Plant-wide Model Research Articles

Plant-wide modeling and techno-economic optimization of a low-pressure microwave-assisted ammonia synthesis process with adsorption separation

Ammonia production has traditionally been done by using the Haber-Bosch process, that operates at extremely high pressure (200–300 bar), has a large carbon footprint, and requires significant energy. For ammonia to be used as a hydrogen carrier, it is desired that it is produced by using modular technologies under benign conditions, yet the economics remain commercially viable. This paper investigates a novel technology for ammonia synthesis by using a microwave-assisted low-pressure reactor. Microwave reactors are compact and can be readily modularized and started/shutdown thus making them ideal to be integrated with the electric grid or with regional/local renewable-based electric generation facilities. For separation of unreacted reactants from the product ammonia, if the traditional condensation separation technology used in the high-pressure Haber-Bosch process is used, then the separation process needs to be operated under cryogenic condition thus adversely affecting the economics. A solid sorbent based separation technology is investigated in this paper. A kinetic model for the microwave-catalytic synthesis process is used. An isotherm model is developed for MgCl2–Si adsorbent and used for modeling the dynamic adsorption-desorption cycle. A plant-wide model with heat and mass integration is developed. An economic model is developed and used for economic optimization by using an equation-oriented approach. Since the adsorption-desorption process is dynamic, for techno-economic optimization, a reduced order model for the key performance measures of the adsorption-desorption process as a function of its input and decision variable is developed under cyclic steady-state conditions. For the optimized MW-assisted process, the levelized cost of ammonia is $772/mt as opposed to $808/mt for the conventional Haber-Bosch process for a hydrogen price of $2.07/kg. The MW-assisted process is found to be economically viable in the US market if the hydrogen price is below $4/kg.

Plant wide modelling and thermodynamic optimization of a petroleum refinery for improvement potentials

In this work, plant wide modelling of a petroleum refinery was conducted for the optimization. An Aspen HYSYS® model of a petroleum refinery was used for collection of the information to perform the thermodynamic (exergy) analysis. The plant wide model consisted of alkylation unit, reformer, naphtha hydrotreater, catalytic cracker, diesel hydrotreater, isomerization unit, hydrocracker, and kerosene hydrotreater. Seventeen (17) independent input streams and twenty-eight (28) output streams of the plant were considered for the analysis. The physical and chemical exergies of the streams were summed for assessing the overall exergy efficiency, exergy destruction, and improvement potentials of the plant. Exergy efficiency of the plant was 91.38 % with exergy destruction of 704054.64 kW and exergetic improvement potential of 60707.50 kW. The current study gives an insight into the plant-wide analysis ranging from physical exergies of the process streams and utilities to the chemical exergies of the fuels (product) produced in the refineries.

Plant-Wide Models for Optimizing the Operation and Maintenance of BTEX-Contaminated Wastewater Treatment and Reuse

Benzene, toluene, ethylbenzene and xylenes, collectively known as BTEX compounds, are significant emerging contaminants in municipal wastewater. Stricter effluent quality regulations necessitate their removal, especially with concerns about organic micropollutant concentrations. Water scarcity further underscores the need for wastewater treatment to ensure safe agricultural or drinking water supplies. Although biological treatment partially reduces BTEX levels through processes like biodegradation and sorption, additional purification using physico-chemical methods is crucial for substantial reduction. This paper aims to outline plant-wide simulation methods for treating BTEX-contaminated sewage and facilitating reuse, adhering to IWA Good Modelling Practice Guidelines. The model, built upon the MiniSumo process model, incorporates equations detailing BTEX metabolism and removal kinetics, informed by an extensive literature review. Using a variant of the Benchmark Simulation Model with granular activated carbon for water reuse, the study examines strategies for improving effluent quality and minimizing operational costs. These strategies include adjusting the sludge retention time and airflow to enhance BTEX degradation and stripping, respectively, and comparing maintenance approaches for the GAC tower.

Optimized process intensification through dynamic performance simulation and evaluation of treatment alternatives for a wastewater treatment plant in Toronto

In this study, a comprehensive plant-wide model of the North Toronto Treatment Plant (NTTP) was developed, focusing on improving operational efficiency and capacity utilization. NTTP, with a rated capacity of 45 MLD, is currently operating at about 18 MLD with treatment processes including physical units (incorporating four primary settling tanks), chemical precipitation (for phosphorus removal using ferrous chloride), and biological processes (utilizing eight plug-flow conventional activated sludge (CAS) aeration tanks), and two sets of final clarifiers. Utilizing Biowin 6.2, the study constructed and calibrated a mechanistic model based on historical plant records and extensive sampling campaign data gathered from July to August 2022. The performance of various process configurations under different operational and seasonal conditions was evaluated. It was observed that the Ludzack-Ettinger (L-E) configuration demonstrated enhanced performance in terms of Environmental Compliance Approval (ECA) objectives and cost-efficiency compared to the CAS process. However, the L-E configuration posed challenges related to the final clarifier loading. The State Point Analysis (SPA) conducted within the study emphasized the effectiveness of the Membrane Aerated Bioreactor (MABR) in producing high-quality effluent, while also reducing the burden on the final clarifiers. This research provides a foundation for potential upgrades to NTTP, leveraging existing infrastructure to approach its full rated capacity while maintaining adherence to current ECA objectives.

A plant-wide modelling framework to describe microalgae growth on liquid digestate in agro-zootechnical biomethane plants

Microalgae cultivation on liquid digestate from the anaerobic co-digestion of agricultural feedstocks is an interesting option for digestate nutrient removal and resource recovery coupled to biomass generation. Both the reactors considered in such a biorefinery system involve complex bioprocesses. Although different pilot-scale systems coupling anaerobic digestion and algae-based bioremediation processes have been described, no previous attempts to model the entire system are available to date. In this work, a plant-wide model, named ADAB (anaerobic digestion algae-bacteria), is presented, coupling two well-established models for anaerobic digestion (IWA – ADM1) and algae-based bioremediation processes (ALBA). The models were modified with necessary equations and extensions to develop a dedicated model interface. Phosphorous dynamics were integrated, including activity corrections and precipitation processes. The ALBA model was also integrated with thermal modelling to simulate outdoor raceway ponds and greenhouse-covered systems. Solid/liquid separation units for digestate pre-treatment were also included. The prediction consistency of the adopted physicochemical sub-model (PCM) was verified with results from both reference literature and Visual MINTEQ. The reduced complexity of the PCM limits the model field of application, but it results in better computational performance and seems to be particularly suitable to simulate agro-zootechnical digesters. A scenario analysis including different co-digester design and operating conditions was carried out to assess the impacts on microalgae cultivation. It highlighted the importance of a proper biorefinery design and yet a noteworthy robustness of the system performance. The use of the ADAB model can facilitate a more realistic assessment of the technical, environmental, and economic feasibility of full-scale microalgal biorefineries based on digestate.

Development of a chemistry-based isotherm model and techno-economic optimization of a moving bed process for CO2 capture using a functionalized metal-organic framework

Amine-appended metal–organic frameworks of the class Mg2(dobpdc) are promising candidates for efficient carbon capture in part due to their step-shaped CO2 adsorption behavior. However, the existing isotherm models are lacking as they are unable to capture the complicated chemisorption mechanisms which are still not well known for these materials. Here, a chemistry-based isotherm model is developed and fit to experimental CO2 adsorption data for dmpn-Mg2(dobpdc). Reactions for a cooperative adsorption mechanism are proposed, and the reaction pathway is optimally selected. The chemistry-based model shows an improvement in prediction by a factor of 6 when compared to a recent isotherm model in literature. A plant-wide model is developed for a moving bed based adsorber/desorber and techno-economic optimization is performed. For likely values of price and lifespan, the moving bed process gives a significant improvement in economics when compared to a fixed bed contactor process and a traditional MEA capture system.

Comparative assessment of different scenarios for upgrading activated sludge wastewater treatment plants in developing countries

Improvement of current wastewater treatment plants (WWTPs) to accommodate the growing influent flow rate and cope with the increasingly stringent regulations is hindered by the allowed space and the difficulty of changing the design parameters. Mathematical modeling is a useful tool for assessing the performance of WWTPs in light of broadening objectives. We herein explore the utilization of mathematical modeling to improve effluent quality in conventional activated sludge systems. BioWin was used to model Mansoura WWTP, one of the largest WWTPs in Egypt. Lab records, design reports, and additional analyses were conducted through site visits and a comprehensive sampling campaign. The wastewater was characterized, and the plant-wide model was calibrated following the protocol of the Dutch Foundation for Applied Water Research STOWA. Important kinetic and stoichiometric parameters were identified and adjusted during the calibration process. The model validity was assessed using different validation periods considering average relative deviation (ARD) values below 20 % as acceptable. The optimized nitrification and denitrification processes involved 16 scenarios with different operational conditions. By changing some zones in the aeration basin from aerobic to anoxic and increasing the return activated sludge, the average ammonia and nitrate concentrations were significantly reduced from 23.06 and 0.5 mg/L to 4.64 and 0.07 mg/L respectively. Furthermore, phosphorus removal optimization was carried out through biological and chemical processes. Chemical phosphorus removal was 85.76 % by using a coagulant dosage of 25 mg/L, resulting in an effluent concentration of 1.04 mg P/L. Biological phosphorus removal was increased to 85.43 % by modifying the volume of anaerobic and aerobic zones with lower power consumption. Overall, this study demonstrates the effectiveness of mathematical modeling in enhancing effluent quality and reducing energy consumption to meet stringent wastewater treatment regulations.

Modelling greenhouse gas emissions from biological wastewater treatment by GPS-X: The full-scale case study of Corleone (Italy)

Greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs) can affect climate change and must be measured and reduced. Mathematical modelling is an attractive solution to get a tool for GHG mitigation. However, although many efforts have been made to create reliable tools that can simulate “sustainable” full-scale WWTP operation, these studies are not considered complete enough to include GHG emissions and energy consumption of biological processes under long-term dynamic conditions. In this study, activated sludge model no. 1 (ASM1) was modified to model nitrous oxide (N2O) emissions with a plant-wide modelling approach. The model is novel compared to the state of the art since it includes three steps denitrification, all N2O production pathways and its stripping in an ASM1. The model has been calibrated and validated through long-term water quality and short-term N2O emissions data collected from Corleone (Italy) WWTP. Different dissolved oxygen (DO) concentrations and return sludge (RAS) ratios were tested with dynamic simulations to optimise the full-scale WWTP. The scenarios have been compared synergistically with effluent quality, direct GHG emissions, and energy footprint by the water-energy‑carbon coupling index (WECCI). This modelling study is novel as it fully covers long-term calibration/validation of the model with N2O measurements and tests the dynamic optimisation. Decision-makers and operators can use this new model to optimise GHG emissions and treatment costs.

Restructuring anaerobic hydrolysis kinetics in plant-wide models for accurate prediction of biogas production

In this study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. A linear correlation was determined between the percentage of primary sludge mass in the total sludge fed to the digester and the overall anaerobic hydrolysis rate. The anaerobic hydrolysis rate of primary sludge was determined to be three times higher than that of biological sludge. The reduction factors for anaerobic hydrolysis (ηHYD,ana) were identified in the range of 0.11–0.30 which is lower compared to the recommended range (0.30–0.50) given in the literature. This study proposes a new model approach where anaerobic degradation kinetics of influent originated (XB) and decay originated (XB,E) particulate biodegradable organics are separated. Current plant-wide models with a single kinetic expression required recalibration of the model for calculating biogas flowrate for each treatment facility with different primary and secondary sludge ratios fed to the digesters. The new model structure is able to predict biogas production of all wastewater treatment plants without any recalibration effort by segregating degradation kinetics of two particulate biodegradable organic fractions (XB, XB,E).

Multi-scale dynamic modeling and techno-economic optimization of a CO2 capture process using microencapsulated carbon sorbents in a moving bed contactors

A detailed 1-D non-isothermal model of moving beds for micro-encapsulated carbon sorbents (MECS) is developed in this study with sodium bicarbonate as the encapsulated sorbent. A rigorous capsule model is also developed and integrated with the bulk phase model leading to a multi-scale reactor model. A heat exchanger embedded in the regenerator is considered to provide the heat required for sorbent regeneration along with the heat input from direct steam. A new correlation for the heat transfer coefficient for heat exchange between the embedded heat exchanger and the moving solids is used. A plant-wide model of the capture system is developed with the absorbers, regenerators, heat recovery systems and the balance of the plant. Several sensitivity studies are conducted evaluating the impact of operating and design variables. An economic model of the process is developed. Key design and operating variables are optimized for minimizing Equivalent Annual Operating Cost (EAOC). Optimal EAOC of the moving bed reactor using MECS with encapsulated sodium carbonate is found to be about 8% better compared to the traditional MEA-based CO2 capture for similar extent of heat recovery. For +50% uncertainty in the capital costs of the moving beds, the moving bed technology using MECS studied here is found to result in about 3% higher EAOC than MEA while for -50% uncertainty in capital cost of moving beds, EAOC for the moving bed process is found to be about 19% lower than the MEA-based capture. Finally, the impact of part load operation on the economics of the capture system is evaluated.

Integrated microalgae-bacteria modelling: application to an outdoor membrane photobioreactor (MPBR)

A mechanistic model describing the key interactions occurring in microalgae-bacteria consortia systems was developed and validated. The proposed model includes the most relevant features of microalgae, such as light dependence, endogenous respiration, growth, and nutrient consumption for different nutrient sources. The model is coupled to the plant-wide model BNRM2, including heterotrophic and nitrifying bacteria, and chemical precipitation processes, among others. A major novelty of the model is microalgae growth inhibition by nitrite. Validation was conducted using experimental data from a pilot-scale membrane photobioreactor (MPBR) fed with permeate from an anaerobic membrane bioreactor (AnMBR). Three experimental periods dealing with different interactions between nitrifying bacteria and microalgae were validated. The model was able to accurately represent the dynamics occurring in the MPBR, predicting the relative abundance of microalgae and bacteria over time. Specifically, >500 pairs of experimental and modeled data were evaluated, giving an average R2 coefficient of 0.9902. The validated model was also used to evaluate different offline control strategies for enhancing process performance. For example, partial-nitrification resulting in NO2-N accumulation (i.e., microalgae growth inhibition) could be avoided by increasing biomass retention time from 2.0 to 4.5 days. It has been also concluded that microalgae biomass growth rate could be also enhanced by punctually increasing the dilution rate, allowing to outcompete nitrifying bacteria.

Optimization of Aeration Diffuser System Design: A Simulation Study

The influence of aeration diffuser system design on electricity usage, effluent water quality, and life-cycle cost in biological wastewater treatment was investigated. A plant-wide model was implemented, and simulations were carried out with different process configurations and aeration systems. Model-aided design of new aeration diffuser systems could significantly decrease electricity usage and life-cycle cost while at the same time avoiding negative effects on the treatment performance. The optimum distribution of diffuser systems in tanks in series was found to be influenced by process configuration, volumetric loading rate, temperature, and the internal recirculation flow rate. Compared with a conventional design approach, increasing the number of diffusers, up to a critical point, led to higher energy efficiency and lower life-cycle cost. This was despite an increasing limitation of the minimum airflow rate, leading to dissolved oxygen levels significantly exceeding control targets. Aeration systems optimized by simulations were found to, independently of process configuration, exhibit 20% lower electricity usage and 16%–18% lower life-cycle costs compared with systems designed based on a more conventional approach typically applied in practice.

Plant-wide modeling and techno-economic analysis of a direct non-oxidative methane dehydroaromatization process via conventional and microwave-assisted catalysis

Direct non-oxidative methane dehydroaromatization (DHA) process via conventional and microwave (MW)-assisted thermo-catalytic catalysis is studied. Rate models for methane DHA reactions, including the effect of catalyst deactivation, are developed by using the in-house experimental data. Model results for gas concentration profile and catalyst deactivation are in good agreement with the experimental data. This rate model is then used for the development of dynamic multi-scale, multi-physics commercial-scale reactor models. Total number of fixed bed reactors desired for a cyclic steady state process is estimated. Plant-wide models are then developed for conventional and MW-assisted processes for producing products of desired specifications. Techno-economic analysis of the methane DHA process is undertaken. Economics of these methane DHA processes are compared with the typical multi-step natural gas to aromatics production process via methanol synthesis. Sensitivity of internal rate of return (IRR) and net present value (NPV) to various economic and process parameters such as plant scale, desired rate of return, reactor cost, feedstock and utility cost, catalyst variable cost, and MW reactor cost is studied. Electric equivalent efficiency of the conventional methane DHA process is found to be 69.2 % and 67.3 % at 750 °C and 800 °C, respectively, while the MW-assisted methane DHA process has the electric equivalent efficiency of 48.9 % at 800 °C. IRRs of the conventional methane DHA process at 750 °C and 800 °C, and MW-assisted process are 15.2 %, 17.5 %, and 18.8 %, respectively for a methane feed flowrate of 19,782 kg/h, while the IRR of the multi-step natural gas to aromatics production process is estimated to be 0 % for the same plant scale. Impact of change in the methane price, electricity price, and catalyst cost is found to be considerable on the process economics, while the cost of the MW reactor is found to have negligible impact.

An improved 1D reactive Bürger-Diehl settler model for secondary settling tank denitrification.

An improved 1D reactive settler model is pursued in order to increase the understanding of reactive settling processes and obtain a better prediction of the nitrogen mass balance in wastewater treatment systems. The developed model is based on the 1D Bürger-Diehl settler model with compression function and the Activated Sludge Model No. 1 biological reactions. Specific attention was paid in the model development phase to optimal selection of settling velocity functions and integration of the correct clarifier geometry. A unique measurement campaign was carried out with different operational scenarios to quantify the denitrification in a secondary settling tank. A detailed step-wise calibration effort demonstrated that by choosing an appropriate settling velocity function (power-law structure) and considering the true clarifier geometry allows to accurately capture the biomass concentration profile, total sludge mass, sludge blanket height, and the reaction rates. The resulting model is able to accurately describe total suspended solids (TSS) and nitrate concentration profiles throughout a settling tank under different operational conditions. As such the model can be applied in further scenario analysis and system optimization. PRACTITIONER POINTS: A unique measurement campaign was carried out to obtain detailed data for a reactive settler model development. A 1-D reactive settler model is developed based on the Bürger-Diehl framework including ASM1 biokinetics and the clarifier geometry. An extensive calibration and model selection effort was performed. The model accurately predicts measured concentration profiles in the settling tank. The developed model can be integrated in a plant-wide model to properly calculate the nitrogen mass balance of a WRRF.

Phosphorus recovery alternatives for sludge from chemical phosphorus removal processes – Technology comparison and system limitations

Several approaches have recently been proposed in the literature for P recovery after metal precipitation, but a robust comparison of these approaches in a techno-economic framework is still lacking. Five phosphorus recovery methods using sewage sludge or sludge ash as feed material were compared based on their specific operational recovery cost by scaling the processes to unified size and operational conditions. The selected technologies were (1) wet leaching + struvite precipitation, (2) magnetic vivianite separation, (3) sludge melt gasification, (4) the thermochemical sodium sulfate process, and (5) white phosphorus recovery. The analyses were based on the literature values in addition to a plant-wide model used to estimate chemical consumption and phosphorus and metal-related sludge properties. The technologies were assessed by operational cost, end-product quality, recovery efficiency, and technology maturity. The choice of the recovery process is dependent on the precipitant used in the wastewater treatment processes. Technologies using sewage sludge ash, (4) and (5), had the highest recovery efficiency, technical maturity, and product quality, but they require mono-incineration. Technology (3) had better recovery efficiency than (1), but the end-product had much lower P content. Technology (2) had the lowest recovery efficiency among all the compared technologies, however, it produced an end-product with the second highest P content. The operational costs were calculated for energy and chemical costs for same scale and operational conditions. The specific recovery cost ranges from 6 to 38 €/kgPrecovered.

Dynamic modeling and comprehensive analysis of direct air-cooling coal-fired power plant integrated with carbon capture for reliable, economic and flexible operation

Coal-fired power plants with direct air-cooling condensers (DACC-CFPP) are water-saving, eco-friendly and thus widely installed in regions rich in coal but short of water. As such regions have better geological conditions for CO2 storage, retrofitting these plants with carbon capture techniques provides a cost-efficient way to reduce carbon emissions and retain dispatchable power. However, the integration of carbon capture poses significant challenges for CFPP and DACC. Therefore, this paper develops a plant-wide model of the 660MWe DACC-CFPP integrated with post-combustion carbon capture (PCC). A connection system, including a steam extraction valve, water spray and condensate returning, is designed, added to the Steam turbine-Feedwater heaters-Condenser system and modeled to reflect dynamic interactions between the DACC-CFPP and PCC. This model is then used to evaluate the reliability, economics and flexibility of the DACC-CFPP-PCC over wide operating conditions. Results show that the integration of PCC causes changes in steam flowrate, pressure and temperature within the turbine, creating reliability risks; brings 5%–10% extra exergy loss to the DACC-CFPP, but not necessarily economic losses; reduces the minimum power load by 44MWe and improve the ramping speed by 3.75MWe/min. This paper provides in-depth insights for decision-makers, designers, and operators to manage the DACC-CFPP-PCC plant.

Economic, technical, and environmental evaluation of retrofitting scenarios in a full-scale industrial wastewater treatment system

The use of mathematical models is a well-established procedure in the field of (waste) water engineering to “virtually” evaluate the feasibility of novel process modifications. In this way, only options with the highest chance of success are further developed to be implemented at full-scale, while less interesting proposals can be disregarded at an early stage. Nevertheless, there is still lack of studies, where different plant-wide model predictions (effluent quality, process economics, and technical aspects) are comprehensibly verified in the field with full-scale data. In this work, a set of analysis/evaluation tools are used to assess alternative retrofitting options in the largest industrial wastewater treatment plant in Northern Europe. A mechanistic mathematical model is simulated to reproduce process behavior (deviation < 11%). Multiple criteria are defined and verified with plant data (deviation < 5%). The feasibility of three types of scenarios is tested: (1) stream refluxing, (2) change of operational conditions and (3) the implementation of new technologies. Experimental measurements and computer simulations show that the current plant´s main revenues are obtained from the electricity produced by the biogas engine (54%) and sales of the inactivated bio-solids for off-site biogas production (33%). The main expenditures are the discharge fee (39%), and transportation and handling of bio-solids (30%). Selective treatment of bio-solid streams strongly modifies the fate of COD and N compounds within the plant. In addition, it increases revenues (+3%), reduces cost (-9%) and liberates capacity in both activated sludge (+25%) and inactivation reactors (+50%). Better management of the buffer tank promotes heterotrophic denitrification instead of dissimilatory nitrate conversion to ammonia. In this way, 11% of the incoming nitrogen is removed within the anaerobic water line and does not overload the activated sludge reactors. Only a marginal increase in process performance is achieved when the anaerobic granular sludge reactor operates at full capacity. The latter reveals that influent biodegradability is the main limiting factor rather than volume. Usage of either NaOH or heat (instead of CaO) as inactivation agents allows anaerobic treatment of the reject water, which substantially benefits revenues derived from higher electricity recovery (+44%). However, there is a high toll paid on chemicals (+73%) or heat recovery (-19%) depending on the inactivation technology. In addition, partial nitration/Anammox and a better poly-aluminum chloride (PAC) dosage strategy is necessary to achieve acceptable (< 2%) N and P levels in the effluent. The scenarios are evaluated from a sustainability angle by using life cycle impact assessment (LCIA) in form of damage stressors grouped into three categories: human health, ecosystems quality, and resource scarcity. The presented decision support tool has been used by the biotech company involved in the study to support decision-making on how to handle future expansions.

Smart-Plant Decision Support System (SP-DSS): Defining a multi-criteria decision-making framework for the selection of WWTP configurations with resource recovery

The development of the Smart-Plant Decision Support System (SP-DSS) is presented, which helps to find the optimal water resource recovery facility (WRRF) configuration for a specific case. A general plant superstructure is defined to allow the evaluation of different combinations among the available process unit options, considering technical, economic, and environmental impact criteria. The complete evaluation is based on a five-step framework: (i) design problem set-up, (ii) wastewater inflow generation, (iii) superstructure generation and plant-wide model simulation under dynamic conditions, (iv) estimation of multi-criteria objective values (greenhouse gas emissions, accumulation of effluent violations, effluent quality index, net present value, system readiness level and plant land area), and (v) design configuration multi-criteria sorting with the technique for order of preference by similarity to ideal solution (TOPSIS). SP-DSS application is shown comparing the mainstream shortcut enhanced phosphorus and polyhydroxyalkanoate (PHA) recovery (SCEPPHAR) technology with a conventional anaerobic/anoxic/aerobic (A2O) configuration for a medium size WWTP (Manresa, Spain). The comparison shows both configurations allow meeting discharge limits, and among other criteria, the SCEPPHAR novel configuration, with respect to A2O, shows higher pollutant contents in the effluent (3.30 vs 2.34 gPoll/m3), higher capital expenditures (CAPEX 0.191 vs 0.130 €/m3), lower operational expenditures (OPEX 0.397 vs 0.515 €/m3), lower required tariff (0.654 vs 0.674 €/m3) and higher greenhouse gas emissions (GHG 0.19 vs 0.14 kgCO2/m3). Overall, TOPSIS sorting indicates A2O is still the best configuration for this specific case.

Predictive modeling of a subcritical pulverized-coal power plant for optimization: Parameter estimation, validation, and application

As renewable power generation deployment increases, fossil fuel plants are increasingly required to operate more flexibly. Many coal-fired power plants were originally designed to operate at base load and do not operate optimally at partial load. Predictive first-principles plant-wide models can be employed to identify opportunities for flexibility improvements and diagnose low-load operating issues. This paper describes the application of the Institute for the Design of Advanced Energy Systems Integrated Platform (IDAES) to model and optimize flexible power plant operations. The key benefits of using IDAES are that it provides an open-source, fully equation-oriented modeling framework for efficient modular model construction, reuse, and customization, together with a mathematical optimization framework leveraging powerful, state-of-the-art solvers. The process systems engineering workflow from predictive process simulation to parameter estimation, model validation, and plant optimization is applicable to a variety of existing and next-generation energy systems as well as other chemical and environmental processes. To demonstrate this capability, a physics-based, steady-state model was developed to improve full- and part-load performance of the Escalante Generating Station, a 245 MWe (net) subcritical pulverized coal-fired power plant owned and operated by Tri-State Generation and Transmission Association. Specifically, sixty-nine model parameters were simultaneously estimated from several months of operating data enabling prediction of flow rates, temperatures, pressures, and steam quality throughout the plant. The validated model was leveraged by Escalante to reduce the minimum operating load from 90 MW to 50 MW by diagnosing a low-load water-hammer issue, enabling coal usage and emissions reductions during periods of low power demand. Additionally, opportunities for heat rate reduction (i.e., efficiency improvement) through a steeper sliding-pressure approach to load-following and optimization of other boiler operating variables were also identified and quantified. For example, a potential efficiency improvement of 0.7 percentage points was observed at half-load operation.

Evaluation of an Open-source Chemical Process Simulator Using a Plant-wide Oil and Gas Separation Plant Flowsheet Model as Basis

In this paper, a detailed evaluation of the open source process simulator DWSIM is presented. Using a previously published simulation model of an oil and gas separation plant, the results obtained with DWSIM are compared to a commercial process simulator widely used in the industry. The modelled flow scheme comprises a vast number of unit operations including separators (flash vessels), valves, splitters, mixers, compressors, heat exchangers, pumps and recycles (tear streams). The results obtained with DWSIM both for characterization of the inlet fluid as well as for a single operating state for the entire process, compare very well with the data obtained using a commercial tool. A rigorous comparison is made and generally, compared results are within 1% in deviation with a few exceptions. Further, an elaborate comparison is made for over 90 simulations with different settings where 10 independent variables are randomly varied over a wide range. Again, good agreement is found between the two tools. The results are very encouraging and provide fidelity in the use of the investigated open source process simulation tools in a professional environment.