A 1.5D model of a complex geometry laboratory scale fuidized bed clc equipment

The awareness of the climate changes has resulted in the development of new technologies allowing to increase the effectiveness and to lower the costs of CO2 separation from the flue gas. One of the most promised combustion technology of fossil fuels is Chemical Looping Combustion (CLC). The technology is considered to be one of the cheapest techniques for CO2 capture (1). Since it is still an emerging technology and the complexity of processes are still not sufficiently recognized, the development of a simple model of CLC equipment is of practical significance. The paper presents a 1.5D model of the laboratory-scale fluidized bed CLC equipment for Innovative Idea for Combustion of Solid Fuels via Chemical Looping Technology – NewLoop. The idea combines two technologies making them complementary: Chemical looping with Oxygen Uncoupling (CLOU) and In-situ Gasification Chemical Looping (iG-CLC). Experimental studies, calculations and model validation were performed for the CLC unit (Fig. 1). The unit constitutes two cycles: the main cycle and internal cycle with Air Reactor (AR) and Fuel Reactor (FR). Smooth glass microspheres with the Sauter mean diameter of particles of 141 µm and the density of 2450 kg/m3 were used during the investigation. Since the model is in the development stage the study was conducted for the cold tests at which the unit operated stably and smoothly. The model is performed by the use of Comprehensive Simulator of Fluidized and Moving Bed equipment (CeSFaMB). The CeSFaMB has its first successful version completed in 1987. Since then, various versions have been developed and validated for a wide range of cases (2). The first operational results with this CLC unit, i.e. fluidization dynamics are discussed, since the geometry of the system is rather complex. Pressure drops, void fractions, bubble diameter and rising velocity are determined. The results show good agreement between calculated and experimental parameters. On the matter of fluidization dynamics, CeSFaMB produces the parameters as function of vertical coordinate. As an example, the void fractions as well as bubble diameter and rising velocity in the dense region of the Air Reactor are illustrated in Fig 2. Please click Additional Files below to see the full abstract

Experiences from oxy co-combustion of sewage sludge and coal in circulating fluidized bed

Termiczne metody unieszkodliwiania komunalnych osadów ściekowych ze względu na uwarunkowania prawne i techniczne stały się jedną z popularnych form zagospodarowania osadów w Polsce. Proces ten realizowany jest albo poprzez termiczne suszenie osadów do postaci granulek o wysokiej zawartości suchej masy albo poprzez poddanie spalaniu w reaktorach, w tym głównie pracujących w technologii fluidalnej. Obecnie w Polsce funkcjonuje 11 monospalarni o całkowitej przepustowości 160 tys. Mg s.m./rok. Proces spalania w tych obiektach prowadzony jest w atmosferze powietrza, przyczyniając się do znaczących emisji między innymi gazów cieplarnianych. Stąd celem autorów było przeprowadzenie badań współspalania osadów ściekowych z węglem w technologii spalania tlenowego. Badania wykonano na stanowisku wielkolaboratoryjnym pracującym w układzie cyrkulacyjnej warstwy fluidalnej o mocy 0,1 MW mocy cieplnej. Badania procesu spalania mieszanek węglowych o 50, 30 i 10 % udziale masowym osadów przeprowadzono w mieszaninie modyfikowanej o zmiennym udziale tlenu o udziale objętościowym z zakresu od 21 do 30 %. Prowadzono badania emisji zanieczyszczeń, w tym CO2, CO, SO2, SO3, H2S, NO2, NO, N2O, NH3, HCN.On the basis of formal and legal conditions sewage sludge utilization by thermal methods has become one of basic methods of sewage sludge management in Poland in recent years. It should be noted that currently in Poland there are 11 mono-incinerators with the total processing capability of 160,000 Mg d.m./year. The process of sludge incineration in these facilities occurs through conventional combustion under conditions of air atmosphere. However, the change in combustion atmosphere involving the replacement of air with the mixture of oxygen and carbon dioxide, where the concentration of oxygen is higher than in air is an interesting technology for reducing CO2 emissions. Other benefit is a reduction in NOx emissions resulting from a substitute of N2 by CO2. It is predicted that the implementation of oxy-fuel technique in connection with circulating fluidized bed technology is a good solution for treatment of wide range of fuels including sewage sludge due to both techniques’ advantages. Oxy-fuel co-combustion of municipal dried sewage sludge and coal was conducted to observe the combustion characteristics as well as pollutant emissions generated under different oxygen injection rate in oxyfuel atmosphere in 0.1 MWth CFB reactor. As a feed gas a mixture of oxygen and carbon dioxide was used. Oxygen concentration in a feed gas varied from 21 to 30 % per volume. The combustion temperature was not fixed since it was a resulting parameter mostly from calorific value of different fuel components and oxygen supplied to the riser. The following blending ratios of sewage sludge to coal were chosen: 50, 30 and 10 %. Flue gas components were on-line measured by a gas analyzer, determining CO2, CO, SO2, SO3, NO2, NO, N2O, NH3, HCN concentrations by non-dispersive infrared absorption. The experimental results showed a strong influence of oxygen concentration on temperature in the combustion chamber during sewage sludge utilization. To realize which component in a flue gas played a main role the conversion ratios of sulfur and nitrogen contained in blending fuel to NO, NO2, N2O, NH3, HCN, SO2, SO3 and H2S were obtained. The values of sulfur conversion ratio to sulfur dioxide were relatively high and exceeded the level of 80 % under oxy-fuel conditions. What’s interesting conversion to SO3 was negligible. In the case of nitrogen conversion ratio remained low in the whole range of investigated conditions

Emissions of CO2, CO, NOx and N2O from dried lignite combustion in oxygen-enriched O2/CO2 atmospheres in a circulating fluidized bed boiler

The paper presents the idea of oxygen-enhanced dried lignite combustion in a circulating fluidized bed (CFB) boiler as it gives a possibility of reduction of gaseous pollutants emissions. Calculations were conducted using one-dimensional model, which describes crucial processes associated with combustion of solid fuels under circulating fluidized bed conditions, e.g., hydrodynamics of bed material, fuel devolatilization, volatiles and char combustion and heat transfer. The paper is focused on CO2, CO, NOx and N2O emissions from a 670 t/h CFB boiler during dried lignite combustion in O2/CO2 atmosphere. The dependence of the gaseous pollutants’ emissions on oxygen fraction in an inlet gas as well as moisture content in lignite were studied. The oxygen fraction was increased from 21 to 30% vol., whereas moisture content was decreased from 43.5 to 10% – simulating fuel pre-drying. A case study considers solution when process is run with recirculation of CO2. The obtained results was compared to the case where CO2 is not recycled

The Effect of Oxygen Staging on Nitrogen Conversion in Oxy-Fuel CFB Environment

This paper presents a study on nitrogen conversion in oxy-fuel coal combustion in a pilot scale CFB 0.1 MWth facility. The paper is focused on fuel-N behaviour in the combustion chamber when the combustion process is accomplished under oxy-fuel CFB conditions. The analysis is based on infurnace sampling of flue gas and calculations of the conversion ratios of fuel-nitrogen (fuel-N) to NO, NO2, N2O, NH3 and HCN. For the tests, O2/CO2 mixtures with the oxygen content of 21 vol.% (primary gas) and with the oxygen content varied from 21 to 35 vol.% (secondary gas), were used as the fluidising gas. Measurements were carried out in 4 control points located along the combustion chamber: 0.43 m, 1.45 m, 2.50 m and 4.88 m. Results presented below indicate that an increased oxygen concentration in the higher part of the combustion chamber has strong influence on the behaviour of fuel based nitrogen compounds