Boiler fuel efficiency calculation method using SNCR denitration technology

Abstract

The application discloses a kind of coal-fired power plant boiler fuel efficiency calculation method using SNCR denitration technology, the boiler fuel efficiency of the present application is obtained by respectively calculating the exhaust heat loss rate after SNCR operation, gas incomplete combustion heat loss rate, solid incomplete combustion heat loss rate, boiler heat loss rate, ash physical sensible heat loss rate, SNCR reaction heat loss rate, boiler other heat loss rate, external heat and the percentage of low calorific value of fuel;Wherein, SNCR reaction heat loss rate includes urea melting phase change absorption heat, liquid water in urea solution is heated and vaporized absorption heat, and the heat loss rate caused by heat release caused by urea chemical reaction.This application first proposes the method that the urea solution sprayed into the furnace is accurately divided to unit mass fuel by calculating the difference of air preheater outlet flue gas humidity of SNCR boiler when operating and stopping, solves the problem that the quality of fuel into the furnace and the accurate measurement of urea solution into the furnace are difficult.

Description

Technical Field

[0001] This invention presents a method for calculating the fuel efficiency of a coal-fired power plant boiler using SNCR denitrification technology. Background Technology

[0002] In recent years, with increasingly stringent environmental protection requirements, many coal-fired power generating units in China have added SNCR (Synthetic Non-Combustion Catalytic Reduction) flue gas denitrification technology to control nitrogen oxide emissions. SNCR denitrification technology involves injecting a 5-10% urea solution into the furnace for pyrolysis to generate ammonia, which then reduces NO. Due to the large volume of water injected into the furnace, the impact on boiler fuel efficiency is significant. Therefore, experimental measurements and calculations of boiler fuel thermal efficiency after adopting SNCR denitrification technology are of great value in evaluating the operating costs of SNCR.

[0003] Currently, the calculation methods for the fuel efficiency of large-scale coal-fired power plant boilers in China are all based on GB / T10184-2015. This standard specifies the calculation methods for the boiler efficiency of coal-fired power plant boilers and the boiler efficiency after the injection of calcium-based desulfurizing agent into the furnace. However, it is not applicable to the calculation of the fuel efficiency of boilers using SNCR denitrification technology. The main reasons are as follows: 1. It does not consider the influence of the SNCR injection water volume on the heat loss carried away by water vapor in the boiler flue gas heat loss; 2. It does not consider the heat loss of the SNCR denitrification reaction; 3. It does not consider the influence of the SNCR denitrification reaction on the heat loss of dry flue gas. If the method in the standard is used to calculate the fuel efficiency of coal-fired power plant boilers using SNCR denitrification technology, it is very easy to ignore the above three major aspects, resulting in a 1-2% underestimation of the boiler fuel efficiency, which is a huge error.

[0004] Because the metering of urea injected by SNCR denitrification technology is inaccurate, the amount of coal fed into the boiler of a coal-fired power plant cannot be accurately calculated, and the reaction process of the urea solution injected into the furnace is complex, it is difficult to accurately measure and calculate the fuel efficiency of a coal-fired power plant boiler after adopting SNCR denitrification technology, and there is currently no accurate method. Summary of the Invention

[0005] The purpose of this invention is to address the deficiencies in the existing technology and provide a method for calculating the fuel efficiency of a coal-fired power plant boiler after the commissioning of an SNCR denitrification system.

[0006] To achieve the above objectives, this invention discloses a method for calculating boiler fuel efficiency using SNCR denitrification technology. The boiler fuel efficiency η of this invention... SNCR The flue gas heat loss rate q after the SNCR is put into operation is calculated separately. 2,SNCR Heat loss rate q due to incomplete combustion of gas 3,SNCR Heat loss rate q of incomplete combustion of solids 4,SNCR Boiler heat loss rate q 5,SNCR , Physical sensible heat loss rate of ash and slag q6,SNCR SNCR reaction heat loss rate q 7,SNCR Other heat loss rates of the boiler, q qt,SNCR The percentage of external heat to the lower heating value of fuel (q) w1,SNCR The heat loss rate q of the SNCR reaction is obtained. 7,SNCR This includes the heat loss rate caused by the heat absorbed during the melting phase change of urea, the heat absorbed by the vaporization of liquid water in the urea solution, and the heat released during the chemical reaction of urea.

[0007] in,

[0008] η SNCR =100-q 2,SNCR -q 3,SNCR -q 4,SNCR -q 5,SNCR -q 6,SNCR -q 7,SNCR -q qt,SNCR +q w1,SNCR ,%.

[0009] This invention fully considers the impact of the SNCR reaction on boiler fuel efficiency by increasing the calculation of the heat loss rate of the SNCR denitrification reaction. At the same time, it adopts the turnkey reaction calculation to calculate the heat loss of the SNCR denitrification reaction, making the calculation more accurate.

[0010] Among them, the flue gas heat loss rate q 2,SNCR This includes the heat loss rate caused by the dry flue gas produced by fuel combustion and the heat loss rate caused by the water vapor in the flue gas carrying away heat from the system; the dry flue gas produced by fuel combustion also includes the dry flue gas generated by the SNCR reaction per unit mass of fuel, and the water vapor in the flue gas also includes the moisture brought in by the urea solution and the moisture generated by the SNCR reaction.

[0011] In calculating the flue gas heat loss rate, this invention considers not only the heat loss caused by dry flue gas and the heat carried away by water vapor contained in the flue gas, but also the effects of the urea solution injected into the furnace by the SNCR system and its reaction on the volume of dry flue gas and the amount of water vapor, making the calculation more accurate.

[0012] In the specific calculation, the flue gas heat loss rate q 2,SNCR ,%=Q 2,SNCR / Q net,SNCR ×100; Q 2,SNCR Q represents the heat loss caused by the combustion of a unit mass of fuel in the flue gas after the SNCR is put into operation. net,SNCR The lower heating value of the fuel fed into the furnace; the volume of dry flue gas generated by the SNCR reaction per unit mass of fuel. The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get:

[0013] In calculating the effect of SNCR reaction on dry flue gas volume, this invention establishes a calculation model by evenly distributing the urea solution injected into the furnace by the SNCR system onto a unit mass of fuel, making the calculation more accurate and convenient.

[0014] Among them, the heat loss Q caused by the flue gas generated by the combustion of fuel per unit mass after the SNCR is put into operation. 2,SNCR Including the heat Q carried away by the dry flue gas from the system 2,gy The heat carried away by the water vapor contained in the flue gas

[0015] Q 2，gy =V gy，SNcR C p，gy，SNCR (t gy，ky，o，SNCR -t jz );

[0016] In the formula, The volume of air theoretically required for combustion of a unit mass of fuel, m 3 / kg; m is the volume of dry flue gas produced by the SNCR reaction per unit mass of fuel. 3 / kg; α is the excess air coefficient at the air preheater outlet after the SNCR is put into operation.

[0017] The heat carried away by water vapor in the flue gas after the SNCR system is put into operation Calculated using the following formula:

[0018]

[0019] In the formula, The volume of water vapor in the flue gas at the air preheater outlet generated per unit mass of fuel combustion after the SNCR system is put into operation, in m³. 3 / kg; t jz The reference temperature for the test is ℃; t gy，ky，o，SNCR The outlet flue gas temperature of the air preheater after the SNCR system is put into operation, in °C; For water vapor from t jz To t gy，ky，o，SNCR Specific heat capacity at constant pressure, kJ / (m 3 .K);

[0020] Among them, the volume of water vapor in the flue gas at the air preheater outlet generated per unit mass of fuel combustion after the SNCR system is put into operation This also includes the water introduced into the urea solution after the SNCR system is put into operation and the water generated by the SNCR reaction.

[0021] In calculating the volume of water vapor in the flue gas at the outlet of the air preheater, this invention also fully considers the influence of water in the urea solution and the water generated by the reaction after the SNCR system is put into operation.

[0022] In specific calculations, the volume of water vapor in the flue gas at the air preheater outlet generated per unit mass of fuel combustion after the SNCR system is put into operation is... Calculated using the following formula:

[0023]

[0024] In the formula, H ar The received hydrogen content of the fuel, %; M ar Moisture content of the fuel as received, in %; The volume of air theoretically required for combustion of a unit mass of fuel, m 3 / kg; h kq，ab It is the absolute moisture content of the air, kg / kg; the mass fraction of the urea solution injected into the furnace by the c-SNCR system, %.

[0025] This invention relates to the heat loss rate q of the SNCR reaction. 7,SNCR The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get:

[0026]

[0027] In the formula, a—molar ratio of injected urea to NO in flue gas; b—densification efficiency of the SNCR reaction system, %; c—mass fraction of urea solution injected into the furnace by the SNCR system, %.

[0028] This invention establishes a method for calculating the heat loss term of the SNCR denitrification reaction by introducing two parameters: the ammonia-nitrogen molar ratio and the denitrification efficiency.

[0029] This invention addresses the heat loss rate q due to incomplete combustion of gas. 3,SNCR The calculation of flue gas volume also includes the dry flue gas generated by the SNCR reaction per unit mass of fuel. The dry flue gas generated by the SNCR reaction corresponding to the unit mass of fuel The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get:

[0030] In calculating the heat loss rate of incomplete combustion of gas, this invention also fully considers the impact of the SNCR system on the volume of dry flue gas.

[0031] In this invention, the percentage q of external heat to lower heating value of fuel w1,SNCRThe external heat also includes the sensible physical heat Q brought in by the urea solution. f,SNCR .

[0032] This invention relates to the physical sensible heat Q introduced by urea solution. f,SNCR Calculated using the following formula:

[0033]

[0034]

[0035]

[0036] In the formula, The sensible heats of urea and water are respectively, in kJ / kg;

[0037] , respectively, are the specific heat capacities of urea and water, in kJ / (kg·K); Temperatures of urea and water entering the system boundary, in °C; mass fraction of urea solution injected into the furnace by the c-SNCR system, in %.

[0038] In calculating the percentage of external heat to lower heating value of fuel, this invention also fully considers the impact of the SNCR system.

[0039] The above corresponds to the mass of urea solution injected into the furnace by the SNCR system per unit mass of fuel. Calculated using the following method:

[0040]

[0041] In the formula, The difference in moisture content between the dry flue gas outlet of the air preheater after the SNCR system is put into operation and before operation, expressed in kg / m³. 3 V gy，no-SNCR The volume of dry flue gas at the outlet of the air preheater before the SNCR system is put into operation, in m³. 3 / kg; mass fraction of urea solution injected into the furnace by the c-SNCR system, %.

[0042] The present invention has the following advantages over the prior art:

[0043] 1. For the first time, a method was proposed to accurately and evenly distribute the urea solution injected into the furnace onto a unit mass of fuel by calculating the difference in moisture content of the flue gas at the outlet of the air preheater of the SNCR boiler during commissioning and shutdown. This method effectively solves the problem of difficulty in accurately measuring the quality of the fuel entering the furnace and the urea solution entering the furnace.

[0044] 2. A new heat loss term for boilers—SNCR denitrification reaction heat loss—was introduced. Based on the denitrification elementary reaction, a method for calculating SNCR denitrification reaction heat loss using a turnkey reaction was proposed. By introducing two parameters, the ammonia-nitrogen molar ratio and denitrification efficiency, a calculation method for the SNCR denitrification reaction heat loss term was established, making the calculation of boiler thermal efficiency under SNCR commissioning conditions more accurate.

[0045] 3. A process for calculating the fuel efficiency of coal-fired power plant boilers after adopting SNCR denitrification technology was established, providing theoretical and technical support for the impact of SNCR operation on boiler fuel efficiency. Attached Figure Description

[0046] Figure 1 This invention provides a process for testing and calculating the fuel efficiency of coal-fired power plant boilers using SNCR denitrification technology. Detailed Implementation

[0047] The present invention will now be described in detail with reference to specific embodiments.

[0048] I. Establishing a Mathematical Model

[0049] 1. General expression for boiler fuel efficiency

[0050]

[0051] In the formula: η SNCR —Boiler efficiency after SNCR commissioning, %;

[0052] Q 2,SNCR —Heat loss per unit mass of fuel combustion caused by flue gas after SNCR is put into operation, kJ / kg;

[0053] Q 3,SNCR —After the SNCR is put into operation, the heat loss caused by the incomplete combustion of gas produced per unit mass of fuel is quantified as kJ / kg.

[0054] Q 4,SNCR —Heat loss per unit mass of fuel due to incomplete combustion of solids after SNCR is put into operation, kJ / kg;

[0055] Q 5,SNCR —Boiler heat loss per unit mass of fuel after SNCR is put into operation, kJ / kg;

[0056] Q 6,SNCR —The physical sensible heat loss per unit mass of fuel in ash after SNCR is put into operation, kJ / kg;

[0057] Q 7,SNCR —Relative to the heat loss caused by SNCR reaction per unit mass of fuel, kJ / kg;

[0058] Q qt,SNCR —After SNCR is put into operation, the unit mass of fuel is reduced by Q 2,SNCR ~Q 7,SNCR Other heat losses in the boiler besides the above, kJ / kg;

[0059] Q net,ar —Lower heating value of fuel (as received), kJ / kg;

[0060] Q wl,SNCR —All input heat other than the calorific value of the fuel entering the furnace, kJ / kg.

[0061] After conversion, equation (1) can be expressed as:

[0062] η SNCR =100-q 2,SNCR -q 3,SNCR -q 4,SNCR -q 5,SNCR -q 6,SNCR -q 7,SNCR -q qt,SNCR +q wl,SNCR (2)

[0063] In the formula: η SNCR —Boiler efficiency after SNCR commissioning, %;

[0064] q 2,SNCR —Heat loss from flue gas after SNCR commissioning, %;

[0065] q 3,SNCR —Heat loss due to incomplete combustion of gas after SNCR operation, %;

[0066] q 4,SNCR —Heat loss due to incomplete combustion of solids after SNCR commissioning, %;

[0067] q 5,SNCR —Boiler heat loss after SNCR commissioning, %;

[0068] q 6,SNCR —Physical sensible heat loss of ash and slag after SNCR commissioning, %;

[0069] q 7,SNCR —SNCR reaction heat loss after commissioning, %;

[0070] q qt,SNCR —After SNCR is put into operation, except for q 2,SNCR ~q 7,SNCR Other heat losses in the boiler besides those mentioned above, %;

[0071] q wl,SNCR —Percentage of external heat input to lower heating value of fuel, %.

[0072] 2. Heat loss Q caused by flue gas generated from the combustion of fuel per unit mass after SNCR is put into operation. 2,SNCR

[0073] The heat loss per unit mass of fuel combustion caused by the flue gas after the SNCR is put into operation includes two parts: one is the heat loss caused by the dry flue gas produced by fuel combustion, and the other is the heat loss caused by water vapor in the flue gas carrying away heat from the system. It can be expressed as:

[0074] Q 2,SNCR =Q 2,gy +Q 2,H2O (3)

[0075] In the formula: Q 2,gy —Heat carried away from the system by the dry flue gas, kJ / kg;

[0076] —The heat carried away by the water vapor contained in the flue gas, kJ / kg.

[0077] 2.1 Heat Q carried away by dry flue gas from the system 2,gy

[0078] The heat carried away from the system by the dry flue gas in equation (3) can be calculated using the following formula:

[0079] Q 2,gy =V gy,SNCR C p,gy,SNCR (t gy,ky,o,SNCR -t jz (4)

[0080] In the formula: V gy,SNCR —Volume of dry flue gas at the air preheater outlet per unit mass of fuel combustion and corresponding SNCR reaction, in m³ 3 / kg;

[0081] C p,gy,SNCR —After the SNCR is put into operation, the flue gas outlet of the air preheater will be from t jz To t gy,ky,o,SNCR Specific heat capacity at constant pressure, kJ / (m 3 .K).

[0082] t gy,ky,o,SNCR —Air preheater outlet flue gas temperature after SNCR is put into operation, °C.

[0083] t jz —Test reference temperature, °C.

[0084] In equation (4) above, C p,gy,SNCR It is calculated based on the flue gas composition table. The specific algorithm is calculated according to formula (73) on page 45 of GB / T10184-2015.gy,ky,o,SNCR and t jz It was measured during the experiment.

[0085] In equation (4) above, V gy,SNCR It was calculated using the following method:

[0086]

[0087] In the formula: —The theoretical flue gas volume produced per unit mass of fuel combustion, in m³ 3 / kg;

[0088] —The theoretical air volume required for combustion of a unit mass of fuel, in m 3 / kg;

[0089] —Volume of dry flue gas generated per unit mass of fuel in SNCR reaction, m 3 / kg.

[0090] α—Excess air coefficient at the outlet of the air preheater after SNCR is put into operation.

[0091] In the above formula (5) Calculate according to the following formula (6):

[0092]

[0093] In the formula: C ar —Based carbon content of the fuel, %;

[0094] S ar —Base sulfur content of the fuel, %;

[0095] N ar —Based nitrogen content of fuel, %.

[0096] In equations (5) and (6) above Calculate according to the following formula (7):

[0097]

[0098] In the formula: O ar —Oxygen content of the fuel received, %;

[0099] H ar —Based hydrogen content of the fuel, %.

[0100] The content of carbon, hydrogen, oxygen, nitrogen and sulfur in the fuel in formulas (6) and (7) can be obtained from the coal quality analysis during the test.

[0101] In the above formula (5), α is calculated according to the following formula (8):

[0102]

[0103] In the formula: —Oxygen volume fraction at the dry flue gas outlet of the SNCR after commissioning;

[0104] In the above formula (5) This refers to the volume of dry flue gas generated during the SNCR reaction. After entering the boiler, urea reacts with nitrogen oxides (mainly NO) in the furnace, with the final products being N2, H2O, and CO2. Therefore, the overall reaction equation for the reaction between urea and NO is:

[0105]

[0106] Where: a—molar ratio of ammonia nitrogen in injected urea to NO in flue gas;

[0107] Denitrification efficiency of the b-SNCR reaction system, %.

[0108] From reaction equation (9), it can be seen that injecting 1 mol of urea into the furnace will consume (b / a) mol of NO and (3a-b / 2a) mol of oxygen in the dry flue gas, while releasing (2a+b) / 2a mol of N2 and 1 mol of CO2 into the dry flue gas. Subtracting the amount of dry flue gas consumed from the amount of dry flue gas generated, it can be seen that injecting 1 mol of urea into the furnace will result in a reduction of 0.5 mol of flue gas. Therefore, the effect of injecting urea on the flue gas volume can be expressed as:

[0109]

[0110] In the formula: —The mass of urea solution injected into the furnace per unit mass of SNCR fuel, in kg / kg.

[0111] The amount of urea per unit mass of fuel in the above formula (10) corresponds to the amount of SNCR system. Calculated through the following process:

[0112] a. Measure the moisture content d of the flue gas at the air preheater outlet after the SNCR denitrification system is put into operation. SNCR ;

[0113] b. Calculate the moisture content d in the flue gas at the air preheater outlet when SNCR is not in operation, based on the test results of the coal samples taken during the test. no-SNCR The calculation method is as follows:

[0114]

[0115]

[0116] In the formula: —H2O content in the flue gas at the outlet of an unoperated SNCR space preheater, kg / kg;

[0117] d no-SNCR —Moisture content per unit volume of dry flue gas at the outlet of an unoperational SNCR space preheater, kg / m³ 3 ;

[0118] d SNCR —Moisture content per unit volume of dry flue gas at the outlet of the SNCR space preheater during commissioning, kg / m³ 3 ;

[0119] V gy,no-SNCR —Dry flue gas volume at the air preheater outlet when SNCR is not in operation, m³ 3 / kg.

[0120] In formula (12) and Calculate according to equations (6) and (7).

[0121] In equation (11), the mass of water vapor in the flue gas at the outlet of the air preheater when the SNCR is not in operation It mainly includes the following parts:

[0122] (1) Water vapor produced by the combustion of hydrogen in fuel;

[0123] (2) Water vapor from the evaporation of fuel moisture;

[0124] (3) Water in the air.

[0125]

[0126] Where: M ar —Moisture content of the fuel as received, %;

[0127] h kq,ab —Absolute moisture content of air, kg / kg;

[0128] c. Calculate the increase in moisture content per unit volume of dry flue gas after the SNCR denitrification system is put into operation:

[0129]

[0130] In the formula: —The difference in moisture content of the dry flue gas at the outlet of the air preheater of the SNCR denitrification system between those in operation and those in shutdown, in kg / m³ 3 ;

[0131] d. Convert the urea solution injected into the furnace by the SNCR denitrification system into the unit mass of fuel.

[0132] Given: The concentration of the urea solution injected into the furnace by the SNCR denitrification system is c. The increase in the moisture content of the dry flue gas calculated by formula (14) mainly includes two parts: (1) the moisture carried by the urea solution injected into the furnace; (2) the moisture generated by the SNCR reaction.

[0133] From equation (9), it can be seen that 1 mol of urea entering the furnace can generate 2 mol of water vapor through reaction. Therefore, the following relationship exists:

[0134]

[0135] In the formula: —The mass of urea solution injected into the furnace per unit mass of SNCR fuel, kg / kg;

[0136] c—Urea mass fraction (concentration) in urea solution, %;

[0137] From equation (15), the mass of fuel injected into a urea solution with a concentration of c% per unit mass can be calculated as follows:

[0138]

[0139] 2.2 Heat carried away by water vapor in flue gas after the SNCR denitrification system is put into operation

[0140]

[0141] In the formula: —Volume of water vapor generated per unit mass of fuel combustion at the air preheater outlet after SNCR is put into operation, m 3 / kg;

[0142] —Water vapor from t jz To t gy,ky,o,SNCR Specific heat capacity at constant pressure, kJ / (m 3 .K).

[0143] In equation (17) The calculation process is as follows:

[0144] After the SNCR denitrification system is put into operation, the water vapor in the flue gas at the air preheater outlet mainly comes from the following sources:

[0145] (1) Water vapor produced by the combustion of hydrogen in fuel;

[0146] (2) Water vapor from the evaporation of fuel moisture;

[0147] (3) Moisture in the air;

[0148] (4) Water carried in by the urea solution after the SNCR denitrification system is put into operation;

[0149] (5) Water generated by the SNCR reaction.

[0150]

[0151] The isobaric specific heat capacity of water vapor in equation (17) It can be found in Appendix E of GB10184-2015.

[0152] In equation (17), t gy,ky,o,SNCR and t jz It was measured during the experiment.

[0153] In equation (18) h kq,ab It is the absolute humidity content of the air, which can be obtained through measurement.

[0154] 3. After the SNCR is put into operation, the incomplete combustion of gases produced per unit mass of fuel causes a heat loss Q. 3，SNCR

[0155] After the SNCR is put into operation, the heat loss due to incomplete combustion of gases per unit mass of fuel is mainly caused by unburned CO, H2, CH4, and CxHy contained in the flue gas, which can be calculated according to the following formula:

[0156]

[0157] In the formula: and —CO, H2, CH4, C in the dry flue gas at the air preheater outlet x H y Volume fraction, %.

[0158] In equation (19) V gy,SNCR Calculated according to formula (5), and It was measured through experiments.

[0159] 4. Heat loss Q caused by incomplete combustion of solids per unit mass of fuel after SNCR is put into operation. 4，SNCR

[0160] After the SNCR is put into operation, the heat loss due to incomplete combustion of solids per unit mass of fuel mainly consists of the heat contained in the combustibles in the ash and slag produced by fuel combustion, which can be calculated according to the following formula:

[0161]

[0162] In the formula: A ar —Ash content of fuel received, %;

[0163] —Average mass fraction of combustibles in fly ash and slag, %

[0164] In equation (20), A ar This was obtained through industrial analysis of the experimental coal. The results were obtained through experimental sampling of fly ash and slag for combustible analysis.

[0165] 5. The boiler heat loss Q per unit mass of fuel after SNCR is put into operation. 5，SNCR

[0166] Boiler heat loss refers to the heat lost from the boiler system's walls, auxiliary equipment, and high-pressure, high-temperature pipelines within the boiler boundary to the surrounding environment. The magnitude of boiler heat loss is related to the boiler unit's heat load, external surface temperature, and ambient wind speed. Therefore, the boiler heat loss per unit mass of fuel after SNCR is put into operation will not change significantly compared to when SNCR is not in operation. Boiler heat loss can be found in Appendix I of GB / T10184-2015, or measured actual according to GB / T8174 and GB / T17357.

[0167] 6. The sensible heat loss per unit mass of fuel in ash residue after SNCR is put into operation, Q 6，SNCR

[0168] The ash and slag from coal-fired power plant boilers mainly come from three sources: slag, settling ash from the bottom of the economizer, and fly ash from the dust collector. After the SNCR (Single-Stage Reactor) system is put into operation, the sensible heat loss per unit mass of fuel due to the ash and slag consists of the sensible heat from these three sources, which can be calculated using the following formula:

[0169]

[0170] In the formula: ω lz ω cjh ω fh —The mass fraction of slag, settling ash, and fly ash in fuel ash, %;

[0171] C lz C cjh C fh —Specific heat of slag, settling ash and fly ash, kJ / (kg·K);

[0172] t lz t cjh t fh —Temperature of slag, settling ash and fly ash, °C;

[0173] —Mass fraction of solid combustibles in slag, settling ash and fly ash, %.

[0174] During the experiment, slag, settled ash, and fly ash samples were obtained by isokinetic sampling at the boiler ash inlet, the lower settling chamber of the economizer, and the flue gas duct before the dust collector. The specific heat of the slag, settled ash, and fly ash can be found in Appendix of GB / T10184-201 or estimated in Appendix F. The temperature t of the slag, settled ash, and fly ash was also determined. lz t cjh t fh It can be calculated based on the flue gas temperature at the sampling location. This can be obtained through analysis of the solid combustibles in three ash samples. The mass fraction ω of slag, settled ash, and fly ash in the fuel ash content can be determined. lz ω cjh ω fh It is generally determined according to the design value.

[0175] 7. The heat loss Q caused by the SNCR reaction per unit mass of fuel 7，SNCR

[0176] Compared to a non-operational SNCR denitrification system, the operation of the SNCR system adds urea pyrolysis and redox reactions between ammonia and NO / O to the furnace. The urea ((NH2)2CO) solution injected into the furnace is first evaporated, heated to a molten state, and undergoes a phase change. Then, it undergoes pyrolysis to decompose into NH3 and CO2. Most of the pyrolysis produces NH3 and CO2, which can reduce NOx; this pyrolysis reaction is not endothermic. Some of the NH3 produced by urea pyrolysis reacts with NO in the flue gas to produce N2 and H2O, while simultaneously consuming some oxygen in the flue gas. The reduction of NO by NH3 is an exothermic reaction. Additionally, some NH3 also reacts with oxygen to produce NO or N2. The reaction process of urea injected into the furnace can be described as follows:

[0177] CO(NH2)2(s)→CO(NH2)2(l) (22)

[0178] H2O(l)→H2O(g) (23)

[0179] CO(NH2)2 + H2O = CO2 + 2NH3 (24)

[0180] 4NH3 + 4NO + O2 = 4N2 + 6H2O (25)

[0181] 4NH3 + 5O2 = 4NO + 6H2O (26)

[0182] Therefore, the heat loss caused by the SNCR reaction of the urea solution injected into the furnace mainly consists of three parts: first, the urea absorbs heat during the melting phase change; second, the liquid water in the urea solution absorbs heat during heating and vaporization; and third, the urea releases heat through a chemical reaction. This can be represented as:

[0183]

[0184] In the formula: —The heat absorbed by the melting phase change of fuel urea per unit mass, kJ / kg;

[0185] —The heat absorbed by the water in the urea solution injected into the furnace per unit mass of fuel during heating and gasification, in kJ / kgQ 7,fy,SNCR —Total heat released by pyrolysis, oxidation and reduction reactions of unit mass of fuel urea, kJ / kg.

[0186] Urea melts at 140°C and decomposes at 180°C; therefore, the melting phase transition of urea absorbs heat. for:

[0187]

[0188] The latent heat absorbed by water vaporization in a unit mass of fuel urea solution is:

[0189]

[0190] From reaction equations (23) to (25), it can be seen that whether the ammonia gas generated by urea pyrolysis reacts with nitrogen oxides (mainly NO) in the furnace or with O2, the final products are N2, H2O and CO2. Therefore, the overall reaction equation for the reaction between urea and NO can be expressed as:

[0191]

[0192] Where: a—molar ratio of ammonia nitrogen in injected urea to NO in flue gas;

[0193] Denitrification efficiency of the b-SNCR reaction system, %.

[0194] Q represents the heat of reaction in the denitration reaction, calculated as Q = 544 + 89.86b / a, kJ / mol.

[0195] Since the SNCR system cannot be shut down during the test after the boiler achieves ultra-low emissions, the initial NOx concentration can be referenced from historical data under the same operating conditions or DCS parameters. If the accuracy requirement is not high, α can also be taken as the design value.

[0196]

[0197] 8. After the SNCR is put into operation, the amount of fuel per unit mass is reduced by Q. 2,SNCR ~Q 7,SNCR Other heat losses in the boiler besides Q qt,SNCR

[0198] After the SNCR is put into operation, the unit mass of fuel is degraded by Q 2,SNCR~Q 7,SNCR Other than the heat loss from the boiler, there are no new additions besides the heat carried away by the coal and cooling water system. These two loss items can be calculated according to GB / T10184-2015 based on the operating boundary conditions.

[0199] 9. All input heat Q other than the calorific value of the fuel entering the furnace. wl,SNCR

[0200] After SNCR is put into operation, all other input heat except for the fuel fed into the furnace is basically the same as when SNCR is not in operation, but the physical sensible heat brought in by the urea solution is added. The physical sensible heat brought in by the cooling air and the air atomizing the urea solution is incorporated into the dry air because they participate in combustion. The specific expression is as follows:

[0201]

[0202] In the formula: Q rl —The physical sensible heat of the fuel, kJ / kg;

[0203] Q f,SNCR —The physical sensible heat introduced by the urea solution, kJ / kg.

[0204] Q gkq —The physical sensible heat introduced by dry air, kJ / kg;

[0205] —The physical sensible heat per unit mass of fuel, carried in by water vapor in the air, in kJ / kg;

[0206] Q aux —Heat brought in by auxiliary equipment within the system, kJ / kg.

[0207] The sensible physical heat introduced by the urea solution in equation (32) can be determined by the following method:

[0208]

[0209] In the formula: — is the sensible physical heat of urea and water, kJ / kg;

[0210]

[0211]

[0212] In the formula: — is the sensible physical heat of urea and water, kJ / kg;

[0213] , respectively, are the specific heat capacities of urea and water, kJ / (kg·K);

[0214] The temperature of urea and water entering the system boundary is ℃.

[0215] Other external heat sources can be determined by referring to the method in GB / T10184-2015.

[0216] II. Experiment and Calculation Procedure

[0217] This invention discloses a method for calculating the boiler fuel efficiency of coal-fired power generation units using SNCR denitrification technology. This method proposes to distribute the urea solution injected into the furnace into a unit mass of fuel by measuring and calculating the difference in moisture content of the flue gas after SNCR operation, thus solving the problem of difficult accurate measurement of fuel mass and urea solution entering the furnace. This method introduces a new heat loss term for the boiler—the SNCR denitrification reaction heat loss term, which includes the heat absorbed by the urea melting phase change, the heat absorbed by water gasification, and the heat released by the SNCR reaction. Based on the denitrification elementary reactions, it proposes to calculate the SNCR denitrification reaction heat loss using a comprehensive reaction calculation method. By introducing two parameters—the ammonia-nitrogen molar ratio and the denitrification efficiency—a calculation method for the SNCR denitrification reaction heat loss term is established, which can accurately obtain the boiler thermal efficiency under SNCR operation conditions, providing a theoretical and technical basis for evaluating the impact of SNCR operation on boiler fuel efficiency.

[0218] The steps of the method for calculating the fuel efficiency of a coal-fired power plant boiler using SNCR denitrification technology proposed in this invention are as follows:

[0219] 1. Under the requirement of stable unit load during the test, measure the moisture content, temperature, oxygen content, and concentrations of CO, CO2, H2, CH4, and CxHy in the flue gas at the air preheater outlet after the SNCR denitrification technology is put into operation; measure the oxygen content and temperature of the flue gas at the economizer outlet; take raw coal from the pulverizer inlet and perform industrial and elemental analysis; take slag and fly ash from a designated location in the boiler and perform carbon content analysis; measure the temperature and moisture content of the air near the blower inlet; measure the flue gas temperature at the slag discharge port or the slag temperature at the dry slag machine.

[0220] 2. Based on the results of industrial and elemental analysis of the test coal, the moisture content of the flue gas at the outlet of the air preheater was calculated when the SNCR denitrification technology was not in operation, combined with the moisture content of the air and the oxygen content of the flue gas at the outlet of the air preheater. The results were obtained by applying equations (6) to (8) and (11) to (13).

[0221] 3. Calculate the moisture content difference in the flue gas at the outlet of the SNCR denitrification air preheater obtained from the measurement and calculation in steps (1) and (2), and calculate the mass of urea solution injected into the furnace for the corresponding unit mass of fuel based on the concentration (mass fraction of urea) of the urea solution injected into the furnace for the SNCR denitrification technology. Apply formulas (14) to (16) to calculate the result.

[0222] 4. Based on the industrial analysis and elemental analysis of raw coal, the temperature and oxygen content of the flue gas at the air preheater outlet, the moisture content of the air, and the mass of urea solution injected into the furnace per unit mass of fuel obtained in step (1), calculate the heat loss Q caused by the flue gas generated by the combustion of fuel per unit mass after the SNCR is put into operation. 2,SNCR The results are obtained by applying equations (3) to (5) and (17) to (18).

[0223] 5. Based on the raw coal industrial analysis and elemental analysis, the concentrations of CO, H2, CH4, and CxHy in the flue gas at the air preheater outlet, and the mass of urea solution injected into the furnace per unit mass of fuel, calculate the heat loss Q caused by incomplete combustion of gases produced per unit mass of fuel after the SNCR is put into operation. 3，SNCR The result is obtained by applying formula (19).

[0224] 6. Based on the combustible content of fly ash and slag measured in step (1), and the industrial and elemental analysis of raw coal, calculate the heat loss Q caused by incomplete combustion of solids per unit mass of fuel after the SNCR is put into operation. 4，SNCR The result is obtained by applying formula (20).

[0225] 7. Refer to Appendix I of GB / T10184-2015, or measure the boiler heat loss Q per unit mass of fuel after SNCR is put into operation according to GB / T8174 and GB / T17357. 5，SNCR ;

[0226] 8. Based on the slag temperature, economizer outlet flue gas temperature, and air preheater outlet flue gas temperature measured in step (1), calculate the physical sensible heat loss Q of ash and slag per unit mass of fuel after the SNCR is put into operation. 6，SNCR The result is obtained by applying formula (21).

[0227] 9. Based on the mass of urea solution injected into the furnace per unit mass of fuel and the mass concentration of urea, calculate the heat loss Q caused by the SNCR reaction per unit mass of fuel. 7，SNCR The results are obtained by applying formulas (27) to (31).

[0228] 10. Calculate the fuel per unit mass after commissioning of the SNCR based on the operating boundary conditions according to GB / T10184-2015. 2,SNCR ~Q 7,SNCR Other heat losses in the boiler besides Q qt,SNCR ;

[0229] 11. Based on the temperature of the urea solution, the ambient air temperature and humidity, and the temperature of the raw coal, calculate Q for all input heats other than the calorific value of the fuel entering the furnace. wl,SNCR The results are obtained by applying formulas (32) to (35).

[0230] 12. Based on the heat loss calculated in the above steps, use formulas (1) to (2) to calculate the fuel thermal efficiency of the boiler.

[0231] The above parameters are obtained and calculated as follows: Figure 1 As shown.

[0232] III. Calculation Examples

[0233] This embodiment describes a 660MW supercritical unit boiler, model DG-2141 / 25.4-II12. The boiler is a supercritical parameter, W-type flame combustion, vertical coil water-cooled wall variable pressure operation once-through boiler, with single-pass reheat, damper-regulated reheat steam temperature, balanced ventilation, open-air layout, solid ash discharge, all-steel frame, and fully suspended Π-type boiler.

[0234] The test condition was a 660MW load condition. The coal quality data and test measurement data for the test condition are shown in the table below:

[0235]

[0236]

[0237] The boiler efficiency calculation after the SNCR system is put into operation is shown in the table below.

[0238]

[0239] The calculation results in the table show that the boiler efficiency calculated by the method of this patent, considering the impact of SNCR on the boiler efficiency heat loss term, is 92.8%, while GB10184 / T-2015, which does not consider the impact of SNCR on the boiler heat loss term, calculates a boiler efficiency of 93.36%. The difference between the two methods is 0.38%, equivalent to a coal consumption deviation of 1 g / kWh. The calculation method of this invention is more accurate.

Claims

1. A method for calculating boiler fuel efficiency using SNCR denitrification technology, characterized in that, The boiler fuel efficiency η SNCR The flue gas heat loss rate q after the SNCR was put into operation was calculated separately. 2,SNCR Heat loss rate q due to incomplete combustion of gas 3,SNCR Heat loss rate q of incomplete combustion of solids 4,SNCR Boiler heat loss rate q 5,SNCR , Physical sensible heat loss rate of ash and slag q 6,SNCR SNCR reaction heat loss rate q 7,SNCR Other heat loss rates of the boiler, q qt,SNCR The percentage of external heat to the lower heating value of fuel (q) w1,SNCR The heat loss rate q of the SNCR reaction is obtained. 7,SNCR This includes the heat loss rate caused by the heat absorbed during the melting phase change of urea, the heat absorbed by the vaporization of liquid water in the urea solution, and the heat released during the chemical reaction of urea. The flue gas heat loss rate q 2,SNCR This includes the heat loss rate caused by the heat carried out of the system by the dry flue gas generated from fuel combustion, and the heat loss rate caused by the heat carried out of the system by the water vapor in the flue gas; the dry flue gas generated from fuel combustion also includes the dry flue gas generated by the SNCR reaction per unit mass of fuel; the water vapor in the flue gas also includes the moisture introduced by the urea solution and the moisture generated by the SNCR reaction; The SNCR reaction heat loss rate q 7,SNCR The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get: ； In the formula, a—molar ratio of injected urea to NO in flue gas; b—densification efficiency of the SNCR reaction system, %; c—mass fraction of urea solution injected into the furnace by the SNCR system, % The incomplete combustion heat loss rate q of the gas 3,SNCR The calculation of flue gas volume also includes the dry flue gas generated by the SNCR reaction per unit mass of fuel. The dry flue gas generated by the SNCR reaction corresponding to the unit mass of fuel The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get: .

2. The boiler fuel efficiency calculation method according to claim 1, characterized in that, The flue gas heat loss rate q 2,SNCR , %=Q 2,SNCR / Q net,SNCR ×100; the Q 2,SNCR Q represents the heat loss caused by the combustion of a unit mass of fuel in the flue gas after the SNCR is put into operation. net,SNCR The lower heating value of the fuel fed into the furnace; the volume of dry flue gas generated by the SNCR reaction per unit mass of fuel. The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system was calculated. get: .

3. The boiler fuel efficiency calculation method according to claim 2, characterized in that, The heat loss Q caused by the flue gas generated by the combustion of fuel per unit mass after the SNCR is put into operation 2,SNCR Including the heat Q carried away by the dry flue gas from the system 2,gy The heat carried away by the water vapor contained in the flue gas : ； ； In the formula, The volume of air theoretically required for combustion of a unit mass of fuel, m 3 / kg; m is the volume of dry flue gas produced by the SNCR reaction per unit mass of fuel. 3 / kg; This refers to the excess air coefficient at the outlet of the air preheater after the SNCR is put into operation.

4. The boiler fuel efficiency calculation method according to claim 3, characterized in that, The heat carried away by the water vapor in the flue gas after the SNCR system is put into operation Calculated using the following formula: ； In the formula, The volume of water vapor in the flue gas at the air preheater outlet generated per unit mass of fuel combustion after the SNCR system is put into operation, in m³. 3 / kg; The reference temperature for the test is ℃; The outlet flue gas temperature of the air preheater after the SNCR system is put into operation, in °C; For water vapor from to Specific heat capacity at constant pressure, kJ / (m 3. K); After the SNCR system is put into operation, the volume of water vapor in the flue gas at the outlet of the air preheater generated per unit mass of fuel combustion is [missing information]. This also includes the water introduced into the urea solution after the SNCR system is put into operation and the water generated by the SNCR reaction.

5. The boiler fuel efficiency calculation method according to claim 4, characterized in that, After the SNCR system is put into operation, the volume of water vapor in the flue gas at the outlet of the air preheater generated per unit mass of fuel combustion is [missing information]. Calculated using the following formula: ； In the formula, The received hydrogen content of the fuel, % . The moisture content of the fuel as received, % . The volume of air theoretically required for combustion of a unit mass of fuel, m 3 / kg; It is the absolute moisture content of the air, kg / kg; the mass fraction of urea solution injected into the furnace by the c-SNCR system, %.

6. The boiler fuel efficiency calculation method according to claim 1, characterized in that, The percentage of external heat to the lower heating value of fuel, q w1,SNCR The external heat also includes the sensible physical heat Q brought in by the urea solution. f,SNCR .

7. The boiler fuel efficiency calculation method according to claim 6, characterized in that, The physical sensible heat Q introduced by the urea solution f,SNCR Calculated using the following formula: ； ； In the formula, , The sensible heats of urea and water are respectively, in kJ / kg; , , respectively, are the specific heat capacities of urea and water, kJ / (kg•K); , The temperatures of urea and water entering the system boundary are, respectively, in °C; the mass fraction of urea solution injected into the furnace by the c-SNCR system is, in %.

8. The boiler fuel efficiency calculation method according to claim 6 or 7, characterized in that, The mass of urea solution injected into the furnace by the corresponding unit mass fuel SNCR system Calculated using the following method: ； In the formula, The difference in moisture content between the dry flue gas outlet of the air preheater after the SNCR system is put into operation and before operation, expressed in kg / m³. 3 ; The volume of dry flue gas at the outlet of the air preheater before the SNCR system is put into operation, in m³. 3 / kg; mass fraction of urea solution injected into the furnace by the c-SNCR system, %.

Images