Simplified calculation method for thermal efficiency of boiler

Abstract

The invention discloses a simplified calculation method for boiler thermal efficiency, and mainly relates to the field of thermal equipment performance state monitoring, analysis and diagnosis. Comprising the following steps: S1, determining various heat losses of a boiler, and constructing an anti-balance calculation model of boiler heat efficiency; s2, determining the heat efficiency of the boiler; by simplifying the measurement steps and the calculation formula, the thermal efficiency of the boiler can be quickly estimated without a high-precision instrument. According to the method, key parameters such as the exhaust gas temperature and the oxygen content are selected, and the empirical formula is combined, so that the complexity of measurement and calculation is remarkably reduced. The system is suitable for daily monitoring and operation adjustment of the boiler, helps an enterprise to timely discover low-efficiency conditions and take energy-saving measures, and reduces the operation cost while improving the operation convenience.

Description

Technical Field

[0001] The present invention relates to the field of performance status monitoring, analysis and diagnosis of thermal equipment, and specifically to a simplified calculation method for boiler thermal efficiency. Background Art

[0002] The boiler thermal efficiency is an important indicator to measure the energy conversion ability of the boiler. In the industrial field, improving the boiler thermal efficiency can significantly reduce energy consumption and operating costs. Therefore, accurately calculating the boiler thermal efficiency is of great significance for energy conservation and consumption reduction. However, the traditional calculation methods for boiler thermal efficiency are relatively complex and require comprehensive consideration of multiple factors, including the lower calorific value of the fuel, the boiler flue gas temperature, the excess air coefficient, the oxygen content in the flue gas, the moisture and ash content of the fuel, etc. The measurement and calculation of these parameters often require professional equipment and a relatively long time, and are suitable for precise analysis and evaluation. However, in some actual working conditions, especially in daily operation and maintenance, enterprises may not have these professional equipment. Therefore, there is an urgent need for a simplified calculation method to quickly evaluate the working efficiency of the boiler. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems existing in the prior art. Aiming at the problem of complex calculation of traditional boiler thermal efficiency, the present invention is based on the boiler indirect balance method and combines the concepts of empirical equations and differential thinking to propose a simplified calculation method for boiler thermal efficiency.

[0004] To achieve the above object, the present invention is realized through the following technical solutions:

[0005] A simplified calculation method for boiler thermal efficiency includes the steps of:

[0006] S1. Determine the various heat losses of the boiler and construct an indirect balance calculation model for the boiler thermal efficiency:

[0007] Q Input =Q Effective +Q Flue.G +Q Unburned.G +Q Unburned.S +Q Heat +Q Ash ;

[0008] Q Input ≈Q ar,net ;

[0009] Wherein: Q Input is the heat input to the boiler; Q Effective is the effectively utilized heat of the boiler; Q Flue.G is the heat loss due to boiler flue gas; Q Unburned.G is the heat loss due to incomplete combustion of gas; Q Unburned.S is the heat loss due to incomplete combustion of solid; Q Heatis the heat loss of boiler; Q Ash is the physical heat loss of ash; Q ar,net is the net calorific value of the fuel as received;

[0010] S2. Determine the boiler thermal efficiency. The expression of the boiler thermal efficiency is:

[0011]

[0012] where, η Boiler is the boiler thermal efficiency.

[0013] Preferably, in step S1, the heat loss of the boiler's flue gas is calculated through the flue gas temperature and the ambient temperature. The heat loss of the boiler's flue gas Q Flue.G is expressed as:

[0014]

[0015] where: V Flue.G is the dry flue gas generated by the combustion of 1 kg of coal; is the flue gas temperature of the boiler; t Ambient.T is the ambient temperature; c Flue.G is the average constant pressure specific heat capacity of the dry flue gas at ; M Received is the moisture content of the coal as received; α Air outlet is the excess air coefficient at the outlet of the air preheater; k Flue.G is the coal quality coefficient in the flue gas volume; k Air is the coal quality coefficient in the air volume;

[0016] The flue gas temperature of the boiler is calculated using the following empirical equation:

[0017]

[0018] where, α Rating is the excess air coefficient at the rated load; D Rating is the rated load of the boiler; D Actuality is the actual load of the boiler; is the flue gas temperature at the rated load; t Design is the designed value of the ambient temperature.

[0019] Preferably, in step S1, the following calculation equation is used to determine the operating oxygen content at the outlet of the unit air preheater, that is:

[0020]

[0021] where, O Oxygen is the volume percentage content of oxygen.

[0022] Preferably, in step S1, Q Unburned.G is calculated by the formula:

[0023]

[0024] where CO is the percentage of the gas volume in the dry flue gas volume;

[0025] The concentration of CO is calculated by the following empirical formula:

[0026]

[0027] Preferably, in step S1, Q Unburned.S is calculated by the following empirical formula:

[0028]

[0029] where A1, y0, t1, x0 are empirical coefficients.

[0030] Preferably, in step S1, the heat loss Q Heat is calculated by the formula:

[0031]

[0032] Preferably, in step S1, the physical heat loss Q of the ash residue Ash is expressed as:

[0033]

[0034] where A Received is the percentage of ash in the coal quality; c Fly ash is the average constant pressure specific heat capacity of the fly ash from t Ambient.T to ; c Slag is the average constant pressure specific heat capacity of the slag from t Ambient.T to θ Slag ; a Fly ash , a Slag are the shares of the ash amounts in the fly ash and the slag in the total ash amount of the fuel; θ Slag is the slag temperature.

[0035] Preferably, in step S1, the calculation equation Q of the positive balance boiler thermal efficiency Effective heat is expressed as:

[0036]

[0037] where Q Effective heat is the effective heat utilization of the boiler, kW; G Main Steam is the main steam flow rate of the boiler, kg / s; h Main Steam is the main steam enthalpy value of the boiler, kJ / kg; hWater is the feed water enthalpy value of the boiler, kJ / kg; G reheat is the reheater steam flow rate of the boiler, kg / s; is the outlet enthalpy value of the reheater steam of the boiler, kJ / kg; is the inlet enthalpy value of the reheater steam of the boiler, kJ / kg.

[0038] Preferably, in step S1, the calculation equation Q of the lower calorific value of the fuel for the positive balance boiler thermal efficiency ar,net is expressed as:

[0039]

[0040] where B is the fuel quantity, kg / s.

[0041] Preferably, in step S1, first calculate the effective heat utilization Q of the boiler based on the boiler operation parameters Effective heat , then estimate a boiler thermal efficiency η Boiler , and from the equation calculate the lower calorific value Q of the fuel ar,net , then use the positive balance method to calculate the new boiler thermal efficiency until the difference between the two calculated boiler thermal efficiencies meets the calculation accuracy requirements, and the calculation stops.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The present invention is a simplified calculation method for boiler thermal efficiency, which solves the problems of complex traditional calculation methods, high measurement costs, and long time consumption. By simplifying the measurement steps and calculation formulas, the present invention can quickly estimate the thermal efficiency of the boiler without the need for high-precision instruments. This method significantly reduces the complexity of measurement and calculation by selecting key parameters such as flue gas temperature and oxygen content and combining empirical formulas. It is applicable to the daily monitoring and operation adjustment of boilers, helps enterprises promptly detect low-efficiency situations and take energy-saving measures, and reduces operating costs while improving operation convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the simplified calculation method for boiler thermal efficiency;

[0045] Figure 2 is a schematic diagram of the algorithm principle of the simplified calculation method for boiler thermal efficiency;

[0046] Figure 3 is a schematic diagram of the calculation flow of the simplified calculation method for boiler thermal efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by this application.

[0048] Simplified boiler thermal efficiency calculation methods are usually based on the estimation of key parameters and empirical formulas. This method can provide a relatively intuitive efficiency index, facilitating daily monitoring and adjustment by operators. Although the simplified method cannot replace precise calculations, it can provide valuable references for enterprises in specific situations, helping to optimize operating conditions and reduce energy consumption.

[0049] Embodiment: As shown in the appendix Figures 1-3 , the present invention relates to a simplified calculation method for boiler thermal efficiency, based on the following concept:

[0050] The boiler inverse balance method is a simplified thermal efficiency calculation method. It is based on the principle of energy conservation and calculates the thermal efficiency by analyzing the energy losses in the boiler system. Different from the direct balance method (calculating the ratio of heat input to output energy), the inverse balance method focuses on estimating various energy losses in the boiler to obtain the proportion of thermal energy effectively utilized in the system. By reasonably estimating the energy losses of the boiler, the inverse balance method simplifies the thermal efficiency calculation process, is applicable to daily boiler monitoring and evaluation, can provide quick references for operators, and facilitates timely optimization of boiler operation.

[0051] Based on the above concept, according to the boiler balance equation and relying on the differential deviation theory, the present invention further proposes the principle followed by the technical solution of the present invention, that is:

[0052] 1. The boiler flue gas temperature is approximately regarded as a function of the boiler load and the boiler excess air coefficient. An empirical equation is used to determine the flue gas temperature of the boiler after the boiler boundary conditions change. The operating oxygen content can be jointly determined by the heat loss due to incomplete combustion of solid fuel and the excess air coefficient;

[0053] 2. The boiler flue gas volume can be expressed as a function of the fuel calorific value, moisture content, coal type correction coefficient, and excess air coefficient. At the same time, it is considered that the CO content in the flue gas is only related to the boiler load and the excess air coefficient. After obtaining the flue gas volume and the CO content in the flue gas by using the empirical equation, the heat loss due to incomplete combustion of gas can be calculated;

[0054] 3. In the construction of the simplified model, it can be considered that the heat loss due to incomplete combustion of solid fuel is related to the fuel ash content and the operating oxygen content. The heat loss due to incomplete combustion of solid fuel under different loads can be obtained through an empirical fitting equation;

[0055] 4. Determine the physical heat loss of ash slag by the ash content and unburned carbon content. The boiler heat dissipation loss is only related to the boiler load. Thus, the physical heat loss of ash slag and the boiler heat dissipation loss can be calculated and obtained.

[0056] The specific implementation steps of the present invention are as follows:

[0057] (a) Determination link of each heat loss of the boiler

[0058] Assuming that the coal quality components do not change, an inverse balance calculation model of the boiler thermal efficiency can be constructed. According to the principle of the energy balance equation in the boiler, we have:

[0059] Q Input =Q Effective +Q Flue.G +Q Unburned.G +Q Unburned.S +Q Heat +Q Ash (1)

[0060] In the formula: Q Input is the heat input to the boiler, kJ / kg; Q Effective is the effectively utilized heat of the boiler, kJ / kg; Q Flue.G is the heat loss of the boiler flue gas, kJ / kg; Q Unburned.G is the heat loss of incomplete combustion of gas, kJ / kg; Q Unburned.S is the heat loss of incomplete combustion of solid, kJ / kg; Q Heat is the heat dissipation loss of the boiler, kJ / kg; Q Ash is the physical heat loss of ash slag, kJ / kg.

[0061] If the heat brought into the boiler by air and fuel heating steam is not considered, the heat input to the boiler can only consider the heat brought into the boiler by the lower calorific value of coal, that is:

[0062] Q Input ≈Q ar,net (2)

[0063] In the formula: Q ar,net is the received-base lower calorific value of the fuel, kJ / kg.

[0064] Among them, the heat loss of the boiler flue gas is the largest heat loss item of the boiler, which can be calculated by the flue gas temperature and the ambient temperature. The heat loss of the boiler flue gas Q Flue.G can be expressed as:

[0065]

[0066] In the formula: V Flue.G is the dry flue gas generated by burning 1 kg of coal, m 3 / kg; is the flue gas temperature of the boiler, °C; t Ambient.T is the ambient temperature, °C; c Flue.G The average constant pressure specific heat capacity of dry flue gas at is kJ / (m 3 ·°C); M Received is the moisture content of the coal as received, %; α Air outlet is the excess air coefficient at the outlet of the air preheater; k Flue.G is the coal quality coefficient in the flue gas volume. For lean coal and anthracite, k Flue.G = 0.0162; for bituminous coal and lignite, k Flue.G = -0.006; k Air is the coal quality coefficient in the air volume. For lean coal and anthracite, k Air = 0.083; for bituminous coal and lignite, k Air = 0.23.

[0067] For the convenience of simplified calculation, when the coal type is certain, it can be considered that the flue gas temperature of the boiler is only related to the boiler load and the excess air coefficient of the boiler. Therefore, the flue gas temperature of the boiler can be approximately calculated by the following empirical equation, that is:

[0068]

[0069] In the formula: α Rating is the excess air coefficient at the rated load, which can be determined by interpolation method. The value of α Air outlet is shown in Table 1; D Rating , D Actuality are the rated load and actual load of the boiler, t / h; is the flue gas temperature at the rated load, °C; t Design is the designed value of the ambient temperature, °C.

[0070] Table 1 Empirical parameter value table

[0071]

[0072] After the excess air coefficient of the boiler is determined, the following calculation equation can be used to determine the operating oxygen content at the outlet of the air preheater of the unit, that is:

[0073]

[0074] In the formula: O Oxygen is the volume content percentage of oxygen, %.

[0075] The unburned heat loss of the gas is mainly caused by combustible gases in the flue gas. After neglecting trace combustible gases such as H2 and C m H n etc. in the flue gas, QUnburned.G It can be expressed as:

[0076]

[0077] In the formula: CO is the percentage of the gas volume in the dry flue gas volume, %.

[0078] In equation (6), the prediction calculation of the CO concentration is the key to determining the heat loss due to incomplete combustion of the gas. During operation, it can be considered that CO is mainly generated by volatile matter, and it is approximately considered that the CO concentration is mainly a function of the boiler load and the operating oxygen content. Therefore, the CO concentration can be expressed by an empirical equation as:

[0079]

[0080] In the construction of the simplified model, it can be considered that the heat loss due to incomplete combustion of solids is related to the unburned carbon contained in the ash, that is, the heat loss of solid unburned Q Unburned.S It can be expressed by the following empirical formula:

[0081]

[0082] In the formula: A1, y0, t1, x0 are the empirical coefficients of formula (8), as shown in Table 2,

[0083] Table 2 Empirical coefficient table of formula (8)

[0084]

[0085] When the boiler operates at a non-rated evaporation capacity, since the temperature change of the boiler outer surface is not significant, the total heat dissipation of the boiler also changes little. It can be approximately considered that the heat dissipation loss is inversely proportional to the boiler operating load, that is, the heat dissipation loss Q Heat Under non-rated evaporation capacity, it can be expressed as:

[0086]

[0087] In addition, the heat carried out when the boiler slag is discharged out of the furnace forms the physical heat loss of the ash slag. The physical heat loss of the ash slag Q Ash Can be expressed as:

[0088]

[0089] In the formula: A Received Is the percentage of ash in the coal quality, %; c Fly ash Is the average constant pressure specific heat capacity of the fly ash from t Ambient.T To Of, kJ / (kg·°C), which can be determined by interpolation method, as shown in Table 3; c Slag Is the average constant pressure specific heat capacity of the slag from t Ambient.T To θSlag Average specific heat capacity at constant pressure, kJ / (kg·℃); a Fly ash 、a Slag is the proportion of fly ash and slag ash in the total ash of fuel, and a is Fly ash =0.9, a Slag =0.1;θ Slag is the slag temperature, ℃, and is 600℃.

[0090] Table 3 Specific heat values of fly ash at constant pressure at different temperatures in formula (10)

[0091]

[0092] (b) Determination of boiler thermal efficiency

[0093] Combining the above equations (1) to (10), we can get the boiler thermal efficiency η Boiler The expression is:

[0094]

[0095] Where: η Boiler is the boiler thermal efficiency, %.

[0096] The computer software program of the present invention is compiled based on automatic control and computer processing technology, which is a technology familiar to those skilled in the art.

[0097] The present invention is based on the counter-balance calculation principle, and determines the thermal efficiency of the boiler by calculating the various heat losses of the boiler. It successfully achieves the purpose of simply and quickly evaluating the thermal efficiency of the boiler, and solves the problem that the traditional thermal efficiency calculation method is complicated, time-consuming, and relies on expensive measuring equipment. Without the need for high-precision measuring equipment, operators can quickly calculate various losses. This process simplifies the traditional energy input and output calculations, greatly improves the speed and convenience of efficiency calculations, and is particularly suitable for daily boiler operation monitoring and adjustment, enabling enterprises to promptly discover problems in boiler operation, take measures to improve efficiency, and reduce energy consumption.

[0098] Calculation example: Taking a 600MW supercritical coal-fired power unit as an example, based on the coal quality and unit operation data, as shown in Table 4, a calculation and diagnosis case is given for the effect of boiler load changes on the economic performance of the coal-fired power unit when burning anthracite.

[0099] Table 4 Boundary condition operating parameters collected by the unit

[0100] As-received moisture content: 5% Designed to meet the flue gas temperature of 125°C for downward exhaust As-received ash content: 22.8% Excess air coefficient at designed load: 1.2 Lower calorific value: 23040 kJ / kg Ambient temperature at rated load: 25°C Ambient temperature at designed load: 20°C Main steam flow rate at rated load: 1226 t / h Main steam flow rate at designed load: 1913 t / h Excess air coefficient at rated load: 1.32

[0101] (a) Determination of boiler thermal efficiency

[0102] Boiler exhaust gas temperature

[0103]

[0104] Heat loss due to flue gas heat of the boiler, Q Flue.G :

[0105]

[0106] Operating oxygen content O at the outlet of the unit air preheater Oxygen :

[0107]

[0108] Concentration of CO:

[0109]

[0110] Heat loss due to unburned gas, Q Unburned.G :

[0111]

[0112] Heat loss due to unburned solids, Q Unburned.S :

[0113]

[0114] Heat loss due to heat dissipation, Q Heat :

[0115]

[0116] Heat loss due to physical heat of ash and slag, Q Ash :

[0117]

[0118] Boiler thermal efficiency, η Boiler :

[0119]

Claims

1. A simplified calculation method for the thermal efficiency of a boiler, characterized by comprising the steps: S1. Determine the various heat losses of the boiler and construct an inverse balance calculation model for the thermal efficiency of the boiler: Q Input = Q Effective + Q Flue.G + Q Unburned.G + Q Unburned.S + Q Heat + Q Ash ; Q Input ≈Q ar,net ; Wherein: Q Input Heat input to the boiler; Q Effective Effectively utilized heat of the boiler; Q Flue.G Heat loss due to flue gas of the boiler; Q Unburned.G Heat loss due to incomplete combustion of gas; Q Unburned.S Heat loss due to incomplete combustion of solid; Q Heat Heat loss due to heat dissipation of the boiler; Q Ash Heat loss due to physical heat of ash and slag; Q ar,net Net calorific value as received of the fuel S2. Determine the thermal efficiency of the boiler, and the expression for the thermal efficiency of the boiler is: Among them, η Boiler is the boiler thermal efficiency.

2. The simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the heat loss due to flue gas of the boiler is calculated based on the flue gas temperature and the ambient temperature. The heat loss due to flue gas of the boiler, Q Flue.G is expressed as: Where: V Flue.G is the dry flue gas generated by the combustion of 1 kg of coal; is the flue gas exhaust temperature of the boiler; t Ambient.T is the ambient temperature; c Flue.G is the average isobaric specific heat capacity of the dry flue gas at ; M Received is the moisture content of the coal as received; α Air outlet is the excess air coefficient at the outlet of the air preheater; k Flue.G is the coal quality coefficient in the flue gas volume; k Air is the coal quality coefficient in the air volume; Flue gas temperature of the boiler It is calculated using the following empirical equation: Among them, α Rating is the excess air coefficient under the rated load; D Rating is the rated load of the boiler; D Actuality is the actual load of the boiler; is the flue gas temperature under the rated load; t Design is the designed value of the ambient temperature.

3. The simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the following calculation equation is used to determine the operating oxygen content at the outlet of the air preheater of the unit, that is: where O Oxygen is the volume percentage of oxygen.

4. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, Q Unburned.G The calculation formula is: Wherein, CO is the percentage of the gas volume in the dry flue gas volume; The concentration of CO is calculated by the following empirical formula:

5. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, Q Unburned.S is calculated using the following empirical formula: Wherein, A1, y0, t1, x0 are empirical coefficients.

6. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the heat dissipation loss Q Heat is calculated by the following formula:

7. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the physical heat loss Q of the ash residue Ash is expressed as: Among them, A Received is the percentage of ash in the coal quality; c Flyash is the average isobaric specific heat capacity of fly ash from t Ambient.T to ; c Slag is the average isobaric specific heat capacity of slag from t Ambient.T to θ Slag ; a Flyash , a Slag are the shares of the ash amounts in fly ash and slag in the total ash amount of the fuel; θ Slag is the slag temperature.

8. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the calculation equation Q of the positive balance boiler thermal efficiency Effectiveheat is expressed as: Among them, Q Effectiveheat is the effectively utilized heat of the boiler, in kW; G MainSteam is the main steam flow rate of the boiler, in kg / s; h MainSteam is the enthalpy value of the main steam of the boiler, in kJ / kg; h Water is the enthalpy value of the feed water of the boiler, in kJ / kg; G reheat is the reheated steam flow rate of the boiler, in kg / s; is the outlet enthalpy value of the reheated steam of the boiler, in kJ / kg; is the inlet enthalpy value of the reheated steam of the boiler, in kJ / kg.

9. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, the calculation equation Q of the thermal efficiency of the positive balance boiler based on the lower calorific value of the fuel ar,net is expressed as: Wherein, B is the fuel quantity, kg / s.

10. A simplified calculation method for the thermal efficiency of a boiler according to claim 1, characterized in that the steps In S1, first calculate the effective heat utilization Q of the boiler based on the boiler operation parameters Effectiveheat , then estimate a boiler thermal efficiency η Boiler , and from the equation calculate the lower calorific value Q of the fuel ar,net , then use the direct balance method to calculate the new boiler thermal efficiency until the difference between the two calculated boiler thermal efficiencies meets the calculation accuracy requirements, and the calculation stops.

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