Simplified online monitoring method for combustion efficiency of power station boiler

Abstract

The invention discloses a simplified online monitoring method for the combustion efficiency of a power station boiler, and belongs to the technical field of thermal equipment performance state monitoring and diagnos.The method comprises the steps that unit generation power, the fuel quantity, the total air volume and coal composition parameters are collected; calculating fuel converted carbon content, lower calorific value, theoretical air quantity and excess air coefficient; defining a carbon burnout coefficient and a fuel characteristic coefficient, and constructing and iteratively solving an incomplete combustion equation taking the carbon burnout coefficient as an unknown number; and calculating the combustion efficiency of the boiler according to the solved carbon burnout coefficient. According to the method, the carbon contents of the fly ash and the slag are unified to the carbon burn-out coefficient, and based on combustion mechanism derivation, high-precision and all-working-condition online monitoring of the boiler combustion efficiency can be realized without an additional expensive monitoring instrument, and the technical problem that the boiler combustion efficiency is difficult to accurately monitor online is solved.

Description

Technical Field

[0001] This invention belongs to the field of thermal equipment performance status monitoring and diagnosis technology, specifically a simplified online monitoring method for the combustion efficiency of power plant boilers. Background Technology

[0002] One of the main technical challenges in real-time online monitoring of energy consumption in coal-fired power units lies in the online monitoring of boiler combustion efficiency. Among these challenges, the online monitoring of carbon content in fly ash and slag is a major technical bottleneck restricting online monitoring of boiler combustion efficiency. Given the importance of boiler energy efficiency to the overall unit energy consumption, extensive research has been conducted both domestically and internationally in recent years on methods for online monitoring of boiler energy efficiency. However, due to the numerous operational factors influencing carbon content in ash and slag, it is difficult to accurately provide a quantitative functional relationship between these factors and the carbon content in ash and slag. Although intelligent algorithms have great potential in solving the problem of predicting carbon content in ash and slag, they often require a large amount of sample data and coverage of more operating conditions to achieve good prediction accuracy across all operating conditions. Calculating the carbon content of fly ash in the furnace has always been a major technical challenge restricting online monitoring of boiler combustion efficiency. In recent years, some domestic researchers have gradually shifted their focus to exploring the mechanistic level. Based on the kinetic data of coal and char combustion reactions, they have established a pulverized coal boiler combustion efficiency prediction model suitable for engineering calculations. Calculations using this model on actual operating boilers show that it can predict the unburned carbon content in fly ash relatively accurately. However, this method is computationally complex and requires numerous boundary parameters, which is not conducive to the real-time calculation and effective monitoring of the unburned carbon content and combustion efficiency of fly ash.

[0003] Therefore, to solve the problem of online calculation of boiler combustion efficiency, this invention uses the carbon burnout coefficient to characterize the degree of unburned pulverized coal and uses it to calculate boiler combustion efficiency. Based on the incomplete combustion equation in the furnace, a functional relationship is constructed between the carbon burnout coefficient and flue gas composition and operating parameters. On this basis, an online monitoring model and method for boiler combustion efficiency are established using communication and computer equipment, solving the technical problem of difficulty in online monitoring of boiler combustion efficiency. This invention has certain practical engineering significance for the economical operation and management of power plant boiler performance. Summary of the Invention

[0004] The technical solution of this invention is as follows: a simplified online monitoring method for the combustion efficiency of a power plant boiler, characterized by comprising the following steps:

[0005] S1: Real-time parameters of the power plant boiler unit's operation are collected through a data acquisition system. These real-time parameters include: unit power generation P. e A. Fuel quantity fed into the boiler; B. Total air volume fed into the boiler. Simultaneously, obtain the coal quality composition parameters of the current coal, including: carbon content (C) in the fuel. ar Hydrogen content in fuel (H)ar Oxygen content in fuel ar Nitrogen content in fuel (N) ar Sulfur content in fuel (S) ar ,

[0006] S2: Based on the data collected and acquired in S1, calculate the following key intermediate parameters:

[0007] Carbon content (K) in fuel ar The lower heating value Q of the fuel ar,net Theoretical air volume V The Excess air coefficient γ Exce ;

[0008] S3: Define carbon burnout coefficient Define the fuel characteristic coefficient β and construct a system based on the carbon burnout coefficient. Incomplete combustion equation with unknowns, setting the carbon burnout coefficient. The initial estimate is then substituted into the incomplete combustion equation for iterative calculation, until the result of two consecutive iterations is obtained. The difference between the values ​​is less than the set convergence threshold, thus solving for the carbon burnout coefficient under the current operating conditions;

[0009] S4 is based on the carbon burnout coefficient obtained from the solution. The combustion efficiency of the boiler is calculated using a formula.

[0010] Furthermore, in step S3, the equation for incomplete combustion is:

[0011]

[0012] Wherein, O2 is the percentage of oxygen volume in the dry flue gas volume.

[0013] Furthermore, in step S4, the formula is:

[0014] Furthermore, the convergence threshold is 0.01.

[0015] A simplified online monitoring device for the combustion efficiency of a power plant boiler, comprising:

[0016] Data acquisition and communication unit: including a communication gateway computer, used to safely and unidirectionally acquire real-time parameters of unit operation from the power plant's distributed control system (DCS);

[0017] Data processing and calculation unit: including a field workstation computer connected to the data acquisition and communication unit, used to receive the real-time parameters and manually input coal quality parameters, and run the calculation program stored thereon to execute the key parameter calculation steps, the carbon burnout coefficient iterative solution steps, and the combustion efficiency calculation steps;

[0018] Data storage and publishing unit: includes a server connected to the data processing and calculation unit, used to store the calculated combustion efficiency data and publish it over the network.

[0019] The beneficial effects of this invention are as follows:

[0020] The mechanism is clear and the model is simplified: Starting from the mass conservation principle of combustion chemical reaction, this invention cleverly unifies the carbon content of fly ash and slag into a whole variable for solution by introducing the core concept of "carbon burnout coefficient", avoiding the difficulty of monitoring the two separately. The physical meaning of the model is clear and the structure is simple.

[0021] High online real-time performance: The input parameters required by this invention are all conventional monitoring data of the power plant DCS system (such as power, coal quantity, air volume, and oxygen quantity) and coal quality data that can be obtained periodically. No additional expensive online monitoring instruments are required. The calculation process is efficient and can meet the requirements of online real-time monitoring.

[0022] High computational accuracy and good applicability: Based on mechanism derivation, this invention avoids the dependence of intelligent algorithms on data samples. Through iterative solution, it can adapt to different coal types and operating conditions, and can maintain high computational accuracy across the entire operating range, with strong universality.

[0023] High engineering practical value: This invention provides a complete implementation plan from method to hardware. The hardware system is simple to build, securely isolated from existing DCS systems, and easy to implement and promote in existing power plants. It provides an effective technical means for the economic operation and performance diagnosis of power plant boilers. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the principle of the monitoring method of the present invention;

[0025] Figure 2 This is a flowchart of the detection method of the present invention;

[0026] Figure 3 This is a hardware system architecture diagram of the monitoring device of the present invention;

[0027] Figure 4 This is a schematic diagram of the data flow and interface of the online monitoring system of the present invention. Detailed Implementation

[0028] Based on the definition of excess air coefficient in boilers, and combined with the concepts of incomplete combustion equation and carbon burnout coefficient, a functional relationship is established between excess air coefficient, operating oxygen content, theoretical air volume, equivalent carbon content, and carbon burnout coefficient. By collecting operating data and manually inputting some coal quality data, the carbon burnout coefficient is calculated using a background algorithm, and then the boiler's combustion efficiency is calculated based on the carbon burnout coefficient.

[0029] Reference Figures 1-4 The present invention provides a simplified online monitoring method and device for the combustion efficiency of a power plant boiler, comprising the following:

[0030] (a) Determination of online monitoring model for boiler combustion efficiency

[0031] The excess air coefficient can be expressed as:

[0032]

[0033] In the formula: γ Exce V is the excess air coefficient for the boiler. The The theoretical air volume for the boiler is Nm³. 3 / kg,

[0034] Compared to the same amount of carbon particles burning to form CO2, assuming x kg of carbon particles per kilogram of fuel do not participate in combustion, then according to the stoichiometric equation of combustion, the oxygen in the flue gas will be 1.866x m more. 3 oxygen,

[0035] If we ignore the effects of CO and NO in the flue gas on oxygen, the actual volume of oxygen in the flue gas when the fuel is not completely burned can be expressed as:

[0036] (γ Exce -1)0.21V The =V Oxy -1.866x (2)

[0037] In the formula: V oxy The oxygen volume in the flue gas, Nm 3 / kg,

[0038] The percentage of oxygen in the dry flue gas volume can be expressed as:

[0039]

[0040] In the formula: V Dry.G The volume of dry flue gas produced per kilogram of fuel combustion, in Nm³. 3 / kg; O2 is the percentage of oxygen volume in the dry flue gas volume, %.

[0041] Substituting the percentage of oxygen in the dry flue gas volume into equation (2), it can be further expressed as:

[0042] 21(γ Exce -1)V The =O2V Dry.G -186.6x (4)

[0043] According to the combustion equation of coal, the volume of dry flue gas produced by burning one kilogram of fuel can be expressed as:

[0044]

[0045] K ar =C ar +0.375S ar (6)

[0046] Where: K ar RO2 is the carbon content in the fuel, expressed as a percentage; CO2 is the sum of the volume percentages of CO2 and SO2 in the dry flue gas, expressed as a percentage; C ar Carbon content in fuel, %; S ar The sulfur content in fuel, %.

[0047] Based on boiler principles, neglecting the content of nitric oxide and carbon monoxide in the flue gas formed by fuel combustion, the equation for incomplete combustion in a boiler can be expressed as:

[0048] 21=(1+β)RO2+O2 (7)

[0049] In the formula: β is the fuel characteristic coefficient, which is only related to the coal composition.

[0050] The fuel characteristic coefficient considering incomplete combustion of carbon can be expressed as:

[0051]

[0052] In the formula: H ar Hydrogen content in fuel, %; O ar Oxygen content in fuel, %; N ar δ represents the nitrogen content in the fuel, in percent; δ represents the unburned carbon particles per unit mass of fuel, in kg / kg.

[0053] Combining equations (4)-(7), the equation for incomplete combustion in a boiler can be obtained as follows:

[0054]

[0055] The carbon content of boiler fly ash and slag can be unified to define a carbon burnout coefficient, which represents the ratio of completely burned carbon to the total carbon content of each kilogram of fuel. The fuel carbon burnout coefficient can be expressed as:

[0056]

[0057] In the formula: Characterized by the carbon burnout coefficient of fuel,

[0058] The relationship between the mass of unburned carbon particles per unit mass of fuel and the carbon burnout coefficient of the fuel can be expressed as:

[0059] φ=1-δ (11)

[0060] Substituting equation (9) into equation (8) can be further expressed as:

[0061]

[0062] For a specific type of coal, the calorific value of the coal and the theoretical air requirement usually have a certain proportional relationship, which can be expressed as:

[0063]

[0064] In the formula: γ is the proportionality coefficient, which can be calculated by fitting based on the actual coal type; here it is determined to be 2.63; Q ar,net The lower heating value of the fuel, kJ / kg.

[0065] If the type of coal changes, based on the energy balance of the power plant, the lower heating value of the coal can be considered a function of the power generation capacity and the amount of coal burned. Simultaneously, the theoretical air quantity can be considered a function of the lower heating value of the coal, meaning the theoretical air quantity satisfies the following functional relationship:

[0066]

[0067] In the formula: M is the energy conversion coefficient of the coal-fired power unit, which can be taken as 9000; P e B is the generator's power output in kW, and B is the amount of fuel fed into the boiler in kg / h.

[0068] The excess air coefficient actually fed into the boiler in equation (12) can be expressed as:

[0069]

[0070] In the formula: The total air volume supplied to the boiler is expressed in kg / h; ρ k The density of air under standard conditions, kg / m³ 3 The value is 1.306.

[0071] The combustion efficiency of a boiler can be expressed as:

[0072]

[0073] (b) Solving the online monitoring model for boiler combustion efficiency

[0074] First estimate Based on the calculation of δ according to equation (11), the coal quality test parameters, namely the hydrogen content in the fuel, can be input. ar Oxygen content in fuel, O ar Nitrogen content in fuel (N)ar Carbon content (C) in fuel ar Sulfur content in fuel (S) ar The carbon content K in the fuel is calculated based on equation (6). ar The power generation of the unit and the amount of coal fed into the boiler are collected through the DCS database, and the lower heating value Q of the fuel is calculated according to equation (14). ar,net The theoretical air volume V is calculated based on equation (13). The Based on equation (8), the fuel characteristic coefficient β is determined, and the total air volume fed into the boiler is collected through the DCS database to determine the actual excess air coefficient γ. Exce Finally, the carbon burnout coefficient of the fuel is determined according to equation (12). If the estimated and calculated values ​​meet the calculation accuracy requirement of 0.01, then the fuel efficiency is calculated according to equation (16); otherwise, it needs to be re-estimated.

[0075] (c) Hardware equipment for online monitoring of boiler combustion efficiency

[0076] The hardware of the boiler combustion efficiency monitoring system includes a communication gateway computer, a server, and a field workstation computer. Real-time data from the DCS control system is sent to the field workstation through the communication gateway computer. The data is transmitted in one direction to ensure effective isolation between the unit's DCS control system and the real-time monitoring system. The field workstation performs secondary processing of real-time and offline data to obtain the boiler combustion efficiency and real-time data. The data is then published on the network through the server and stored on the server.

[0077] The computer software program of this invention is developed based on automation control and computer processing technology, which is a technology familiar to those skilled in the art.

[0078] Calculation Example: Taking a 600MW unit as an example, the coal quality and unit operation data are collected as shown in Table 1. The online monitoring steps and implementation case of boiler combustion efficiency are explained in detail below.

[0079] Table 1 Operating parameters of the 600MW unit

[0080] The generating capacity of the unit is 600*103kW <![CDATA[Proximate analysis of coal as received, S ar = 0.41%]]> The amount of coal fed into the boiler is 250,991 kg / h. <![CDATA[Proximate analysis of as-received coal A ar = 15.0%]]> The air volume supplied to the boiler is 2,470,755.40 kg / h. <![CDATA[Proximate analysis of as-received coal M ar = 13.0%]]> <![CDATA[Proximate analysis of coal as received, component C ar = 57.33%]]> <![CDATA[Proximate analysis of as-received coal, O ar = 9.94%]]> <![CDATA[Proximate analysis of coal as received, H ar = 3.62%]]> <![CDATA[Proximate analysis of coal as received, nitrogen content N ar = 0.7%]]>

[0081] (a) First estimate

[0082] estimate

[0083] Calculate the equivalent carbon content K in the fuel based on equation (6). ar

[0084] K ar =C ar+0.375S ar =57.33 + 0.375 * 0.41 = 57.48

[0085] The lower heating value Q of the fuel was calculated based on equation (14). ar,net

[0086]

[0087] The theoretical air volume V is calculated based on equation (13). The

[0088]

[0089] The fuel characteristic coefficient β is determined based on equation (8).

[0090]

[0091] γ Exce Substituting β into equation (12):

[0092]

[0093] Solving If the accuracy requirement is not met, a bisection method is used for iteration until the calculation accuracy requirement is met, and finally determined.

[0094] exist Once determined, the fuel efficiency is calculated based on equation (16).

[0095]

[0096] Ultimately, the online calculation yielded a boiler combustion efficiency of 89.59%.

[0097] By using the mass conservation principle in the combustion equation, the relationship between the boiler excess air coefficient, the degree of carbon burnout, and the coal composition can be established.

[0098] Further, the functional relationship between the excess air coefficient and the theoretical air volume, the converted carbon content, the fuel characteristic coefficient and the operating oxygen volume can be derived. In fact, it is a clever idea to convert heat into coal volume.

[0099] Equations for calculating the equivalent carbon content, actual excess air coefficient, and theoretical air volume are provided. The excess air coefficient cannot be calculated using a definition-based formula; it requires data collection of total air volume and total coal volume. The theoretical air volume is calculated using an empirical equation. Finally, after calculating the carbon burnout coefficient, the boiler's combustion efficiency can be calculated.

[0100] This invention overcomes the shortcomings of inaccurate online calculation of boiler combustion efficiency and boiler performance diagnosis. The calculation method is simple, accurate and scientific, and can achieve precise calculation of boiler combustion efficiency and performance diagnosis of boiler furnace.

[0101] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A simplified online monitoring method for the combustion efficiency of a power plant boiler, characterized in that, Includes the following steps: S1. Collect real-time parameters of the power plant boiler unit's operation through a data acquisition system. These real-time parameters include: unit power generation P. e A. Fuel quantity fed into the boiler; B. Total air volume fed into the boiler. Simultaneously, obtain the coal quality composition parameters of the current coal, including: carbon content (C) in the fuel. ar Hydrogen content in fuel (H) ar Oxygen content in fuel ar Nitrogen content in fuel (N) ar Sulfur content in fuel (S) ar ; S2. Based on the data collected and acquired in S1, calculate the following key intermediate parameters: Carbon content (K) in fuel ar The lower heating value Q of the fuel ar,net Theoretical air volume V The Excess air coefficient γ Exce ; S3, Define carbon burnout coefficient Define the fuel characteristic coefficient β and construct a system based on the carbon burnout coefficient. Incomplete combustion equation with unknowns, setting the carbon burnout coefficient. The initial estimate is then substituted into the incomplete combustion equation for iterative calculation, until the result of two consecutive iterations is obtained. The difference between the values ​​is less than the set convergence threshold, thus solving for the carbon burnout coefficient under the current operating conditions; S4. Based on the carbon burnout coefficient obtained from the solution... The combustion efficiency of the boiler is calculated using a formula.

2. The simplified online monitoring method for combustion efficiency of a power plant boiler according to claim 1, characterized in that, In step S3, the equation for incomplete combustion is: Wherein, O2 is the percentage of oxygen volume in the dry flue gas volume.

3. The simplified online monitoring method for combustion efficiency of a power plant boiler according to claim 1, characterized in that, In step S4, the formula is:

4. The simplified online monitoring method for combustion efficiency of a power plant boiler according to claim 1, characterized in that, In step S3, the convergence threshold is 0.

01.

5. A simplified online monitoring device for the combustion efficiency of a power plant boiler, characterized in that, To implement the method described in claims 1-4, comprising: Data acquisition and communication unit: including a communication gateway computer, used to safely and unidirectionally acquire real-time parameters of unit operation from the power plant's distributed control system (DCS); Data processing and calculation unit: including a field workstation computer connected to the data acquisition and communication unit, used to receive the real-time parameters and manually input coal quality parameters, and run the calculation program stored thereon to execute the key parameter calculation steps, the carbon burnout coefficient iterative solution steps, and the combustion efficiency calculation steps; Data storage and publishing unit: includes a server connected to the data processing and calculation unit, used to store the calculated combustion efficiency data and publish it over the network.

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