Kogenerační cykly ve vodotrubných kotlech

Cogeneration – joint generation of electricity and heat brings savings in consumption of primary fuels. Therefore, it contributes to reduction of harmful substances emission to the atmosphere (CO2 emission), which also means reduction of external costs of energy and heat generation. Until present, the cogeneration cycles have not been used in heating plants equipped with water boilers (in particular the water-tube ones). This paper presents a concept of innovative cogeneration cycle which operates with a water heating or industrial boiler. The cogeneration cycle does not change the approval of technical parameters of the boiler and it does not limit the scope of its use. The developed comparative cycles in the h-s and T-s systems and simulation model of the unit cogeneration cycle are presented as diagrams and cogeneration indicators. Furthermore, economic indicators of cogeneration are presented for water boilers.Kogenerace - společná výroba elektřiny a tepla přináší úspory spotřeby primárních paliv. Proto přispívá ke snížení emisí škodlivých látek do ovzduší (emise CO2), což také znamená snížení externích nákladů na výrobu energie a tepla. Dosud nebyly kogenerační cykly používány v teplárnách s parními kotly (zejména vodotrubnými). Tento článek představuje koncept inovačního kogeneračního cyklu, který pracuje s ohřevem vody u průmyslového kotle. Kogenerační cyklus nemění schválené technické parametry kotle a neomezuje rozsah jeho použití. Vyvinuté srovnávací cykly v systémech h-s a T-s a simulační model kogeneračního cyklu jednotky jsou prezentovány jako diagramy a ukazatele kogenerace. Dále jsou představeny ekonomické ukazatele kogenerace pro vodotrubné kotle

Studies on the effectiveness of SCR catalysts during combustion of pulverized coal

The motivation of this paper is new NOx emission regulations according to IED Directive 2010/75/EU of EU which introduce the BAT’s conclusions as binding. The paper presents the methodology and results of research on the effectiveness of SCR catalysts during combustion of pulverised coal in a model furnace installed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology (IPET). The aim of the research was to search for catalysts that could be placed in a regenerative rotary air heater - RAH-SCR. Two catalysts were tested: a commercial plate-type based on V2O5 and a prototype ceramic based on platinum. Presented results of investigation demonstrate a potentially high efficiency of RAH-SCR installations which can meet new environmental regulations of NOx emission. The highest NOx reduction efficiency (92.87%) was obtained for an industrial catalyst at 329°C, from about 436.3 to 31.1 mg/m3 as NO2 @ 6%O2 to 31,1. At lower temperature, 260°C maximum efficiency of NOx reduction does not exceed 60%, from 440,0 to 169,6 mg/m3. The placement of the catalyst in the RAH can also be a support for SNCR installations due to the increase in DeNOx efficiency and reduction of NH3 slip

Obieg kogeneracyjny w wodnych kotłach ciepłowniczych

Kogeneracja - wspólne wytwarzanie energii elektrycznej i ciepła przynosi oszczędności w zużyciu paliw pierwotnych. W związku z tym przyczynia się do redukcji emisji szkodliwych substancji do atmosfery (CO2), co również oznacza zmniejszenie kosztów zewnętrznych wytwarzania energii i ciepła. Do tej pory cykle kogeneracyjne nie były stosowane w ciepłowniach wyposażonych w kotły wodne (wodno-rurowe lub płomienicowo-płomieniówkowe). W artykule przedstawiono koncepcję innowacyjnego obiegu kogeneracji, który współpracuje z wodnym kotłem ciepłowniczym lub przemysłowym, a instalacja kogeneracji nie zmienia zatwierdzenia parametrów technicznych kotła i nie ogranicza zakresu jego użytkowania. Przedstawiono opracowane obiegi porównawcze w układach h-s i T-s, pasmowy wykres energii Sankey'a oraz wykresy wybranych wskaźników kogeneracji. Ponadto przedstawiono wskaźniki ekonomiczne kogeneracji dla kotłów wodnych

Co-Firing of Biomass and Waste Derived Syngas in Coal Power Boiler

The paper deals with waste gasification as a technology allowing indirect co-firing of large quantities of biodegradable wastes in coal-fired power boilers. In contrast to common landfilling and direct co-firing, gasification of wastes presents a number of advantages. Problematic species in original feedstocks can be partly safely incinerated in the furnace and partly retained in the gasification residues. The choice of gasification technology determines whether these residues could be further used in the construction industry or should nevertheless be landfilled, but benefiting from significantly reduced volume with respect to that of the original waste. The paper focuses on the impact of indirect co-firing on basic boiler parameters and performance. The work carried out was in the form of a case study for co-firing LCV gas in 230 t/h dual fuel pulverized coal-gas fired boiler. Thermal shares of 10, 20 and 40 % have been investigated for two extreme LCV gas qualities represented in the calculations by its calorific value of 2.0 and 8.5 MJ/m3n respectively, thus six calculation cases are given. The results of the study reveal that even high thermal shares of LCV gas may be achieved for co-firing of better quality gas without significant effects on boiler operation. For lower quality gas, even a 10 % thermal share influenced boiler operation to a great extent. This paper also gives consideration in relation to avoided CO2 emissions accomplished via indirect co-firing.JRC.F.2-Cleaner energie

Co-firing of Wastes Derived Syngas in Power Generation Boiler - Operating Impacts

The paper deals with waste gasification as a technology allowing co-firing of large quantities of biodegradable wastes in power boilers. In contrast to common landfilling and direct co-firing, gasification of wastes presents a number of advantages. Problematic species in original feedstocks can be partly safely incinerated in the furnace and partly retained in the gasification residues. Little effect on power boiler operation in terms of long term phenomena like fouling or corrosion is expected to be associated with co-firing of low calorific gas in standard coal powered boilers. Moreover, combustion characteristics in the furnace can even benefit from the co-firing of biodegradable wastes due to an enhanced reburning effect. The paper focuses on proper introduction of low-calorific gases derived from gasification of biomass and wastes into solid fuel fired boilers. Possible injection methods are described and the influence of co-firing low calorific value gas on power boiler operation is discussed.JRC.F.2-Cleaner energie

Possibility analysis of combustion of torrefied biomass in 140 t/h PC boiler

The study attempts to evaluate the impact of combustion of torrefied willow (Latin: Salix viminalis) and palm kernel shell (Latin: Elaeis guineensis) on the heat exchange in a 140 t/h PC boiler through an analysis of 6 cases for different boiler loads (60 %, 75 % and 100 %) and a comparison with coal combustion. The analysis is premised on a 0-dimensional model based on the method presented in [15, 16, 17] and long-standing experimental measurements. Inter alia, the following results are presented: the temperature distribution of flue gases and the working medium (water/steam) in characteristic points of the boiler as well as heat transfer coefficients for each element thereof. The temperature distribution of both fluids and the heat transfer coefficients are similar for all analysed fuels for each boiler load. However, the flue gas temperature at the outlet is higher in the case of torrefied biomass combustion. Due to that, there is an increase in the stack loss, which involves a decrease in the boiler efficiency. The conclusion is that torrefied biomass combustion is possible in a PC boiler without the need to change the boiler construction. However, it would be less effective than coal combustion

Simplified method for calculating SNCR system efficiency

SNCR (Selective Non-Catalytic Reduction) technology is aimed at reducing NOx emissions. SNCR efficiency is appropriately high only for the reaction temperature range called ‘the SNCR temperature window’. It is a narrow temperature range defined in various ways in the literature, which makes it difficult to evaluate the DeNOx system’s efficiency. Therefore, this study attempts to approximate the relationship between SNCR system efficiency and the flue gas temperature. The approximation was performed on the basis of literature data and verified using data from an experiment. Measurements were performed in a Polish boiler with a maximum continuous rating of 230 t/h. The verified, evaluated function could be used to forecast efficiency of SNCR systems in existing units that use urea or ammonia as a reagent. The approximation results are polynomial functions that depend on flue gas temperature, which fit the literature data with the coefficient of determination R2 = 0.83-0.86. Therefore, these equations could be used by the designer or operator of the boiler for preliminary determination of current SNCR system efficiency

Experimental verification of a CFD model intended for the determination of restitution coefficients used in erosion modelling

Erosion caused by solid particles transported with the steam or flue gas has a negative impact on the power unit reliability and availability. The erosion rate depends inter alia on the restitution of the particle velocity upon impact. The restitution coefficients determine the angle of the particle reflection off the tube surface and the particle post-impingement velocity, i.e., they determine the direction of the particle path, which has a substantial impact on the erosion phenomenon inside the tube. An attempt is made herein to develop a method of determination of restitution coefficients by means of numerical modelling assisted by experimental testing on physical models that will be implemented further in the Ansys Fluent code. Such a numerical procedure will verify the model of erosion caused by particles of iron oxides. The erodent impingement angle α1, the impingement velocity w1, and the reflection velocity w2 are measured using the Casio High-Speed Exilim EX-F1 camera, which enables filming at a high rate. The film is then processed graphically for “frame-by-frame” tracking. The following erodents were used in the testing: iron oxides, quartz sand with a different grain size (490, 1000, 1500, 2000 μm), and 1000 μm-diameter steel balls. The steel balls, due to their ideal shape, were treated as the comparative analysis reference standard. Erosion of three types of 5x10 cm plates was tested: a plasma-coated plate with an anti-erosion layer, an aluminium plate; and a steel sheet plate. Based on the restitution coefficient testing results, numerical simulations were performed of the particle reflection off the surface

Investigation of sewage sludge gasification with use of flue gas as a gasifying agent

The paper presents results of investigation of low-temperature sewage sludge gasification with use of flue gas as a gasifying agent. Tests were conducted in a laboratory stand, equipped with a gasification reactor designed and constructed specifically for this purpose. During presented tests, gas mixture with a composition of typical flue gases was used as a gasifying agent. The measuring system ensures online measurements of syngas composition: CO, CO2, H2, CH4. As a result of gasification process a syngas with combustible components has been obtained. The aim of the research was to determine the usability of sewage sludge for indirect cofiring in power boilers with the use of flue gas from the boiler as a gasifying agent and recirculating the syngas to the boiler’s combustion chamber. Results of presented investigation will be used as a knowledge base for industrial-scale sewage sludge gasification process. Furthermore, toxicity of solid products of the process has been determined by the use of Microtox bioassay. Before tests, solid post-gasification residues have been ground to two particle size fractions and extracted into Milli-Q water. The response of test organisms (bioluminescent Aliivibrio fischeri bacteria) in reference to a control sample (bacteria exposed to 2% NaCl solution) was measured after 5 and 15 minutes of exposure. The obtained toxicity results proved that thermal treatment of sewage sludge by their gasification reduces their toxicity relative to water organisms

Experimental verification of a CFD model intended for the determination of restitution coefficients used in erosion modelling

Erosion caused by solid particles transported with the steam or flue gas has a negative impact on the power unit reliability and availability. The erosion rate depends inter alia on the restitution of the particle velocity upon impact. The restitution coefficients determine the angle of the particle reflection off the tube surface and the particle post-impingement velocity, i.e., they determine the direction of the particle path, which has a substantial impact on the erosion phenomenon inside the tube. An attempt is made herein to develop a method of determination of restitution coefficients by means of numerical modelling assisted by experimental testing on physical models that will be implemented further in the Ansys Fluent code. Such a numerical procedure will verify the model of erosion caused by particles of iron oxides. The erodent impingement angle α1, the impingement velocity w1, and the reflection velocity w2 are measured using the Casio High-Speed Exilim EX-F1 camera, which enables filming at a high rate. The film is then processed graphically for “frame-by-frame” tracking. The following erodents were used in the testing: iron oxides, quartz sand with a different grain size (490, 1000, 1500, 2000 μm), and 1000 μm-diameter steel balls. The steel balls, due to their ideal shape, were treated as the comparative analysis reference standard. Erosion of three types of 5x10 cm plates was tested: a plasma-coated plate with an anti-erosion layer, an aluminium plate; and a steel sheet plate. Based on the restitution coefficient testing results, numerical simulations were performed of the particle reflection off the surface