Impact of Fluctuating Energy Prices on the Operation Strategy of a Trigeneration System

Trigeneration systems are potentially more energetically and economically efficient than cogeneration systems due to possibility to extend operation at nominal load. However, these systems also face challenges of future development characterised by reduced heating and cooling demands, as a consequence of implementation energy efficiency measures, and fluctuating electricity prices, as a consequence of increased penetration of intermittent renewable energy sources. The main objective of the paper is to research the operation strategies of trigeneration systems and to derive the optimal ones. The model proposed in this paper consists of two different systems, a conventional system and a trigeneration system. The heating, refrigerating and electric loads are known. The price of gas is constant while electricity prices are fluctuating at hourly basis. The optimization method is based on two criteria – energy and economic, which were applied hierarchically. Therefore, two optimal operation strategies are introduced. A mixed integer non-linear programming model provides energy and cost savings up to 32% and 28% respectively in comparison with conventional system. In addition, optimal capacity of trigeneration system is explored

Modelling of Temperature and Syngas Composition in a Fixed Bed Biomass Gasifier using Nonlinear Autoregressive Networks

To improve biomass gasification efficiency through process control, a lot of attention had been given to development of models that can predict process parameters in real time and changing operating conditions. The paper analyses the potential of a nonlinear autoregressive exogenous model to predict syngas temperature and composition during plant operation with variable operating conditions. The model has been designed and trained based on measurement data containing fuel and air flow rates, from a 75 kWth fixed bed gasification plant at Technical University Dresden. Process performance changes were observed between two sets of measurements conducted in 2006 and 2013. The effect of process performance changes on the syngas temperature was predicted with prediction error under 10% without changing the model structure. It was concluded that the model could be used for short term predictions (up to 5 minutes) of syngas temperature and composition as it strongly depends on current process measurements for future predictions. For long term predictions other types of dynamic neural networks are more applicable

Matematički model i simulacija dinamike procesa polimerizacije polietilena niske gustoće u cijevnom reaktoru

The mathematical model of the dynamics of thermohydraulic processes in a high pressure tubular reactor for production of low-density polyethylen has been presented. The equations of the mathematical model have been formulated based on one-dimensional fluid flow assumptions. Polyethylen production has been modelled by multivaribale, nonlinear function defining dependence on temperature, concentration and flow velocity. Simulations results of typical operating conditions (start-up, regular operation, transient response to coolant temperature changes) provide a realistic description of the process.U radu je opisan matematički model dinamike termohidrauličkih procesa u visokotlačnom cijevnom reaktoru za proizvodnju polietilena niske gustoće. Matematički model izveden je primjenom pretpostavke jednodimenzijskog strujanja fluida. Produkcija polietilena opisana je viševarijabilnom, nelinearnom funkcijom koja definira ovisnost brzine produkcije polietilena o temperaturi reakcijske smjese, koncentraciji reaktanata i brzini strujanja. Rezultati simulacija karakterističnih pogonskih stanja: upuštanja, normalnog pogona i poremećaja hlađenja, pokazuju da model pruža realističnu sliku procesa s relativno malim razlikama između proračunskih i izmjerenih vrijednosti temperatura reakcijske smjese

Analiza isplativosti energane na otpad

In the paper the techno-economical analysis of the waste-to-energy plant that includes combined heat and power production is presented. The technology of waste combustion on the grate is chosen as the proven technology most often in use even today. Selection of this technology assumes application of all the most stringent environmental protection standards. The paper analyses two variants of flue gas cleaning systems. Due to high requirements on environmental protection, the operating and maintenance costs of the facility are rather high while the calorific value of the municipal waste burned is relatively low (around 10 MJ/kg), which brings the waste-to-energy plant under consideration to the brink of economical viability for the given annual capacity of 100.000 tons of waste and the limiting gate fee value of 105 EUR per tone of waste, if solely direct cost-effectiveness is considered. The parameters on which the cost-effectiveness of the waste-to-energy cogeneration plant depends range from purely technical, like plant capacity and the waste calorific value (including percentage of moisture and biodegradable matter) to entirely economical, such as loan conditions, costs of flue gas cleaning, costs of hazardous waste disposal, revenue from selling of electricity and heat, and the most important factor – charge levied upon a waste received at a waste-to-energy plant (the gate fee). High costs of ash and residue disposal could influence the total economic viability of the plant.U radu je predstavljena tehno-ekonomska analiza postrojenja za energetsku oporabu otpada koje uključuje i kogeneracijsku proizvodnju toplinske i električne energije. Odabrana je, danas još uvijek najzastupljenija, tehnologija izgaranja otpada na rešetki. Izbor te tehnologije podrazumijeva primjenu svih najstrožih standarda zaštite okoliša. U radu su analizirane dvije varijante sustava za čišćenje dimnih plinova. Zbog visokih zahtjeva na zaštitu okoliša, troškovi pogona i održavanja postrojenja su visoki, te uz relativno nisku kalorijsku vrijednost komunalnog otpada koji se spaljuje (oko 10 MJ/kg) čine spalionicu otpada granično isplativom za odabrani kapacitet od 100.000 tona otpada godišnje i graničnu vrijednost naknade za zbrinjavanje otpada od 105 EUR/t otpada, ako se razmatra isključivo ekonomska računica. Parametri o kojima ovisi isplativost kogeneracijskog postrojenja na otpad kreću se od čisto tehničkih poput kapaciteta spalionice i ogrjevne vrijednosti otpada (postotak vlage, odnosno biorazgradive tvari), do sasvim ekonomskih poput uvjeta kreditiranja, troškova čišćenja dimnih plinova, naknade za zbrinjavanje opasnog otpada, cijene koja se može postići prodajom električne i toplinske energije, te najvažnijeg parametra – ulazne cijene prihvata otpada (naknada za zbrinjavanje otpada). Visoki troškovi zbrinjavanja pepela i ostataka mogu utjecati na ukupnu ekonomsku isplativost postrojenja

Operation Strategies of a Solar Trigeneration Plant in a Residential Building

Actual trends of increased utilization of renewable sources in residential sector impose new requirements for domestic energy system operation. Recent research results have shown that a high level of energy autonomy could be achieved by the utilization of such systems in a residential building located within the European continental climate zone. That is particularly interesting in the light of the fact that in near future access to the hourly electricity market will be enabled to all households thus acting as prosumers. In this paper, the energy system comprising of a photovoltaic thermal collector, heat storage, heat pump and auxiliary energy sources, sized to cover the most of electricity, heating and cooling demand of a selected low-energy family house (180 m2 heated and cooled area, 75 m2 useful roof area, located in northwest Croatia) was considered. By analysis of yearly operational profiles, required exchange of energy on electricity market was estimated. Detailed mathematical model of the system was used for hourly simulation in order to evaluate impact of operational strategies on both renewable energy sources utilization and profitability. Two different control strategies were compared in typical days defined by profiles of energy demands, solar irradiance and electricity price. The simulation results showed how the change in operation strategy can reduce operational cost