Comparison of Fuels and Effluents Originating from Washing and Hydrothermal Carbonisation of Residual Biomass

Abstract

A series of four different biomass feedstock was washed and hydrothermally carbonized at temperatures of 50 °C and 150–270 °C for four hours, respectively. For the first time both the resulting solid and liquid products were characterised and evaluated in a comprehensive study. Concerning fuel properties, HTC had a higher impact on the fuel quality than washing. HTC yielded hydrochar with higher carbon content than the starting material leading to a significant increase in heating value, while washing only had a minor effect on elemental composition and heating value. Treatment temperature was found to have the highest impact on LHV and elemental composition. Both washing and HTC proved effective in reducing potassium and chlorine content, while earth alkaline, phosphorous and silicon removal was limited. Process water characterisation revealed that filtrates from washing and HTC are acidic, with acidity being increased by HTC. Electrical conductivity of the effluent was found to correlate with the amount of electrolytes Na, K, Mg and Ca in the feedstock, thereby being feedstock dependent. COD, BOD5 and TOC values determined revealed that effluent from both washing and HTC is strongly contaminated by organic matter. The organic load was significantly higher in HTC effluents. Feedstock type was found to be the main influencing factor on effluent characteristics rather than HTC temperature. Nutrients were found in low concentrations. Graphic Abstract

Continuous Hydrothermal Carbonization of Olive Pomace and Orange Peels for the Production of Pellets as an Intermediate Energy Carrier

“…These results clearly show that large increases in the reactor size and the amount of feed do not have an effect on the hydrothermal carbonization process. The obtained values are slightly lower than previously reported solid yields for the HTC of olive pomace (55-75%) [9,26,35,[42][43][44][45][46], which could be a result of the high moisture content of the applied reaction mixture. The small-scale screening study with orange peels showed that the orange peels (milled into small pieces) could not be used as received, as this feedstock could not be stirred.…”

“…Another benefit of water as the reaction medium is the removal of many water-soluble alkali metals and salts from the solid phase. This significantly enhances the combustion behavior of the hydrochar solid product, according to reduced slagging and corrosion at an elevated temperature, due to the reduction in the potassium and chlorine content [11,26,27]. In the past years many application studies have been performed on hydrochar.…”

“…In recent years, there have been many reports on hydrothermal carbonization of olive pomace and orange peels at a wide range of temperatures. At the mildest processing temperatures (180-200 • C), solid yields of 55-75% have been reported for olive pomace [9,26,35,[42][43][44][45][46], whereas with orange peel, the solid yield ranges from 34 to 45% at these temperatures [1][2][3]34]. These relatively low values clearly show that valorization of the liquid stream, e.g., as biogas, is essential for the economic feasibility of the process [8,47], complemented with the recovery of valuable bioactive compounds [6].…”

Influence of Hydrothermal Carbonization on Catalytic Fast Pyrolysis of Agricultural Biomass

“…On the other hand, the best fit for ash yield (Figure 5) was achieved using a 2nd-order polynomial. Moreover, the polynomial reaches values close to 1.0 at temperatures below 100 • C. This seems sensible since Y a < 1 indicates that a part of the inorganic content of raw biomass was washed out during the treatment, and it has been reported in the literature that washing biomass with hot water can remove a part of its ash [90,91].…”

“…Moreover, the polynomial reaches values close to 1.0 at temperatures below 100 °C. This seems sensible since Ya < 1 indicates that a part of the inorganic content of raw biomass was washed out during the treatment, and it has been reported in the literature that washing biomass with hot water can remove a part of its ash [90,91]. Energy yields, shown in Figure 4, are higher than respective mass yields, which is caused by the fact that Y e is the result of the multiplication of Y m by respective energy densification ratio (ED) [85,86].…”