Minimization of life cycle CO2 emissions in steam and power plants

A methodology is presented to minimize life cycle CO₂ emissions through the selection of the operating conditions of a steam and power generation plant. The battery limits of the utility plant are extended to include CO₂ emissions of: (1) extraction and transport of natural gas burned in its boilers, (2) generation of imported electricity by nuclear, hydroelectric and thermoelectric plants and (3) exploration, extraction and transport of natural gas, oil, coal and uranium consumed by thermoelectric and nuclear plants. The operating conditions of the utility plant are selected optimally to minimize the life cycle CO₂ emissions. There are continuous operating conditions such as temperature and pressure of the high, medium and low pressure steam headers and binary operating conditions to represent discrete decisions to select optional pumps drivers between electrical motors and steam turbines or whether some equipment is on or off. A Mixed Integer Nonlinear Programming problem is formulated and solved in GAMS. Significant reductions in life cycle CO₂ emissions, natural gas consumption and operating cost are achieved simultaneously in the steam and power generation system of an ethylene plant. This is an important tool to support a decision making process to reduce CO₂ emissions in a key industrial sector. An erratum to this article can be found at     

CO2 capture at high temperature using calcium-based sorbents

Calcium-based sorbents synthesized from CaO, CaCO₃, and Ca(OH)₂ precursors were demonstrated as high-temperature CO₂ capture materials. The effect on CO₂ capture capability of calcium-based sorbents receiving different activations was also investigated. After proper activation, the best carbon capturing material is CaO that captured 75% of available CO₂ in nine cyclic tests and captured 61% even after 40 cyclic experiments. The correlation of the structural difference in the three activated sorbents and CO₂ conversion has been discussed. The sintering effect is presumably a major cause for activity decline of calcium-based sorbents… after cyclic carbonation/decarbonation runs.     

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.

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.     

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     

Effect of amine structure on CO2 capture by polymeric membranes

Abstract

Poly(amidoamine)s (PAMAMs) incorporated into a cross-linked poly(ethylene glycol) exhibited excellent CO₂ separation properties over H₂. However, the CO₂ permeability should be increased for practical applications. Monoethanolamine (MEA) used as a CO₂ determining agent in the current CO₂ capture technology at demonstration scale was readily immobilized in poly(vinyl alcohol) (PVA) matrix by solvent casting of aqueous mixture of PVA and the amine. The resulting polymeric membranes can be self-standing with the thickness above 3 μm and the amine fraction less than 80 wt%. The gas permeation properties were examined at 40 °C and under 80% relative humidity. The CO₂ separation performance increased with increase of the amine content in the polymeric membranes. When the amine fraction was 80 wt%, the CO₂ permeability coefficient of MEA containing membrane was 604 barrer with CO₂ selectivity of 58.5 over H₂, which was much higher than the PAMAM membrane (83.7 barrer and 51.8, respectively) under the same operation conditions. On the other hand, ethylamine (EA) was also incorporated into PVA matrix to form a thin membrane. However, the resulting polymeric membranes exhibited slight CO₂-selective gas permeation properties. The hydroxyl group of MEA was crucial for high CO₂ separation performance.     

The clathrate hydrate process for post and pre-combustion capture of carbon dioxide

One of the new approaches for capturing carbon dioxide from treated flue gases (post-combustion capture) is based on gas hydrate crystallization. The basis for the separation or capture of the CO(2) is the fact that the carbon dioxide content of gas hydrate crystals is different than that of the flue gas. When a gas mixture of CO(2) and H(2) forms gas hydrates the CO(2) prefers to partition in the hydrate phase. This provides the basis for the separation of CO(2) (pre-combustion capture) from a fuel gas (CO(2)/H(2)) mixture. The present study illustrates the concept and provides basic thermodynamic and kinetic data for conceptual process design. In addition, hybrid conceptual processes for pre and post-combustion capture based on hydrate formation coupled with membrane separation are presented.     

某天然气热电联产项目噪声控制

天然气热电联产项目因其高效、环保、占地面积小、耗水少及建设周期短等优点而受到各国的广泛关注,但燃气电站噪声污染问题较为突出,通过声学照相机识别厂区内的噪声源,确定厂界的噪声值,对噪声源声学特性进行分析,建立噪声源及建筑的声学模型并进行仿真计算,确定噪声源对项目边界的影响并提出声学设计方案,对最终方案实施后的效果进行实测。结果表明该方案满足了声环境要求,可供同类大型燃气电厂的噪声控制项目参考。     

Clover leaf-shaped Al2O3 extrudate as a support for high-capacity and cost-effective CO2 sorbent

Amine-functionalized clover leaf-shaped Al₂O₃ extrudates (CA) were prepared for use as CO₂ sorbent. The as-synthesized materials were characterized by N₂ adsorption, XRD, SEM and elemental analysis followed by testing for CO₂ capture using simulated flue gas containing 15.1% CO₂. The results showed that a significant enhancement in CO₂ uptake was achieved with the introduction of amines into CA materials. A remarkably high volume-based capacity of 70.1 mg/mL of sorbent of this hybrid material suggests that it can be potentially used for CO₂ capture from flue gases and other stationary sources, especially those with low CO₂ concentration. The novel adsorbent reported here performed well during prolonged cyclic operations of adsorption-desorption of CO₂.     

High power single mode output CO2 laser

Abstract

While attempting to reach TEMoo single mode high output power, the transverse discharge method was adopted. The optic axis, the direction of glow discharge and gas flow velocity are all mutually orthogonal. The discharge region has a 2.3 liter medium volume, and 100 m/sec gas flow. This small signal gain exceeds 0.8/m in the local region. We also adopted a stable multi‐path cavity for coordinating the larger volume laser medium. Under auxiliary discharge, the maximum output power can reach 1500W, at an efficiency of 9%.     

The influence of flue gas recirculation on oxy-oil combustion in an existing furnace

Oxy-fuel combustion has received increasing attention as one of the major solutions for CO₂ capture. This study aimed to obtain a better understanding on the oxy-oil firing process and to gain experience handling flue gas recirculation. A 300 kW_th multi-fuel combustion test furnace at National Cheng-Kung University in Tainan, Taiwan was chosen as the experimental facility. This experimental study had successfully converted a conventional air-fired furnace to operate on oxy-fuel firing with various operating conditions. Oxygen-enriched combustion and oxy-fuel combustion tests were conducted. The effects of oxygen enrichment, flue gas recirculation, fuel type, and thermal loading on the operational characteristics of the furnace such as temperature distribution, pressure variation, and emission characteristics were examined and discussed. Several concerns about a conventional air-fired furnace adapted for oxy-fuel combustion were scrutinized, including optimization of flue gas recirculation for better combustion efficiency, higher SO₂ concentration in the flue gas under oxy-fuel operation, and air leakage coming from negative pressure operation. These findings provided valuable data to improve the performance of oxy-fuel combustion and to allow better conceptual designs in future development.     

A study of parameters affecting the continuous CO2 laser cuts

Abstract

This work attempts to discover, by experimentation, some of the parameters governing cutting efficiency in perspex of a continuous CO₂ laser. The experimentation took the form of taking cuts in specimen pieces with the laser. While varying the parameters of speed of cut and position of the focal plane of the laser beam relative to the surface of the perspex, all other parameters were kept constant. These experiments produced conclusive ideas of the optimum position of the focal plane and the best speeds for cutting perspex at the same time producing the best cut quality obtainable. When the theoretically predicted minimum cut width is compared with the experimentally obtained results, the agreement is found to be almost exact.     

A study of uv preionization pulsed tea CO2 laser

Abstract

A uniform volumetric discharge was obtained by means of an auxiliary UV preionization in a home‐made TEA CO₂ laser. The maximum output pulse energy of this laser system was about 12J per pulse with a pulse duration of 80 ns. The ratio of electric field to neutral particle density (E/N) in this laser was 7.6×10^‐16 V cm². The peak power and pulse shape of the laser were studied. The time delay between the predischarge and the maindischarge during the stable operation of this laser system has also been studied. It was observed that the laser was operating with uniform glow discharges when the time delayed between the predischarge and the maindischarge was in the range of 1.0 μs to 6.0 μs. The spark array used as a preionizer for producing the UV radiation in this system is new, simple, durable, and can be easily fabricated.     

Removal of Nano-sized Particles Using Carbon Dioxide (CO2) Gas Cluster Cleaning without Pattern Damage

As pattern size of semiconductor device becomes less than 20 nm, the removal of particles smaller than 10 nm without pattern damages requires new physical dry cleaning technology. CO₂ gas cluster cleaning is an alternative dry cleaning process to meet these cleaning requirements. To demonstrate gas cluster cleaning performance, particle removal efficiency (PRE) and gate structure pattern damages were evaluated. When pressurized and low temperature CO₂ gas was passed through a convergence–divergence (C–D) nozzle, high energy CO₂ gas clusters were generated at high speed in a vacuum atmosphere. The cleaning force of the CO₂ gas cluster is related to the flow rate of the CO₂ gas. The optimum CO₂ gas flow rate for the particle removal without pattern damage was found to be 6 L/min (LPM). Removal efficiency for 50 nm silica particles was greater than 90%, and no pattern damage was observed on 60 nm poly-Si and a-Si gate line patterns. It was confirmed that the CO₂ gas cluster cleaning force could be controlled by the CO₂ gas flow rate supplied to nozzle.     

Catalytic reduction of CO2 to alcohol with Cu2Se-combined graphene binary nanocomposites

Photocatalytic reduction of CO₂ over a Cu₂Se–graphene nanocatalyst has been investigated. The nanocomposite material was successfully prepared via a modified hydrothermal method. The structure and properties of the prepared composite were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray microscopy, transmission electron microscopy, Raman spectroscopic analysis, and X-ray photoelectron spectroscopy. A synergetic effect of the combination of Cu₂Se and graphene appeared in the form of excellent photocatalytic reduction capability of CO₂. The photocatalytic efficiencies of the samples were characterized by testing for the photoreduction of CO₂ to alcohol under visible light irradiation, which produced results such as to suggest that there is a significant potential for graphene-based semiconductor hybrid materials to be used as photocatalysts for reduction of CO₂.     

Low temperature biomimetic synthesis of the Li2ZrO3 nanoparticles containing Li6Zr2O7 and high temperature CO2 capture

Li₂ZrO₃ nanoparticles containing Li₆Zr₂O₇ were prepared by a biomimetic soft solution route and characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption. The results show that the tetragonal Li₂ZrO₃ nanoparticles containing monoclinic Li₆Zr₂O₇ can be obtained using this simple method. The mean diameter of the nanoparticles is approximately 90 nm and the corresponding specific surface area is 23.7 m² g^− 1. Moreover, the Li₂ZrO₃ nanoparticles obtained were thermally analyzed under a CO₂ flux to evaluate their CO₂ capture capacity at high temperature. It was found that the as-prepared Li₂ZrO₃ nanoparticles would be an effective acceptor for high temperature CO₂ capture.     

CO2 + R23 Binary System: Virial Coefficients Derived from Burnett Measurements

Burnett PVT measurements were performed on trifluoromethane (R23) and mixtures of R23 with carbon dioxide (CO₂). The Burnett apparatus was calibrated using helium. Fourteen expansions were performed for 5 isotherms and in a pressure range from 130 kPa to 6 MPa for R23. Second and third virial coefficients were derived from the collected data and compared with literature values; good agreement was found between them. PVTx measurements for the binary CO₂+R23 system were carried out for five isotherms (303, 313, 323, 333, and 343 K). In all, 18 runs were performed in a pressure range from 150 kPa to 5.9 MPa. The composition of the mixtures was measured with a gas chromatograph after it had been calibrated using samples prepared gravimetrically. Second and third virial coefficients for the system were derived, together with the second and third cross virial coefficients, from experimental results using virial coefficients for CO₂ from previous measurements (for the same sample as used in the present study). Samples for composition measurements were collected during the first Burnett expansion. Second virial coefficients for the system showed positive deviations from ideal values, while the third virials were negative. No previous experimental results were found for the PVTx properties of this binary system.     

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.     

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.     

Pressure influences on CO2 reaction with cyclohexylamine using ionic liquid as reaction medium and catalyst

Inserting carbon dioxide (CO₂) into ammonia molecules to produce urea is a traditional CO₂ utilization method. An ionic liquid (IL), 1-butyl-3-methylimidazolium bromide ([Bmim]Br), was used as reaction medium and [Bmim]Br/KOH as catalyst. This study investigates CO₂ carbonylation of cyclohexylamine and its reaction performance in a number of low- and high-pressure CO₂/IL systems. The reaction yield was greatly increased as pressure ranges changed from 15–50 bar to 80–100 bar; the physiochemical properties of substrates and catalyst were greatly affected by CO₂ in supercritical state. The yield was improved from 69% at 30 bar to 91.6% at 100 bar, much better than a previous study result of 53.5%, but as pressures further increased, a significant decrease was observed. The reaction activation energy was calculated to be 3.942 and 4.354 kcal/mol in mild and supercritical conditions. This process shows a low threshold reaction energy and great potential for industrial applications to store CO₂ in amine molecular structures.