Effect of specimen size on ultimate compressive strength of Bio-coke produced from green tea grounds

Abstract

Various sizes of high-density biomass briquette, named 'Bio-coke,' were produced from spent green tea grounds. The mechanical properties at room temperature of the Bio-coke samples were investigated using a compression testing machine. From the results, the relationship between the specimen size of Bio-coke and the ultimate compressive strength at room temperature showed that the ultimate compressive strength depends on the specimen size of Bio-coke. The maximum value of the ultimate compressive strength among the different specimen sizes of Bio-coke was at 67 MPa, obtained from the 12-mm diameter sample. In addition, at 12 mm diameter or smaller, there is hardly any difference in the ultimate compressive strengths measured. Hence, the cold compressive strength properties are divided into two groups based on the uniformity of the structure of the main components along the horizontal cross section of a Bio-coke. Results indicate that the state of the structure, composed of cellulose, hemi-cellulose, and lignin, appears to be consistent resulting from uniform permeation conditions at the 12-mm diameter or smaller samples. Meanwhile, at diameters of 20 mm or larger, the condition of the periphery of the samples were not consistent with that of the middle region because of the temperature, stress gradient and number of void occurring inside the Bio-coke caused by specimen size effect.

Estimation of maximum Bio-coke compressive strength based on chemical composition

“…This tendency was particularly remarkable when the mixing ratio was 60wt.% or more. Mizuno et al also reported that the apparent density of Bio-coke decreases when the production temperature exceeds a certain temperature (Mizuno et al, 2016). Although the reason for this relationship remains incompletely understood, in the present study, an increase in volume, rather than a change in weight, caused the decrease in apparent density.…”

“…Compressive strength was measured with a compression testing machine (SHIMADU) (Mizuno et al, 2016). A load was applied from the top of the Bio-coke at a loading rate of 1.5 mm/min.…”

The Effect of Wood Tar and Molasses Composition on Calorific Value and Compressive Strength in Bio-coke Briquetting

“…The compressive strength was affected by the diameter of the briquettes. When the diameter of the briquettes was reduced, the compressive strength increased (Mizuno et al, 2016). Table 3 shows the proximate and ultimate analyses based on different binder compositions.…”

Types and Composition of Biomass in Biocoke Synthesis with the Coal Blending Method

“…It is organic matter that comes from living organisms such as plant residue and animal waste. Biomass is a porous Energies 2021, 14, 6570 2 of 18 and fibrous material that consists of moisture, volatile matter, fixed carbon, ashes, and inorganic compounds such as Al, Si, K, Ca, and Na [4]. Biomass is a clean energy source that can partially substitute fossil fuels directly or be converted into gas, liquid, and solid fuels through different routes, namely, thermochemical and bioconversion.…”

“…A binding agent is necessary to improve the cohesion and bounding of the combustible materials to prevent the compressed material from crumbling. Compared to conventional coke, which has a value of 20-30 MJ/kg [16,17], the new, densified briquettes that were manufactured by Mizuno et al under high thermal compression (20 MPa and 200 • C) exhibited better properties, such as higher density, improved mechanical strength, and high calorific value [18]. Yustanti et al studied the maximal temperature of briquetting processes in order to generate maximal compressive strength.…”