WO2022142321A1

WO2022142321A1 - Air volume control method suitable for pulverized coal boiler

Info

Publication number: WO2022142321A1
Application number: PCT/CN2021/109478
Authority: WO
Inventors: 刘珠伟; 顾常杰; 史汝超; 宋祥磊; 王婕; 周怀春
Original assignee: 江苏海洋大学
Priority date: 2020-12-30
Filing date: 2021-07-30
Publication date: 2022-07-07
Also published as: CN112664975A; CN112664975B; LU501110B1

Abstract

An air volume control method suitable for a pulverized coal boiler. Said method comprises: first, according to historical operation data of a unit, selecting three parameters, i.e. an coal amount as fired F, a total air volume A and actual generated power P in the same load section; by means of data fitting, establishing a correlation between P/F and A/F in the load section, so as to obtain a linear relationship established between P/F and A/F in each load section; then, continuously analyzing the value range of P/F when A/F changes from small to large, so as to obtain the minimum value of power-to-coal ratio P/F_min and the maximum value of power-to-coal ratio P/F_max; and calculating the total air volume A under the load P according to a formula, and introducing same into an original unit control system for air volume control. The method can solve the problem of unstable operation parameters of a unit due to poor air volume control, poor response sensitivity and poor accuracy of control and adjustment during current combustion adjustment process of boilers, thereby improving the response speed of air supply volume adjustment and the stability and safety of the unit operation.

Description

A kind of air volume control method suitable for pulverized coal boiler

technical field

The invention belongs to the technical field of boiler control in coal-fired power stations, and in particular relates to an air volume control method suitable for pulverized coal boilers.

Background technique

The air supply automatic adjustment system is an important part of the thermal automatic adjustment system of the thermal power plant, which plays a very important role in ensuring the safe and economical operation of the boiler. The basic task of air volume control is to fully burn the fuel and improve the thermal efficiency of the boiler. In the operation of the boiler, the excess air coefficient α at the furnace outlet is generally used as the adjustment standard for the air volume. If the excess air coefficient α at the furnace outlet is too small, it will cause insufficient oxygen in the furnace and incomplete combustion, which not only increases coal consumption but also pollutes the environment; α is too large , it may make the flame center move up, resulting in coking and overheating of the superheater, and at the same time, it will also increase the loss of exhaust gas and reduce the efficiency of the boiler. Therefore, the air volume should be controlled in an appropriate range, so as to ensure the economy and stability of the boiler combustion process.

In the existing coordinated control system, the air volume is adjusted according to the oxygen feedback signal at the furnace outlet. However, since it is difficult to determine the optimal air volume required for combustion in the furnace, the corresponding function from the power generation to the oxygen content of the flue gas is generally determined according to the design experience of the commissioning personnel. When the oxygen content of the flue gas reaches the set value, the The combustion state is not necessarily optimal. At the same time, due to the limitation of the service life and measurement accuracy of the oxygen meter, it may not be able to accurately reflect the oxygen content of the flue gas at the outlet of the furnace. In this way, due to the deviation between the setting and measurement of the oxygen amount signal, the air supply volume control also has a deviation.

The current research on boiler air supply is still based on the basic understanding that there is a great correlation between the air volume and the quality of coal combustion, and the air supply volume needs to be adjusted according to the quality of coal combustion. The ideal air-to-coal ratio is to calculate the air volume based on the amount of coal burned, and to continuously correct the supply air volume according to the oxygen concentration in the flue gas. However, the air-to-coal ratio also depends on the type of coal and the type of boiler. When the operating load of the unit changes rapidly, it is more difficult to determine the ideal air-to-coal ratio. Additionally, changes in the oxygen concentration in the flue gas are not only dependent on the heat of the fuel, but are also affected by the start, stop and trip of the pulverization system, as well as soot and coking.

To sum up, the existing technology has the following shortcomings: for the boiler air supply volume control system, it is difficult to establish the optimal air-to-coal ratio in the process of unit load regulation, and it is also difficult to adjust the air volume by using the oxygen content of the flue gas as a feedback. There are deficiencies. Therefore, it is necessary to develop new control ideas for the adjustment of air supply in the furnace.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an air volume control method suitable for pulverized coal boilers, so as to improve the unstable operation parameters of the unit due to poor air volume control and poor response sensitivity and accuracy of control adjustment in the current boiler combustion adjustment process. question.

Technical solutions

The inventor's research has found that for a specific boiler, the boiler must generate a certain amount of steam under a certain power generation power, and the heat generated in the furnace only changes with the power generation power. Carbon in pulverized coal, as the main combustible element, is the main source of heat generated in the combustion process. If the carbon content is used to calculate the calorific value of other elements in coal, that is, the heat released by coal combustion is all generated by carbon, and it is called the equivalent carbon content. According to the combustion reaction mechanism of carbon, the equivalent carbon content corresponds to a certain oxygen content required for complete combustion, and the corresponding required air amount can be obtained. Under a certain power generation, according to the coal type, the combustion heat all comes from the equivalent carbon content, and the corresponding air volume is basically unchanged. Under a certain unit load, the purpose of adjusting the fuel volume is to ensure the stability of the total calorific value of coal supply, and the purpose of air volume control is to ensure that the air supply can achieve the best combustion state in the furnace. So the air flow is a function of the generating capacity of the unit, and has nothing to do with the fuel entering the furnace and its quality. When A/F (ratio of fuel per unit mass to air supply) and P/F (ratio of fuel per unit mass to generator power) have the same trend of change, it indicates that the combustion adjustment in the furnace during this period is Satisfactory, therefore, the function relationship between the generated power and the supply air volume can be established. After establishing the functional relationship between the air volume and the generating power of the unit, the target value of the air volume under different generating powers can be established, and then introduced into the original unit coordination control system to participate in the optimization of the air supply volume, and the control of the total air volume no longer needs to follow the coal powder entering the furnace. Frequent control is carried out due to quality fluctuations, thereby realizing the basic decoupling of wind and coal. The specific plans are as follows:

An air volume control method suitable for a pulverized coal boiler, comprising the following steps:

(1) According to the historical data of the operation of the unit, select the three parameters of the coal amount F, the total air volume A and the actual power generation P under the same load section, and establish the relationship based on the maximum power generation corresponding to the unit fuel amount. The corresponding linear relationship between A/F and P/F under the load section, the same method is used to obtain the linear relationship under other load sections, and the linear relationship is:

P/F=k·A/F+b Formula (I)

(2) According to the linear relationship under different load sections established in step (1), perform data fitting to obtain the k value and b value under different load sections, and substitute into the linear relationship to obtain the P/value under each load section. The established linear relationship between F and A/F, under the established linear relationship, continue to analyze the value range of P/F when A/F changes from small to large, and obtain the minimum value P/F _min and P/F min of the power-to-coal ratio P/F. Maximum value P/F _max . The power-to-coal ratio P/F refers to the power generation corresponding to the combustion of a unit mass of fuel. The maximum value P/F _max means that the power generation per unit mass of fuel is the largest, indicating that the combustion adjustment in the furnace is in an optimal state during this period. The calculation basis for the air supply volume of the boiler is the best, but considering the errors in the historical data collection and measurement process, the calculation basis for the air supply volume of the boiler needs to be adjusted. Adjustment method: _When calculating the air supply volume with the minimum value P/F _min in the value range of the power-to-coal ratio, the air flow control effect is the worst, which is represented by the number 0; When the air volume is used, the air volume control effect is the best, and it is represented by the

number

1, and 0 to 1 represents the adjustment interval of the optimal value of the air supply volume. According to the above consideration of historical data errors, the present invention takes 0.7 out of 0 to 1 as the calculation basis for the air supply volume of the boiler.

After determining 0.7 as the calculation basis for the air supply volume of the boiler, the following formula can be used for conversion:

From formula (II), it can be obtained: F=P·[P/F _min +0.7·(P/F _max -P/F _min )] ^-1 , after calculating the F value of the coal amount fed into the furnace under the current load, Substitute the relational expression A=k ^-1 ·(P-bF) obtained by formula (I), calculate the air supply volume A under the current load, and calculate the total air supply volume A under each load section in the same way. After the polynomial After fitting, the functional relationship between P and A is obtained, which is introduced into the original unit control system for air volume control.

Further, in step (1), the historical data of the operation of the unit should be selected for at least one month, and when the historical data is selected, a good linear relationship between A/F and P/F should be satisfied.

Beneficial effects of the present invention: Aiming at the deficiencies of the air volume control method for pulverized coal boilers in the prior art, the present invention provides an air volume control method suitable for pulverized coal boilers, and the control of the total air volume no longer needs to follow the coal entering the furnace. This method can improve the problem of unstable operation parameters of the unit due to poor air volume control and poor response sensitivity and accuracy of control adjustment in the current boiler combustion adjustment process.

Description of drawings

Figure 1 shows the deviation results of the theoretical air volume required for the combustion of 124 coal samples to generate 100MJ of energy;

Fig. 2 is the flow chart of the air volume control method suitable for pulverized coal boiler;

Figure 3 shows the corresponding relationship between the power-to-coal ratio and the wind-to-coal ratio under four typical loads;

Figure 4 shows the corresponding relationship between the power-coal ratio and the wind-coal ratio when the load is 270MW;

Figure 5 shows the corresponding relationship between the total air volume and the generated power.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

Example 1

Taking the 300MW subcritical pulverized coal boiler in Handan Matou Power Plant of China Datang Group Co., Ltd. as an example, the calculation and verification of the change of air volume tracking power generation power are carried out, and the method is as follows:

124 coal samples (28 anthracite coal samples, 77 bituminous coal samples and 19 lignite samples) with ash content between 1% and 42% were selected. The theoretical air volume required to generate 100 MJ was calculated based on the high calorific value and equivalent carbon content. Among them, the equivalent carbon content is defined as the conversion of the calorific value of other elements to the carbon content, that is, it is considered that all the heat released by coal combustion is entirely generated by carbon. The equivalent carbon content is obtained from the empirical formula of high calorific value. The empirical formula used is as follows:

Anthracite: HHVE=78.1C ^r +320H ^r +22(S ^r -O ^r )-8(A ^g -10)

Bituminous coal: HHVE=80C ^r +310H ^r +22S ^r -26O ^r -4 (A ^g -10)

Lignite: HHVE=80C ^r +305H ^r +22S ^r -26O ^r -6(A ^g -10)

The above formula is a general formula in the technical field, wherein ^HHVE is an estimated high calorific value, and C ^r , H ^r , S ^r , Or and ^Ag represent the mass fractions of carbon, hydrogen, sulfur, oxygen and ash, respectively.

Taking anthracite as an example, the formula for calculating the equivalent carbon content is:

The theoretical air volume required is:

The relative deviation of the theoretical air volume is calculated by the high calorific value and the equivalent carbon content, respectively. The deviation of the theoretical air volume required for the combustion of 124 coal samples to generate 100MJ of energy is shown in Figure 1. It can be found that the anthracite samples calculated by the two methods are at 95% The relative deviations of the upwind amounts of the confidence intervals were ±2.91% and ±1.76%, respectively, ±2.97% and ±1.81% for the bituminous coal samples, and ±2.32% and ±1.74% for the lignite samples, respectively. Among the three selected coals, except for 7 coal samples, the relative deviations of the theoretical air volume calculated by the two methods for the remaining 117 coal samples are all less than ±3%. The relative deviations of 23 coal samples ranged from ±2% to ±3%, and the relative deviations of the remaining 94 coal samples were all less than ±2%. The results show that under the same energy level and output power of the unit, the theoretical air volume required for the combustion of different coals to generate the same heat is basically unchanged.

The flow chart of the air volume control method applicable to the pulverized coal boiler of the present invention is shown in Fig. 2, and the pulverized coal boiler of the above-mentioned power plant is also used for the test.

(1) Start with a large number of historical data of unit operation in the DCS system, select data for at least one month, and select the amount of coal entering the furnace F, the total air volume A (or other parameters that reflect these physical quantities, such as boiler master control instructions, blowers The corresponding relationship between A/F and P/F is established based on the three parameters of the door opening, the fan current, etc.) and the actual power generation power P. The maximum power generation power corresponding to the unit fuel amount is the basis for establishing the relationship, and the different parameters are analyzed in turn. The target total air volume under the load section; when selecting historical data, a good linear relationship between A/F and P/F should be satisfied.

Taking the operation data of the power plant at typical loads of 270, 280, 290 and 300 MW as an example, according to the statistical historical data, the corresponding relationship between the power-to-coal ratio and the wind-to-coal ratio of the power plant under four typical loads is shown in Figure 2.

Taking the operation data of a power plant with typical loads of 270, 280, 290 and 300 MW as an example, the method of the present invention is described, and the selected data is shown in FIG. 2 . According to the fitting results, the corresponding linear relations of the four load segments are obtained as:

270MW:P/F=9.61A/F-0.39 280MW:P/F=9.51A/F-0.54

290MW:P/F=11.30A/F-2.51 300MW:P/F=8.51A/F-0.40

(2) Taking the load of 270MW as an example, the corresponding relationship between the power-coal ratio and the wind-coal ratio at 270MW is shown in Figure 3. From Figure 3, it can be concluded that when A/F _min =0.62, P/F _min =5.57, When A/F _max =0.81, P/F _max =7.50. That is, the value range of the power-to-coal ratio is 5.57-7.50. When the power-to-coal ratio is equal to the maximum value of 7.50, it means that the combustion adjustment state in the furnace is good during this period, and the air supply volume is adjusted optimally. The present invention uses 0.7 in the adjustment interval 0 to 1 of the optimal value of the air supply as the basis for calculating the air supply, which can be converted by the following formula:

From formula (II), it can be obtained: F=P·[P/F _min +0.7·(P/F _max -P/F _min )] ^-1 , after calculating the F value of the coal amount fed into the furnace under the current load, Substitute the relational expression A=k ^-1 ·(P-bF) obtained by formula (I), and calculate the air supply volume A under the current load. In this embodiment, calculate the air supply volume A under the load of P=270WM = 204.8, every 10MW is regarded as a load section, and the optimal air supply volume for typical load sections of 280MW, 290MW and 300MW is calculated to be 210.8, 222.4, and 237.5, respectively. The above-mentioned air supply volume A is a relative value. For the coordinated control system of different power plants, it can be represented by parameters such as the door opening of the blower and the fan current of the blower. Using the above method, the air supply volume of the entire unit operating load section is calculated in turn, and the results are shown in Figure 4.

Polynomial fitting is performed on the air supply volume under different load segments, and the relationship between the two is obtained as:

A=3.39×10 ^-5 P ³ -0.022P ² +4.82P-179.83

Take this as the basis for adjusting the total air volume of the boiler, and participate in the coordinated control system of the air supply volume of the unit. The proportion of the air volume control method proposed in the present invention participating in the control can be adjusted according to the operating conditions of the unit. The use of this method plays a very good role in alleviating the fluctuation of the main steam pressure of the boiler caused by the large adjustment of the combustion conditions of the pulverized coal boiler, and increases the safety and stability of the unit operation. At the same time, the method is suitable for various types of coal-fired boilers, and the processing method of historical data is flexible, which is an effective independent decoupling control method of air volume.

Claims

An air volume control method suitable for a pulverized coal boiler, characterized in that it comprises the following steps:

(1) According to the historical data of the operation of the unit, select the three parameters of the coal amount F, the air supply amount A and the actual power generation P under the same load section, and establish the relationship based on the maximum power generation corresponding to the unit fuel amount. The corresponding linear relationship between P/F and A/F under the load section, the same method is used to obtain the linear relationship under other load sections, and the linear relationship is:

P/F=k·A/F+b Formula (I)

(2) According to the linear relationship under different load sections established in step (1), obtain the k value and b value under different load sections, and then obtain the linear relationship established by P/F and A/F under each load section , under the established linear relationship, continue to analyze the value range of P/F when A/F changes from small to large, and obtain the minimum value P/F min of the power coal ratio and the maximum value P/F of the power coal ratio under different load sections max ; when the power-to-coal ratio is P/F min , the air volume control effect is the worst, represented by a number 0, and when the power-to-coal ratio is P/F max , the air volume control effect is the best, represented by a number 1, considering the sampling of historical data And the measurement error, taking 0.7 as the calculation basis for the air supply volume of the boiler, the following relationship is obtained:

After using the formula (II) to calculate the coal amount F value under the current load, substitute the formula (I) to calculate the air supply volume A under the current load, and use the same method to calculate the total air supply volume A under each load section. , after polynomial fitting, the functional relationship between P and A is obtained, which is introduced into the original unit control system for air volume control.
The air volume control method suitable for pulverized coal boilers according to claim 1, characterized in that, in step (1), the historical data of the unit operation is at least selected from data of more than one month, and when the historical data is selected, the A/F requirement must be satisfied. It has a good linear relationship with P/F.