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Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 404
Author(s):  
Yuping Li ◽  
Maolin Ye ◽  
Fenghua Tan ◽  
Chenguang Wang ◽  
Jinxing Long

Thermodynamic performance of three conceptual systems for biomass-derived olefin production with electricity cogeneration was studied and compared via exergy analysis at the levels of system, subsystem and operation unit. The base case was composed of the subsystems of gasification, raw fuel gas adjustment, methanol/light olefin synthesis and steam & power generation, etc. The power case and fuel case were designed as the combustion of a fraction of gasification gas to increase power generation and the recycle of a fraction of synthesis tail gas to increase olefin production, respectively. It was found that the subsystems of gasification and steam & power generation contribute ca. 80% of overall exergy destruction for each case, of which gasifier and combustor are the main exergy destruction sources, due to the corresponding chemical exergy degrading of biomass and fuel gas. The low efficiency of 33.1% for the power case could be attributed to the significant irreversibility of the combustor, economizer, and condenser in the combined-cycle subsystem. The effect of the tail gas recycle ratio, moisture content of feedstock, and biomass type was also investigated to enhance system exergy performance, which could be achieved by high recycle ratio, using dry biomass and the feedstock with high carbon content. High system efficiency of 38.9% was obtained when oil palm shell was used, which was 31.7% for rice husk due to its low carbon content.


2021 ◽  
Vol 13 (24) ◽  
pp. 13665
Author(s):  
Jasmine Sie Ming Tiong ◽  
Yi Jing Chan ◽  
Jun Wei Lim ◽  
Mardawani Mohamad ◽  
Chii-Dong Ho ◽  
...  

Food waste (FW) utilized as substrate for anaerobic digestion (AD) to produce biogas is promising. Simultaneously, waste is handled and value-added products such as biogas and fertilizer are produced. Palm oil mill effluent (POME) is used as the co-substrate. This study aims to simulate the complete process flow of anaerobic co-digestion (AcoD), consisting of pre-treatment of feedstock, biogas upgrading, wastewater treatment and sludge dying using SuperPro Designer. Parameters, namely hydraulic retention time (HRT), recycle ratio of sludge, water to FW ratio (kg/kg) and co-substrate to FW ratio (kg/kg), would affect the performance of digester. The optimization of these parameters is performed using Design-Expert software, involving response surface methodology (RSM). The effects on responses such as methane flow, chemical oxygen demand (COD) and volatile solid (VS) removal efficiencies are analyzed. In treating 25,000 kg/h of feed, the optimized values for HRT, recycle ratio, water to feedstock ratio, POME to FW ratio are 37.2 days, 0.381, 0.027 and 0.004, respectively. The methane yield is 0.30 L CH4/g of COD removed, with COD and VS removal efficiencies of 81.5% and 68.9%, respectively. The project is profitable, with a payback period of 6.14 years and net present value (NPV) of $5,680,000. A comprehensive understanding of AD matures it for commercialization purposes.


Mathematics ◽  
2021 ◽  
Vol 9 (21) ◽  
pp. 2787
Author(s):  
Rubayyi T. Alqahtani ◽  
Shabir Ahmad ◽  
Ali Akgül

To lower the concentration of organic pollutants in the effluent stream, wastewater must be treated before being discharged into the environment. The question of whether wastewater treatment facilities can successfully reduce the concentration of micropollutants found in their influent streams is becoming increasingly pressing. The removal of micropollutants in treatment plants is investigated using a model that incorporates biodegradation and sorption as the key processes of micropollutant removal. This article provides the mathematical analysis of the wastewater model that describes the removal of micropollutant in treatment plants under a non-local operator in Caputo sense. The positivity of the solution is presented for the Caputo fractional model. The steady state’s solution of model and their stability is presented. The fixed point theorems of Leray–Schauder and Banach are used to deduce results regarding the existence of the solution of the model. Ulam–Hyers (UH) types of stabilities are presented via functional analysis. The fractional Euler method is used to find the numerical results of the proposed model. The numerical results are illustrated via graphs to show the effects of recycle ratio and the impact of fractional order on the evolution of the model.


Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1124
Author(s):  
Jun Wei Roy Chong ◽  
Yi Jing Chan ◽  
Siewhui Chong ◽  
Yeek Chia Ho ◽  
Mardawani Mohamad ◽  
...  

This study highlights an innovative piece of hybrid technology, whereby the combination of anaerobic and aerobic processes into a single reactor, namely, the integrated anaerobic–aerobic bioreactor (IAAB) can surpass the limits of conventional methods treating palm oil mill effluent (POME). Optimisation of IAAB using SuperPro Designer V9 simulator for maximum biogas yield while addressing its economic and environmental trade-offs was conducted for the first time. Parameters such as hydraulic retention time (HRT) and organic loading rate (OLR) were optimised in the anaerobic compartment from 10 days and 6.2 g COD/L day to 9 days and 6.9 g COD/L day, respectively. Furthermore, sludge recycle ratio was optimised from 20% to 50% in the aerobic compartment. The optimisation was successful where the biogas yield increased from 0.24 to 0.29 L CH4/g CODremoved with excellent Chemical Oxygen Demand (COD), and Biological Oxygen Demand (BOD) removal efficiencies up to 99% with 5.8% lower net expenditure. This simulation results were comparable against the pre-commercialized IAAB with 11.4% increase in methane yield after optimisation. Economic analysis had proven the optimised process to be feasible, resulting in return on investment (ROI), payback time, and internal rate of return (IRR) of 24.5%, 4.1 years, and 17.9%, respectively.


Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 461
Author(s):  
Rubayyi T. Alqahtani ◽  
Samir Kumar Bhowmik ◽  
Abdelhamid Ajbar ◽  
Mourad Boumaza

This paper proposes and analyzes a mathematical model for the production of bioethanol in a continuous bioreactor with recycling. The kinetics correspond to the use of Saccharomyces bayanus for the fermentation of sugars found in wastewater from soft drinks. The proposed model considers product growth latency, which was experimentally found in batch studies of ethanol production. Furthermore, the inhibition effect of ethanol is expressed by a modified version of the classical Andrew’s model for substrate inhibition. The proposed model consists of only three ordinary differential equations containing a minimal number of operating parameters, which include the bioreactor residence time, glucose feed concentration, recycle ratio and the fraction of biomass removed from the reactor by the flow. The positivity and the boundedness of solutions of the model were confirmed under reasonable restrictions of parameters. The stability analysis showed that there is a value of residence time at which an exchange of stability occurs between the trivial washout and non-washout solutions. This critical value depends only on the substrate feed concentration, biomass death rate, recycle ratio and purge fraction. Dynamic simulations of the model were carried out for substrate concentration in the range of 100–250 g/L, commonly used for the production of ethanol. An inverse response due to the inhibition effects of ethanol was observed in the time evolution of substrate and biomass concentrations. Parametric studies showed that ethanol concentration increases with the recycle ratio, with the inverse of residence time and with the inverse of purge fraction. The effect of ethanol latency has, on the other hand, a substantial effect on ethanol concentration. Despite its unstructured nature and the fact that some parameters such as temperature and acidity were not taken into consideration, the proposed model managed to provide useful results on the bioreactor-settler stability and the effect of key parameters on its dynamic behavior, which could pave the way for future optimization studies.


Author(s):  
Lei Ye ◽  
Biao Xing ◽  
Jichang Liu ◽  
Xinglong Qin ◽  
Wenxin Yu ◽  
...  

Based on the structure-oriented lumping method, a molecular-level reaction kinetic model of the delayed coking process, which adopted 24 structural increments to construct the feed molecular matrix containing 2,944 molecules, was established with a reaction network containing 74,581 reactions using MATLAB. The reliability of the model was verified by experimental results. According to the discriminant rules of structural increments, 173 structural vectors in gasoline and 1,132 structural vectors in diesel were classified into different group compositions, respectively. The model could track the reaction path of any specific molecule in the complex thermal cracking reaction network. The influences of operation conditions such as recycle ratio on the product distribution could be discovered through the calculation of the molecular-level model, which is helpful for the process optimization and precise regulation of product composition for the delayed coking plants.


2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Fereshteh Samimi ◽  
Mehrzad Feilizadeh ◽  
Seyedeh Bahareh Najibi ◽  
Mohammad Arjmand ◽  
Mohammad Reza Rahimpour

AbstractThe conversion of CO2 to methanol holds great promise, as it offers a pathway to reduce CO2 level in the atmosphere and also produce valuable components. In this study, a typical methanol synthesis plant for CO2 conversion was numerically modeled. Effect of fresh feed to plant parameters (i.e., pressure and CO2 concentration) as well as the influence of recycle ratio on the reactor performance was investigated. Hence, all essential equipment, including compressor, mixer, heat exchanger, reactor, and liquid–vapor separator were considered in the model. Then, at the best operating conditions, thermal behavior and components distribution along the length and radius of the reactor were predicted. Finally, the effect of inert gases was investigated in the methanol production process and the results were compared with the conventional route (CR), which uses natural gas for methanol synthesis. The results revealed that in the absence of inert gases and by employing a recycle stream in the process, CO2 hydrogenation leads to 13 ton/day production of methanol more than CR. While in the feedstock containing 20% inert gases, which is closer to the realistic case, methanol production rate is 45 ton/day lower than CR. These findings prospect a promising approach for the production of green methanol from carbon dioxide and hydrogen.


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