Recirculation Line Research Articles

Design of a bench scale unit for continuous CO2 capture via temperature swing adsorption—Fluid-dynamic feasibility study

The design of a bench scale unit (BSU) for continuous CO2 capture via temperature swing adsorption (TSA) is introduced. The BSU comprises two, interconnected multi-stage fluidized bed columns that allow for counter-current contact of adsorbent and gas streams during adsorption and desorption, respectively. From a fluid-dynamic point of view, the system is capable to capture 100kg of CO2 per day from a feed gas stream having 5vol.% CO2 content. In order to study the fluid-dynamic operability of the proposed BSU design, a cold flow model (CFM) representing half of the BSU system was constructed and operated. The CFM consists of five consecutive stages of bubbling fluidized beds and a recirculation line that comprises a mechanical screw conveyor, a pneumatic transport riser and a gas–solids separator. A comprehensive CFM campaign that included variations of the main operating parameters was conducted using air as fluidizing agent and polystyrene particles as bed material. Pressure drops across the individual stages and along the transportation riser were continuously measured to monitor the solids distribution within the system. Results from CFM experiments showed that continuous operation of the multi-stage fluidized bed system is possible within a broad range of operating conditions. After completion of the first experimental campaign, a further test was conducted to study the expansion of the dense phase of the fluidized bed within an individual stage, using long-time exposure photography. The obtained pictures delivered qualitative explanations for the results obtained from the parameter variations conducted in the first campaign. Altogether, the CFM test campaign clearly proved the fluid-dynamic feasibility of the proposed BSU design. In a next step, the results of this study will be used to elaborate the detailed design of the actual BSU for continuous CO2 capture via temperature swing adsorption.

Near-field flow structures about subcritical surface roughness

Laminar flow over a periodic array of cylindrical surface roughness elements is simulated with an immersed boundary spectral method both to validate the method for subsequent studies and to examine how persistent streamwise vortices are introduced by a low Reynolds number roughness element. Direct comparisons are made with prior studies at a roughness-based Reynolds number Rek (=U(k) k/ν) of 205 and a diameter to spanwise spacing ratio d/λ of 1/3. Downstream velocity contours match present and past experiments very well. The shear layer developed over the top of the roughness element produces the downstream velocity deficit. Upstream of the roughness element, the vortex topology is found to be consistent with juncture flow experiments, creating three cores along the recirculation line. Streamtraces stemming from these upstream cores, however, have unexpectedly little effect on the downstream flowfield as lateral divergence of the boundary layer quickly dissipates their vorticity. Long physical relaxation time of the recirculating wake behind the roughness remains a prominent issue for simulating this type of flowfield.

Study of the Flash Cycle Using Liquid Heat Recirculation (FC-LHR) for Energy Saving in Industry

The flash cycle (FC) has been proposed as a power cycle for heat recovery at low temperature. The FC is not constrained by the pinch point of the heat exchanger in the heat source in contrast to the Rankine cycle (RC), because the temperature difference for heat exchange is reduced by sensible heat exchange. However, the energy efficiency of the conventional FC is insufficient because of the low efficiency of power generation. It is considered that the low efficiency is mainly due to the flash rate at low temperature being low theoretically. Moreover, the heat of the saturated liquid is not used sufficiently. Hence, an energy- saving FC was proposed as an improvement of the conventional FC in this research. The proposed FC includes not only an expander line from the flash evaporator to generate power, but also a liquid heat recirculation line from the flash evaporator to use the sensible heat of the saturated liquid. The liquid heat recirculation increases the efficiency of power generation.

Two-phase plate-fin heat exchanger modeling for waste heat recovery systems in diesel engines

This paper presents the modeling and model validation for a modular two-phase heat exchanger that recovers energy in heavy-duty diesel engines. The model is developed for temperature and vapor quality prediction and for control design of the waste heat recovery system. In the studied waste heat recovery system, energy is recovered from both the exhaust gas recirculation line and the main exhaust line. Due to the similar design of these two heat exchangers, only the exhaust gas recirculation heat exchanger model is presented in this paper. Based on mass and energy conservation principles, the model describes the dynamics of two-phase fluid flow. Compared to other studies, the model is able to capture multiple phase transitions along the fluid flow by combining finite difference approach with moving boundary approaches. The developed model has low computational complexity, which makes it suitable for control design and real-time implementation.To validate the model, experiments are performed on a state-of-the-art Euro-VI heavy-duty diesel engine equipped with the waste heat recovery system. Simulation results show good accuracy, over the complete engine operating range, with average error below 4%. This is demonstrated on transitions between stationary operating points and on a dynamic response to a standard world harmonized transient cycle for both cold-start and hot-start conditions.

Kuosheng Mark III containment analyses using GOTHIC

Kuosheng nuclear power plant in Taiwan is a twin-unit BWR/6 plant, and both units utilize the Mark III containment. Currently, the plant is performing a stretch power uprate (SPU) project to increase the core thermal power to 103.7% OLTP (original licensed thermal power). However, the containment response in the Kuosheng Final Safety Analysis Report (FSAR) was completed more than twenty-five years ago. The purpose of this study is to establish a Kuosheng Mark III containment model using the containment program GOTHIC. The containment pressure and temperature responses under the design-basis accidents, which are the main steam line break (MSLB) and the recirculation line break (RCLB) accidents, are investigated. Short-term and long-term analyses are presented in this study. The short-term analysis is to calculate the drywell peak pressure and temperature which happen in the early stage of the LOCAs. The long-term analysis is to calculate the peak pressure and temperature of the reactor building space. In the short-term analysis, the calculated peak drywell to wetwell differential pressure is 140.6kPa for the MSLB, which is below than the design value of 189.6kPa. The calculated peak drywell temperature is 158°C, which is still below the design value of 165.6°C. In addition, in the long-term analysis, the calculated peak containment pressure is 47kPaG, which is below the design value of 103.4kPaG. The calculated peak values of containment temperatures are 74.7°C, which is lower than the design value of 93.3°C. Therefore, the Kuosheng Mark III containment can maintain the integrity after the design-basis accidents under the stretch power uprate condition.

Rapid accelerated hemodialysis in children with end-stage renal disease: A randomized clinical trial

In rapid accelerated hemodialysis (R-AHD), blood partially recirculates from the venous (outflow) to the arterial (inflow) line through a recirculation line (R) to selectively increase the filter blood flow rate (BFR). R-AHD PR uses two blood pump segments at the patient segment of the arterial line and at (R). To determine the effectiveness of R-AHD with regard to increasing anticoagulation and dialysis efficiency, we studied ten children with end-stage renal disease in two stages: stage 1 with 10 routine heparin R-AHD, then 10 half-dose heparin R-AHD, then 145 routine heparin R-AHD sessions for 1 month and then routine heparin double needle hemodialysis (DNHD) for one month (control). In stage 2, we dialyzed the patients with 10 routine heparin-mixed AHD PR and DNHD sessions, then eight low-dose heparin R-AHD PR" sessions, then one of the children with 10 no-heparin R-AHD PR sessions and then 10 routine heparin DNHD sessions" (control). Signs of blood clotting and dialysis efficiency were monitored. Blood clots appeared in four out of 165 R-AHD 0 (one pump circuit) sessions but in none of the 28 R-AHD PR sessions. In stage 1, the mean urea reduction rate was 0.60, 0.60 and 0.70 for the R-AHD protocols, compared with 0.71 for the control (P >0.05). In stage 2, the arterial blood urea nitrogen was reduced by 0.66 ± 0.15 after an R-AHD PR period, compared with 0.79 ± 0.18 after a DNHD period (P = 0.059). In conclusion, R-AHD PR allowed successful low heparin and no heparin hemodialysis in children without increasing the patients' BFR. However, the technique did not increase the efficiency of dialysis.

Solar‐powered in situ soil washing with surfactant to collect LNAPL

AbstractThis article presents the findings of a sustainable, surfactant‐enhanced, product recovery pilot‐scale study (PSS) completed between January 2010 and May 2010 at the Hydrocarbon Burn Facility located at the John F. Kennedy Space Center in Florida. The goal of this study was to implement a unique, simple, and sustainable light nonaqueous‐phase liquid (LNAPL) recovery process and evaluate site‐specific volumes and rates of LNAPL that could be collected and the degree of soil and groundwater cleanup that could be achieved. The recovery process was a combination of groundwater recirculation at a rate of approximately 2.9 gallons per minute (11.0 liters per minute), soil washing via LNAPL mobilization, and collection of LNAPL via a hydrophobic LNAPL skimmer. A biodegradable surfactant, ECOSURFTM SA‐15, was added to the recirculation line to lower the interfacial tension and facilitate LNAPL recovery via mobilization. All equipment (submersible pump, LNAPL skimmer, surfactant feed pump, controls, and various other equipment) used was powered by a solar panel array. Approximately 60 gallons (227 liters) or 429 pounds (195 kilograms) of LNAPL were collected at the recirculation site over approximately three months during the PSS. The data suggest that surfactant amendments greatly enhanced free product collection. The maximum rate of free product collection was approximately 1 gallon (3.8 liters) per day. © 2012 Wiley Periodicals, Inc.

Activated sludge process coupled with intermittent ozonation for sludge yield reduction and effluent water quality control

AbstractBACKGROUND: Ozone is applied in wastewater treatment for effluent water quality improvement (post‐ozonation) as well as for excess sludge reduction (in the recirculation line). There is some evidence that ozone dosed directly to aerobic biooxidation (ABO) process enhances degradation of recalcitrant compounds into intermediates, following their biodegradation in the same reactor. However, no information regarding the influence of ozone on sludge yield in this system was found. Therefore, the current work aimed to evaluate the effect of ozone on the sludge yield when ozone is dosed directly to the ABO process. In addition, batch and continuous treatment schemes for phenolic wastewater treatment are compared.RESULTS: The results revealed that an optimal ozone dose of ∼30 mgO3 L−1 day−1 reduced the sludge yield by ∼50%, while effluent water quality in terms of total chemical oxygen demand (TCOD), compared with a conventional ABO process, was improved by 35.5 ± 3.6%. Slight improvement in soluble COD removal at the same ozone dose was also detected. The toxicity of effluent water was reduced as the ozone dose was increased.CONCLUSIONS: In an integrated ozonation‐ABO process it is possible to simultaneously reduce sludge yield and to improve effluent water quality, as COD and toxicity are reduced. Copyright © 2011 Society of Chemical Industry

Pressure and temperature analyses using GOTHIC for Mark I containment of the Chinshan Nuclear Power Plant

Chinshan Nuclear Power Plant in Taiwan is a GE-designed twin-unit BWR/4 plant with original licensed thermal power (OLTP) of 1775 MWt for each unit. Recently, the Stretch Power Uprate (SPU) program for the Chinshan plant is being conducted to uprate the core thermal power to 1858 MWt (104.66% OLTP). In this study, the Chinshan Mark I containment pressure/temperature responses during LOCA at 105% OLTP (104.66% OLTP + 0.34% OLTP power uncertainty = 105% OLTP) are analyzed using the containment thermal-hydraulic program GOTHIC. Three kinds of LOCA (Loss of Coolant Accident) scenarios are investigated: Recirculation Line Break (RCLB), Main Steam Line Break (MSLB), and Feedwater Line Break (FWLB). In the short-term analyses, blowdown data generated by RELAP5 transient analyses are provided as boundary conditions to the GOTHIC containment model. The calculated peak drywell pressure and temperature in the RCLB event are 217.2 kPaG and 137.1 °C, respectively, which are close to the original FSAR results (219.2 kPaG and 138.4 °C). Additionally, the peak drywell temperature of 155.3 °C calculated by MSLB is presented in this study. To obtain the peak suppression pool temperature, a long-term RCLB analysis is performed using a simplified RPV (Reactor Pressure Vessel) volume to calculate blowdown flow rate. One RHR (Residual Heat Removal) heat exchanger is assumed to be inoperable for suppression pool cooling mode. The calculated peak suppression pool temperature is 93.2 °C, which is below the pool temperature used for evaluating the net positive suction head of pumps of the RHR system and the Emergency Core Cooling Systems (96.7 °C). The peak containment pressure and temperature are well below the design value (386.1 kPaG and 171.1 °C). Containment integrity of Chinshan Plant can be maintained under the SPU condition.

Raman spectroscopy for the process analysis of the manufacturing of a suspension metered dose inhaler

The purpose of this research was to demonstrate the utility of Raman spectroscopy for process analysis of a suspension metered dose inhaler manufacturing process. Chemometric models were constructed for the quantification of ethanol and active pharmaceutical ingredient such that both could be monitored in real-time during the compounding and filling operations via tank measurements and recirculation line flow-cell measurements. Different spectral preprocessing techniques were used to delineate the effects of mixing speed and temperature changes from actual concentration effects. Raman spectroscopy offers advantages in time savings and quality of information over the standard methods of analysis for respiratory formulations, such as a drug content assay via HPLC and ethanol testing via GC. The successful implementation of this work will allow formulation scientists to quantitatively assess both the formulation (e.g., the concentration of active pharmaceutical ingredient (API) and ethanol), as well as the manufacturing process (e.g., determination of mixing endpoints) in real-time.

Performance of a pilot-scale sewage treatment: An up-flow anaerobic sludge blanket (UASB) and a down-flow hanging sponge (DHS) reactors combined system by sulfur-redox reaction process under low-temperature conditions

Performance of a wastewater treatment system utilizing a sulfur-redox reaction of microbes was investigated using a pilot-scale reactor that was fed with actual sewage. The system consisted of an up-flow anaerobic sludge blanket (UASB) reactor and a down-flow hanging sponge (DHS) reactor with a recirculation line. Consequently, the total CODCr (465±147 mg L(-1); total BOD of 207±68 mg L(-1)) at the influent was reduced (70±14 mg L(-1); total BOD of 9±2 mg L(-1)) at the DHS effluent under the conditions of an overall hydraulic retention time of 12 h, a recirculation ratio of 2, and a low-sewage temperature of 7.0±2.8 °C. A microbial analysis revealed that sulfate-reducing bacteria contributed to the degradation of organic matter in the UASB reactor even in low temperatures. The utilized sulfur-redox reaction is applicable for low-strength wastewater treatment under low-temperature conditions.

The BIOZO process – a biofilm system combined with ozonation: occurrence of xenobiotic organic micro-pollutants in and removal of polycyclic aromatic hydrocarbons and nitrogen from landfill leachate

We present an assessment of xenobiotic organic micro-pollutants (XOM) occurrence and removal of polycyclic aromatic hydrocarbons (PAHs) in a novel biofilm system combined with ozonation, the BIOZO concept, treating partly stabilised landfill leachate. A novel, staged moving-bed biofilm reactor (SMBBR) design was implemented in laboratory- and pilot-scale, and the PAHs removal efficiency of controlled ozonation was assessed installing the ozonation step in the nitrate recirculation line (Position 1) or between the pre-anoxic and aerobic zones (Position 2). COD removal in a laboratory- and in a pilot-scale SMBBR system with and without ozonation is additionally addressed. Results obtained in a screening study (GC-ToF-MS) were used to compile a priority list of XOMs in leachate based on relative occurrence, showing PAHs as the predominant fraction. Biological treatment is shown to be an effective means to remove PAHs detected in the aqueous phase. PAH removal takes in most part place in the pre-anoxic zone, thereby decreasing toxicity exhibited by PAH on autotrophic nitrifier bacteria in the aerobic zone. Ozonation installed in Position 2 is shown to be superior over Position I in terms of COD, PAH and nitrogen removal efficiencies. We additionally demonstrate the potential of intermittent sludge ozonation as a means to decrease PAH concentrations in sludge wasted and to improve nitrogen removal in the BIOZO system.

Emissão de óxido nitroso de estação de tratamento de esgoto de lodos ativados por aeração prolongada - estudo preliminar

Nitrous oxide emissions from an activated sludge plant which serves a research institute in Rio de Janeiro city were estimated from six unit processes (grit tank, sand trap, aeration tank, secondary settling tank, sludge recirculation line and aerobic digester sludge tank) and also from the plant effluent. Total estimated annual flux was 3.2 x 104 g N2O yr-1 of which about 90% was from the aeration tank. Emission factors estimated from population served, wastewater flow and nitrogen load (conversion ratio) were 13 g N2O person-1 yr-1, 9.0 x 10-5 g N2O Lwastewater-1 and 0.14%.

Analysis of a Coupled Blowdown from Both RPV and BOP with RELAP5-3D/K for a Limiting FWLB of an ABWR for Containment Design

The limiting blowdown event for the design of an advanced boiling water reactor (ABWR) containment shifts from a conventional recirculation line break to a feedwater line break (FWLB) by implementing reactor internal pumps. As a result, coupled blowdown from both the reactor pressure vessel (RPV) and the balance of plant (BOP) is involved in the limiting FWLB. Coupled blowdown from both RPV and BOP for the FWLB of the Lungmen ABWR has been successfully analyzed using the advanced RELAP5-3D/K code. To simulate adequately both the RPV and BOP blowdown, the essential simulation scope of an ABWR includes the reactor system, the main steam and turbine systems, the condensate and feedwater systems, the protection system, and the emergency core cooling system. As compared to what was presented in the preliminary safety analysis report of the Lungmen ABWR, unexpected prolonged decays of BOP blowdown flow and enthalpy were calculated. The revised blowdown flow and enthalpy calculated by RELAP5-3D/K from both RPV and BOP breaks provide a new and solid basis for the final safety analysis of ABWR containment for the Lungmen plant, which is scheduled for commercial operation in 2011. The successful modeling of the entire RPV and BOP with RELAP5-3D/K and associated application to the FWLB licensing blowdown analysis indicate that the advanced RELAP5 code can extend its traditional reactor safety analysis to the simulation and analysis of the entire power generation and conversion systems.

New theoretical model for convergent nozzle ejector in the proton exchange membrane fuel cell system

A new theoretical model for the convergent nozzle ejector in the anode recirculation line of the polymer electrolyte membrane (PEM) fuel cell system is established in this paper. A velocity function for analyzing the flow characteristics of the PEM ejector is proposed by employing a two-dimensional (2D) concave exponential curve. This treatment of velocity is an improvement compared to the conventional 1D “constant area mixing” or “constant pressure mixing” ejector theories. The computational fluid dynamics (CFD) technique together with the data regression and parameter identification methods are applied in the determination of the velocity function's exponent. Based on the model, the anode recirculation performances of a hybrid PEM system are studied under various stack currents. Results show that the model is capable of evaluating the performance of ejector in both the critical mode and subcritical mode.

Development of Parameter-Identification Capability for MAAP4 Code

The MAAP4 code is a fast-running severe accident analysis and management code widely used in nuclear industrial applications. It has been used as a severe accident analysis tool with which the timing of key events and source terms in the accident are assessed in Taiwan for many years. In the case of a loss-of-coolant accident (LOCA), it needs to know its break area and break elevation prior to reconstructing the accident for further analysis. For the system with more than one unknown parameter, it is not easy to identify these parameters since their tuning work becomes sophisticated.The purpose of this paper is to find a better solution for this problem by coupling an optimization module with the MAAP4 simulation code. In this paper, a recirculation line break LOCA of the Kuosheng nuclear power plant is cited as a reference case. Different recirculation line break areas are tested and verified. This optimization module coupled with the MAAP4 code can be used to identify the break elevation and area if the shroud water level drops below the break point.

Control ofLegionella pneumophilaContamination in a Respiratory Hydrotherapy System With Sulfurous Spa Water

To evaluate the effectiveness of different disinfection treatments in a spa water system contaminated by Legionella pneumophila and associated with a case of Legionella pneumonia. During an 18-month period, the spa water was analyzed by taking samples from the well, the recirculation line, and the final distribution devices (nebulizers and nasal irrigators). Various attempts were made to eradicate Legionella organisms by chemical and thermal shock. The final protocol consisted of heat shock treatment at 70 degrees C-75 degrees C for 3 hours, 2 nights per week, followed by a lowering of the water temperature to 30 deg C+/-1 deg C for use in the plant. In addition, 3 times a week superheated steam (at a pressure of 1 atmosphere) was introduced for 1 hour into the nebulization machines. A spa at which sulfurous water was used for hydrotherapy by means of aerosol and nasal irrigation. A 74-year-old woman with legionnaires disease. After the case of infection occurred, L. pneumophila was isolated from the recirculation line at a concentration of 400,000 cfu/L and from the nebulizers and nasal irrigators at levels ranging from 3,300 to 1,800,000 cfu/L. The colonizing organisms consisted of a mixture of L. pneumophila serogroup 1 (12%) and serogroup 5 (88%). The shock treatment with chlorine dioxide and peracetic acid resulted in the eradication of Legionella organisms from the recirculation line but not from the water generated from the final distribution devices. After the restructuring of the plant and the application of thermal shock protocol, an evaluation after 12 months revealed no evidence of Legionella contamination. To prevent Legionella colonization, disinfection treatment is effective if associated with carefully selected materials, good circuit design, and good maintenance practices.

Discrete model for analysis and design of grinding mill-classifier systems

Discrete mathematical and computer models are developed for the simulation of grinding mill-classifier systems on the basis of distributed parameter models of continuous grinding processes. The discrete model is derived from the partial integro-differential equation describing axial mixing and breakage of particles in grinding mills. The convective flow and axial dispersion in the mill are modeled as particle size-dependent processes, while the recirculation line is described as plug flow of the classifier rejected material involving also some time delay. The resulted set of recursive linear algebraic equations was the basis of computer model developed in MATLAB environment. The capabilities of the computer model are demonstrated by presenting and analyzing results obtained by numerical experiences. The influence of both the kinetic and process parameters of the mill-classifier system on the size distribution of the ground material as well the dynamic behavior of the system are presented and analyzed. The computer model is suitable for designing the configuration and operational conditions of both open- and closed-circuit grinding mill-classifier systems efficiently.

Multi-wavelength fluorometry for anaerobic digestion process monitoring

Applicability of multi-wavelength fluorometry for anaerobic digestion process monitoring was investigated in a 3.5 L upflow anaerobic sludge bed (UASB) lab-scale reactor. Both off-line and on-line monitoring of key process parameters was tested. Off-line emission spectra were measured at an angle of 90 degrees to the excitation beam using a cuvette. On-line measurements were carried out using a fiber optic probe in the external recirculation line of the digester. Fluorescence spectra were correlated to available analytical measurements to obtain partial least square regression models. An independent set of measurements was used to validate the regression models. Model estimations showed reasonable agreement with analytical measurements with multiple determination coefficients (R2) between 0.6 and 0.95. Results showed that offline fluorescence measurements can be used for fast estimation of anaerobic digestor effluent quality. At the same time, the on-line implementation of multi-wavelength fluorescence measurements can be used for realtime process monitoring and, potentially, for on-line process control.

Fifty Years of Open Heart Surgery at the Mayo Clinic

Fifty Years of Open Heart Surgery at the Mayo Clinic