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During the drying and pyrolysis phases of kraft black liquor combustion, significant swelling of individual liquor particles occurs. Swollen volumes can reach 20 to 30 times the original volume during combustion. The swelling process can conceivably affect the combustibility of black liquor and the amount of carryover in a recovery furnace.The composition of black liquor was found to have a large influence on swelling. A combination of sugar acids and kraft lignin swelled to a larger extent than when either component was pyrolyzed separately. A 1:1 ratio of these two components resulted in maximum swelling for the various ratios tested. The molecular weight of kraft lignin had an effect on swollen volume with higher molecular weight fractions producing lower swelling chars.Other components were found to reduce the swelling of black liquors. Extractives interfered with the swelling by appearing to change the deformable properties of the pyrolyzing material. Inorganic salts acted as a diluent.Analysis of the surface characteristics of chars revealed that good swelling chars were composed of small bubbles 50 to 150 microns in diameter. Poor swelling liquors did not exhibit this phenomenon. The formation of bubbles was found to be initiated at 240°C, which closely corresponded to the thermal decomposition temperature of a sugar acid. Kraft lignin appeared to have a major influence on the viscous properties of the pyrolyzing particle. The composition of black liquor determines to a large extent the surface active and viscous forces present in black liquor; these forces are believed to be responsible for the extent to which kraft black liquors deform and swell during pyrolysis.

Iron oxide supported on alumina is a promising catalyst/absorbent for use in the simultaneous removal of NO, and SO, from power plant stack gases. A dry-contacting process is under development which would operate under net reducing conditions at temperatures of 370° to 540OC. Iron oxide is converted to the ferrous state, NO is reduced to Nz or NH3, and SOz is removed as ferrous sulfide or sulfate. Regeneration with air produces SO2 and reforms Fe20s.The reduction of SOz by CO and H2 was studied in fixed-bed reactors to determine the effects of temperature and of the other reactive components of flue gas (excepting fly ash) on the rate of reaction and the products formed. H2S and COS react with FeO to form FeS. Under readily attainable conditions, virtually complete removal of sulfur compounds was achieved for gas-phase residence times of about 1 to 10 ms. NO and Oz were also reduced. Conditions under which oxygen poisons the catalyst were determined. DAVID T. CLAY and SCOTT LYNN Department of Chemical EngineeringUniversity of California Berkeley, Colifornia 94720 SCOPESulfur dioxide and nitric oxide are major air pollutants in the United States. Fossil-fueled power plants are major sources of both. Wet processes for SO2 removal are currently being developed commercially, but to date no process for simultaneous SO2 and NO removal has passed the laboratory scale. A dry removal process would be preferred, since this would avoid flue-gas reheating, the problems of contacting the gas with a liquid or slurry, and the crystallization phenomena usually encountered in flue-gas scrubbing. The objective of this study was to develop a dry process which not only achieves high NO and SO2 removals, but also converts NO to innocuous materials and SO2 to a salable product and is potentially economical to operate.The process flow sheet is shown in Figure 1. Iron oxide, supported on alumina, acts as a catalyst for the reduction of both SOz and NO by CO and H2. Simultaneously, it acts as an absorbent for sulfur compounds, converting them to FeS. The catalyst/absorbent is in the form of fine pellets (0.05 to 0.10 mm) and contacts the gas as a falling bed in concurrent flow at 370° to 540OC. The solid is regenerated with air at 675OC to produce a rich stream of SO2, suitable for conversion to H2SO4 or elemental sulfur. Fez03 is reformed in the particles. Experiments in fixed-bed reactors using mixtures of helium and one or more reactant gases were run to demonstrate the basic process chemistry, to estimate rates for preliminary design purposes, and to look for interfering reactions. A preliminary estimation of the capital and operating costs of the process was made on the basis of the results obtained. CONCLUSIONS AND SIGNIFICANCEThe overall reactions listed in Table 1 were shown to proceed rapidly at 370" to 540°C in fixed-bed reactors using pellets of supported iron oxide 3.2 mm x 3.2 mm or particles 0.25 to 0.50 mm diameter. Iron oxide was reduced to the ferrous state, SO2 was reduced by both CO and H2, and the sulfur was absorbed ...

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Fourier transform infrared absorption spectroscopy has been used to determine the rotational temperatures of high-temperature (≤1273 K) CO/N2 gas samples. To achieve this objective, a special gas cell was constructed which permitted the acquisition of absorption spectra of samples containing CO at concentrations of 1–10% by volume in N2 and at temperatures between 295 and 1273 K. The absorption spectra were recorded with the use of a moderate-resolution (0.25 cm−1) FT-IR spectrometer. The rotational temperatures were calculated from the spectra after rigorous correction for photometric errors. Temperatures calculated from the P branch of CO spectra had accuracies of 3.2% or better. In all cases, the calculated temperatures were lower than temperatures recorded with a thermocouple, which had an accuracy of ±0.75%. An important factor in the success of these determinations was the adoption of measures to prevent the modulated spectral emission of the hot gases from reaching the detector.

The boiling point rise (BPR) of black liquor with solids content of 85 to 98% was measured in superheated steam. The BPR for 85 and 95% solids content liquor is 28 and 5 2 T , respectively. A surprisingly large amount of liquor swelling occurs in this environment. A swelling mechanism is proposed.

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