1 the concept and content of coal analysis
Coal is a very complex nature of solid combustible material, due to the formation of the original material and the different sedimentary environment, the nature and composition of coal are also different. In order to further study the structure of coal, the nature of coal and the change rule of coal quality were studied. In order to determine the composition and properties of coal processed products, the fast and on-line analysis of the coal production and processing utilization were established.
Coal is widely used, the use of a variety of ways, process and coal equipment to the nature of the coal and special technical requirements. Therefore, the analysis method of coal should have the properties that can reflect the characteristics of the test object, and can be used to distinguish the different properties of the sample. The method is accurate and reproducible. The method and equipment are simple and easy to be standardized. In addition to the above basic requirements, the coal test method has many special requirements and characteristics, such as the characteristics of the coal is complex and changeable, and the test method is highly standardized, the sample is not homogeneous, the sample composition and the properties of the samples are large.
In view of the complexity and variability of coal and the different requirements of different uses, the results of the analysis of various coal quality and the data have a common understanding, and do not produce misunderstanding. China has also formulated the national standard of coal analysis test method. National standards from the coal sample determination method, reagent, reagent solution preparation, analysis of the results of the calculation and expression, precision, symbol, analysis and report of the value of a variety of "base" conversion, etc., have made a unified provisions.
1.1 coal sample
Coal sample is a representative sample of a representative sample of a large number of coal products. The average quality of the batch is obtained from a large number of coal products. Must be in accordance with the provisions of sampling, sample preparation and analysis of laboratory tests, to obtain a variety of specific indicators of analysis. Coal quality analysis, because of the particularity of coal itself and different indicators of coal samples have different technical requirements, to get a representative and more accurate analysis results, in the coal sample to take and prepare a strict operation method.
1.2 determination
In the analysis of coal quality, in addition to the special requirements, each of the analysis tests to deal with the same coal samples for the two parallel, commonly referred to as repeated measurement or parallel determination. The difference between the two values is not more than the specified limit that allows the error "T", the arithmetic mean as a result of the third measurements, the average value of the 3 measurements is fourth times less than 1.2T, and the average value of the 4 test is less than 1.3T, and the average value of 3 measurements is 3. If the above conditions are not reached, then should abandon all the results, and check the instrument and operation, and then re - determination.
1.3 reagent
Chemical reagent is usually divided into the analysis of chemical reagents, reagent, reagent and standard reagent gr. As with the general chemical analysis method, the reagent used in the analysis of coal quality is not high, and can be used as a standard solution for titration. In the coal analysis, the water used in the water is distilled water or the same purity of water, the requirements of strict analysis, sometimes need to be treated by anion exchange resin.
1.4 solution
In the analysis of coal quality, except for the solution of the solute, the solution containing a certain amount of solute should be determined by the solution. The concentration of the solution is expressed as the amount of substance in the unit volume solution.
1.5 precision of measurement method
The precision of the method in the analysis of coal is expressed as the repeatability and reproducibility.
Repeatability, which is the same as the one in the laboratory, refers to the critical value of the same analysis of coal samples and the difference of the results measured by the same instrument in the short term.
Reproducibility of different laboratory of allowable error is defined in different laboratories, from the coal samples shrinkage aliquot out of the final stage of the coal samples with representative sample of repeated measurement results of average value (in a certain probability of critical value.
1.6 results calculation and expression
Determination results of coal quality analysis of general according to four homes to five data rounding rules, behind the effective number of where the bottom of the first digit is greater than 5 in the an increase by 1, less than 5 is rounding; where the bottom number behind the first digit equal to 5, and after five figures are not all zero, in the top 5 single digit increase 1; such as 5 behind the figures all is zero, and 5 in front of a digit is odd in 5 before
1.6 results calculation and expression
Determination results of coal quality analysis of general according to four homes to five data rounding rules, behind the effective number of where the bottom of the first digit is greater than 5 in the an increase by 1, less than 5 is rounding; where the bottom number behind the first digit equal to 5, and 5 behind the numbers are not all zero. In the top 5 single digit increase 1. Figures such as 5 behind the all zero, and 5 in front of a digit is odd, in five of the first digit plus 1; such as before an even (including zero) will be 5 rounding. In intends to abandon the numbers. If two or more numbers, can not be carried out continuously repeated revision should be according to plans to give up the size of the numbers on the left of the first digit, according to the provisions of a rounding out the determination results. 2 error causes
Although modern analytical instruments and techniques have been widely used in the analysis of coal quality, it is the result of the analysis of the quality of coal by using instruments and drugs, and after certain operation steps such as weighing, melting, dissolving and separation. In the above process, even the most skilled laboratory personnel, the use of the most sophisticated equipment and purity of the highest reagent, but also due to the limitations of measuring instrument accuracy, the sensitivity of human sensory organs, and the relative nature of the purity of reagents and so on, and can not obtain the absolute accuracy of the test results. There is always a difference between the results and the real value of the measurement. The analysis error can be divided into two categories: systematic error and random error.
2.1 systematic error
The system error is due to the difference between the fixed cause, these errors are close to the value of the same symbol (positive or negative), and often repeat the same. There are 3 kinds of causes of system error: one is the instrument. For example due to the use of uncorrected weight weighing, or arm of arm length scales ranging; another example is the use of uncorrected buret will lead to the system error. Two is the reagent. For example, reagent impurities or distilled water containing impurities caused by the same symbol, the value of repeated error. Three is the measurement method. For example, the error caused by the point and the end point is not the same as in the acid-base titration.
2.2 accidental error
Accidental error is not fixed, can change, in a few times, there is a large, small, positive, negative. Although the accidental error does not appear regularly as the systematic error, it can be found that the random error is found to be a small number of errors. The cause of accidental error is roughly the following two factors: first, the operator's negligence. Such as in the burette readings, since the last one reading (less than 0.1 ml) is to estimate the repeatedly estimating different values can be caused by accidental errors. Two is an accident factor. For example, the change of environmental temperature, current, voltage instability, etc., these are the conditions that the operator can not control, they will cause accidental error.
3 method of reducing error
To understand the cause of the error in the coal analysis, we can take the method to reduce the error.
3.1 systematic error
Because the system error is caused by the instrument, reagent, and measurement method, we must use the calibrated instrument in the test. Such as the weight of the balance, and so on arm balance arm length and electronic balance, thermocouple, and so on a regular identification, periodic calibration sample testing, so as to control the operation of the instrument. Reagents must be used in the analysis of pure reagents, containers must be clean, to ensure that distilled water does not contain impurities. In measurement methods, such as acid-base titration, as a result of using different indicators, can come to different end point, of course, the end of the titration end point will not happen and so when the point is consistent, so the use of indicators will become an important issue. This requires us to test several times in the test, select the pH value of the color range and so when the point pH close to the indicator can reduce the titration error.
3.2 accidental error
Because of the particularity of coal and different indicators of coal samples with different technical requirements, representative and accurate analysis results are obtained. In the coal samples were taken and prepared should be strictly in accordance with the provisions of the state of coal sample take, preparation, laboratory, such as in the wagon, coal flow sampling, be sure to do uniform, does not leak, sample weight not less than prescribed weight etc.. As the coal is a kind of porous structure of the material, the water in the air and the environment has a great influence on the actual quality of the sample. In order to avoid the difference of air humidity in different time and area, the coal quality analysis result is obviously different, and the indexes such as ash, volatile, element analysis and calorific value are all the best. In the actual work, such as can not be achieved at the same time, it should be in a short period of time, that is, the coal sample water does not change significantly the period (up to 7 days) within the. After the coal sample is made, the container should be loaded into the container, usually with a glass bottle with a close grinding mouth or plastic plug. Before weighing the coal sample
Before weighing, the coal sample should be fully mixed, and then carry out, test, and at the same time in the broken, shrinkage must be operated according to the regulations.
At present, due to the use of modern instrument, may reduce the subjective estimation of the data, but sometimes still need estimates, such as in the burette readings, estimates for the last bit readings by repeatedly estimating different may cause accidental error, which requires our operation personnel to a kind of inertia of standard readings, as far as possible to reduce the error.
Due to environmental changes, current, voltage and other factors caused by the error, we can try to make the laboratory in a relatively closed environment, the use of the current more advanced equipment, so that the temperature and humidity of the laboratory in a relatively stable environment, you can reduce the error caused by this.
Accidental error and systematic error, after repeated measurements can be found in the absolute value of the positive and negative numbers appear the same, therefore, the accidental error can be reduced to a close by multiple parallel measurement.
Accuracy is the measure of the value and the true value of the degree of accuracy, we want to get higher accuracy, must make the system error to a minimum, in the premise of minimizing the system error, minimize accidental error, so that can reduce the error in coal analysis.
Due to the particularity of coal, the coal quality analysis test method is more powerful. Although the error in the measurement process is very difficult to avoid, but as long as the skilled master operation technology, carefully in accordance with the national standards for work, you can make the error tends to be minimal. Therefore, the coal quality analysis workers should be good at judging the correctness of the analysis results, find out the cause of the error, to be corrected, so that the error of coal analysis in the minimum.