, the given value is SO which should be removed in the slurry circulation loop in unit time and is characterized by the parameter of spraying slurry_XThe amount of (d) is recorded as a sulfur amount command; the controlled variable is SO which can be removed in unit time and is characterized by parameters of spraying slurry under the transient working condition of the slurry circulation loop when the controlled variable is measured_XThe amount of (d) is recorded as the sulfur signal; the manipulated variable is the supply flow of the slurry circulation loop.

2. The method of claim 1, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the sulfur amount instruction and the sulfur amount signal are characterized by the pH value of the slurry sprayed in the slurry circulation loop.

3. The method as claimed in claim 2, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the sulfur amount instruction isThe sulfur content signal isWherein H is the flue gas load working condition represented by the pH value of the spraying slurry,f is the flow rate of the spraying slurry, H⁰Spraying slurry pH value F under rated working condition⁰Spraying slurry flow rate and pH value under rated working condition_(sp)Is the set value of the pH value of the spraying slurry, pH_(pv)And C is the tower volume coefficient, which is the pH value measured value of the sprayed slurry.

4. The method of claim 1, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: in the prediction controller, the value of the output manipulated variable is obtained by a transfer function model of the slurry supply flow and the pH value of the spraying slurry, and the transfer function model is a first-order inertia transfer function model with pure delay.

5. The method as claimed in claim 4, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the transfer function model is modeled by adopting a step disturbance test method.

6. The method as claimed in claim 5, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the model building process comprises the following steps:

the method comprises the following steps: selecting a gypsum-method desulfurization device in a stable flue gas load state as experimental equipment, and adjusting a circulating pump (3) to be in a manual regulation state;

step two: increasing the slurry supply flow in a step mode, and recording the rising condition of the pH value of the sprayed slurry;

step three: and looking up a historical curve, and evaluating delay time, inertia time and gain conditions from the change of the slurry supply flow to the change of the pH value of the spraying slurry to be used as a prediction model of the prediction controller.

7. The method of claim 1, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the slurry supply flow is controlled by an automatic valve, which is designated as a new slurry supply valve.

8. The method of claim 7, wherein the pH of the wet desulfurization spray slurry is controlled by the following steps: the opening of the new slurry supply valve is regulated in a cascade control mode, an outer loop of the cascade control is the prediction controller, an inner loop of the cascade control is the PID controller, and the PID controller carries out feedback regulation by taking the slurry supply flow as a feedback value.

9. The method of claim 8, wherein the pH of the wet desulfurization spray slurry is controlled by the following steps: predicting the output value of the controller with the flue gas SO_XThe variable quantity of the load is used as a given value of the inner loop after feedforward compensation is carried out on the disturbance quantity.

10. The method of claim 1, wherein the pH value of the wet desulfurization spray slurry is controlled by the following steps: the spray slurry pH value control method is applied to a single-tower double-circulation desulfurization device, and the control of the pH values of the spray slurries in the two slurry circulation loops is independent.

Technical Field

The invention relates to the technical field of waste gas purification by a semi-liquid phase method, in particular to a sensitive and economical wet desulphurization spraying slurry pH value control method.

Background

The lime/limestone slurry is used as an absorbent for wet desulphurization, and is a main method for flue gas desulphurization in the existing coal-fired power plants.

In the existing desulfurization device, part of slurry which is contacted with flue gas is mixed with new slurry and then pumped back to an absorption tower by a circulating pump for spraying, so that the liquid-gas ratio is improved and an absorbent is fully utilized. The absorption tower is divided into two sections by a collecting bowl, each section is provided with a set of slurry circulation loop, in the two slurry circulation loops, the pH value of slurry sprayed in a lower circulation mode is lower SO as to facilitate calcium sulfite oxidation and gypsum crystallization, and the pH value of slurry sprayed in an upper circulation mode is higher SO as to fully absorb SO_XSince the residence time of the upper circulation is short, it is also necessary to provide the upper circulation with an oxidation tower to extend the oxidation time of the slurry in the upper circulation.

However, since the combustion condition of the boiler is constantly fluctuating, the SO of the flue gas entering the desulfurizer_XThe load is constantly changing. To adapt to SO_XLoad changes require adjustments to the flow rate of the sprayed slurry in the slurry circulation loop (to adjust the liquid-to-gas ratio), and adjustments to the slurry supply flow rate (slurry supply flow rate is a term in the industry that refers to the flow rate of new slurry, and changing the slurry supply flow rate can be used to adjust the pH of the sprayed slurry).

At present, the two flows are relatively coarsely regulated, the flow of the spraying slurry is regulated by changing the starting number and frequency of the circulating pumps according to experience of operators, the flow of the slurry supply is regulated by a PID controller, the given value in the PID controller is the set value of the pH value of the spraying slurry, the controlled variable is the actual pH value of the spraying slurry, and the manipulated variable is the opening degree of a slurry supply valve of the new slurry. The value of the given value in the PID controller is manually given by an operator in the DCS according to the smoke condition.

The pH control of the current spraying slurry has three problems:

1, setting values in a PID controller by an operator in a DCS according to the smoke condition, and failing to operate fully automatically;

2. an operator gives a given value according to experience, in order to ensure the desulfurization effect, the given value is usually quite conservative, the slurry supply flow is usually obviously higher than the actual requirement, and serious waste is caused;

3. the pH value of the sprayed slurry is used as a controlled variable, so that the sensitivity is low and the lag is serious.

Disclosure of Invention

The invention provides a sensitive and economical method for controlling the pH value of wet desulphurization spray slurry.

The technical problem to be solved is that:

1, setting values in a PID controller by an operator in a DCS according to the smoke condition, and failing to operate fully automatically;

2. an operator gives a given value according to experience, in order to ensure the desulfurization effect, the given value is usually quite conservative, the slurry supply flow is usually obviously higher than the actual requirement, and serious waste is caused;

3. the pH value of the sprayed slurry is used as a controlled variable, and the sensitivity is low.

In order to solve the technical problems, the invention adopts the following technical scheme: a sensitive and economic wet desulphurization spraying slurry pH value control method is used for controlling the pH value of spraying slurry in a slurry circulation loop when desulphurization is carried out by adopting a gypsum method, and the pH value of the spraying slurry is controlled by a prediction controller;

in the predictive controller, the given value is SO which should be removed in the slurry circulation loop in unit time and is characterized by the parameter of spraying slurry_XThe amount of (d) is recorded as a sulfur amount command; the controlled variable is SO which can be removed in unit time and is characterized by parameters of spraying slurry under the transient working condition of the slurry circulation loop when the controlled variable is measured_XThe amount of (d) is recorded as the sulfur signal; the manipulated variable is the supply flow of the slurry circulation loop.

Further, the sulfur amount command and the sulfur amount signal are characterized by the pH value of the spraying slurry in the absorption tower.

Further, the sulfur amount instruction isThe sulfur content signal isWherein H is characterized by the pH of the spray slurryThe working condition of the flue gas load of the gas turbine,f is the flow rate of the spraying slurry, H⁰Spraying slurry pH value F under rated working condition⁰Spraying slurry flow rate and pH value under rated working condition_(sp)Is the set value of the pH value of the spraying slurry, pH_(pv)And C is the tower volume coefficient, which is the pH value measured value of the sprayed slurry.

Further, in the predictive controller, the output manipulated variable value is obtained by a transfer function model of the slurry supply flow rate and the pH value of the spraying slurry, and the transfer function model is a first-order inertia transfer function model with pure delay.

Further, the transfer function model is modeled by a step disturbance test method.

Further, the model building process comprises the steps of:

the method comprises the following steps: selecting a gypsum-method desulfurization device in a stable flue gas load state as experimental equipment, and adjusting a circulating pump to be in a manual regulation state;

step two: increasing the slurry supply flow in a step mode, and recording the rising condition of the pH value of the sprayed slurry;

step three: and looking up a historical curve, and evaluating delay time, inertia time and gain conditions from the change of the slurry supply flow to the change of the pH value of the spraying slurry to be used as a prediction model of the prediction controller.

Further, the slurry supply flow is controlled by an automatic valve, which is designated as a new slurry supply valve.

Further, the opening of the new slurry supply valve is regulated in a cascade control mode, an outer loop of the cascade control is the prediction controller, an inner loop of the cascade control is the PID controller, and the PID controller carries out feedback regulation by taking the slurry supply flow as a feedback value.

Further, the output value of the controller is predicted as the flue gas SO_XThe variable quantity of the load is used as a given value of the inner loop after feedforward compensation is carried out on the disturbance quantity.

Further, the spray slurry pH value control method is applied to a single-tower double-circulation desulfurization device, and the control of the spray slurry pH values in the two slurry circulation loops is independent.

Compared with the prior art, the pH value control method for wet desulphurization spray slurry has the following beneficial effects:

in the invention, SO which should be removed per unit time in a slurry circulating loop is removed_XThe amount of the slurry (represented by the pH value of the sprayed slurry, the same below) is used as a given value of a controller, and SO which can be removed in a unit time of a slurry circulation loop under the transient working condition during measurement is used_XThe amount of the slurry is used as a controlled variable, then the slurry supply flow is given by adopting a predictive controller, the given value does not need to be manually changed according to the flue gas condition like the existing PID control mode, and the full-automatic control is realized;

in the invention, the slurry supply flow is given by the transfer function model, the actual requirement of the desulfurization device is met, and compared with the condition that an operator gives a given value of the PID controller according to experience, the PID controller changes the slurry supply flow, the waste caused by overlarge slurry supply flow can be avoided on the premise of ensuring the desulfurization effect;

in the invention, the controlled variable of the predictive controller is SO which can be removed in a unit time of the slurry circulation loop under the transient working condition during measurement_XIn the traditional control method, the purpose of controlling the pH value of the sprayed slurry is to control SO which can be removed in a unit time of a slurry circulation loop under the transient working condition during measurement_XThe control method directly selects the desulfurization capacity as a controlled variable, the influence of a manipulated variable on the controlled variable is more direct and sensitive, and the control sensitivity is higher;

in the invention, the pulp supply flow is output by taking the predictive controller as an outer loop, and then the flue gas SO is used_XThe load is used for carrying out feedforward compensation on the output value and then is input into the PID controller as a given value of the inner loop to control the new slurry supply valve, so that the control sensitivity is further improved, and the anti-interference capability is improved.

Drawings

FIG. 1 is a flow chart of a sensitive and economical method of controlling the pH of a wet desulfurization spray slurry in accordance with the present invention;

FIG. 2 is a schematic view of two slurry circulation circuits using the single-tower double-circulation desulfurization apparatus of the present invention, in which a blast line and a slurry withdrawal line are omitted;

wherein, the method comprises the steps of 1-an absorption tower, 11-a collection bowl, 2-an oxidation tower, 3-a circulating pump, 4-a fresh slurry pipe and 5-a spraying slurry pipe.

Detailed Description

In the invention, all the expressions of 'the amount of XX' can be carried out by adopting various expressions such as volume, mass, amount of substances and the like, and only the dimension in the calculation process is required to be ensured to be correct. Similarly, the "XX flow rate" can be expressed in various ways such as volume flow rate, mass flow rate, and only the dimension in the calculation process needs to be ensured to be correct.

In this embodiment, all "XX amounts" are mass, and all "XX flow rates" are mass flow rates. SO (SO)_XWith SO₂To count the remaining types of SO_XNeglected.

As shown in fig. 1, a sensitive and economical method for controlling the pH value of spray slurry in wet desulphurization is used for controlling the pH value of spray slurry in a slurry circulation loop during desulphurization by a gypsum method, and the pH value of the spray slurry is controlled by a prediction controller;

the present invention can be applied to a desulfurization apparatus by a gypsum method or a desulfurization apparatus by a double alkali method, but when applied to a desulfurization apparatus by a double alkali method, the advantageous effects are not as remarkable as those of a desulfurization apparatus by a gypsum method, and therefore the present embodiment will be described only with respect to a desulfurization apparatus by a gypsum method using limestone slurry as an absorbent.

In the prediction controller, the given value is SO which should be removed in a unit time and is characterized by the parameters of spraying slurry in a slurry circulation loop_XThe amount of (d) is recorded as a sulfur amount command; the controlled variable is SO which can be removed in unit time and is characterized by parameters of spraying slurry under the transient working condition of the slurry circulation loop when the controlled variable is measured_XThe amount of (d) is recorded as the sulfur signal; the manipulated variable is the supply flow of the slurry circulation loop.

The controlled variable here is in fact the desulfurization capacity of the slurry circulation loop, but is characterized by the pH of the spray slurry.

The reason why the pH value of the spraying slurry is used for representing the amount of the sulfur oxides which should be removed/can be removed in unit time is not directly expressed by mass, and is to conveniently use a transfer function model to obtain the flow rate of the slurry supply.

The sulfur amount command and the sulfur amount signal are both characterized by the parameters of the slurry sprayed in the absorption tower 1. That is, the sulfur amount command and the sulfur amount signal are functions of the parameters of the spraying slurry.

In this embodiment, the sulfur command and the sulfur signal are represented by the pH of the slurry sprayed in the slurry circulation loop.

The sulfur amount command isThe sulfur content signal isWherein H is the flue gas load working condition represented by the pH value of the spraying slurry.

According to the current SO_XLoad, determining SO to be removed per unit time_XThe amounts were as follows:

pH_(sp)-spraying a slurry pH setting value; here, unlike the prior art PID control of spray slurry pH, pH_(sp)When in use, the operator does not need to repeatedly adjust the DCS interface, but an automatic set value is given by an economic objective function;

pH_(pv)-spraying the slurry pH measurement;

f, spray slurry flow rate, which is used for representing the flue gas load working condition and has the unit of t/h;

c' -the coefficient of desulfurization capacity of the absorption tower 1 represented by the flow of the spray slurry, and the unit is t/h & s.

The above equation can be further written as:

in the formula, H represents the flue gas load working condition represented by the pH value of the spraying slurry;

c-the coefficient of desulfurization ability of the absorption tower 1 represented by the pH value of the spray slurry, and the unit is s, C is a numerical value related to the absorption tower 1, and can be recorded as a tower volume coefficient through experimental measurement.

K is the conversion coefficient between the flow rate of the spraying slurry and the pH value of the spraying slurry under the rated working condition,that is to sayH⁰Spraying slurry pH value F under rated working condition⁰The flow of the slurry is sprayed under the rated working condition.

Both sides of the above formula are divided by K simultaneously:

after conversion, the slurry supply flow rate can be obtained by using a transfer function model mentioned later.

In the prediction controller, the value of the output manipulated variable is obtained by a transfer function model of the slurry supply flow and the pH value of the spraying slurry, and the transfer function model is a first-order inertia transfer function model with pure delay.

The transfer function model is modeled by a step disturbance test method.

A model building process comprising the steps of:

the method comprises the following steps: selecting a gypsum-method desulfurization device in a stable flue gas load state as experimental equipment, and adjusting a circulating pump 3 to be in a manual regulation state;

step two: increasing the slurry supply flow in a step mode, and recording the rising condition of the pH value of the sprayed slurry; of course, because the relation between the slurry supply flow and the valve opening is not linear, if the slurry supply flow cannot be increased in a step mode, the opening of a new slurry supply valve can be increased in a step mode;

step three: and looking up a historical curve, and evaluating delay time, inertia time and gain conditions from the change of the slurry supply flow to the change of the pH value of the spraying slurry to be used as a prediction model of the prediction controller.

The slurry supply flow is controlled by an automatic valve, which is recorded as a new slurry supply valve.

The opening of the new slurry supply valve is regulated in a cascade control mode, an outer loop of the cascade control is a prediction controller, an inner loop of the cascade control is a PID (proportion integration differentiation) controller, and the PID controller carries out feedback regulation by taking the slurry supply flow as a feedback value.

Predicting the output value of the controller with the flue gas SO_XThe variable quantity of the load is used as a given value of the inner loop after feedforward compensation is carried out on the disturbance quantity. This flue gas SO_XThe variation of the load, generally referred to as flue gas SO_XThe variation of the load over time can be derived from the AGC load curve. Of course, the amount of change is not limited thereto, and various disturbance amounts may be counted. Here the flue gas SO_XLoad, meaning SO that should be removed per unit time in the slurry circulation loop_XThe amount of (c). The feedforward compensation is carried out, so that the control sensitivity can be improved, and the anti-interference capability can be improved.

As shown in fig. 2, the spray slurry pH control method is applied to a single-tower dual-cycle desulfurization device, and the control of the spray slurry pH in the two slurry circulation loops is independent of each other, i.e., each of the two slurry circulation loops has a corresponding control system.

The desulfurization unit in this example is a typical single-column, double-cycle apparatus.

The absorption tower 1 is divided into two sections by the collecting bowl 11, so that two slurry circulation loops of upper circulation and lower circulation exist in the device, and the flue gas passes through the absorption tower 1 from bottom to top. The upper circulation is provided with an oxidation tower 2, the pH value set value of the spray slurry of the upper circulation is about 6, and the pH value set value of the spray slurry of the lower circulation is about 5. The new slurry in the new slurry pipe 4 and the slurry extracted from the absorption tower 1 are mixed and then pumped back to the absorption tower 1 along the spraying slurry pipe 5 by the circulating pump 3. The circulating pump 3 in the lower circulation comprises two power frequency pumps and a variable frequency pump, and the two circulating pumps 3 in the upper circulation are both power frequency pumps.

In the single-tower double-circulation desulfurization device in this embodiment, the pH values of the slurry sprayed in the two slurry circulation loops are respectively controlled by the corresponding cascade control systems.

Note that since the control system of the present invention is fully automatic, and there is no manual intervention after a problem arises, it is necessary to keep the conventional PID control system as a backup. In this embodiment, a cut-in and cut-out button of a new control system is designed on the DCS interface, and the following cut-in and cut-out limiting conditions are provided in addition to the button:

the new control system switches in the enabling conditions:

the deviation between the pH set value and the actual value is less than a certain value;

the new control system switches out the condition, satisfies one and switches out automatically:

the new slurry supply valve is in a manual regulation state;

the intelligent DPU heartbeat signal is abnormal.

The designed pH value inner loop controls the switching-in from a PID controller and a new slurry flow manual operator, when the original control system is switched in, the new control system is in a tracking state, the predictive controller and the PID controller adopt display tracking, and when the new control system is switched in, the original control system is in the tracking state;

the new control system and the original control system share one set value module, only when the new slurry flow manual operator is in manual operation, the set value module is in a tracking state, and in other modes, the set value module does not track a feedback value.

The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.