renewable energy sources have significant potential for limiting climate change and reducing greenhouse gas emissions due to the increased global energy demand. Fluidized bed gasification of biomass is a substantial contribution to meeting the global energy demand in a sustainable way. however, ashrelated problems are the biggest challenge in fluidized bed gasification of biomass. bed agglomeration is a result of interaction between the bed material and alkali metals present in the biomass ash. The agglomerates interfere with the fluidization process and might result in total de-fluidization of the bed. The study focuses on ash challenges related to the fluidization behavior in gasification of biomass. a model is developed and verified against results from previous performed experiments in a cold flow model of a bubbling fluidized bed. The commercial computational particle fluid dynamics (CPFD) software barracuda Virtual reactor is used for the computational study. The simulations show that the CPFD model can predict the fluidization process of an agglomerated fluidized bed gasifier.
Deep geologic injection of supercritical carbon dioxide (CO 2 ) for enhanced oil recovery (EOR) has been widely used for improved oil recovery from depleted oilfields since early 1970s. The CO 2 injection maintains the pressure, mobilize the oil and release the petroleum resources that would otherwise be inaccessible. In addition to improving the oil recovery, the CO 2 -EOR contributes to minimize the impact of CO 2 -emissions to the atmosphere. The injected CO 2 will be remained trapped in the underground geological formations, as the CO 2 replace the oil and water in the pores. Carbonate reservoirs are characterized by low permeability and high heterogeneity, resulting in early breakthrough of gas and water and hence low oil recovery. The presence of naturally fractures in carbonate reservoirs is a major problem for the oil industry using CO 2 -EOR, because significant amount of CO 2 are recycled to the well, and thereby not distributes in the reservoir. This study focuses on CO 2 injection into a naturally fractured carbonate reservoir, including near-well simulations of CO 2 -distribution in the rock matrix. The simulations are carried out using the reservoir simulation software Rocx in combination with OLGA. The simulations show that CO 2 -injection into a naturally fractured carbonate reservoir in combination with closing of the fractured zones result in good distribution of CO 2 in the reservoir.
Method of identifying an operating regiMe in a bubbling fluidized bed gasification reactor rajan jaiswal, nora c. i. s. furuvik, rajan k. thapa & britt M. e. Moldestad department of natural science and Maritime science, university of southeastern norway, porsgrunn, norway abstract this work presents a new method for identifying the bubbling regime of a fluidized bed gasification reactor. the method has been developed using experimental measurements and a computational model. pressure drops are measured in experiments, and pressure drop as well as solid volume fraction fluctuations are calculated by implementing the model. experiments are carried out with sand and limestone particles of mean diameter 346 m µ and 672 m µ , respectively. a computational particle fluid dynamics (cpfd) model has been developed for the reactor and implemented using a commercial cpfd software barracuda vr. the model is validated against experimental measurements. the validated model is used to analyse the fluctuation of pressure drop and solid volume fraction as a function of superficial air velocity. the change in standard deviation of pressure drop and solid volume fraction fluctuation is used to predict the transition from one regime to another. the method can be used in the design and operation of a bubbling fluidized bed gasification reactor. the results show that the minimum fluidization velocity for sand and limestone are 0.135 m/s and 0.36 m/s, respectively and are independent of the particle aspect ratio. both types of particle beds make the transition into bubbling regime as soon as they get fluidized. the bed aspect ratios have almost no effect on the onset of bubbling fluidization regime. the slugging velocity decreases with increasing aspect ratio for both types of particles. the operating range of the bubbling fluidized bed for sand particle is 0.2-0.4 m/s and 0.5-0.8 m/s for the limestone particles.
Segregation of biomass in a gasification reactor is an inevitable problem that can jeopardize the advantages such as uniform temperature control and proper mass circulation, and good solid-gas contacting area of the fluidized bed. This work investigates the mixing and segregation behavior of the biomass in a bubbling fluidized bed using a Computational Particle Fluid Dynamic (CPFD) model. The model is simulated in the CPFD software Barracuda VR. The sand particles and wood chips are used as the bed material and biomass. The simulations are carried out with different volume percentage of the biomass at constant bed aspect ratio. The results show that the minimum fluidization velocity is decreased from 0.08 m/s to 0.06 m/s with the increase in biomass volume from 5% to 20% in the bed. The complete segregation of biomass occurs at the superficial gas velocity that is 3.5 times greater than minimum fluidization velocity. With the increase in superficial gas velocity, 0 ≥ 6. , the biomass again starts to mix with the bed material. However, the mixing of woodchips is mainly limited to the upper part of the bed.
The agglomeration tendency during gasification of grass pellets in a bubbling fluidized bed reactor was studied. Particle agglomeration occurs as a consequence of interactions between the bed particles and the biomass ash during the thermal conversion of biomass in fluidized beds. The continuous operation and high efficiency of the fluidized beds are in these cases limited by partial or complete de-fluidization.In order to study the agglomeration tendency of grass pellets at defined operating conditions, controlled agglomerations tests are performed in a laboratory scaled 20 kW bubbling fluidized bed reactor. The effect of the ratio between the superficial fluidization velocity (u0) and the minimum fluidization velocity (umf) on the agglomeration tendency for grass pellets is reported. The results show that agglomeration in the bed can be recognized by fluid dynamic disturbances in the bed, and if not counteracted, de-fluidization will occur. The ratio u0/umf influences the agglomeration tendency and the de-fluidization of bed. As the ratio u0/umf increases, the agglomeration tendency and the de-fluidization time decreases. The de-fluidization temperature was not influenced by the changes in the superficial velocity ratio.
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