Simple method for determining moisture of coal powder
Technical Field
The invention relates to the technical field of pulverized coal moisture selection, in particular to a simple calculation method for determining pulverized coal moisture, which is suitable for a medium-speed mill and steel ball milling direct-blowing or medium-storage pulverizing system for hot air drying.
Background
The drying output calculation of the coal pulverizing system is one of important indexes required by the type selection of a coal mill and the design of a boiler, the moisture of the coal powder participating in the drying calculation is usually obtained through related experience, and if the moisture of the coal powder is selected to be too large, the problem of insufficient drying or conveying capacity of the coal pulverizing system designed according to the method occurs in the actual operation; on the contrary, if the moisture content of the pulverized coal is too small, the cold air doping amount of the designed powder making system is too large in actual operation, so that the exhaust gas temperature of the boiler is increased, and the boiler efficiency is reduced. Therefore, the selection of the moisture of the pulverized coal is an important parameter for the design of a pulverizing system and the design of a boiler, and the safe and economic operation of a unit is directly influenced.
At present, the selection of the moisture of the pulverized coal is mainly based on the Chinese electric power industry standard DL/T466-2017 power station coal mill and powder making system model selection guide rule, and the guide rule clearly stipulates that the moisture of the pulverized coal is mainly related to the total moisture of coal and the outlet temperature of the coal mill. For the direct-blowing and intermediate storage pulverizing system, when the hot air is dried and the anthracite, the poor coal and the bituminous coal are ground, the water content of the pulverized coal is selected according to the attached drawing in the standard DL/T466-2017 of the Chinese power industry.
There are also data indicating that the general range of values for coal fines moisture is:
Mpc=(0.5~1.0)Mad
wherein M ispcIs the water content,%, M of coal powderadIs the air-dry basis moisture of the coal sample.
On one hand, the coal powder moisture is determined in a graph checking mode, the moisture is complicated, the deviation is easily caused, and the coal powder moisture detection method is not convenient to apply to intelligent coal blending and burning software. On the other hand, the coal mill drying output design is carried out according to the coal dust moisture selected from the drawings in the Chinese electric power industry standard DL/T466-2017, most of the coal mill drying output design can meet the unit operation requirements, but the problem of insufficient drying output occurs in the actual operation of some units burning high-moisture coal or processing coal types such as coal slime, semicoke and the like, tests show that the air-dry basis moisture of the coal is low, and the coal dust moisture is lower than the selected value according to the drawings in the Chinese electric power industry standard DL/T466-2017.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a simple method for determining the moisture of coal powder, which is suitable for a medium-speed mill and a steel ball milling direct-blowing or medium-storage pulverizing system. The calculation method is simple, convenient and quick, has high calculation precision, and can be used for calculating the drying output of the intelligent power plant.
In order to achieve the purpose, the invention adopts the following technical scheme:
a simple method for determining the moisture content of coal dust comprises the following steps:
the first step is as follows: according to the calculation of the total moisture M of the coal sampletjThe values, high and low, are determined by comparison in Table 1, and the total moisture near but higher than the calculated total moisture of the coal sample is defined as the high moisture Mt1(ii) a The total moisture near but slightly lower than the calculated total moisture of the coal sample is defined as the low moisture Mt2(ii) a High moisture M in Table 1t1Corresponding coefficient A1、B1、C1Low water content Mt2Corresponding coefficient A2、B2、C2(ii) a Total moisture MtjHigh moisture Mt1And low water content Mt2The units are all percent;
TABLE 1 ABC coefficient values at different moisture
Total moisture Mt%
|
Coefficient A
|
Coefficient B
|
Coefficient C
|
10
|
0.0063
|
-0.8517
|
29.35
|
15
|
0.0026
|
-0.5015
|
24.882
|
20
|
0.0041
|
-0.8092
|
42.304
|
25
|
0.0034
|
-0.7072
|
41.662
|
30
|
0.0039
|
-0.837
|
50.91
|
35
|
0.005
|
-1.0737
|
66.417
|
40
|
0.0055
|
-1.1946
|
76.313
|
45
|
0.0096
|
-1.7788
|
104.46
|
50
|
-0.0086
|
0.4642
|
40.948
|
55
|
0.0003
|
-0.6016
|
77.667
|
60
|
-0.0062
|
0.2401
|
55.987 |
Secondly, according to the high-moisture corresponding coefficient A1、B1、C1And a low moisture coefficient of2、B2、C2Determining and calculating coefficient A under coal sample total moisture correspondence by using an interpolation methodj、Bj、Cj;
Thirdly, combining the outlet temperature T of the coal mill2Obtaining the calculated coal powder moisture M of the coal samplepcj;
Mpcj=Aj×T2 2+Bj×T2+Cj
Fourthly, determining the final moisture M of the coal dustpcz;
When outlet temperature of coal mill>Comparing the calculated coal powder moisture M of the coal samples at 60 DEG CpcjAnd air-dried basis moisture Mad,
When M ispcj<MadWhen M is in contact withpcz=Mpcj
When M ispcj≥MadWhen M is in contact withpcz=Mad
When outlet temperature of coal mill<At 60 ℃ Mpcz=Mpcj。
Compared with the prior art, the invention has the following advantages:
the invention relates to a simple method for determining the moisture of coal powder, which is suitable for a medium-speed mill and a steel ball milling direct-blowing or medium-storage pulverizing system for hot air drying. The invention fully considers the characteristics of influence of hot air drying on the moisture of the pulverized coal, and has the following advantages:
(1) the mode of checking the graph is converted into a digital calculation method, so that on one hand, the precision is improved, and on the other hand, convenience is provided for the thermodynamic calculation of a pulverizing system of an intelligent power plant;
(2) the invention fully considers the coal quality characteristics of the coal sample, namely the influence of the air-dry-based moisture on the moisture of the coal powder;
(3) the method finally obtains the rule of selecting the moisture of the pulverized coal through the field tests of a plurality of power plants, is closer to the actual power plants, can better guide the design of a pulverizing system of the power plants, and particularly for high-moisture east-west coal, the sufficient drying output can not only improve the load carrying capacity of a unit, but also ensure the outlet temperature of a coal mill and improve the operation safety of the unit. Meanwhile, the method is also suitable for special coal types such as processed coal slime, semicoke and the like.
Detailed Description
Example 1 Total moisture Mt28% dry basis moisture MadCoal dust moisture M of 12.00 percent east Junggar coal at the outlet temperature of a coal mill of 65 DEG Cpcz
The first step is to calculate the total moisture M of the coal sampletThe values in Table 1 for high and low moisture are determined by comparison, close to but higher than the calculated total moisture of the coal sampleIs defined as high moisture; low moisture is defined as near to, but slightly below, the calculated total moisture of the coal sample. High moisture corresponds to coefficient A in Table 11、B1、C1Coefficient A corresponding to low moisture2、B2、C2. Total moisture MtThe unit is%.
TABLE 1 ABC constant values at different moisture levels
Total moisture Mt%
|
Coefficient A
|
Coefficient B
|
Coefficient C
|
10
|
0.0063
|
-0.8517
|
29.35
|
15
|
0.0026
|
-0.5015
|
24.882
|
20
|
0.0041
|
-0.8092
|
42.304
|
25
|
0.0034
|
-0.7072
|
41.662
|
30
|
0.0039
|
-0.837
|
50.91
|
35
|
0.005
|
-1.0737
|
66.417
|
40
|
0.0055
|
-1.1946
|
76.313
|
45
|
0.0096
|
-1.7788
|
104.46
|
50
|
-0.0086
|
0.4642
|
40.948
|
55
|
0.0003
|
-0.6016
|
77.667
|
60
|
-0.0062
|
0.2401
|
55.987 |
When the total moisture Mt of the coal sample is calculated to be 28%, the corresponding high moisture content is 30%, and the corresponding high moisture coefficient A is1=0.0039、B1=-0.837、C150.91; corresponding to a low water content of 25%, corresponding to a low water content coefficient A2=0.0034、B2=-0.7072、C2=41.662;
Secondly, according to the high-moisture corresponding coefficient A1、B1、C1And a low moisture coefficient of2、B2、C2Determining and calculating coefficient A under coal sample total moisture correspondence by using an interpolation methodj、Bj、Cj;
Thirdly, combining the outlet temperature T of the coal mill2(DEG C) obtaining the calculated coal dust moisture M of the coal samplepcj;
Mpcj=Aj×T2 2+Bj×T2+Cj=0.0037×652-0.7851×65+47.2108=11.81
Fourthly, determining the final moisture M of the coal dustpcz;
When outlet temperature of coal mill>Comparing the water content M of coal powder at 60 DEG CpcjAnd air-dried basis moisture Mad,
When M ispcj<MadWhen M is in contact withpcz=Mpcj
When M ispcj≥MadWhen M is in contact withpcz=Mad
When outlet temperature of coal mill<At 60 ℃ C,Mpcz=Mpcj.
Outlet temperature of this coal mill>M of Oriental coal at 60 deg.CpcjWhen the ratio is 11.81%, M ispcj<MpcsFinally determined moisture M of the pulverized coalpcz=Mpcj=11.81%。
Example 2 Total moisture Mt22% water content on an air-dry basis MadCoal dust moisture M of coal slime with 5.00 percent at 70 ℃ of coal mill outletpc
The first step is to calculate the total moisture M of the coal sampletThe numerical values, high moisture and low moisture are determined by a comparison method in table 1, and the high moisture is defined as the value close to but higher than the calculated total moisture of the coal sample; low moisture is defined as near to, but slightly below, the calculated total moisture of the coal sample. High moisture corresponds to coefficient A in Table 11、B1、C1Coefficient A corresponding to low moisture2、B2、C2. Total moisture MtThe unit is%.
TABLE 1 ABC constant values at different moisture levels
When the total moisture Mt of the coal sample is calculated to be 22 percent, the corresponding moisture content is 25 percent, and the corresponding moisture content coefficient A is high1=0.0034、B1=-0.7072、C141.662; corresponding to a low water content of 25%, corresponding to a low water content coefficient A2=0.0041、B2=-0.8092、C2=42.3040;
Secondly, according to the high-moisture corresponding coefficient A1、B1、C1And a low moisture coefficient of2、B2、C2Determining and calculating coefficient A under coal sample total moisture correspondence by using an interpolation methodj、Bj、Cj;
Thirdly, combining the outlet temperature T of the coal mill2(DEG C) obtaining the calculated coal dust moisture M of the coal samplepcj;
Mpcj=Aj×T2 2+Bj×T2+Cj=0.0038×702-0.7684×70+42.072=6.98%
Fourthly, determining the final moisture M of the coal dustpcz;
When outlet temperature of coal mill>Comparing the water content M of coal powder at 60 DEG CpcjAnd air-dried basis moisture Mad,
When M ispcj<MadWhen M is in contact withpcz=Mpcj
When M ispcj≥MadWhen M is in contact withpcz=Mad
When outlet temperature of coal mill<At 60 ℃ Mpcz=Mpcj.
Outlet temperature of this coal mill>M of coal slime at 60 DEG CpcjWhen the ratio is 6.98%, then Mpcj≥MadFinally determined moisture M of the pulverized coalpcz=Mad=5.00%。