Method for converting the emission concentration of gaseous pollutants from a boiler based on flue gas recirculation

Abstract

The application relates to a boiler gas-phase pollutant emission concentration conversion method based on a flue gas recirculation technology, and relates to the field of boiler environmental protection technologies adopting the flue gas recirculation technology. The traditional boiler gas-phase pollutant emission concentration conversion method is only applicable to the case that the dilution gas is air which exists in the tail flue gas of the boiler actively or passively. In the application scene of the flue gas recirculation technology, when the dilution gas becomes the mixed gas of air and the circulating flue gas, the conversion precision is low. The application collects boiler data, simultaneously analyzes the fuel components of the boiler, obtains the air volume V air required for complete combustion of unit fuel, and the dry flue gas volume V tfgv generated by complete combustion of unit fuel, and obtains the air-flue gas ratio m V . The flue gas recirculation rate k fg is constructed by introducing the air-flue gas ratio m V , so that the traditional boiler gas-phase pollutant emission concentration conversion process is further modified in the application scene of the flue gas recirculation technology. The application is mainly used for the conversion of the boiler gas-phase pollutant emission concentration under the unified reference oxygen concentration.

Description

Technical Field

[0001] This invention relates to the field of boiler environmental protection technology that employs flue gas recirculation technology. Background Technology

[0002] In order to more scientifically and fairly assess whether boiler gaseous pollutant (nitrogen oxides, sulfur oxides, etc.) emissions meet the standards, and to avoid the false impression of compliance caused by subjective or objective factors such as air dilution, it is necessary to convert the actual measured gaseous pollutant emission concentration to the gaseous pollutant emission concentration under a given and unified benchmark oxygen concentration, and use this as the basis for assessment.

[0003] Currently, the commonly used conversion methods are mainly the excess air coefficient conversion method (Formula 1) and the flue gas oxygen content conversion method (Formula 2). The flue gas oxygen content conversion method (Formula 2) is more accurate and has a wider range of applications than the excess air coefficient conversion method (Formula 1).

[0004]

[0005] In the formula, ρ gp,converted This is the converted value of gaseous pollutant emission concentration (gp: gas pollutant), mg / m³. 3 ;ρ gp,actual The actual concentration of gaseous pollutants emitted in flue gas, in mg / m³. 3 ;α actual α is the excess air coefficient of the actual flue gas, dimensionless; converted ρ is the excess air coefficient corresponding to the baseline oxygen concentration, dimensionless; O2,air Oxygen concentration in the air, vol%; ρ O2,converted The baseline oxygen concentration is vol%, and this parameter is a known value; ρ O2,actual This represents the actual oxygen concentration in the flue gas, expressed as vol%.

[0006] When excess air, either actively or passively, exists in the flue gas at the boiler tail end as a dilution gas, that is, when the flue gas at the boiler tail end is diluted by air, ρ gp,actual It will decrease, α actual and ρ O2,actual This will increase, at which point ρ will be obtained using formula 1 or 2 at the same baseline oxygen concentration. gp,converted The effect of air dilution is eliminated, and the accuracy of the traditional emission concentration conversion methods using formulas 1 and 2 remains unaffected.

[0007] However, when the diluent gas is not air, Equations 1 and 2 may no longer apply. For example, when the diluent gas is pure nitrogen, as the volume of the diluent gas (N2) increases, ρ... gp,actual α actual and ρ O2,actualBoth will decrease simultaneously, as shown by ρ obtained from formula 1 or 2. gp,converted It will also decrease synchronously, which clearly violates the original intention of converting gaseous pollutant emission concentrations, making ρ at this time... gp,converted Below the true ρ gp,converted There is a significant discrepancy between the two, greatly reducing the accuracy of the conversion and contradicting objective facts, easily creating a false impression of emission compliance. This is because when fuel is completely burned and all air is consumed, the oxygen concentration of the generated theoretical flue gas is zero. When the theoretical flue gas is diluted by air, the oxygen concentration of the total flue gas (the mixture of theoretical flue gas and air) increases, and the total flue gas volume also increases (i.e., the total flue gas volume and oxygen concentration are directly proportional), but the concentration of gaseous pollutants decreases. The total emission of gaseous pollutants is equal to the product of the gaseous pollutant emission concentration and the total flue gas volume. Because the dilution of theoretical flue gas by air varies among different boilers, the equivalent decrease in gaseous pollutant emission concentration differs. Therefore, it is necessary to standardize the degree of air dilution and the total flue gas volume for different boilers, i.e., convert it to a given and unified benchmark oxygen concentration. Then, by evaluating the converted value of the gaseous pollutant emission concentration, the compliance status of the total gaseous pollutant emission can be obtained. Here we can see that when the oxygen concentration of the diluent gas is inconsistent with the oxygen concentration of the air, the correspondence between the total flue gas volume and the oxygen concentration will deviate, causing errors in the calculations of Formula 1 and Formula 2. In other words, when a gas with an oxygen concentration lower or higher than that of air is used as the diluent gas, Formula 1 and Formula 2 are no longer applicable.

[0008] Flue gas recirculation (FGR) technology is an effective means of reducing nitrogen oxide emissions from boilers and is widely used both domestically and internationally. The recirculated flue gas drawn from the tail flue can be directly fed into the boiler, or it can be mixed with primary or secondary air before being fed into the boiler. The recirculated flue gas originates from the boiler tail flue gas, and its oxygen concentration ρ... O2,actual Since emissions from nitrogen oxides (NOx) are significantly lower than those from air, boilers employing flue gas recirculation (FGR) technology cannot directly use formulas 1 and 2 to calculate the concentrations of other gaseous pollutants; both methods require correction. Furthermore, traditional methods for calculating boiler gaseous pollutant emission concentrations are only applicable when the diluent gas in the boiler tail gas is actively or passively present as air. In FGR applications, when the diluent gas becomes a mixture of air and recirculated flue gas, the calculation accuracy is low. These issues urgently need to be addressed. Summary of the Invention

[0009] The purpose of this invention is to address the problem that traditional methods for calculating boiler gaseous pollutant emission concentrations are only applicable when the diluent gas in the boiler tail gas is air (either actively or passively present). In applications using flue gas recirculation technology, the calculation accuracy is low when the diluent gas becomes a mixture of air and recirculated flue gas. This invention provides a method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology.

[0010] A method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology, comprising the following steps:

[0011] Step 1: Collect boiler data; boiler data includes ρ gp,actual ρ O2,air ρ O2,cfg k fan and Q F ;

[0012] ρ gp,actual ρ represents the actual concentration of gaseous pollutants emitted in the flue gas. O2,air ρ represents the oxygen concentration in the air. O2,cfg k represents the actual oxygen concentration in the flue gas. fan Q is the opening degree of the circulating flue gas flow control valve; F This represents the actual load on the boiler.

[0013] Fuel composition analysis of boiler fuel was performed to obtain the air volume V required for complete combustion of a unit unit of fuel. air The amount of dry flue gas V generated by the complete combustion of a unit of fuel tfgv Then according to V air and V tfgv To obtain the air-to-smoke ratio

[0014] Step 2, combine m V k fan ρ O2,air ρ O2,cfg and Q F Construct the flue gas recirculation rate k fg ;

[0015] Step 3, combine with k fg ρ gp,actual ρ O2,air and ρ O2,cfg The converted value of gaseous pollutant emission concentration ρ was obtained. gp,converted .

[0016] Preferably,

[0017] Where, ρ O2,converted The baseline oxygen concentration.

[0018] Preferably,

[0019] Where, k fg,max α is the percentage of the upper limit of the circulating flue gas volume to the actual flue gas volume under the boiler's rated load conditions. design Excess air coefficient for boiler design.

[0020] Preferably, when the boiler is a solid fuel boiler, V is obtained. air and V tfgv The implementation method is as follows:

[0021] Step 111: Perform fuel composition analysis on the boiler fuel to obtain ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar ;

[0022] ω C,ar The carbon content of the solid fuel received; ω S,ar The content of basic sulfur received by solid fuel; ω H,ar The content of basic hydrogen received by solid fuel; ω O,ar The content of basic oxygen received by solid fuel; ω N,ar The content of nitrogen received by solid fuels;

[0023] Step 112, according to ω C,ar ω S,ar ω H,ar and ω O,ar V air ;

[0024] Step 113, according to V air ω C,ar ω S,ar and ω N,ar , to obtain V tfgv .

[0025] Preferably,

[0026] Among them, V C,air V is the theoretical amount of air required for the complete combustion of carbon. S,air V represents the theoretical amount of air required for the complete combustion of sulfur. H,air V represents the theoretical amount of air required for the complete combustion of hydrogen. O,air This represents the theoretical amount of air corresponding to oxygen.

[0027] Preferably,

[0028] Among them, V C,fg The theoretical dry flue gas volume generated by the complete combustion of carbon; VS,fg V is the theoretical dry flue gas volume generated by the complete combustion of sulfur. N,fg This represents the theoretical amount of dry flue gas generated by the complete combustion of nitrogen.

[0029] Preferably, when the boiler is a gas-fired boiler, V is obtained. air and V tfgv The implementation method is as follows:

[0030] Step 121: Perform fuel composition analysis on the boiler fuel to obtain... and

[0031] This represents the volume fraction of CO in the gaseous fuel. This represents the volume fraction of H2 in the gaseous fuel. This represents the volume fraction of H2S in the gaseous fuel. C in gaseous fuel m H n The volume fraction; m is C m H n The number of carbon atoms in the middle; n is the number of carbon atoms in C. m H n Number of hydrogen atoms; m and n are variables; This represents the volume fraction of O2 in the gaseous fuel. This represents the volume fraction of CO2 in the gaseous fuel. This represents the volume fraction of N2 in the gaseous fuel.

[0032] Step 122, according to and Get V air ;

[0033] Step 123, according to V air , and Get V tfgv .

[0034] Preferably,

[0035] Preferably,

[0036] Preferably, for a solid fuel boiler, ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar Under any one or more unavailable conditions: when the solid fuel is coal, m V Take an empirical value of 1.02; when the solid fuel is biomass, m V Take the experience value as 1.01.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention provides a method for calculating the emission concentration of gaseous pollutants from boilers based on flue gas recirculation technology, by introducing the air-to-smoke ratio m. V To construct the flue gas recirculation rate k fg This allows for further correction of the gaseous pollutant emission concentration calculated by the traditional gaseous pollutant emission concentration conversion method in the application scenario of flue gas recirculation technology, so as to obtain the converted gaseous pollutant emission concentration value more accurately.

[0039] Compared to traditional methods for calculating the emission concentration of gaseous pollutants, this invention adds (1+k) fg The traditional method for calculating gaseous pollutant emission concentrations yields gaseous pollutant emission concentrations that are inversely proportional to (1+k). fg Multiplying these values ​​allows for further correction of the calculated concentration of gaseous pollutants in the application scenarios of flue gas recirculation technology.

[0040] Boilers employing flue gas recirculation technology, depending on their operating parameters, k fg The value is generally between 0.1 and 0.3. The converted values ​​of gaseous pollutant emission concentrations obtained by traditional methods are 9%-23% lower than those obtained by this invention. The conversion accuracy of traditional methods is significantly lower than that of this invention, and they are more likely to produce the false impression that gaseous pollutant emissions meet the standards.

[0041] This invention can more accurately obtain the converted values ​​of gaseous pollutant emission concentrations of boilers using flue gas recirculation technology, thereby enabling a more scientific and fair assessment of whether the boiler's gaseous pollutant emissions meet the standards, urging non-compliant boilers to rectify the situation in a timely manner, which helps to continuously and deeply fight the battle to protect blue skies, effectively safeguard the health of the people, and promote high-quality economic development through continuous improvement of air quality. Attached Figure Description

[0042] Figure 1 This is a flowchart of the boiler gaseous pollutant emission concentration conversion method based on flue gas recirculation technology described in this invention;

[0043] Figure 2 This is a schematic diagram illustrating the application principle of the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0046] Example 1:

[0047] The following is combined Figure 1 This embodiment describes a method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology. The method includes the following steps:

[0048] Step 1: Collect boiler data, including ρ gp,actual ρ O2,air ρ O2,cfg k fan and Q F ;

[0049] Where, ρ gp,actual ρ represents the actual concentration of gaseous pollutants emitted in the flue gas. O2,air ρ represents the oxygen concentration in the air. O2,cfg The actual oxygen concentration in the flue gas is equivalent to ρ in Formula 2. O2,actual ;k fan Q is the opening degree of the circulating flue gas flow control valve; F This represents the actual load on the boiler.

[0050] Fuel composition analysis of boiler fuel was performed to obtain the air volume V required for complete combustion of a unit unit of fuel. air The amount of dry flue gas V generated by the complete combustion of a unit of fuel tfgv Then according to V air and V tfgv To obtain the air-to-smoke ratio

[0051] Step 2, combine m V k fan ρ O2,air ρ O2,cfg and Q F Construct the flue gas recirculation rate k fg ;

[0052] Step 3, combine with k fg ρ gp,actual ρ O2,air and ρ O2,cfgThe converted value of gaseous pollutant emission concentration ρ was obtained. gp,converted .

[0053] In this embodiment, see Figure 2 Boiler data from boiler system 3 can be collected through the online boiler data acquisition system 1. This boiler data includes boiler operating data ρ. O2,air k fan and Q F and boiler tail flue gas data ρ gp,actual and ρ O2,cfg The fuel composition of the fuel consumed by the boiler system 3 can be analyzed through the online fuel composition analysis system 2.

[0054] In this embodiment, an air-to-smoke ratio m is introduced. V To construct the flue gas recirculation rate k fg Combined with k fg ρ gp,actual ρ O2,air and ρ O2,cfg The converted value of gaseous pollutant emission concentration ρ was obtained. gp,converted By constructing the flue gas recirculation rate k fg In the application scenario of flue gas recirculation technology, further corrections can be made to the gaseous pollutant emission concentrations calculated by the traditional gaseous pollutant emission concentration conversion method, so as to obtain more accurate converted gaseous pollutant emission concentration values.

[0055] Furthermore,

[0056]

[0057] In the formula, ρ O2,converted As the baseline oxygen concentration, k fg,max α is the percentage of the upper limit of the circulating flue gas volume to the actual flue gas volume under the boiler's rated load conditions. design Excess air coefficient for boiler design.

[0058] In this preferred embodiment, compared to traditional methods for calculating gaseous pollutant emission concentrations, the present invention adds (1+k) fg The traditional method for calculating gaseous pollutant emission concentrations yields gaseous pollutant emission concentrations that are inversely proportional to (1+k). fg Multiplying these values ​​allows for further correction of the calculated concentration of gaseous pollutants in the application scenarios of flue gas recirculation technology.

[0059] Boilers employing flue gas recirculation technology, depending on their operating parameters, k fgThe value is generally between 0.1 and 0.3. The converted values ​​of gaseous pollutant emission concentrations obtained by traditional methods are 9%-23% lower than those obtained by this invention. The conversion accuracy of traditional methods is significantly lower than that of this invention, and they are more likely to produce the false impression that gaseous pollutant emissions meet the standards.

[0060] Furthermore, for boilers that burn solid fuels, and ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar Under any one or more unavailable conditions: when the solid fuel is coal, m V Take an empirical value of 1.02; when the solid fuel is biomass, m V Take the experience value as 1.01.

[0061] In practical applications, for solid fuel boilers, the lack of an online fuel composition analysis system 2 or a malfunction of the online fuel composition analysis system 2 leads to ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar Given that one or more of the following conditions cannot be obtained, such that m V It also cannot be obtained. Under these constraints, by using m V Even with empirical values, more accurate gaseous pollutant emission concentration conversion results can still be obtained compared to traditional gaseous pollutant concentration conversion methods.

[0062] And in m V In the case of availability, for The solution, i.e., V air and V tfgv The solution needs to be discussed separately for solid fuel boilers and gas fuel boilers. Specifically:

[0063] (i) When the boiler is a solid fuel boiler, V is obtained air and V tfgv The implementation method is as follows:

[0064] Step 111: Perform fuel composition analysis on the boiler fuel to obtain ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar ;

[0065] ω C,ar The carbon content of solid fuel as received, mass%; ω S,ar The content of basic sulfur in solid fuels, mass%; ωH,ar The content of hydrogen received by solid fuel, mass%; ω O,ar The oxygen content of solid fuel received, mass%; ω N,ar The nitrogen content of solid fuels, in mass%;

[0066] See Figure 2 ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar The information was obtained by analyzing the boiler fuel composition using the online fuel composition analysis system 2.

[0067] Step 112, according to ω C,ar ω S,ar ω H,ar and ω O,ar , to obtain V air ;

[0068]

[0069] Among them, V C,air This represents the theoretical amount of air required for the complete combustion of carbon, taken as 8.889m³. 3 / kg; V S,air This represents the theoretical amount of air required for the complete combustion of sulfur, taken as 3.333m³. 3 / kg; V H,air This represents the theoretical amount of air required for the complete combustion of hydrogen, taken as 26.667 m³. 3 / kg; V O,air The theoretical air volume corresponding to oxygen is taken as 3.333m³. 3 / kg.

[0070] Step 113, according to V air ω C,ar ω S,ar and ω N,ar , to obtain V tfgv ;

[0071]

[0072] Among them, V C,fg The theoretical dry flue gas volume generated by the complete combustion of carbon is taken as 1.867 m³. 3 / kg; V S,fg The theoretical dry flue gas volume generated by the complete combustion of sulfur is taken as 0.7 m³. 3 / kg; V N,fg The theoretical dry flue gas volume generated by the complete combustion of nitrogen is taken as 0.8 m³. 3 / kg. Here V air and Vtfgv The unit is m 3 / kg.

[0073] (ii) When the boiler is a gas-fired boiler, V is obtained. air and V tfgv The implementation method is as follows:

[0074] Step 121: Perform fuel composition analysis on the boiler fuel to obtain... and

[0075] The volume fraction of CO in the gaseous fuel, expressed as vol%. The volume fraction of H2 in the gaseous fuel, expressed as vol%. The volume fraction of H2S in the gaseous fuel, vol%. C in gaseous fuel m H n Volume fraction, vol%. m is C. m H n The number of carbon atoms in the medium is dimensionless; n is the number of carbon atoms in C. m H n The number of hydrogen atoms in the sample is dimensionless; m and n are variables. The volume fraction of O2 in the gaseous fuel, expressed as vol%. The volume fraction of CO2 in the gaseous fuel, expressed as vol%. The volume fraction of N2 in the gaseous fuel, expressed as vol%.

[0076] See Figure 2 , and The information was obtained by analyzing the boiler fuel composition using the online fuel composition analysis system 2.

[0077] Step 122, according to and Get V air ;

[0078]

[0079] Step 123, according to V air , and Get V tfgv ;

[0080]

[0081] When the boiler is a gas-fired boiler, here V air and V tfgv The unit is m 3 / m3 .

[0082] As can be seen from the above, see Figure 2 The data collected by the boiler online data acquisition system 1 includes ρ gp,actual ρ O2,air ρ O2,cfg k fan and Q F ;

[0083] For solid fuel boilers, the data collected by the online fuel composition analysis system 2 includes ω C,ar ω S,ar ω H,ar ω O,ar and ω N,ar ;

[0084] For gas-fired boilers, the data collected by the online fuel composition analysis system 2 includes: and

[0085] Where, ρ gp,actual The actual concentration of gaseous pollutants emitted in flue gas, in mg / m³. 3 ;ρ O2,air Oxygen concentration in the air, vol%; ρ O2,cfg The actual oxygen concentration in the flue gas, vol%; k fan For the opening degree of the circulating flue gas flow control valve, %; Q F This represents the actual load of the boiler, in percentages.

[0086] ω C,ar The carbon content of solid fuel as received, mass%; ω S,ar The content of basic sulfur in solid fuels, mass%; ω H,ar The content of hydrogen received by solid fuel, mass%; ω O,ar The oxygen content of solid fuel received, mass%; ω N,ar The nitrogen content of solid fuels, in mass%;

[0087] The volume fraction of CO in the gaseous fuel, expressed as vol%. The volume fraction of H2 in the gaseous fuel, expressed as vol%. The volume fraction of H2S in the gaseous fuel, vol%. C in gaseous fuel m H n Volume fraction, vol%. The volume fraction of O2 in the gaseous fuel, expressed as vol%. The volume fraction of CO2 in the gaseous fuel, expressed as vol%. The volume fraction of N2 in the gaseous fuel is expressed as vol%.

[0088] Example 2:

[0089] See Figure 2 A boiler gaseous pollutant emission concentration conversion device based on flue gas recirculation technology is provided. The conversion device is implemented using the boiler gaseous pollutant emission concentration conversion method based on flue gas recirculation technology described in Example 1.

[0090] Boilers employing flue gas recirculation (FGR) technology have a dilution gas in their tail-end flue gas that is a mixture of air and recirculated flue gas. Traditional methods for calculating gaseous pollutant emission concentrations are only applicable when the dilution gas is solely air. Using these traditional methods for boilers with FGR technology is equivalent to assuming the oxygen concentration in the recirculated flue gas is identical to that in air, which leads to significant discrepancies. Recirculated flue gas originates from boiler flue gas; the Special Equipment Safety Technical Specification TSG 91-2021, "Technical Regulations for Energy Conservation and Environmental Protection of Boilers," stipulates that the oxygen concentration in flue gas under rated boiler load, depending on the boiler type, generally does not exceed 3 vol%-9 vol%, significantly lower than the oxygen concentration in air. Therefore, using traditional methods for calculating gaseous pollutant emission concentrations in boilers with FGR technology results in low accuracy.

[0091] Boilers employing flue gas recirculation technology, depending on their operating parameters, k fg The value is generally between 0.1 and 0.3. The converted values ​​of gaseous pollutant emission concentrations obtained by traditional methods are 9%-23% lower than those obtained by this invention. The conversion accuracy of traditional methods is significantly lower than that of this invention, and they are more likely to produce the false impression that gaseous pollutant emissions meet the standards.

[0092] Verification section:

[0093] The effectiveness of this invention is demonstrated by explaining the origin of its concept. The specific origin of the concept is as follows:

[0094] To simplify the conversion process of boiler gaseous pollutant emission concentrations, the following assumptions are generally made: (a) the gaseous pollutant emission concentrations are based on dry flue gas under standard conditions (0℃, 101325Pa); (b) the boiler combustion conditions remain unchanged before and after conversion; and (c) the efficiency of the boiler flue gas purification system remains unchanged before and after conversion.

[0095] (1) According to the conservation of gaseous pollutants, we can obtain:

[0096] G gp =ρ gp,actual ×V actual =ρ gp,converted ×Vconverted Formula 3;

[0097] In the formula, G gp V represents the total emissions of gaseous pollutants, in mg / h. actual For actual dry flue gas volume, m 3 / h;V converted To calculate the dry flue gas volume, m 3 / h;ρ gp,actual The actual concentration of gaseous pollutants emitted in flue gas, in mg / m³. 3 ;ρ gp,converted This is a converted value of the emission concentration of gaseous pollutants, in mg / m³. 3 .

[0098] (2) If the residual amount of combustible gases such as CO in the actual dry flue gas is small and negligible, then the actual dry flue gas volume V actual It consists of the following parts: ① Total theoretical dry flue gas volume V, taking into account fuel consumption. tfgv,total,actual ② Actual excess air volume V ea,actual (Including air leakage and excess combustion air distribution), ③ Circulating flue gas volume V cfg,-1 This V cfg,-1 It was extracted from the flue at some point in the previous period and then sent into the furnace via a circulating fan.

[0099] Equivalent dry flue gas volume V converted It mainly consists of the following parts: ①V tfgv,total,actual (Because the boiler combustion conditions remain unchanged before and after the conversion, this part of the flue gas volume also remains unchanged), ② based on ρ O2,converted Excess air volume V ea,converted , where ρ O2,converted The baseline oxygen concentration is expressed as vol%.

[0100] Formula 3 can be evolved as follows:

[0101]

[0102] V tfgv,total,actual =B×V tfgv Formula 5;

[0103] V ea,converted =B×V air ×(α converted -1) Formula 6;

[0104] In the formula, V tfgv,total,actual To account for the total theoretical dry flue gas volume of fuel consumption, m 3 / h;V ea,actual The actual excess air volume, m 3 / h;V cfg,-1The circulating flue gas volume, i.e., the circulating flue gas originating from a previous time period, is expressed in m. 3 / h;V ea,converted For ρ O2,converted Excess air volume, m 3 / h; B is fuel consumption, kg / h (for solid fuel boilers) or m 3 / h (gas-fired boiler); V tfgv The amount of dry flue gas produced by the complete combustion of a unit of fuel, m 3 / kg (solid fuel boiler) or m 3 / m 3 (Gas-fired boiler); V air The amount of air required for the complete combustion of a unit of fuel, m 3 / kg (solid fuel boiler) or m 3 / m 3 (Gas-fired boiler); ρ gp,actual The actual concentration of gaseous pollutants emitted in flue gas, in mg / m³. 3 ;α converted The excess air coefficient corresponding to the baseline oxygen concentration is dimensionless.

[0105] (3) The amount of air V required for complete combustion of a unit of fuel air The amount of dry flue gas V generated by the complete combustion of a unit of fuel tfgv It only depends on the composition of the fuel, because the boiler combustion conditions remain unchanged before and after the conversion, so V air and V tfgv The ratio between them should be constant.

[0106] V air =m V ×V tfgv Formula 7;

[0107] In the formula, m V The air-to-smoke ratio, i.e., V tfgv and V air The conversion coefficients between them are dimensionless.

[0108] (4) Meanwhile, assuming that the total theoretical dry flue gas volume V, considering fuel consumption, is... tfgv,total,actual And the actual excess air volume V ea,actual The following relationship exists between them:

[0109] V ea,actual =n V ×V tfgv,total,actual Formula 8;

[0110] In the formula, n V For V tfgv,total,actual and V ea,actual The conversion coefficients between them are dimensionless.

[0111] (5) As for V cfg,-1 We need to introduce a concept: flue gas recirculation rate k. fg Characterizing the circulating flue gas volume V cfg,-1 The ratio of the circulating flue gas volume to the boiler's conventional flue gas volume is related to the parameters of the circulating fan and the opening degree of the circulating flue gas flow control valve, therefore, the following formula applies:

[0112] V cfg,-1 =k fg ×(V tfgv,total,actual,-1 +V ea,actual,-1 ) Formula 9;

[0113] In the formula, k fg V is the flue gas recirculation rate, dimensionless; tfgv,total,actual,-1 The total theoretical dry flue gas volume for a certain period of time, m 3 / h;V ea,actual,-1 The actual excess air volume over a certain period of time, m 3 / h. Because the gas velocity inside the boiler is very high, the residence time of the extracted circulating flue gas inside the furnace is very short, so it can be simplified to consider V for a certain period of time before. tfgv,total,actual,-1 V ea,actual,-1 V is equivalent to the current time period tfgv,total,actual V ea,actual Therefore, Formula 9 can be simplified as follows:

[0114] V cfg,-1 =k fg ×(V tfgv,total,actual +V ea,actual ) Formula 10;

[0115] (6) Because considering the total theoretical dry flue gas volume V of fuel consumption tfgv,total,actual Since it contains no oxygen, according to the law of conservation of oxygen, the actual dry flue gas volume V actual The total amount of oxygen in the flue gas is equal to the circulating flue gas volume V. cfg,-1 And the actual excess air volume V ea,actual The sum of the total oxygen in the body can be obtained as follows:

[0116] ρ O2,air ×V ea,actual +ρ O2,cfg,-1 ×V cfg,-1 =ρ O2,cfg ×(V tfgv,total,actual +V ea,actual +V cfg,-1 ) Formula 11;

[0117] In the formula, ρ O2,cfg,-1 For V cfg,-1 Oxygen concentration in, vol%; ρ O2,cfg For Vactual The oxygen concentration, vol%, is equivalent to ρ in Formula 2. O2,actual Consistent with the simplification approach of formulas 9 and 10, ρ can be considered... O2,cfg,-1 Equivalent to ρ O2,cfg Substituting formulas 8 and 10 into formula 11, formula 11 can be simplified as follows:

[0118]

[0119] (7) The following is about α converted Let's derive the equation. Based on the law of conservation of oxygen, we have...

[0120] (α converted -1)×V air ×ρ O2,air =ρ O2,converted ×[V tfgv +(α converted -1)×V air ] Formula 13;

[0121] Substituting formula 7 into formula 13, we get formula 14. Then, rearranging formula 14, we get formula 15.

[0122]

[0123] Formulas 14 and 15 require separate explanation here. Regarding the excess air coefficient α... converted Empirical Formula 16 exists:

[0124]

[0125] It can be observed that Formula 16 is based on m V Approximately equal to 1 (i.e., V) tfgv and V air The simplification of Formula 14 based on approximate equality contains certain errors. Therefore, α cannot be solved using empirical Formula 16 first. converted Then substitute the values ​​into formula 14 or 15 to solve for m. V Thus, skipping the initial solution of V air and V tfgv Then solve for m using Formula 7. V The process. The error between Formula 16 and Formula 14 is also the main reason why Formula 1 is less accurate than Formula 2 in the background technology.

[0126] (8) The following is an explanation of the flue gas recirculation rate k in Formula 9. fg Solve the problem.

[0127] Flue gas recirculation rate k fgThe parameters of the circulating fan and the opening of the circulating flue gas flow control valve are related. The parameters of the circulating fan are the maximum flow rate V of the circulating fan. fan,max The opening degree of the circulating flue gas flow control valve is determined by k. fan express.

[0128] Maximum flow rate V of circulating fan fan,max It can be obtained from the following formula:

[0129]

[0130] In the formula, V fan,max The maximum flow rate of the circulating fan is m 3 / h;B rated Fuel consumption of the boiler at rated load, kg / h (for solid fuel boilers) or m³ 3 / m 3 (Gas-fired boiler), this parameter is a known design value; α design The excess air coefficient for boiler design is dimensionless and is a known design value; k fg,max The percentage of the upper limit of circulating flue gas volume to the actual flue gas volume under the rated load condition of the boiler is vol%. This parameter is a known value in the design.

[0131] At the same time:

[0132]

[0133] In the formula, Q F This represents the actual load of the boiler, %.

[0134] Because the circulating flue gas originates from the flue gas drawn from the boiler's tail flue by the circulating fan, the circulating flue gas volume V cfg,-1 Equal to the circulating fan flow rate, i.e., the maximum circulating fan flow rate V. fan,max and the opening degree k of the circulating flue gas flow control valve fan The product of , therefore we have:

[0135]

[0136] In the formula, V fan The flow rate of the circulating fan is m 3 / h, equivalent to V cfg,-1 ;k fan The opening degree of the circulating flue gas flow control valve is %.

[0137] Substituting formulas 7 and 17 into formula 19, we get:

[0138]

[0139] Substituting formulas 5, 8, 12, 18, and 20 into formula 10, we can obtain the flue gas recirculation rate k.fg :

[0140]

[0141] (9) Substituting formulas 5, 6, 7, 8, 10, 12, 15, and 21 into formula 4, we can obtain...

[0142]

[0143] Formula 22 is a method for calculating the concentration of gaseous pollutants emitted from boilers based on flue gas recirculation technology. It can be observed that Formula 22 multiplies by an additional (1+k) compared to Formula 2. fg The item indicates the corrected converted value of gaseous pollutant emission concentration ρ. gp,converted and flue gas recirculation rate k fg They are directly proportional; and from formula 10, we can see that the flue gas recirculation rate k fg and circulating flue gas volume V cfg,-1 They are directly proportional, so the corrected converted value of gaseous pollutant emission concentration ρ gp,converted and circulating flue gas volume V cfg,-1 The direct proportionality is a logical deduction.

[0144] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for calculating the emission concentration of gaseous pollutants from boilers based on flue gas recirculation technology, characterized in that, The method includes the following steps: Step 1: Collect boiler data. Boiler data includes... , , , and ; This represents the actual concentration of gaseous pollutants emitted in the flue gas. The concentration of oxygen in the air; This represents the actual oxygen concentration in the flue gas. To control the opening degree of the circulating flue gas flow control valve; This represents the actual load on the boiler. Fuel composition analysis of boiler fuel is performed to obtain the amount of air required for complete combustion of a unit of fuel. The amount of dry flue gas generated by the complete combustion of a unit of fuel ; and then according to and To obtain the air-to-smoke ratio ; Step 2, Combining , , , and Build flue gas recirculation rate ; ； in, This represents the percentage of the upper limit of the circulating flue gas volume to the actual flue gas volume under the boiler's rated load conditions. Excess air coefficient for boiler design; Step 3, Combining , , and The converted values ​​of gaseous pollutant emission concentrations were obtained. ; ; in, The baseline oxygen concentration.

2. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 1, characterized in that, When the boiler is a solid fuel boiler, the following is obtained and The implementation method is as follows: Step 111: Perform fuel composition analysis on the boiler fuel to obtain... , , , and ; The carbon content of solid fuels received; The content of basic sulfur in solid fuels; The content of hydrogen received by solid fuel; The content of basic oxygen received by solid fuel; The content of nitrogen received by solid fuels; Step 112, according to , , and ,get ; Step 113, according to , , and ,get .

3. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 2, characterized in that, in, This is the theoretical amount of air required for the complete combustion of carbon. This represents the theoretical amount of air required for the complete combustion of sulfur. This represents the theoretical amount of air required for the complete combustion of hydrogen. This represents the theoretical amount of air corresponding to oxygen.

4. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 2, characterized in that, in, The theoretical amount of dry flue gas generated by the complete combustion of carbon; The theoretical dry flue gas volume generated by the complete combustion of sulfur; This represents the theoretical amount of dry flue gas generated by the complete combustion of nitrogen.

5. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 1, characterized in that, When the boiler is a gas-fired boiler, the following is obtained: and The implementation method is as follows: Step 121: Perform fuel composition analysis on the boiler fuel to obtain... , , , , , and ; This represents the volume fraction of CO in the gaseous fuel. This represents the volume fraction of H2 in the gaseous fuel. This represents the volume fraction of H2S in the gaseous fuel. C in gaseous fuel m H n The volume fraction; m is C m H n The number of carbon atoms in the middle; n is the number of carbon atoms in C. m H n Number of hydrogen atoms; m and n are variables; φ O2 φ represents the volume fraction of O2 in the gaseous fuel. CO2 φ represents the volume fraction of CO2 in the gaseous fuel. N2 This represents the volume fraction of N2 in the gaseous fuel. Step 122, according to , , , and ,get ; Step 123, according to , , , , and ,get .

6. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 5, characterized in that, 7. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 5, characterized in that, 8. The method for calculating boiler gaseous pollutant emission concentrations based on flue gas recirculation technology according to claim 1, characterized in that, For boilers that burn solid fuels , , , and Under any one or more unavailable conditions: when the solid fuel is coal, m V Take an empirical value of 1.02; when the solid fuel is biomass, m V Take the experience value as 1.01.

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