Xing Xiuyun 1, 2, Zhang Kerui1
(1. National Coal Quality Supervision and Inspection Center, Beijing 100013, China; 2. Coal Analysis Laboratory, Coal Science Research Institute, Beijing 100013, China)
Abstract: Based on the characteristics of the composition of ash composition of solid biomass fuel and the composition of coal ash, the test scheme of determination of ash composition of solid biomass fuel was put forward by referring to national standard GB / T 1574 and EU standard DD CEN / TS 15290. The feasibility of the determination of the method and the accuracy of the assessment, for the development of solid biomass fuel ash composition of the national standard for technical preparations.
Solid biomass energy as a renewable resource, its development and utilization has attracted the attention of the world.One solid biomass energy is one of the main uses of its direct combustion power generation, China, the European Union, the United States and other countries are built Combustion of solid biomass fuel for power plants.
The ash component index of solid biomass fuel is a necessary indicator for the direct combustion power generation of solid biomass fuel. Based on this index, the melting and slagging habits of solid biomass fuel ash can be predicted to guide the boiler process. Countries are actively pursuing the development of experimental methods for the study of solid biomass fuels and the development of relevant standards, in which EU member countries are at the forefront. In 2006, the EU has issued a series of solid biomass fuels in the form of a draft technical specification study And the first to put forward the development of solid biomass fuel ISO standards.Currently for the detection of biomass components of biomass fuels are mostly referred to GB / T 1574 "coal ash composition analysis method." Although the composition of solid biomass fuel ash Composition and coal ash composition is roughly the same, but in the actual work found that the existence of the two components of the content of the difference between the level of significant differences, and some testing methods are adapted to the solid biomass ash composition determination, remains to be further studied, it is necessary to establish Standard for determination of ash composition for solid biomass fuels.
The technical basis of the study is based on the national standard GB / T 1574 "coal ash composition analysis method" [1], And the method for the determination of the ash composition of solid biomass fuels, in conjunction with the European Standard 'DD CEN / T S 15290: 2006 Solid biofuels-Determination of major elements'.
1 method to select and determine the basis
1.1 Ashing temperature
Ashing the temperature is the basis of ash composition analysis, the ashing temperature is different, the solid biomass fuel combustion and decomposition of different degrees, and thus the final determination of ash composition may be different, in order to make the results comparable, ashing temperature EU standard, the ashing temperature of this test is determined to be 550 ℃.
1.2 Determination of the project
According to GB GB / T 21923-2008 "Solid Biomass Fuel Inspection General" provisions [3], For the measurement of gray elements in the determination of the provisions of the SiO 2, Al 2O3, Fe 2O3, CaO, MgO, K 2O, Na 2O, P 2O5, TiO 2, SO 3Project a total of 10, different from the EU standard 9, more than a SO 3project.
1.3 Determination of method selection
(1) Fe 2O3, CaO, MgO, K 2O, Na 2O, P 2O5Determination of coal used in the national standard GB / T 1574 in the relevant methods, the use of HF2HClO4 decomposition of solid biomass fuel ash samples, and then atomic absorption method for the determination of Fe 2O3, CaO, MgO, K 2O, Na 2O5(Consistent with EU standards), P 2O5Determination of the use of phosphorus molybdenum blue spectrophotometric method.In view of the solid biomass fuel ash composition and coal ash similar to the above methods are very mature coal ash composition analysis method is also applicable to solid biomass fuel ash Fe 2O3, CaO, MgO, K 2O, Na 2O, P 2O5The determination of several indicators because of solid biomass fuel ash in the CaO content are mostly in 10% to 40%, K 2O content is mostly in 10% to 30%, P 2O5Content of most of the 5% to 10%, so much higher than the content of ordinary coal ash detection range, therefore, in the quality of the sample weighed on the EU standard requirements of the amount of 0.05g and GB GB / T 1574 sample volume 0.10g, the results show that the amount of 0.05g is more appropriate, on the one hand to simplify the operation of the experiment, on the other hand can reduce the dilution caused by the dilution error.
(2) SiO 2, Al 2O3, TiO 2The determination of the three indicators using GB / T 1574 "coal ash composition analysis" in the semi-microanalysis method, that is, with sodium hydroxide melting solid biomass fuel ash samples, and then acidification of hydrochloric acid, constant volume, respectively, Solution, silicon molybdenum blue spectrophotometric method 2Determination of Al by Fluoride Instead of EDTA Complexometric Titration 2O3Determination of TiO by Diantipyrylmethane Spectrophotometry 2, The above methods are coal ash analysis of the classical chemical analysis method, due to solid biomass fuel ash in the SiO 2, Al 2O3, TiO 23 indicators of the level of content and coal ash content of the equivalent, so the use of test conditions consistent.
(3) SO 3Determination of quasi-selected GB / T 1574 in the classical chemical analysis method barium sulfate mass spectrometry and Coulomb potentiometric titration, solid biomass fuel ash in the chlorine content is relatively high (1.70% ~ 5.44%), the Coulomb method, the chlorine Determination of SO by Coulometric Method 3There is interference, so the need for Coulometric determination of solid biomass fuel ash in the SO 3Feasibility study.
2 Test procedure
A variety of biomass fuels include 30 to 40 samples of rice husk, bark, branches, straw, sawdust, corn cob, corn stalks, sugarcane, grass, wood and so on. According to the selected method, Solid biomass fuel ash samples were repeated determination of the data results for statistical processing, on the one hand the Coulometric determination of SO 3The feasibility of the selected test method on the one hand to assess the accuracy.
The specific test steps are as follows:
(1) The sample was completely ashed at 550 ° C.
(2) Weigh 0.1g ash sample, according to GB / T 1574-2007 in the semi-microanalysis method for gray-like treatment, and test the preparation of mother liquor, and then were measured by silicon molybdenum blue spectrophotometry SiO 2Determination of Al by Fluoride Instead of EDTA Complexometric Titration 2O3Determination of TiO by Diantipyrylmethane Spectrophotometry2.
(3) Weigh 0.05g of gray sample, according to GB / T 1574-2007 atomic absorption method of the analysis steps for gray-like treatment and testing of mother liquor preparation work from the mother liquor were divided into 2mL solution (for CaO, MgO), 10 mL of solution (for Fe 2O3), 1 mL of solution (for K) 2O), 10 mL of solution (for Na 2O) to 100 mL volumetric flask, according to the provisions of GB / T 1574 were measured Fe 2O3, CaO, MgO, K 2O, Na2O.
(4) 1 mL of the solution was taken from the mother liquor developed in step (3) into a 50 mL volumetric flask, and the P (P) was determined by the phosphomolybdenum blue spectrophotometric method according to GB / T 1574-20072O5.
(5) SO 3Respectively, according to GB / T 1574-2007 barium sulfate mass method and coulometric titration method were tested.
Evaluation of each method
Determination of SO by Coulometric Titration 3The feasibility of the two methods (barium sulfate mass method and coulometric titration) test results between the existence of significant differences between the test formula is as follows:
According to the above formula (1), (2), (3) calculation, 30 kinds of samples of two test methods (Coulomb titration results minus barium sulfate mass method results) the average difference d = -0.50, the difference between the standard value Sd = 0.44, t = 5.21, the table was t0.05, 20 = 2.09, due to t> t0.05, 20, indicating that there are significant differences between the two methods, coulometric titers were lower than the barium sulfate mass method , The difference between the two methods of the value of 95% confidence interval of 0.42 ~ -1.42, the maximum end value is much greater than the national standard GB / T 1574-2007 specified reproducibility critical difference of 0.60, so the two methods can not replace each other, May be the solid biomass fuel ash in the high content of chlorine on the Coulometric determination of sulfur dioxide interference, so the coulometric titration method is not suitable for solid biomass fuel ash in the determination of sulfur dioxide. Solid biomass fuel ash in the sulfur trioxide Determination of GB / T 1574-2007 should be used in the barium sulfate mass method.
3.2 Determination of precision of each measurement method
The precision assessment formula is as follows:
3.2.1 SiO 2Determination of the accuracy of the method
A total of 37 different kinds of biomass samples were selected and tested from 2.66% to 87.00%. Seven of the samples were not more than 10.00%, 20 samples were measured at 10.00% ~ 60.00%, 10 samples Measured value greater than 60.00%, due to a wide range of measured values, so the use of sub-statistical data were processed separately.
When SiO 2When the content is less than 10.00%, the standard deviation Sr = 0.047 and the repeatability r = 0.13 are calculated in the formulas (4) and (5). When 10.00%60.00%, the standard deviation of the formulas (4) and (5) is 0.2 = 0.275 and the reproducibility limit r = 0.78.
The repeatability limit of the segmentation statistics is less than the repeatability limit specified in GB / T 1574-2007, so the precision of the test method is good.
3.2.2 Al 2O3Determination of the accuracy of the method
37 different kinds of biomass samples Al 2O3In the measured value, 36 of which are less than 10%, only one of the measured values is greater than 10% to 11.54%, the measured range is 0.53% ~ 11.54%, by the precision evaluation formula: standard deviation Sr = 0.068, repeat The limit of r = 0.19, the repeatability limit is less than the repeatability limit of 0.60 specified in GB / T 1574-2007, so the method has good precision.
3.2.3 Fe 2O3Determination of the accuracy of the method
37 Fe 2O3In the test data, 35 values were less than 5.00% and the measurement range was 0.32% ~ 4.74%. Only two measured values were more than 5.00%, 6.40% and 7.75% respectively. Therefore, the precision assessment was carried out with 5.00% . The standard deviation Sr = 0.052 for the repeated determination of 35 experimental values less than 5.00%, the reproducibility limit r = 0.15; when only greater than 5.00%, the only two measurements of repetition difference were 0.22 and 0.03, respectively, The results are less than the precision values specified in GB / T 1574-2007, so the method has good precision.
3.2.4 Precision assessment of CaO determination method
Among the 37 CaO test data, the seven measurement ranges were less than 5.00% (content range 0.98% ~ 4.91%), and the range of 7 measurements was 5.00% ~ 10.00% (content range 5.34% ~ 7.72%), 23 The measured value is greater than 10.00% (content range of 10.50% ~ 43.16%) .When CaO ≤ 5.00%, 7 samples of the repeated determination of the difference is less than 0.20 (this value is the standard GB / T 1574 CaO ≤ 5.00% of the repeatability limit); when 5.00% When the CaO content is greater than 10.00%, the calculated reproducibility limit r = 0.90, slightly higher than the repeatability limit 0.80 specified in GB / T 1574-2007, and 23 samples of more than 10.00% The content of CaO in solid biomass fuel ash is generally in the high content range, which is much larger than that of coal ash, Linear correlation, so the range of precision value is slightly larger than the coal ash precision value belongs to the normal situation, the method does not exist on the test value.
3.2.5 Precision evaluation of MgO determination method
The content of MgO in the five samples is less than 2.00%, the content range is 0.29% ~ 1.99%, the repeatability is less than 0.20 in the range of coal ash. The content of 32 samples is more than 2.00%, the content range is 2.17% ~ 10.96% Of the repeatability limit of 0.17, less than the coal ash standard of 0.20, so the method of good precision.
3.2.6 K2O measurement method
37 samples K 2O content range of 3.96% ~ 25.72%, of which 13 samples less than 10.00%, 24 samples greater than 10.00%, it can be seen, solid biomass fuel K 2O content is generally higher than its content in coal ash, and most of the high value range, so coal ash K 2The segmentation accuracy of O is not applicable to solid biomass fuels, with a repeatability limit of 0.22, greater than 10.00%, with a repeatability limit of 0.64, based on 10.00% Biomass fuels 2O content of the case of high, this method is good precision.
3.2.7 Na 2O measurement method
14 samples of Na 2O content of less than 1.00% (content range 0.21% ~ 0.78%), 23 samples Na 2O content greater than 1.00% (content range of 1.11% ~ 18.90%), calculated when less than 1.00% of the repeatability limit of 0.08, when greater than 1.00% repeatability limit of 0.19, are less than GB / T 1574-2007 specified repeat The limits of 0.10 and 0.20, so the method of good precision.
3.2.8 P2O5Determination of the accuracy of the method
5 samples 2O5The content is less than 1.00%, the content range is 0.18% ~ 0.94%, the repeatability is less than the deduction limit of the coal ash standard; when 1.00%
2O5≤5.00%, the content range is 1.02% ~ 4.00%, 23 samples in this range, the calculated repeatability limit of 0.08, less than the ash standard 0.15; 9 samples P 2O5The content is more than 5.00%, the content range is 5.38% ~ 14.04%, the calculated repeatability limit is 0.32, so the method has good precision.
3.2.9 Precision evaluation of TiO2 determination method
The TiO2 content of 37 samples is less than 1.00%, the content range is 0.00% ~ 0.55%, the calculated repeatability is 0.03, which is less than 0.10 of the coal ash standard, so the precision of the method is good.
3.2.10 SO 3Determination of the accuracy of the method
18 samples were selected for SO 3Assay, there are 14 samples of SO 3Content of less than 5.00%, content range of 0.60% to 4.15%, there are four samples of SO 3Content of more than 5.00%, content range of 5.56% ~ 7.04%. When SO 3Not more than 5.00%, the repeatability limit of 0.08, less than the coal standard of 0.20; when the SO 3When the temperature is more than 5.00%, the repeated measurement of the four measurements is less than 0.30 of the coal ash standard, so the method has good precision.
4 technical summary and project innovation
The research project is based on the GB / T 1574-2007 "coal ash composition analysis method", and the determination of the ash composition of solid biomass fuel is made with reference to the EU standard 'DD CEN / TS15290: 2006 Solid Biofuels-Determination of major elements' Methods, the main research results are reflected in the following aspects.
(1) For the characteristics of solid biomass fuels, the ashing temperature of the solid biomass fuel ash component was determined to be 550 ° C.
(2) The determination of SO in solid biomass fuels by coulometric titration was investigated 3The feasibility of the conclusion is not feasible.
(3) for solid biomass fuel ash samples of CaO, K 2O, P 2O5High content of more cases, the determination of Fe 2O3, CaO, MgO, K 2O, Na 2O, P 2O56, the sample size will be changed from 0.1g to 0.05g.
(4) Determination of the selected method (atomic absorption method for the determination of Fe 2O3, CaO, MgO, K 2O, Na 2Determination of phosphorus by spectrophotometric method 2O5Spectrophotometric Determination of SiO in Lithium Molybdenum Blue 2Determination of Al by Fluoride Instead of EDTA Complexometric Titration 2O3Determination of TiO by Diantipyrylmethane Spectrophotometry 2Determination of SO by barium sulfate mass spectrometry 3), The conclusion is that the precision of each method is good and the method is accurate and reliable.
The innovation of the project is that the "test method of ash composition of solid biomass fuel" has not only considered the domestic inspection situation, but also examined the relevant international standards, the method is easy to facilitate the promotion of the characteristics of the The study fills the gaps in the field of research in this area.
references:
'1'GB / T 1574-2007, coal ash composition analysis method' S '.
'2'DD CEN / TS15290: 2006 Solid Biofuels-Determination of major elements''.
'3'GB / T 21923-2008, General rules for the determination of solid biomass fuels' S'.
