CN111666654A - Method for evaluating influence of two-section combined type economizer with parallel air preheater on boiler - Google Patents

Method for evaluating influence of two-section combined type economizer with parallel air preheater on boiler Download PDF

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CN111666654A
CN111666654A CN202010377859.XA CN202010377859A CN111666654A CN 111666654 A CN111666654 A CN 111666654A CN 202010377859 A CN202010377859 A CN 202010377859A CN 111666654 A CN111666654 A CN 111666654A
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economizer
boiler
air preheater
flue gas
coal
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CN111666654B (en
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苏攀
于鹏峰
刘林波
张才稳
肖申
靖浩然
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Huadian Electric Power Research Institute Co Ltd
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Abstract

The invention discloses an evaluation method of influence of two sections of combined economizers connected in parallel on a boiler of an air preheater, which comprises an evaluation method of influence of switching on and off of the two sections of combined economizers on heat loss of the boiler, a test method of heat exchange efficiency of a body of the two sections of combined economizers, an evaluation method of change of air leakage rate of the two sections of combined economizers on the air preheater and an evaluation method of heat loss of boiler exhaust smoke caused by change of smoke temperature at an inlet of a dust removal system under the operation state of the two sections of economizers; the invention simultaneously selects a proper boiler system heat balance boundary and establishes a mathematical algorithm based on parameters of boiler fuel, an air-smoke system and the like, theoretically calculates the heat loss of the boiler and the air leakage rate change of an air preheater, evaluates the influence of the switching-on and switching-off of the two-section combined economizer on the performance of the boiler, simultaneously provides the performance of the two-section combined economizer body and a calculation method of the influence of the smoke temperature change of the inlet of a dust removal system on the heat loss of the boiler in the operating state of the economizer, and is beneficial to the operation optimization control of the boiler of the coal-fired unit of the modified type.

Description

Method for evaluating influence of two-section combined type economizer with parallel air preheater on boiler
Technical Field
The invention relates to an evaluation method for influence of two sections of combined economizers with air preheaters connected in parallel on performance of a boiler system.
Background
The exhaust gas temperature is one of important technical and economic small indexes which are focused in the operation of a power station boiler, the change of the exhaust gas temperature can greatly influence the operation economy of the boiler, and the exhaust gas temperature is increased, so that the heat loss of the exhaust gas is increased and the thermal efficiency of the boiler is reduced. In the daily operation of the boiler, the types of reasons for increasing the exhaust gas temperature are more, and one type of reasons for increasing the exhaust gas temperature due to measurement deviation generally comprise ash accumulation and fault of an exhaust gas temperature measurement element and poor representativeness of a measurement point position; in addition, the main reasons of boiler operation and equipment are the actual rising of the exhaust gas temperature, such as upward movement of the flame center of the hearth, poor heat exchange effect of the air preheater, design defects of the boiler and the like.
The problems that the combustion condition of the boiler is limited and the temperature of the exhaust gas is high due to equipment reasons are solved, the boiler combustion adjustment and other measures cannot solve the problems, and the boiler equipment needs to be modified for recovering the heat loss of the exhaust gas of the available boiler. At present, a certain coal-fired power plant implements the improvement of an air preheater parallel connection two-section combined economizer, the main scheme is that a path of air preheater flue gas bypass flue is connected between an inlet and an outlet of an air preheater, a certain amount of inlet flue gas is separated into the bypass flue, two stages of heat exchange devices are additionally arranged in the bypass flue and are respectively communicated with a high-pressure water supply system and a condensed water system of the system, the flue gas in the bypass flue sequentially heats the water supply and the condensed water which are pumped out from the water system, the cooled flue gas is returned to the original flue again to be collected, and enters the inlet collecting flue of an electric dust collector, so that the purpose of recycling the waste heat of a boiler is achieved, and the.
Aiming at the modified coal-fired unit, no evaluation method for evaluating the influence of the operation and the retreat of the two-section combined economizer on the heat loss of the boiler and the operation of an air preheater is available at present, scientific calculation basis is lacked, and the evaluation of the performance of the economizer body and the influence of the change of the smoke temperature at the inlet of a dust removal system on the heat loss of the boiler in the operation state of the economizer are not facilitated.
Disclosure of Invention
The invention aims at the problem that a boiler system of an air preheater parallel two-section combined economizer lacks a proper performance evaluation method, simultaneously selects a proper boiler system heat balance boundary and establishes a mathematical algorithm based on parameters such as boiler fuel and an air-smoke system, theoretically calculates the heat loss of the boiler and the air leakage rate change of the air preheater, evaluates the influence of the switching on and off of the two-section combined economizer on the performance of the boiler, and simultaneously provides a calculation method of the influence of the body performance of the two-section combined economizer and the smoke temperature change of an inlet of a dust removal system on the heat loss of the boiler in a running state of the economizer.
The technical scheme adopted by the invention for solving the problems is as follows: the method for evaluating the influence of the parallel two-section combined type economizer of the air preheater on the boiler is characterized by comprising a method for evaluating the influence of the switching on and off of the two-section combined type economizer on the heat loss of the boiler, a method for testing the heat exchange efficiency of a body of the two-section combined type economizer, a method for evaluating the change of the switching on and off of the two-section combined type economizer on the air leakage rate of the air preheater and a method for evaluating the heat loss of the boiler exhaust smoke caused by the change of the smoke temperature at the inlet of a dust removal system in the operating state of the two-;
the method for evaluating the influence of the operation and the retreat of the two-section combined economizer on the heat loss of the boiler comprises an evaluation method 1 and an evaluation method 2;
in the evaluation method 1, the economizer is taken as the heating surface of the boiler system and is included in the boundary of the boiler heat balance system, the influence on the boiler heat loss comprises the heat loss of exhaust smoke and the heat loss change of external heat, and the calculation formula is as follows:
Figure BDA0002480886600000021
Figure BDA0002480886600000022
wherein the evaluation method is based on1，Δq1,pThe heat loss change of boiler exhaust smoke before and after the coal economizer is put into operation; Δ q of1,exThe heat loss of the external boiler heat is changed before and after the coal economizer is put into operation; vk,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the unit volume of dry flue gas of fuel is discharged; c. Ck,oThe constant-pressure specific heat capacity of the dry flue gas at the outlet is obtained after an air preheater and an economizer are connected in parallel before the economizer is put into operation; t is tk,oThe temperature of the flue gas at the outlet of the air preheater and the economizer which are connected in parallel before the economizer is put into operation; t is teIs a reference temperature; vh,k,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the volume of water vapor in unit fuel smoke is discharged; c. Ch,k,oThe constant-pressure specific heat capacity of the water vapor at the outlet of the economizer after the air preheater and the economizer are connected in parallel before the economizer is put into operation; qnet,arThe heating value of the boiler fuel before the coal economizer is put into operation; v' typek,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the unit volume of dry flue gas of fuel is output; c' liquidk,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the dry flue gas is output; t' typek,oThe temperature of the flue gas at the outlet of the air preheater and the economizer after the economizer is put into operation is connected in parallel; t' typeeIs a reference temperature; v' typeh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the volume of water vapor in unit fuel smoke is discharged; c' liquidh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the water vapor at the outlet is obtained; q. q.ss,1The flow of the working medium at the first section after the coal economizer is put into operation; c. Cs,1Is a section of working medium with constant pressure and specific heat capacity; Δ ts,1Raising the temperature of a section of working medium; q. q.ss,2The flow of the two-stage working medium after the coal economizer is put into operation; c. Cs,2The specific heat capacity of the two-section working medium of the economizer is constant pressure; Δ ts,2Raising the temperature of the two-stage working medium; q' typenet,arThe heating value of the boiler fuel after the coal economizer is put into operation; m is the total fuel quantity of the boiler after the coal economizer is put into operation;
in the evaluation method 2, the economizer is not taken as the heating surface of the boiler system and is not included in the boundary of the boiler heat balance system, the influence of the boiler heat loss is mainly the change of the heat loss of the exhaust smoke, and the calculation formula is as follows:
Figure BDA0002480886600000023
wherein, based on the evaluation method 2,. DELTA.q2,pThe heat loss of the boiler exhaust smoke before and after the coal economizer is put into operation is changed; q. q.ss,k,oThe method comprises the following steps of (1) connecting an air preheater and an economizer in parallel after the economizer is put into operation, and measuring the smoke flow at a front outlet; c. Cs,k,oThe air preheater is connected with the economizer in parallel after the economizer is put into operation, and the flue gas at the front outlet has a constant pressure and specific heat capacity; t is ts,k,oThe temperature of the flue gas at the front outlet of the air preheater and the economizer which are connected in parallel after the economizer is put into operation; q. q.ss,iThe flue gas flow at the inlet of the economizer is obtained after the economizer is put into operation; t is ts,iThe temperature of the inlet flue gas of the economizer after the economizer is put into operation; c. Cs,iThe specific heat capacity of inlet flue gas at constant pressure after the coal economizer is put into operation ts,oThe temperature of the flue gas at the outlet of the economizer after the economizer is put into operation;
according to the method for testing the heat exchange efficiency of the two-section combined type economizer body, the heat exchange efficiency calculation formula is as follows:
Figure BDA0002480886600000034
wherein, ηsThe heat exchange efficiency of the economizer body is improved;
the method for evaluating the change of the air leakage rate of the air preheater by the switching on and off of the two-section combined economizer has the following calculation formula:
Figure BDA0002480886600000031
wherein, Delta ηkThe air leakage rate of the air preheater is changed before and after the coal economizer is put into and taken out;
Figure BDA0002480886600000035
the volume fraction of oxygen in the flue gas at the outlet of the air preheater before the coal economizer is put into operation;
Figure BDA0002480886600000036
the volume fraction of oxygen in the inlet flue gas of the air preheater before the coal economizer is put into operation;
Figure BDA0002480886600000037
the volume fraction of oxygen in the flue gas at the outlet of the air preheater after the coal economizer is put into operation;
Figure BDA0002480886600000038
the volume fraction of oxygen in the inlet flue gas of the air preheater after the coal economizer is put into operation;
the method for evaluating the heat loss of boiler exhaust smoke caused by the change of the smoke temperature at the inlet of the dust removal system in the operating state of the two-stage economizer comprises an evaluation method A and an evaluation method B;
in the evaluation method A, the economizer is taken as the heating surface of the boiler system and is brought into the boundary of the boiler heat balance system, the influence on the boiler heat loss comprises the change of the exhaust gas heat loss, and the calculation formula is as follows:
Figure BDA0002480886600000032
wherein Δ q is based on the evaluation method AA,pThe loss of boiler exhaust heat caused by the change of the temperature of the smoke at the inlet of the dust removal system after the two-section coal economizer is put into operation is changed; delta t-k,oAfter the economizer is put into operation and the flue gas temperature at the inlet of the dust removal system changes, the air preheater is connected with the economizer in parallel, and then the flue gas temperature at the outlet changes;
in the evaluation method B, the economizer is not taken as the heating surface of the boiler system and is not included in the boundary of the boiler heat balance system, the influence of the boiler heat loss is mainly the change of the heat loss of the exhaust smoke, and the calculation formula is as follows:
Figure BDA0002480886600000033
wherein Δ q is based on the evaluation method BB,pThe loss of boiler exhaust heat caused by the change of the temperature of the smoke at the inlet of the dust removal system after the two-section coal economizer is put into operation is changed; t is ts,k,oThe temperature change value of the flue gas at the outlet of the air preheater and the economizer is obtained after the economizer is put into operation and the flue gas temperature at the inlet of the dust removal system is changed.
Compared with the prior art, the invention has the following advantages and effects: the invention selects a proper boiler system heat balance boundary and establishes a mathematical algorithm aiming at the coal-fired unit which implements the reconstruction of the air preheater two-section combined economizer connected in parallel, quantitatively calculates the heat loss of the boiler and the air leakage rate change of the air preheater, and can be used for accurately calculating the boiler heat efficiency of the coal-fired unit of the reconstruction type; meanwhile, the performance of the two-section combined type economizer body and a method for calculating the influence of the change of the smoke temperature of the inlet of the dust removal system on the heat loss of the boiler in the running state of the economizer are provided, and the operation optimization control of the improved coal-fired unit boiler is facilitated.
Drawings
FIG. 1 is a schematic diagram of a boiler system with an air preheater connected in parallel with a two-stage combined economizer in an embodiment of the present invention;
FIG. 2 is a diagram of the thermal equilibrium boundary of evaluation method 1 and evaluation method A according to an embodiment of the present invention;
FIG. 3 is a diagram of the thermal equilibrium boundary of evaluation method 2 and evaluation method B according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.
Examples are given.
A boiler of No. 1 unit of a certain company is a DG 1900/25.4-II 1 type supercritical parameter variable-pressure direct-current Bunsen boiler produced by Oriental boiler (group) Limited company of 600MW unit, and the boiler has a one-time reheating structure, a single-hearth structure and a tail double-flue structure, adopts a flue gas baffle plate to adjust the temperature of reheated steam, solid-state slag removal, an all-steel framework structure and an all-suspension structure, and has balanced ventilation, open-air arrangement and front-rear wall opposed firing. Each furnace is provided with 24 HT-NR3 type rotational flow pulverized coal burners produced by Hitachi-Babecker corporation (BHK), and matched with 6 BBD4060 double-inlet and double-outlet coal mills produced by Shanghai heavy machinery factories, Inc. The designed coal is a poor coal for Shanxi Lu' an mining group Co. The #1 unit is modified by an air preheater connected with two sections of combined economizers in parallel in 2016.
TABLE 1 two-stage combined economizer one-stage design parameters
Figure BDA0002480886600000041
Figure BDA0002480886600000051
TABLE 2 two-stage design parameters of two-stage combined economizer
Parameter(s) Unit of Numerical value
Amount of flue gas kg/s 153
Inlet temperature of flue gas ℃ 220
Inlet temperature of flue gas ℃ 100
Smoke side resistance (two-section body) Pa 200
Flue duct Pa 100
Inlet water temperature ℃ 78
Outlet water temperature ℃ 140
Water supply flow t/h 260
The method for evaluating the influence of the operation and the retreat of the two-section combined economizer on the heat loss of the boiler adopts an evaluation method 1; the economizer is used as a heating surface of a boiler system and is brought into the boundary of a boiler heat balance system, the influence on the heat loss of the boiler comprises the heat loss of exhaust smoke and the heat loss change of external heat, and the calculation formula is as follows:
Figure BDA0002480886600000052
Figure BDA0002480886600000053
wherein, based on the evaluation method 1,. DELTA.q1,pThe heat loss change of boiler exhaust smoke before and after the coal economizer is put into operation; Δ q of1,exThe heat loss of the external boiler heat is changed before and after the coal economizer is put into operation; vk,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the unit volume of dry flue gas of fuel is discharged; c. Ck,oThe constant-pressure specific heat capacity of the dry flue gas at the outlet is obtained after an air preheater and an economizer are connected in parallel before the economizer is put into operation; t is tk,oThe temperature of the flue gas at the outlet of the air preheater and the economizer which are connected in parallel before the economizer is put into operation; t is teIs a reference temperature; vh,k,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the volume of water vapor in unit fuel smoke is discharged; c. Ch,k,oFor saving coalBefore the device is put into operation, the air preheater and the economizer are connected in parallel, and the constant-pressure specific heat capacity of the water vapor at the outlet is obtained; qnet,arThe heating value of the boiler fuel before the coal economizer is put into operation; v' typek,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the unit volume of dry flue gas of fuel is output; c' liquidk,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the dry flue gas is output; t' typek,oThe temperature of the flue gas at the outlet of the air preheater and the economizer after the economizer is put into operation is connected in parallel; t' typeeIs a reference temperature; v' typeh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the volume of water vapor in unit fuel smoke is discharged; c' liquidh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the water vapor at the outlet is obtained; q. q.ss,1The flow of the working medium at the first section after the coal economizer is put into operation; c. Cs,1Is a section of working medium with constant pressure and specific heat capacity; Δ ts,1Raising the temperature of a section of working medium; q. q.ss,2The flow of the two-stage working medium after the coal economizer is put into operation; c. Cs,2The specific heat capacity of the two-section working medium of the economizer is constant pressure; Δ ts,2Raising the temperature of the two-stage working medium; q' typenet,arThe heating value of the boiler fuel after the coal economizer is put into operation; m is the total fuel quantity of the boiler after the coal economizer is put into operation;
the heat exchange efficiency test method of the two-section combined type economizer body comprises the following heat exchange efficiency calculation formula:
Figure BDA0002480886600000061
wherein, ηsThe heat exchange efficiency of the economizer body is improved;
the method for evaluating the change of the air leakage rate of the air preheater by the switching on and off of the two-section combined economizer has the following calculation formula:
Figure BDA0002480886600000062
wherein, Delta ηkThe air leakage rate of the air preheater is changed before and after the coal economizer is put into and taken out;
Figure BDA0002480886600000064
the volume fraction of oxygen in the flue gas at the outlet of the air preheater before the coal economizer is put into operation;
Figure BDA0002480886600000066
the volume fraction of oxygen in the inlet flue gas of the air preheater before the coal economizer is put into operation;
Figure BDA0002480886600000067
the volume fraction of oxygen in the flue gas at the outlet of the air preheater after the coal economizer is put into operation;
Figure BDA0002480886600000065
the volume fraction of oxygen in the inlet flue gas of the air preheater after the coal economizer is put into operation;
the method for evaluating the heat loss of the boiler exhaust smoke caused by the change of the smoke temperature at the inlet of the dust removal system in the operating state of the two-stage economizer adopts an evaluation method A; the economizer is taken as a heating surface of a boiler system and is brought into the boundary of a boiler heat balance system, the influence on the heat loss of the boiler comprises the change of the heat loss of exhaust smoke, and the calculation formula is as follows:
Figure BDA0002480886600000063
wherein Δ q is based on the evaluation method AA,pThe loss of boiler exhaust heat caused by the change of the temperature of the smoke at the inlet of the dust removal system after the two-section coal economizer is put into operation is changed; delta t-k,oAfter the economizer is put into operation and the flue gas temperature at the inlet of the dust removal system changes, the air preheater is connected with the economizer in parallel, and then the flue gas temperature at the outlet changes;
those not described in detail in this specification are well within the skill of the art.
Although the present invention has been described with reference to the above embodiments, it should be understood that the scope of the present invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (1)

1. The method for evaluating the influence of the parallel two-section combined type economizer of the air preheater on the boiler is characterized by comprising a method for evaluating the influence of the switching on and off of the two-section combined type economizer on the heat loss of the boiler, a method for testing the heat exchange efficiency of a body of the two-section combined type economizer, a method for evaluating the change of the switching on and off of the two-section combined type economizer on the air leakage rate of the air preheater and a method for evaluating the heat loss of the boiler exhaust smoke caused by the change of the smoke temperature at the inlet of a dust removal system in the operating state of the two-;
the method for evaluating the influence of the operation and the retreat of the two-section combined economizer on the heat loss of the boiler comprises an evaluation method 1 and an evaluation method 2;
in the evaluation method 1, the economizer is taken as the heating surface of the boiler system and is included in the boundary of the boiler heat balance system, the influence on the boiler heat loss comprises the heat loss of exhaust smoke and the heat loss change of external heat, and the calculation formula is as follows:
Figure FDA0002480886590000011
Figure FDA0002480886590000012
wherein, based on the evaluation method 1, △ q1,p△ q for boiler exhaust heat loss change before and after coal economizer operation1,exThe heat loss of the external boiler heat is changed before and after the coal economizer is put into operation; vk,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the unit volume of dry flue gas of fuel is discharged; c. Ck,oThe constant-pressure specific heat capacity of the dry flue gas at the outlet is obtained after an air preheater and an economizer are connected in parallel before the economizer is put into operation; t is tk,oThe temperature of the flue gas at the outlet of the air preheater and the economizer which are connected in parallel before the economizer is put into operation; t is teIs a reference temperature; vh,k,oBefore the coal economizer is put into operation, the air preheater and the coal economizer are connected in parallel, and then the volume of water vapor in unit fuel smoke is discharged; c. Ch,k,oThe constant-pressure specific heat capacity of the water vapor at the outlet of the economizer after the air preheater and the economizer are connected in parallel before the economizer is put into operation; qnet,arThe heating value of the boiler fuel before the coal economizer is put into operation; v' typek,oAir preheater for coal economizer after operationThe volume of dry flue gas per unit fuel is discharged after the dry flue gas is connected with the economizer in parallel; c' liquidk,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the dry flue gas is output; t' typek,oThe temperature of the flue gas at the outlet of the air preheater and the economizer after the economizer is put into operation is connected in parallel; t' typeeIs a reference temperature; v' typeh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the volume of water vapor in unit fuel smoke is discharged; c' liquidh,k,oAfter the economizer is put into operation, the air preheater is connected with the economizer in parallel, and the constant-pressure specific heat capacity of the water vapor at the outlet is obtained; q. q.ss,1The flow of the working medium at the first section after the coal economizer is put into operation; c. Cs,1△ t is a section of working medium with constant pressure and specific heat capacitys,1Raising the temperature of a section of working medium; q. q.ss,2The flow of the two-stage working medium after the coal economizer is put into operation; c. Cs,2△ t which is the constant pressure specific heat capacity of the two-stage working medium of the economizers,2Raising the temperature of the two-stage working medium; q' typenet,arThe heating value of the boiler fuel after the coal economizer is put into operation; m is the total fuel quantity of the boiler after the coal economizer is put into operation;
in the evaluation method 2, the economizer is not taken as the heating surface of the boiler system and is not included in the boundary of the boiler heat balance system, the influence of the boiler heat loss is mainly the change of the heat loss of the exhaust smoke, and the calculation formula is as follows:
Figure FDA0002480886590000021
wherein, based on the evaluation method 2, △ q2,pThe heat loss of the boiler exhaust smoke before and after the coal economizer is put into operation is changed; q. q.ss,k,oThe method comprises the following steps of (1) connecting an air preheater and an economizer in parallel after the economizer is put into operation, and measuring the smoke flow at a front outlet; c. Cs,k,oThe air preheater is connected with the economizer in parallel after the economizer is put into operation, and the flue gas at the front outlet has a constant pressure and specific heat capacity; t is ts,k,oThe temperature of the flue gas at the front outlet of the air preheater and the economizer which are connected in parallel after the economizer is put into operation; q. q.ss,iThe flue gas flow at the inlet of the economizer is obtained after the economizer is put into operation; t is ts,iThe temperature of the inlet flue gas of the economizer after the economizer is put into operation; c. Cs,iThe specific heat capacity of inlet flue gas at constant pressure after the coal economizer is put into operation ts,oThe temperature of the flue gas at the outlet of the economizer after the economizer is put into operation;
according to the method for testing the heat exchange efficiency of the two-section combined type economizer body, the heat exchange efficiency calculation formula is as follows:
Figure FDA0002480886590000022
wherein, ηsThe heat exchange efficiency of the economizer body is improved;
the method for evaluating the change of the air leakage rate of the air preheater by the switching on and off of the two-section combined economizer has the following calculation formula:
Figure FDA0002480886590000023
wherein, △ηkThe air leakage rate of the air preheater is changed before and after the coal economizer is put into and taken out;
Figure FDA0002480886590000024
the volume fraction of oxygen in the flue gas at the outlet of the air preheater before the coal economizer is put into operation;
Figure FDA0002480886590000025
the volume fraction of oxygen in the inlet flue gas of the air preheater before the coal economizer is put into operation;
Figure FDA0002480886590000026
the volume fraction of oxygen in the flue gas at the outlet of the air preheater after the coal economizer is put into operation;
Figure FDA0002480886590000027
the volume fraction of oxygen in the inlet flue gas of the air preheater after the coal economizer is put into operation;
the method for evaluating the heat loss of boiler exhaust smoke caused by the change of the smoke temperature at the inlet of the dust removal system in the operating state of the two-stage economizer comprises an evaluation method A and an evaluation method B;
in the evaluation method A, the economizer is taken as the heating surface of the boiler system and is brought into the boundary of the boiler heat balance system, the influence on the boiler heat loss comprises the change of the exhaust gas heat loss, and the calculation formula is as follows:
Figure FDA0002480886590000028
wherein, based on the evaluation method A, △ qA,pThe heat loss of boiler exhaust gas caused by the temperature change of the flue gas at the inlet of the dust removal system after the two-stage coal economizer is put into operation is changed, △ t ″k,oAfter the economizer is put into operation and the flue gas temperature at the inlet of the dust removal system changes, the air preheater is connected with the economizer in parallel, and then the flue gas temperature at the outlet changes;
in the evaluation method B, the economizer is not taken as the heating surface of the boiler system and is not included in the boundary of the boiler heat balance system, the influence of the boiler heat loss is mainly the change of the heat loss of the exhaust smoke, and the calculation formula is as follows:
Figure FDA0002480886590000031
wherein △ q is based on the evaluation method BB,pThe loss of boiler exhaust heat caused by the change of the temperature of the smoke at the inlet of the dust removal system after the two-section coal economizer is put into operation is changed; t is ts,k,oThe temperature change value of the flue gas at the outlet of the air preheater and the economizer is obtained after the economizer is put into operation and the flue gas temperature at the inlet of the dust removal system is changed.
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