Efficiency of a power generation alternative regarding the composition of feeding biomass-glycerol slurry; theoretical assessment
Introduction
The efforts to improve the share of renewables as sources for power generation are increasing. To provide an example, units consuming sugar-cane bagasse (SCB) are already responsible for 27% of the total 160 GW Brazilian installed capacity [1]. On the other hand, the rate of biodiesel country’s production is also growing, nearing now 4.5 million m3 per year [2].
As a residue, raw glycerol represents around 10% of the biodiesel production, was considered for applications in various industrial fields [3]. However, others have shown high relatively high costs involved in its purification [4]. Alternatively, some have studied the feasibility of raw glycerol as fuel and fuel additives [5] and others the opportunity of co-gasification of that residue with biomass for the generation of fuel gas [6]. On the other hand, feeding solid particulate fuels into pressurized equipment require special measures to avoid interruptions and high-maintenance costs. Since long, it has been verified [7] that slurry-feeding greatly simplifies the more conventional methods using series of lock-hoppers [8]. Nonetheless, fibrous particles might entangle inside a hopper, thus preventing them to proceed to rotary valve beneath it. This is particularly true in cases of SCB. In addition, lock-hoppers require to be under cooled inert atmospheres (such a nitrogen) to preclude fuel pyrolysis and combustion inside them. Thus, slurry-feeding brings substantial savings on capital, operation, and maintenance of power generation units based on pressurized combustion or gasification. Therefore, added to the enhancement of SCB as fuel by mixing it with raw glycerol, that strategy allows easy feeding of the solid fuel into pressurized equipment composing the power generation process.
Section snippets
State of Art
The present work adds to a series of theoretical ones aiming the application of biomass, and other residual solid fuels, mixed with water and pumped into boilers. In all of them the concept of fuel slurry-feeding, with the advantages described above, have been applied.
The Karita Power Station (Kyushu Electric Power Co., Japan) was the first and only reported unit operating with pressurized boiler combustion chamber into which a water slurry of coal was pumped [9,10]. The basic conceptual idea
Objective
Differently from a previous theoretical work [29], the present one concentrates on Configuration A (Fig. 4) to study the influence of glycerol proportion in the slurry with SCB fed into the gasifier on the overall process power generation efficiency. This might provide parameters for the decision-taking phase related to the application of RG toward enhancing power generation based on SCB. Six cases with different amount of the dry solid content in the slurry are analyzed.
Tools
The optimization procedures described here were accomplished by applying two simulation software.
CeSFaMB©2 was used to optimize the gasifier and dryer operations. It provides detailed descriptions of temperatures, pressures, and flows inside the equipment as well important overall operational data. The mathematical model behind the simulator is described elsewhere [9] and summarized in the Appendix. The simulator has been validated against real operational of boilers [[30], [31],
Methodology
For the present optimization study, the following methodology has been followed:
- 1)
First Stage: Initial gasifier optimization. As seen, dried SCB and glycerol are fed into the gasifier (Fig. 4). To be conservative, the dry particles entering the gasifier were assumed to be at the ambiance temperature. Thus, the gasifier and dryer optimizations could be accomplished independently. At this step, the rate of air injected into the gasifier and the mass flow of glycerol added to the slurry with SCB,
Premises
The following were assumed during this investigation:
- 1.
The gasifier and dryer operate under the bubbling fluidized bed (BFB) technique. SCB leaving the mill might carry small rocks and other materials along the harvested cane. BFB units are capable of operating within a wide range of feeding particle sizes and densities [30,42]. Well-designed equipment might allow for the removal of heavier materials that might drop on the distributor surface without interrupting the operation. Nonetheless, other
Results and discussions
Having in mind the assumptions listed above, preliminary simulations verified that a 5 m internal diameter bed allowed for a wide range of gasification operations, most of them within the feasible bubbling fluidization regime. Therefore, that was taken for this first round of optimization.
Fig. 6 depicts the EE for different rates of air injected into the equipment against the feeding slurry DSC. Few points were not be plotted because they led to operational conditions outside the feasible range
Conclusions
The theoretical investigation regarding the influence of sugar-cane bagasse (SCB) and raw glycerol slurry composition on the efficiency of an alternative power generation unit has been carried. The FGSIG/GT (Fuel-glycerol Slurry Integrated Gasifier/Gas Turbine) process operating under the option of biomass drying prior to its mixing with glycerol has been chosen. This differs from a previous study [29], which applied the alternative of wet SCB-glycerol slurry gasification.
The work also presents
Credit author statement
Marcio L. de Souza-Santos, Conceptualization, Methodology, Software, Review, Final text (in English), Answers to reviewers. Carina Crisp Cadavez, Computations, Simulations, Result analysis, Figures, Original Text (in Portuguese)
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors are grateful for the grant received from the National Council for Scientific and Technological Development (CNPq).
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