Effects of Process Water Recycling and Particle Sizes on Hydrothermal Carbonization of Biomass

Abstract

Hydrothermal carbonization (HTC) is a promising thermochemical process for the conversion of biomass with high moisture content, and therefore, interest in the development of continuous technology is growing. However, the development of continuous HTC systems requires the in-depth understanding of reaction kinetics, heat transfer mechanisms, exothermic or endothermic nature of the reaction, effect of operational parameters, recyclability of process water, and variability in biomass feedstock. The current paper discusses the effects of recyclability of process water and particle size on the product yield. To investigate the water recycling effect, HTC experiments were performed on sawdust using recycled water in a batch reactor. Moreover, to study the particle size effect, 3 small reactors containing specific particle sizes of biomass were placed in a larger reactor simultaneously to ensure consistency in the process condition. The results showed that the process water recycling increases the mass yield and higher heating value (HHV) of the solid product by 12% and 2%, respectively, after the first recycle. Physicochemical properties of hydrochar were studied by carrying out the ultimate and proximate, HHV, thermogravimetric coupled with Fourier transform infrared spectroscopy, and Brunauer−Emmett−Teller analysis, and results are discussed. Regarding the particle size study, higher mass yield, a decrease in heating value, and an increase in total organic carbon in the process water were observed by increasing the particle size.

Numerical Comparison of a Combined Hydrothermal Carbonization and Anaerobic Digestion System with Direct Combustion of Biomass for Power Production

“…More details on the procedure of these characterization tests and the composition of the products can be found in Ref. [15].…”

“…The process water from HTC is acidic and it contains water, acetic acid, and a number of other organic acids [15]. According to Kambo et al [14], these organic acids mainly contain acetic acid, 5-Hydroxyl Methyl Furfural (HMF), and levulinic acid.…”

“…In addition to the use of hydrochar for power generation, the process water can enter an existing AD system. The pH of the PW is in the range of 2.7-3.5 [14,15] and, hence, it can accelerate the hydrolysis step in AD. Ease of conversion in the AD system is expected, as hydrolysis is considered to be the limiting factor of AD systems [16].…”

Hydrothermal Carbonization of Organic Waste and Biomass: A Review on Process, Reactor, and Plant Modeling

“…Starting from experimental data (relevant to 39 HTC tests), Heidari et al [80] made an attempt to predict the effect of several severity factor values (3.83, 5.01, and 6.19) on the hydrochar mass yield, higher heating value (HHV), and carbon content. With the same aim, in a work dealing with the water recycling effect during the HTC of sawdust, Heidari et al [81] used severity factors between 4.3 and 5.3. Similarly, Basso et al [82] reported the solid, liquid, and gaseous phase yields resulting from HTC of grape marc constituents as a function of the severity factor.…”

Determination of exothermic batch reactor specific model parameters

“…However, from this concept, processes with a previously unknown or only partially known input substances composition are beyond the scope. Examples of a such process may be recycling or regeneration processes [1][2][3]. The input substances here can be wasted, polluted, or otherwise contaminated raw materials with a major impact on the system's behaviour, and of course also on the system model and/or model parameters.…”