M. Jeremiáš

Effect of SO2 and steam on CO2 capture performance of biomass-templated calcium aluminate pellets

Four types of synthetic sorbents were developed for high-temperature post-combustion calcium looping CO2 capture using Longcal limestone. Pellets were prepared with: lime and cement (LC); lime and flour (LF); lime, cement and flour (LCF); and lime, cement and flour doped with seawater (LCFSW). Flour was used as a templating material. All samples underwent 20 cycles in a TGA under two different calcination conditions. Moreover, the prepared sorbents were tested for 10 carbonation/calcination cycles in a 68 mm-internal-diameter bubbling fluidized bed (BFB) in three environments: with no sulphur and no steam; in the presence of sulphur; and with steam. When compared to limestone, all the synthetic sorbents exhibited enhanced CO2 capture performance in the BFB experiments, with the exception of the sample doped with seawater. In the BFB tests, the addition of cement binder during the pelletisation process resulted in the increase of CO2 capture capacity from 0.08 g CO2 per g sorbent (LF) to 0.15 g CO2 per g sorbent (LCF) by the 10th cycle. The CO2 uptake in the presence of SO2 dramatically declined by the 10th cycle; for example, from 0.22 g CO2 per g sorbent to 0.05 g CO2 per g sorbent in the case of the untemplated material (LC). However, as expected all samples showed improved performance in the presence of steam, and the decay of reactivity during the cycles was less pronounced. Nevertheless, in the BFB environment, the templated pellets showed poorer CO2 capture performance. This is presumably because of material loss due to attrition under the FB conditions. By contrast, the templated materials performed better than untemplated materials under TGA conditions. This indicates that the reduction of attrition is critical when employing templated materials in realistic systems with FB reactors.

Attrition of dolomitic lime in a fluidized-bed reactor at high temperatures

Results of an experimental study on the rate of attrition of lime catalyst/sorbent in a high-temperature, turbulent fluidized bed with quartz sand are presented. Batch measurements were conducted at 850°C in an electrically heated gasification reactor of the inner diameter of 5.1 cm with three samples of high-grade dolomitic lime of the particle size 450 μm, 715 μm, and 1060 μm, respectively. In addition to the influence of the particle size, the effect of operating (elapsed) time was investigated at different superficial gas velocities. Assuming that the attrition rate decreases exponentially with time, a simple mechanistic model, enabling the correlation of the measured experimental data, was developed. The course of the lime particles attrition is described as a function of the elapsed time, excess gas velocity, and particle size. The presented approach and the results might be applicable for the attrition of high-grade dolomitic lime, particularly in fluidized gasification of biomass.

Operation of a 25 kWth calcium looping pilot-plant with high oxygen concentrations in the calciner

Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO2 sorbent. While the technology has been widely studied, there are a few available options that could be applied to make it more economically viable. One of these is to increase the oxygen concentration in the calciner to reduce or eliminate the amount of recycled gas (CO2, H2O and impurities); therefore, decreasing or removing the energy necessary to heat the recycled gas stream. Moreover, there is a resulting increase in the energy input due to the change in the combustion intensity; this energy is used to enable the endothermic calcination reaction to occur in the absence of recycled flue gases. This paper presents the operation and first results of a CaL pilot plant with 100% oxygen combustion of natural gas in the calciner. The gas coming into the carbonator was a simulated flue gas from a coal-fired power plant or cement industry. Several limestone particle size distributions are also tested to further explore the effect of this parameter on the overall performance of this operating mode. The configuration of the reactor system, the operating procedures, and the results are described in detail in this paper. The reactor showed good hydrodynamic stability and stable CO2 capture, with capture efficiencies of up to 70% with a gas mixture simulating the flue gas of a coal-fired power plant.

Thermodynamic Possibilities and Limits for Producer Gas Desulfurization and HCL Related Interferences for Zn, Mn, Ce and La Based Sorbents of Sulfur Compounds

The study is concentrated on thermodynamic analyses of gas desulfurization process (deep removal of H2S, COS, thiophene) by selected solid sorbents (ZnO, MnO, CexOy and La2O3) and on interferences caused by presence of hydrogen halides in a temperature range 500-1100 K. The results show that theoretically Ce2O3 and La2O3 are the best sorbents for sulfur compounds at temperatures over approx. 700 K. The CexOy, La2O3 and MnO based sorbents can suffer from significant interferences caused by higher concentrations of HCl and HF in gas phase. The thermodynamic equilibria suggest that removal of HCl (HF) by soda based sorbents at temperatures 650 – 850 K is practically without interferences from sulfur compounds. The common alkali carbonates are less suitable than the calcium based (Ca (OH)2, CaCO3) sorbents for deep removal of HF.