Faculty of Chemical Engineering and Technology

The paper discusses the possibility of using the reversible reaction CaCO3 ↔ CaO + CO2 for the cyclic capture and release of CO2 directly inside a fluidised bed combustor. This could lead to the lowering of CO2 emissions into the atmosphere, as part of an effort to mitigate the greenhouse effect associated with the rising atmospheric CO2 concentrations resulting from obtaining energy from burning fossil fuels.
An enrichment coefficient E has been introduced and defined as a measure of the production of CO2 (on calcining CaCO3) or its removal (on carbonation of CaO) with respect to the level associated with fuel combustion alone. The observations made on the effect of introducing an additional external stream of CO2 on the efficiency of the chemical capture process have been described. Through an appropriate control of the temperature inside the reactor it is possible to change the value of E over the range [-0.8; 0.8]. This implies that up to about 80% of the CO2 derived from the fuel can be temporarily retained within the bed and released later, at a higher concentration. The proposed method of burning fuel in a chemically active fluidised bed could be an available method leading to CO2 isolation from the flue gases and leading to its eventual sequestration.

This study presents the use of fluidised bed combustion to produce thermal energy, aluminium recovery and the reduction of the Tetra Pak and Combibloc packaging waste stream. Fluidisation and the pneumatic transport, which take place in the same apparatus, allow recovering bits of the aluminium foil from the combustion zone. The limited time spent in the high temperature zone leads to a high content of free metal in the solids separated in the ash trap and cyclone. Other solid products are practically chemically inert and may be disposed in a landfill of municipal or inert wastes.

The paper discusses the possibility of applying the reversible reaction CaCO3 ↔ CaO + CO2 in cyclic capture and release of CO2 directly inside a fluidised bed combustor. This would cause lowering CO2 emissions to the atmosphere, thanks to obtaining energy from burning fossil fuels. Observations made on the effect of introducing an additional external stream of CO2 on the efficiency of the chemical capture process are described. It is implied that CO2 derived from the fuel can be temporarily retained within the bed to be released later at a higher concentration. The proposed method of burning fuel in a chemically active fluidised bed could be an available method leading to CO2 isolation from flue gases and to its eventual sequestration.

The subject of the research was the influence of N2O on propane combustion in a fluidized bed reactor with active and chemically inert beds. It was determined that CaO has a significant influence on shifting the area in which the reaction is most intensive deeper into the bed and on the combustion result. It was also observed that adding nitrous oxide causes a decrease in VOC and CO concentration in exhaust gas. It was established that N2O, when added, is the determining factor of NOx creation, which takes place in a similar manner as via the prompt mechanism.

Burning premixed fuel-air mixtures in a bubbling fluidized bed is accompanied by some characteristic phenomena. The most striking one is the production of acoustic effects, indicating that combustion is not really continuous. A second, less obvious effect, is the NOx concentration in the flue gases falling with increasing bed temperature, observed above a certain critical mean bed temperature. To investigate the periodic burning of portions of methane-air mixture, photometric and acoustic signals were recorded simultaneously. Using a laboratory quartz reactor, explosions could be optically recorded in the bed, millimeters above distributor. With ethane fuel, the effective "combustion zone" in the reactor was also located by determining vertical temperature profiles, using eight thermocouples. When the bed temperature rises, maxima in the vertical temperature profiles associated with the "reaction zone" move from above the bubbling bed to the distributor. A mathematical model of unsteady combustion in a single bubble surrounded by bed material was used to simulate the process. Computed temperature maxima were compared with the experimental profiles. This meant finding the region where bubbles of premixed gases exploded, experimentally and from the model. A correlation between the NOx concentration and the location of the explosions (and diameter of the exploding bubbles) has also been found.

The paper presents the results of the disposal of packaging waste from two companies: Tetra Pak and Combibloc, carried out in a fluidized bed boiler of rated thermal power 0.5 MW. The material introduced into the fluidized bed boiler underwent thermal and mechanical degradation in a sand bed of the temperature between 750 and 850°C. The process proceeds auto-thermally, without the need of additional fuel. The appropriately chosen fluidization parameters caused the separation of the solid products of combustion from the deposit material. Presence of aluminum, part of it in an un-oxidized form, was confirmed in separated dust. The gaseous products of combustion contained the traces of oxides of nitrogen and sulfur, mainly originating from the remnants of food products contained in the packaging. However, the concentration of these oxides met the requirements of emission standards.

A bubbling fluidised bed reactor has been used for investigating how combustion propagates between bubbles of premixed fuel + air, rising from the distributor towards the surface. Earlier work has shown that when the temperature of the sand gradually rises, the gases first burn in flames above the bed, regime A, then combustion moves under its surface, to occur in bubbles travelling up the bed, under regime B. Above a certain temperature, characteristic of the gas mixture composition, combustion descends towards the bottom of the bed. Ignition then occurs in small bubbles near the distributor, under the stable regime C. The kinetic model, used to calculate the delay for thermal ignition inside gas bubbles rising through the bed, gives correct predictions for regimes A and C but not for B. Under regime B, bubbles of the mixture begin to ignite under the bed’s surface while their residence time in the bed is remains shorter than the delay times for thermal ignition derived from the kinetic model. As the temperature rises, the ignition delay rapidly decreases, and regime C is reached, in accordance with the model. In this work attention was focused on regime B. A laboratory reactor of quartz glass was used, with a bed of quartz sand. Fast video recording was employed to capture ignition phenomena as the bed’s temperature was raised or lowered. Records of freeboard concentrations of O2, CO and of total hydrocarbons, VOCs, were obtained, confirming the specific aerodynamic and chemical character of regime B. It has been shown that combustion spreads from the surface to bubbles near the bed’s surface and then to other bubbles close by. Such transfer of the reaction stabilizes combustion inside the bed, at temperatures appreciably lower than that for the thermal ignition of the mixture, given by the kinetic model. This is consistent with earlier findings, which have shown that the combustion of gaseous mixtures in bubbling fluidised beds is controlled by gas phase processes, as in flames.

W prezentowanej pracy przedstawiono wyniki badań eksperymentalnych procesu spalania paliw gazowych w inertnym złożu fluidalnym. Zaprezentowano efekty spalania związane ze składem spalin oraz zjawiska dynamiczne zachodzące wewnątrz warstwy fluidalnej. Wskazano na powiązanie zjawisk dynamicznych ze stopniem konwersji paliwa oraz
stężeniem CO i NO w spalinach.

The paper presents the parametric analysis of the autothermicity and multiplicity of steady states for a system consisting of two fluidized bed reactors, in which coal gasification takes place, connected by solids recycle. All important design and operational parameters which characterise the system have been taken into account. The results obtained are presented graphically, in the form of steady state hysteresis loops. On the basis of the relationships obtained it is possible to consider the feasibility of coal gasification in the system with separation of endothermic (gasification) and exothermic (combustion) processes.

The paper presents a parametric analysis of the autothermicity and multiplicity of steady states for a system consisting of two fluidized bed reactors, in which coal gasification takes place, connected by solids recycle. All important design and operational parameters which characterize the system have been taken into account. The results obtained are presented graphically, in the form of steady state hysteresis. On the basis of the relationships obtained it is possible to consider the feasibility of coal gasification in a system with separation of endothermic (gasification) and exothermic (combustion) processes.

Acoustic effects accompany the combustion of gaseous fuels in bubbling fluidized beds of inert materials. In an exploratory study of this effect, using a laboratory-size fluidized bed in which a mixture of propane and butane was burned, the bed's temperature was monitored continuously and the acoustic effects were recorded. The temperature ranges over which combustion was 'noisy' and 'quiet' were identified; the acoustic signals were shown to fall into a number of characteristic patterns, which can yield information about the character of the combustion process, in relation to 'mini- explosions' in bubbles of the combustible mixture rising through the bed, their intensity and frequency. The results could be used to develop a new method of controlling the operation of fluidized beds burning a gaseous fuel.
Acoustic effects accompany the combustion of gaseous fuels in bubbling fluidized beds of inert materials. In an exploratory study of this effect, using a laboratory-size fluidized bed in which a mixture of propane and butane was burned, the bed's temperature was monitored continuously and the acoustic effects were recorded. The temperature ranges over which combustion was `noisy' and `quiet' were identified; the acoustic signals were shown to fall into a number of characteristic patterns, which can yield information about the character of the combustion process, in relation to `mini-explosions' in bubbles of the combustible mixture rising through the bed, their intensity and frequency. The results could be used to develop a new method of controlling the operation of fluidized beds burning a gaseous fuel.

There is presented a theoretical analysis of the statics and dynamics of systems based on a cascade of continously stirred tank reactors. Three types of systems were numerically investigated: a simple cascade of reactors, a cascade with a mass recirculation and one with flow reversal. In all these cases complicated statics and fully developed dynamics were found. In the last two cases chaos was observed.