Feed materials chemical composition

Suitability of waste feed to a SCWO system is determined by several factors, including heating value/concentration, chemical composition, and material form. Considerations in regard to these factors are provided as follows. 

Chemical Composition. With regard to chemical composition, feed materials containing only carbon, hydrogen, oxygen, and nitrogen (CHON) are readily treated without difficulty from corrosion or solids separation. The presence of... 

In contrast to chemical processes, where the feed materials and process aids (catalysts) are in most cases well defined, clean, and consistent, the particulate solids in mechanical process technologies, especially if they are or were derived from naturally occurring raw materials (minerals, concentrates), may vary widely in composition and/ or physical characteristics. As mentioned before (Chapter 3), when agglomeration processes are involved, the surface properties of the particles (macroscopic and microscopic shape, roughness, contamination by adsorption and absorption) are of particular importance and modifications that are sometimes difficult to detect, may require a new set of operating parameters or the introduction of for example, binders, surfactants, or other additives. 

The raw materials are blended and milled to produce an intimate mixture of the correct chemical composition. An analysis of a typical cement kiln feed is given in Table 9.1 [9.6]. 

The process is remarkably flexible in terms of the raw materials used to achieve the required chemical composition. The presence of silica, alumina and iron oxide (e.g., in the form of clay) in a calcium oxide-containing material is not a problem, as the producer requires some of those materials in the feed to the kiln. Table 9.2 lists some of the CaO-containing raw materials that are used [9.8]. 

In this book, the data concerning chemical composition, which were collated and summarised by AFZ, are identical for all species. The data for nutritional values were mainly derived from in vivo measurements performed in seven INRA laboratories. These data were then corrected to make them consistent with the chemical composition of the feed materials. An innovative feature of this work is the traceability of the methods used to calculate the published values. 

The chemical composition values have been collected by AFZ using its own database of feed information. Started in 1989, this database contains more than one million values of chemical, physical and nutritional characteristics of feed materials, most of them obtained from the participating laboratories (the list of companies and organisations is presented in the Acknowledgements section p. 7). 

The residual standard deviations for these equations were between 2 and 4% of OMd. The equations were then applied to the chemical composition of the feed materials presented in the tables. With this method, we obtained consistent values for OMd for more than 85% of the feed materials. In the case of some rarely used by-products, no recent data of in vivo digestibility were available, and we derived their digestibility values from the tables of Becker and Nehring (1965), an old but well-documented source of feed information. 

The final average values were chosen after paying particular attention to the consistency between chemical and nutritional parameters. Therefore, for each feed material, the proposed nutritional value was adjusted by taking into account the average chemical composition published in the tables. For feed materials with a large variability, the users can correct the nutritional values through specific equations based on analytical parameters. This was the case of alfalfa using the crude fibre content (CF in % dry matter) ... 

Metabolisable energy (ME) can be predicted from digestible energy using regression equations between the ME/DE ratio and the chemical composition of the feed materials. These equations were established by INRA, using a data file of 79 results. 

Estimation of the UFC value using the chemical composition and the digestible components of feed materials... 

The UFC values of the feed materials were also calculated by using a set of equations previously described (p. 58). These equations take into account the chemical composition and the digestible components of the feed materials. 

The DOM value was calculated from the organic matter and OMd. For the majority of feed materials, the DOM data come from measurements (literature and/or INRA). For dehydrated alfalfa and for dehydrated grass, OMd was predicted from the chemical composition given in the tables and INRA equations linking OMd and the crude fibre content (expressed in % dry... 

The differences between the UFC values calculated either by the analytical method or the prediction equations, for the feed materials for which the digestibility could be accurately estimated, are very low (- 0.04 < A UFC < + 0.02) and are not significantly related to the chemical composition. They are consistent with those calculated from a separate data file containing 43 feed materials for which both chemical composition and digestibilities were available. 

Equations associating chemical composition criteria with a digestible element, DE, when OMd could be established with adequate precision (59 feed materials)... 

Equations based on the chemical composition of feed materials for which DOM or DE could not be established with precision (22 feed materials). 

The vectors for the chemical composition of the feed materials and their digestibility values in the present tables were compared with the previous INRA tables (INRA, 1984 INRA, 1990). 

The chemical composition and digestibility values sometimes differ significantly for feed materials common to the old and new tables, so that DEC values can be different. In addition, the energy value of the reference barley increased slightly from 9.21 MJ/kg (INRA, 1984) to 9.42 MJ/kg based on the latest INRA research (Vermorel and Martin-Rosset, 1997). 

The present tables are more complete (81 feed materials) than the previous INRA tables (33 feed materials). This was made possible by using prediction equations based exclusively on the chemical composition. However, we did not wish to extend this method to all the feed materials in the new tables, since it was important to remain within the validity range of the equations. 

When applicable, the other data (chemical composition and nutritive value) are simply corrected for the dry matter content of the processed feed materials on a dry matter basis, these data are identical for the processed and unprocessed feed material. 

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