Principle of Establishment of Wood Particle Fuel Inspection Method

Based on the analysis of the quality characteristics of wood pellet fuel and coal (solid fossil fuel), the basic principle of the method of cutting wood pellet fuel is proposed, including mining and sample preparation.

Biomass energy has the dual characteristics of renewable and environment-friendly, and its development and utilization has become a hot research topic to solve the energy crisis and environmental pollution, causing the world's attention. Sawdust pellet fuel direct combustion or co-firing with coal, both at home and abroad have many institutions in the research and development and utilization. Europe has a lot of burning biomass fuel power plant built and normal operation, accumulated some more mature experience. China in recent years has also actively carried out research and development work in this field, to June 2008, China has about 60 or so burning biomass fuel power plant built power generation. For the full and efficient use of biomass energy, the further development of wood pellet fuel power generation and other application technology, must be established as soon as possible for the characteristics of wood pellet fuel inspection methods and related standards. At present, the International Organization for Standardization has not yet established a standard for the inspection of wood chip fuel characteristics. Only the EU and the United States have issued a series of draft technical specifications (DD) and standards for trial on wood pellet fuel inspection.

Because of the application and development of the sawdust pellet fuel in China, it has not yet established a complete inspection method and standard of wood pellet fuel. It has become a bottleneck in the development of high-level development of wood pellet fuel application technology. It is necessary to develop a special, A series of inspection standards for particulate fuels. Over the past two years, with the support of the National Standards Committee, the National Coal Inspection Center has started the research work on the "inspection general rule" from the sawdust particle fuel to a series of "test methods". National Standard GB / T 21923-2008 "Wood pellet fuel inspection general rules" was released on May 26, 2008, November 1, 2008 formally implemented. Series of "test methods" research work is ongoing.

This paper is intended to analyze the similarities and differences between composition and characteristics of wood pellet fuel and solid fossil fuels (represented by coal). The basic principles that should be followed when studying the method of establishing the wood pellet fuel inspection method are put forward, which can provide reference for the quick and efficient establishment of accurate, reliable and suitable method for the inspection of wood pellet fuel.

Similarities and Differences of Wood Particle Fuel and Solid Fossil Fuel

The wood pellet fuel is "solid fuels produced directly or indirectly by biomass"; and biomass refers to "substances that are biologically originating, not including buried in the form of underground and converted into fossils" (see GB / T 21923 "sawdust Particle Fuel Inspection General "). Coal is derived from plants, is the plant debris in the crustal uplift process, was buried in the ground, through complex biochemistry, geochemistry, physical and chemical transformation of solid organic combustible sedimentary rocks. As a solid fuel, biomass fuels and fossil fuels are similar in composition and properties. Such as wood pellet fuel and the main combustible parts of coal are organic hydrocarbons, the combustion heat are derived from the organic hydrocarbon oxidation combustion reaction:

C + O2 - CO2 + Q

H2 + O2 - H2O + Q

Therefore, most of the test methods used for coal quality characteristics can also be applied to wood pellet fuel. However, compared with coal, wood pellet fuel density is small, volatile high, flammable, easy to spray, high water content, strong water absorption. In addition, the composition of wood pellet fuel and coal components are also quite different, such as most of the wood pellet fuel ash is less than 10%, volatile in 60% to 80%, total sulfur is less than 0.15%, very low; carbon content of 40 % ~ 50%, chlorine content is very high, and the content range is very wide, from about 0.01% to about 2%, two orders of magnitude more; most of the sample chlorine content of more than 0.5%; potassium, sodium, calcium, Most are also much higher than coal. This characteristic and composition difference determines that most of the quality test methods of coal can not be fully applied to the wood pellet fuel. It is necessary to further study and improve the various test conditions in the coal test method in order to establish a series of suitable conditions for wood pellet fuel , Accurate and reliable composition and characteristics of the test method.

The basic principle of establishing the method of wood pellet fuel inspection

2.1 sampling and sample preparation

The acquisition and preparation of wood pellet fuel samples is critical to obtaining accurate and reliable test results.

The basic requirement for sampling is that the samples taken should represent the characteristics of the collected batch. It is therefore desirable that each of the particles in the batch or batch of materials be of the same opportunity to be included in the sample. The sampling method developed should meet this requirement as much as possible.

Compared with coal bulk materials, wood pellet fuel situation is more complex. From the product form, there are granular, powdery, the size of the block, flaky, coarse, thin stalk-like, bundled, compression molding, etc .; different shapes, different types of material density vary greatly, some quality characteristics A large difference between the degree of uniformity is also a large difference. From the sampling site, from the raw material growth, from the production plant, from the transport, from the storage, or into the furnace before the sample, the situation will be very different; more fresh plants, wood, there are more dry plants , Wood, etc., and even various types of biomass fuels mixed together, to take a representative sample caused great difficulties.

Therefore, in the development of wood pellet fuel sampling method, the need for the sampling of granular materials, large, large pieces of material sampling, straw, branches of the sample, the overall sampling of the package, the package and the container, Etc., given the applicable sampling tools and sampling methods. Sampling from the conveyor belt, sampling from the downflow, sampling from the biomass fuel in the bucket elevator, scraper conveyor, bucket bucket or jaw feeder, from the train, And the sample of motor transport, should be given sub-sample number, sub-sample size, sub-sample layout and other reasonable provisions; this provision for different situations should be different. The general purpose is to ensure that the samples taken are representative of the bulk of the material. At the same time, the sampling method should also be given on the sampling precision assessment method, so that people can be based on the desired precision design sampling program.

The basic requirement for sample preparation is that the final analytical sample must be sufficiently representative of the original sample and meet the requirements of each test method. Sample preparation is usually to shrink the sample to one or more particle size smaller than the original, the quality is less than the original, can be used directly for the test sample. The sample preparation process requires that the composition and properties of the samples collected from the site are not changed at each stage of the sample preparation. Each division should be adequately represented as it is.

For sample preparation, the biggest difference between wood pellet fuel and coal is its different shapes, most samples of high water content, toughness, and some samples there is a certain oily, it is difficult to break it to the required size, in particular, Stem-like, branched, and high-skinned samples. Therefore, in the preparation of wood pellet fuel sample preparation method, it must be noted that crushing equipment should have a cutting function, and the power should be appropriate to avoid local heat accumulation and strong airflow caused by excessive moisture loss of samples and some changes in quality characteristics.

Sample shrinkage should be based on the shape and characteristics of materials, as well as the size of the situation, respectively, the most appropriate, the most simple and convenient way. For each mass fractionation stage, it is important to retain sufficient sample quality, otherwise the resulting division may not be representative. Unlike coal, the minimum sample quality that should be retained when the sawdust particles are fractionated depends on the nominal maximum particle size of the sample and is also related to the bulk density of the sample. It should be noted that the minimum amount of sample required for each shrinkage of the sample is specified. In addition, the drying, crushing, screening and shrinkage procedures should be used rationally so that the particle size of the prepared sample can be as small as possible, and the smaller the size of the analytical sample is helpful to improve the precision of the test results.

According to EU standards and US standards, the sample size is analyzed at least less than 1mm. However, it is possible to make the size of the prepared analytical sample less than 0.5 mm or even less than 0.2 mm by using suitable crushing equipment and crushing methods, as well as the rational application of the drying process (temperature and time).

In the preparation of wood pellet fuel sample preparation method, through the study and test to determine the test sample can not only ensure the full representation, but also to make the sample size as small as possible, and the sample preparation time is also shorter the best system Like procedure. In this procedure, there is a need for different types of test samples, for crushing equipment and other sample preparation tools, sample breaking methods, sample shrinkage methods, particle size and minimum retention of each fractionated sample; pre-drying stages and Drying temperature, drying time; sample crushing method, analysis of the sample size, the way the air dry state, sample preparation method of precision assessment made reasonable.

2.2 Industrial Analysis

Industrial analysis includes moisture, ash, volatiles, and fixed carbon calculations.

In the development of wood pellet fuel moisture determination method, should pay attention to the impact of drying temperature. Sawdust pellet fuel volatile high, high moisture content. (105 ± 2) ° C and the US standard selection (103 ± 1) ° C, the EU standard selection (105 ± 2) ℃ and the US standard selection (103 ± 1) ℃, the EU standard selection (105 ± 2) ℃ and the US standard selection (103 ± 1) ℃ As the temperature of the wood chips, the moisture content of the fuel does not exceed 104 ° C to 107 ° C. In the determination of wood moisture content of wood chips, the drying temperature may be subject to strict control.

In the development of wood pellet fuel ash determination method, should focus on the impact of ashing temperature and ashing speed. Most of the wood chips in the fuel potassium, sodium, chlorine content are much higher than the coal, and the above elements of inorganic, organic compounds are mostly above 600 ℃ began to evaporate, resulting in 815 ℃ measured ash results may be low, The amount of minerals contained in the sample can not be properly reacted. Therefore, the EU standard selected (550 ± 10) ℃ and the US standard selected (575 ± 25) ℃ as wood pellet fuel ash measured temperature, no more than 600 ℃. In addition, if the wood pellet fuel sample heating rate is too fast, may lead to sample detonation fly out of the porcelain boat, and therefore should also be reasonable to specify the ashing rate.

In the development of wood pellet fuel volatiles determination method, the main should pay attention to the applicability of muffle furnace, pre-elevated furnace temperature. The purpose is to ensure that the furnace temperature in 3 minutes to rise to (900 ± 10) ℃ and the total heating time 7min will not exceed 910 ℃. In addition, because the vast majority of wood chips fuel samples are much higher than the evaporation of coal, the release rate is faster, it should be concerned about the heating process whether the sample splash and oxidation phenomenon, to ensure that the determination of the results of the volatile accuracy.

2.3 calorific value

It has been mentioned that there are many similarities in the composition of the wood pellet fuel and the solid fossil fuel coal, and the thermal energy of the coal is basically the same. The oxygen bomb for the determination of the calorific value of the coal can be used for the wood pellet The However, compared with coal, the density of wood pellet fuel is small, volatile high, flammable, easy to spray, high water content, strong water absorption and so on. Therefore, when the oxygen bomb calorimetry is used for the determination of the calorific value of the wood pellet fuel, the problem of incomplete burning or burning of the sample should be focused on. Based on years of experience in high volatiles and explosive coal samples, the main factors that cause incomplete combustion or detonation of the sample are the amount of oxygen, oxygenation and the state of the sample. Burning fast, low-density powdery samples, such as benzoic acid powder, such as no pressure cake, the combustion is not complete. Powdered wood pellet fuel can not be completely burned in the oxygen bomb, need to squeeze the cake, into the burning bags and capsules, or paper, it may make it completely burned. When developing the calorific value of wood pellet fuel (oxygen bomb calorimetric method), it is necessary to determine the test conditions which can effectively prevent the splashing and incineration of the sample.

2.4 carbon, hydrogen, sulfur, chlorine and other elements of the analysis

In the process of measuring the total sulfur and high temperature combustion-hydrolysis method, the pretreatment of the samples was carried out by measuring the total amount of sulfur Tube furnace burning coal samples, so that the quantitative release of the measured elements and then measured. The above method should be applied to the wood pellet fuel, should pay attention to several aspects of the problem.

(1) Sawdust pellet fuel volatile high, low density, burning speed, easy to spray, analysis of the sample should not be directly into the high temperature zone, usually from the low temperature area began to push the sample. When developing this type of test method, a reasonable injection procedure should be established to prevent the sample from being burned and to ensure the quantitative release and quantitative determination of the measured element.

(2) the chlorine content of wood pellet fuel is much higher than that of coal, and the interference of chlorine to hydrocarbon determination should be taken into account when making the determination method of hydrocarbon particulate fuel hydrocarbon. In the hydrocarbon determination method of coal described above, the interference of chlorine is eliminated by the silver filament; whether the amount of silver wire loaded in the furnace is sufficient to eliminate the interference of chlorine in the hydrocarbon measurement of the wood pellet fuel, and whether it needs to be more frequent To replace the silver wire roll, etc. need to be determined.

(3) Chlorine on the Coulometric titration method for the determination of sulfur particles in the presence of sulfur in the presence of fuel, to be observed through the test. Another concern is that the sample burning speed and sulfur release rate is too fast, whether it will cause the end of the titration overshoot, or titration is not complete and so on. Therefore, the injection method and air flow to be studied to determine the best conditions.

(4) the development of wood pellet fuel chlorine determination method, should pay special attention to high chlorine content, content range span (0101% ~ 2%) problem. The optimum test conditions should be determined by studying the effects of the amount of sample, combustion reaction time, injection procedure, oxygen flow rate and steam generation amount, concentration of potentiometric titration solution, so that the high temperature combustion hydrolysis method can be better applied In the wood chip fuel.

Analysis of ash composition and ash fusion

According to the characteristics of wood pellet fuel, ash ash and ash melting analysis of the ash should be 550 ℃ ~ 600 ℃ burning completely ash, rather than as coal ash 815 ℃ burning ash. The contents of K2O and P2O5 in wood ash are much higher than that of coal ash. CaO and MgO are mostly higher than those of coal ash. Most of Al2O3 and Fe2O3 are much lower than that of coal ash. In the development of ash composition analysis method, Concentration and range of the standard curve, it should also be considered by adjusting the volume of the sample, the volume of the volume, or the volume of the solution to the measured component in the linear range of the standard curve to ensure the accuracy of the measurement results The In the development of ash melting analysis method, it is considered that the ash of the wood pellet fuel is obtained by burning at a relatively low temperature, and its ash composition is also very different from that of coal ash. Therefore, in the process of ash melting, With the furnace temperature rise gray cone shape changes and coal ash may also be different, gray cone 4 forms of temperature range may be larger than the ash, pay attention to the starting point of temperature control and observation of the starting point of the deformation temperature and other issues The

There are many similarities in the basic composition and properties of wood pellets and solid fossil fuels, and the coal test method can be applied to wood pellet fuel. It is a quick and effective way to establish a wood pellet fuel inspection method by referring to the coal inspection method. But there are many differences between wood pellet fuel and coal, a simple copy of the coal inspection method is not feasible. It is necessary to establish a series of accurate and reliable test methods for the inspection of wood pellet fuel by carefully studying the applicability of the test conditions in the inspection methods for the difference of the characteristics of wood chips and coal. The paper according to the National Coal Inspection Center in recent years of wood chips burning