Steady-state Mass Balance Research Articles

Impacts of implementing Healthy Building guidelines for daily PM2.5 limit on premature deaths and economic losses in urban China: A population-based modeling study

Given a large fraction of people’s exposure to urban PM2.5 occur indoors, reducing indoor PM2.5 levels may offer a more feasible and immediate way to save substantial lives and economic losses attributable to PM2.5 exposure. We aimed to estimate the premature mortality and economic loss reductions associated with achieving the newly established Chinese indoor air guideline and a few hypothetical indoor PM2.5 guideline values. We used outdoor PM2.5 concentrations from 1497 monitoring sites in 339 Chinese cities in 2015, coupled with a steady-state mass balance model, to estimate indoor concentrations of outdoor-infiltrated PM2.5. Using province-specific time-activity patterns for urban residents, we estimated outdoor and indoor exposures to PM2.5 of outdoor origin. We then proceeded to use localized census-based concentration-response models and the value of statistical life estimates to calculate premature deaths and economic losses attributable to PM2.5 exposure across urban China. Finally, we estimated potentially avoidable mortality and corresponding economic losses by meeting the current 24-hour based guideline and various hypothetical indoor limits for PM2.5. In 2015 in urban areas of mainland China, the city-specific annual mean outdoor and indoor PM2.5 concentrations ranged 9–108 μg/m3 and 5–56 μg/m3, respectively. Indoor exposures contributed 62%–91% daily and 68%–83% annually to the total time-weighted exposures. The potential reductions in total deaths and economic losses for the scenario in which daily indoor concentrations met the current guideline of 75 μg/m3, 37.5 μg/m3, and 25 μg/m3 were 16.9 (95% CI: 0.7–62.1) thousand, 87.7 (95% CI: 9.7–197.7) thousand, and 165.5 (95% CI: 30.8–304.0) thousand, respectively. The corresponding reductions in economic losses were 5.7 (95% CI: 0.2–34.8) billion, 29.4 (95% CI: 2.4–109.6) billion, and 55.2 (95% CI: 7.7–168.0) billion US Dollars, respectively. Deaths and economic losses would be reduced exponentially within the range of 0–75 μg/m3 for hypothetical indoor PM2.5 limits. The findings demonstrate the effectiveness of reducing indoor concentrations of outdoor-originated PM2.5 in saving substantial lives and economic losses in China. The analysis provides quantitative evidence to support the implementation of an indoor air quality guideline or standard for PM2.5.

Steady-State Mass Balance Model for Predicting Particle-Gas Concentration Ratios of PBDEs.

Assuming equilibrium partitioning between the gas and particle phases has been shown to overestimate the fraction of low-volatility chemicals in the particle phase. Here, we present a new steady-state mass balance model that includes separate compartments for fine and coarse aerosols and the gas phase and study its sensitivity to the input parameters. We apply the new model to investigate deviations from equilibrium partitioning by exploring model scenarios for seven generic aerosol scenarios representing different environments and different distributions of emissions as the gas phase, fine aerosol, and coarse aerosol. With 100% of emissions as the particle phase, the particle–gas concentration ratio in our model is similar to the equilibrium model, while differences are up to a factor of 106 with 100% of emissions as the gas phase. The particle–gas concentration ratios also depend on the particle size distributions and aerosol loadings in the different environmental scenarios. The new mass balance model can predict the particle–gas concentration ratio with more fidelity to measurements than equilibrium models. However, further laboratory-based evaluations and calibrations of the standard sampling techniques, field investigations with preferably size-resolved measurements of aerosol particle composition, together with the appropriate process modeling for low-volatility chemicals are warranted.

Metabolic flux configuration determination using information entropy.

Constraint-based models use steady-state mass balances to define a solution space of flux configurations, which can be narrowed down by measuring as many fluxes as possible. Due to loops and redundant pathways, this process typically yields multiple alternative solutions. To address this ambiguity, flux sampling can estimate the probability distribution of each flux, or a flux configuration can be singled out by further minimizing the sum of fluxes according to the assumption that cellular metabolism favors states where enzyme-related costs are economized. However, flux sampling is susceptible to artifacts introduced by thermodynamically infeasible cycles and is it not clear if the economy of fluxes assumption (EFA) is universally valid. Here, we formulated a constraint-based approach, MaxEnt, based on the principle of maximum entropy, which in this context states that if more than one flux configuration is consistent with a set of experimentally measured fluxes, then the one with the minimum amount of unwarranted assumptions corresponds to the best estimation of the non-observed fluxes. We compared MaxEnt predictions to Escherichia coli and Saccharomyces cerevisiae publicly available flux data. We found that the mean square error (MSE) between experimental and predicted fluxes by MaxEnt and EFA-based methods are three orders of magnitude lower than the median of 1,350,000 MSE values obtained using flux sampling. However, only MaxEnt and flux sampling correctly predicted flux through E. coli’s glyoxylate cycle, whereas EFA-based methods, in general, predict no flux cycles. We also tested MaxEnt predictions at increasing levels of overflow metabolism. We found that MaxEnt accuracy is not affected by overflow metabolism levels, whereas the EFA-based methods show a decreasing performance. These results suggest that MaxEnt is less sensitive than flux sampling to artifacts introduced by thermodynamically infeasible cycles and that its predictions are less susceptible to overfitting than EFA-based methods.

Steady-State Methodology for Activated Sludge Model 1 (ASM1) State Variable Calculation in MBR

The complexity of Activated Sludge Model No. 1 (ASM1) is one of the main obstacles slowing its widespread use, particularly among wastewater treatment plant (WWTP) professionals. In this paper, a simplification procedure based on steady-state mass balances is proposed for the conventional activated sludge process (ASP) configuration, consisting of an aerated bioreactor and a perfect settler (without particular compounds in the outlet). The results do, in fact, show perfect suitability to a membrane bioreactor process (MBR). Both organic carbon and nitrogen removal were investigated. The proposed approach was applied to ASM1, and simple analytical expressions of the state variables were obtained. These analytical expressions were then validated by comparison to simulations given by the original ASM1 (implemented in GPS-X software). A strong match (less than 4% of error overall) was obtained between both results in the steady-state; consequently, these analytical expressions may be useful as tools for quickly estimating the main state variables, feeding the filtration models, or identifying the interaction between operating parameters. Moreover, this enables a sensitivity analysis, covering relevant factors such as kinetics or operating parameters. For instance, the sludge retention time (SRT) effect is lower on XBH and XS at high SRT (˃20 days), while it is more pronounced on XP and XI as their variations with SRT are linear.

Modeling and simulation of an industrial slurry phase ethylene polymerization reactor: effect of reactor operating variables

A hierarchical and computationally efficient mathematical model was developed to explain the polymerization of high-density polyethylene (HDPE) in an isothermal, industrial, continuous stirred tank slurry reactor (CSTR). A modified polymeric multi-grain model (PMGM) was used. Steady-state macroscopic mass balance equations were derived for all species (namely, monomer, solvent, catalyst and polymer) to obtain the final particle size and the required monomer and solvent input rates for a given catalyst input and the reactor residence time. The interphase mass transfer coefficients were calculated for the industrial CSTR using the operating data on the reactor. The present model was tuned with some data on an isothermal industrial reactor and the simulation results were compared with data on another set of industrial reactor. The comparison revealed that the present tuned model is capable of predicting the productivity and the polymer yield at various catalyst feed rates and the mean residence times. The effects of variation of two operating variables (catalyst feed rate and mean residence time) on the productivity, the polymer yield, the polydispersity index (PDI) and the operational safety were analyzed. The present study indicated that an optimal value of the reactor residence time (for maximum productivity per catalyst particle) exists at any catalyst feed rate.

Hydrogeological controls on heterogeneous groundwater discharge to a large glacial lake

Lacustrine groundwater discharge (LGD) can be an important pathway for delivering pollutants to large lakes but this pathway is often neglected. This is in part because characterizing the magnitude and spatial variability of LGD to large lakes is highly resource intensive. To better target efforts, particularly in glacial environments where the hydrogeology is often highly complex, there is a need to understand linkages between spatial LGD patterns and hydrogeological features. The objective of this study was to evaluate the magnitude and spatial variability of nearshore LGD to Lake Simcoe (area = 722 km2) and use this information to explore hydrogeological controls on the observed spatial LGD patterns. LGD was quantified by applying a steady state mass balance model to radon-222 (222Rn) data obtained from boat surveys conducted along ~80% of the lake’s shoreline. Overall, LGD was highly spatially variable with total LGD to Lake Simcoe estimated to range from 7 ± 1% to 16 ± 2%, respectively, of the total volume of tributary inputs during summer. No large regional scale differences in LGD were found despite the diverse hydrogeological conditions around the lake. Rather, discrete shoreline areas with high LGD were observed around the lake. Areas with high LGD were related to permeable nearshore surficial sediments and tunnel channel aquifers which provide connectivity between large recharge features (moraines), regional aquifer units, and the lake. The study findings are needed to inform actions aimed at managing non-point pollution sources to large glacial lakes including LGD.

A comparison of topologies in recirculating aquaculture systems using simulation and optimization

Recirculating aquaculture systems (RAS) are often designed using simplified steady-state mass balances, which fail to account for the complex dynamics that biological water treatment systems exhibit. Because of the very slow dynamics, experimental development is also difficult. We present a new, fast and robust Modelica implementation of a material balance-based dynamic simulator for fish growth, waste production and water treatment in recirculating aquaculture systems. This simulator is used together with an optimization routine based on a genetic algorithm to evaluate the performance of three different water treatment topologies, each for two fish species (Rainbow trout and Atlantic salmon) and each in both a semi-closed (no denitrification) and a fully recirculating version (with denitrification). Each case is furthermore evaluated at both saturated and supersaturated oxygen levels in the fish tank influent. The 24 cases are compared in terms of volume required to maintain an acceptable TAN concentration in the fish tank. The results indicate that the smallest volume is obtainable by introducing several bypass flows in the treatment system of a semi-closed RAS and that the gains can be significant. We also show that recycling already treated water back upstream in the treatment process degrades performance and that if one wishes to have a fully recirculating system with minimal water exchange, then the flows of oxygen, carbon and nitrogen must be carefully considered. For several of the cases, no optimum with denitrification could be found. We thus demonstrate that the best configuration and operation strategy for water treatment varies with the conditions imposed by the fish culture, illustrating the complexity of RAS plants and the importance of simulations, but also that computer-driven optimal design has the potential to increase the treatment efficiency of biofilters which could lead to cheaper plants with better water quality.

Modeling of gas-phase heterogeneous photocatalytic oxidation reactor in the presence of mass transfer limitation and axial dispersion

Mass transfer plays a critical role in the efficiency of photocatalytic oxidation (PCO) technology for air purification applications. There has been limited work on the exploration of mass transfer in the PCO reactor with the non-ideal flow. In this work, the performance of a continuous heterogeneous ultraviolet photocatalytic oxidation (UV-PCO) reactor was investigated and addressed under mass transfer limitation and axial dispersion. First, CFD modeling was used to determine the flow distribution in the reactor at various airflow rates. The residence time distribution (RTD) analysis with a tracer gas (CO2) was carried out for the experimental validation of the simulation model and good agreement between experimental and simulation data was achieved. Further, a quick and straightforward methodology employing an axial dispersion plug flow model was used to study the RTD. The proposed model could predict the residence time distribution of CO2 with high accuracy. Results of the RTD for CO2 in the presence and absence of a PCO filter (silica fiber felts (SFF) modified with TiO2) were almost identical due to the high porosity of the filter. The model was then used for the evaluation of the axial dispersion of methyl ethyl ketone (MEK) at different flow rates. Owing to a low value of the Peclet number (Pe < 100), the flow in the reactor deviated from an ideal plug flow and dispersion could not be ignored. The photocatalysis reaction of MEK by the SFF filter under the mass-transfer-controlled regime was further addressed. A steady-state mass balance equation was implemented for the assessment of the performance of the UV-PCO reactor in the presence of axial dispersion and mass transfer limitation. The mass transfer coefficient was calculated with the use of the developed model and a correlation for the Sherwood number was proposed to relate the mass transfer coefficient to the flow rate and fiber structure. The proposed correlation was assessed and compared with the other empirical formulas available in the literature.

Study on kinetics and bio-oil production from rice husk, rice straw, bamboo, sugarcane bagasse and neem bark in a fixed-bed pyrolysis process

In this study, rice husk, rice straw, bamboo, sugarcane bagasse, and neem bark were pyrolyzed in a fixed-bed pyrolyzer to examine the influence of operating conditions, such as the temperature of the pyrolysis process, residence time of volatiles, and reactor length, on the yield of bio-oil and individual gas components. The temperature of pyrolysis was varied from 350 to 650 °C at increments of 50 °C, and the length of the reactor was varied from 45 to 60 cm at intervals of 5 cm. The maximum bio-oil production of 46.93 wt% and the pyrolysis char of 26.2 wt% was obtained for bamboo at 450 °C. The highest amount of clean syngas (carbon monoxide and hydrogen) was produced for neem bark (52.61 vol%). The gaussian distributed activation energy model data exhibited a superior fit with the experimental data compared with the single-reaction model for bio-oil and all other individual component gases. The presence of C–H, CC, alcohols and phenolic compounds indicated that the bio-oil obtained from all the biomass species could potentially be used as fuel. The steady-state mass and energy balances for the entire pyrolysis plant were obtained using the Aspen Plus simulation.

Climate during the Last Glacial Maximum in the Northern Sawatch Range, Colorado, USA

Temperature-index modeling is used to determine the magnitude of temperature depression in the northern Sawatch Range required to maintain steady-state mass balances of six reconstructed glaciers at their extent during the local Last Glacial Maximum (LLGM), dated at ~21 ka. Assuming no significant differences in precipitation compared to modern values, mean annual temperatures in the region were on average 8.8 + 0.5/– 0.8 °C cooler than they are today. Allowing for modest (± 10 cm) increases or decreases in precipitation, required temperature depressions only differ by ±0.2 °C. Temperature depression in the northern Sawatch Range is consistent, although slightly greater, with those determined in other ranges in Colorado using similar approaches. The estimates presented here are, however, substantially less than those suggested by several downscaled simulations of global Last Glacial Maximum (LGM) climate, that might be due to the need for improved calibration of such downscaled simulations, or the models from which they are derived. Our estimates of LGM temperature depression are considerably greater than that previously determined in the study area and those in two other ranges in Colorado derived using different methodologies, the latter being most likely responsible for the discrepancies.

Carbon mass balance, isotopic tracers of biogenic methane, and the role of acetate in coal beds: Powder River Basin (USA)

A multi-isotope (C, H, O) investigation of biogenic gas (δ13C−CH4, δ13C−CO2, δD−CH4) and coal bed waters (δD, δ18O, δ13C-DIC, δ13C-acetate) was conducted along a ∼25-km basinward sampling transect in the Powder River Basin (PRB) in Wyoming and Montana (USA) to address inconsistencies among isotope fingerprinting techniques and to apply mass balance isotope modeling to biogenic coalbed methane (CBM). Results include the first published compound-specific δ13C-acetate values from a natural biogenic CBM system, providing new constraints on acetate’s role in biogenic CH4 generation. Coal bed water chemistry is anoxic and dominated by Na+ and HCO3−, with high alkalinity concentrations (14.8–33.0meq/L). The deep basin interior environment contains sulfate-free, Na+−HCO3−-dominated waters exhibiting signs of methanogenesis. CH4 and CO2 generally become 13C-enriched from the shallow basin edge to the deep basin interior (δ13C−CH4 −78.2 to −56.2‰ and δ13C−CO2 -24.7 to 4.7‰). Also, compound-specific δ13C-acetate is more positive in the basin interior compared to the basin edge setting (range −34.3 to −15.1‰). Using a steady-state mass balance isotope model, the observed variations in δ13C-CH4 and δ13C-CO2 can be explained in terms of the favorability of methanogenesis (fCH4) relative to heterotrophic bacterially-mediated non-methanogenic pathways, such as bacterial sulfate reduction, which compete with methanogenesis for substrates. At the basin interior, fCH4 exceeds 0.4, approaching its inferred limiting value hypothesized from the oxidation state of low-molecular weight compounds detected in PRB formation waters. Therefore, methanogenesis is likely a dominant biogeochemical pathway consuming substrates in the deeper coal beds. The basinward shift toward 13C-enriched acetate broadly indicates linkage between acetate, CH4, and CO2, and likely records acetate synthesis effects modified by methanogenic fractionation. These results suggest that acetate plays a role in methanogenesis in PRB coal beds (not necessarily a dominant role), while other C isotope and microbial evidence suggests that hydrogenotrophic methanogenesis is also a significant methane-producing pathway. The results of this study broadly suggest multiple viable methanogenic pathways and C cycling that affects acetate, a more complex view of coal bed geochemistry than implied by traditional C and H isotope fingerprinting of accumulated products (CH4, CO2) and coexisting water.

Estimation and analysis of ventilation rates in schools in Indian context: IAQ and Indoor Environmental Quality

The prolonged exposure to indoor air pollution may affect the health, comfort and performance of the occupants. Failing to address Indoor Air Quality (IAQ) problems may lead to short-term and long-term health problems. The health effects may vary for different individuals depending on factors like age and medical conditions, children being young and sensitive to the environment, are more susceptible to the same. The primary focus of this research is to estimate the ventilation rates in schools in Ahmedabad by using carbon dioxide (CO2) exhaled by the occupants, using steady state mass balance method. The air flow in the naturally ventilated classrooms was between 61.5 l/s per person to 15.6 l/s per person. The air flow in air-conditioned classrooms was 0.9 l/s per person and 1.0 l/s per person. The air flow in naturally ventilated classrooms are excessively high, more than meeting prescribed rates, while air flow in air-conditioned classrooms is far below the prescribed outdoor air rate per person as provided in ASHRAE 62.1: 2016 [1] and in the Bureau of Indian Standards [2].

Triple oxygen isotope signatures of evaporation in lake waters and carbonates: A case study from the western United States

Evaporation can increase the δ18O values of lake waters and carbonates by several per mil. If not accounted for in geological studies, this can lead to substantial misinterpretation of δ18O values in terms of paleoclimate and paleoelevation. Evaporation also leads to a lowering in residual waters of Δ17O, a measure of the departure of δ′17O from a characteristic relationship with δ′18O. We present new triple oxygen isotope data from waters and carbonates from lakes and their source rivers in the western United States (Bear Lake, Great Salt Lake, Lake Tahoe, Mono Lake, and Pyramid Lake). Consistent with predictions from steady-state isotopic mass balance models, the data illustrate marked lowering of Δ17O in closed basin lakes and freshwater lakes relative to their source rivers. The evaporation slope in triple oxygen isotope space (λlake) is similar for these lakes, averaging 0.5229 and ranging between 0.5219 and 0.5239. Moreover, models and data both show that the evaporation slope correlates with Δ17O, meaning that the slope can be estimated on the basis of the measured Δ17O value of the carbonate. We show how triple oxygen isotopes in lake waters and carbonates and ‘clumped isotopes’ (Δ47) in carbonates can be combined to reconstruct the δ18O values of primary (unevaporated) catchment precipitation (δ18Orucp). We use our lacustrine carbonate data as a test case for this approach, and find that δ18Orucp values closely approximate independently-measured δ18O values of catchment precipitation. However, the δ18Orucp values are consistently higher than δ18O of catchment precipitation by ∼2‰, which may reflect present incomplete understanding of a number of triple oxygen isotope parameters used in the calculation, such as the fractionation exponent for carbonate-water equilibrium, the evaporation slope λlake, and the Δ17O values of unevaporated meteoric waters. In conclusion, triple oxygen isotope analysis of lake waters and lacustrine carbonates is a promising new method for studying evaporation in fossil lake systems, but will benefit from additional research into triple oxygen isotope systematics relevant to meteoric waters, lake systems, and carbonate–water fractionation.

Investigating a new model-based calibration procedure for optimizing the emissions and performance of a turbocharged diesel engine

Today, diesel engines are no longer mentioned for generating huge amount of soot and high level of noise. These achievements are owing to the employment of numerous mechatronic systems implemented in the engine. Altogether, with the increase of the number of controllable parameters, the complexity of control and calibration tasks has been increased. In the conventional calibration processes, numerous tests are required for calibration of engine controllers, making it a time consuming and expensive procedure. However, in this paper a model-based calibration procedure based on evolutionary algorithms is investigated to fulfill the feed-forward controller look-up tables. The look-up tables obtain the fuel injection and air induction system parameters based on engine speed and relative load and guarantee the optimal operation of engine. The developed procedure guarantees the maximum attainable torque in full load. The proposed method decreased the time, cost and complexity of whole calibration procedure to high extent. Artificial neural network is employed for modeling the combustion process while steady-state mass and energy balance equations are used for inlet and exhaust models. The models have been validated using experimental data. The optimization is done in two phases: full load curve shaping and part load optimization. The aim of former is attaining maximum possible torque with the minimum emissions and fuel consumption in every engine speed while the aim of latter is delivering the required torque with the lowest possible emissions and fuel consumption. The results of tests show that the proposed model-based calibration method can effectively reduce the fuel consumption and emissions in whole engine operation regime and decrease the time and cost of calibration.

A small marine biosphere in the Proterozoic.

The riverine supply of the globally limiting nutrient, phosphorus, to the ocean accounts for only a few percent of nutrient supply to photosynthetic organisms in surface waters. Recycling of marine organic matter by heterotrophic organisms provides almost all of the phosphorus that drives net primary production in the modern ocean. In the low-oxygen environments of the Proterozoic, the lack of free oxygen would have limited rates of oxic respiration, slowing the recycling of nutrients and thus limiting global rates of photosynthesis. A series of steady-state mass balance calculations suggest that the rate of net primary production in the ocean was no more than 10% of its modern value during the Proterozoic eon, and possibly less than 1%. The supply of nutrients in such a world would be dominated by river input, rather than recycling within the water column, leading to a small marine biosphere found primarily within estuarine environments.

Chemistry of atmospheric dust and critical load assessment in Delhi region (India)

ABSTRACTThis is the first study in the Delhi region that assesses the critical load capacity of soil systems with respect to the atmospheric deposition and air quality, from July to October in 2012. Trend analysis of NO2 and SO2 in Delhi, using the Central Pollution Control Board (CPCB) data, showed interesting patterns matching with the trends in vehicular load in the city. This was followed by the calculation of the critical load of atmospheric acidity for sulphur and nitrogen in order to check the vulnerability of the soil systems in Delhi. Here, the steady state mass balance approach was majorly applied and the study conducted in the Agra region was taken as reference. The calculated values of critical loads of sulphur (225–275 eq/ha/yr) and nitrogen (298–303 eq/ha/yr), for the soil system in Delhi, were calculated with respect to three plant species, namely Anjan grass, Hibiscus and Black siris. The present loads of sulphur (PL(S) = 26.40 eq/ha/yr) and nitrogen (PL(N) = 36.51 eq/ha/yr) were found to be much lower than their respective critical loads. From the results, it can be concluded that the present loads of atmospheric acidic deposition in Delhi region do not pose any danger of acidification of soil system because it is countered by buffering capacity of soil generated dust. However, considering the pace at which the city is growing, it is likely that in coming decades, the present load will increase and thus the values evaluated in this study are likely to serve as an important reference for future assessment of the pollution scenario in the city.

Redesigning C and N mass flows for energy-neutral wastewater treatment by coagulation adsorption enhanced membrane (CAEM)-based pre-concentration process

From the perspective of mass flow, the conventional municipal wastewater treatment based on active sludge process (CAS) removes pollutants by aerobically converting organic carbon (C) into useless CO2 with excess sludge as a by-product and removing nitrogen (N) in the form of N2 by nitrification/denitrification with aeration energy and the carbon source input. To improve sustainability, in this paper, we propose a novel process based on the coagulation adsorption enhanced membrane (CAEM) method, which redesigns the C and N mass flows for energy-neutral wastewater treatment. A pilot-scale operation conducted over two months demonstrated that up to 85.6% chemical oxygen demand (COD) was rejected by CAEM, which could be directed into the anaerobic energy recovery unit in a concentrated form with high biodegradability. Meanwhile, 74.9% nitrogen was kept in the mainstream for the subsequent autotrophic deammonification. Modelling results based on steady-state mass balance and stoichiometric calculations indicated the changes in the C and N mass flows induced by CAEM. The amount of organics (COD) used for energy production increased remarkably compared with that in the CAS process. Combined with mainstream deammonification, this CAEM-based process also avoided the COD consumed by denitrification and heterotrophic oxidation, leading to less aeration and energy consumption (0.22 kWh/t in the CAS process vs. 0.05 kWh/t in the CAEM-based process). The proposed CAEM-based process redesigned a larger C mass flow to the anaerobic energy recovery unit than energy-intensive aerobic oxidation and more N removal by autotrophic deammonification than by heterotrophic deammonification, making it feasible to achieve energy neutrality.

A Mass Balance Model to Assess Food Limitation in Commercial Oyster Nurseries

This work aims to provide oyster farmers a tool to estimate the stock biomass to hold in their nursery. Herein, a steady-state single-compartment mass balance model, which includes the feeding activity of oyster spat, was developed. This model applies to nurseries such as floating upweller systems or land-based tanks and estimates (1) the optimal stock as a function of external food concentration or (2) the food concentration required for a given stock. The model was implemented for the Pacific oyster (Crassostrea gigas Thunberg) and is available online: http//seaplusplus4.com/oysterspatbud.html. The model was evaluated using published data and further tested by simulating a general rule of thumb regarding the spat-holding capacity for a given nursery. According to a general rule of thumb, 1 hectare of a shallow pond can hold between 1 and 3 tons of spat. The model allows to further specify the rule depending on the spat grade to stock. If the spat is around 0.38 g, the model estimates a holding stock within the range of the rule of thumb; however, if the spat is around 0.04 g, the biomass stock sustained is lower (between 0.7 and 2 tons).

Ventilation rates in recently constructed U.S. school classrooms.

Low ventilation rates (VRs) in schools have been associated with absenteeism, poorer academic performance, and teacher dissatisfaction. We measured VRs in 37 recently constructed or renovated and mechanically ventilated U.S. schools, including LEED and EnergyStar-certified buildings, using CO2 and the steady-state, build-up, decay, and transient mass balance methods. The transient mass balance method better matched conditions (specifically, changes in occupancy) and minimized biases seen in the other methods. During the school day, air change rates (ACRs) averaged 2.0±1.3hour-1 , and only 22% of classrooms met recommended minimum ventilation rates. HVAC systems were shut off at the school day close, and ACRs dropped to 0.21±0.19hour-1 . VRs did not differ by building type, although cost-cutting and comfort measures resulted in low VRs and potentially impaired IAQ. VRs were lower in schools that used unit ventilators or radiant heating, in smaller schools and in larger classrooms. The steady-state, build-up, and decay methods had significant limitations and biases, showing the need to confirm that these methods are appropriate. Findings highlight the need to increase VRs and to ensure that energy saving and comfort measures do not compromise ventilation and IAQ.

Issue Highlights

The Canadian Journal of Chemical EngineeringVolume 95, Issue 6 p. 1022-1022 Issue HighlightsFree Access Issue Highlights First published: 21 April 2017 https://doi.org/10.1002/cjce.22849AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat 1023 Benchmarking the Timmins Process - A Novel Approach for Low Energy Pre-Combustion Carbon Capture in IGCC Flowsheets Bart Hallmark, Julian Parra-Garrido, Andrew Murdoch, Ian Salmon and Chris Hodrien The Timmins Process is a novel pre-combustion carbon capture process that combines industrially-tested unit operations in a novel and unique configuration, with the aim of providing high levels of carbon capture with minimal energy penalty. This paper reports an initial benchmarking study of this process in the context of an IGCC flowsheet, and concludes that the net efficiency of the plant incorporating the Timmins Process varies between 33.8 % and 34.3 % at a carbon capture level of 91.8 % (on a mass basis) depending on the process configuration and the cooling water temperature.1 1093 A Soft Sensor for the Sulphur Dioxide Converter in an Industrial Smelter Jianjun He, Junfeng Zhang and Helen Shang A catalytic reactor that converts sulphur dioxide to sulphur trioxide is a key operation in a sulphuric acid plant. The sulphur dioxide conversion ratio represents an important performance indicator for a sulphur dioxide converter. In this paper, a soft sensor is developed for the sulphur dioxide conversion ratio and outlet concentration. The soft sensor is built based on the steady state mass balance model of the converter and industrial dynamic data analysis. It provides a real-time estimate of the unmeasured variables from available industrial real-time measurement.2 1171 Modelling of Dynamic Mass Transfer in a Vapour Extraction Heavy Oil Recovery Process Qiong Wang, Xinfeng Jia and Zhangxin Chen This study presents a new method to determine the effective diffusivity between a vaporized solvent and a crude heavy oil in a vapour extraction heavy oil recovery process. It is found that both constant and variable diffusivities can achieve a satisfactory match in cumulative oil production data, but the latter gives more accurate characterization of transition zone properties. Some correlations are also regressed to convert a constant diffusivity to an equivalent variable diffusivity. Moreover, back-calculated constant effective diffusivity is found to be about 10–30 times of the corresponding molecular diffusivity measured in the laboratory.3 References 1 B. Hallmark, J. Parra-Garrido, A. Murdoch, I. Salmon, C. Hodrien, Can. J. Chem. Eng. 2017, 95, 1023. 2 J. He, J. Zhang, H. Shang, Can. J. Chem. Eng. 2017, 95, 1093. 3 Q. Wang, X. Jia, Z. Chen, Can. J. Chem. Eng. 2017, 95, 1171. Volume95, Issue6June 2017Pages 1022-1022 ReferencesRelatedInformation