Cogeneration Energy Systems Research Articles

Economic Power and Heat Dispatch in Cogeneration Energy Systems Using Manta Ray Foraging Optimizer

Economic Power and Heat Dispatch (EPHD) in Cogeneration Energy Systems (CES) is considered as one of non linear hard optimization problems. It is optimally scheduling the of heat and power generation units. It aims at minimizing the total fuel cost (TFC) of cogeneration units considering their operational limits. In this paper, a Manta Ray Foraging Optimization Algorithm (MRFOA), which is a recent meta-heuristic optimization technique, is developed to solve the EPHD problem in CES with additional non-convex valve point effects. The simplicity and effectiveness motivate the attempt of employing the MRFOA to minimize the TFC for power units only, cogeneration units and heat units only. The equality constraints by supplying the total loading of power and heat is are maintained. In addition, the inequality operational bounds of power only and heat only units are satisfied while the dynamic operational bounds of cogeneration units are not jeopardized. Three test systems are analyzed to estimate the MRFOA performance for solving the EPHD problem in CES, which involve 5 units, 7 units, and 48 units. It is worth noticing that the optimal solutions demonstrate MRFOA capability, feasibility and efficiency of better solutions obtained in terms of TFC compared with other optimization methods and the ability of implementation of MRFOA on EPHD issue in CES..

Predictive Protective Control for Flexible Energy System

The paper deals with the predictive control applied to flexible cogeneration energy system (FES). The FES was designed and developed by the VITKOVICE POWER ENGINEERING joint-stock company and represents a new solution of decentralized cogeneration energy sources. In FES, the heating medium is flue gas generated by combustion of a solid fuel. The heated medium is power gas, which is a gas mixture of air and water steam. Power gas is superheated in the main heat exchanger and led to gas turbines. To protect the main heat exchanger against damage by overheating, the novel predictive protective control based on the mathematical model of exchanger was developed. The paper describes the principle, the design and simulation of the predictive protective method applied to main heat exchanger of FES.

A rolling-horizon optimization algorithm for the long term operational scheduling of cogeneration systems

A rolling-horizon algorithm is proposed for optimizing the operating schedule of a given cogeneration energy system while taking into account time-variable loads, tariffs and ambient conditions, as well as yearly fiscal incentives. The presented algorithm is based on the Mixed Integer Linear Programming (MILP) model developed by the authors for optimizing the daily schedule of cogeneration systems and networks of heat and power plants.First the MILP model is extended to optimize the weekly operation schedule to better manage the heat-cold storage systems. However, in order to account for the European qualification framework for high efficiency cogeneration, as well as for country-specific incentive policies, it is necessary to consider average yearly-basis energy saving indexes, thus requiring to tackle the problem for the whole year. Since the extension of the MILP model from one day to seven days already increases remarkably the computational requirements, a simple application of the same optimization approach to a whole year would be practically unfeasible; therefore, this work proposes a rolling-horizon algorithm in which a sequence of weekly MILP submodels is solved, while considering production and consumption estimates based on demand profiles from historical data. The results obtained for a real-world test case are reported and discussed.

IDENTYFIKACJA KLUCZOWYCH ATUTÓW I SŁABOŚCI 19 SPALANIA BIOMASY ORAZ WĘGLA KAMIENNEGO 20 W SKOJARZONEJ GOSPODARCE ENERGETYCZNEJ

IDENTYFIKACJA KLUCZOWYCH ATUTÓW I SŁABOŚCI 19 SPALANIA BIOMASY ORAZ WĘGLA KAMIENNEGO 20 W SKOJARZONEJ GOSPODARCE ENERGETYCZNEJ

The Temperature Time Responses of the Heat Exchanger Equipped by the Protective Control

Abstract: VITKOVICE POWER ENGINEERING joint-stock company designs and constructs the decentralized flexible energy cogeneration system (FES) with combined Brayton - Rankine cycle which represents a new solution of decentralized cogeneration energy sources. In FES, the heating medium is flue gas generated by combustion of a solid fuel. The heated medium is power gas, which is a gas mixture of air and water steam. Power gas is superheated in the main heat exchanger (MHE) and is led to the gas turbine that drives the asynchronous generator. In this paper, the principle of FES is briefly described. The protective control which prevents the damage of MHE by overheating is discussed. The dynamics of the MHE with respect to dynamics of protective control is presented.

Energetic analysis of a novel vehicle power and cooling/heating cogeneration energy system using cascade cycles

This study proposes and investigates a novel VCES (Vehicle power and cooling/heating Cogeneration Energy System), including a topping vehicle engine subsystem, and a bottoming waste-heat recovery subsystem which uses the zeotropic working fluid. The various grade exhaust and coolant waste-heat of the topping subsystem are cascade recovered by the bottoming subsystem, and slide-temperature thermal match in waste heat recovery heat exchangers and the condenser is considered also, obtaining power output and cooling/heating capacity. Based on the experimental data from an actual vehicle's energy demands and its waste-heat characteristics, the proposed VCES (vehicle cogeneration energy system) model is built and verified. Using ammonia-water as working fluid of the bottoming subsystem, integrated thermodynamic performances of the VCES are discussed through introducing three variables: an ambient temperature, the vehicle's velocity and the number of seated occupants. The influence of above three variables on the proposed VCES′ overall thermodynamic performance is analyzed by comparing it to a conventional VCES, and suitable operation conditions are recommended under cooling and heating conditions.

Concentration photovoltaic–thermal energy co-generation system using nanofluids for cooling and heating

New designs of dual concentration photovoltaic–thermal (CPV/T) systems can provide both electrical and thermal energy, while reducing solar cell material usage via optical techniques. The overall system efficiency can be improved by using advanced dual-purpose liquids with enhanced heat transfer characteristics, such as nanofluids. In this paper the use of nanofluids, i.e., dilute nanoparticle suspensions in liquids, are considered for improved efficiency of a CPV/T system for the first time. Specifically, a 2-D model coupling thermal analysis and computational fluid dynamics simulations has been developed to calculate efficiencies of individual subsystems as well as the overall system. A new thermal conductivity model for nanofluids, which was validated with experimental data sets, was employed. The electrical and thermal performances of the system were evaluated for different climatic conditions. The results show that using nanofluids improves the electrical and total efficiencies of the system, especially when using silicon solar cells. For example, if the nanofluid outlet temperature of the solar cell is set to 62°C via a controlled flow rate, the system overall efficiency could reach 70% with electrical and thermal contributions amounting to 11% and 59%, respectively. In summary, a nanofluid-based system is preferable to water-based systems in the long run.

Selected Problems of Cogeneration Energy Systems Designing, Fueled with Landfill Biogas

The article discusses the impact of the quality of biogas fuel for operation of generating sets with internal combustion engines. There are presented selected investigation results of landfill biogas fueled gensets operation. The article includes also discussion of the possibility of increasing the efficiency of biogas fuelled cogeneration systems. It also presents guidelines for the optimal design of landfill biogas fueled engines, ensuring their reliability.

Institutional scale operational symbiosis of photovoltaic and cogeneration energy systems

Due to the negative environmental effects of fossil fuel combustion, there is a growing interest in both improved efficiency in energy management and a large-scale transition to renewable energy systems. Using both of these strategies, a large institutional-scale hybrid energy system is proposed here, which incorporates both solar photovoltaic energy conversion to supply renewable energy and cogeneration to improve efficiency. In this case, the photovoltaic reduces the run time for the cogeneration to meet load, particularly in peaking air conditioning times. In turn, however, the cogeneration system is used to provide power back up for the photovoltaic during the night and adverse weather conditions. To illustrate the operational symbiosis between these two technical systems, this study provides a case study of a hybrid photovoltaic and cogeration system for the Taleghani hospital in Tehran. Three design scenarios using only existing technologies for such a hybrid system are considered here:1) single cogeneration + photovoltaic, 2) double cogeneration + photovoltaic, 3) single cogeneration + photovoltaic + storage. Numerical simulations for photovoltaic and cogeneration performance both before and after incorporating improved thermal energy management and high efficiency lighting were considered. The results show that the total amount of natural gas required to provide for the hospitals needs could be lowered from the current status by 55 % for scenario 1 and 62 % for both scenarios 2 and 3, respectively. This significant improvement in natural gas consumption illustrates the potential of hybridizing solar photovoltaic systems and cogeneration systems on a large scale.

A multisyringe sequential injection method for monitoring water in the energy cogeneration system of a municipal waste incinerator

Leading-edge urban solid waste ashing plants use burning heat energy to obtain electrical power. Water fed to their boilers for conversion into steam should be highly pure in order to minimize corrosion, scaling and similar phenomena, which can lead to malfunctioning and a reduced useful life but can be avoided by proper management and control of the water supply. In this work, we developed a multiparameter monitor based on multisyringe sequential injection for the sequential determination of up to eight important parameters, namely: pH, specific and acid conductivity, hydrazine, ammonium, phosphate, silicate and total iron. Acid conductivity was determined by passing the sample through a cation-exchange resin in order to retain ammonium ion and release protons. This parameter was deemed the most accurate indicator of dissolved solids in boiler water. Chemical parameters were determined spectrophotometrically: hydrazine by reaction with p-dimethylaminobenzaldehyde, ammonium by the modified Berthelot reaction, iron with o-phenanthroline, and phosphate and silica by formation of a molybdoheteropoly blue dye in the presence of ascorbic acid as reductant. Use of the optimum chemical and physical operating conditions provided 3s blank detection limits of 0.01 mg l −1 N 2H 4, 0.13 mg l −1 NH 4 +, 0.04 mg l −1 Fe, 0.03 mg l −1 SiO 2 and 0.05 mg l −1 PO 4 3−, and relative standard deviations not greater than 2.5%. The methods integrated in the proposed monitor were successfully applied to real samples from the water–steam cycle at the Son Reus ashing plant in Palma de Mallorca (Spain).

BETTER SELL BAGASSE THAN SURPLUS ELECTRICITY?

Over the past decade, electricity consumption in Brazil grew faster than generation capacity. This situation obliged an urgent return to investment in the sector, and revitalization of the restructuring in the national electricity sector. In these circumstances, the use of renewable energy sources, such the biomass, became an option for decentralized electricity generation. Sugar cane bagasse is one of the most important biomasss residues for electricity generation. The present publication analyses an investment made in the expansion of the energy cogeneration system in an industry that produces sugar and alcohol, from sugar cane, considering the seasonal bagasse price, energy generation costs and a 10 year period. With the new cogeneration system the factory became self-sufficient in energy, with a saleable surplus of 21,240 MWh, at an average power of 4,000 kW. However, an economic analysis indicated that the best option would have been to maintain the original system and sell surplus bagasse at R$ 26.00/t.

99/01718 Energy cogeneration systems and energy management strategy : Benelmir, R. and Feidt, M. Energy Convers. Manage., 1998, 39, (16–18), 1791–1802

99/01718 Energy cogeneration systems and energy management strategy : Benelmir, R. and Feidt, M. Energy Convers. Manage., 1998, 39, (16–18), 1791–1802

Energy cogeneration systems and energy management strategy

An energy cogeneration system allows the optimisation of the use of energy sources through a maximal exploitation of energy products. The investment is higher than for conventional energy systems but the pay-back time is shorter and the benefit is even higher beyond this time. Moreover, in addition to these economic advantages, energy cogeneration systems allow the preservation of the environment due to a rational use of energy sources.The assessment of a thermoeconomic balance, on one hand for a cogeneration system producing heat and electrical power, and on the other hand for a conventional energy system producing the same amount of heat using the same type of energy resource, leads to an expression for the minimum cost of the produced electrical power which depends on the cogeneration system’s electricity production efficiency and on the global efficiencies of the cogeneration system and of the conventional system due to the introduction of the unit cost of heat production. These cogeneration systems have to present well-designed thermal energy recuperation and electrical energy production devices in order for the unit cost of the produced electrical power to be higher than that of a conventional system.A thermoeconomic analysis of three existing cogeneration systems was conducted and led to the conclusion that these cogeneration systems were not profitable enough due to a lack of a strong energy management strategy which is constrained by the tariffing of local utilities. The main analysis was focused on the cogeneration system of a hospital. This later is based on a thermal engine using natural gas as a primary resource and producing 2.8 MW of electricity and 2.7 MW of heat coupled with the heat production of natural-gas-fired boilers ranging about a maximum of 31 MW. Based on the particular tariffing of the local utilities, the investment cost of this cogeneration system should not exceed 64% of the cost of a conventional electrical production system in order to present a shorter pay-back time. We have shown how this cogeneration system will not be competitive with a conventional system if it was operated at some tariffing mode and that the lifetime of the equipment has an impact on the profitability of the system.