Annual Capital Cost Research Articles

Economical process design of reactive-extractive distillation combining variable pressure and heat integration for separating a ternary azeotropic mixture

Research and development of environmentally friendly processes that can generate significant profits has always been a focus of attention in pharmaceutical and chemical fields. In this study, a novel reactive-extractive pressure-swing distillation (REPSD) process was designed to separate tetrahydrofuran (THF)-methanol-water (TMW) ternary azeotropic mixtures. Ethylene oxide (EO) is reacted with water to form ethylene glycol (EG) in a reactive distillation (RD) column, which removes the water from the mixture. Then, the THF-methanol (TM) mixture is separated by extractive distillation (ED) and pressure-swing distillation (PSD). A multi-objective genetic algorithm (MUOGA) with total annual cost (TAC) and total capital cost (TCC) as objective functions, along with heat integration techniques were used to optimise the designed REPSD process. Optimal operating conditions to achieve maximum economic benefits were obtained for the process. Subsequently, the environmental benefits of the process were evaluated. The results showed that the proposed REPSD with heat integration can significantly reduce the TAC and CO2 emissions by 29.1 and 26.9 %, respectively, compared to existing optimal heat integration extractive distillation (HIED) processes. This study provides a new perspective on the separation and purification of ternary azeotropic mixtures.

A stepwise optimization method for topology structure of fluid machinery network

A stepwise optimization method for topology structure of fluid machinery network

ZIF-8 membranes for efficient C3H6 recovery from the Hydrogen Peroxide to propylene oxide process

The ZIF-8 membrane has emerged as a promising candidate for C3H6/C3H8 separation. However, the feasibility of ZIF-8 membranes for applications has rarely been investigated with gas provided directly by the industry sector. Herein, the C3H6/C3H8 mixture collected from the backend of the Hydrogen Peroxide to Propylene Oxide (HPPO) process was applied as feed gas to examine the separation performance of tubular ZIF-8 membranes. The membranes exhibited excellent separation performance and long-term stability under 9 bar and 50 °C. Noticeably, upon scaling up to a membrane area of 452.16 cm2 by connecting six three-channel modules in series (multi-step membrane), its separation performance satisfied the C3H6 circulation requirements during the HPPO process (purity ≥97.5 % and recovery rate ≥85 %). Furthermore, a simulation of membrane operation under industrial working conditions (22 bar and 56.3 °C) was performed. By fixing the separation factor at 15, a minimum membrane area of 800 m2 met the requirements at the cost of membrane permeance with 120 GPU. The corresponding economic calculation indicated a maximum of 91.8 % annual capital cost saving compared with the distillation process, paving the way for the practical application of membranes.

Trends in Hybrid Renewable Energy System (HRES) Applications: A Review

Microgrids and hybrid renewable energy systems play a crucial role in today’s energy transition. They enable local power generation and distribution, reducing dependence on large centralized infrastructures, can operate independently or connected to a grid, and can provide backup power, thus increasing system resilience. In addition, they combine multiple renewable energy sources, such as solar, wind, hydro, and biomass, to maximize the efficiency and reliability of the supply, and are also adaptable to location-specific conditions, taking advantage of locally available energy resources and reducing the need for energy imports. Moreover, they contribute to decarbonization goals by offering a cleaner and more sustainable alternative. In this article, a documentary review is presented on the interaction of Homer Pro software 3.16.2 (July 2023), used for the design of hybrid renewable energy systems (HRES), with other methods of optimization or sizing. Allusion is made to the type of architecture in the most prominent clean and fossil source configurations, the levelized cost, net annual cost, and maintenance and capital investment cost. A comparison is made among the works reported in the last five years regarding the use of this software tool, based on load demand, geographical area, renewable energy sources, fossil sources, and objective functions, applied to the educational, rural, and industrial sectors. It is shown that India is one of the countries that has reported the most number of HRES techno-economic environmental analysis works, and that the case studies have focused approximately 47% on rural areas, 20% on educational agencies, 14% on commerce and industry, and 29% on urban buildings.

Exploring Cost Effective Fleet Electrification Possibilities for Public Transit Services in Kutch Region

The extensive use of fossil fuels in transit buses has led to both environmental problems and fuel scarcity. Renewable energy has emerged as a potential solution to mitigate these issues. Many countries worldwide have already adopted renewable energy to address these challenges. Similarly, the Indian government has initiated e-vehicle adoption in various sectors through subsidies to reduce dependence on conventional fuels. This research investigates two key areas: Fuel consumption dependency and air quality impact assessment for diesel-operated public buses (GSRTC) and Exploring fleet electrification possibilities. The recent significant rise in fossil fuel costs has exposed the inherent conflicts between achieving net-zero goals, ensuring energy security, and maintaining affordability. This research employs a three-stage energy modeling methodology: Route energy planning, charging infrastructure planning and total cost of ownership (TCO) analysis. This study explores the potential for fleet electrification at the Mundra depot, aiming to replace existing diesel-powered internal combustion engines (ICEs) with environmentally friendly electric vehicles (EVs). A total of 18 buses from the Mundra depot, covering 22routes with 103 trips, were surveyed. An optimal route requiring minimal energy was prioritized. Based on this and a minimum state-of-charge requirement of 25%, five buses were chosen for further study. An analysis of annual capital costs for both ICE diesel and electric buses was conducted, considering bus capitalization, battery capitalization, charging infrastructure, and annual operation costs. The findings revealed that the TCO for an EV bus is significantly lower than that of a diesel bus (49.64 Rs/km vs. 72.80 Rs/km).

Capabilities of compressed air energy storage in the economic design of renewable off-grid system to supply electricity and heat costumers and smart charging-based electric vehicles

The study presents the sizing of a hybrid renewable islanded system that can feed both electrical and thermal energy simultaneously. The aforementioned energies are generated through the utilization of wind systems and bio-waste units. The integration of combined heat and power technology in the bio-waste unit enables the concurrent generation of electricity and heat power. Electric vehicles consume electric energy, but function based on a smart charging. The study employs compressed air energy storage as a means to bridge the disparity between the patterns of electric power generation and consumption, with the aim of enhancing energy efficiency and reducing planning expenses. Thermal energy storage serves as an intermediary between renewable power and load profiles within the thermal sector. Objective here is find the minimum annual capital and maintenance costs of sources, storages, and power electronic converters. Problem is constrained to operational model of renewable sources, storages, and electric vehicles. The present model prioritizes the utilization of renewable sources for the purpose of supplying electrical and thermal loads. Electric vehicles regulate their active power to minimize the disparity between load and electric production profiles. Storages perform charging and discharging functions to bridge the disparity between power generation and consumption. Strategy incorporates uncertainty related to load, wind speed, bio-waste-derived gas production, and electric vehicles parameters. The study employs a point estimate method to attain a dependable solution. The numerical results indicate that incorporation of compressed air storage in the hybrid system results in a decrease of 7.7 % (12.9 %) in the planning costs relative to system with batteries (hydrogen storage). The proposed design's concurrent provision of electrical and thermal energy leads to an approximately 57 % increasing in planning costs when compared to a system that solely provides electrical energy. The implementation of a smart charging strategy for electric vehicles drop the hybrid system's overall scheduling cost by 3.9 %.

A comparative study of polyamine and piperazine as promoter for CO2 absorption performance in aqueous methyldiethanolamine blend system: 430 MW power plant data simulation and economic assessment

Fossil fuel power plants play a significant role in fulfilling global energy demands but are also responsible for high CO2 emissions. Amine-based post-combustion CO2 capture (PCC) is one of the technologies used in such power plants to reduce CO2 emissions. However, high energy consumption in amine-based PCC technology causes a reduction in the overall energy efficiency of power plants. The energy consumption significantly depends on the solvents used in the PCC process. Therefore, in this work, we performed CO2 absorption in the piperazine (PZ), triethylenetetramine (TETA), and N-methyldiethanolamine (MDEA) blend and tri-blend solvents. For the absorption performance and energy consumption calculation, a simulation is performed for the 430 MW power plant data in the DWSIM software. Initially, solvent screening was done, and four solvents are selected based on the optimum energy consumption of various solvents. Further, the solvents’ performance in terms of energy consumption is done based on the effect of different temperatures, CO2 composition in feed, and %CO2 recovery. Overall, the TETA+PZ MDEA tri-blend solvent showed optimum energy consumption for most of the conditions. Additionally, a techno-economy assessment was done considering annual capital cost and annual operating cost, and results revealed that the cost per ton of CO2 capture in 5 %TETA+ 5 %PZ+ 20 %MDEA solvent is 27.33 % lesser than industrial MEA solvent, and 1.56 % lower than 10 %PZ+ 20 %MDEA.

Design, energy, exergy, economy, and environment (4E) analysis, and multi-objective optimization of a novel integrated energy system based on solar and geothermal resources

Increasing energy consumption rates and concerns over environmental problems like global warming have led researchers to provide new energy supply solutions, one of which is the use of combined energy systems. Combining conventional fossil energy cycles with renewable cycles is one of the most effective ways to improve their performance and also help harvest green energy. To address this solution, in this paper, a hybrid novel energy system including a gas cycle, a steam cycle, two organic Rankine cycles (ORC), and a renewable cycle based on geothermal and solar energy sources using concentrating photovoltaic thermal panels (CPVT) is proposed. A comprehensive study has been conducted on this system from the perspective of energy, efficiency, economy, and the environment. Different fluids have been investigated for use in ORC subsystems in this study. Additionally, a parametric study has been conducted to determine how the cycle's overall performance is affected. Multi-objective optimization using the Non-dominated Sorting Genetic Algorithm second version (NSGA-II) has been performed based on the objective variables of exergy efficiency and capital costs. In this paper, Engineering Equation Solver (EES) and MATLAB are used for modeling and optimization. The results show that the best fluids to use in ORC are R123 in the first cycle and Ammonia in the second cycle, which energy efficiency, exergy efficiency, exergy destruction rate, and generated power in the base state for the whole cycle are 50.59%, 25.44%, 1537.35 kW and 524.66 kW, respectively. Also, the amount of annual capital cost and the amount of carbon dioxide emission from energy and exergy are 107,034 dollars, 11,672, and 35,401 kg per month, respectively. The optimization results indicate a 0.25% improvement in exergy efficiency and a 500$ annual capital cost reduction at the optimal point.

A preliminary techno-economic analysis of photofermentative hydrogen production

Photofermentative hydrogen production promises sustainable energy using cheap feedstock and sunlight. While successful laboratory and pilot-scale photofermentative production studies are widespread, overall economic feasibility remains to be demonstrated. In this study, a preliminary techno-economic analysis of photofermentative production based on current technology was carried out, and the results were compared to alternatives such as photovoltaic electrolysis.Specific photofermentative hydrogen cost was estimated based on an existing outdoor, pilot-scale (20 L) photobioreactor system. The annual capital cost was calculated as 124 USD/year including equipment and land. Operating cost was calculated as 42 USD/year including maintenance, energy consumption and feedstock. The specific hydrogen production cost was found as 2.7 USD/mol (1362 USD/kg H2), and 395 USD/kg H2 when equipment cost is subsidized. Further analysis shows that utilization of wastewater as feedstock and a boost in hydrogen productivity could reduce specific cost of hydrogen to levels competitive with alternative technologies.

Economic Assessment of Operation Strategies on Park-Level Integrated Energy System Coupled with Biogas: A Case Study in a Sewage Treatment Plant

Operation strategies for a park-level integrated energy system (PIES) in terms of carbon prices and feed-in tariffs, have not been adequately studied. This paper addresses this knowledge gap by proposing operation strategies based on the PIES driven by biogas, solar energy, natural gas, and the power grid. Meanwhile, the electricity-driven dispatching strategy (EDS), thermal-driven dispatching strategy (TDS), cost-driven dispatching strategy (CDS) are compared to assess their impacts on operation cost, carbon dioxide emissions, etc. The flexibility and complementarity of the three operation strategies in energy supply are analyzed in detail. The results indicated that biogas was the main energy supply fuel, accounting for 46% to 72% of the total energy supply. About 33% to 54% of electricity was transmitted to the grid each month using the TDS. The annual initial capital cost of the CDS was only 1.39% higher than that of the EDS. However, the annual operation cost of the EDS was 16.86% higher than that of the CDS. The emissions of the EDS were the lowest, and the CDS had 38.51% higher emissions than the EDS. In the CDS, the ratio of carbon emission costs to operation costs was as high as 0.80 when the carbon tax reached USD 100/ton. The carbon tax had a greater impact on the CDS than the other strategies. Feed-in tariffs had a greater impact than the carbon tax on the TDS. This study provides an effective method for the selection of optimal operation strategies in regards to carbon prices and feed-in tariffs.

Techno-economic investigation and dual-objective optimization of a stand-alone combined configuration for the generation and storage of electricity and hydrogen applying hybrid renewable system

In this study, a solar driven co-generation structure of hydrogen and electricity is techno-economically investigated to be installed in the Farakhi village. In addition, a combined renewable configuration is also designed and integrated to the proposed system so as to provide required direct current for utilization in solid oxide electrolyzer. The presented scheme is modeled and simulated by MATLAB, ASPEN HYSYS, and HOMER Pro software. Economic, exergy as well as exergoeconomic approaches are applied to determine and to monitor the performance of the system and also to specify prominent factors through sensitivity analysis. The annual capital cost, yearly maintenance cost, and yearly operating cost of system were 15584.784 $/year, 455.062 $/year, and 245113 $/year, respectively. The system produced 29.2 ton of hydrogen per year, with a LCOP of 8.94 $/kg H2. The yearly cost of the system (ACS) was determined to be 261153 $/year. The largest amount of exergy destruction was related to reactor of the SOEC sub-unit with a value of 22.9 kW, which accounts for 47.33% of the total exergy destruction in the system. Moreover, the greatest share in the irreversibility of the whole combined renewable configuration was related to photovoltaic modules with a value of 86.62% and then biogas generator with a value of 8.03%. The largest and least values of exergoeconomic factor belonged to the solar collectors (100%) and reactor (9.91%), respectively. Ultimately, the economic, exergy, and exergoeconomic parametric analyses were carried out to generalize the results of the presented study to other geographical locations. The values of current density, operating temperature of SOEC, voltage of SOEC and temperature of fluids leaving the thermoelectric generator at the optimum point were determined to be 0.337 A/cm2, 791.5 °C, 1.212 V, and 197.5 °C, respectively.

Economic evaluation of induction motor based on motor’s nameplate data and initial cost

This paper presents a practical approach to calculate the total owning cost (TOC) of a three-phase Induction Motor, which is based on the motor’s nameplate data and the purchasing price. The economic evaluation is performed considering both the induction motor electrical energy losses and its amortized annual capital cost. The proposed technique consists of three stages, where the total power losses are determined analytically in the first stage. The load loss factor (LSF) is statistically obtained to determine the total energy losses in the second stage. In the third stage, the economic evaluation was conducted. The obtained results show that the proposed approach is a helpful tool for the decision-maker when comparing the received offers from different vendors and finding the answer to the question of which offer has less TOC. Finally, the proposed method is illustrated through a numerical example and software using MATLAB was performed. Results and conclusions have been summarized and discussed.

Heat exchanger network design for the optimization of total annual cost of the Catalytic Reforming Unit

This research involved the energy integration of the Catalytic Reforming Unit of a Refinery using Aspen Pinch 11.1 Software. The operating data of the unit was analyzed on composite and grand composite curves from the Software to obtain an optimum minimum temperature of 15oC, pinch temperature of 149.5oC and hot and cold utilities targets of 37094 kW and 22440 kW respectively. Problem table algorithm (PTA) was used as a sensitivity tool to test the accuracy of these values; the exact same values were obtained with less than 0.4% difference between the energy targets. This integration achieved a minimum heat recovery (QREC) of 55465.00 kW with an increase in the number of heat exchangers from eighteen (18) to twenty one (21) with total area of 1995.80m2. Power law correlation was used for the heat exchanger costing to obtain a minimum Annual Capital Cost of $5,918.25/yr, Annual Energy Cost of $2,892.28/yr and Total Annual Cost (TAC) of $57,442.90/yr. By extension, these will certainly reduce the annual operating cost in terms of cost of utilities as well as minimize pollution emissions. Pinch analysis provides the best target for the minimum energy consumption as well as minimum total annualized cost.

Eco-efficient heat-integrated extractive distillation process using ionic liquid as entrainer for ethyl acetate-isopropyl alcohol-water mixture

Ethyl acetate-isopropyl alcohol-water is a common ternary mixture in pharmaceutical and chemical industries, containing multiple binary minimum azeotropes. Highly efficient separation for this mixture is of great significance to reduce environmental risk, recover valuable resource and maintain eco-sustainability. In this work, various enhanced extractive distillation processes using ionic liquid (IL) as entrainer are compared with conventional extractive distillation process (CED) in terms of the reductions of cost, energy and carbon emissions. First of all, ethylene glycol (EG) and 1-ethyl-3-methylimidazolium acetate ([BMIM][OAC]) as the most promising conventional and IL entrainers are screening out through quantum chemistry calculation based on COSMO-SAC model. Secondly, two methods of improving energy efficiency such as differential pressure heat integration and divided-wall column are applied to the CED process. Finally, the resulting six configurations are optimized by simulated annealing algorithm, taking minimum total annual cost (TAC) as goal, and subsequently evaluated from four aspects of TAC, annual capital cost (ACC), annual operating cost (AOC) and CO2 emission. The results show that the new heat-integrated extractive distillation configuration with [BMIM][OAC] as entrainer, known as EDHI-IL is the best solution for ecological efficiency. As compared to the CED process, TAC, ACC, AOC and CO2 emission of this process are reduced by 38.86%, 36.51%, 41.41% and 41.36%, respectively.

Thermodynamic, Economic and Environmental Analyses of Ammonia-Based Mixed Refrigerant for Liquefied Natural Gas Pre-Cooling Cycle

Analyzing the entire liquefaction cycle, using a large temperature span with many degrees of freedom, may not always result in a practical solution. The objective of this paper is to investigate the feasibility of using an environmentally friendly refrigerant compound, ammonia, in the mixed refrigerant (MR) for the liquefied natural gas (LNG) pre-cooling cycle through thermodynamic performance, economic analyses and environmental impact. Fifteen cases studies within three major mixed refrigerants groups of MR-1, MR-2 and MR-3 were developed by adding ammonia to various molar compositions of lighter and heavier hydrocarbons. The thermodynamic analysis shows increasing ammonia’s concentrations in the mixed refrigerant by 10% had the largest enhancement on coefficient of performance (COP) of MR-1 by 0.67 and decreased the specific energy consumption of the pre-cooling cycle by 128 kJ/kg compared to the base case. Economic analyses revealed that the mixed refrigerant MR-1, with ammonia, methane, ethane and propane, benefited the most from higher concentration of ammonia in the mixed refrigerant, which resulted in both lower annual capital and operational costs by $2.52 MM and $3.67 MM, respectively. Lastly, reducing the methane concentration in MR and replacing it with ammonia, decreased the amount of refrigerant leakage through compressor’s seals and reduced the global warming potential index (GWPI) of mixed refrigerant up to 24.3%.

A configuration optimization framework for renewable energy systems integrating with electric‐heating energy storage in an isolated tourist area

AbstractThe renewable energy system integrates various power generating units, heating units, energy conversion devices, and energy storage devices, which is an effective way to improve energy efficiency and realize clean energy utilization. In this paper, a renewable energy system integrating with photovoltaic electric power generation systems, wind‐driven generators, gas‐driven generators, gas‐fired boilers, electric chillers, electric and heating energy storage devices is constructed in an isolated tourist area. Considering the complex multi‐energy flows in renewable energy systems, an energy hub with power and heat is established to concentrate and distribute electric and heating energy flow for balancing energy supply and demand in a CCHP system. Introducing the constraints of renewable energy penetration index and energy supply reliability index, a collaborative optimization framework for system configuration is constructed to minimize annual capital cost, fuel cost, and maintenance cost. The simulation results show that the model and algorithm in this paper are feasible and applicable, and the optimization scheme has good economic benefits and optimal performance, which can promote the consumption of renewable energy and reduce the surplus of electric energy and heat energy.

A novel dual-temperature ejector-compression heat pump cycle - exergetic and economic analyses

• Two dual-temperature air-source heat-pump systems are compared. • Different eco-friendly refrigerants are evaluated in the systems, and their effects are compared. • The DAHP-II outperforms the DAHP-I system significantly in terms of economic and exergy efficiency. • The refrigerant type shows slightly effect on system exergy efficiency, while affects the economic obvious. High-efficiency air source heat pumps are of great importance for energy saving and environmental protection, especially for the cold area in north China. In this study, the thermo-economic performance of the dual-temperature ejector-compression air-source heat-pump (DAHP) cycle, is conducted wherein R1234yf, R290, and R134a are used as refrigerants. Two configurations are examined: DAHP-I (without an ejector, conventional system for comparison) and DAHP-II (enhanced by an ejector). The effects of the principal operating parameters on the system performance, including the exergy destruction ( Ex d_tot ), exergy efficiency ( η ex _sys ) and economic, are investigated, and the two systems are compared. The results indicate that the DAHP-II significantly outperforms the DAHP-I in terms of Ex d_tot , η ex _sys and economic index, and the R290 is the most suitable refrigerant applied for the DAHP-II system. Compared with DAHP-I, the Ex d_tot for DAHP-II is reduced by 24.0%–54.8%. For DAHP-II, although the refrigerant type affects Ex d_tot and η ex _sys slightly, while the effect on economic is noticeable. Comparing with R1234yf, the system using the R134a and R290 as the working fluid, the total annual capital cost rate ( C ˙ t o t ) can be reduced by 6.2% and 11.0% respectively. Besides, the DAHP-II outperforms the DAHP-I system significantly with the R134a, R290 and R1234yf as refrigerant in terms of economic. The relative decrease ratio in total annual capital cost rate ( C ˙ t o t ) are 21.6%, 13.5% and 24.0% respectively. This study provides a basis for the application of DAHP system.

Techno-economic assessment of solar thermal and alternative energy integration in supercritical water gasification of microalgae

Supercritical water gasification (SCWG) as a pathway for biofuel production, presents an attractive option for processing assorted biomass feedstock due to its ability to process wet feedstock with higher hydrogen yield. However, SCWG requires significant thermal energy input to reach its high operating temperatures leading to overall process inefficiency. Although previous studies have found microalgae-based SCWG process to be uneconomic, investigations on the choice of energy integration and process-energy configuration options to make the process economically viable has not been considered. As such, this work focused on the economic viability of integrating energy alternatives such as solar thermal options (solar tower and parabolic trough collector), natural gas (NG), and electricity in a microalgae-based SCWG fuel plant. The syngas fuel plant of 19,000 t/y was modelled in Aspen Plus using nine different energy configurations of solar and conventional energy. The economic results of the energy integrations delivered minimum fuel selling prices (MFSPs) of 52–73 AUD/GJ. The most economic options for supplying energy to the plant were shown to be NG alone or using solar parabolic trough combined with supplementary NG to further boost the feedstock temperature in the SCWG reactor. The annual variable operational cost was found to contribute 77% towards MFSP and was highly dependent on the price of microalgae and hydrogen. At higher capital cost, MFSP was affected by the discount rate and the cost of energy which are susceptible to the cost of solar energy infrastructure or price of conventional energy. Sensitivity and switch value analysis showed that natural gas and parabolic trough-natural gas energy integrations could deliver lower MFSP at considerable reductions in annual operational cost and the solar energy components of the annual capital cost. The choice of energy option and process-energy configuration was demonstrated to play a significant role in making SCWG process economical. While solar tower technology may not be viable for high temperature process plant energy utilization, combining solar parabolic trough with natural gas was determined to be a more promising outcome for lower energy cost. Higher prices of conventional energy, carbon tax credit and government policies could make the SCWG technology with algae feedstock economically viable and 100% renewable in the future.

Techno-economic and environmental assessment of rice husk in comparison to coal and furnace oil as a boiler fuel

The aim of this study was to analyze the cost and technological benefits of rice husk as boiler fuel by comparing it with primary boiler fuel like coal and furnace oil. Rice husk is a major agricultural waste that has the potential to produce clean energy. This study was based on the collection of data on boiler site, and measurements of stack emissions. Through the collected data, the annual fuel, labor, operational and maintenance costs, as well as ash disposal, chemical costs, payback period, the lifetime of the plant, particle control methods, and efficiency of the boiler were determined. The results show that the annual capital cost of rice husk, coal fire, and furnace oil boiler was is USD 1.613, 1.663, and 1.5787 million, respectively. From the analysis, it was determined that payback periods of rice husk, coal, and furnace oil boiler were 6, 36, and 60 months, respectively. The lifetime of rice husk coal-fired, and furnace oil boiler was 5, 25, and 15 years, respectively. Stack emissions for oxygen were 12.40%, CO2 was found to be 4.55%, and CO was determined to be 1345.1 mg/Nm3 for rice husk boiler. It was also ascertained that the stack emissions of rice husk boiler were lower than coal-fired and furnace oil boilers. This study proved that rice husk can be adopted as the primary boiler fuel, which will not only reduce the capital cost and payback period for the plant but will also help alleviate the environmental impacts caused by conventional boiler fuels.

Heat integration of two-stage autothermal thermophilic aerobic digestion system for reducing the impact of uncertainty

The operation of Autothermal Thermophilic Aerobic Digestion (ATAD) wastewater treatment systems is subjected to daily uncertainties regarding the parameters of the inlet streams, which lead to prolongation of the process and increase the energy consumption. This, together with the heat loss in the environment from the product tank, makes the ATAD system energy inefficient. Heat integration plays an important role in improving the sustainability of ATAD systems. In this study an approach for optimal redesign of heat integrated two-stage ATAD system operating under uncertainties is presented. It includes a two-stage stochastic optimization model for heat integration with an optimization criterion - the annual capital cost for redesign of the heat integrated system and its operating costs. Artificial Neural Network (ANN) models of the bioreactors are used for simulation of the system operation. They are combined with the heat integration model for the obtained with the stochastic approach values of design parameters of the heat integration equipment. The simulation results show a thermal shock reduction of 5–6 °C, an increase of the inlet sludge temperature of 8–10 °C, achievement of close to normal operating temperatures in the ATAD system and reduction of solids in both bioreactors by about 2 wt%.