Simultaneous Steam Reforming of Tar and Steam Gasification of Char from the Pyrolysis of Potassium-Loaded Woody Biomass

Abstract

This paper proposes a two-stage conversion of biomass into gas, which consists of pyrolysis at 500–600 °C and steam reforming/gasification at 600–700 °C, and has a special feature of recycling of the potassium (K) catalyst. The proposed process was simulated experimentally employing K-loaded cedar as the feedstock and char from its pyrolysis as the catalyst for tar reforming. Tar from the pyrolysis was reformed over the char in a sequence of carbon deposition onto the pore surface and K-catalyzed steam gasification of the deposit, while K-catalyzed char gasification created active pores simultaneously. At the steam/carbon molar ratio of 0.55–1.10, the catalysis of K simultaneously realized the concentration of heavy tar (boiling point temperature > 336 °C) in the product gas as low as 20 mg m3 N dry and progress of the char gasification as fast as that of char formation by the pyrolysis. The concentration of hydrogen in the product gas exceeded 50 vol % dry. A portion of K was released from the pyrolyzing cedar, fully captured by the char bed of the reformer, and involved in the steam reforming and gasification. A major portion of K retained in/on the spent char was extracted with water. The resulting aqueous solution of K was ready to be used as spray for K loading on the feedstock.

Kinetics and Mechanism of Steam Gasification of Char from Hydrothermally Treated Woody Biomass

“…The apparent slowdown of the mass release at t ≈ 2 min is not due to that of the gasification but to the evaporation of K species as KOH. 55 Thus, char IIa-K2 was gasified completely within 2 min. values for both chars are clearly lower than those for char II and char IIa.…”

“…On the other hand, the removal of AAEM species, in other words, the major catalytic species, will considerably change the characteristics of gasification of char 26−29 and reforming of volatiles over the char. 30,31 The gasification of char from the pyrolysis of biomass is contributed by non-catalytic gasification and AAEM-catalyzed gasification. 29 These two modes of gasification differ clearly from each other regarding the rate of reaction and its variation with the progress of char conversion.…”

Physically activated wheat straw-derived biochar for biomass pyrolysis vapors upgrading with high resistance against coke deactivation

“…Despite the fact that the value of Yg was relatively low, it was considerably higher than that obtained using a bed of silica sand. This can indicate that, given the extremely low porosity of the non-activated biochar, the presence of inherent inorganic species available on their surface, especially K and Ca (see Table A.3), could lead to a certain catalytic activity [48,49]. On the other hand, slightly better results were obtained for physically activated biochar at mild conditions (BO = 15%).…”

“…3a, the steam reforming (SR) test conducted using the PAC40 catalyst under the same conditions than those used for the catalytic cracking test (700 °C and a GHSV of 19500 h -1 ) revealed a marked increase in the production of H2 (and, to a lesser extent, CO2) at the expense of CO and CH4. A possible explanation for this finding is the fact that the water fed into the reactor was not only involved in reforming reactions (reactions 2 and 3 in Table 4), but also helped to keep the catalyst active through steam gasification of both the catalyst and formed coke (reaction 6 in Table 4) [12,48]. In addition, and as pointed out by Feng et al [49], the oxidative nature of steam can lead to the formation of O-containing functional groups and related crystal lattice defects, which could provide further active sites for gasification.…”

Thermal decomposition and gasification of biomass pyrolysis gases using a hot bed of waste derived pyrolysis char

“…Hosokai et al (2008) investigated the decomposition of benzene and naphthalene over charcoal and concluded that the decomposition of tar over char was mainly due to the coking rather than decomposition of aromatic compounds. In addition, the accumulation of coke on the surface of the chars may block the available active sites (metal species in the char) thus decreasing the char activity with time (Sueyasu et al, 2012). As a consequence, the BET surface area and the pore volumes of the tested char were decreased.…”