Papers by Keyword: Carbon Dioxide CO₂

Abstract: The (H)CFC-phase out and the fear for future problems for other synthetic working fluids, because of their known and unknown impact on the environment, have introduced a rising interest in environmentally safe natural working fluids. CO₂ is one of the few non-toxic and non-flammable working fluids that do not contribute to ozone depletion or global warming, if leaked to the atmosphere. Because the critical temperature of CO₂ is only 31.1°C, the transcritical cycle can be used to improve the coefficient of performance of the system. The experimental investigation and theoretical analysis on transcritical carbon dioxide heat pump system are carried out in this paper. It points out that there is an optimum operational pressure on transcritical carbon dioxide heat pump cycle, when the outlet temperature of gas cooler is constant, the coefficient of performance increases with increasing evaporating temperature at the same conditions, and the operational efficiency increased with decrease of gas cooler exit temperature. So in order to obtain the optimum performance, the influence of evaporating temperature, gas cooler exit temperature, and the operational pressure should be considered during the designing and operating transcritical carbon dioxide heat pump system.

Abstract: The purpose of this paper is to investigate the effects of ionic liquids (ILs) oil-in-water emulsion on CO₂ absorption. 1-octyl-3-methylimidazolium hexafluorophosphate as ILs was dispersed into water forming oil-in-water emulsion to absorb carbon dioxide. Effects of dispersed phase volume fraction, droplet size, and the regeneration of dispersion were studied. Experimental results indicate that ILs oil-in-water emulsion can enhance the CO₂ absorption rate under lower dispersion phase volume fraction, and the CO₂ mass transfer rate increases with dispersion phase volume fraction. The smaller droplet size can help droplet go into the boundary layer to load CO₂ so as to increase the CO₂ mass transfer rate. ILs emulsion can be regenerated, but their enhancement effect becomes weaken with the increase of regeneration times.

Abstract: A polymer drilling fluid containing high content of hydrogen sulfide was used as the corrosive medium to investigate the effects of temperature, flow velocity, pH value and partial pressure ratio of CO₂/ H₂S on the corrosion behavior of high strength drill pipe steel S135 and G105. The morphology and composition of the corrosion products were analyzed as well. It was found that the average corrosion rate of the two types of steel increased with increasing temperature of the corrosive medium, with the corrosion rate to decrease slightly within 60°C-80°C and keep almost unchanged above 120°C. At the same time, the corrosion rate of the drill pipe steels had little to do with the flow rate but increased with decreasing pH value of the corrosive medium. Moreover, the partial pressure ratio of CO₂/ H₂S had a slight effect on the corrosion behavior of the drill pipe steel. However, the two types of drill pipe steel showed a larger corrosion rate in gas phase than in liquid phase corrosive medium, which was contrary to what were observed in gas and liquid phases corrosion tests of conventional acidic drilling fluids. In addition, it was confirmed by sulfide stress corrosion test that the drill pipe steel of a higher strength had smaller critical stress, and the resistance of the drill pipe to stress attack was ranked as G105(C)＞G105(D)＞S135(B)＞S135(A). It was anticipated that the present research results could be used to guide the selection of materials for drilling pipe steels used in natural gas field of high acidity.

Abstract: This paper reports design, modeling and simulation of MEMS based sensor working in dynamic mode with fully differential piezoresistive sensing for monitoring the concentration of exhaled carbon dioxide (CO2) gas in human breath called capnometer. CO2 being a very important biomarker, it is desirable to extend the scope of its monitoring beyond clinical use to home and ambulatory services. Currently the scope of capnometers and its adaption is limited by high cost, large size and high power consumption of conventional capnometers . In recent years, MEMS based micro resonant sensors have received considerable attention due to their potential as a platform for the development of many novel physical, chemical, and biological sensors with small size, low cost and low power requirements. The sensor is designed using 0.35 micron CMOS technology. CoventorWare and MATLAB have been used as simulation software. According to the developed model and simulation results the resonator has resonant frequency 57393 Hz and mass sensitivity of 3.2 Hz/ng. The results show that the longitudinal relative change of resistance is 0.24%/µm while the transverse relative change of resistance is -0.03%/µm.

Abstract: CO2 injection is a very promising and effective technology for promoting oil recovery ratio. But the lack of high pureness CO2 resources restricts the popularization and application of this technology. It is an effective approach to resolve such problem by capturing and purifying CO2 from electric plant and boiler emission gases. Shengli oil field of SINOPEC has researched on high efficiency absorbent, key equipment, capture and purification technique, and forms a technology of CO2 Capture and Purification. This technology not only helps to obtain the CO2 needed by EOR, increasing the economic income, but also to store the CO2 into the abandoned oil wells, preventing the CO2 from being emitted into the atmosphere.

Abstract: Carbon dioxide (CO2) gas sensor using surface acoustic wave (SAW) device based on Zinc oxide (ZnO) was developed and fabricated in this paper. The center frequency of SAW device is 203.528 MHz. The input and two output interdigital transducers (IDT) apodized by Morlet wavelet function can improve the side lobe rejection compared with uniform IDT. The ZnO film sensitive to CO2 gas was fabricated in measurement acoustic track of SAW device. Experiments results confirm that the CO2 gas sensor using SAW device based on ZnO film has good response characteristics to different concentrations CO2 gas. Furthermore, the CO2 gas sensor using SAW device based on ZnO film has good stability and linearity.

Abstract: In this paper, the three straight casing tubes and the double helix casing tubes were modeled using the Gambit software. And the fluid flowing in tubes was simulated by Fluent software. According to the simulation results, with the field synergy principle, two casing tubes’ flow and temperature distribution of carbon dioxide and water have been analyzed. Simulation data show that the double helix casing tubes is better than the three straight casing tubes on heat transfer and synergy. Lay the good foundation for design optimization and efficiency of heat exchanger of carbon dioxide heat pump system.

Abstract: The purpose of this study is to investigate whether calcite blocks with high mechanical property could be obtained for a short period from calcium hydroxide (Ca(OH)₂) compact using heat-treatment under carbon dioxide (CO₂) atmosphere. The Ca(OH)₂ disks compacted with different pressure was heated at different temperature ranging from 200°C to 800°C for an hour under CO₂ atmosphere. From the X-ray diffractometry, Ca(OH)₂ converted into calcite along with the rise of the heating temperature. Small amount of unreacted Ca(OH)₂ remained in samples heated at 600°C whereas samples treated at 800°C converted to calcite with very small amount of calcium oxide. The diametral tensile strength (DTS) value increased with the rise of heating temperature up to 600°C then decreased down to 800°C. Meanwhile, the porosity decreased with the rise of heating temperature up to 600°C then slightly increased up to 800°C. From the scanning electron microscope observation, grains grew bigger along with the rise of heating temperature. Intergranular space between grains decreased from 200°C to 600°C. The highest DTS value (14 MPa±1.3) at 600°C could be the result of lesser intergranular space due to sintering.

Abstract: Use the Monoclinic phase of nano-scale ZrO₂ , Li₂ZrO₃ and MgO as raw materials, with high temperature solid state reaction, we synthesized the Lithium zirconate materials which can directly absorb CO₂ at high temperatures of 450~550°C. Then use the scanning electron microscopy (SEM) and X-ray diffraction (XRD) for the morphology and structure analysis. The CO₂ absorption properties were tested by thermal analyzer (TG). The experimental results showed that the amount of MgO addition affected the Lithium zirconate’s CO₂ absorption properties, but to the pH and surface area, there is on influence.

Abstract: Si-doped lithium zirconate Li₂Si_xZr_(1-x)O₃(0≤x≤0.4) sorbents were prepared by a solid-state reaction method from nano-sized monoclinic ZrO₂. The morphology phase, structure and adsorption properties of the prepared lithium zirconate were respectively determined by using scanning electron microscope (SEM) , X-ray diffraction (XRD) and thermogravimetric analyzer (TG).The results showed the CO₂ adsorption properties of material could be improved by doping suitable amount Si.