Reforming natural gas for CO2 pre-combustion capture in combined cycle power plant

The aim of this study is to assess the conversion of a natural gas combined cycle power plant (NGCC) using an advanced gas turbine (GE9H) for CO₂ pre-combustion capture. The natural gas is reformed in an auto-thermal reformer (ATR) either with pure oxygen or with air. After water-shift conversion of CO into CO₂ and physical CO₂ recovery, the synthesis gas contains a high fraction of H₂. It is diluted with N₂ and steam to lower its low heating value (LHV) for NO _X emission control. Oxygen purity and reforming pressure have little impact on the performances. High-pressure reforming is preferred to reduce the process size. Air reforming results in a slightly higher efficiency but in a bigger process too. The CO₂ recovery rate has a big impact on the power plant efficiency since a lot of steam is required to lower the heating value (LHV) of the synthesis gas leaving the recovery process. Two values of LHV have been assessed. Steam consumption for natural gas reforming and synthesis gas dilution are the main consuming elements. An erratum to this article can be found at     

Assessment of pre-combustion decarbonisation schemes for polygeneration from fossil fuels

This article deals with emerging poly-generation schemes that employ pre-combustion decarbonisation of fossil fuels—eventually with options for geological storage of the CO₂. Inevitably, such schemes are highly complex, and may require new approaches and knowledge on interactions between key components in large plants, as even new technologies and features are expected to occur in due course as the experience from polygeneration matures. Reference is made to the European DYNAMIS project and the Sino-European project COACH—both conducted under the auspices of the European Commission.

Decomposition characteristics of carbon dioxide by gas tunnel-type plasma jet

The increase of warm-room gas is thought to cause the rise of atmosphere temperature, which is called the warm-room effect. Therefore, the decomposition treatment of carbon dioxide (CO₂) gas is an important research subject in order to solve the global environmental problem. In this study, a high-energy plasma process was used to decompose CO₂ gas as a warm-room gas, and the decomposition mechanism was clarified by varying the plasma operation conditions. The possibility of transforming of the CO₂ gas to various resources was also discussed. Firstly, the performance test of the gas tunnel-type plasma jet used for decomposition of CO₂ was conducted, and decomposition characteristics of CO₂ gas by the gas tunnel-type plasma jet was determined under various conditions. The decomposition ratio of CO₂ was about 30%, when the power input was P=8 kW, and the CO₂ content in argon was 10%. Secondly, the improvement of operating conditions of the plasma jet was discussed in order to enhance its performance.     

Effects of thermal conduction in microchannel gas coolers for carbon dioxide

A numerical code was developed for an accurate fully three-dimensional simulation of crossflow compact heat exchangers using finned flat tubes with internal microchannels; such components are often employed as gas coolers in transcritical refrigerating machines CO₂ operated. The equations describing the system were discretised by means of a finite-volume and finite-element hybrid technique for strictly adhering to the real heat transfer process regarding the finned surfaces. The numerical code uses recent correlations by different authors for predicting the heat transfer coefficients both refrigerant side and air side. The results of simulations are verified against experimental data reported in the open literature.The aim of this work is to investigate the effects of thermal conduction inside metal on the overall performance of the considered gas coolers; high-resolution meshes for the discretisation of separating wall and fins makes it possible to avoid much of the approximations typical of the traditional approaches. In particular the efficiency of finned surfaces, the real distribution of thermal fluxes between the two fin roots and the effects of thermal conduction along the walls of microchannel flat tubes are extensively discussed.The numerical simulations confirm that the traditional approach for describing fins, which assumes them as adiabatic at the middle section in order to decouple the equations accounting for the effect of different temperatures at the fin roots, can be considered acceptable in a wide range of applications. In a similar way, the conduction on fins along the direction of the air velocity and the longitudinal conduction on tubes produce a negligible effect on the performance of the considered class of heat exchangers.     

Transcritical carbon dioxide microchannel heat pump water heaters: Part I - validated component simulation modules

An experimental and analytical study on the performance of carbon dioxide heat pumps for water heating was conducted. The performance of compact, microchannel, water-coupled gas coolers, evaporator, and suction line heat exchanger (SLHX) were evaluated in an experimental facility. Analytical heat exchanger models accounting for the flow orientation and changing CO₂ thermophysical properties were developed and validated with data. Heat transfer coefficients were predicted with correlations available in the literature and local heat duty calculated using the effectiveness-NTU approach. The gas cooler, evaporator, and SLHX models predicted measured heat duties with an absolute average error of 5.5%, 1.3%, and 3.9%, respectively. Compressor isentropic and volumetric efficiency values were found to range from 56% to 67% and 62%-82%, respectively. Empirical models for compressor efficiency and power were developed from the data. The resulting component models are implemented in a system model in a companion paper (Part II).     

Biomass derived 5-hydroxymethylfurfural as carbon precursor to form hollow carbon nanospheres for CO2 capture

We prepare the hollow carbon nanospheres (HCNs) by employing SiO₂ nanospheres as hard template, 5-Hydroxymethylfurfural (HMF) as carbon precursor under hydrothermal conditions. The HCNs show uniform spherical morphology copied from SiO₂ nanospheres and exhibit large cavity, thin shell structure with the surface area of 790 m² g^?1 and pore volume of 2.23 cm³ g^?1. Owing to their large internal voids and high surface area, the HCNs exhibit a promising prospect for CO₂ capture with the capacity of 3.04 mmol g^?1 at 1.0 bar and 298 K, as well as good recyclability for CO₂ after ten adsorption-desorption cycles.     

High pressure carbon dioxide adsorption on nanoporous carbons prepared by Zeolite Y templating

Nanoporous carbons were synthesized by chemical vapor deposition using furfuryl alcohol/butylene as a carbon source and zeolite Y as a hard template (ZYC). The ZYC were characterized by PXRD, N₂ sorption, and SEM. The carbon materials exhibited predominant microporosity, and the specific surface area increased from 2563 to 3010 m² g⁻¹ as the pyrolysis temperature was raised from 800 to 1000 °C. ZYC prepared at 1000 °C showed a CO₂ adsorption capacity of 986 mg g⁻¹_adsorbent at 40 bar 298 K, which surpasses the capacities of commercial carbons and mesoporous carbon CMK-3, and closely approaches the best performance of the metal organic framework MOF-177. The CO₂ adsorption capacities of the adsorbents were found to be closely correlated with the BET surface areas of the materials tested.     

Polyethyleneimine functionalised nanocarbons for the efficient adsorption ofcarbon dioxide with a low temperature of regeneration

Polyethyleneimine (PEI) conjugates with a range of nanocarbons (NCs) have been prepared, and their performances with regard to carbon dioxide absorption and liberation are compared. PEI-functionalised multi-walled carbon nanotubes (PEI-MWNTs) prepared by the reaction of branched PEI (25,000 Da) with F-MWNTs in the presence of pyridine, showed a lower CO₂ capacity at 25 °C (5 wt%, 1.1 mmol CO₂/g adsorbent) as compared to PEI-SWNTs (9.2 wt%, 2.1 mmol CO₂/g adsorbent), consistent with the interior layers of the MWNTs adding weight to the base NC without adding functionality. PEI-functionalised graphite/graphene was prepared by three routes: fluorinated graphite intercalation compounds, prepared from natural graphite powder, were reacted with PEI in EtOH with pyridine; exfoliated natural graphite powder was reacted with Boc–Phe(4-N₃)–OH, and subsequently PEI to give PEI-Phe(4-N-G); graphite oxide (GO) was reacted with PEI in the presence of NEt₃ to give PEI-GO. The CO₂ capacity of PEI-GO at 25 °C (8 wt%, 1.8 mmol CO₂/g adsorbent) was comparable to that of PEI-SWNTs making GO a valid and cheaper alternative to the SWNT scaffold. The temperature of CO₂ desorption of the PEI-NCs was 75 °C, providing a lower energy load for regeneration compared to current amine-based scrubbing units. The rate of CO₂ uptake is seen to depend on the curvature of the NC substrate.     

Reduction of greenhouse gases in integrated pulp and paper mills: possibilities for CO2 capture and storage

Earlier work has shown that capturing the CO₂ from flue gases in the recovery boiler at a market pulp mill can be a cost-effective way of reducing mill CO₂ emissions. In this paper, it is investigated whether the same is valid for an integrated pulp and paper mill. Five configurations are compared, supplying the extra energy needed by a biofuel boiler, an NGCC, a heat pump or by reducing the steam demand at the mill in combination with a biofuel boiler or an NGCC. The configurations have been evaluated with energy market scenarios and the avoidance cost has been calculated. The NGCC configurations have the lowest avoidance costs in all scenarios and they also have the advantage of liberating biofuel for use in other parts of society. An erratum to this article can be found at     

Fabrication of hydrophilic paclitaxel-loaded PLA-PEG-PLA microparticles via SEDS process

In this work, chemically bonded poly(D, L-lactide)-polyethylene glycol-poly(D, L-lactide) (PLA-PEG-PLA) triblock copolymers with various PEG contents and PLA homopolymer were synthesized via melt polymerization, and were confirmed by FTIR and ¹H-NMR results. The molecular weight and polydispersity of the synthesized PLA and PLA-PEG-PLA copolymers were investigated by gel permeation chromatography. Hydrophilicity of the copolymers was identified by contact angle measurement. PLA-PEG-PLA and PLA microparticles loaded with and without PTX were then produced via solution enhanced dispersion by supercritical CO₂ (SEDS) process. The effect of the PEG content on the particle size distribution, morphology, drug load, and encapsulation efficiency of the fabricated microparticles was also studied. Results indicate that PLA and PLA-PEG-PLA microparticles all exhibit sphere-like shape with smooth surface, when PEG content is relatively low. The produced microparticles have narrow particle size distributions and small particle sizes. The drug load and encapsulation efficiency of the produced microparticles decreases with higher PEG content in the copolymer matrix. Moreover, high hydrophilicity is found when PEG is chemically attached to originally hydrophobic PLA, providing the produced drug-loaded microparticles with high hydrophilicity, biocompatibility, and prolonged circulation time, which are considered of vital importance for vessel-circulating drug delivery system.     

Semiconducting BaTiO3-CuO mixed oxide thin films for CO2 detection

A full study of the BaTiO₃-CuO thin-film technology properties as carbon dioxide sensing material is presented. The coatings are deposited by RF-Sputtering and the CO₂ concentration is monitored by impedance measurements. Theoretical foundations are correlated to the experimental results and the principal fabrication and operation parameters are clarified: working temperature and frequency, thickness influence and the introduction of silver as an additive. The BaTiO₃-CuO layer shows higher sensitivity than the actual low-cost commercial CO₂ sensors in the range of the principal applications.     

Production of graphene nanosheets by supercritical CO2 process coupled with micro-jet exfoliation

A facile and cost-effective method which combines supercritical CO₂ and micro-jet exfoliation has been developed for producing graphene nanosheets with high-quality. CO₂ molecules can intercalate into the interlayer of graphite because of their high diffusivity and small molecule size in supercritical operation. The tensile stress induced by graphite interfacial reflection of compressive waves exert on the graphite flakes, which lead to further exfoliation of graphite. Scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM), Raman spectrum and X-ray diffraction (XRD) are used to identify morphology and quality of the exfoliated graphene nanosheets, which reveal that the graphite was successfully exfoliated into graphene and more than 88% of graphene nanosheets are less than three layers. The yield of graphene nanosheets is about 28 wt% under optimum conditions, which can be greatly improved by repeated exfoliation of the graphene sediment. The pure graphene film has a high conductivity of 2.1 × 10⁵ S/m.     

Polymer synthesis and characterization in liquid / supercritical carbon dioxide

The use of carbon dioxide as an inert solvent has emerged recently as an important development in polymer chemistry. The past year has seen major advances in the synthesis of a variety of polymeric materials in carbon dioxide. At the same time complementary studies have successfully elucidated the physical behavior of a range of polymers in carbon dioxide solution. Herein we review both synthetic and physical studies that are defining the scope of this approach.     

The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC

This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO₂ was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO₂ prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO₂ was approximately 8.71% with the N719 dye under 100 mW cm⁻² simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO₂ than on the nano-sized TiO₂ particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO₂ film.     

Efficiency of the indicated process of CO2-compressors

The compressor of a refrigerant compression process is the component with the major influence on the efficiency and reliability of the entire system. Due to the fluid properties of carbon dioxide (CO₂), the pressure ratio of the refrigeration process with CO₂ as the working fluid is, in relation to common refrigeration processes, rather low while the pressure difference is extremely high. From experimental and theoretical considerations it becomes obvious that at these conditions a high volumetric and energetic efficiency of the compressor may be achieved if its design is appropriate. In this paper, the effects on the efficiency of the indicated compression process of a CO₂-compressor are discussed and evaluated and a promising design concept for an efficient CO₂-compressor is derived.     

Diesel emission control system using combined process of nonthermal plasma and exhaust gas components' recirculation

A NO_x aftertreatment system, using nonthermal plasma (NTP) reduction and exhaust gas components' recirculation, is investigated. A pilot-scale system is applied to a stationary diesel engine. In this system, NO_x is first removed by adsorption, and subsequently, the adsorbent is regenerated by thermal desorption. NO_x desorbed is reduced by using nitrogen NTP. Moreover, NO_x, CO₂, and water vapor recirculated into the engine intake reduce NO_x. In this study, approximately 57% of the NO_x of the exhaust (NO_x: 240-325 ppm, flow rate = 300 NL/min) can be continuously treated for 58 h. A system energy efficiency of 120 g (NO₂)/kWh is obtained.     

Optimization of the cutting process of multi-wall carbon nanotubes for enhanced dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated based on multi-wall carbon nanotube (MWCNT)-TiO₂ photo-anodes, which were prepared by the procedures of cutting MWCNTs and subsequent immobilization TiO₂ on MWCNTs. Through a detailed study, we found that cut-MWCNTs with proper ultrasonication time (2 h) and proper content (0.075%) resulted in 58 and 40% increase in short-circuit photocurrent and overall energy conversion efficiency, respectively, compared with that of a DSSC using only TiO₂ photo-anode. The enhancement of cut-MWCNTs for DSSC was attributed to the introduction of percolative conductive paths which facilitate the rapid electron transfer.     

Effect of lubricating oil on cooling heat transfer of supercritical carbon dioxide

In this research, the cooling heat transfer coefficient and pressure drop of supercritical CO₂ with PAG-type lubricating oil entrained were experimentally investigated. The inner diameter of the test tubes ranged from 1 to 6 mm. The experiments were conducted at lubricating oil concentrations from 0 to 5%, pressures from 8 to 10 MPa, mass fluxes from 200 to 1200 kg m⁻² s⁻¹, and heat fluxes from 12 to 24 kW m⁻².In comparison to the oil-free condition, when lubricating oil entrainment occurred, the heat transfer coefficient decreased and the pressure drop increased. The maximum reduction in the heat transfer coefficients—about 75%—occurred in the vicinity of the pseudocritical temperature. The influence of oil was significant for a small tube diameter and a large oil concentration. From visual observation, it was confirmed that this degradation in the heat transfer was due to the formation of an oil-rich layer along the inner wall of the test tube. However, when the oil concentration exceeded 3%, no further degradation in the heat transfer coefficient could be confirmed, which implies that the oil flowing along with CO₂ in the bulk region does not influence the heat transfer coefficient and the pressure drops significantly. For a large tube at a lower mass flux, no significant degradation in the heat transfer coefficient was observed until the oil concentration reached 1%. This is due to the transition of the flow pattern from an annular-dispersed flow to a wavy flow for a large tube, with CO₂ flowing on the upper side and the oil-rich layer on the lower side of the test section.     

Sulfur dioxide initiates global climate change in four ways

Global climate change, prior to the 20th century, appears to have been initiated primarily by major changes in volcanic activity. Sulfur dioxide (SO²) is the most voluminous chemically active gas emitted by volcanoes and is readily oxidized to sulfuric acid normally within weeks. But trace amounts of SO₂ exert significant influence on climate. All major historic volcanic eruptions have formed sulfuric acid aerosols in the lower stratosphere that cooled the earth's surface ~ 0.5 °C for typically three years. While such events are currently happening once every 80 years, there are times in geologic history when they occurred every few to a dozen years. These were times when the earth was cooled incrementally into major ice ages. There have also been two dozen times during the past 46,000 years when major volcanic eruptions occurred every year or two or even several times per year for decades. Each of these times was contemporaneous with very rapid global warming. Large volumes of SO₂ erupted frequently appear to overdrive the oxidizing capacity of the atmosphere resulting in very rapid warming. Such warming and associated acid rain becomes extreme when millions of cubic kilometers of basalt are erupted in much less than one million years. These are the times of the greatest mass extinctions. When major volcanic eruptions do not occur for decades to hundreds of years, the atmosphere can oxidize all pollutants, leading to a very thin atmosphere, global cooling and decadal drought. Prior to the 20th century, increases in atmospheric carbon dioxide (CO₂) followed increases in temperature initiated by changes in SO₂.By 1962, man burning fossil fuels was adding SO₂ to the atmosphere at a rate equivalent to one “large” volcanic eruption each 1.7 years. Global temperatures increased slowly from 1890 to 1950 as anthropogenic sulfur increased slowly. Global temperatures increased more rapidly after 1950 as the rate of anthropogenic sulfur emissions increased. By 1980 anthropogenic sulfur emissions peaked and began to decrease because of major efforts especially in Japan, Europe, and the United States to reduce acid rain. Atmospheric concentrations of methane began decreasing in 1990 and have remained nearly constant since 2000, demonstrating an increase in oxidizing capacity. Global temperatures became roughly constant around 2000 and even decreased beginning in late 2007. Meanwhile atmospheric concentrations of carbon dioxide have continued to increase at the same rate that they have increased since 1970. Thus SO₂ is playing a far more active role in initiating and controlling global warming than recognized by the Intergovernmental Panel on Climate Change. Massive reduction of SO₂ should be a top priority in order to reduce both global warming and acid rain. But man is also adding two to three orders of magnitude more CO₂ per year to the climate than one “large” volcanic eruption added in the past. Thus CO₂, a greenhouse gas, is contributing to global warming and should be reduced. We have already significantly reduced SO₂ emissions in order to reduce acid rain. We know how to do it both technically and politically.In the past, sudden climate change was typically triggered by sudden increases in volcanic activity. Slow increases in greenhouse gases, therefore, do not appear as likely as currently thought to trigger tipping points where the climate suddenly changes. However we do need to start planning an appropriate human response to future major increases in volcanic activity.