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Pre-normative work on sampling and testing of solid biofuels for the development of quality management (BIONORM)

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For an unobstructed biofuel use (i.e. fuel handling, storage, transhipment and energetic conversion) particle size dimensions and their distributions in a bulk have often been identified as a key quality parameter. The results revealed that the analysis of biofuels particle size is associated with high measuring uncertainties. This is basically due to the fact, that the tested major measuring principles (i.e. horizontal and rotary screening as well as image analysis) produced results that were largely incompatible. Results acquired from the image analysis system showed highest conformity to the reference values (standard samples). For all horizontal and vertical screening machines the median value of the size distribution (according to particle length) was only between one third to half of the reference median value. This is attributed to the high particle misplacement particularly found in larger fractions. For rotary screening the median particle length is between the results of image analysis and horizontal screening. Based on this, comparable measurements must consistently be made using only one of the three principles, while for the same principle modifications of the equipment type (e.g. different dimensional shaking operations) are usually acceptable. With regard to influencing factors, for horizontal screening a critical shaking frequency (~ 190 rpm) was identified, while the chosen initial sample volume was found to be less important. For the screening duration a larger effect was observed; a fixed minimum time requirement of about 15min was identified to be meaningful. For rotary screening the influencing factors are mainly the rotation speed and the inclination angle of the rotating drum. Also the feeding rate and the moisture content of the sample play an important role, as reflected by the measured differences in the calculated median particle size. Generally, it should be attend to sample preparation due to the possible inhomogeneous moisture content within the sample. Coupled with this, the fixation of a tolerable moisture range is required if results from different fuels and test methods shall be compatible. However, high reproducibility is only given, when all relevant measuring variables and the influencing factors are carefully considered and standardised accordingly.
Methods for sampling and sample reduction that are of importance with regard to testing methods of fuel properties in order to ensure that the required fuel properties are met (e.g. methods for reducing samples for sample preparation for physical-mechanical and chemical tests). The potential impact of this issue on the biofuel markets is considerable. The experimental work has allowed the relative bias of different sampling methods and the influence on sampling variability of different increment sizes to be assessed. This work has also allowed the number of sampling increments required to give a satisfactory level of sampling variability to be estimated, for the biofuels investigated (i.e. woody-fuels such as GROT, pellets and sawdust as well as straw bales). On the basis of these experiments it can be concluded that none of the methods used in the experiments gave disastrous results. Thus, no method can be ruled out from practical use and should be included in the CEN standard. For sampling in sum it is revealed: with exception of particle size distribution, no evidence of a relative bias between the methods of sampling and testing can be revealed for testing moisture, ash and chlorine content of the fuels investigated. Sampling from tipped lorry-loads is not biased relative to sampling from a conveyor for the methods recommended for GROT and sawdust. Based on the work on GROT it can be concluded that for moisture and ash, the results on the relative bias do not provide any reason for preferring sampling from the conveyor over sampling from the heap. Different from that, particle size distribution shows relative bias implying the necessity for the CEN standard to define one preferred method. For moisture and ash of sawdust analysis the results concerning the relative bias of the two methods show the same as for GROT. For particle size distribution, the results imply a relative bias between the two methods in case of smaller increment sizes (0.2 litres or 1 litre). Thus, if sampling from the stopped conveyor will be the reference method, then sampling from the heap is acceptable provided that sufficiently large increments are taken. The results obtained for pellets in the investigation of relative bias indicate that the moisture and ash content vary from lorry-load to lorry-load. However, both are not affected by the handling, what is true for the particle size distribution. For straw bales, the experiment results have shown that sampling with the hook is not biased relative to sampling with the coring machine. Taking five increments per bale will results a relative sampling error of about 10%. Furthermore, doing one determination per sample will give a relative error of test results (i.e. repeatability) of about 5%. Both relative errors might be acceptable for routine tests. Due to the effect of straw bales position, when using either the hook or the coring machine, for sampling straw bales should be turned on their side. In addition, increments should be taking from both sides, and from the full depth of the bale. Preferred methods for sample reduction (i.e. those gave least variations between sub-samples) in each of the experiments are outlined. Some general conclusions may be drawn tentatively from this. "Riffle" is the preferred method to use with the coarser materials (GROT and pellets), if a rotary divider is not available. If available, a rotary divider is the preferred method for determinations of moisture and particle size distribution on pellets. An explanation should be sought for the poor performance of the rotary divider in comparison with the riffle when determining ash. ¿Coning¿ is the preferred method with sawdust, but the riffle performed nearly as well. The special method used to sub-sample straw, handful sampling (on straw coarse cut prior to reduction), is the preferred method for determination of liberated or partially liberated properties of straw, but not for determination of moisture. In general is was revealed, when a sample is taken for the purpose of determination of moisture-content, sample reduction should be avoided, since the materials dried noticeably during the reduction process and the result of the test will be affected. However, it is important that technicians should regularly and routinely check the achieved repeatability with whatever sample reduction methods applied for. Finally, it is suggested that there is further need to: - Extend the work on sampling other solid biofuels in order to cover the breadth of materials to be found throughout Europe (e.g. wood chips, bark, reed canary grass, olive waste and briquettes), - Develop a guideline on how users of CEN standards can ensure reliable results of sampling and sample reduction procedures as well as can decide the frequency of sampling.
To assess biofuel quality it is of high importance to know the concentration of sulphur, chlorine and nitrogen in biofuels. This is particularly true for biomass conversion processes. Contents of sulphur and chlorine in biofuels are of relevance for corrosion and fouling, for emissions of SOx, HCl and PCDD/F as well as for aerosol formation. The concentration of nitrogen causes NOx emissions. Standards defining analytical methods for the determination of these elements are not available for solid biofuels so far. Hence, different approaches and procedures are in use. The individual laboratory methods and system devices applied are originally designed for the analysis of coal samples, whereby certain deviations result. Concerning sample preparation, for S, Cl and N analysis a particle size of < 1 mm is sufficient in most cases. Smaller particles increase the repeatability but also increase the risk of contaminations with metals (i.e. from the inner materials of the used mills). The reproducibility of chemical analyses is usually improved when larger sample amounts are used (e.g. 1 g for the determination of S and Cl). Furthermore, in laboratory practise it should be especially considered that (i) the samples are always be within the calibration, and (ii) if low nitrogen concentrations are to be analysed, an increase in sample amount may improve the result. Besides this, the method evaluation for element analysis led to the conclusions and recommendations given below. Basically, except for the Kjeldahl method, all of the identified most promising methods such as IC ("ion chromatography"), ICP ("inductively coupled plasma") and titration as well as the automated analysers are recommended for standardisation. They are described in detail in the corresponding best practice guideline and draft standards. Chlorine and sulphur determination: Sample combustion in an oxygen bomb and the quantification of sulphate and chloride in the receiving solution is currently the best method. It enables the application of procedures presently standardised on European level. For chlorine, the determination applying the method of water-soluble chlorine led to similar results compared to the bomb combustion method (at least for all untreated biofuels investigated). For samples characterised by a high ash content even higher values were obtained. In general, the required repeatability and reproducibility can only be obtained when strictly abided to the standard procedures. Solid biofuels that are characterised by low concentrations of sulphur and chlorine are difficult to analyse. Since currently the reproducibility is not satisfactorily, there is more need on research and method improvement. Coupled with this, the INAA method (¿irradiation neutron activation analysis¿) may be of interest for further scientific investigations, as for instance absolute values can be obtained. Furthermore, this method could contribute to improve and validate analytical methods. Nitrogen determination From the comparison of the obtained results for automated analysers (different and same brands and types) and for the Kjeldahl method the following was revealed. With respect to certain types or brands of automated analysers available no systematic deviations were found. However, there were differences between the participating laboratories (persons operating the systems). Thus, for the obtained results the operation and especially the calibration is critical. Nevertheless, automated analysers are suitable for the nitrogen determination in solid biofuels and thus, involved in respective draft standardised. Since recognising comparable results for different designs of automated analysers, no specific system design is recommended in the draft standard. However, the applied apparatus should meet the functional requirements. No influence of moisture content on the nitrogen concentration could be found. Hence, it is not necessary to used dried samples that are difficult to handle since they are in general very hygroscopic. Against the standardised methods developed so far, the work has generally revealed that there is further need on improvement with regard to the test methods, the lack of reference material and laboratory experiences as well as on own laboratory practice. Final recommendations involve to further investigating the chemical fuel concentrations of bromine and iodine (especially e.g. for recovered fuels, fruity biomass and seaweed).
Work package VI of BioNorm dealt with the national conditions of New Member States (NMS) and Newly Associated States (NAS) respectively, and their research exchange with the countries of EU 15. This work package is aimed to primarily increase the information flow between NMS/NAS and the pre-normative work of BioNorm. Therefore, country reports were prepared by the partners from the NMS/NAS (i.e. Bulgaria, Czech Republic, Latvia, Lithuania, Poland and Hungary) with focus on solid biofuels as energy source, existing standards and guidelines, needs for standardisation as well as recommendations. Moreover, national platforms were established as an interface between project consortium and solid biofuel standardisation bodies and involved companies of the NMS/NAS. The survey of the reported country situations has been revealed the following, which is true to a large extent for all the NMS/NAS considered within the BioNorm project: (i) In general, it is required to boost the share of RES on the national primary energy consumption in order to increase the internal security of energy supply and be in line with respective European directives (e.g. climate change mitigation). (ii) Major promising potentials for the energetic application of biomass (particularly solid biofuels such as agriculture and wood residues) within the RES have been identified. This is primarily linked to local conditions (e.g. characteristics of land use, energy consumption structure and power supply services, level of technologies for biomass application and present consumption). (iii) Basically, increasing use of bioenergy is an item of national energy policies. However, for the broad biomass utilisation changes in national legislation systems are needed with regard to the harmonisation of laws and regularly documents with requirements of the EU (e.g. environment quality standards), the harmonisation of the taxes, prices and tariffs as well as requirements of external and domestic markets. (iv) The current limited experience in utilisation of refined solid biofuels and R&D contributes to a lack of solid biofuels standards concerning measurements fuel properties and quality assurance guidelines. In turn this contribute to a further lack of solid biofuels classification and thus of information about solid biofuels prices on the national market. Consequently, it seems to be quite more difficult to develop a diversified solid biofuels market. (v) Albeit, it is assumed an emerged market (i.e. mainly abroad) for more developed solid biofuels will stimulated the production of wood briquettes and pellets in many of the NMS/NAS. Comprising, it was clearly stated by all NAS/NMS-partners as well as the members of the national working groups that common standards are urgently needed for increasing the market shares of solid biofuels in the NAS/NMS, particularly in terms of biofuels export. Moreover, the European standards currently being developed by CEN need to be quickly adopted by the NAS/NMS. This was expressed explicitly in all country reports. Today, several NAS/NMS used national standards of EU 15 countries, mainly the Swedish, German and Austrian pellets and briquettes standards. Finally, it was emphasised the importance to further cooperate with the European countries, where biomass is already used efficiently and the legislation as well as biofuels standards are harmonious developed.
The determination of biofuels ash melting behaviour is of high importance for all thermal conversion processes. The temperature range of sintering, softening and melting can vary broadly, depending primarily on ash composition. Although biofuels ashes were tested by seven methods, only from improved DIN ("German industry norm"), MAF ("melt area fraction") and CFBA ("controlled fluidised bed agglomeration") temperature information can be derived that can be compared directly. For synthetic samples it was revealed that only the DIN and the MAF method are able to quantify melting temperatures. However, DIN and MAF are ash-testing methods suitable for standardisation whereas CFBA may be used as reference for agglomeration/sintering. The recently developed MAF method shows large potential to become reproducible and repeatable. The MAF method has been proven to determine the temperature of 10% and 50% melt in the ash samples tested. Though, some modifications are needed for problematic ashes, e.g. straw ash, which tends to form "cakes" (agglomerates) during handling. Moreover, further improvement is required concerning melt viscosity and the possible sample shrinking. The technologies of TGA/SDTA ("thermogravimetric analysis"/"simultaneous differential thermal analysis") cannot be standardised at present, but they have the potential to confirm various phenomena associated with ash melting behaviour. SEM-EDS ("scanning electron microscope" combined with an "energy dispersive x-ray analyser") is predestined for providing valuable information on the ash compositions and species. Testing the XRD ("X-ray diffraction") method revealed that the amount of amorphous phase is valuable if the connection between amorphous phase and melt phase is clarified before. Besides the suitability of test methods, issues such as really required information to forecast ash melting and the relation of acceptable analysis cost. It is generally accepted that testing of initial melt temperature as well as the rate of melt formation is essential. With regard to the costs, bed sintering methods and methods as TGA/SDTA that produce results that have to be evaluated by specialists can be eliminated. The improved DIN method is an attempt to get around with comparatively simple and low-cost manner in the standards. This is also true for the MAF method. However, there certainly are some problems about the identification of the characteristic temperatures for biomass ashes. This is also true for variations (not studied within BioNorm) in the density of the test specimen that is produced by compression. Furthermore, the reproducibility has to be improved.
For appraising quality of solid biofuels important chemical parameters are the content of major (i.e. (Al, Ca, Fe, K, Mg, Na, P, Si, Ti) and minor (i.e. As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Tl, V, Zn) elements. Major elements are of key relevance referring to ash melting, deposit and slag formation as well as to corrosion. Minor elements are of special importance for particulate emissions as well as the environmental impact of produced ashes and their subsequent utilisation. In term of sample preparation, particle sizes < 1mm or < 0.25mm should provide satisfactory homogeneity to be used for the analyses of wood and bark mixtures or straw. Regarding this, it is noted to pay attention during size reduction in order to avoid contamination from the inner materials of the used mills. Thus, materials of that mill parts having contact with the sample should be chosen depending on the elements to be determined. If, for instance, minor elements such as Cr and Ni have to be determined, it is not advised to use stainless steel materials, and recommended to use e.g. tungsten carbide or titanium instead. Generally, high-speed mills should not be used due to the higher abrasion rate. In conclusion of the validation results, for solid biofuel analyses wet digestion with H2O2 / HNO3 / HF / H3BO3 are proved to be the most suitable for the determination of major elements. For minor elements wet digestion using H2O2 /HNO3 /HF are recommended. Depending on the specific element to be determined, the application ranges revealed the suitability of tested methods for a wide concentration range, including potential concentrations in both natural and contaminated solid biofuels. According to detection limits, the most suitable determination methods are summarised for the different elements in solid biofuels. Thus, (i) atomic absorption spectrometry (AAS) such as FAAS ("flame"), GFAAS ("graphite furnace"), CVAAS ("cold vapour") and (ii) inductively coupled plasma spectrometry such as ICP-OES ("inductively coupled plasma optical emission spectrometry") or ICP-MS (¿inductively coupled plasma mass spectrometry") can be applied. These determinations showed good agreement between the different results for many elements investigated. Other determination methods applied are hydride generation AAS ("atomic absorption spectrometry"), XRF ("X-ray fluorescence spectrometry") as well as direct Hg determination. Basically, applying XRF detection would be a suitable and fast alternative method for the determination of several major and minor elements. However, due to the requirement of reliable calibration standards, which are not available for solid biofuels so far, XRF systems for element determination presently not be recommended. Thus, the development of such standards is desirable.
The physical fuel quality of densified biofuels like pellets and briquettes is primarily characterised by durability (i.e. fuel resistance towards shocks and tensions) and particle density (i.e. ratio between mass and volume of a sample that is appropriate to estimate durability). Thus, durability is important with regard to handling, transportation and end-conversion processes. Durability: For the estimation of the briquettes durability the most repeatable and reproducible method is to tumble the briquettes for 105 rotations corresponding to 5min treatment. Nevertheless, the briquettes durability testing leads to highly variable results. But the variability of the method is influenced by the fuel itself and is smaller for briquettes of high durability. Furthermore, if all the tested briquettes are considered, it seems illusive to reach a higher accuracy than 10 %. Also for determination of pellets durability, using the tumbling device (ASAE standard) shows better results compared to the pneumatic tester (ÖNORM standard). Though, there is no accurate relation between the results of pellets durability obtained by both devices. It clearly appears that the level of durability influences the variability of results: i.e. the lower the pellet durability, the higher the variability. Taking into account the number of replication needed, an accuracy level of 1 % could be reached in practice with the tumbling device. Particle density The different results revealed that the hydrostatic and buoyancy methods based on liquid displacement give lower repeatability and reproducibility than the stereometric methods and thus performed better. For all tested methods, it clearly appears that the fuels type influences the variability of the results. For each analysed parameter the stereometric methods led to higher variability, higher bias between participated laboratories, higher values of repeatability and reproducibility and needed more replications to reach a given exactness. The liquid displacement methods showed similar standard deviation. The values of repeatability and reproducibility were similar. This is particularly true for briquettes. Methods with addition of wetting agent give higher results than those obtained with paraffin coating methods. In the case of pellets, the buoyancy method using non-coated samples and wetting agent mixed with water gives the lowest values in repeatability and reproducibility. However, the choice of the liquid displacement method used may be based on the material available at the laboratory. Thus, e.g. hydrostatic with paraffin coating needs to have a balance that can weight in a range of 10 to 15kg with an accuracy of 0.1g. Indeed applying buoyancy without paraffin coating decreases the time of sample preparation but the water has often to be changed because briquettes start to disintegrate very fast. Generally, it is concluded that for given fuel types, the number of replications needed to reach a given accuracy level is by far smaller than for the others. It is suggested to further determine on which other parameters the number of replications (or the expected accuracy) may be based. Comparing particle density and durability by using the most accurate methods for both parameters, no relation has been found between those two parameters. Thus, the particle density cannot be used to estimate the durability.
Moisture content is a primary property for a successful utilisation of solid biofuels within the entire supply chain (e.g. for transportation costs, storage management, calorific value and conversion at end use). Strongly linked to the moisture content of solid biofuels is the bulk density, which is an important property with regard to space for storage and transportation and for volume based payment of biofuels. Furthermore, bulk density is influencing rapid moisture content measurements. Thus, a wide scope of fuels from all over Europe was analysed to cover the broad range of biomass. Basic results of methods for testing moisture content and bulk density of solid biofuel, which are identified to be the most promising for standardisation in terms of e.g. suitable performance and high reproducibility, are briefly summarised below. Moisture content - reference method: The applied moisture determination results gave overall comparable results. A statistical significant difference was found among the oven drying method between the standard method at 105 degrees Celsius compared to the temperatures 80 degrees Celsius and 130 degrees Celsius, respectively. According to this, a slightly increased amount of evaporated matter (volatiles and moisture) results for each temperature step. The freeze-drying method determined significantly lower moisture content values compared to the standard method, whereas the results from the xylene method were deviating only for some of the fuels. This difference was partly attributed by the small sample size used for xylene distillation. The GS-MS-method ("gas chromatography - mass spectrometry") has shown promising results as a standard reference method. So it was found that the amount of volatile matter was in order of 0.06 to 11.33% calculated as percentage of moisture content. Furthermore, it was revealed that the mass loss differences found among the different methods were primarily due to alpha- and beta-pinenes. Though, a more throughout optimisation of the method is required. Moisture content ¿ rapid methods: Among the seven tested rapid test devices about four types were identified to be particularly applicable to measure the moisture content of solid biofuels. These are: - As on-site types: the thermogravimetric Mettler-Toledo HB45 as well as the capacitive devices Pandis FMG3000 and the Schaller FS2002-H. - As on-line type: the optical MESA MM710. Although MESA was only tested in a reduced moisture range of 10 to 40% MC but the method is applicable to the full range of 0 to 100% MC. However, the small nominal size and high time need (both Mettler-Toledo) as well as the need of fuel specific calibrations (Pandis, Schaller and MESA) should be considered when selecting the device. For the electrical devices including the bulk density in the calibration function can significantly increase measuring exactness. Moreover, reducing the scope of fuels increases the power of the calibration functions. The Moist100, Wile25 and ACO estimated the moisture content with a higher variation and therefore cannot be recommended for moisture content determination in solid biofuels. Generally, further work is required to optimise and evaluate e.g. blank values, recovery, adsorption and extraction efficiency as well as response factors. Bulk density: The following was concluded for best practice in bulk density determination of solid biofuels: - For all tested solid biofuels a measuring container size of 50 l is acceptable. A cylindrical container shape should be preferred for practical reasons due to higher stability and easier manageability. - A standardised shock impact on the filled container significantly increases the measured bulk density (e.g. 6% for wood pellets, 10 to 12% for fuel chips and 18% for chopped miscanthus), while there was only found a minor improvement for the relative repeatability limits. - The fuels moisture content during the measurement is of high importance, and consequently has to be recorded since an obvious increase in bulk density (wet basis) was observed with increasing moisture content. Thus, the comparability of bulk density data is only given if any inconsistency in moisture content between the samples is accounted for by the use of a correction factor of 0.712% for each 1% moisture difference. Moisture content effects are largely restricted to the moisture content range up to 25%. Beyond this point possible effects can be neglected.
Closely linked to the previous work packages, this work package dealt with Quality Assurance systems for the provision of solid biofuels. Standardisations of solid biofuel properties contribute to promote a more widespread use of biofuels by providing a base to facilitate the business of operators within the market. Work-package IV (WPIV) of the project provided information to support the Technical Specification on Quality Assurance for solid biofuels that is being drafted by Working Group 2 of CEN/TC335 (WG2). The aim of WPIV was to fill gaps in knowledge about Quality Assurance in the field of solid biofuels, and this has been achieved in three tasks. In the first task in WPIV (Task IV.1), a review of existing, relevant Quality Management systems as already maintained by different biofuel producers, was elaborated. This review covered solid biofuels and excluded recovered fuels. On the basis of a list of 11 questions, the review yields an indication how Quality Assurance and Quality Control - as parts of Quality Management - are currently performed in ten different cases, representing six different countries (Denmark, Finland, Germany, Netherlands, UK, Sweden) and six different product categories (agricultural products, pelletised animal feed, used wood, straw bales, fresh wood chips, wood pellets). As a result of the review performed in Task IV.1 and the analysis of ISO 9001:2000 as an international Quality Management standard, a report has been produced with the pros and cons of Quality Assurance and Quality Control systems as well as the basic ideas of a Quality Management system especially adapted to solid biofuels. After a description of the results, important conclusions are drawn for the design of a guideline for Quality Assurance (including Quality Control) for solid biofuels, emphasis of the work in IV.2. In the second task (Task IV.2) a first draft of a guideline for Quality Assurance was elaborated. The guideline sets out a step-by-step methodology to help each operator within a supply chain of solid biofuels to design a manual for Quality Assurance. Based on the ideas of this first draft guideline and conclusions of the review of Task IV.1 draft manuals how to deal with Quality Assurance and Quality Control were tried out in practical situations. This was accomplished at the industrial premises of a range of producers, traders and users of solid biofuels, referred to as "hosts". These activities are known as the "field-trials." The selection of the host companies ensured, that the overall supply chain of solid biofuels as producing, preparing, trading, handling and/or using of solid biofuels was covered. Furthermore, the geographical distribution within Europe was considered. The hosts fell into two broad classes: Class-A companies that buy raw biomass, such as residues from agriculture and/or forestry and convert them into higher-grade biofuels for onward sale to third parties; and Class-B companies that buy such raw biomass and use it in processes to produce electricity and (sometimes) heat for sale. Both classes play key roles in the expanding market for biofuels. Beyond it, there was a wide range of possible circumstances to be covered. Most of those were included in a spectrum lying between two extreme cases: (a) small-scale (especially domestic) users who require high-grade fuels, and (b) large-scale users who can take advantage of lower-cost raw materials by the use of appropriately designed combustion plant. The field trials have underlined the need of a guideline with a general methodology applicable by all operators throughout the overall supply chain. The first draft of the guideline and its successor documents were optimised and improved on the basis of the findings and information gathered during the field trials. The final version of the guideline is the Deliverable IV.2.D4. Besides the work in the field trials a proposal for a standard for Quality Assurance was elaborated in Task IV.3. This was done in close cooperation with WG2 from CEN/TC 335. WG2 expressed the need of a guideline as supporting document for the Technical Specification (TS) "Fuel QA for solid biofuels" and supporting information to improve these TS. Thereupon WPIV commented the work of WG2 from their scientific point of view and participated in the further elaboration of the TS. This channel of communication and some common membership ensured a good linkage between the work of WPIV and WG2. Due to this close cooperation the proposal for a standard to be developed in Task IV.3 based upon the Technical Specification under development in TC 335/WG 2. It could found an agreement of a common document for the proposal of a standard and the TS from WG2. The outcome of Task IV.2 (the guideline as Deliverable IV.2.D4) will be further adapted to the Technical Specification from WG2 and published as CEN technical report.

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