Alkaline Black Liquor Research Articles

Kinetics of CO2 Gasification of Alkaline Black Liquor from Wheat Straw. Influence of CO and CO2 Concentrations on the Gasification Rate

Interest in the use of nonwoody biomass as a raw material for pulp and paper production is growing worldwide. Moreover, new technologies are being developed to solve the problems caused by the silica present in alkaline black liquor (ABL) from straw in heat recovery systems. Because, among the various possible technologies, gasification is becoming attractive as a new alternative recovery system for ABL, in-depth studies of ABL gasification are therefore required. The present work is focused on the study of CO2 gasification of a char obtained from the ABL pyrolysis. Specifically, the influence of [CO] and [CO2] on the gasification rate at different gasification temperatures has been studied. The process may be described by a Langmuir−Hinshelwood equation for a specific range of operating conditions. The data obtained suggest that this operational range could be broader if the number of catalytic sites is considered as a function of [CO] and the final pyrolysis temperature rather than as constant.

Thermal Degradation of Alkaline Black Liquor from Wheat Straw. 2. Fixed-Bed Reactor Studies

The usual problems experienced with common recovery boilers are aggravated in processes involving alkaline black liquor derived from straw. The consequent need to develop alternative processes for the use of black liquor for energy purposes, such as pyrolysis or gasification, requires a good understanding of the thermochemical behavior of this substance. There is, however, little information available. Part 1 of this work (Gea, G.; Murillo, M. B.; Arauzo, J. Ind. Eng. Chem. Res. 2002, 41, 4714), therefore, studied the thermal degradation of alkaline black liquor from straw in a thermogravimetric system. The present work also focuses on its pyrolysis. In particular, the influence has been analyzed of the final pyrolysis temperature (250−900 °C) and the heating rate (5−30 °C/min) on the product yields, gas composition, and specific surface area of the resulting char in a fixed-bed reactor. The results obtained show that both the energy recovery and the specific surface area of the char increase with a rise ...

Thermal Degradation of Alkaline Black Liquor from Straw. Thermogravimetric Study

Both pyrolysis and gasification can be considered as alternatives to conventional boilers for recovering chemicals and energy from black liquor. The present work is focused on the study of pyrolysis of alkaline black liquor from straw, and its interest is enhanced by the fact that the material used has hardly been studied before. The influence has been studied of the final pyrolysis temperature (500-900°C), the heating rate (5-30°C/min), and the addition of a determined CO concentration in the N 2 atmosphere (5-40% vol) on both the final solid conversion and the devolatilization rate. The results show that the thermal decomposition of the organic matter fraction of black liquor takes place at temperatures below 550°C in N 2 atmosphere. The weight loss observed at temperatures higher than 550°C is mainly due to reduction reactions of alkaline compounds by the carbon. The final solid conversion and the devolatilization rate are also noticeably influenced by the addition of a certain CO flow rate in N 2 atmosphere.

Separation characteristics of modified polysulfone ultrafiltration membranes using NOx

Abstract Commercially available polysulfone membranes are known to be hydrophobic and are prone to fouling due to strong interaction with variety of solutes. In order to overcome this, the 5 K molecular weight cut off (MWCO) and 20 K MWCO polysulfone ultrafiltration membranes have been modified by gas phase nitration using NOx (a mixture of NO and NO2). These membranes were subsequently aminated using hydrazine hydrate and as a result of this, membranes were observed to give considerably higher rejection for nonionic molecules (polyethylene glycol) with simultaneous increase in resistance to the flow. Experimental measurements have shown that the modified membranes have the exchange capacity of 4.17 meq per dry g of membrane and we show that this exchange capacity can be obtained only when there are about two exchangeable amine groups per repeat unit of every polysulfone molecule. A careful examination of the increase in resistance suggests that one of the mechanisms of separation of nonionic solutes is due to the reduction of average pore size of the membranes. However, for sodium chloride solution we show that the modified membranes have a 13% rejection (as opposed to none for unmodified one); while for a complex feed, like alkaline black liquor, the rejection (for all dilutions) is twice that for unmodified membranes. Due to this modification, it appears that the membrane is entering into nanofiltration zone.

Anaerobic digestion of alkaline black liquor using an up‐flow anaerobic sludge blanket reactor

AbstractThe anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up‐flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m−3 day−1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm3 per dm3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster‐like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability.

Alkaline black liquor treatment by continuous electrodialysis

Investigations were carried out to study the feasibility of electrodialytic regeneration of alkaline black liquor in a continuously operated three-compartment electrodialyzer. Effects of current density (5–25 mA/cm 2), flow velocities of black liquor (0–20.9 cm/min) and distilled water (9.9–39.9 cm/min), and percent soda recovery with various membrane arrangements were studied. A cation exchange—neutral membrane arrangement gave better percent caustic recovery than did a neutral cellophane—cellophane arrangement. The effect of current density on current efficiency and variation of specific energy consumption with percent caustic recovery were also studied. The specific energy consumption can be used as a criterion for selection of operating conditions. Higher percent caustic recovery, lower kW-hr/kg and lower lignin precipitation were observed at lower velocities of black liquor and water.

Alkaline black liquor treatment by batch electrodialysis

Regeneration d'une lessive noire de papeterie dans un electrodialyseur discontinu a trois compartiments: on etudie les influences de la densite de courant, du pH, du temps de sejour et du pourcentage de recuperation de soude pour plusieurs arrangements de membranes

Electrodialysis in the regeneration of paper mill spent liquor

Experiments have been carried out on the electrodialytic regeneration of soda and lignin from alkaline black liquor with the abatement of environ- mental pollution for a smaller capacity rice straw-based pulping plant. To predict the performance capability of the system, the hydrodynamic characteristics of a multi-compartment electrodialysis cell have been correlated with the polarizing parameters in the following simplified equations: ▪ For efficient and economical recovery of soda along with lignin, a two stage electromembrane process, consisting of conventional ED with a -C-N-C-N-C arrangement, followed by an electrogravitational technique is recommended.