The results are presented of a study conducted to examine the reactivity of NaHCO 3 and its thermally decomposed product, Na 2 CO 3 , with SO 2 as a function of temperature and particle size in a simulated flue gas. The NaHCO 3 reaction was found to be significantly more efficient than the Na 2 CO 3 reaction for temperatures less than 450°F (230°C) with a maximum efficiency of conversion occurring between 250 and 350°F. In the temperature range of 450-650°F, both compounds were observed to behave similarly. The Na 2 CO 3 reaction with SO 2 was found to be dependent on particle size in the range of 20-200 /tm for temperatures less than 450°F. The focus on sodium bicarbonate (NaHCOs) as a dry additive injection material for flue gas desulfurization (FGD) systems has come about mainly from the abundance and proximity of nahcolite to oil shale reserves, and the desire to identify an all dry FGD system. Nahcolite is a naturally occurring form of sodium bicarbonate (70% NaHC0 3 , remainder inerts), found in large underground deposits in northwestern Colorado, northeast Utah and southeast Wyoming which places it within a reasonable transportation range for coalfired steam plants located in the western part of the U.S. In addition, trona (Na 2 CO 3 NaHCOg • 2H 2 O) is also a candidate for FGD and is located in large deposits in the.U.S. Data have been collected on a variety of pilot and full scale fabric filter collectors to demonstrate the ability of the above compounds to remove SO2. 1 "" 3 These reports have concluded that the temperature, size of additive and type of injection technique (continuous versus batch) have been observed to affect the performance. Also it has been shown that sodium carbonate (N&2CO3), the product of decomposition of NaHC(>3, does not react as readily with SO2 as the parent NaHCO3. A possible explanation for this behavior may stem from the effect of the heated flue gas on thermally decomposing the NaHCOg into the product Na2COs while undergoing simultaneous reaction with SO2. The decomposition reaction for NaHC03 is given by: 2NaHCO 3 (s) Na 2 CO 3 (s) CO 2 (g) + H 2 O(g) (1)
Airborne black carbon from urban traffic is a climate forcing agent and has been associated with health risks to near-road populations. In this paper, we describe a case study of black carbon concentration and compositional variability at and near a traffic-laden multi-lane highway in Cincinnati, Ohio, using an onsite aethalometer and filter-based NIOSH Method 5040 measurements; the former measured 1-min average black carbon concentrations and the latter determined the levels of organic and elemental carbon (OC and EC) averaged over an approximately 2-h time interval. The results show significant wind and temperature effects on black carbon concentration and composition in a way more complex than predicted by Gaussian dispersion models. Under oblique low winds, namely ux[= u × sin(g=q)]~ (0,−0.5 m s−1), which mostly occurred during morning hours, black carbon concentrations per unit traffic flow were highest and had large variation. The variability did not always follow Gaussian dispersion but was characteristic of a uniform distribution at a near-road distance. Under all other wind conditions, the near-road black carbon variation met Gaussian dispersion characteristics. Significant differences in roadside dispersion are observed between OC and EC fractions, between PM2.5 and PM10–2.5, and between the morning period and rest of the day. In a general case, the overall black carbon variability at the multi-lane highway can be stated as bimodal consisting of Gaussian dispersion and non-Gaussian uniform distribution. Transition between the two types depends on wind velocity and wind angle to the traffic flow. In the order of decreasing importance, the microclimatic controlling factors over the black carbon variability are: 1) wind velocity and the angle with traffic; 2) diurnal temperature variations due to thermal buoyancy; and 3) downwind Gaussian dispersion. Combinations of these factors may have created various traffic–microclimate interactions that have significant impact on near-road black carbon transport.
The thermal decomposition of sodium bicarbonate, a candidate material for Ilue gas desulfunzation. has been investigated over the temperature range of 225-350°F (.380-450K) and over the particle size range of 51-140 ,urn. The shrinking core model, with chemical reaction as the rate controlling step, provides a good fit to the data in the temperature range investigated. However, caution should be exercised in extrapolating these results into the range of about 600"F (about 590K) where sintering of this material is reported to occur. The activation energy of the decomposition reaction is 20.5 kcal/mol (85.7 k.l/rnol).
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