Mathematical model for digital simulation of steam turbine set dynamics and on-line turbine load distribution

The general structure and purposes of the distributed control systems (DCS) are reminded in connection with the capability to use them for on-line optimization of the load distribution in large, multiunit power stations. The basic assumptions, equations and structure of a model of backpressure extraction turbine are presented. The tasks, realized using this model in collaboration with the DCS’s measuring and archive systems, are defined. The principles of using and correcting the input data for the considered tasks are described. Model calculation results and recorded measuring data are compared. The input data quality and influence of the DCS record mode on the abilities to use the model appropriately are discussed

Two-dimensional CFD modeling of the heat and mass transfer process during sewage sludge drying in a solar dryer

The paper presents key assumptions of the mathematical model which describes heat and mass transfer phenomena in a solar sewage drying process, as well as techniques used for solving this model with the Fluent computational fluid dynamics (CFD) software. Special attention was paid to implementation of boundary conditions on the sludge surface, which is a physical boundary between the gaseous phase - air, and solid phase - dried matter. Those conditions allow to model heat and mass transfer between the media during first and second drying stages. Selection of the computational geometry is also discussed - it is a fragment of the entire drying facility. Selected modelling results are presented in the final part of the paper

SOFC-based micro-CHP system as an example of efficient power generation unit

Microscale combined heat and power (CHP) unit based on solid oxide fuel cells (SOFC) for distributed generation was analyzed. Operation principle is provided, and the technology development in recent years is brie.y discussed. System baseline for numerical analysis under steady-state operation is given. Grid-connected unit, fuelled by biogas corresponds to potential market demand in Europe, therefore has been selected for analysis. Fuel processing method for particular application is described. Results of modeling performed in ASPEN Plus engineering software with certain assumptions are presented and discussed. Due to high system electrical efficiency exceeding 40%, and overall efficiency over 80%, technology is an example of highly competitive and sustainable energy generation unit

Mathematical model of a plate fin heat exchanger operating under solid oxide fuel cell working conditions

Heat exchangers of different types find application in power systems based on solid oxide fuel cells (SOFC). Compact plate fin heat exchangers are typically found to perfectly fit systems with power output under 5 kWel. Micro-combined heat and power (micro-CHP) units with solid oxide fuel cells can exhibit high electrical and overall efficiencies, exceeding 85%, respectively. These values can be achieved only when high thermal integration of a system is assured. Selection and sizing of heat exchangers play a crucial role and should be done with caution. Moreover, performance of heat exchangers under variable operating conditions can strongly influence efficiency of the complete system. For that reason, it becomes important to develop high fidelity mathematical models allowing evaluation of heat exchangers under modified operating conditions, in high temperature regimes. Prediction of pressure and temperatures drops at the exit of cold and hot sides are important for system-level studies. Paper presents dedicated mathematical model used for evaluation of a plate fin heat exchanger, operating as a part of micro-CHP unit with solid oxide fuel cells

A design procedure for “liquid to air” type atomisers based on air and water mixture outflow velocity

The paper proposes a procedure which enables to determine selected geometric and operating parameters for twin-fluid liquid-to-air atomisers with internal mixing. The presented approach assumes that in order to ensure proper operation of an atomiser it is necessary to design its structure and flow parameters in such a way so that the flow inside the mixing chamber has a dispersive character. In order to calculate a required exhaust cross-section for the analysed atomiser, conditions within the exhaust plane: pressure, density and outflow velocity were estimated. In order to determine diameter and number of orifices supplying the liquid to the mixing chamber of the investigated atomiser type, a multi-parameter analysis based on numerical fluid mechanics was performed. The final part of the paper presents selected results obtained from experimental stand measurements made on an atomiser designed according to the presented procedure

Analiza termodynamiczna pracy układu CAES

The compressed air energy storage (CAES) technology and electricity generation by this system are described. General performances and possible system efficiency definitions of those kinds of systems are indicated. Hybrid systems which consist of CAES and other renewable technologies (RT), e.g., wind turbines, are presented. A possibility of CAES-RT location in Poland is indicated. Dynamic mathematical model of CAES is presented; using this model the results for compressing and expanding operating modes are obtained.Przedstawiono technologię CAES (ang. compressed air energy storage) oraz możliwości generowania energii elektrycznej z jej udziałem . Pokazano głównie parametry eksploatacyjne oraz możliwe tutaj do zastosowania definicje sprawności takich układów. Występują tutaj możliwości budowy układów hybrydowych CAES + technologie odnawialne, takie jak np. elektrownie wiatrowe. Zaproponowano potencjalne lokalizacje takich hybrydowych rozwiązań. Wyniki obliczeń oparto o model dynamiczny układu CAES - ładowanie i rozładowanie kawerny

The effect of parallel hot windbox repowering on 387 MW fossil fuel power plant

The paper presents the concept of repowering in existing power plant. Among technologies for existing steam power plants, the hot windbox repowering is the fastest way to respond to the energy demand, improve efficiency and reduce the pollutants emissions. Thermodynamic analysis of power plant model with fossil boiler before and after hot windbox repowering, has been investigated using commercial software. The purpose of this work is to understand and analyze the effect of hot windbox repowering on 387 MW fossil fuel power plant as well as the effect of additional heat exchangers, which have been installed parallel with regeneration system to use the heat of boiler exhaust gases. In this way, after repowering the summary power of power plant in base load is 615 MW, which has been reached adding gas turbine (176.9 MW). To analyze the model, calculations were performed in 3 stages: 1) calculation and comparison of the thermodynamic parameters as well as carbon dioxide emissions of power plant model before and after repowering, 2) analysis of the optimal value of feed water mass flow through heat exchangers installed after economizer, 3) calculation of thermodynamic parameters in values 100%, 90%, 80% and 75% of fossil boiler heat loads