Gas Mass Ratio Research Articles

Energy, safety, and absorption efficiency evaluation of a pilot-scale H2S abatement process using MDEA solution in a coke-oven gas

This study models an H2S removal unit for steel-manufacturing coke-oven gas and suggests optimal operating conditions and safety analysis for absorption and regeneration columns. Sensitivity analysis was performed on H2S removal to identify the minimum methyldiethanolamine (MDEA) solution flow rate using 99% H2S removal as a constraint and minimal heat duty. The optimized L/G ratio and regeneration column pressure were investigated accordance with change in H2S emission limit or desulfurization efficiency (99–99.9%), to reflect the different usage of COG. For the absorption column, the MDEA solution and heating duty were expected to be reduced in optimal conditions by 35% and 23% respectively when absorbent to gas mass ratio was decreased from 2.0 to 1.3, respectively. The most effective operating pressure for the distillation column was 2.5 bar (Basis pressure: 1.2 bar) based on a trade-off between reboiler energy and the H2S remaining in the recycle stream. According to optimization result with variation in efficiency, the higher optimized L/G ratio, higher reboiler duty, higher intermediate heat exchanger duty, and lower optimized regenerator pressure were required to maintain higher efficiency with different COG utilization. To ensure safe operating conditions, chemical reactivity tests were conducted for mixture of chemicals. Additionally, Gas dispersion analysis predicted the concentration and distance of gas spread to ensure safety from gas leak accident.

Effect of seawater alkalinity on the performances of a marine diesel engine desulphurization scrubber

Since the last fifteen years, Flue Gas Desulphurization (FGD) plants based on seawater scrubbing found an interesting application in the maritime transportation, as an answer to the stringent regulations imposed by International Maritime Organization (IMO) on sulphur emissions. This work reports the experimental results on desulphurization in a pilot seawater scrubber (DN 400) from a marine Diesel engine (80 kW) operated under different loads (10, 25 and 50%). The pilot scrubber was fed with a gas velocity 0.15 m/s and a liquid to gas mass ratio 1-3 kg/kg. The scrubbing liquid was available at different alkalinity and salinity levels representing the ion speciation of marine water in different geographic areas. The experiments evaluate the SO2 removal efficiency of the scrubber as a function of seawater alkalinity and pH. Finally, the paper reports a correlation to assess the seawater flow rate required to comply with the current IMO restrictions. This correlation allows tuning the seawater flow rate during the ship navigation based on the registered marine alkalinities and to the operating conditions of the engine. The model can be integrated in the scrubber control system to identify optimal operating conditions and reduce pumping costs, helping to reduce the EEDI and the SEEMP ships energy indexes.

An experiment of lubricating oil gas concentration in the standardized driving cycles

There always is cavitation in the positive displacement pump, and the bubbles in the lubricating oil have a great influence on the lubricating performance. This paper aims to measure the lubricating oil gas concentration of a passenger car gasoline engine in the standardized driving cycles. We use a passenger car engine lubricating system in the lubricating experiment, simulating the lubricating oil pump working state in the standardized driving cycles. The lubricating oil density and flow rate are measured to calculate the gas concentration in the lubricating oil, according to the engine work state in the standardized driving cycles, including NEDC Urban, NEDC Ultra Urban, WLTC High Speed. The test results show that under the steady-state conditions, the gas volume ratio decreases linearly with the increase of the outlet pressure, the air mass ratio increases with the increase of the pump speed. In the driving cycles, the air mass ratio also increases with the increase of outlet pressure, and it has a high positive correlation with lubricating oil flow and pump speed. With the increase of oil temperature from 25 to 100°C, the air volume ratio decreases by 72.6%, and the air mass ratio decreases by 84.3%. In the engine accelerating state, the rate of lubricating oil flow gain lags behind the pump speed, which makes the lubricating oil gas mass ratio in the accelerating state is significantly higher than that in the decelerating state.

Influence of water port injection on cycle-to-cycle variations in heavy-duty natural gas engine under low load

Water injection is regarded as an effective approach to decrease thermal load and suppress knock onset in heavy-duty natural gas engines. However, the cycle-to-cycle variations in heavy-duty natural gas engines via water injection has rarely been investigated. In this study, the effects of water port injection on cycle-to-cycle variations in a natural gas engine were analyzed experimentally. The engine speed was fixed at 1600 r/min, and engine load was set at a low load with a brake mean effective pressure of 0.387 MPa. Three excess air-fuel ratios (λ = 1.0, 1.2, and 1.4) were defined; and four water to natural gas mass ratios (WNMRs) were set. The results demonstrated that the variations of multicycle cylinder pressure traces consistently increased with the increase in WNMR. The interdependence between the peak in-cylinder pressure (Pmax) and its corresponding crank angle became more dispersed, and the frequency distribution of Pmax covered a wider range with increasing WNMR. The obvious fluctuations and wide range of distribution of indicated mean effective pressure (IMEP) were determined by water addition. The higher the λ, the larger the fluctuations and wider the range of distribution of IMEP. The coefficient of variation of IMEP (COVIMEP) increased with the increase in WNMR and λ. However, the maximum COVIMEP among the three λs and four WNMRs did not exceed 3%. Thus, it can be concluded that no drivability problem is associated with water injection under low load.

Experimental and numerical studies on metrological characteristics of swirlmeters with different swirler helix angles in a gas–solid two-phase flow

Swirlmeters are widely used to measure natural gas because of their simple structure, absence of internal moving parts and high measurement accuracy. However, fine particles in natural gas can affect swirlmeters’ metering accuracy. Hence, this study evaluated the metrological characteristics of swirlmeters measuring gas–solid two-phase flow with fine particles and different swirler helix angles. Experiments and simulations for swirlmeters with different solid–gas mass ratios and helix angles were performed. The results demonstrated that the swirlmeter meter factors decreased and pressure losses increased as the solid–gas mass ratio increased. With different solid–gas mass ratios, the most effective sensor detection position was at the throat outlet a half radius from the centre of the runner. The swirler with a smaller helix angle could significantly increase the meter factor, while the swirler with a larger helix angle could significantly decrease pressure losses. The swirlmeter internal flow losses were mainly derived from the swirler.

커먼레일압력과 천연가스 질량비율에 따른 이중연료 디젤엔진의 유해 배기배출물 특성

There are many studies on multi-fuel diesel engine, and the most prominent among these are natural gas dual fuel diesel engines. The purpose of this study is to investigate the effect of common rail pressure and natural gas mass fraction on the emission of natural gas dual fuel diesel engines. Experiments were performed with differential common rail pressures and natural gas mass fractions at three loads, and engine revolutions were fixed at 2,000 RPM. As a result, the specific emission of NOx increased and CO and THC decreased as the common rail pressure increased; however, CO₂ did not change. There was no effect of the natural gas mass ratio on the trend of specific emission of NOx and CO. In the case of THC, it increased as the natural gas mass ratio increased at the lower output. In the case of CO₂, the reduction rate was about 45%, and it decreased by about 4% per 12 kW output as the natural gas mass ratio increased.

Experimental study of the effects of spark timing and water injection on combustion and emissions of a heavy-duty natural gas engine

The growing concern over global warming and stricter emissions regulations (EURO 6 standards) have led to natural gas engines being operated in stoichiometric combustion conditions with three-way catalytic (TWC) and exhaust gas recirculation (EGR) equipment. However, natural gas engines suffer from high thermal load, knock onset, and high turbine inlet temperatures at stoichiometric combustion conditions. Water injection is a promising approach to reduce thermal load and NOx emissions and suppress knock onset. In this study, the effects of water injection on the combustion and performance characteristics of a heavy-duty natural gas engine were experimentally studied. The experiments were conducted with four water to natural gas mass ratios (WNMRs) and various spark timings. The results showed that water injection decreased the burning velocity of natural gas, leading to a decrease in peak in-cylinder pressure, peak heat release rate, and combustion temperature. The flame development period (CA0-10) and the flame propagation period (CA10-90) increased with an increase in WNMR. Compared to pure natural gas, the brake thermal efficiency at the optimum spark timing increased from 27.8% to 28.2% at WNMR = 0.35. BSNOx emissions consistently decreased with an increase in WNMR, while BSTHC emissions and BSCO emissions increased slightly.

Multiphase outflows in post-starburst E+A galaxies - II. A direct connection between the neutral and ionized outflow phases

ABSTRACT Post-starburst E+A galaxies are systems that hosted a powerful starburst that was quenched abruptly. Simulations suggest that these systems provide the missing link between major merger ULIRGs and red and dead ellipticals, where AGN feedback is responsible for the expulsion or destruction of the molecular gas. However, many details remain unresolved and little is known about AGN-driven winds in this short-lived phase. We present spatially resolved IFU spectroscopy with MUSE/VLT of SDSS J124754.95-033738.6, a post-starburst E+A galaxy with a recent starburst that started 70 Myr ago and ended 30 Myr ago, with a peak SFR of $\sim 150\, \mathrm{M_{\odot }\,yr^{ -1}}$. We detect disturbed gas throughout the entire field of view, suggesting triggering by a minor merger. We detect fast-moving multiphased gas clouds, embedded in a double-cone face-on outflow, which are traced by ionized emission lines and neutral NaID emission and absorption lines. We find remarkable similarities between the kinematics, spatial extents, and line luminosities of the ionized and neutral gas phases, and propose a model in which they are part of the same outflowing clouds, which are exposed to both stellar and AGN radiation. Our photoionization model provides consistent ionized line ratios, NaID absorption optical depths and EWs, and dust reddening. Using the model, we estimate, for the first time, the neutral-to-ionized gas mass ratio (about 20), the sodium neutral fraction, and the size of the outflowing clouds. This is one of the best ever observed direct connections between the neutral and ionized outflow phases in AGN.

The flickering nuclear activity of Fornax A

We present new observations of Fornax A taken at ∼1 GHz with the MeerKAT telescope and at ∼6 GHz with the Sardinia Radio Telescope (SRT). The sensitive (noise ∼16 μJy beam−1), high-resolution (≲10″) MeerKAT images show that the lobes of Fornax A have a double-shell morphology, where dense filaments are embedded in a diffuse and extended cocoon. We study the spectral properties of these components by combining the MeerKAT and SRT observations with archival data between 84 MHz and 217 GHz. For the first time, we show that multiple episodes of nuclear activity must have formed the extended radio lobes. The modelling of the radio spectrum suggests that the last episode of injection of relativistic particles into the lobes started ∼24 Myr ago and stopped 12 Myr ago. More recently (∼3 Myr ago), a less powerful and short (≲1 Myr) phase of nuclear activity generated the central jets. Currently, the core may be in a new active phase. It appears that Fornax A is rapidly flickering. The dense environment around Fornax A has lead to a complex recent merger history for this galaxy, including mergers spanning a range of gas contents and mass ratios, as shown by the analysis of the galaxy’s stellar- and cold-gas phases. This complex recent history may be the cause of the rapid, recurrent nuclear activity of Fornax A.

Adaptive Internal Model Based Control of the RGF Using Online Map Learning and Statistical Feedback Law

Residual gas fraction (RGF) defined as the ratio of residual gas mass to the mass of total gas burned in one cylinder is an important variable for managing combustion quality and combustion mode. This article proposes an adaptive internal model control (AIMC) based framework that synthesizes on-board map calibration and statistical feedback criterion to track a desired RGF target. The model structure of plant dynamics (or its inverse) in AIMC is derived as a cascade combination of a steady mapping and a parameter-varying variable valve timing (VVT) dynamics (or inverse). The on-board map calibration algorithm is employed to adapt the operating-point-dependent steady mapping since the system behavior may change. Then, a VVT compensatory controller in the AIMC was designed based on the online identification of the parameter-varying VVT dynamics model and its inverse. Moreover, a statistical criterion, namely, the hypothesis test was creatively introduced in the feedback channel of the AIMC to filter out the stochastic noise of the RGF. The experiment results show that the AIMC-based framework significantly improves the RGF tracking performance in both steady and transient states.

The ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe

Aims.The purpose of this work is the characterization of the main scaling relations between all of the interstellar medium (ISM) components, namely dust, atomic, molecular, and total gas, and gas-phase metallicity, as well as other galaxy properties, such as stellar mass (Mstar) and galaxy morphology, for late-type galaxies in the Local Universe.Methods.This study was performed by extracting late-type galaxies from the entire DustPedia sample and by exploiting the large and homogeneous dataset available thanks to the DustPedia project. The sample consists of 436 galaxies with morphological stage spanning fromT= 1−10,Mstarfrom 6 × 107to 3 × 1011M⊙, star formation rate from 6 × 10−4to 60M⊙yr−1, and oxygen abundance from 12 + log(O/H) = 8−9.5. Molecular and atomic gas data were collected from the literature and properly homogenized. All the masses involved in our analysis refer to the values within the optical disks of galaxies. The scaling relations involving the molecular gas are studied by assuming both a constant and a metallicity-dependent CO-to-H2conversion factor (XCO). The analysis was performed by means of the survival analysis technique, in order to properly take into account the presence of both detection and nondetection in the data.Results.We confirm that the dust mass correlates very well with the total gas mass, and find –for the first time– that the dust mass correlates better with the atomic gas mass than with the molecular one. We characterize important mass ratios such as the gas fraction, the molecular-to-atomic gas mass ratio, the dust-to-total gas mass ratio (DGR), and the dust-to-stellar mass ratio, and study how they relate to each other, to galaxy morphology, and to gas-phase metallicity. Only the assumption of a metallicity-dependentXCOreproduces the expected decrease of the DGR with increasing morphological stage and decreasing gas-phase metallicity, with a slope of about 1. The DGR, the gas-phase metallicity, and the dust-to-stellar mass ratio are, for our galaxy sample, directly linked to galaxy morphology. The molecular-to-atomic gas mass ratio and the DGR show a positive correlation for low molecular gas fractions, but for galaxies rich in molecular gas this trend breaks down. To our knowledge, this trend has never been found before, and provides new constraints for theoretical models of galaxy evolution and a reference for high-redshift studies. We discuss several scenarios related to this finding.Conclusions.The DustPedia database of late-type galaxies is an extraordinary tool for the study of the ISM scaling relations, thanks to its homogeneous collection of data for the different ISM components. The database is made publicly available to the whole community.

Study of hydrodynamics performance of a multi-venturi filtering system for BWR severe accident venting strategies

The aim of this project was to determine the capacity of a multi-venturi scrubber filtering system to cope with vented gas mass-flow rate coming from a BWR Mark II primary containment during a long-term station blackout. The multi-venturi filtering system CFD models were developed in the environment of the open source platforms SALOME and OpenFoam. The first geometrical model was created based on the dimensions of a well-known experimental setup, and the results of the pressure drop along the streamwise co-ordinate showed a maximum difference of 10 % in relation to the experimental values for different cases of liquid to gas mass ratios. Then a full scale multi-venturi model was developed. To study the performance of this system during conditions expected in a severe accident, a gas mixture similar to that occurring in a BWR Mark II containment at venting pressure was used as inlet gas. The gas mass-flow that can be cleansed by individual venturis and the pressure required to activate those venturis were computed. The pressure drop profiles in each sector were also determined as the function of different liquid loadings. The results showed good agreement with the capacity of the design taken as the reference model.

CO observations of major merger pairs at z = 0: molecular gas mass and star formation

We present CO observations of 78 spiral galaxies in local merger pairs. These galaxies represent a subsample of a Ks-band-selected sample consisting of 88 close major-merger pairs (HKPAIRs), 44 spiral–spiral (S+S) pairs, and 44 spiral–elliptical (S+E) pairs, with separation <20 h−1 kpc and mass ratio <2.5. For all objects, the star formation rate (SFR) and dust mass were derived from Herschel PACS and SPIRE data, and the atomic gas mass, MHI, from the Green Bank Telescope HI observations. The complete data set allows us to study the relation between gas (atomic and molecular) mass, dust mass, and SFR in merger galaxies. We derive the molecular gas fraction (MH2/M*), molecular-to-atomic gas mass ratio (MH2/MHI), gas-to-dust mass ratio and SFE (= SFR/MH2) and study their dependences on pair type (S+S compared to S+E), stellar mass, and the presence of morphological interaction signs. We find an overall moderate enhancement (∼2×) in both molecular gas fraction (MH2/M*) and molecular-to-atomic gas ratio (MH2/MHI) for star-forming galaxies in major-merger pairs compared to non-interacting comparison samples, whereas no enhancement was found for the SFE nor for the total gas mass fraction ((MHI + MH2)/M*). When divided into S+S and S+E, low mass and high mass, and with and without interaction signs, there is a small difference in SFE, a moderate difference in MH2/M*, and a strong difference in MH2/MHI between subsamples. For the molecular-to-atomic gas ratio MH2/MHI, the difference between S+S and S+E subsamples is 0.55 ± 0.18 dex and between pairs with and without interaction sign 0.65 ± 0.16 dex. Together, our results suggest that (1) star formation enhancement in close major-merger pairs occurs mainly in S+S pairs after the first close encounter (indicated by interaction signs) because the HI gas is compressed into star-forming molecular gas by the tidal torque; and (2) this effect is much weakened in the S+E pairs.

A near-infrared study of the multiphase outflow in the type-2 quasar J1509+0434

ABSTRACT Based on new near-infrared spectroscopic data from the instrument Espectrógrafo Multiobjeto Infra-Rojo (EMIR) on the 10.4 m Gran Telescopio Canarias, we report the presence of an ionized and warm molecular outflow in the luminous type-2 quasar J150904.22+043441.8 (z = 0.1118). The ionized outflow is faster than its molecular counterpart, although the outflow sizes that we derive for them are consistent within the errors (1.34 ± 0.18 and 1.46 ± 0.20 kpc, respectively). We use these radii, the broad emission-line luminosities and in the case of the ionized outflow, the density calculated from the trans-auroral [O ii] and [S ii] lines, to derive mass outflow rates and kinetic coupling efficiencies. While the ionized and warm molecular outflows represent a small fraction of the AGN power (≤0.033 and 0.0001 per cent of Lbol, respectively), the total molecular outflow, whose mass is estimated from an assumed warm-to-cold gas mass ratio of 6 × 10−5, has a kinetic coupling efficiency of ∼1.7 per cent Lbol. Despite the large uncertainty, this molecular outflow represents a significant fraction ofLbol and it could potentially have a significant impact on the host galaxy. In addition, the quasar spectrum reveals bright and patchy narrow Paα emission extending out to 4 arcsec (8 kpc) south-east and north-west from the active nucleus.

Experimental study on the evaporation and chlorine migration of desulfurization wastewater in flue gas.

Wastewater from a limestone-gypsum wet desulfurization system cannot be directly reused or discharged due to its high suspended matter content and complex water composition. Desulfurization wastewater evaporation in flue gas is an effective way to dispose wastewater. Multicomponent soluble chlorine salts exist in the desulfurization wastewater. During the evaporation, chlorine enters into the flue gas due to volatilization, which accelerates the enrichment rate of the Cl- concentration in the desulfurization slurry and leads to an increase in wastewater production. This study explored the chlorine migration of various chlorine salt solutions and typical desulfurization wastewater at high temperature during the evaporation process of concentrated wastewater by a laboratory-scale tube furnace and a pilot-scale system. Results showed that when NaCl-evaporated substance was heated, the chlorine ion hardly volatilized. For the evaporated substances of CaCl2 and MgCl2 solutions, some of the crystal water was lost, and hydrolysis occurred to generate gaseous HCl. NH4Cl was easily sublimed, and the decomposition temperature was lowest. A pilot study on spray evaporation of desulfurization wastewater in flue gas showed that the particle size of the evaporated product increased and the main particle size was within 2.5-10μm with increasing flue gas temperature. Increasing the mass ratio of gas to liquid significantly reduced the particle size of the atomized particles, thereby reducing the average particle size of the evaporated particles. The HCl concentration increased with increasing flue gas temperature. When the flue gas temperature was 350°C, the concentration of HCl was 40ppm, and the escape rate of chlorine in the desulfurization wastewater was approximately 30% using typical wastewater from a limestone-gypsum wet desulfurization system.

Concurrent Starbursts in Molecular Gas Disks within a Pair of Colliding Galaxies at z = 1.52

Abstract We report on the discovery of a merger-driven starburst at z = 1.52, PACS-787, based on high signal-to-noise ALMA observations. CO(5–4) and continuum emission (850 μm) at a spatial resolution of 0.″3 reveal two compact (r 1/2 ∼ 1 kpc) and interacting molecular gas disks at a separation of 8.6 kpc, indicative of an early stage in a merger. With an SFR of 991 M ⊙ yr−1, this starburst event should occur closer to final coalescence, as is usually seen in hydrodynamical simulations. From the CO size, inclination, and velocity profile for both disks, the dynamical mass is calculated through a novel method that incorporates a calibration using simulations of galaxy mergers. Based on the dynamical mass, we measure (1) the molecular gas mass, independent from the CO luminosity, (2) the ratio of the total gas mass and the CO(1–0) luminosity ( ), and (3) the gas-to-dust ratio, with the latter two being lower than typically assumed. We find that the high star formation triggered in both galaxies is caused by a set of optimal conditions: a high gas mass/fraction, a short depletion time (τ depl = 85 and 67 Myr) to convert gas into stars, and the interaction of likely counter-rotating molecular disks that may accelerate the loss of angular momentum. The state of interaction is further established by the detection of diffuse CO and continuum emission, tidal debris that bridges the two nuclei and is associated with stellar emission seen by HST/WFC3. This observation demonstrates the power of ALMA to study the dynamics of galaxy mergers at high redshift.

Exergetic and exergoeconomic evaluation of co-firing biomass gas with natural gas in CCHP system integrated with ground source heat pump

The comprehensive utilization of renewable energy and clean fossil fuel contributes to improving the stability of energy supply system and reducing environmental impact. Therefore, a bio-gas and natural gas co-firing in combined cooling, heating and power (CCHP) system based on ground source heat pump is presented and modeled using exergetic and exergoeconomic methods. The exergy and exergy cost flows of CCHP system are presented under three different gas mass ratios and the influences of some key parameters (biomass and natural gas cost, interest rate, service life and operating time coefficient) on unit exergy cost of products are also analyzed. The results indicate that the introduction of natural gas improves the exergy efficiency; when the gas mass ratio varies from 0 to 1.0 the unit exergy cost of electricity generated by gas turbine, chilled water and hot water decrease from 11.26 $/GJ, 92.21 $/GJ and 69.92 $/GJ to 3.84 $/GJ, 43.52 $/GJ and 23.73 $/GJ, respectively. Furthermore, the sensitivity analysis shows that unit exergy cost of products increases with the increasing of biomass cost, natural gas cost and interest rate; while decreases non-linearly with the increasing of service life and operating time coefficient. The proposed CCHP system provides an idea for other hybrid renewable energy system, and exergoeconomic methodology shows a better understanding of complex energy system performance in terms of both exergy and economic aspects.

The Molecular Gas Content and Fuel Efficiency of Starbursts at z ∼ 1.6 with ALMA

Abstract We present an analysis of the molecular gas properties, based on CO (2−1) emission, of 12 starburst galaxies at z ∼ 1.6 selected by having a boost (≳4×) in their star formation rate (SFR) above the average star-forming galaxy at an equivalent stellar mass. ALMA observations are acquired of six more galaxies than previously reported through our effort. As a result of the larger statistical sample, we significantly detect, for the first time at high z, a systematically lower /L IR ratio in galaxies lying above the star-forming “main sequence” (MS). Based on an estimate of α CO (i.e., the ratio of molecular gas mass to ), we convert the observational quantities (e.g., /L IR) to physical units (M gas/SFR) that represent the gas depletion time or its inverse, the star formation efficiency. We interpret the results as indicative of the star formation efficiency increasing in a continuous fashion from the MS to the starburst regime, whereas the gas fractions remain comparable to those of MS galaxies. However, the balance between an increase in star formation efficiency and gas fraction depends on the adopted value of α CO as discussed.

Two-fluid dusty gas in smoothed particle hydrodynamics: Fast and implicit algorithm for stiff linear drag

Simulation of the dynamics of dust-gas circumstellar discs is crucial in understanding the mechanisms of planet formation. The dynamics of small grains in the disc is stiffly coupled to the gas, while the dynamics of grown solids is decoupled. Moreover, in some parts of the disc the concentration of the dust is low (dust to gas mass ratio is about 0.01), while in other parts it can be much higher. These factors place high requirements on the numerical methods for disc simulations. In particular, when gas and dust are simulated with two different fluids, explicit methods require very small timestep (must be less than dust stopping time $t_{\rm stop}$ during which the velocity of a solid particle is equalized with respect to the gas velocity) to obtain solution, while some implicit methods requires high temporal resolution to obtain acceptable accuracy. Moreover, recent studies underlined that for Smoothed particle hydrodynamics (SPH) when the gas and the dust are simulated with different sets of particles only high spatial resolution $h<c_{\rm s} t_{\rm stop}$ guaranties suppression of numerical overdissipation due to gas and dust interaction. To address these problems, we developed a fast algorithm based on the ideas of (1) implicit integration of linear (Epstein) drag and (2) exact conservation of local linear momentum. We derived formulas for monodisperse dust-gas in two-fluid SPH and tested the new method on problems with known analytical solutions. We found that our method is a promising alternative for the previously developed two-fluid SPH scheme in case of stiff linear drag thanks to the fact that spatial resolution condition $h<c_{\rm s} t_{\rm stop}$ is not required anymore for accurate results.

Thermodynamic and economic assessment of a novel CCHP integrated system taking biomass, natural gas and geothermal energy as co-feeds

The combined cooling, heating and power (CCHP) system based on biomass, geothermal energy and fossil energy contributes to less fossil fuel-dependent, alleviate the climate change and improve the flexibility of integrated system. Therefore, this paper presents a novel combined cooling, heating and power (CCHP) system based on biomass, natural gas and geothermal energy. The CCHP system consists of an air-biomass gasification subsystem, steam turbine electricity generation subsystem, gas turbine electricity generation subsystem, waste heat utilization subsystem and ground source heat pump subsystem. The thermodynamic and economic analysis of proposed system are investigated, and the influences of some key operating parameters (gas mass ratio and flue gas split ratio) and economic factors (such as biomass and natural gas price, interest rate, operating time coefficient and service life) on integrated system performances are also carried out. The results indicate that the introduction of natural gas contributes to improve the overall energy efficiency of proposed CCHP system and reduce the levelized cost of energy significantly. In the case study (gas mass ratio: 0.5, flue gas split ratio: 0.5), the overall energy efficiency and electricity generation efficiency of CCHP system can be reached at about 97.05% and 30.89%, respectively; the levelized cost of energy is 0.0315 $/kWh. The proposed system provides a new way for utilization of renewable energy and fossil fuels based poly-generation system, which is a promising approach for the utilization of biomass, natural gas and geothermal energy in the rural of China.