Simulation and optimization of multi-component organic Rankine cycle integrated with post-combustion capture process

A multi-component working fluid organic Rankine cycle (ORC) with advanced configuration is proposed and optimized in this paper. The proposed ORC utilizes the wasted heat of a CO₂ capture process as a heat source, and waste heat utilization is optimized through heat integration. The ORC employs advanced configurations: multi component working fluid, a cold energy recuperating in multi stream cryogenic heat exchanger (MSCHE), and a vapor recondensation process (VRP), thus, its power generation efficiency is much higher than that of conventional ORCs that utilize wasted heat. Process optimization is achieved through exergy evaluation. The results indicate that the proposed cycle is able to produce 304 kJ per kg liquefied natural gas (LNG), and its corresponding second-law efficiency is approximately 46.2%. With the power generation of the ORC, the power de-rate caused by the CO₂ capture process installation is completely compensated and produces more electricity compared with the original power plant.     

集成NGL回收的新型天然气液化系统AP-XTM的概念设计与模拟分析

为提高液化天然气能量集成与设备共用水平,提出了一种基于大型AP-X^TM液化流程，综合气体过冷技术（GSP）的集成NGL（天然气凝液）回收工艺的天然气液化系统的概念设计。基于化工流程模拟软件Aspen HYSYS进行模拟和分析，将集成工艺多流股换热器性能、全流程的单位功耗和乙烷回收率作为衡量系统性能的三项指标。模拟和分析的结果表明，集成NGL回收的AP-X^TM液化工艺单位功耗降低至0.45 kW·h·(kg LNG)^-1，较单产系统能耗降低了6%，同时乙烷回收率达到93%，实现了NGL的高效分离。通过热力学分析、?分析和经济性分析得出本设计流程具有较高的性能和经济价值，可为天然气液化工艺的集成设计和技术改造提供指导借鉴。     

A novel conceptual design by integrating NGL recovery and LNG regasification processes for maximum energy savings

Natural gas liquids (NGL) recovery from shale gas needs large amounts of cold energy for cooling, while liquefied natural gas (LNG) regasification requires tremendous hot energy for heating. Thus, recycling the cold energy from LNG regasification process at a receiving terminal to assist the NGL recovery process has great economic benefits on both energy saving and high‐value product recovery. A novel conceptual design by integrating NGL recovery from shale gas and LNG regasification at receiving terminals has been developed. It first generates a process superstructure. Then, a simulation‐assisted mixed‐integer linear programming (MILP) model is developed and solved for the optimal process synthesis. Next, heat exchange network (HEN) design and analysis are performed to accomplish the maximum energy‐saving target. Finally, rigorous plant‐wide simulations are conducted to validate the feasibility and capability of the entire conceptual design coupling of separation and heat integration. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4673–4685, 2013     

Some process fundamentals of biomass gasification in dual fluidized bed

The dual fluidised bed gasification technology is prospective because it produces high caloric product gas free of N₂ dilution even when air is used to generate the gasification-required endothermic heat via in situ combustion. This study is devoted to providing the necessary process fundamentals for development of a bubbling fluidized bed (BFB) biomass gasifier coupled to a pneumatic transported riser (PTR) char combustor. In a steam-blown fluidized bed of silica sand, gasification of 1.0 g biomass, a kind of dried coffee grounds containing about 10 wt.% water, in batch format clarified first the characteristics of fuel pyrolysis (at 1073 K) under the conditions simulating that prevailing in the gasifier intended to develop. The result shown that via pyrolysis more than 60% of fuel carbon and up to 75% of fuel mass could be converted into product gas, while the simultaneously formed char was about 22% of fuel mass. With all of these data as the known input, a process simulation using the software package ASPEN then revealed that the considered dual bed gasification plant, i.e. a BFB gasifier + a PTR combustor, is able to sustain its independent heat and mass balances to allow cold gas efficiencies higher than 75%, given that the fuel has suitable water contents and the heat carried with the product gas from the gasifier and with the flue gas from the char combustor is efficiently recovered inside the plant. In a dual fluidized bed pilot gasification facility simulating the gasification plant for development, the article finally demonstrated experimentally that the necessary reaction time for fuel, i.e. the explicit residence time of fuel particles inside the BFB gasifier computed according to a plug granular flow assumption, can be lower than 160 s. The results shown that varying the residence time from 160 to 1200 s only slightly increased the gasification efficiency, but the reaction time available in the PTR, say, about 3 s in our case, was too short to assure the finish even of fuel pyrolysis.     

Methane dry reformer by application of chemical looping combustion via Mn-based oxygen carrier for heat supplying and carbon dioxide providing

In this study, the production of H₂ utilizing chemical looping combustion (CLC) in a methane dry reformer assisted by H₂ perm-selective membranes in a CLC-DRM configuration has been investigated. CLC via employment of a Mn-based oxygen carrier generates large amounts of heat in addition to providing CO₂ as the raw material for the dry reforming (DR) reaction. The main advantage of the CLC-DRM configuration is the simultaneous capturing and consuming of CO₂ as a greenhouse gas for H₂ production.A steady state one dimensional heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC-DRM configuration. Simulation results show that CH₄ is completely consumed in the fuel reactor (FR) of the CLC-DRM and pure CO₂ is captured by condensation of H₂O. Also, CH₄ conversion and H₂ yield reach 73.46% and 1.459 respectively at the outlet of the DR side in the CLC-DRM. Additionally, 4562 kmol h⁻¹ H₂ is produced in the DR side of the CLC-DRM.Finally, results indicate that by increasing the FR feed temperature up to 880 K, CH₄ conversion and H₂ production are enhanced to 81.15% and 4790 kmol h⁻¹ respectively.     

Air blown partial gasification of coal in a pilot plant pressurized spout-fluid bed reactor

The advanced high efficiency cycles are all based on gas turbine technology, so coal gasification is the heart of the process. A 2 MW_th spout-fluid bed gasifier has been constructed to study the partial gasification performance of a high ash Chinese coal. This paper presents the results of pilot plant partial gasification tests carried out at 0.5 MPa pressure and temperatures within the range of 950–980 °C in order to assess the technical feasibility of the raw gas and residual char generated from the gasifiier for use in the gas turbine based power plant. The results indicate that the gasification process at a higher temperature is better as far as carbon conversion, gas yield and cold gas efficiency are concerned. Increasing steam to coal ratio from 0.32 to 0.45 favors the water–gas and water–gas shift reactions that causes hydrogen content in the raw gas to rise. Coal gasification at a higher bed height shows advantages in gas quality, carbon conversion, gas yield and cold gas efficiency. The gas heating value data obtained from the deep-bed-height displays only 6–12% lower than the calculated value on the basis of Gibbs free energy minimization. The char residue shows high combustion reactivity and more than 99% combustion efficiency can be achieved.     

Transesterification of palm oil with methanol in a reactive distillation column

The higher feedstock and processing costs for biodiesel production can be reduced by applying reactive distillation (RD) in transesterification process. The effects of reboiler temperature, amount of KOH catalyst, methanol to oil molar ratio and residence time on the methyl ester purity were determined by using a simple laboratory-scale RD packed column. The results indicated that from the empty column, the system reached the steady state in 8 h. Too high reboiler temperature and the amount of catalyst introduce more soap from saponification in the process. The optimal operating condition is at a reboiler temperature 90 °C, a methanol to oil molar ratio of 4.5:1.0, KOH of 1 wt.% respect to oil and 5 min of residence time in the column. This condition requires the fresh feed methanol 25% lower than in the conventional process and produces 92.27% methyl ester purity. Therefore this RD column can be applied in small or medium biodiesel enterprise.     

Anti-fouling surface modified stainless steel for food processing

Fouling on food contact surfaces (e.g. heat exchangers, work tables, conveyors) during food processing has a significant impact on operating efficiency and can promote biofilm development. Processing raw milk on plate heat exchangers results in significant fouling of proteins as well as minerals, and is exacerbated by the wall heating effect. The surface of 316L stainless steel heat exchanger plates was modified to resist fouling during food processing. An electroless nickel plating process was used to co-deposit fluorinated nanoparticles onto 316L stainless steel. The ability to resist fouling was demonstrated on a pilot plant scale plate heat exchanger. The fluorinated nanoparticle modified steel reduced surface energy from 41.4 to 24.7 mN/m, and reduced foulant accumulation by 97%. The anti-fouling coating was demonstrated to improve heat transfer efficiency. Repeatability studies were performed and confirmed that the EN-PTFE surface coating maintained its anti-fouling properties through 10 independent processing runs. Co-deposition of fluorinated particles during electroless nickel plating represents an effective and commercially scalable method to prepare anti-fouling coatings on stainless steel.     

The influence of the carbon precursor,carbon feed rate and helium gas flow rate on the synthesis of fullerenes from carbon powder in an entrained flow 3-phase AC plasma reactor operating at atmospheric pressure

We studied an entrained flow 3-phase AC plasma reactor operating at atmospheric pressure with helium for the synthesis of fullerenes from different carbon powder precursors through an evaporation–condensation process. A parametric study focusing on gas flow rate and carbon powder feed rate was carried out using three commercial carbon materials: Y50A acetylene black from SN2A, E 250 carbon black from TIMCAL, and KS 4 graphite powder from TIMCAL. This study revealed a strong dependence of these parameters with fullerene yield and rate of fullerene production. It also revealed the key role of the carbon black purity. The best results were obtained using acetylene black Y50 A, for which a rate of fullerene production of the order of 17 g h^?1 corresponding to a 480 g h^?1 carbon feed rate at 3.6% fullerene content (C60 + C70) were obtained. The specific energy input defined as the plasma power related to carbon precursor feed rate and rate of fullerene production were estimated to 0.039 kWh g^?1 and 1.11 kWh g^?1 respectively.     

Effect of calcination temperature of mesoporous nickel–alumina catalysts on their catalytic performance in hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous nickel–alumina (Ni–A-NS) catalysts prepared by a non-ionic surfactant-templating method were calcined at various temperatures for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of nickel–alumina catalysts on their physicochemical properties and catalytic activity for steam reforming of LNG was investigated. Nickel oxide species were finely dispersed on the surface of Ni–A-NS catalysts through the formation of nickel aluminate phase. Reducibility, nickel surface area, and nickel dispersion of Ni–A-NS catalysts decreased with increasing calcination temperature. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas decreased with increasing calcination temperature of Ni–A-NS catalysts. Nickel surface area and reducibility of Ni–A-NS catalysts were well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni–A-NS700 (nickel–alumina catalyst calcined at 700 °C) with the highest nickel surface area and the highest reducibility exhibited the best catalytic performance.     

Biodiesel production from waste tallow

In the present investigation an attempt has been made to use waste tallow as low cost sustainable potential feed stock for biodiesel production. Effect of various process parameters such as amount of catalyst, temperature and time on biodiesel production was investigated. The optimal conditions for processing 5 g of tallow were: temperature, 50 and 60 °C; oil/methanol molar ratio 1:30 and 1:30, amount of H₂SO_4, 1.25 and 2.5 g for chicken and mutton tallow, respectively. Under optimal conditions, chicken and mutton fat methyl esters formation of 99.01 ± 0.71% and 93.21 ± 5.07%, was obtained after 24 h in the presence of acid. The evaluation of transesterification process was followed by gas chromatographic analysis of tallow fatty acid esters. A total of 98.29% and 97.25% fatty acids were identified in chicken and mutton fats, respectively. Both fats were found highly suitable to produce biodiesel with recommended fuel properties.     

Pilot experimental study on shell and tube heat exchangers with small-angles helical baffles

In this paper, the experimental comparisons of shell side thermodynamic and hydraulics performance are made among three helical baffles heat exchangers and one segmental baffles heat exchanger. The experiment scale is larger than the previous experimental setup as the diameter of test heat exchangers are 500 mm and the effective tube length are 6 m; the experiment mainly focuses on the small helical angle scheme as the helical angle ranges from 7° to 25°. Among all the four heat exchangers, both the shell side heat transfer rate and the shell side pressure drop peak when helical angle equals 7°, and the shell side heat transfer rate per unit pressure drop at this angle is the smallest. This phenomenon could be easily illustrated as the concept ‘fluid-flow distance’ is presented. At last, the correlations for the shell side Nusselt number and friction factor are presented as a reference.     

Characteristics of the product from steam activation of sewage sludge

Steam activation of a dried sewage sludge was studied to produce hydrogen rich gas and sludge char for converting to energy and resources. A batch-type wire mesh reactor was used to study the characteristics of the steam activation. The characteristics of activation product (i.e., producer gas, gravimetric tar, light tar, and sludge char) were identified.With the increase in the steam feed rate, the sludge char decreased but the producer gas increased, having higher gas heating value. And tar generation slightly increased when a small amount of steam was fed, but when the steam feed rate significantly increased, tar decreased because part of the tar was converted into light gas.Hydrogen and carbon monoxide increased with the increase in the steam feed rate. And carbon dioxide, methane, ethylene, and ethane reached their maximum according to different production mechanisms up to decreasing the species.The gradually increase in the steam feed rate resulted in the creation of micropores, which developed to the maximum when the steam flow rate was 14 mL/g min. When excessive steam was supplied, however, micropores sank due to the resulting sintering phenomenon, and the adsorption capacity deteriorated. The sludge char had a mean pore size of 6.229 nm, which is the size of mesopores from which condensible tar (the cause of damage on the device) is properly adsorbed and removed.     

Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems

Biomass gasification processes are more commonly integrated to gas turbine based combined heat and power (CHP) generation systems. However, efficiency can be greatly enhanced by the use of more advanced power generation technology such as solid oxide fuel cells (SOFC). The key objective of this work is to develop systematic site-wide process integration strategies, based on detailed process simulation in Aspen Plus, in view to improve heat recovery including waste heat, energy efficiency and cleaner operation, of biomass gasification fuel cell (BGFC) systems. The BGFC system considers integration of the exhaust gas as a source of steam and unreacted fuel from the SOFC to the steam gasifier, utilising biomass volatilised gases and tars, which is separately carried out from the combustion of the remaining char of the biomass in the presence of depleted air from the SOFC. The high grade process heat is utilised into direct heating of the process streams, e.g. heating of the syngas feed to the SOFC after cooling, condensation and ultra-cleaning with the Rectisol^® process, using the hot product gas from the steam gasifier and heating of air to the SOFC using exhaust gas from the char combustor. The medium to low grade process heat is extracted into excess steam and hot water generation from the BGFC site. This study presents a comprehensive comparison of energetic and emission performances between BGFC and biomass gasification combined cycle (BGCC) systems, based on a 4th generation biomass waste resource, straws. The former integrated system provides as much as twice the power, than the latter. Furthermore, the performance of the integrated BGFC system is thoroughly analysed for a range of power generations, ～100–997 kW. Increasing power generation from a BGFC system decreases its power generation efficiency (69–63%), while increasing CHP generation efficiency (80–85%).     

Experimental and modeling studies on the enantio-separation of 3,5-dinitrobenzoyl-(R),(S)-leucine by continuous liquid–liquid extraction in a cascade of centrifugal contactor separators

The continuous enantioselective liquid–liquid extraction of aqueous 3,5-dinitrobenzoyl-(R),(S)-leucine (A_R,S) using O-(1-t-butylcarbamoyl)-11-octadecylsulfinyl-10,11-dihydro-quinine (C, a cinchona alkaloid) as extractant in 1,2-dichloroethane (DCE) was studied experimentally in a countercurrently operated pilot scale cascade of six centrifugal contactor separators (CCS) at 294 K. The extractant was efficiently recovered by back-extraction in a single CCS allowing the cascade to be run continuously for 10 h. The steady-state ee of A_R (ee_R) in the raffinate was 42% at a 99% yield, the A_S was obtained with high purity (98% ee_S) and a yield of 55% in the back-extraction raffinate. In total 2.23 g of A_S was obtained at steady-state operation from 8.11 g racemate feed. Deterioration of the ee in time was not observed, demonstrating the robustness of the chemistry. The experiments were modeled using an equilibrium stage approach. The correlation between model and experiment was satisfactory. The model was applied to optimize the production of both enantiomers in >97% ee. At zero reflux, 12 stages are required for 99% ee for both enantiomers. Application of a reflux allows a 25% reduction of the total liquid flow through the system by reduction of the wash feed as well as a reduction in the number of stages from 12 to 11. With a configuration of 12 CINC-V02’s operating at an aqueous feed flow of 360 mL/min, the model predicts that 17.7 kg racemate per week may be separated into both enantiomers with 99% ee using only 60 g of extractant.     

Novel three-dimensional microfluidic device for process intensification

Microchannel heat exchangers and chemical reactors have extensive applications in process industries, especially in electronics cooling, air conditioning, and chemical industries. Microchannel devices provide enhanced heat and mass transfer characteristics by controlled flow conditions and high surface-to-volume ratios. The different designs of microchannels are based on planar structures from various fabrication technologies. In the present study a novel three-dimensional micro-structured device, the micro coiled flow inverter (MCFI) with 0.38–0.8 mm internal diameter, has been numerically investigated as a micro heat exchanger. In comparison micro helical coil (MHC) and straight tube of same heat transfer area (d_t = 0.5 mm, A = 3.9 × 10⁻⁴ m²) has been studied, too. The Reynolds and Prandtl numbers are varied from 25 to 1200 and 0.74 to150, respectively. The MCFI offers a four-fold heat transfer enhancement as compared to straight tube of same heat transfer area at N_Re = 1200 and N_Pr = 7. Furthermore, the heat transfer coefficient in MCFI augments by 38.5% as compared to MHC, with slight increase (5–16%) in friction factor. New design correlations are developed for Nusselt number and friction factor in MCFI. The MCFI device offers 1.15–1.7-folds higher thermal merit as compared to micro straight tube.     

Catalytic gasification of woody biomass in an air-blown fluidized-bed reactor using Canadian limonite iron ore as the bed material

A Canadian limonite iron ore was tested for the first time as a catalytic bed material for air-blown gasification of pine sawdust at various equivalence ratios (ER, 0.20–0.35) on a pilot-scale fluidized bed gasifier, in comparison to a conventional olivine bed material. Effects of bed materials (iron ore and olivine) on tar formation and gasification efficiencies were comparatively investigated. The use of Canadian limonite iron ore as the bed material was found to be more active than olivine for tar reduction in the fluidized bed gasification of biomass at a small ER (?0.3), leading to a very low tar yield of 15–25 g/kg biomass at ER = 0.30. The yields of combustible gas (carbon monoxide hydrogen, methane and C₂ hydrocarbon gases) and cold gas efficiency were generally the highest at medium values of ER (0.25–0.30) for both bed materials. The iron ore was less active than olivine for producing combustible gases, leading to a lower cold gas efficiency (50% at ER = 0.30) compared to 75% for olivine. However, the use of the iron ore produced a higher yield of hydrogen than that of olivine in the gasification: 5.0 mol hydrogen per kg of biomass with the iron ore at ER = 0.30 which was about 25% higher than that with olivine.     

Evaluation of membrane reactor with hydrogen-selective membrane in methane steam reforming

A comparative analysis of a conventional industrial process and a membrane reactor plant for hydrogen production via natural gas steam reforming is proposed by calculating two sustainability metrics: mass and energy intensities. The analysis takes into account membrane reactors equipped with hydrogen-selective membranes (Pd-based) which can operate at milder temperature (500 °C) and pressure (1.0 MPa) conditions and at higher CH₄ conversion levels (90–100%) than that achieved in conventional industrial systems.The use of the MR retentate stream to produce the steam required as feed for the reforming section is proposed and for this option a reduced mass intensity is calculated (reduced amount of fuel to the process) with respect to the conventional plant. The reduction is in the range 25–32% for the MRs operated at m=3 and 44–50% for the MRs operated at m=2. A more important saving concerns the energy use.     

Effect of feed rate on the production of nitrogen-doped graphene from liquid acetonitrile

We have investigated the production of nitrogen-doped graphene (NG) from liquid acetonitrile and demonstrated that there is a critical feed rate of acetonitrile for the growth of NG. Graphene sheets could be obtained at feed rate lower than 0.08 mL/min. While at 0.08 mL/min or above, only polycrystalline carbon films could be obtained. Therefore, selective synthesis of NG or carbon films could be achieved by simply altering the feed rate of acetonitrile, which provides an effective way to control the growth of NG sheets. Furthermore, NG sheets (0.06 mL/min sample) and carbon films (0.08 mL/min sample) exhibit light transmittance of ～90% and 70% at 550 nm, and sheet resistance of ～1400 and 1000 Ω/sq, respectively, showing their potential applications in carbon-based nanoelectronics.     

Recovery of carbon dioxide from sugarcane fermentation broth in the ethanol industry

Ethanol is one alternative to the use of petroleum-based fuels. It is produced on a large scale in Brazil from sugarcane to the magnitude of billions of liters per year. During the ethanol production step, a considerable amount of byproducts is obtained and treated as waste. Carbon dioxide is one of these byproducts and a substance of interest especially for food industries. Because the production of 1000 kg of ethanol generates approximately 950 kg of CO₂, this work intends to analyze a cryogenic distillation process for the production of CO₂ by means of computational simulations. The results obtained were in agreement with real operational conditions, achieving CO₂ concentrations up to 100% (v/v). With an initial CO₂ concentration of 95% (v/v), 7 separation stages were obtained, achieving the limit of 5 stages for higher CO₂ concentrations in the raw gas. The effect of initial CO₂ concentrations on the final product and the concentration profiles along the column are also presented. In order to optimize the process, it was observed that, for a maximum feed flow of 3333 kg/h (CO₂ concentration of 99%), the plant was able to obtain 10.48 kgCO₂/kW, recovering about 2828 kgCO₂/h at a final product concentration of 99.90% (v/v) at ?25 °C.