A method for determining the maximum blending rate of coal-fired sludge and its application

Abstract

The present application proposes a method and application for determining the maximum blending rate of coal-fired coupled sludge, wherein the method for determining the maximum blending rate of coal-fired coupled sludge includes: obtaining the theoretical maximum blending rate of sludge when the decline in the standard theoretical efficiency of the boiler is less than or equal to the first preset value; based on the pulverizing constraint sludge blending rate, obtaining the output of all coal mills and the temperature of the outlet air-powder mixture, and obtaining the pulverizing constraint sludge blending rate according to the output and temperature of the coal mill; based on the combustion constraint blending rate, obtaining the furnace temperature and flame fullness of the boiler, and obtaining the combustion constraint blending rate. The method for determining the maximum blending rate of coal-fired coupled sludge described in the present application, based on theoretical calculations, through the blending test method, with the working conditions of the coal mill, the working conditions of the boiler burner, the actual efficiency of the boiler and the pollutant emissions as the limiting conditions, gradually determines the maximum blending amount of sludge, which can provide technical support for the safe and environmentally friendly incineration and disposal of sludge by coal-fired boilers.

Description

Technical Field

[0001] The present application relates to the technical field of sludge disposal, and in particular to a method for determining a maximum blending rate of coal-fired coupled sludge and its application. Background Art

[0002] The calorific value of sludge is generally low, which is quite different from the properties of coal. The safety hazards of sludge co-combustion, such as improper co-combustion ratio during production operation, causing boiler coking corrosion and efficiency reduction, flue gas pollutant emission control problems and comprehensive utilization of ash, have all attracted attention.

[0003] Coal-fired boiler coupling sludge should not affect the normal production of the original boiler and the pollutant emission standards. However, because the composition of sludge is very different from that of coal, especially the sludge containing more heavy metals and other harmful components from industrial wastewater treatment plants, it may cause harm to the coal-fired boiler and flue system and produce secondary pollutant emissions. On the other hand, the maximum blending amount calculated theoretically often deviates greatly from the actual situation and cannot be directly used for actual blending control. Therefore, it is crucial to reasonably and scientifically determine the key parameter of the maximum sludge blending amount.

[0004] Sludge can be divided into dry sludge (moisture content not more than 40%), wet sludge (moisture content 80% and above) and semi-dry sludge (moisture content between dry sludge and wet sludge) according to different moisture content. Dry sludge and semi-dry sludge are economical to blend and burn, and are commonly used for blending and burning. External sludge is transported to the factory by closed vehicles, and is temporarily stored in the sludge storage bin after being dried or not dried in the factory, and then sent to the coal mill or raw coal bin through the feeding system (and then falls into the coal mill through the coal feeder device). The maximum blending amount of dry sludge is affected by multiple equipment and is a parameter constrained by multiple conditions. Summary of the invention

[0005] In view of this, one purpose of the present application is to provide a method for determining the maximum blending rate of coal-fired coupled sludge. On the basis of theoretical calculations, through the method of blending test, with the working conditions of the pulverizer, the working conditions of the boiler burner, the actual efficiency of the boiler and the pollutant emissions as limiting conditions, the maximum sludge blending amount is gradually determined, which can provide technical support for the safe and environmentally friendly incineration and disposal of sludge in coal-fired boilers.

[0006] Another object of the present application is to provide an application of a method for determining the maximum blending rate of coal-fired coupled sludge.

[0007] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a method for determining the maximum blending rate of coal-fired coupled sludge, comprising:

[0008] Obtaining the theoretical maximum sludge blending rate when the decrease in the boiler standard theoretical efficiency is less than or equal to the first preset value;

[0009] Based on the theoretical maximum sludge blending rate, the output of all coal mills and the temperature of the outlet air-powder mixture are obtained, and according to the output and the temperature, the pulverizing constraint sludge blending rate is obtained;

[0010] Based on the pulverizing constrained sludge blending rate, the furnace temperature and flame fullness of the boiler are obtained, and according to the furnace temperature and flame fullness, the combustion constrained blending rate is obtained;

[0011] Based on the combustion constraint blending rate, obtaining the actual efficiency of the boiler, and obtaining the furnace efficiency constraint blending rate according to the actual efficiency and a second preset value;

[0012] Based on the furnace efficiency constraint blending rate, the pollutant emission value of the boiler is obtained, and according to the pollutant emission value, the emission constraint blending rate is obtained, and the maximum blending rate of the coal-fired coupled sludge is determined based on the emission constraint blending rate.

[0013] In some embodiments, obtaining the emission-constrained blending rate according to the pollutant emission value includes:

[0014] Determining whether the pollutant emission value is less than or equal to the pollutant emission standard value;

[0015] If the pollutant emission value is less than or equal to the pollutant emission standard value, the furnace efficiency constraint blending rate is used as the emission constraint blending rate;

[0016] If the pollutant emission value is greater than the pollutant emission standard value, the steps of obtaining the pulverizing constraint sludge blending rate, obtaining the combustion constraint blending rate and obtaining the furnace efficiency constraint blending rate are repeated in sequence.

[0017] In some embodiments, determining the maximum blending rate of the coal-fired coupled sludge based on the emission constraint blending rate includes:

[0018] Determining whether the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the maximum;

[0019] If the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the largest, the emission constraint blending rate is used as the maximum blending rate of the coal-fired coupled sludge;

[0020] If the emission constraint blending rate is not the emission constraint blending rate when the sludge blending amount is the largest, the steps of obtaining the pulverizing constraint sludge blending rate, the combustion constraint blending rate, the furnace efficiency constraint blending rate and the emission constraint blending rate are repeated in sequence.

[0021] In some embodiments, obtaining the theoretical maximum sludge blending rate when the decrease in the theoretical efficiency of the boiler is less than or equal to the first preset value includes:

[0022] Obtaining elemental analysis and industrial analysis results of the sludge and the coal;

[0023] Based on the elemental analysis and industrial analysis results, the sludge is mixed with the coal at different theoretical blending ratios to obtain different mixed fuels;

[0024] Obtaining theoretical calorific values ​​of different mixed fuels and using them as different theoretical efficiencies of the boiler;

[0025] A first difference between the different theoretical efficiencies and the standard theoretical efficiency is obtained, and the theoretical blending ratio corresponding to the maximum first difference that is less than or equal to the first preset value is taken as the theoretical maximum sludge blending ratio.

[0026] In some embodiments, obtaining the pulverizing-constrained sludge co-combustion rate comprises:

[0027] Taking the theoretical sludge amount corresponding to 50% of the theoretical maximum sludge blending rate as the initial sludge amount, gradually increase or decrease the sludge amount entering the coal mill, and the total increase or decrease is less than or equal to 50% of the theoretical maximum sludge blending rate;

[0028] Determine whether the output of all coal mills under different sludge amount conditions is less than or equal to the preset output limit, and whether the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature; the sludge amount when the output of all coal mills is less than or equal to the preset output limit, the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature, the output of all coal mills is closest to the preset output limit, and the temperature of the outlet air-powder mixture of all coal mills is closest to the preset limit temperature is taken as the final sludge amount entering all coal mills; and the ratio of the final sludge amount to the total amount of coal entering all coal mills simultaneously is taken as the pulverizing constraint sludge blending rate.

[0029] In some embodiments, the amount of sludge added to the coal mill each time is 0.1-1 t / h.

[0030] In some embodiments, obtaining a combustion constrained blending ratio includes:

[0031] Blending sludge at the pulverizing constraint sludge blending rate is performed to obtain the furnace temperature and flame fullness of the boiler burner layer for blending sludge;

[0032] Determining whether a second difference between a target furnace temperature and the furnace temperature is less than or equal to a third preset value, or determining whether the flame fullness meets the target flame fullness;

[0033] If the second difference is less than or equal to the third preset value, or the flame fullness meets the target flame fullness, the pulverizing constraint sludge blending rate is used as the combustion constraint blending rate;

[0034] If the second difference is greater than the third preset value, and the flame fullness does not meet the target flame fullness, the step of obtaining the pulverizing constraint sludge blending rate is repeated.

[0035] In some embodiments, obtaining the furnace efficiency constrained blending rate according to the actual efficiency and the second preset value includes:

[0036] Determining whether the actual efficiency decrease is less than or equal to the second preset value;

[0037] If the actual efficiency decrease is less than or equal to the second preset value, the combustion constraint blending rate is used as the furnace efficiency constraint blending rate;

[0038] If the actual efficiency decrease is greater than the second preset value, the steps of obtaining the pulverizing constraint sludge blending rate and the combustion constraint blending rate are repeated in sequence.

[0039] In some embodiments, the pollutants include one or more of carbon monoxide in flue gas, nitrogen oxides in flue gas, and heavy metals in ash.

[0040] To achieve the above objectives, the second aspect of the present application proposes the application of the method for determining the maximum blending rate of coal-fired coupled sludge as in the embodiment of the present application in the field of sludge disposal.

[0041] The method for determining the maximum blending rate of coal-fired coupled sludge in the embodiment of the present application can bring the following beneficial effects:

[0042] Based on theoretical calculations, the maximum amount of sludge blending is gradually determined through the blending test method, with the working conditions of the coal mill, the working conditions of the boiler burner, the actual efficiency of the boiler and the pollutant emissions as the limiting conditions, which can provide technical support for the safe and environmentally friendly incineration and disposal of sludge by coal-fired boilers. This method is applicable to the disposal of sludge with all moisture contents.

[0043] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0045] Figure 1 The schematic diagram is a principle block diagram of a method for determining the maximum blending ratio of coal-fired coupled sludge according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0047] Throughout the application, the disclosure of numerical ranges includes all values ​​within the entire range and disclosure of further subdivided ranges, including endpoints and subranges given within those ranges.

[0048] In the application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be produced through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0049] A method for determining the maximum blending ratio of coal-fired coupled sludge according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0050] Figure 1 It is a principle block diagram of a method for determining the maximum blending rate of coal-fired coupled sludge according to an embodiment of the present application.

[0051] like Figure 1 As shown, the embodiment of the present application proposes a method for determining the maximum blending rate of coal-fired coupled sludge, comprising the following steps:

[0052] S101. Obtaining a theoretical maximum sludge blending rate when a decrease in the standard theoretical efficiency of the boiler is less than or equal to a first preset value.

[0053] In some embodiments, obtaining the theoretical maximum sludge blending rate when the decrease in the theoretical efficiency of the boiler is less than or equal to the first preset value includes:

[0054] Obtain elemental and industrial analysis results of sludge and coal;

[0055] Based on the results of elemental analysis and industrial analysis, sludge and coal were mixed at different theoretical blending ratios to obtain different mixed fuels;

[0056] Obtain the theoretical calorific values ​​of different mixed fuels and use them as different theoretical efficiencies of boilers;

[0057] A first difference between different theoretical efficiencies and a standard theoretical efficiency is obtained, and a theoretical blending ratio corresponding to a maximum first difference that is less than or equal to a first preset value is taken as a theoretical maximum sludge blending ratio.

[0058] Among them, the elemental analysis and industrial analysis results of sludge and coal can be obtained based on, but not limited to, relevant national and power industry analysis and testing standards, such as "Coal Sample Preparation Method" (GB / T474-2008), "Industrial Analysis Method of Coal" (GB / T212-2008), etc.

[0059] In this application, the sludge and coal are subjected to elemental analysis and industrial analysis respectively, and the thermal parameters of the boiler and the stable safety performance of the heating surface under different sludge blending ratios are calculated by thermal calculation, and the acceptable reduction level of boiler efficiency is considered (that is, the first preset value, different power plant boilers and fuel conditions are different, and the percentage of boiler reduction acceptable to the operation management personnel is different, which is allowed to be freely determined according to actual conditions), and the amount of mixed fuel that needs to be invested (coal and sludge combined) is calculated by weighting by mass, so that the mass percentage of sludge in coal can be obtained, which is recorded as the theoretically calculated maximum sludge blending rate M0. At this time, the corresponding mass of the blended sludge is the theoretical maximum sludge blending amount.

[0060] In some embodiments, the first preset value includes but is not limited to less than 2%. As a non-limiting example, the first preset value includes but is not limited to 0.5%, 1%, 1.5 or 2%, etc.

[0061] S102. Based on the theoretical maximum sludge blending rate, the output of all coal mills and the temperature of the outlet air-powder mixture are obtained, and according to the output of all coal mills and the temperature of the outlet air-powder mixture, the pulverizing constraint sludge blending rate is obtained.

[0062] In some embodiments, obtaining the pulverizing-constrained sludge co-combustion rate comprises:

[0063] Taking the theoretical sludge amount corresponding to 50% of the theoretical maximum sludge blending rate as the initial sludge amount, gradually increase or decrease the sludge amount entering the coal mill, and the total increase or decrease is less than or equal to 50% of the theoretical maximum sludge blending rate;

[0064] Determine whether the output of all coal mills under different sludge amount conditions is less than or equal to the preset output limit, and whether the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature; the sludge amount when the output of all coal mills is less than or equal to the preset output limit, the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature, the output of all coal mills is closest to the preset output limit, and the temperature of the outlet air-powder mixture of all coal mills is closest to the preset limit temperature is taken as the final sludge amount entering all coal mills; and the ratio of the final sludge amount to the total amount of coal entering all coal mills simultaneously is taken as the pulverizing constraint sludge blending rate.

[0065] The method of the present application starts the test with 50% of the theoretically calculated maximum sludge blending amount, i.e. 0.5M0 as the initial sludge amount, and gradually adjusts the sludge amount entering the coal mill to obtain the sludge amount that can enter the coal mill.

[0066] The amount of sludge that can enter the coal mill is subject to the output limit of the coal mill and the temperature requirements of the air-powder mixture at the coal mill outlet, that is, there is a preset output limit and a preset limit temperature. The preset output limit and the preset limit temperature are related to the type and scale of the coal mill, which are well known in the art and will not be described here. However, the sludge has high moisture and ash content and low calorific value. The sludge blending requires the pulverizing system to increase its output, which occupies the margin of the coal mill output. If the pulverizing system cannot meet the unit's demand for rated evaporation under the maximum design output, it is necessary to consider reducing the blending ratio and reducing the amount of low calorific value sludge added. It should be noted that if multiple coal mills are used for blending, they should each meet the normal operating procedures of each coal mill. At this time, the ratio of the total amount of sludge entering all coal mills to the total amount of coal entering the coal mill simultaneously is the ratio M1 that can enter the coal mill. At the same time, according to the combustion conditions of the downstream boiler, etc., the initial amount of sludge entering the coal mill is adjusted. When the coal mill output or the temperature of the air-powder mixture at the coal mill outlet cannot meet the requirements, the adjustment should be stopped. At this time, M1 is the pulverizing constraint sludge blending rate.

[0067] In some embodiments, the amount of sludge added into the coal mill each time is 0.1-1 t / h, including but not limited to 0.1 t / h, 0.5 t / h or 1 t / h, etc.

[0068] S103, based on the pulverizing constraint sludge blending rate, obtain the furnace temperature and flame fullness of the boiler, and obtain the combustion constraint blending rate according to the furnace temperature and flame fullness.

[0069] In some embodiments, obtaining a combustion constrained blending ratio includes:

[0070] The sludge is blended and burned at the pulverizing constraint sludge blending rate to obtain the furnace temperature and flame fullness of the boiler burner layer for blending and burning sludge;

[0071] Determining whether the second difference between the target furnace temperature and the furnace temperature is less than or equal to a third preset value, or determining whether the flame fullness meets the target flame fullness;

[0072] If the second difference is less than or equal to the third preset value, or the flame fullness meets the target flame fullness, the pulverizing constraint sludge blending rate is used as the combustion constraint blending rate;

[0073] If the second difference is greater than the third preset value and the flame fullness does not meet the target flame fullness, the step of obtaining the pulverizing constraint sludge blending rate is repeated.

[0074] In some embodiments, the third preset value includes but is not limited to below 80° C. As non-limiting examples, the third preset value includes but is not limited to 80° C., 70° C., 60° C., 50° C., 40° C. or 30° C., etc.

[0075] In some embodiments, the target flame fullness refers to a high flame fullness, a bright golden flame, and no obvious dark areas. The flame fullness can be qualitatively observed by a flame detection camera, which is a qualitative sensory indicator, wherein the criteria for judging the absence of obvious dark areas include but are not limited to defining it by the area ratio of the red dark area on the flame image to the entire flame image. If the defined area ratio is met, it is considered that there is no obvious dark area and the flame fullness is high. As a non-limiting example, if the flame image is bright golden as a whole, and the area ratio of the red dark area on the flame image to the entire flame image is between 0-20%, it is considered that there is no obvious dark area and the flame fullness is high, which can be regarded as the target flame fullness.

[0076] It should be noted that the definition of target flame fullness in the present application is only an illustrative enumeration. In other standards, documents, etc., as long as it involves the target flame fullness of the boiler or similar flame fullness definitions used as comparative reference standards, the method of the present application can be applied. The only difference is that the defined standards are different and the screening scales may differ. However, this does not affect the use of the overall method of the present application to determine the maximum blending rate of coal-coupled sludge.

[0077] In the present application, the determination of the sludge blending ratio for maintaining stable furnace combustion (also known as the combustion constraint blending ratio) is based on maintaining the pulverizing constraint sludge blending ratio M1, testing the furnace temperature of the burner layer fuel combustion of the sludge blending and observing the flame fullness, judging their compliance with the target furnace temperature and target flame fullness, and then adjusting the sludge blending ratio M2 for maintaining stable furnace combustion. In particular, the blending of wet sludge can easily cause a drop in furnace temperature, and even a drop in flame fullness, with the flame turning red and dark in some areas. Generally, when the furnace temperature drops by more than the third preset value, the amount of sludge blending should be reduced, or when the flame turns red and dark in some areas, the upper limit of the blending ratio that can be tolerated for safe and stable combustion is basically reached, thereby obtaining the sludge blending ratio M2 for maintaining stable furnace combustion, which is the combustion constraint blending ratio.

[0078] S104. Based on the combustion constraint blending rate, obtain the actual efficiency of the boiler, and obtain the furnace efficiency constraint blending rate according to the actual efficiency and the second preset value.

[0079] In some embodiments, obtaining the furnace efficiency constraint blending rate according to the actual efficiency and the second preset value includes:

[0080] Determining whether the actual efficiency decrease is less than or equal to a second preset value;

[0081] If the actual efficiency decrease is less than or equal to the second preset value, the combustion constraint blending rate is used as the furnace efficiency constraint blending rate;

[0082] If the actual efficiency decrease is greater than the second preset value, the steps of obtaining the pulverizing constraint sludge blending rate and the combustion constraint blending rate are repeated in sequence.

[0083] In some embodiments, the second preset value includes but is not limited to less than 2%. As a non-limiting example, the second preset value includes but is not limited to 0.5%, 1%, 1.5 or 2%, etc.

[0084] In this application, under the condition of combustion safety, on the basis of maintaining the combustion constraint blending rate M2 and the sludge ratio, the economic acceptability of boiler operation is the focus of the operator, and the economic efficiency of boiler operation is related to the actual operating efficiency of the boiler. This is because the addition of sludge increases the moisture content and ash content of the mixed fuel, reduces the calorific value of the fuel, and reduces the amount of heat absorbed by radiation in the furnace. At the same time, the flue gas flow rate and velocity increase, which ultimately leads to an increase in the exhaust temperature, an increase in boiler exhaust losses, and a decrease in boiler efficiency. This is contrary to the economic operation of the boiler, and a large decline (exceeding the second preset value) is generally unacceptable. The amount of sludge added is adjusted to obtain a controllable sludge blending ratio M3 for boiler efficiency, that is, the furnace efficiency constraint blending rate.

[0085] S105. Based on the furnace efficiency constraint blending rate, obtain the pollutant emission value of the boiler, obtain the emission constraint blending rate according to the pollutant emission value, and determine the maximum blending rate of coal-fired coupled sludge based on the emission constraint blending rate.

[0086] In some embodiments, obtaining the emission-constrained blending rate according to the furnace efficiency-constrained blending rate and the pollutant emission value includes:

[0087] Determine whether the pollutant emission value is less than or equal to the pollutant emission standard value;

[0088] If the pollutant emission value is less than or equal to the pollutant emission standard value, the furnace efficiency constraint blending rate shall be used as the emission constraint blending rate;

[0089] If the pollutant emission value is greater than the pollutant emission standard value, the steps of obtaining the pulverizing constraint sludge blending rate, obtaining the combustion constraint blending rate and obtaining the furnace efficiency constraint blending rate are repeated in sequence.

[0090] The boiler meets the emission standard of the sludge co-combustion ratio M4 (also known as the furnace efficiency constraint co-combustion ratio). This mainly refers to the CO and NO in the flue gas. xThe emission of heavy metals in the ash and slag and other indicators is up to standard. Due to the different quality of sludge from different industrial sources, such as the heavy metal content of papermaking, printing and dyeing, and municipal life sludge, the content varies greatly. However, it is not allowed to cause secondary pollution due to excessive mixing and burning of a certain sludge, or to cause adverse effects on the reuse of ash and slag. The maximum sludge mixing and burning rate determined by this is M4, which is the emission constraint mixing and burning rate.

[0091] In some embodiments, determining the maximum blending rate of coal-fired coupled sludge based on the emission constraint blending rate includes:

[0092] Determine whether the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the maximum;

[0093] If the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the largest, the emission constraint blending rate shall be taken as the maximum blending rate of coal-fired coupled sludge;

[0094] If the emission constraint blending rate is not the emission constraint blending rate when the sludge blending amount is the largest, the steps of obtaining the pulverizing constraint sludge blending rate, the combustion constraint blending rate, the furnace efficiency constraint blending rate and the emission constraint blending rate are repeated in sequence.

[0095] It should be noted that in the present application, one of the purposes of the method for determining the maximum blending rate of coal-fired coupled sludge is to increase the sludge disposal volume and realize resource utilization. Therefore, when determining the maximum blending rate of coal-fired coupled sludge based on the working condition restrictions of the coal mill, the working condition restrictions of the boiler burner, the actual efficiency restrictions of the boiler and the pollutant emission restrictions, it is also necessary to consider whether the sludge disposal volume (that is, the sludge blending volume) is maximized. If so, the maximum blending rate of coal-fired coupled sludge at this time is the final maximum blending rate of coal-fired coupled sludge. If not, it is necessary to repeat the steps of obtaining the pulverizing constraint sludge blending rate, the combustion constraint blending rate, the furnace efficiency constraint blending rate and the emission constraint blending rate in sequence, and re-screen and determine the final maximum blending rate of coal-fired coupled sludge.

[0096] In addition, in the present application, no matter which link of the combustion constraint blending rate, furnace efficiency constraint blending rate, emission constraint blending rate, and coal-fired coupled sludge maximum blending rate is returned to the pulverizing constraint sludge blending rate step, and the subsequent steps are continued. Generally, it is necessary to adjust the amount of sludge entering the coal mill in the pulverizing constraint sludge blending rate step according to the situation, and then adjust the pulverizing constraint sludge blending rate. This adjustment may be to increase the amount of sludge entering the coal mill, thereby increasing the pulverizing constraint sludge blending rate, or to reduce the amount of sludge entering the coal mill, thereby reducing the pulverizing constraint sludge blending rate, and then achieve the corresponding adjustment of the subsequent combustion constraint blending rate, furnace efficiency constraint blending rate, emission constraint blending rate, and coal-fired coupled sludge maximum blending rate. However, no matter how the adjustment is made, it must be under the conditions of satisfying the working conditions of the coal mill, the working conditions of the boiler burner, the actual efficiency of the boiler, and the pollutant emission limits, to achieve the purpose of maximizing the sludge disposal volume as much as possible.

[0097] In the present application, after determining the final maximum blending rate of coal-fired coupled sludge, the maximum blending amount of sludge can be obtained in combination with the weight of the coal.

[0098] It should be noted that the first preset value, the second preset value and the third preset value in the present application may have different values ​​in actual operation depending on factors such as different coal-fired power plants, different boiler structures, different fuel conditions, etc., but the different values ​​do not affect the use of the method of the present application to determine the maximum blending rate of coal-coupled sludge.

[0099] In some embodiments, the moisture content of the sludge is not limited, and it can be dry sludge with a moisture content not greater than 40%, or wet sludge with a moisture content of 80% or more, or semi-dry sludge with a moisture content between dry sludge and wet sludge.

[0100] The method for determining the maximum blending rate of coal-fired coupled sludge in the embodiment of the present application, based on theoretical calculations, gradually determines the maximum blending amount of sludge through blending tests, with the working conditions of the coal mill, the working conditions of the boiler burner, the actual efficiency of the boiler and the pollutant emissions as limiting conditions. It can provide technical support for the safe and environmentally friendly incineration and disposal of sludge in coal-fired boilers, so as to make up for the shortcomings of theoretical calculations.

[0101] The method for determining the maximum blending rate of coal-fired coupled sludge in the embodiment of the present application can be widely used in the field of sludge disposal, wherein the sludge can be sludge with various sludge moisture contents, such as dry sludge, wet sludge, and semi-dry sludge.

[0102] As a possible example, the method for determining the maximum blending rate of coal-fired coupled sludge according to the embodiment of the present application can be applied to a coal-fired cogeneration boiler that blends dry sludge.

[0103] The method for determining the maximum blending rate of coal-fired coupled sludge in the embodiment of the present application is explained below with reference to specific application examples.

[0104] Project Overview: For a 350MW coal-fired boiler in a power plant, when burning lignite as the main coal, the boiler coal consumption is 175t / h under the rated evaporation capacity of the boiler, and the designed low calorific value is 16.30MJ / kg. It is planned to carry out coal-fired coupled sludge transformation to dispose of about 400 tons / day of dried sludge (water content of 40%) from outside the plant.

[0105] The first step is to calculate the maximum theoretical sludge blending rate. According to the relevant analytical and testing standards of the country and the power industry, the elemental analysis and industrial analysis results of dry sludge and commonly used coal-fired lignite are shown in Table 1. The calorific value of the mixed fuel of dried sludge with a moisture content of 40% and commonly used coal-fired lignite was calculated at 3wt%, 6wt%, 10wt% and 12wt% sludge blending rates. The low calorific value of the commonly used coal lignite is 16.30MJ / kg. After adding 3wt% of dried sludge, the calorific value of the mixed fuel drops to 15.90MJ / kg; when the blending ratio increases to 6wt%, the calorific value of the sludge drops to 15.50MJ / kg; when the blending ratio increases to 10wt%, the calorific value of the sludge drops to 14.97MJ / kg; when the blending ratio increases to 12wt%, the calorific value of the sludge drops to 14.70MJ / kg. As the blending ratio increases, the calorific value of the mixed fuel shows a downward trend, as shown in Table 2. When sludge with a certain moisture content is added to coal, the calorific value of the mixed fuel decreases, which will inevitably affect the boiler thermal system. According to the "Power Plant Boiler Performance Test Procedure", the performance parameters of the boiler at different drying sludge blending ratios are calculated, and some calculation results are shown in Table 3.

[0106] Table 1 Composition analysis results of common coal and sludge in boilers

[0107]

[0108] Table 2 Theoretical calorific value of mixed fuels of common coal and sludge at different blending ratios

[0109]

[0110]

[0111] Table 3 Boiler performance parameters at different blending rates

[0112] name unit Raw coal lignite Method 1 Method 2 Method 3 Method 4 Sludge combustion ratio wt% 0 3 6 10 12 Total fuel kg / h 175000 180250 185500 192500 196000 Coal consumption kg / h 175000 175000 175000 175000 175000 Dry sludge dosage kg / h 0 5250 10500 17500 21000 Carbon content of fly ash wt% 0.5 0.49 0.25 0.36 0.51 Slag carbon content wt% 2 2.12 1.98 1.1 0.92 Theoretical combustion temperature ℃ 1935 1929 1916 1907 1896 Boiler efficiency ％ 91.3 90.9 90.4 89.4 88.9

[0113] When the decline in the standard theoretical efficiency of the boiler acceptable to the power plant operation management personnel does not exceed 2 percentage points (ie, the first preset value is 2%), the theoretical maximum sludge blending rate M0 is about 10%.

[0114] In the second step, a trial blending and burning test is carried out using the sludge amount corresponding to 50% of the theoretical maximum sludge blending and burning rate M0 calculated theoretically, i.e. 10% / 2=5%, as the initial sludge input amount.

[0115] The amount of sludge entering the coal mill is constrained by the coal mill's designed coal mill output limit (i.e., the preset limit output) and the temperature of the air-powder mixture at the coal mill's designed outlet (i.e., the preset limit temperature). The sludge has high moisture and ash content and low calorific value. The co-firing of sludge requires the pulverizing system to increase its output, which occupies the margin of the coal mill's output. If the pulverizing system cannot meet the unit's rated evaporation requirements under the maximum design output, it is necessary to consider reducing the co-firing ratio and reducing the amount of low calorific value sludge added. The preset limit output of the coal mill is 51.5t / h, and the preset limit temperature of the outlet air-powder mixture is 56°C.

[0116] An automatic weighing device is used to control the feeding and mixing amount of sludge, so that the moisture content of the mixed fuel is within the allowable range (the allowable range of moisture content is 0-±1%), and the temperature of the air-powder mixture at the pulverizer outlet is not seriously lower than the design outlet temperature (that is, the preset limit temperature), which should be less than 3°C to ensure that the downstream combustion needs are met and that there will be no coal accumulation and blockage in the pulverizer outlet pulverized coal pipe during the pulverizing process.

[0117] The amount of sludge entering the coal mill is gradually increased (e.g., each increase is about 0.5 t / h), and the operating parameters of the coal mill such as the raw coal flow, driving motor current, coal mill output, and outlet air-powder mixture temperature, as well as the furnace temperature of the boiler and the combustion fullness and stability are monitored at the same time. When the sludge blending rate is adjusted to 8.0wt%, the coal mill output is 47.2t / h, the total amount of fuel supplied is 189t / h, and the boiler can reach the rated evaporation capacity. At this time, the temperature of the coal mill outlet air-powder mixture is 2.8℃ lower than the preset limit temperature, which is less than the requirement of 3℃. Within the allowable range of coal mill operation, considering the change in the moisture content of coal quality, the sludge blending rate is temporarily not increased to obtain the amount of sludge that can enter the coal mill. Therefore, the sludge blending rate of 8.0wt% is regarded as the pulverizing constraint blending rate M1.

[0118] Note: If two coal mills are used for blending, the ratio of the sum of the sludge entering the two coal mills to the total amount of coal entering all the operating coal mills simultaneously should be the sludge pulverizing constraint blending rate M1 that can enter the coal mill, under the condition that the normal operating procedures of each coal mill are met.

[0119] The third step is to determine the mixing rate (also known as the combustion constraint mixing rate) M2 that maintains stable combustion in the furnace. The normal operation of the pulverizing system is the prerequisite for ensuring stable combustion in the furnace, and the two parameters that reflect stable combustion in the furnace are the furnace temperature and flame fullness of the fuel combustion in the furnace burner layer, which can be observed by the temperature sensor of the online temperature measurement system and the remote flame detection camera, respectively. When the moisture content of the mixed combustion is 40% dry sludge and the mixing rate reaches 8wt%, the furnace temperature is 1185℃, and the furnace temperature change is about 70℃ lower than the furnace temperature (1255℃) when the sludge is not mixed (the third preset value is 80℃); the flame temperature measurement results at different heights of the furnace show that the temperature from the bottom to the top is between 1130 and 1305℃, and the maximum deviation of each point in each layer is within 15℃. The influence of different sludge mixing rates on the flue gas temperature in the furnace is relatively small, and there is no obvious local low temperature area at the same height layer. Observe the furnace flame fullness image, the flame fullness is high, bright golden flame, no obvious dark area (the red dark area on the flame image accounts for about 15% of the area of ​​the entire flame image), the furnace combustion is stable. Considering the theoretical calculation of the acceptable range of boiler efficiency decline, the sludge blending rate is no longer adjusted, and the sludge combustion constraint blending rate M2 = M1 = 8wt% is now.

[0120] The fourth step is to control the boiler efficiency by the sludge blending ratio (i.e., the furnace efficiency constraint blending ratio) M3. According to the "Power Plant Boiler Performance Test Procedure GB / T 10184-2015", the actual boiler efficiency is actually tested and calculated. Under the condition of the sludge blending ratio of 8wt% as the combustion constraint blending ratio, the actual boiler efficiency is calculated to be 89.7%, which is 1.6% lower than the design, and is still within the acceptable boiler efficiency decrease of 2% (the second preset value) for the operation management personnel, and there is still margin. Therefore, the combustion constraint blending ratio is used as the furnace efficiency constraint blending ratio, that is, the furnace efficiency constraint blending ratio of the sludge is 8wt%. Considering that there is still a margin between the decrease in the actual boiler efficiency and the second preset value, in order to further increase the amount of sludge disposed, return to step 2 and gradually increase the sludge blending ratio.

[0121] Repeat steps 2 to 4. When the sludge blending rate reaches 10.0wt%, the actual boiler efficiency is 89.5% when other conditions remain basically unchanged. The calculated actual boiler efficiency is 1.8% lower than the design value, which is within the 2% drop in boiler efficiency acceptable to operation managers (that is, the drop in the actual boiler efficiency is less than the second preset value).

[0122] When trying to increase the sludge blending rate by 12wt%, the actual boiler efficiency was tested to be 88.9%, the CO concentration in the flue gas reached 390ppm, and the actual boiler efficiency was 2.4% lower than the design value, exceeding the acceptable boiler efficiency drop of 2% (that is, the actual boiler efficiency drop was greater than the second preset value).

[0123] When trying to reduce the sludge blending rate to 11wt%, the actual boiler efficiency was tested to be 89.1%, and the CO concentration in the flue gas reached 255ppm. The actual boiler efficiency was 2.2% lower than the design value, which still exceeded the acceptable boiler efficiency drop (that is, the actual boiler efficiency drop was greater than the second preset value).

[0124] Using the stepwise approximation method, when the sludge blending rate was further reduced to 10.5wt%, the actual boiler efficiency was tested to be 89.3%, and the CO concentration in the flue gas reached 193ppm. The actual boiler efficiency was 2.0% lower than the design value, which was within the acceptable range of boiler efficiency decrease (that is, the actual boiler efficiency decrease was equal to the second preset value).

[0125] At this time, the furnace efficiency constraint blending rate of sludge M'3 is ≤10.5wt%.

[0126] The fifth step is to meet the emission standards for the sludge blending ratio (also known as the emission constraint blending ratio) M4. This mainly refers to the CO and NO in the flue gas. x The emission of heavy metals in ash and slag is in compliance with the standards. Since an SCR flue gas denitrification device is installed downstream, NO x Not tested.

[0127] In the process of repeating the second to fourth steps, it was found that when the sludge blending rate increased by 12wt%, the CO emission concentration in the boiler flue gas reached 390ppm, which exceeded the CO emission concentration required by the design (not more than 100ppm). When the sludge blending rate reached 10.5wt%, the CO emission concentration in the boiler flue gas reached 193ppm. At this time, the second to fourth steps were repeated, and the sludge blending rate was further reduced to 10.3wt%. The actual boiler efficiency was tested to be 89.4%, and the CO concentration in the flue gas reached 93ppm (the actual boiler efficiency was 1.9% lower than the design value, which was within the acceptable boiler efficiency drop of 2%).

[0128] Under this condition, the heavy metal leaching liquid of ash and slag after combustion was tested and all met the technical performance index requirements of "Concentration Limits of Hazardous Components in Leaching Liquid" (GB5085.3-2007).

[0129] Table 4 Analysis of harmful components in fly ash slag leachate

[0130]

[0131] At this time, the emission constraint blending rate M4 = 10.3wt%, slightly higher than the theoretical maximum blending rate. This is mainly because the calorific value and other indicators of the currently commonly used coal quality are better than the original design coal quality, achieving a larger blending rate.

[0132] Step 6: Based on the above parameters, the maximum sludge blending rate Mmax = M4 = 10.3wt% is determined. Multiplying it by the total coal consumption of 193t / h, the actual maximum sludge blending rate is 19.6t / h. The operation is about 20 hours a day, which can just complete the sludge disposal target of 400 tons / day.

[0133] When the quality of the coal changes significantly, that is, the change exceeds the range specified by the boiler calibration coal type, the maximum sludge blending rate and maximum blending amount should be re-determined according to the above steps 2 to 5. If necessary, the combustion air distribution should be optimized, mainly including the adjustment of air input parameters (including air volume supply, air volume distribution, burner nozzle wind speed, etc.) and the adjustment of the combustion state in the furnace (such as flame center position adjustment, temperature distribution state adjustment, etc.). The adjustment operation can be carried out in accordance with the "Coal-fired Boiler Combustion Adjustment Test Method" (published by Water Resources and Electric Power Press, the authors are Xi'an Thermal Engineering Research Institute and Northeast Electric Power Bureau Technical Improvement Bureau).

[0134] It should be noted that boilers have designed coal types and verified coal types, which also determine the range of fuel changes that the boiler can use. This is the fluctuation range of the fuel indicators determined when the boiler is designed. When it deviates from the applicable fuel change range, it is a larger change. This point is well known to boiler operators and will not be elaborated here.

[0135] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0136] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for determining the maximum blending rate of coal-fired coupled sludge, characterized in that: include: Obtaining the theoretical maximum sludge blending rate when the decrease in the boiler standard theoretical efficiency is less than or equal to the first preset value; Based on the theoretical maximum sludge blending rate, the output of all coal mills and the temperature of the outlet air-powder mixture are obtained, and according to the output and the temperature, the pulverizing constraint sludge blending rate is obtained; The method of obtaining the pulverizing constraint sludge blending rate comprises: Taking the theoretical sludge amount corresponding to 50% of the theoretical maximum sludge blending rate as the initial sludge amount, gradually increase or decrease the sludge amount entering the coal mill, and the total increase or decrease is less than or equal to 50% of the theoretical maximum sludge blending rate; Determine whether the output of all coal mills under different sludge amount conditions is less than or equal to the preset output limit, and whether the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature, and take the sludge amount when the output of all coal mills is less than or equal to the preset output limit, the temperature of the outlet air-powder mixture of all coal mills is less than or equal to the preset limit temperature, and the output of all coal mills is closest to the preset output limit, and the temperature of the outlet air-powder mixture of all coal mills is closest to the preset limit temperature as the final sludge amount entering all coal mills, and take the ratio of the final sludge amount to the total amount of coal entering all coal mills synchronously as the pulverizing constraint sludge blending rate; Based on the pulverizing constrained sludge blending rate, the furnace temperature and flame fullness of the boiler are obtained, and according to the furnace temperature and flame fullness, the combustion constrained blending rate is obtained; the obtaining of the combustion constrained blending rate includes: Blending sludge at the pulverizing constraint sludge blending rate is performed to obtain the furnace temperature and flame fullness of the boiler burner layer for blending sludge; Determining whether a second difference between a target furnace temperature and the furnace temperature is less than or equal to a third preset value, or determining whether the flame fullness meets the target flame fullness; If the second difference is less than or equal to the third preset value, or the flame fullness meets the target flame fullness, the pulverizing constraint sludge blending rate is used as the combustion constraint blending rate; If the second difference is greater than the third preset value, and the flame fullness does not meet the target flame fullness, repeating the step of obtaining the pulverizing constraint sludge blending rate; Based on the combustion constraint blending rate, the actual efficiency of the boiler is obtained, and according to the actual efficiency and a second preset value, the furnace efficiency constraint blending rate is obtained; the furnace efficiency constraint blending rate is obtained according to the actual efficiency and the second preset value, including: Determining whether the actual efficiency decrease is less than or equal to the second preset value; If the actual efficiency decrease is less than or equal to the second preset value, the combustion constraint blending rate is used as the furnace efficiency constraint blending rate; If the actual efficiency decrease is greater than the second preset value, the steps of obtaining the pulverizing constraint sludge blending rate and the combustion constraint blending rate are sequentially repeated; Based on the furnace efficiency constraint blending rate, the pollutant emission value of the boiler is obtained, the emission constraint blending rate is obtained according to the pollutant emission value, and the maximum blending rate of the coal-fired coupled sludge is determined based on the emission constraint blending rate; the obtaining of the emission constraint blending rate according to the pollutant emission value includes: Determining whether the pollutant emission value is less than or equal to the pollutant emission standard value; If the pollutant emission value is less than or equal to the pollutant emission standard value, the furnace efficiency constraint blending rate is used as the emission constraint blending rate; If the pollutant emission value is greater than the pollutant emission standard value, the steps of obtaining the pulverizing constraint sludge blending rate, obtaining the combustion constraint blending rate, and obtaining the furnace efficiency constraint blending rate are sequentially repeated; The determining of the maximum blending rate of the coal-fired coupled sludge based on the emission constraint blending rate includes: Determining whether the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the maximum; If the emission constraint blending rate is the emission constraint blending rate when the sludge blending amount is the largest, the emission constraint blending rate is used as the maximum blending rate of the coal-fired coupled sludge; If the emission constraint blending rate is not the emission constraint blending rate when the sludge blending amount is the largest, the steps of obtaining the pulverizing constraint sludge blending rate, the combustion constraint blending rate, the furnace efficiency constraint blending rate and the emission constraint blending rate are repeated in sequence.

2. The method for determining the maximum blending rate of coal-fired coupled sludge according to claim 1 is characterized in that: The obtaining of the theoretical maximum sludge blending rate when the decrease in the theoretical efficiency of the boiler is less than or equal to the first preset value comprises: Obtaining elemental analysis and industrial analysis results of the sludge and the coal; Based on the elemental analysis and industrial analysis results, the sludge is mixed with the coal at different theoretical blending ratios to obtain different mixed fuels; Obtaining theoretical calorific values ​​of different mixed fuels and using them as different theoretical efficiencies of the boiler; A first difference between the different theoretical efficiencies and the standard theoretical efficiency is obtained, and the theoretical blending ratio corresponding to the maximum first difference that is less than or equal to the first preset value is taken as the theoretical maximum sludge blending ratio.

3. The method for determining the maximum blending rate of coal-fired coupled sludge according to claim 1 is characterized in that: The amount of sludge entering the coal mill is increased by 0.1-1 t / h each time.

4. The method for determining the maximum blending rate of coal-fired coupled sludge according to claim 1 is characterized in that: The pollutants include carbon monoxide in the flue gas, nitrogen oxides in the flue gas and heavy metals in the ash.

5. Application of the method for determining the maximum blending ratio of coal-fired coupled sludge as described in any one of claims 1 to 4 in the field of sludge disposal.

Images