Determination of Length of Individual Pellets and Pellets’ Lengths Distribution

Mykola Zhovmir

doi:10.48077/scihor.24(6).2021.24-33

Abstract

A form and dimensions of fuel particles influence the intensity of their burning and approaches to the mathematic description of the process. Known methods do not allow correctly measuring all pellets’ lengths and describing pellets’ lengths distribution. The purpose of the study is to substantiate method for determining the individual pellet length and to specify statistical characteristics of pellets’ lengths distribution. The purpose was achieved by applying the proposed method of indirect determination of the length of each pellet by weighing it, followed by calculation of the equivalent length and modal cluster analysis of the distribution of pellets by length, based on the probability density distribution. The most noteworthy results are that the experimental calculation of the equivalent length gives results that coincide with direct measurements for pellets of the correct shape, but in contrast to direct measurements can also be used to determine the equivalent lengths of irregularly shaped pellets and their fragments. Clustering allowed grouping pellets around objectively existing local maxima in the probability density distribution, which can be identified at intervals of pellet lengths not exceeding 2 mm. The importance of the obtained results is that the indirect method of determining the length of pellets allows replacing the measurement of pellet lengths by their weighing, which eliminates subjective factors when measuring the length of irregularly shaped pellets and their fragments. Clustering characterised the granulometric composition of pellets with histograms of probability, mass fraction, and average length by clusters. Upon using proposed approaches, granulometric composition of industrially produced pellets was specified and increased probabilities were noted for 8 mm pellets in clusters of smaller lengths, compared to 6 mm pellets; while straw pellets are characterised by a higher probability in clusters with shorter lengths compared to wood pellets

Highlights

A considerable part of the territory of Ukraine is located in the steppe zone with intensive grain production, so the energy use of cereal straw is promising, the annual resources of which, according to various estimates, amount to more than 10 million toe
The possibility of determining the equivalent length of pellets by an indirect experimental calculation method based on their individual weighing, identification of the average diameter and average density characteristic of the studied portion of pellets is substantiated
The method of indirect determination of the equivalent length of pellets is suitable for determining the length of all pellets, including irregular pellets and fragments

Summary

Introduction

A considerable part of the territory of Ukraine is located in the steppe zone with intensive grain production, so the energy use of cereal straw is promising, the annual resources of which, according to various estimates, amount to more than 10 million toe. Attempts to burn straw pellets instead of wood pellets in retort burners and burners with moving grates led to agglomeration of ash due to low temperature characteristics of its melting, to disruption of work with a considerable decrease in heat output and energy efficiency, increased CO emissions [4; 5]. These obstacles necessitated more detailed studies on the differences in the properties of wood and straw, differences in their combustion processes. Many papers are devoted to the study of the composition of the mineral part of wood and straw, transformations of the mineral part during the formation of ash, temperature characteristics of its melting [6,7,8]

Objectives

Methods

Findings

Conclusion