Gas Loop Research Articles

Macroscopic structural behavior on the small-scale PHE prototype under high-temperature test condition

PHE (Process Heat Exchanger) is a key component to transfer the high temperature heat generated from a VHTR (Very High Temperature Reactor) to the chemical reaction for massive production of hydrogen. Korea Atomic Energy Research Institute established a small-scale gas loop for the performance test of VHTR components and manufactured a PHE prototype in order to test in the small-scale gas loop. In this study, in order to investigate the macroscopic structural characteristics and behaviour of the PHE prototype under the test condition of the small-scale gas loop, we carried out high-temperature structural analysis modelling, thermal analysis, and an elastic/elastic-plastic structural analysis for the PHE prototype under the loop test conditions as a precedent study prior to the performance test in the small-scale gas loop. The results obtained in this study will be compared with the performance test results in the near future.

Soft sensor for better control of carbon dioxide removal process in ethylene glycol plant

Low Carbon-dioxide in cycle gas loop of Ethylene Glycol (EG) plant improves catalyst selectivity and overall economics of the plant. Carbon-dioxide produced as a bi-product in ethylene oxide reactor is removed by Benfield process. In this process the carbonate and bicarbonate ratio in lean carbonate solution is considered as an important quality control (QC) variable as the efficiency of carbon-dioxide removal is largely depends on it. In the event of a process malfunction or operating under suboptimal condition, the CO2 content in cycle gas loop will continue to rise until corrective action is taken after obtaining lab results for carbonate and bicarbonate ratio. This time consuming sampling process can be overcome by implementing a technological solution in form of an accurate and robust mathematical model capable of real time QC variable prediction. For well understood processes, the structure of the correlation for QC variables as well as the choice of the inputs may be well known in advance. However, Benfield process is too complex and the appropriate form of the correlation and choice of input variables are not obvious. Here, the processes knowledge, operating experience and statistical methods were applied in developing the soft sensor. This paper describes a systematic approach to the development of inferential measurements of carbonate and bicarbonate ratio using Support Vector Regression (SVR) analysis. Given historical process data, a simple SVR-based soft sensor model is found capable of identifying and capturing the cause and effect relationship between operating variables (model inputs) and QC variables (model outputs). Special care was taken to choose input variables, so that the final correlation and regression coefficient make senses from process engineering point of view. The developed soft sensor is implemented in commercial ethylene glycol plant in an Exaquantum interface and found satisfactorily predicting the carbonate and bicarbonate ratio in real time.

헬륨가스루프 시험용 공정열교환기에 대한 고온구조해석 모델링(II)

초고온가스로에서 생성된 950℃ 정도의 초고온 열을 이용하여 수소를 경제적이며 또한 대량으로 생산하기 위한 시스템이 원자력수소생산시스템이며, 이 시스템에서 공정열교환기는 초고온 열과 황-요오드 공정을 통해 수소를 생산하는 핵심 기기이다. 한국원자력연구원에서는 초고온가스로에 사용될 기기에 대한 성능시험을 위해 헬륨가스루프를 구축하고 공정열교환기 시제품을 제작하였다. 본 연구는 공정열교환기 시제품을 헬륨가스루프에서 시험하기 전에 미리 공정열교환기 시제품의 고온 구조건전성을 평가하기 위한 작업의 일환으로 공정열교환기 시제품에 대한 고온구조해석 모델링, 열해석 및 열팽창해석 결과들을 정리한것이다. 해석 결과는 공정열교환기 시제품 성능시험 장치 설계에 반영할 것이다.

Thermal hydraulic test with 6 MPa nitrogen gas loop for developing the Korean He cooled test blanket

In considering the requirements for a DEMO-relevant blanket concept, Korea (KO) has proposed a Helium Cooled Molten Lithium (HCML) Test Blanket Module (TBM) for testing in the International Thermonuclear Experimental Reactor (ITER). The performance analysis for thermal-hydraulics and safety analysis for an accident caused by loss of a coolant for the KO TBM has been carried out with a commercial CFD code, ANSYS-CFX V11 and system code, GAMMA (GAs Multicomponent Mixture Analysis). In order to verify the codes, a basic thermal-hydraulic test with a high pressure nitrogen gas loop up to 6 MPa pressure and 950 °C temperature was performed. In the experiment, single TBM First Wall (FW) mock-up made from the same material as the KO TBM, Ferritic Martensitic Steel, was used and the test was performed under the conditions of pressures of 20 and 36 bar and flow rates of 0.75 and 0.92 kg/min. As one-side of the mock-up was heated to 230 °C, the wall temperatures were measured by installed thermocouples. The measured temperatures show a strong parity with codes’ results simulated with the same test conditions. An additional test with higher pressure and temperature has been prepared for the future.

헬륨가스루프 시험용 공정열교환기에 대한 고온구조해석 모델링 (I)

초고온가스로에서 생성된 950℃ 정도의 초고온 열을 이용하여 수소를 경제적이며 또한 대량으로 생산하기 위한 시스템이 원자력수소생산시스템이며, 공정열교환기는 초고온 열과 황-요오드 공정을 통해 수소를 생산하는 원자력수소생산시스템에서의 핵심 기기이다. 한국원자력연구원에서는 초고온가스로에 사용될 기기에 대한 성능시험을 위해 최대 작동 설계온도 1000℃인 헬륨가스루프를 구축하고 있으며 공정열교환기를 설계하였다. 본 연구에서는 구축중인 헬륨가스루프에서 성능시험을 수행할 예정으로 설계된 공정열교환기에 대한 고온구조건전성을 미리 평가하기 위한 작업의 일환으로 고온구조해석 모델링, 열해석 및 열팽창 해석을 수행한 결과를 정리한 것이다. 해석결과를 이용하여 설계된 공정열교환기의 구조건전성을 유지하기 위한 1 차 및 2 차 열매체의 유입/유출 파이프라인에서의 적절한 구속조건을 결정하였으며 이를 향후 제작될 공정열교환기 시제품의 성능시험장치 설계에 반영할 것이다.

Design and Control of a Methanol Reactor/Column Process

Methanol is one of the prime candidates for providing an alternative to petroleum-based liquid transportation fuels. It can be made from any renewable biomass hydrocarbon source by partial oxidation in an oxygen-blown gasifier to produce synthesis gas, which is then converted into methanol. The purpose of this paper is to develop the economically optimum design of a methanol reactor/distillation column system with three gas recycle streams to produce high-purity methanol from synthesis gas. The economics consider capital costs, energy costs, the value of the methanol product, and the heating value of a vent stream that is necessary for purging off inert components entering in the feed. A plantwide control structure is developed that is capable of effectively handling large disturbances in the production rate and synthesis gas composition. The unique features of this control scheme are a lack of control of pressure in the reactor/recycle gas loop and a high-pressure override controller to handle stoichiome...

Quantum logic as superbraids of entangled qubit world lines

Presented is a topological representation of quantum logic that views entangled qubit spacetime histories (or qubit world lines) as a generalized braid, referred to as a superbraid. The crossing of world lines is purely quantum in nature, most conveniently expressed analytically with ladder-operator-based quantum gates. At a crossing, independent world lines can become entangled. Complicated superbraids are systematically reduced by recursively applying novel quantum skein relations. If the superbraid is closed (e.g. representing quantum circuits with closed-loop feedback, quantum lattice gas algorithms, loop or vacuum diagrams in quantum field theory), then one can decompose the resulting superlink into an entangled superposition of classical links. In turn, for each member link, one can compute a link invariant, e.g. the Jones polynomial. Thus, a superlink possesses a unique link invariant expressed as an entangled superposition of classical link invariants.

Evaluation of system codes for analyzing naturally circulating gas loop

Steady-state natural circulation data obtained in a 7 m-tall experimental loop with carbon dioxide and nitrogen are presented in this paper. The loop was originally designed to encompass operating range of a prototype gas-cooled fast reactor passive decay heat removal system, but the results and conclusions are applicable to any natural circulation loop operating in regimes having buoyancy and acceleration parameters within the ranges validated in this loop. Natural circulation steady-state data are compared to numerical predictions by two system analysis codes: GAMMA and RELAP5-3D. GAMMA is a computational tool for predicting various transients which can potentially occur in a gas-cooled reactor. The code has a capability of analyzing multi-dimensional multi-component mixtures and includes models for friction, heat transfer, chemical reaction, and multi-component molecular diffusion. Natural circulation data with two gases show that the loop operates in the deteriorated turbulent heat transfer (DTHT) regime which exhibits substantially reduced heat transfer coefficients compared to the forced turbulent flow. The GAMMA code with an original heat transfer package predicted conservative results in terms of peak wall temperature. However, the estimated peak location did not successfully match the data. Even though GAMMA's original heat transfer package included mixed-convection regime, which is a part of the DTHT regime, the results showed that the original heat transfer package could not reproduce the data with sufficient accuracy. After implementing a recently developed correlation and corresponding heat transfer regime map into GAMMA to cover the whole range of the DTHT regime, we obtained better agreement with the data. RELAP5-3D results are discussed in parallel.

Thermal instability of glow discharge in the gas loop of CO2 laser with extended disk fans-heat exchangers

CO2 lasers with transverse discharge and convective gas cooling find ever-increasing application. On strategy in making such lasers more efficient radiators is increasing the rate of the gas flow through the discharge zone with the help of diametral disk fans-heat exchangers. The application of such fans-heat exchangers, however, entails serious difficulties related to the glow discharge-gas flow interaction. In the present study, we investigate the stability problem for volume discharge in the gas loop of a CO2 laser with diametral dis fans-heat exchangers.

Simulation of the MELiSSA closed loop system as a tool to define its integration strategy

Inspired by a terrestrial ecosystem, Micro-Ecological Life Support System Alternative (MELiSSA) is a project focused on a closed-loop life support system intended for future long-term manned missions (Moon and Mars bases). Started by the ESA in 1989, this 5-compartment concept has evolved through a mechanistic engineering approach designed to acquire both theoretical and technical knowledge. In its current state of development, the project can now start to demonstrate the MELiSSA loop concept at pilot scale. Thus, an integration strategy for a MELiSSA Pilot Plant (MPP) has been defined, describing the different test phases and connections between compartments. The integration steps are due to be started in 2008 and completed with a complete operational loop in 2015. The ultimate objective is to achieve a closed liquid and gas loop fulfiling 100% of oxygen requirements and at least 20% of food requirements for one-man. Although the integration logic could start with the most advanced processes in terms of knowledge and hardware development, this logic needs to be expanded to encompass a high-level simulation policy. This simulation exercise will make it possible to run effective demonstrations of each independent process, followed by progressive coupling with other processes in operational conditions mirroring as far as possible the final configuration. The theoretical approach described in this paper is based on mass balance models of each MELiSSA compartment which are used to simulate each integration step and the complete MPP loop itself. These simulations will help identify criticalities in each integration step and check consistency between objectives, flows, recycling efficiencies and sizing of the pilot reactors. An MPP scenario compatible with current knowledge on the operation of the pilot reactors was investigated, and the theoretical performances of the system were compared against the objectives assigned to the MPP. This scenario makes it possible to highlight the most important integration milestones and simulate their behaviour.

Parametric evaluation of large-scale high-temperature electrolysis hydrogen production using different advanced nuclear reactor heat sources

High-temperature electrolysis (HTE), when coupled to an advanced nuclear reactor capable of operating at reactor outlet temperatures of 800–950 °C, has the potential to efficiently produce the large quantities of hydrogen needed to meet future energy and transportation needs. To evaluate the potential benefits of nuclear-driven hydrogen production, the UniSim process analysis software was used to evaluate different reactor concepts coupled to a reference HTE process design concept. The reference HTE concept included an intermediate heat exchanger and intermediate helium loop to separate the reactor primary system from the HTE process loops and additional heat exchangers to transfer reactor heat from the intermediate loop to the HTE process loops. The two process loops consisted of the water/steam loop feeding the cathode side of a HTE electrolysis stack, and the sweep gas loop used to remove oxygen from the anode side. The UniSim model of the process loops included pumps to circulate the working fluids and heat exchangers to recover heat from the oxygen and hydrogen product streams to improve the overall hydrogen production efficiencies. The reference HTE process loop model was coupled to separate UniSim models developed for three different advanced reactor concepts (a high-temperature helium cooled reactor concept and two different supercritical CO 2 reactor concepts). Sensitivity studies were then performed with the objective of evaluating the affect of reactor outlet temperature on the power cycle efficiency and overall hydrogen production efficiency of the integrated plant design for each of the reactor power cycles. The results of these sensitivity studies showed that overall power cycle and hydrogen production efficiencies increased with reactor outlet temperature, but the power cycles producing the highest efficiencies varied depending on the temperature range considered.

Improved monoterpene biotransformation with Penicillium sp. by use of a closed gas loop bioreactor

A closed gas loop bioprocess was developed to improve fungal biotransformation of monoterpenes. By circulating monoterpene-saturated process gas, the evaporative loss of the volatile precursor from the medium during the biotransformation was avoided. Penicillium solitum, isolated from kiwi, turned out to be highly tolerant towards monoterpenes and to convert alpha-pinene to a range of products including verbenone, a valuable aroma compound. The gas loop was mandatory to reproduce the production of 35 mg L(-1) verbenone obtained in shake flasks and also in the bioreactor. Penicillium digitatum DSM 62840 regioselectively converted (+)-limonene to the aroma compound alpha-terpineol, but shake flask cultures revealed a pronounced growth inhibition when initial concentrations exceeded 1.9 mM. In the bioreactor, toxic effects on P. digitatum during biotransformation were alleviated by starting a sequential feeding of non-toxic limonene portions after a preceding growth phase. Closing the precursor-saturated gas loop during the biotransformation allowed for an additional replenishment of limonene via the gas phase. The gas loop system led to a maximum alpha-terpineol concentration of 1,009 mg L(-1) and an average productivity of 8-9 mg L(-1) h(-1) which represents a doubling of the respective values previously reported. Furthermore, a molar conversion yield of up to 63% was achieved.

Nonlinear Model on Leveling Procedure of Electronically Controlled Air Suspension

Suspension leveling of electronically controlled air suspension is a complicated nonlinear procedure. To research the dgnamic of suspension in leveling procedure with air spring inflated or deflated, and to serve as a basis for the follow-up research on suspension height control strategies, analyses are performed on the gas thermodynamic process in air spring and spring loaded mass dynamic process in leveling procedure of electronically controlled air suspension, from which the equations of air spring pressure gradient, gas loop flow rate, and spring loaded mass dynamics in the open period of and after closing of magnetic valve in leveling procedure are derived. A series of suspension leveling experiments in full scale vehicle with different single pulse exerted magnetic valve to inflate or deflate air spring are conducted to verify the proposed nonlinear model, the results of experiments and simulations show good consistency. The proposed model can correctly depict the gas state in air spring before and after loaded magnetic valve, and the lag characteristic of suspension motion under the action of damping force after the closing of magnetic valve.

Design optimization and experimental testing of the High-Flux Test Module of IFMIF

The design of the High-Flux Test Module of the International Fusion Material Irradiation Facility has been developed continuously in the past few years. The present paper highlights recent design achievements, including a thorough state-of-the-art validation assessment of CFD tools and models. Along with design related analyses exercises on manufacturing procedures have been performed. Recommendations for the use of container, rig, and capsule materials as well as recent progress in brazing of electrical heaters are discussed. A test matrix starting from High-Flux Test Module compartments, i.e. segments of the full module, with heated dummy rigs up to the full-scale module with instrumented irradiation rigs has been developed and the appropriate helium gas loop has been designed conceptually. A roadmap of the envisaged experimental activities is presented in accordance with the test loop facility construction and mock-up design and fabrication schedules.

Thermal hydraulic challenges of Gas Cooled Fast Reactors with passive safety features

Transient response of a Gas Cooled Fast Reactor (GFR) coupled to a recompression supercritical CO 2 (S-CO 2) power conversion system (PCS) in a direct cycle to a Loss of Coolant Accident (LOCA) and a Loss of Generator Load Accident is analyzed using RELAP5-3D. A number of thermal hydraulic challenges for GFR design are pointed out as the designers strive to accommodate cooling of the high power density core of a fast reactor by a gas with its inherently low heat transfer capability, in particular under post-LOCA events when system pressure is lost and when reliance on passive decay heat removal (DHR) is emphasized. Although it is possible to design a S-CO 2 cooled GFR that can survive LOCA by cooling the core through natural circulating loops between the core and elevated emergency cooling heat exchangers, it is not an attractive approach because of various bypass paths that can, depending on break location, degrade core cooling. Moreover, natural circulation gas loops can operate in deteriorated heat transfer regimes with substantial reduction of heat transfer coefficient: as low as 30% of forced convection values, and data and correlations in these regimes carry large uncertainties. Therefore, reliable battery powered blowers for post-LOCA decay heat removal that provide flow in well defined regimes with low uncertainty, and can be easily overdesigned to accommodate bypass flows were selected. The results confirm that a GFR with such a DHR system and negative coolant void worth can withstand LOCA with and without scram as well as loss of electrical load without exceeding core temperature and turbomachinery overspeed limits.

Repeat Laparotomy for the Treatment of Septic Peritonitis in a Bornean Orangutan (Pongo pygmaeus pygmaeus)

A 9-yr-old female Bornean orangutan (Pongo pygmaeus pygmaeus) presented with a 48-hr history of depression, lethargy, anorexia, and mucoid discharge from the rectum. Clinical, radiographic, and ultrasonographic examination demonstrated the presence of multiple distended loops of intestine, intestinal adhesions, and free gas within the abdomen. During exploratory laparotomy, fibrinopurulent diffuse peritonitis as a result of a ruptured intrapelvic abscess with associated large bowel adhesions was evident. The abdomen was thoroughly lavaged, necrotic debris and abscess wall removed, and fibrinous adhesions disrupted. The orangutan was kept sedated for 48 hr to allow for intensive care. Six months later, when the orangutan presented with similar clinical signs, ultrasonographic examination demonstrated the presence of a pelvic abscess. The previous procedure was repeated with the addition of a hysterectomy. This report is the first documentation of long-term management following surgical intervention for internal abdominal abscessation and septic peritonitis in a great ape.

Thermal design of a laboratory—scale SO 3 decomposer for nuclear hydrogen production

Designing of a sulfur trioxide decomposer is one of the main technical challenges in the development of a nuclear hydrogen production system. Korea Atomic Energy Research Institute (KAERI) has developed a hybrid-design decomposer to withstand the severe operating conditions. In this design, the hot gas side is equipped with printed circuit-type heat exchangers (PCHE), and the process gas side is equipped with plate fin-type heat exchangers (PFHE). In this study, the sensitivity analysis is performed to estimate the effects of the various factors on the thermal design of a sulfur trioxide decomposer for its performance test in a small-scale gas loop. The principal factors affecting the decomposer's thermal design are categorized into four groups: rate constants, geometrical parameters, heat transfer parameters, and operating conditions. Our results indicate that the rate constant of the catalyzed reaction and the decomposer retention time are the most important factors dictating the thermo-chemical behavior of the sulfur trioxide decomposer. The information obtained from this analysis will serve to guide the manufacture and operation of this laboratory-scale decomposer.

Venturi Wet Gas Flow Modeling Based on Homogeneous and Separated Flow Theory

Wet gas metering is becoming increasingly important to petroleum and chemical engineering. The Venturi meter is a favored device for the metering of the unprocessed wet natural gas production flows. When Venturi meters are used in wet gas, the measured differential pressure is higher than it would be in gas phases flowing alone. This phenomenon is called over reading. Eight famous over‐reading correlations have been studied by many researchers under low‐ and high‐pressure conditions, the conclusion is separate flow model and homogeneous flow model performing well both under high and low pressure. In this study, a new metering method is presented based on homogeneous and separate flow theory; the acceleration pressure drop and the friction pressure drop of Venturi under two‐phase flow conditions are considered in new correlation, and its validity is verified through experiment. For low pressure, a new test program has been implemented in Tianjin University′s low‐pressure wet gas loop. Three 50 mm Venturi meters with β values of 0.4048, 0.55, and 0.70 have been tested at the working operation pressure of 0.15, 0.20, and 0.25 MPa, the gas densimetric Froude number from 0.6 to 2.5, the modified Lockhart‐Martinelli parameter from 0.0022 to 0.3, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. For high pressure, the National Engineering Laboratory offered their reports on the web and their test range with β values of 0.4, 0.60, and 0.75, pressure of 1.5, 3.0, and 6.0 Mpa, gas Froude number from 0.5 to 5.5, and the modified Lockhart‐Martinelli parameter from 0.0035 to 0.3. The coefficients of the new proposed correlation are fitted with all independent data both under high and low pressure. Finally, the applicability and errors of new correlation are analyzed.

ICONE15-10740 Sensitivity Studies of Advanced Reactors Coupled to High Temperature Electrolysis (HTE) Hydrogen Production Processes

High Temperature Electrolysis (HTE), when coupled to an advanced nuclear reactor capable of operating at reactor outlet temperatures of 800 ℃ to 950 ℃, has the potential to efficiently produce the large quantities of hydrogen needed to meet future energy and transportation needs. To evaluate the potential benefits of nuclear-driven hydrogen production, the UniSim process analysis software was used to evaluate different reactor concepts coupled to a reference HTE process design concept. The reference HTE concept included an Intermediate Heat Exchanger and intermediate helium loop to separate the reactor primary system from the HTE process loops and additional heat exchangers to transfer reactor heat from the intermediate loop to the HTE process loops. The two process loops consisted of the water/steam loop feeding the cathode side of a HTE electrolysis stack, and the sweep gas loop used to remove oxygen from the anode side. The UniSim model of the process loops included pumps to circulate the working fluids and heat exchangers to recover heat from the oxygen and hydrogen product streams to improve the overall hydrogen production efficiencies. The reference HTE process loop model was coupled to separate UniSim models developed for three different advanced reactor concepts (a high-temperature helium cooled reactor concept and two different supercritical CO_2 reactor concepts). Sensitivity studies were then performed to evaluate the affect of reactor outlet temperature on the power cycle efficiency and overall hydrogen production efficiency for each of the reactor power cycles. The results of these sensitivity studies showed that overall power cycle and hydrogen production efficiencies increased with reactor outlet temperature, but the power cycles producing the highest efficiencies varied depending on the temperature range considered.

Molecular Loops in the Galactic Center: Evidence for Magnetic Flotation

The central few hundred parsecs of the Milky Way host a massive black hole and exhibit very violent gas motion and high temperatures in molecular gas. The origin of these properties has been a mystery for the past four decades. Wide-field imaging of the (12)CO (rotational quantum number J = 1 to 0) 2.6-millimeter spectrum has revealed huge loops of dense molecular gas with strong velocity dispersions in the galactic center. We present a magnetic flotation model to explain that the formation of the loops is due to magnetic buoyancy caused by the Parker instability. The model has the potential to offer a coherent explanation for the origin of the violent motion and extensive heating of the molecular gas in the galactic center.