Energy saving opportunities in heat integrated beverage plant retrofit

This paper presents practical applications of mathematical programming for energy integration in a large beverage plant. The opportunities of heat integration between batch operations were analysed by a mixed integer linear programming (MILP) model, which was slightly modified by considering specific industrial circumstances. The feasibility of combined electricity, heating and cooling production was studied using a simplified MILP model, developed for the selection of an optimal polygeneration system. The superstructure includes cogeneration systems with different prime movers (steam turbine and gas turbine), and a trigeneration system with a back-pressure steam turbine. The proposed heat integration scheme and the selected cogeneration system may improve a company’s economic performance and reduce its environmental impact.     

Sequential optimization of a polygeneration plant

This paper presents a two-steps optimization procedure of a polygeneration unit. The unit simultaneously provides power, heat, cooling and fresh water to a Spanish tourist resort (450 rooms). The first step consist on the synthesis and design of the polygeneration scheme: a “superstructure” was constructed to allow the selection of the appropriate choice and size of the plant components, from both economic and environmental considerations. At that first step, only monthly averaged requirements are considered. The second step includes hourly data and analysis as well as energy storage systems. A detailed modelling of pre-selected devices is then required to also fulfil economic and environmental constraints. As a result, a better performance is obtained compared to the first step. Thus, the two-steps procedure explained here permits the complete design and operation of a decentralized plant producing simultaneously energy (power, heat and cooling) but also desalted water (that is, trigeneration + desalination). Remarkable benefits for the analyzed case study are found: a Net Present Value of almost 300,000 €, a primary energy saving ratio of about 18% and more than 850 ton per year of avoided CO₂ emissions.     

Optimization of the design of polygeneration systems for the residential sector under different self-consumption regulations

Polygeneration systems enable natural resources to be exploited efficiently, decreasing CO₂ emissions and achieving economic savings relative to the conventional separate production. However, their economic feasibility depends on the legal framework. Preliminary design of polygeneration systems for the residential sector based on the last Spanish self-consumption regulations RD 900/2015 and RD 244/2019 was carried out in Zaragoza, Spain. Both regulations were applied to individual and collective installations. Several technologies, appropriate for the energy supply to residential buildings, for example, photovoltaics, wind turbines, solar thermal collectors, microcogeneration engines, heat pump, gas boiler, absorption chiller, and thermal and electric energy storage were considered candidate technologies for the polygeneration system. A mixed integer linear programming model was developed to minimize the total annual cost of polygeneration systems. Scenarios with and without electricity sale were considered. CO₂ emissions were also calculated to estimate the environmental impact. Results show that RD 900/2015 discourages the investment in self-consumption systems whereas the RD 244/2019 encourages them, especially in renewable energy technologies. Moreover, in economic terms, it is more profitable to invest in collective self-consumption installations over individual installations. However, this does not necessarily represent a significant reduction of CO₂ emissions with respect to individual installations since the natural gas consumption tends to increase as its unit price decreases because of the increase of its consumption level. Thus, more appropriate pricing of natural gas in residential sector, in which its cost would not be reduced when increasing its consumption, would be required to achieve significant CO₂ emissions reduction. In all cases, the photovoltaic panels (PV) are competitive and profitable without subsidies in self-consumption schemes and the reversible heat pump (HP) played an important role for the CO₂ emissions reduction. In a horizon to achieve zero CO₂ emissions, the net metering scheme could be an interesting and profitable alternative to be considered.     

Operational optimisation of a complex trigeneration system connected to a district heating and cooling network

The combined production of electricity, heat and cold by polygeneration systems ensures maximum utilization of resources by reducing emissions and energy losses during distribution. Polygeneration systems are highly integrated systems characterized by the simultaneously production of different services (electricity, heating, cooling) by means of several technologies using fossil and renewable fuels that operates together to obtain a higher efficiency than that of an equivalent conventional system. The high number of distribution technologies available to produce electricity, heating and cooling and the different levels of integration make it difficult to select of the optimal configuration. Moreover, the high variability in the energy demand renders difficult the selection of the optimal operational strategy. Optimization methodologies are usually applied for the selection of the optimal configuration and operation of energy supply systems. This paper presents a scenario analysis using optimization models to perform an economic, energetic and environmental assessment of a new polygeneration system in Cerdanyola del Vallès (Spain) in the framework of the Polycity project of the European Concerto Program. This polygeneration system comprise high-efficiency natural gas cogeneration engines with thermal cooling facilities and it will provide electricity, heating and cooling for a new area in growth known as Alba park including a Synchrotron Light Facility and a Science and Technological park through a district heating and cooling network of four tubes. The results of the scenario analysis show that the polygeneration plant is an efficient way to reduce the primary energy consumption and CO₂ emissions (up to 24%).     

Thermochemical production of liquid fuels from biomass: Thermo-economic modeling,process design and process integration analysis

A detailed thermo-economic model combining thermodynamics with economic analysis and considering different technological alternatives for the thermochemical production of liquid fuels from lignocellulosic biomass is presented. Energetic and economic models for the production of Fischer–Tropsch fuel (FT), methanol (MeOH) and dimethyl ether (DME) by means of biomass drying with steam or flue gas, directly or indirectly heated fluidized bed or entrained flow gasification, hot or cold gas cleaning, fuel synthesis and upgrading are reviewed and developed. The process is integrated and the optimal utility system is computed. The competitiveness of the different process options is compared systematically with regard to energetic, economic and environmental considerations. At several examples, it is highlighted that process integration is a key element that allows for considerably increasing the performance by optimal utility integration and energy conversion. The performance computations of some exemplary technology scenarios of integrated plants yield overall energy efficiencies of 59.8% (crude FT-fuel), 52.5% (MeOH) and 53.5% (DME), and production costs of 89, 128 and 113 € MWh^?1 on fuel basis. The applied process design approach allows to evaluate the economic competitiveness compared to fossil fuels, to study the influence of the biomass and electricity price and to project for different plant capacities. Process integration reveals in particular potential energy savings and waste heat valorization. Based on this work, the most promising options for the polygeneration of fuel, power and heat will be determined in a future thermo-economic optimization.     

Optimal design of inter-plant waste energy integration

In this paper, a new superstructure for heat integration of an eco-industrial park is proposed. Intra and inter-plant heat exchange for the process streams is allowed. For a proper reuse of the waste heat at low temperature, a set of organic Rankine cycles (ORCs) can be integrated inside the eco-industrial park. This way, the proposed superstructure allows proper heat integration to reduce the use of external cooling and heating utilities as well as the consumption of external electric energy. The proposed superstructure is modeled through a mathematical programming formulation where the objective function considers the simultaneous minimization of the operating and capital costs for the units involved in the system as well the possible revenues from the sales of electricity. The model is formulated in such a way that avoids numerical complications during its solution. Results from the application of the proposed approach show that the interplant-integration offers significant savings compared to the traditional single-plant integration with and without considering ORCs.     

Techno-economics of novel refueling stations based on ammonia-to-hydrogen route and SOFC technology

This paper presents the economic assessment of novel refueling stations, in which through advanced and high efficiency technologies, the polygeneration of more energy services like hydrogen, electricity and heat is carried out on-site.The architecture of these polygeneration plants is realized with a modular structure, organized in more sections.The primary energy source is ammonia that represents an interesting fuel for producing more energy streams. The ammonia feeds directly the SOFC that is able to co-generate simultaneously electricity and hydrogen by coupling a high efficiency energy system with hydrogen chemical storage.Two system configurations have been proposed considering different design concepts: in the first case (Concept_1) the plant is sized for producing 100 kg/day of hydrogen and the power section is sized also for self-sustaining the plant electric power consumption, while in the second one (Concept_2) the plant is sized for producing 100 kg/day of hydrogen and the power section is sized for self-sustaining the plant electric power consumption and for generating 50 kW for the DC fast charging.The economic analysis has been carried out in the current and target scenarios, by evaluating, the levelized cost of hydrogen (LCOH), the levelized cost of electricity (LCOE), the Profitability Index (PI), Internal rate of Return (IRR) and the Discounted Payback Period (DPP).Results have highlighted that the values of the LCOH, for the proposed configurations and economic scenarios, are in the range 6–10 €/kg and the values of the LCOE range from 0.447 €/kWh to 0.242 €/kWh.In terms of PI and IRR, the best performance is achieved in the Concept_1 for the current scenario (1.89 and 8.0%, respectively). On the contrary, in the target scenario, thanks to a drastic costs reduction the co-production of hydrogen and electricity as useful outputs, becomes the best choice from all economic indexes and parameters considered.     

Design of a hybrid polygeneration system with solar collectors and a Solid Oxide Fuel Cell: Dynamic simulation and economic assessment

Solid Oxide Fuel Cells (SOFC) are very promising energy conversion devices, producing electricity and heat from a fuel directly via electrochemical reactions. The electrical efficiency of SOFCs is particularly high, so that such systems are very attractive for integration in complex polygeneration systems. In this paper, the integration of SOFC systems with solar thermal collector is investigated seeking to design a novel polygeneration system producing: electricity, space heating and cooling and domestic hot water, for a university building located in Naples (Italy), assumed as case study. The polygeneration system is based on the following main components: concentrating parabolic through solar collectors, a double-stage LiBr-H₂O absorption chiller and an ambient pressure SOFC fuel cell. The system also includes a number of additional components required for the balance of plant, such as: storage tanks, heat exchangers, pumps, controllers, cooling tower, etc. The SOFC operates at full load, producing electric energy that is in part self-consumed for powering building lights and equipments, and in part is used for operating the system itself; the electric energy in excess is eventually released to the grid and sold to the public Company that operates the grid itself. The system was designed and then simulated by means of a zero-dimensional transient simulation model, developed using the TRNSYS software; the investigation of the dynamic behavior of the building is also included. The results of the case study were analyzed for different time bases, from both energetic and economic points of view. Finally, a thermoeconomic optimization is also presented aiming at determining the optimal set of system design parameters. The economic results show that the system under investigation may be profitable, provided that it is properly funded. However, the overall energetic and economic results are more encouraging than those claimed for other similar polygeneration systems in the recent literature.     

Improvement of the cogeneration plant economy by using heat accumulator

The optimisation code ACOM (Advanced Cogeneration Optimisation Model) is used with purpose of assessing influence of the district heat accumulator on the Elektrana-Toplana (EL-TO) Zagreb cogeneration plant economic performance. The plant supplies hot water for district heating, steam for industry and electric power. It is possible to achieve economic benefits by charging the accumulator during the day time, when the electricity price is high, and by releasing district heat during cheap night hours, when other parts of equipment may be shut down. The consequences of this strategy are the decrease of total annual electricity production and fuel consumption, whereby the savings of some 1.8 mil Euro/a are achieved with the reduction of CO₂ emission by about 23,000 t/a or 6.4% and SO_x by about 200 t/a or 16.9%.     

Technologies to recover exhaust heat from internal combustion engines

The focus of this study is to review the latest developments and technologies on waste heat recovery of exhaust gas from internal combustion engines (ICE). These include thermoelectric generators (TEG), organic Rankine cycle (ORC), six-stroke cycle IC engine and new developments on turbocharger technology. Furthermore, the study looked into the potential energy savings and performances of those technologies. The current worldwide trend of increasing energy demand in transportation sector are one of the many segments that is responsible for the growing share of fossil fuel usage and indirectly contribute to the release of harmful greenhouse gas (GHG) emissions. It is hoped that with the latest findings on exhaust heat recovery to increase the efficiency of ICEs, world energy demand on the depleting fossil fuel reserves would be reduced and hence the impact of global warming due to the GHG emissions would fade away.     

Combined hydrogen,heat and electricity generation via biogas reforming: Energy and economic assessments

Polygeneration systems, designed for providing multiple energy services like hydrogen, heat and electricity, represent a possible solution for the transition to sustainable low-carbon energy systems, thanks to a substantial increase in the overall efficiency. A further step to reach zero-carbon energy systems can be done by using renewables as primary sources.In this study a biogas-based polygeneration system for the combined hydrogen, heat and electricity production is designed and analyzed from energy and economic points of view.The system consists of four sections: a biogas processing unit consisting in an autothermal reactor and a water gas shift reactor, an SOFC power unit, a hydrogen separation unit and a hydrogen compression/storage unit. The syngas generated in the autothermal reforming reactor is split in two fluxes: the first one is sent to the SOFC power unit for generating electricity and heat, the second one is sent to the water gas shift reactor to increase the hydrogen content. The hydrogen rich gas exiting the shifter, purified in the hydrogen separation unit (hydrogen quality is equal to 99.995%), is then compressed up to 820 bars and stored.The system behavior and the energy performances have been investigated by using the numerical simulation based on thermo-electrochemical models. Four operating conditions, related to different SOFC loads (from 30% to 100%), have been analyzed. The evaluated overall efficiencies range from 68.5% to 72.3% and the energy saving, calculated with respect to the separate production of hydrogen, heat and electricity, ranges from about 8% to 26%.The economic assessment, carried out by estimating the total capital investment and the plant profitability, has been performed by analyzing different management strategies (Base Load, Peaker, Ancillary Service and Mobility) and accounting for different technological development levels and market scenarios. Results show that the hydrogen production is the main contributor to the system economic sustainability thanks to the highest prices of hydrogen with respect to the electricity ones.     

Multi-objective,multi-period optimization of biomass conversion technologies using evolutionary algorithms and mixed integer linear programming (MILP)

The design and operation of energy systems are key issues for matching energy supply and demand. A systematic procedure, including process design and energy integration techniques for sizing and operation optimization of poly-generation technologies is presented in this paper. The integration of biomass resources as well as a simultaneous multi-objective and multi-period optimization, are the novelty of this work. Considering all these concepts in an optimization model makes it difficult to solve. The decomposition approach is used to deal with this complexity.Several options for integrating biomass in the energy system, namely back pressure steam turbines, biomass rankine cycles (BRC), biomass integrated gasification gas engines (BIGGE), biomass integrated gasification gas turbines, production of synthetic natural gas (SNG) and biomass integrated gasification combined cycles (BIGCC), are considered in this paper. The goal is to simultaneously minimize costs and CO₂ emission using multi-objective evolutionary algorithms (EMOO) and Mixed Integer Linear Programming (MILP).Finally the proposed model is demonstrated by means of a case study. The results show that the simultaneous production of electricity and heat with biomass and natural gas are reliable upon the established assumptions. Furthermore, higher primary energy savings and CO₂ emission reduction, 40%, are obtained through the gradual increase of renewable energy sources as opposed to natural gas usage. However, higher economic profitability, 52%, is achieved with natural gas-based technologies.     

Dynamic Simulation of a Novel Solar Polygeneration System for Heat,Power and Fresh Water Production based on Solar Thermal Power Tower Plant

A novel solar polygeneration system for heat, power and fresh water production with absorption heat pump(AHP) and humidification-dehumidification(HDH) desalination system was proposed for high-efficiency utilization of solar energy. A case study of the proposed system was investigated based on 1 MW solar thermal power(STP) tower plant located in Beijing. Depending on mathematical modeling of the proposed system, corresponding modules were developed in TRNSYS. Meanwhile, control and operation str...     

Polygeneration and efficient use of natural resources

The consumption of natural resources has been increasing continuously during recent decades, due to the growing demand caused by both the economic and the demographic rise of global population. Environmental overloads that endanger the survival of our civilization and the sustainability of current life support systems are caused by the increased consumption of natural resources—particularly water and energy—which are essential for life and for the socio-economic development of societies. While not yet well utilized, process integration and polygeneration are promising tools which reach the double objective of increasing the efficiency of natural resources, and also minimizing the environmental impact. This paper discusses the concepts of polygeneration and energy integration and various examples of polygeneration systems: (i) sugar and energy production in a sugarcane factory; (ii) district heating and cooling with natural gas cogeneration engines and (iii) combined production of water and energy. It is clearly evident that polygeneration systems which include appropriate process integration significantly increase the efficient use of natural resources.     

Alternative technologies for US residential water heating : Energy savings and economic benefits

This article evaluates the energy savings and direct economic benefits of introducing heat pump and solar water heaters to the US residential market and the effects of a tax credit for solar installations. Energy savings are estimated for ten regions of the USA, as well as for the country as a whole, over the period 1977–2000. Changes in annual fuel bills and capital costs for water heaters are also computed. The results suggest that heat pump water heaters are likely to offer much larger benefits than solar heaters, even with tax credits. This is because heat pumps provide the same electricity savings (about 50%), but at a much lower capital cost.     

Biomass gasification in district heating systems – The effect of economic energy policies

Biomass gasification is considered a key technology in reaching targets for renewable energy and CO₂ emissions reduction. This study evaluates policy instruments affecting the profitability of biomass gasification applications integrated in a Swedish district heating (DH) system for the medium-term future (around year 2025). Two polygeneration applications based on gasification technology are considered in this paper: (1) a biorefinery plant co-producing synthetic natural gas (SNG) and district heat; (2) a combined heat and power (CHP) plant using integrated gasification combined cycle technology. Using an optimisation model we identify the levels of policy support, here assumed to be in the form of tradable certificates, required to make biofuel production competitive to biomass based electricity generation under various energy market conditions. Similarly, the tradable green electricity certificate levels necessary to make gasification based electricity generation competitive to conventional steam cycle technology, are identified. The results show that in order for investment in the SNG biorefinery to be competitive to investment in electricity production in the DH system, biofuel certificates in the range of 24–42 EUR/MWh are needed. Electricity certificates are not a prerequisite for investment in gasification based CHP to be competitive to investment in conventional steam cycle CHP, given sufficiently high electricity prices. While the required biofuel policy support is relatively insensitive to variations in capital cost, the required electricity certificates show high sensitivity to variations in investment costs. It is concluded that the large capital commitment and strong dependency on policy instruments makes it necessary that DH suppliers believe in the long-sightedness of future support policies, in order for investments in large-scale biomass gasification in DH systems to be realised.     

Dynamic multi-objective optimization applied to a solar-geothermal multi-generation system for hydrogen production,desalination, and energy storage

The design of optimal energy systems is vital to achieving global environmental and economic targets. In the design of solar-geothermal multi-generation systems, most previous investigations have relied on the static multi-objective optimization approach (SMOA), which may leave considerable room for improvement under certain conditions. In this numerical study, the optimal condition at which to operate a solar-geothermal multi-generation system – which can simultaneously produce hydrogen, fresh water, electricity, and heat, along with storing energy ? is determined via a dynamic multi-objective optimization approach (DMOA). Optimization is performed using a combination of NSGA-II and TOPSIS, and the results are benchmarked against those of SMOA. The decision variables include the solar area, geothermal water extraction mass flow, and hydrogen storage pressure. The objective functions include the production of electricity, heat, hydrogen, and fresh water, along with the exergy and energy efficiencies and the payback period. It is found that when compared with SMOA, DMOA can significantly improve all the objective functions. The annual production of electricity, heat, hydrogen, and fresh water increases by 14.4, 16.1, 13.5, and 14.3%, respectively, while the average annual exergy and energy efficiencies increase by 5.2 and 3.0%, respectively. The use of DMOA also reduces the payback period from 5.56 to 4.43 years, with a 4.4% reduction in hydrogen storage pressure. This shows that compared with a static approach such as SMOA, DMOA can improve the exergy and energy efficiencies, economic viability, and safety of a solar-geothermal multi-generation system.     

Technical assessment of LNG based polygeneration systems for non-interconnected island cases using SOFC

Liquefied Natural Gas (LNG) is one of the most promising fuels with high calorific value and low specific GHG emissions that offers several advantages as an energy carrier for power generation. In this paper, a novel polygeneration concept based on LNG fired plant for power, cooling and drinking water production in island systems is presented. Two Solid Oxide Fuel Cell based energy systems (one simple SOFC and another hybrid concept of SOFC combined with GT) are modelled in Aspen Plus and compared with two conventional combustion based technologies (internal combustion engine and Gas Turbine Combined Cycle) in terms of overall efficiency. Furthermore, a Low Temperature Multi-Effect Distillation (LT-MED) plant was modelled and coupled with the energy systems to evaluate the waste heat recovery potential for desalinated water production. Moreover, three concepts for cold recovery from the LNG regasification plant were presented and modelled. Process simulations results revealed that the hybrid SOFC-GT plant is the best solution in terms of energy efficiency and the heat recovery of the exhaust gas in a LT-MED unit is a promising option for drinking water production with almost no energy cost. Last, from exergetic point of view, the cryogenic energy storage (CES) via the production of liquid air was evaluated as the best option for waste cold utilization during LNG regasification.     

System study on natural gas-based polygeneration system of DME and electricity

An innovative system for the polygeneration of dimethyl ether (DME) and electricity was proposed in this paper. The system uses natural gas as the raw material. Polygeneration is sequential, with one-step and once-through DME synthesis. Syngas is made to react to synthesize DME first, and then the residual syngas is sent to the power generation unit as fuel. The exergy analysis from the view of cascade utilization was executed for individual generation and for polygeneration. The analysis results showed that both chemical energy and thermal energy in polygeneration were effectively utilized, and both chemical exergy destruction and thermal exergy destruction in polygeneration were decreased. The cause of the decrease in exergy destruction was revealed. The analysis showed that hydrogen-rich (natural gas-based) polygeneration was as desirable as carbon-rich (coal-based) polygeneration. The energy saving ratio of polygeneration was about 10.2%, which demonstrated that high efficiency natural gas-based polygeneration is attainable, and the cascade utilizations of both chemical energy and thermal energy are key contributors to the improvement of performance. Copyright © 2007 John Wiley & Sons, Ltd.     

Paths combination for HENs retrofit

With the significant increase in fuel price, energy conservation projects should be reviewed and analyzed properly. Retrofit of heat exchanger networks (HENs) is among the common projects to reduce the plant operational cost. This paper introduced a new procedure using the path analysis approach for HEN retrofit. The developed procedure attempts at generating options for retrofit solution. These options are created by combining the available utility paths in HEN systematically. Instead of relying on a single path, the heat load could be shifted from HEN utilities using a set of paths simultaneously. To ensure feasible heat transfer between the hot and cold streams throughout, Exchanger Minimum Approach Temperature (EMAT) is maintained while shifting the heat load. The available exchangers’ pressure drop is considered in calculating the heat transfer coefficients. HEN devices are subjected to some additional area without any topological modification. In addition, the investment of such area could be recovered in a short span of time. The calculation of this approach encountered some iteration which has been overcome by mathematical programming. Demonstration example showed some options to be reasonable retrofit solutions. Energy savings ranged between $150 K and $450 K per year with payback time of less than 2 years were possible.