Characterization of a process for the in-furnace reduction of NOx, SO2, and HCl by carboxylic salts of calcium

Calcium magnesium acetate has been assessed as an agent for the reduction of NOx, SO2, and HCl, at the pilot scale, in a down-fired combustor operating at 80 kWth. In addition to this, the chemical and physical processes that occur during heating have been investigated. Benchmarking of calcium magnesium acetate with a suite of five other carboxylic salts (calcium magnesium acetate, calcium propionate, calcium acetate, calcium benzoate, magnesium acetate, and calcium formate) has been performed. NOx reduction involves the volatile organic content of the carboxylic salt being released at temperatures of >1000 °C, where the reaction of CHi radicals with NO under fuel-rich conditions can result in some of the NO forming N2 in a “reburning” process. Thermogravimetry-Fourier transform infrared (TG-FTIR) studies identified the nature of the decomposition products from the low- and high-temperature decompositions. In addition, the rate of weight losses were studied to investigate the influence of the organic decomposition on NOx reduction by reburning. In-furnace reductions of SO2 and HCl are aided by the highly porous, particulate residue, which results from the in situ drying, pyrolysis, and calcination processes. Simultaneous reduction of all three pollutants was obtained, and a synergy between SO2 and HCl capture was identified. A mechanism for this inter-relationship has been proposed. Sorbent particle characterization has been performed by collecting the calcined powder from a spray pyrolysis reactor and compared with those produced from a suite of pure carboxylic salts. Physical properties (including porosity, surface area, and decomposition behavior) have been discussed, relative to reductions in NOx and acid gas emissions

Characteristics of Copper-based Oxygen Carriers Supported on Calcium Aluminates for Chemical-Looping Combustion with Oxygen Uncoupling (CLOU)

Eight different oxygen carriers (OC) containing CuO (60 wt %) and different mass ratios of CaO to Al2O3 as the support were synthesized by wet-mixing followed by calcination at 1000 °C. The method of synthesis used involved the formation of calcium aluminum hydrate phases and ensured homogeneous mixing of the Ca2+ and Al3+ ions in the support at the molecular level. The performance of the OCs for up to 100 cycles of reduction and oxidation was evaluated in both a thermogravimetric analyzer (TGA) and a fluidized bed reactor, covering a temperature range of 800 to 950 °C. In these cycling experiments, complete conversion of the OC, from CuO to Cu and vice versa, was always achieved for all OCs. The reactivity of the materials was so high that no deactivation could be observed in the TGA, owing to mass transfer limitations. It was found that OCs prepared with a mass ratio of CaO to Al2O3 in the support >0.55 agglomerated in the fluidized bed, resulting in an apparent deactivation over 25 cycles for all temperatures investigated. High ratios of mass of CaO to Al2O3 in the support resulted in CuO interacting with CaO, forming mixed oxides that have low melting temperatures, and this explains the tendency of these materials to agglomerate. This behavior was not observed when the mass ratio of CaO to Al2O3 in the support was ≤0.55 and such materials showed excellent cyclic stability operating under redox conditions at temperatures as high as 950 °C.The authors thank Mohammad Ismail and Matthew Dunstan for helping with the XRD analysis and Alex Casabuena-Rodriguez and for helping with the SEM. This work was supported by the Engineering and Physical Sciences Research Council (EPSRC grant EP/I010912/1).This is the final version of the article. It first appeared from ACS via http://dx.doi.org/10.1021/acs.iecr.5b0117

CLOU process performance with a Cu-Mn oxygen carrier in the combustion of different types of coal with CO2 capture

The Chemical Looping with Oxygen Uncoupling (CLOU) process is a Chemical Looping Combustion (CLC) technology that allows the combustion of solid fuels with inherent CO2 separation by using oxygen carriers based on metal oxides. This technology has a low energy penalty and thus low CO2 capture costs. The oxygen carrier used in the CLOU process must be able to release gaseous oxygen, an aspect that limits the availability of metal oxides for this process. This work investigated the suitability of an oxygen carrier containing 34 wt% CuO and 66 wt% Mn-3 O-4 (active phase Cu1.5Mn1.5O4) prepared by granulation regarding the CO2 capture, combustion efficiency and lifetime of the particles. The effect of the different types of coal (two sub-bituminous and a lignite) on combustion and CO2 capture efficiencies by CLOU was studied at different oxygen carrier to coal ratios in a continuous 1.5 kWth rig. It was found that full combustion could be reached regardless of the coal used. However, CO2 capture efficiencies were highly determined by coal rank. Finally, it was found that working with oxygen carrier to coal ratios higher than phi = 4, which corresponded to values of the variation of the oxygen carrier conversion lower than Delta X-oc = 0.25, decreased the effect of chemical stress on the attrition rate. Therefore, it is clearly beneficial for the lifetime of oxygen carrier particles to operate with low variations of the oxygen carrier conversion (Delta X-oc) between fuel and air reactors