Boilers slagging when burning wood pellets

A promising trend for upgrading wastes from timber cutting, processing and treatment is their granulation. It allows to increase their specific heats of combustion by 2.5– 3.5 times and their portability characteristics by 3–4 times, to reduce transportation costs by 6– 10 times and to improve all the operations stages. The construction and commissioning of boiler facilities operating on refined biofuel made it possible to form a stable domestic market for wood pellets. However, 0.5 – 1.5 MW nominal capacity hot water boilers equipped with furnaces and profiled burners at the bottom, in cold seasons had fast accumulation of focal residues deposits in the burners and on the furnace chambers lining. The process was complicated by these deposits hardening due to their melting and sintering. These circumstances cause a decrease in the energy and environmental performance of heat-generating installations and their reliability, and also leads to the unplanned shutdowns to clean the boiler furnaces. To find out the reasons for these negative phenomena and to develop recommendations for their elimination, a set of research operations was carried out with wood pellets shipped by the manufacturer and supplied to the burners of the boilers under the analyses; with focal residues accumulated in the burners and on the lining of the furnace chambers; as well as an analysis of the heat generating facilities operation modes. The studies carried out made it possible to identify the main factors that caused these negative phenomena and to develop the recommendations for their elimination.

Revision and Extension of a Generally Applicable Group-Additivity Method for the Calculation of the Standard Heat of Combustion and Formation of Organic Molecules

The calculation of the heats of combustion DH°c and formation DH°f of organic molecules at standard conditions is presented using a commonly applicable computer algorithm based on the group-additivity method. This work is a continuation and extension of an earlier publication. The method rests on the complete breakdown of the molecules into their constituting atoms, these being further characterized by their immediate neighbor atoms. The group contributions are calculated by means of a fast Gauss–Seidel fitting calculus using the experimental data of 5030 molecules from literature. The applicability of this method has been tested by a subsequent ten-fold cross-validation procedure, which confirmed the extraordinary accuracy of the prediction of DH°c with a correlation coefficient R2 and a cross-validated correlation coefficient Q2 of 1, a standard deviation σ of 18.12 kJ/mol, a cross-validated standard deviation S of 19.16 kJ/mol, and a mean absolute deviation of 0.4%. The heat of formation DH°f has been calculated from DH°c using the standard enthalpies of combustion for the elements, yielding a correlation coefficient R2 for DH°f of 0.9979 and a corresponding standard deviation σ of 18.14 kJ/mol.

Development of a pyrolysis model for oriented strand board. Part I: Kinetics and thermodynamics of the thermal decomposition

Oriented strand board is a widely used construction material responsible for a substantial portion of the fire load of many buildings. To accurately model the response of oriented strand board to fire, thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry tests were carried out to construct a thermal decomposition model using a numerical solver, ThermaKin, and a hill climbing optimization algorithm. The model included a single-step water vaporization reaction and four consecutive reactions representing thermal decomposition of organic constituents of oriented strand board. The experiments and modeling revealed that the first two of the four reactions are endothermic, while the last two are exothermic. The net heat of decomposition was found to be near zero. The heat capacities of condensed-phase species and heats of combustion of evolved gases were also determined. The heats of combustion were found to vary over the course of decomposition—the trend captured by the model. Development of a complete pyrolysis model for this material will be a subject of Part II of this work.

384 Metabolizable energy content of feeds: Errors that need attention

Feedlot performance is predicted reliably from DMI and diet NE. Tabular NE values in turn commonly are calculated from TDN either measured in digestion trials or predicted from nutrient compositions. When estimated from nutrient composition (NRBC, 2016), TDN values for feeds were related imprecisely (R2 = 0.83) to in vivo TDN values (NRC, 2000); deviations ranged from -29% to 162%. Traditionally, DE has been calculated as TDN percentage times 0.044, an assumed calorie content of carbohydrate (4.4 kcal/g). Surprisingly, this value is 5% greater than the heats of combustion of DM from isolated starch, cellulose, and glycogen (4.1788, 4.1810, and 4.1868 kcal/g; Blaxter, 1962; The Energy Metabolism of Ruminants). Being “carbohydrate-equivalent energy,” TDN includes the extra calories from lipid whereas urinary energy (UE) lost during catabolism of digested protein automatically is deducted. When determined calorimetrically, ME equals DE minus both gas energy (GasE) loss and UE. But when DE is being calculated from TDN, UE from digested CP already has been subtracted. Double deduction for UE underestimates ME content of high protein feeds. When DE is calculated from TDN, ME equals DE minus only GasE. Using data assembled by Galyean et al. (2016), multiple regression revealed that GasE was predicted more accurately from dietary NDF and lipid concentrations (GasE, % of DE = 4.87 + 0.131 x NDF - 0.331 x EE; R2 = 0.69) than from diet DE (R2 = 0.27). From this formula, GasE loss as a fraction of DE of feeds ranges from 5 to 15% except for isolated fats than have a negative value; non-additivity across feeds complicates formulation of least cost diets. Correcting discrepancies in calculating ME from TDN should improve reliability of predicting the cost of ME from various feeds and for quantifying feed requirements for maintenance and gain of cattle fed diverse diets.

THERMODYNAMIC PROPERTIES OF ORGANIC ACIDS AND SOME THEIR DERIVATIVES

The heats of vaporization, combustion, formation, entropy and the heat capacities in different phases of different carbonic acids and their derivatives: acetates, esters with fatty radicals, two-, three- and four-basic acids (52 compounds) were analysed in the framework of one-parametric mathematic equations. The experimental data of all chosen one-, two-, three- and four-basic acids were analyzed. It was determined, that all thermodynamic functions of these types of compounds depend on the number of valence electrons N, from which the sum of lone electron pairs g as represented in the equations Δvap,c,fH° = i ± f (N-g) and S°(Cp) = i ± f (N-g) is excluded. The coefficients f in the first equations is in the range of 104-113 kJ mol-1 electron-1, that corresponds to the same values f in the equations, which are mentioned in our earlier papers on the determination of the heats of combustion of organic acids. As concerned of coefficient i in the received equations, necessary to note that situation is not synonymous as with the coefficient f. The magnitudes of this coefficient are different in the equations of vaporization, combustion, formation also as in the equations of entropy and the heat of capacity. On the base of literary experimental data we calculated the 29 new equations, which can be used for the calculation of the same thermodynamic functions for other new organic acids and especially bioorganic substances with the useful properties. Necessary to add, that the received equations can serve as additional material for the calculation of the bond energies of fatty acids and their derivatives in gas phase.

Heats of combustion of the main carbohydrates contained in plant-source foods

In a previous review, the experiments of American chemist W.O. Atwater were critically examined, with the findings demonstrating certain weaknesses that could compromise the validity of the values currently used for metabolizable energy. An examination of published works on the heat of combustion of carbohydrates reveals 2 types of weaknesses: the inaccuracy and imprecision of the calorimetric data used, and the averaging procedure employed to estimate such representative values. The present review focuses on the first type of weakness, namely the inaccuracy and imprecision of the calorimetric data used in previous studies. An exhaustive bibliographic search yielded almost 100 heat of combustion values for some of the 6 main carbohydrates contained in plant-source foods (glucose, fructose, sucrose, maltose, starch, and cellulose). These heats of combustion were subjected to rigorous statistical analysis to propose the following for each carbohydrate: (1) an interval (termed a bibliographic interval) that very likely includes the actual heat of combustion value and (2) a “representative value” (calculated to produce the minimum level of inaccuracy). In addition, an estimation of the maximum level of inaccuracy that could be expected when using such a representative value is reported.