Preparation of Formed Coke from Biomass by Sequence of Torrefaction, Binderless Hot Briquetting and Carbonization

Abstract

This paper proposes a method of preparing high-strength formed coke from woody biomass without binder. Chipped and pre-dried Japanese cedar was heat-treated in an inert atmosphere (i.e., torrefied) at 225-325°C (T t ), pulverized to sizes in three different ranges, molded into briquettes (in the form of thick disk with diameter/thickness ≈ 2.5) at temperature up to 200°C by applying mechanical pressure of 128 MPa. The torrefied/briquetted cedar (TBC) was then converted into coke by heating to 1 000°C in an inert atmosphere at normal pressure. This process sequence enabled to prepare coke having indirect tensile strength (S t ) of 8-32 MPa, which was much higher than that without torrefaction, below 5 MPa. The torrefaction greatly improved pulverizability of the cedar, which was further promoted by increasing T t . S t of TBC and that of coke both increased as the particle sizes of TBC decreased, but this explained only a minor part of significant effect of T t on S t of the coke. S t was maximized at T t = 275°C regardless of the degree of pulverization. The T t effects on physicochemical properties of TBC and coke were investigated in detail. The difference in S t of coke by T t was mainly due to that in the increment of S t along the carbonization at 500-1 000°C. Fracture surfaces of the coke had particular morphologies that had been inherited from the original honeycomb structure of the cedar.

Staged Pyrolytic Conversion of Acid-Loaded Woody Biomass for Production of High-Strength Coke and Valorization of Volatiles

“…More details for the influence of torrefaction on the coke from acid-unloaded CD will be available soon from another work performed in this lab. 47 In comparison with the raw CD and CD-T trf , of notable significance in Figure 7 was that the TS of cokes from acidloaded CDs, 0.7-SA-T trf and 1.0-PA-T trf , similarly showed an increase and decrease with T trf . The result supports the above explanation of this trend for CD-T trf because the presence of pores and char-like substrate in feedstock critically affect the coke strength regardless of acid loading.…”

“…This was inevitable as a result of the torrefaction of CD in the state of small particles with a fast heating rate for effectively releasing the volatiles. More details for the influence of torrefaction on the coke from acid-unloaded CD will be available soon from another work performed in this lab …”

High-Strength Formed Coke from Torrefied Biomass and Its Blend with Noncaking Coal

“…Samples. Sawdust of a Japanese cedar, which was the same as used in our previous study, 24 was used as the biomass feedstock. The composition of the organic portion of the cedar (99.6 wt % of the dry cedar) was estimated in the previous study 24 by the kinetic analysis of thermogravimetric data based on a parallel reaction model.…”

“…CA was further pulverized by gentle ball milling for 10 h, details of which were reported previously. 24 The ball-milled CA will be denoted by CA_BM. The particles sizes of CA_BM were smaller than 30 μm, as shown in Figure S1a in the Supporting Information.…”

“…The cedar was torrefied at 250, 275, or 300 °C in a fixed bed reactor with initial dry sample mass, heating rates, and holding time of 1.0 g, 5 °C/min, and 60 min, respectively. 24 The torrefied cedar (TC) was pulverized in the same cutter mill as mentioned above for 60 s, and its particle sizes were decreased to <100 μm, as shown in Figure S1b. The cedar torrefied at T °C and cutter-milled is herewith denoted by TCT.…”