Dynamic Mass Balance Research Articles

Online identification of the lower heating value of the coal entering the furnace based on the boiler-side whole process models

The lower heating value (LHV, also called net calorific value, NCV) of the coal entering the furnace is one of the most important variables for process optimization. However, in most cases, it is not online measurable in coal-fired power plants. In this paper, an online identification approach of the LHV is proposed based on the boiler-side whole process models together with the real-time data acquired by the distributed control system (DCS). The boiler-side whole process models cover typical facilities of a power plant, and are established based on dynamic mass and energy balances. The accurate estimation of the mass flow rate of the coal entering the furnace and the total output energy of the boiler is the highlight of the approach. Rolling identification of the LHV of the coal is presented to take the intrinsic time variant characteristics of the coal combustion and heat transfer processes into account. To validate the proposed approach, pseudo-online simulations are carried out with the history data of a real 300MW coal-fired power plant. The mean absolute relative error between the calculated LHVs and their original assays is found less than 5.0%, and the mean absolute relative error becomes less than 1.1%, if the rectified assays are used.

Dynamic non-isothermal trickle bed reactor with both internal diffusion and heat conduction: Sugar hydrogenation as a case study

A generic approach was applied to develop a comprehensive Trickle Bed Reactor (TBR) model. The model was based on exact definition of the required equations and development of a program code (in gPROMS ModelBuilder environment) to solve them simultaneously. The model consisted of dynamic mass and energy balances in three phases of heterogeneously catalyzed reaction system. The fluid dynamics was expressed in simple terms (dispersion model, semi-empiric expressions for pressure drop and liquid hold-up) to guarantee a fast running program code. Even though a large number of articles have been published on the topic, only few of these studies penetrate into all details of the system. Most of them focus on the description of few selected physical phenomena. Including most or even all phenomena in a single model is seldom done. Most often, the published reactor models consider two dimensions only, because of mathematical simplicity (i.e. TBR axial and radial coordinates or only TBR axial coordinate and particle radius). Here an attempt was made to present a generic simulation model for tubular reactors working in non-isothermal three-phase systems (gas–liquid–solid) where three dimensions are simultaneously taken into account (TBR axial and radial coordinate and particle radius). All the model development and calculations were made by using the powerful software, which allows solving a large set of partial differential equations and algebraic equations. An example case study of hydrogenation of arabinose to arabitol on a ruthenium catalyst was included.

Modeling of microreactors for ethylene epoxidation and total oxidation

Microreactors are especially well-suited for laboratory-scale studies of rapid exothermic reactions, because they have excellent mass and heat transfer characteristics. Two novel reactor models were used for plate microreactors, one for a washcoated reactor and the other one for a silver plate microreactor. The aim of this modeling study was to precisely explain both the concentration and the temperature dependencies of the reaction rates of ethylene oxide (EO) synthesis over a wide range of operating conditions (p, T, flows) by using all the extensive data generated with our microreactors. Microreactors are especially well suited for producing accurate kinetic data because of the uniformity of reaction conditions in the reactor system.Modeling took into account the reaction and mass transfer effects. The axial and radial concentration profiles and for the washcoated case also the concentration profiles along the coating direction were solved numerically. The models were based on dynamic mass balances for the gas phase, with convection, axial and radial dispersion terms included. From the modeling viewpoint, an interesting phenomenon, the interaction between intrinsic kinetics and diffusion in the porous catalyst layer, was tackled with the aid of mathematical modeling for the washcoated reactor case. The reactor models were solved numerically by using gPROMS software. Ethylene oxidation on silver catalyst was the selected example reaction system, because the main product, ethylene oxide, is a key compound and an important intermediate for chemical industry. The reactor and kinetic models were able to describe all the experimental data with a very satisfactory agreement. The microreactor models developed are generic and applicable to various kinds of heterogeneously catalyzed gas-phase reaction systems.The industrial breakthrough of flow chemistry and catalyzed single phase microreactor technology is expected to take place first in the production of fine and specialty chemicals. For some bulk products (e.g EO), flow chemistry has already arisen interest. The benefits that microreactors can offer are the exact control of process conditions, the compact reactor size and the ease of scalability by simply “numbering up”. For a new product, ease of scalability shortens the time to market, whereas for a bulk product like EO, millireactors (structurally similar to microreactors, just having larger flow channels) may be more potential candidates for on-site production applications.

Modeling of the aerosol infiltration characteristics in a cultural heritage building: The Baroque Library Hall in Prague

Three intensive campaigns in spring, summer and winter 2009 where conducted in the Baroque Library Hall in Prague, Czech Republic. The number concentration of particulate matter (PM) was measured online and simultaneously, both indoors and outdoors with an SMPS (0.014–0.7 μm) and an APS instrument (0.7–20 μm). A dynamic mass balance model was introduced taking account particle penetration from outdoors and indoor losses (deposition, ventilation). The model was used to determine deposition rate k and penetration efficiency P in 13 discrete size intervals. Model performance was evaluated using the coefficient of determination (R2) by selecting different pairs of k and P. No unique solution found, thus, averaged values of k and P from the best correlated pairs were used to estimate infiltration factor. Good agreement between infiltration factor and I/O ratio confirmed that modeled k and P were well-estimated. The deposition rate was found to depend strongly on particle size with higher rates for ultrafine and coarse particles. Penetration efficiency, on the other hand, was not clearly related with particle size. The infiltration factor varied substantially with particle size with less effective removal for accumulation fraction (0.1–0.7 μm). Higher infiltration factor for ultrafine particles, compared to coarse particles, indicates that enrichment of the library at this size is caused by penetration from outdoors. On the other hand, human presence during visiting hours found to contribute significantly to coarse particles by increasing the indoor number concentration by a factor of 3, 3.2 and 2 during spring, summer and winter respectively.

On-line monitoring of ash fouling and soot-blowing optimization for convective heat exchanger in coal-fired power plant boiler

This paper presented a comprehensive approach of on-line monitoring and optimization for the soot-blowing system in coal-fired power plant boilers. Due to ash fouling monitoring of heat transfer surfaces of the boiler based on dynamic mass and energy balance method, on-line calculation of boiler thermal efficiency and soft measurements for gas flow rate at the double breezing tail and steam flow rate of reheaters, the performance of boiler's soot-blowing system can be evaluated on-line. And then, the suitable soot-blowing strategies are developed for soot-blowing frequencies and duration optimization. Monitoring results and analysis of an experimental application are given to illustrate the proposed methodologies. The methods proposed in this paper can be applied to state assessment and guidance of soot-blowing operation of boiler's soot-blowing system in order to achieve the purpose of energy conservation, without demanding special instruments or complex computing systems.

The effectiveness of indoor photocatalytic paints on NOx and HONO levels

There is an increasing concern about the indoor air environment, where we spend most of our time. Common methods of improving indoor air quality include controlling pollution sources, increasing ventilation rates or using air purifiers. Photocatalytic remediation technology was suggested as a new possibility to eliminate indoor air pollutants instead of just diluting or disposing them. Titanium dioxide (TiO2) is a widely used photocatalyst, which is aimed to eliminate organic and inorganic pollutants.Here, we demonstrate that indoor photocatalytic paints which contain TiO2 can substantially reduce the concentrations of nitrogen dioxide (NO2). We show that the efficiency of nitrogen dioxide (NO2) removal increases with the quantity of TiO2 in the range 0–7%. The geometric uptake coefficients increase from 5×10−6 to 1.6×10−5 under light irradiation of the paints. On the other hand, during the reactions of NO2 with this paint (7% of TiO2) nitric oxide (NO) and nitrous acid (HONO) are formed. Nitrous acid (HONO) is an important harmful indoor pollutant and its photolysis leads to the formation of highly reactive OH radicals. Maximum conversion efficiencies of NO2 to HONO and NO of 15% and 33% were observed at 30% RH, respectively.A dynamic mass balance model applied to typical indoor environment predicts a steady state mixing ratio of 5.6ppb of HONO released upon light-induced surface reaction of NO2 with a photocatalytic paint (7% of TiO2) and considering the photolysis process as the most important loss of HONO.The quantity of TiO2 embedded in the paint is of crucial importance with respect to nitrogen oxides NO2 remediation, but may also influence the formation of harmful intermediates like nitrous acid (HONO), which should be considered for future optimization of photocatalytic paints aimed for indoor applications.

Dynamic mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario, Canada

A dynamic mass balance model was developed for the St. Lawrence River near Cornwall, Ontario that predicts and hindcasts mercury concentrations and fluxes in three forms, elemental Hg (Hg0), divalent mercury (Hg2+), and methyl mercury (MeHg), in a six compartment environment (air, water, porewater, sediment, periphyton, and benthic invertebrates). Our objective was to construct a dynamic mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario based on the framework and results of a steady-state mass balance model developed previously for this site. The second objective was to estimate industrial mercury emissions based on mercury residues deposited in sediments prior to 1970, the year when regulations were implemented to reduce mercury pollution in the environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river (area of approximately 100km2) to develop the model. Estimated mercury concentrations in all media were similar to measured data (R2=0.99), with only minor exceptions, providing a satisfactory overall description of the mercury loadings and transformation rates of the different mercury species. The estimated historical emissions prior to 1970 from local industries along the Cornwall waterfront were approximately 400kgyear−1. A storm sewer discharge of 5000m3/day resulted in a significant increase in mercury concentrations, particularly in sediment (617ngg−1 to 624ngg−1; p=0.004). Model results suggest that discharges of mercury from sources such as local industries and storm sewers have an impact on mercury in media such as sediment and water. This model should provide a basis for predicting and hindcasting mercury concentrations in other river environments as well, because it considers three distinct forms of mercury, and contains environmental media common to all rivers, including some (e.g. periphyton) not typically included in previous mercury models.

Recent ice dynamic and surface mass balance of Union Glacier in the West Antarctic Ice Sheet

Abstract. Here we present the results of a comprehensive glaciological investigation of Union Glacier (79°46' S/83°24' W) in the West Antarctic Ice Sheet (WAIS), a major outlet glacier within the Ellsworth Mountains. Union Glacier flows into the Ronne Ice Shelf, where recent models have indicated the potential for significant grounding line zone (GLZ) migrations in response to changing climate and ocean conditions. To elaborate a glaciological base line that can help to evaluate the potential impact of this GLZ change scenario, we installed an array of stakes on Union Glacier in 2007. The stake network has been surveyed repeatedly for elevation, velocity, and net surface mass balance. The region of the stake measurements is in near-equilibrium, and ice speeds are 10 to 33 m a−1. Ground-penetrating radars (GPR) have been used to map the subglacial topography, internal structure, and crevasse frequency and depth along surveyed tracks in the stake site area. The bedrock in this area has a minimum elevation of −858 m a.s.l., significantly deeper than shown by BEDMAP2 data. However, between this deeper area and the local GLZ, there is a threshold where the subglacial topography shows a maximum altitude of 190 m. This subglacial condition implies that an upstream migration of the GLZ will not have strong effects on Union Glacier until it passes beyond this shallow ice pinning point.

Representing moisture fluxes and phase changes in glacier debris cover using a reservoir approach

Abstract. Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a CMB model adapted for debris-covered glaciers. We present the results of two point simulations, using both our new "moist" and the conventional "dry" approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former year coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass-balance dynamics. When water and ice are considered, heat transmission to the underlying glacier ice is lower, as the effective thermal diffusivity of the saturated debris layers is reduced by increases in both the density and the specific heat capacity of the layers. In combination with surface heat extraction by QL, subdebris ice melt is reduced by 3.1% in 2008 and by 7.0% in 2011 when moisture effects are included. However, the influence of the parameterization on the total accumulated mass balance varies seasonally. In summer 2008, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total ablation increases by 4.0%. Conversely, in fall 2011, the modulation of basal debris temperature by debris ice results in a decrease in total ablation of 2.1%. Although the parameterization is a simplified representation of the moist physics of glacier debris, it is a novel attempt at including moisture in a numerical model of debris-covered glaciers and one that opens up additional avenues for future research.

Model-driven experimental evaluation of struvite nucleation, growth and aggregation kinetics

Nutrient stewardship is emerging as an issue of global importance, which will drive the development of nutrient recovery in the near to medium future. This will impact wastewater treatment practices, environmental protection, sustainable agriculture and global food security. A modelling framework for precipitation-based nutrient recovery systems has been developed, incorporating non-ideal solution thermodynamics, a dynamic mass balance and a dynamic population balance to track the development of the precipitating particles. The mechanisms of crystal nucleation and growth and, importantly, aggregation are considered. A novel approach to the population balance embeds the nucleation rate into the model, enabling direct regression of its kinetic parameters. The case study chosen for the modelling framework is that of struvite precipitation, given its wide interest and commercial promise as one possible nutrient recovery pathway. Power law kinetic parameters for nucleation, crystal growth and particle aggregation rates were regressed from an ensemble data set generated from 14 laboratory seeded batch experiments using synthetic solutions. These experiments were highly repeatable, giving confidence to the regressed parameter values. The model successfully describes the dynamic responses of solution pH, the evolving particle size distribution subject to nucleation, growth and aggregation effects and the aqueous magnesium concentration in the liquid phase. The proposed modelling framework could well be extended to other, more complex systems, leading to an improved understanding and commensurately greater confidence in the design, operation and optimisation of large-scale nutrient recovery processes from complex effluents.

Modeling energy consumption in membrane bioreactors for wastewater treatment in north Africa.

Two pilot-scale membrane bioreactors were operated alongside a full-sized activated sludge plant in Tunisia in order to compare specific energy demand and treated water quality. Energy consumption rates were measured for the complete membrane bioreactor systems and for their different components. Specific energy demand was measured for the systems and compared with the activated sludge plant, which operated at around 3 kWh m(-3). A model was developed for each membrane bioreactor based on both dynamic and steady-state mass balances, microbial kinetics and stoichiometry, and energy balance. Energy consumption was evaluated as a function of mixed-liquor suspended solids concentration, net permeate fluxes, and the resultant treated water quality. This work demonstrates the potential for using membrane bioreactors in decentralised domestic water treatment in North Africa, at energy consumption levels similar or lower than conventional activated sludge systems, with the added benefit of producing treated water suitable for unrestricted crop irrigation.

Predicted effects from abatement action against eutrophication in two small bays of the Baltic Sea

The Baltic Sea has abnormal algal blooms during spring and summer which are effects of high concentrations of total phosphorus (TP) and other nutrients in the surface water. Bjornofjarden (BF), a coastal area connected to the Baltic Sea, is selected for investigating whether aluminium treatment of sediments may reduce TP concentrations in the water mass. The aim of this paper is to evaluate effects from different abatement actions in two bays, BF and Nykopingsfjarden (NF). The four investigated scenarios are (1) no action, (2) reducing TP from local sources, (3) fixing TP in sediments with aluminium, and (4) decreasing TP concentrations in the outside sea. Magnitudes of different TP fluxes during the different scenarios were estimated using a dynamic mass balance model, CoastMab, which has previously been tested against data from Swedish coastal waters. Alternative actions such as aluminium treatment and reduction of TP from local sources would result in no or scant effect on the TP concentrations in the two bays according to model simulations. The only action which would result in a significant expected decrease in TP concentrations would be to decrease TP concentrations in the outside sea. It is concluded that BF and NF are not suitable for studying effects from local abatement action because of large TP fluxes from the outside sea.

Removal of selected pharmaceuticals, personal care products and artificial sweetener in an aerated sewage lagoon

A sewage lagoon serving the small municipality of Lakefield in Ontario, Canada was monitored in the summer, fall and winter to determine removals of carbamazepine, trimethoprim, sulfamethoxazole, ibuprofen, gemfibrozil, triclosan, sucralose, HHCB and AHTN. Concentrations of these compounds in untreated and treated wastewater were estimated by deploying POCIS and SPMD passive samplers in the sewage lagoon. Passive samplers were also deployed at several points upstream and downstream of the point of discharge from the lagoon into the Otonabee River. LC–MS/MS and GC–MS were utilized to determine the concentrations of pharmaceuticals and personal care products (PPCPs) and sucralose, an artificial sweetener. Among PPCPs sampled by POCIS, the highest estimated concentration in untreated wastewater was ibuprofen sampled during the fall, at an estimated concentration of 60.3ng/L. The estimated average concentration of sucralose was 13.6ng/L in the untreated wastewaters. Triclosan, HHCB and AHTN in SPMDs were highest during fall season, at 30, 1677 and 109ng/L, respectively. For all compounds except gemfibrozil, carbamazepine and sucralose, removals were highest in the summer (83.0 to 98.8%) relative to removals in the fall (48.4 to 91.4%) and winter (14.0 to 78.3%). Finally, the estimated concentrations of carbamazepine, sulfamethoxazole, triclosan and HHCB were compared with predicted values obtained through application of the WEST® modeling tool, with a new model based on the River Water Quality Model No. 1 and extended with dynamic mass balances describing the fate of chemicals of emerging concern subject to a variety of removal pathways. The model was able to adequately predict the fate of these four compounds in the lagoon in summer and winter, but the model overestimated removals of three of the four test compounds in the fall sampling period. This lagoon was as effective at removing PPCPs as many conventional WWTPs, but removals were better during the summer.

Dynamic modeling of copper flash smelting process at a Smelter in China

Due to the highly dynamic characteristic in copper smelting process at a Copper Smelter in China, it is difficult to maintain high performance level control. As a key process indicator to evaluate smelting performance, matte grade is in urgent need of being monitored online. Thus, a real-time dynamic model of predicting matte grade was developed and validated with data collected at an actual plant. Based on desulfurization ratio of copper concentrate, the model couples dynamic mass balances on each species with equilibrium relationships for major component (Cu, Fe, S, SiO2, et al.) to form a system of differential and algebraic equations. The simulation results illustrate that the maximum relative error and average relative error of matte grade between measured values and predicted value of the model proposed is 3.3%, and the average relative error is 0.54%, which verify the effectiveness of the model developed in providing the guidance for controlling the copper flash smelting process.

Column flotation simulation: A dynamic framework

Since the introduction of column flotation in mineral processing plants in the early 1980s, modelling of this process has become a prevailing field of investigation. Even if significant progresses have been made with every new attempt, most of the proposed models or simulators have been restricted to the steady-state behaviour. When dynamic mass balance equations were considered, a constant pulp level during the simulation was always assumed. The objective of this paper is to present a framework for the fully dynamic simulation of column flotation. The emphasis is placed on the simulation of water, solids and gas flows and their effect on the pulp level and output flow rates.

Prediction of polar oil and grease contamination levels in refinery wastewater through multivariate statistical modeling

A dynamic mass balance was implemented for polar oil and grease contamination in a petroleum refinery wastewater circuit through developing a predictive model for a kerosene caustic washing unit, identified as the major source of polar substances into the industrial wastewater effluent. The model was developed following the Projection to Latent Structures (PLS) approach. Comparison between analytical data for polar oil and grease concentrations in refinery wastewater in the Dissolved Air Flotation (DAF) effluent and the predictions of the dynamic mass balance calculations are in a very good agreement and highlights the dominant impact of spent caustic in increasing the oil and grease contamination levels. The results of this work have led to implementation of the dynamic mass balance in the refinery as an online tool, which allows for prevision of possible contamination situations and taking the required preventive actions, and can serve as a basis for establishing relationships between the oil and grease contamination in the refinery wastewater with the properties of the refined crude oils and the process operating conditions. The PLS model developed could be of great asset in both optimizing the existing and designing new refinery wastewater treatment units or reuse schemes.

Vibration extraction method research for on-line dynamic mass balance

Vibration extraction method research for on-line dynamic mass balance

Real-time online monitoring of thermal efficiency in coal-fired power plant boiler based on coal heating value identification

This paper presents a comprehensive real-time online calculation model of coal-fired boiler thermal efficiency based on the low heating value identification of the coal. At first, online calculation approach is proposed to overcome the difficulty that the coal qualities into furnace are often changing and not well obtained real-time, by means of the dynamic mass and energy balance method. Secondly, the excess air coefficient and unburned carbon in fly ash which are the important parameters to calculate the boiler thermal efficiency are determined by soft measurement methods. The paper illustrates the effectiveness of the models as well as the validation of the online simulation, starting from real operation data. The outcome is that it is possible to significantly satisfy the accuracy of online identification of the low heating value (LHV) of the coal into the boiler, and the real-time of online calculations provided by indirect heat balance method. The models can be used to the real-time control and optimisation of the coal-fired utility boilers.

A New Model for Prediction of the Performance of a Cappuccino Pod

In recent years a lot of attention and efforts have been dedicated on optimizing the design and quality of coffee pods. These would be applicable on professional as well as on household machines such as Senseo or Nestle. By providing a new method to describe the mechanisms of the brewing process within the pod, the research presented in this paper gives deeper insights into the design related aspects to improve the pods. A model incorporating the function of dynamic mass balance and the shrinking core model is employed to describe the dissolution process of the creamer in the pod. This dissolution step is the most important in determining the milky taste wanted in the case of cappuccino. The model was tested by comparing its results with those of a series of experiments. With the model presented in this paper designing better pods should be easier and more efficient.

A Reaction Between High Mn-High Al Steel and CaO-SiO2-Type Molten Mold Flux: Part II. Reaction Mechanism, Interface Morphology, and Al2O3 Accumulation in Molten Mold Flux

Following a series of laboratory-scale experiments, the mechanism of a chemical reaction $$4[\rm{Al}] + 3(\rm{SiO}_2) = 3[\rm{Si}] + 2(\rm{Al}_2\rm{O}_3)$$ between high-alloyed TWIP (TWin-Induced Plasticity) steel containing Mn and Al and molten mold flux composed mainly of CaO-SiO2 during the continuous casting process is discussed in the present article in the context of kinetic analysis, morphological evolution at the reaction interface. By the kinetic analysis using a two-film theory, a rate-controlling step of the chemical reaction at the interface between the molten steel and the molten flux is found to be mass transport of Al in a boundary layer of the molten steel, as long as the molten steel and the molten flux phases are concerned. Mass transfer coefficient of the Al in the boundary layer ( $$k_{\rm{Al}}$$ ) is estimated to be 0.9 to 1.2 × 10−4 m/s at 1773 K ( $$1500\,^{\circ}$$ C). By utilizing experimental data at various temperatures, the following equation is obtained for the $$k_{\rm{Al}}; \ln k_{\rm{Al}} = -14,290/T - 1.1107.$$ Activation energy for the mass transfer of Al in the boundary layer is 119 kJ/mol, which is close to a value of activation energy for mass transfer in metal phase. The composition evolution of Al in the molten steel was well explained by the mechanism of Al mass transfer. On the other hand, when the concentration of Al in the steel was high, a significant deviation of the composition evolution of Al in the molten steel was observed. By observing reaction interface between the molten steel and the molten flux, it is thought that the chemical reaction controlled by the mass transfer of Al seemed to be disturbed by formation of a solid product layer of MgAl2O4. A model based on a dynamic mass balance and the reaction mechanism of mass transfer of Al in the boundary layer for the low Al steel was developed to predict (pct Al2O3) accumulation rate in the molten mold flux.