Mass Balance Principles Research Articles

Transient simulation model and process simulation analysis of fast cut back process in thermal power plant

Fast Cut Back (FCB) technology of large thermal power plant can maintain the isolated operation of auxiliary power after the units are disconnected from the power grid. FCB unit can immediately cut off all external loads without turbine or boiler shutdown in case of large power grid failure, and supply power immediately as the external power grid fault eliminated, which has a very important impact on improving the stability and the recovery speed of the power grid system. Therefore, it is necessary to establish a dynamic mathematical model of thermal power plant to simulate FCB process. According to the principle of mass and energy balance, a dynamic mathematical model of 1050 MW thermal power unit was established. The model considered the change trends of main steam pressure and temperature caused by the action of main steam valve and high-pressure (HP) bypass valve in FCB process, and the action characteristics of safety valve and pressure control valve (PCV) valve in FCB system. This model provides a reference for the simulation and control of FCB process in thermal power unit.

Optimal operation of heat source and air conditioning system with thermal storage tank using nonlinear programming

In this paper, we consider the optimal operations of a thermal system for heat source and air conditioning system with a thermal storage tank using nonlinear programming. Firstly, we develop the mathematical model of the system components by applying the energy and mass balance principles. Secondly, the static balance of the system model is validated by the operational data. Thirdly, by applying the nonlinear programming method, IPOPT (Interior Point OPTimizer), to the mathematical model, we show the optimal operations of a thermal system under variable conditions of chilled water temperature, such as the number of person, heat generating equipment, outdoor and indoor air conditions. Finally, dynamic simulation results showed that, the variable set points of the chilled water temperature for thermal storage tank have an effect on reducing the running cost of a day.

A Comparative Analysis of SIMC-PID with Other Conventional Techniques for Automobile Vehicle Air Conditioning System Control

Decreasing the thermal increase inside vehicles and safeguarding suitable vehicular temperature levels may result in improved vehicle fuel economy, reliability and passenger comfort. However, getting suitable techniques to attain this has been a great challenge to the system engineers. Although, the use of conventional techniques have proffered a great insight in solving the problem of temperature control in air conditioning system, however, they suffered from inefficient and non-lasting solution to the heat generated within the cabin walls. Thus, in this present paper, a Simple Internal Model Control based Proportional Integral Derivative (SIMC-PID) controller for automobile vehicle temperature is proposed. The SIMC method is based on the internal model control (IMC) theory and proposes a simple methodology for the tuning of the PI and PID industrial controllers. The suggested approach is compared with the conventional tuning methods such as Zeigler-Nichols, Cohen-Coon and Chien-Hrones-Reswick based on energy conservation and mass balance principles. Results obtained showed that the proposed SIMC-PID method could be of great significance in controlling the air-conditioning system temperature compared with the conventional tuning techniques.

Real-time indoor PM2.5 monitoring in an urban cohort: Implications for exposure disparities and source control

Fine particulate matter (PM2.5) concentrations are highly variable indoors, with evidence for exposure disparities. Real-time monitoring coupled with novel statistical approaches can better characterize drivers of elevated PM2.5 indoors. We collected real-time PM2.5 data in 71 homes in an urban community of Greater Boston, Massachusetts using Alphasense OPC-N2 monitors. We estimated indoor PM2.5 concentrations of non-ambient origin using mass balance principles, and investigated their associations with indoor source activities at the 0.50 to 0.95 exposure quantiles using mixed effects quantile regressions, overall and by homeownership. On average, the majority of indoor PM2.5 concentrations were of non-ambient origin (≥77%), with a higher proportion at increasing quantiles of the exposure distribution. Major source predictors of non-ambient PM2.5 concentrations at the upper quantile (0.95) were cooking (1.4–23 μg/m3) and smoking (15 μg/m3, only among renters), with concentrations also increasing with range hood use (3.6 μg/m3) and during the heating season (5.6 μg/m3). Across quantiles, renters in multifamily housing experienced a higher proportion of PM2.5 concentrations from non-ambient sources than homeowners in single- and multifamily housing. Renters also more frequently reported cooking, smoking, spray air freshener use, and second-hand smoke exposure, and lived in units with higher air exchange rate and building density. Accounting for these factors explained observed PM2.5 exposure disparities by homeownership, particularly in the upper exposure quantiles. Our results suggest that renters in multifamily housing may experience higher PM2.5 exposures due to a combination of behavioral and building factors that are amenable to intervention.

Method for identifying effective carbonate source rocks: a case study from Middle\u2013Upper Ordovician in Tarim Basin, China

Hydrocarbon expulsion occurs only when pore fluid pressure due to hydrocarbon generation in source rock exceeds the force against migration in the adjacent carrier beds. Taking the Middle–Upper Ordovician carbonate source rock of Tarim Basin in China as an example, this paper proposes a method that identifies effective carbonate source rock based on the principles of mass balance. Data from the Well YW2 indicate that the Middle Ordovician Yijianfang Formation contains effective carbonate source rocks with low present-day TOC. Geological and geochemical analysis suggests that the hydrocarbons in the carbonate interval are likely self-generated and retained. Regular steranes from GC–MS analysis of oil extracts in this interval display similar features to those of the crude oil samples in Tabei area, indicating that the crude oil probably was migrated from the effective source rocks. By applying to other wells in the basin, the identified effective carbonate source rocks and non-source rock carbonates can be effectively identified and consistent with the actual exploration results, validating the method. Considering the contribution from the identified effective source rocks with low present-day TOC (TOCpd) is considered, the long-standing puzzle between the proved 3P oil reserves and estimated resources in the basin can be reasonably explained.

Prediction of size reduction by batch ball milling process for crab shell powder prior hydroxyapatite conversion

The crab (Portunus pelagicus) shell is a marine biowaste produced by seafood industries. Traditionally, crab shells were collected to be converted into animal feed, however many of them are disposed of as industrial waste. A conversion of crab shells into hydroxyapatite is a better option for producing high-value biomaterial. Hydroxyapatite materials can be used as slow-release fertilizer while combining them with traditional fertilizer or as a stand-alone green fertilizer with high phosphatic content. Prior to hydroxyapatite conversion, the size reduction of crab shells is required. In this study, crab shell powder is derived from dried crab shell with the water content is approximately 10% wb. The size reduction is processed by using a customized batch type ball mill. This study is aiming at determining the kinetic model of milling parameters for crab shell milling by using the ball mills. An amount of 1.5 kg of dried crabs shell was milled by using 3-size mixed metal balls. The powder was then analyzed its particle size, and the particle size is used as an input in the mathematical model. The computational study focused on the calculation of optimal rotational velocity and kinetic model during the milling process. The kinetic model was based on Population Balance Equation of the mass balance principle, and the results are compared with experimented data characterized by particle size analyzer. It is observed that there are discrepancies between the model and experimental data due to the characteristic of raw materials; however the kinetic model can be used as a prediction of particle size reduction using the ball mill without conducting the real experiment.

Network resilience of phosphorus cycling in China has shifted by natural flows, fertilizer use and dietary transitions between 1600 and 2012.

The resilience of the phosphorus (P) cycling network is critical to ecosystem functioning and human activities. Although P cycling pathways have been previously mapped, a knowledge gap remains in evaluating the P network's ability to withstand shocks or disturbances. Applying principles of mass balance and ecological network analysis, we examine the network resilience of P cycling in China from 1600 to 2012. The results show that changes in network resilience have shifted from being driven by natural P flows for food production to being driven by industrial P flows for chemical fertilizer production. Urbanization has intensified the one-way journey of P, further deteriorating network resilience. Over 2000-2012, the network resilience of P cycling has decreased by 11% owing to dietary changes towards more animal-based foods. A trade-off between network resilience improvement and increasing food trade is also observed. These findings can support policy decisions for enhanced P cycling network resilience in China.

Control of a process with no reflux rate in heterogeneous extractive distillation (HED)

In this work, a process with no reflux rate (R) of distillate product in heterogeneous extractive distillation (HED) for the separation of close boiling compounds is proposed. The effects of pressure in HED and flowrate of solvent on controllability and economic performance are investigated. Close loop sensitivity tests show that an increase in flowrate of solvent can enhance the controllability but increases the annual total cost (TAC). Simulation shows that higher pressure in HED leads to lower flowrate ratio of solvent (EG) to feed. A lower pressure is preferred for economic index, but has worse controllability. There is trade-off between controllability and economic performance.The interaction between units is analyzed theoretically based on mass balance principle. The analysis can help further design of control structure. A basic control structure (CS1) based on modified alternative process with increased solvent flowrate is proposed first. Then an improved control structure (CS2) based on CS1 is proposed to reject the flowrate disturbance and address the interaction between units. Dual temperatures are applied in the recovery column (C2). The temperatures of two stages are controlled by the ratio of reflux rate to feed (R/F) and reboiler duty in C2, respectively. Pressure-compensated temperature control is applied to compensate temperature in the presence of flowrate disturbance. Dynamic responses show the improved control structure can handle ± 10% feed flowrate and ± 20% composition disturbances.

A Discontinuous ODE Model of the Glacial Cycles with Diffusive Heat Transport

We present a new discontinuous ordinary differential equation (ODE) model of the glacial cycles. Model trajectories flip from a glacial to an interglacial state, and vice versa, via a switching mechanism motivated by ice sheet mass balance principles. Filippov’s theory of differential inclusions is used to analyze the system, which can be viewed as a nonsmooth geometric singular perturbation problem. We prove the existence of a unique limit cycle, corresponding to the Earth’s glacial cycles. The diffusive heat transport component of the model is ideally suited for investigating the competing temperature gradient and transport efficiency feedbacks, each associated with ice-albedo feedback. It is the interplay of these feedbacks that determines the maximal extent of the ice sheet. In the nonautonomous setting, model glacial cycles persist when subjected to external forcing brought on by changes in Earth’s orbital parameters over geologic time. The system also exhibits various bifurcation scenarios as key parameters vary.

Novel Electric Bus Energy Consumption Model Based on Probabilistic Synthetic Speed Profile Integrated With HVAC

This paper proposes a novel and generic model to calculate the Electric Bus Energy Consumption (EBEC) without the need for a high–resolution speed profile data. The proposed model generates a set of speed profiles using the basic information of the bus trip: trip time, trip length, and distances between successive bus stops. The generated speed profiles could accurately reflect the various traffic conditions and speed behaviors of real–world situations. Roadway Level of Service (LoS) is incorporated in the proposed model to simulate different traffic conditions. Further, a stochastic model for the bus speed profile is adopted to simulate the probability of the bus to stop at each on–route designated stop. The generated speed profiles are then inputted to an accurate EBEC model that considers the route topography, auxiliary loads (lighting, sound, and radio systems) and the impact of the weather conditions. The operation of the heat, ventilation and air conditioning system (HVAC) is also incorporated in the model using the thermal mass balance principle. Using the proposed model, the characteristics of EBEC on a given route can be evaluated through generating a set of speed profiles for the studied route. The proposed model provides transit network planners with a useful tool to appropriately design electric–based transit networks when there is a lack or unavailability of real–time and high resolution data.

Adaptive Disturbance Attenuation Control of Two Tank Liquid Level System With Uncertain Parameters Based on Port-Controlled Hamiltonian

This paper investigates the problem of the level control for two tank liquid level system(TTLLS) with parametric uncertainties and lumped disturbances. It is achieved by a novel adaptive disturbance attenuation control method based on the Port-Controlled Hamiltonian (PCH) model. Firstly, the model of TTLLS is established according to the mass balance principle and the PCH model is achieved. Based on the PCH model, the PCH controller of TTLLS is designed and the stability of the closed-loop system is ensured. To reduce the impact of disturbances and unmeasurable parameters, adaptive L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> disturbance attenuation technology is integrated. To achieve the robustness and simplify the calculation, the parameter estimation vector is designed by splitting complex mathematical expressions. Utilizing the properties of the PCH method and merits of the adaptive disturbance attenuation technology, the integrated controller achieves good performance. Moreover, simulation and experimental results are given to show the effectiveness and strong robustness of the proposed control algorithm.

Exergy and sensibility analysis of each individual effect in a kraft multiple effect evaporator

The multiple effect evaporator (MEE) is an energy intensive step in the kraft pulping process. The exergetic analysis can be useful for locating irreversibilities in the process and pointing out which equipment is less efficient, and it could also be the object of optimization studies. In the present work, each evaporator of a real kraft system has been individually described using mass balance and thermodynamics principles (the first and the second laws). Real data from a kraft MEE were collected from a Brazilian plant and were used for the estimation of heat transfer coefficients in a nonlinear optimization problem, as well as for the validation of the model. An exergetic analysis was made for each effect individually, which resulted in effects 1A and 1B being the least efficient, and therefore having the greatest potential for improvement. A sensibility analysis was also performed, showing that steam temperature and liquor input flow rate are sensible parameters.

Nutrient release from fish cage aquaculture and mitigation strategies in Daya Bay, southern China

Finfish cage culture is the most predominant form of mariculture. The rapid expansion of fish cage culture systems has raised concerns about their environmental impact, such as nutrient release. In this study, for the first time, we estimated the release of nitrogen (N) and phosphorus (P) from fish cage culture in Daya Bay, southern China, by constructing N and P budget models based on a mass balance principle. In addition, the contribution and importance of nutrients from fish culture and other nutrient sources, including submarine groundwater discharge, benthic sediments, local rivers, and atmospheric deposition were assessed. The annual amount of N and P released from fish cage culture was 205.6 metric tons (hereafter tons) of N and 39.2 tons of P, including 142.7 tons of dissolved inorganic nitrogen (DIN) and 15.1 tons of dissolved inorganic phosphorus (DIP). Among the analyzed nutrient sources, the contributions of DIN and DIP from fish culture were 7.0% and 2.7%, respectively. For cages consuming conventional trash fish, 142 kg of N and 26 kg of P were released into the environment per ton of fish products, much higher than the values (72 kg N and 17.3 kg P) for cages using formulated feed. In fish culture, the dissolved nutrients were more N rich, but the particulate nutrients were more P rich. The ratio of cage-derived N and P was 21.1, higher than the ratio of coastal seawater (27.1), indicating that cage culture may also impact the local nutrient forms around farming regions. Oyster cultivation and harvest removed 126.3 tons of N and 35.1 tons of P from of the bay. Replacing trash fish with formulated feed and co-culturing of nutrient extractive species (e.g., bivalves, macroalgae) and deposit-feeding species (e.g., sea cucumber) in fish culture zones can be efficient nutrient mitigation strategies.

Computer Simulations of Continuous Flow Peritoneal Dialysis Using the 3-Pore Model-A First Experience.

Background:Continuous flow peritoneal dialysis (CFPD) is performed using a continuous flux of dialysis fluid via double or dual-lumen PD catheters, allowing a higher dialysate flow rate (DFR) than conventional treatments. While small clinical studies have revealed greatly improved clearances using CFPD, the inability to predict ultrafiltration (UF) may confer a risk of potentially harmful overfill. Here we performed physiological studies of CFPD in silico using the extended 3-pore model.Method:A 9-h CFPD session was simulated for: slow (dialysate to plasma creatinine [D/P crea] < 0.6), fast (D/P crea > 0.8) and average (0.6 ≤ D/P crea ≤ 0.8) transporters using 1.36%, 2.27%, or 3.86% glucose solutions. To avoid overfill, we applied a practical equation, based on the principle of mass-balance, to predict the UF rate during CFPD treatment.Results:Increasing DFR > 100 mL/min evoked substantial increments in small- and middle-molecule clearances, being 2 - 5 times higher compared with a 4-h continuous ambulatory PD (CAPD) exchange, with improvements typically being smaller for average and slow transporters. Improved UF rates, exceeding 10 mL/min, were achieved for all transport types. The β2-microglobulin clearance was strongly dependent on the UF rate and increased between 60% and 130% as a function of DFR. Lastly, we tested novel intermittent-continuous regimes as an alternative strategy to prevent overfill, being effective for 1.36% and 2.27%, but not for 3.86% glucose.Conclusion:While we find substantial increments in solute and water clearance with CFPD, previous studies have shown similar improvements using high-volume tidal automated PD (APD). Lastly, the current in silico results need confirmation by studies in vivo.

Mathematical modeling and sensitivity analysis of xylene removal in a scoria‐compost biofilter

AbstractMathematical modeling of biofiltration systems improves our understanding and design of such complex systems. This study focused on the theoretical and technical aspects of the modeling of xylene biofiltration in the absence and presence of a nonionic surfactant. In this regard, a mathematical model was developed based on mass balance principles in gas and biofilm phases. The developed model was calibrated and validated using the experimental data obtained from a lab‐scale scoria‐compost biofilter, which operated for 151 days in the absence and presence of Tween‐20, a nonionic surfactant. First, the model was calibrated using the experimental data obtained at empty bed retention time (EBRT) of 90 s and then validated with the data obtained at two other EBRTs. The biofilter provided maximum elimination capacities (ECmax) of 97.5 and 93.6 g m−3 hr−1, respectively, in the absence and presence of the surfactant at EBRT of 90 s. The corresponding predicted ECmax values were 99.9 and 95.7 g m−3 hr−1, respectively. Both model output and experimental data revealed that the nonionic surfactant improved the performance of the biofilter at moderate inlet loading rates. Various statistical measures, including fractional bias, average absolute relative error, and coefficient of determination (R2), showed good agreement between experimental data and estimated model predictions. Sensitivity analysis of the model showed that the specific surface area and bioreactor length affected strongly the results of the model. In general, the results of this study would in turn form the design basis for engineering purposes.

Knowing how and knowing when: unpacking public understanding of atmospheric CO2 accumulation

It has been demonstrated that most people have a limited understanding of atmospheric CO2 accumulation. Labeled stock-flow (SF) failure, this phenomenon has even been suggested as an explanation for weak climate policy support. Drawing on a typology of knowledge, we set out to nuance previous research by distinguishing between different types of knowledge of CO2 accumulation among the public and by exploring ways of reasoning underlying SF failure. A mixed methods approach was used and participants (N = 214) were enrolled in an open online course. We find that ostensibly similar SF tasks show seemingly contradictory results in terms of people’s understanding of CO2 accumulation. Participants performed significantly better on stock stabilization tasks that explicitly ask about the relationship between stocks and flows, compared with a typical SF task that does not direct the participants’ attention to what knowledge they should use. This suggests that people possess declarative and procedural knowledge of accumulation (knowing about the principles of mass balance, i.e., what and how to use them) but lack conditional knowledge of accumulation (knowing when to use these principles). Additionally, through a thematic analysis of answers to an open-ended question, we identified three overarching ways of reasoning when dealing with SF tasks: system, pattern, and phenomenological reasoning, providing additional theoretical insights to explain the large difference in performance between the different SF tasks. These more nuanced perspectives on SF failure can help inform interventions aimed at increasing climate science literacy and point to the need for more detailed explorations of public knowledge needed to leverage climate policy support.

Integrating data reconciliation into material flow cost accounting: The case of a petrochemical wastewater treatment plant

Material flow cost accounting analyzes input/output relations of material flows in the production process based on mass balance principles. However, the measured data of a process contains errors representing a mass imbalance in the system such as that of a wastewater treatment plant. Therefore, measured data should be verified before establishing mass balance and, subsequently, material flow cost accounting. Hence, in this work, a novel practical stepwise methodology using data reconciliation technique is introduced to improve the accuracy and certainty of measurements before material flow cost accounting. A full-scale petrochemical wastewater treatment plant was selected to establish this methodology. The presented results of this case study show an error of −3.22% (−35244 t/year) between total input and output streams of wastewater treatment plant demonstrating mass imbalance in the system. However, the overall mass balance could be closed by simultaneously solving the incidence matrix (system of balances). The results revealed that by including data reconciliation into material flow cost accounting, an accurate mass balance can be performed, which is a key element in material flow cost accounting calculations. The comparison results showed a relatively significant difference between material flow cost accounting for reconciled and measured data (unreconciled). The developed approach provides a reliable set of data for implementing material flow cost accounting in the system. Therefore, using this novel stepwise approach will help decision-makers to enhance both financial and environmental performances more confidently and to define appropriate improvement plans.

IR spectroscopic measurement of hydrogen production kinetics in methane dry reforming

Dry reforming of methane (DRM) is a reaction that converts two greenhouse gases, CH4 and CO2, to syngas (H2 + CO). Gas chromatography (GC) is almost exclusively used to evaluate catalyst performance. In order to measure the hydrogen production rate with GC, an inert gas with a constant flow rate is usually fed into the system as an internal standard. In this work, an IR spectroscopy-based method is used to achieve the same technical goal with much higher time resolution and much smaller measurement errors. IR measures the molar fractions of CH4, CO2, CO and H2O in the reaction effluent. By applying general mass balance principle and the relevant reaction stoichiometries, H2 production rate is successfully measured without an internal standard. The results are quite close to those obtained by GC with much higher time resolution, making it possible to observe fast reaction kinetics.

Mathematical Modeling of Transport Phenomena of Carbon Dioxide in Concrete Structures

Concrete has a reputation as a “low tech” material, but it is actually very complex and worthy of study. It’s the most widely used construction material in the world. Carbonation process in concrete regularly involves a chemical reaction between carbon dioxide ( CO2) and the products of cement hydration. By treating transport phenomena as a concrete carbonation process, this study presented a two-dimensional linear partial differential equation derived based on the principle of mass balance and convective-dispersive equation incorporating rate constant for zero-order production. We assume the diffusion coefficient of CO2&nbsp;in any direction of concrete is all the same. The analytical solution of the model is achieved by the eigenfunctions expansion technique. The results obtained are presented graphically and discussed. It is revealed that the relationships among CO2 concentration, carbonation depth and time that can be used to state a carbonation transport phenomena in concrete structures are influenced by the diffusion coefficient.

Water Allocation Computation Model for River and Multi-Reservoir System with Sustainability-Efficiency-Equity Criteria

Limitation and inequality of water in interspace and time opposite to the increased water demand indicated from the density of headwork nodes in the river system. It requires proportional-equal water allocation determined by the model. Existing models are not based on water as a public good and not using the sustainability-efficiency-equity criteria despite irrigation is the biggest use. The Water Allocation Model Equalization or in Indonesian it is called “Model Ekualisasi Alokasi Air” (MEQAA) is proposed. MEQAA modeling system is inspired by the shortage of irrigation water for a quite extended period of time and the complexity of the water allocation system in the Lombok river basin. MEQAA is assisted by MS Excel-VBA 2016 that can be tracked automatically on an independent river system scheme to create a network equation with mass balance principle and operation rule. This model is based on the dynamic-deterministic, so the performance test can be used with synthetic data. This experiment was compared with the output from the equalization method and the “first-come, first-served” (FCFS) method. The conclusions of this experiment are: (a) MEQAA can build a specific model according to a network-flow configuration for optimization-simulation with iteration of K-factor (release portion) and C-factor (storage portion) in order to get a maximum and equal and (b) the FCFS method can be detrimental to the river system. MEQAA is suggested as a decision support tool for water allocation planning or real-time operation.