Particulate residence time

Buesseler KO, Charette MA (2000) Commentary on How accurate are the based particulate residence times in the ocean by G. Kim, N. Hussain and T. Church. Geophys Res Lett 27 1939-1940 Buesseler KO, Steinberg DK, Michaels AF, Jonson RJ, Andrews JE, Valdes JR, Price JF (2000) A comparison of the quantity and quality of material caught in a neutrally buoyant versus surface-tethered sediment trap. Deep-Sea Res 147 277-294... 

Kim G, Hussain N, Church TM (1999) How accurate are the based particulate residence times in the ocean . Geophys Res Lett 26 619-622... 

Two versions of the ACP have been developed (1) an open-loop configuration in which the dry spent absorbent is simply removed from the system for disposal and fresh alkali is continuously fed to the spray dryer, and (2) a closed-loop process in which the spent absorbent is regenerated and reused. The open-loop system was installed on the 410 MW, Coyote Station at Beulah, North Dakota (Botts et al., 1978). The plant used a spray dryer followed by a fabric filter for simultaneous SO2 and dust removal. As indicated by the flow diagram of Figure 7-32, the process is extremely simple. Because the particulate collected on the fabric filter bags remains on the fobric for a period of time, the gas-solids contact time is extended beyond the particulate residence time in the spray diyo so additional absorption of SO2 by the alkaline material occurs. After this system went conunercial in 1981. no other large soda ash spray dryers were built. About 1990, this scrubber was converted finm soda ash to lime to eliminate solids build-up in the dryer vessel and to use lower cost lime. The... 

Often the required pressure drop through the downstream particulate removal device is not estabUshed until actual operation, and furnaces are sized assuming Httle or no pressure drop across the particulate removal device to allow adequate furnace residence time under all operating conditions. 

In AFBC units, heat is removed from the flue gas by a convection-pass tube bank. The particulates leaving the boiler with the flue gas consist of unreacted and spent sorbent, unburned carbon, and ash. Multiclones after the convection pass remove much of the particulate matter and recvcle it to the combustor, increasing the in-furnace residence time an improving combustion efficiency and sulfur retention performance. Bubbling PFBC units do not have convection-pass tube banks and do not recycle solids to the boiler. 

Tubular reactors have been the main tools to study continuous flow processes for vapor or gas-phase reactions. These are also used for reaction in tv o flowing phases over a solid catalyst. When the catalyst is in a fixed bed, the contact between the liquid on the outside surface of the particulate is uncertain. For slurry-type solid catalyst the residence time of the catalyst or the quantity in the reactor volume can be undefined. 

The deposition velocities depend on the size distribution of the particulate matter, on the frequency of occurrence and intensity of precipitation, the chemical composition of the particles, the wind speed, nature of the surface, etc. Typical values of and dj for particles below about 1 average residence time in the atmosphere for such particles is a few days. 

Indeed Kim et al. (1999) have argued that better agreement is obtained from a one-box model approach, in which the particulate Th residence time is calculated as the difference between the residence times of total Th and dissolved Th (effectively the difference in the l/k values calculated from Eqns. 5 and 6). However, Buesseler and Charette (2000) argued in a response to Kim et al. (1999) that there is abundant evidence to support the notion that residence times of POC and Th are different in the euphotic zone. 

Buesseler et al. (1992b) proposed a method to circumvent these difficulties in comparing residence times. They argued that the deficiency in total " Th with respect to indicates a flux of " Th in association with particles sinking out of the euphotic zone. If the POC (or particulate organic nitrogen, PON)/ Th ratio of these sinking particles is known, a POC (or PON) flux can be calculated as ... 

Baskaran and Santschi (1993) examined " Th from six shallow Texas estuaries. They found dissolved residence times ranged from 0.08 to 4.9 days and the total residence time ranged from 0.9 and 7.8 days. They found the Th dissolved and total water column residence times were much shorter in the summer. This was attributed to the more energetic particle resuspension rates during the summer sampling. They also observed an inverse relation between distribution coefficients and particle concentrations, implying that kinetic factors control Th distribution. Baskaran et al. (1993) and Baskaran and Santschi (2002) showed that the residence time of colloidal and particulate " Th residence time in the coastal waters are considerably lower (1.4 days) than those in the surface waters in the shelf and open ocean (9.1 days) of the Western Arctic Ocean (Baskaran et al. 2003). Based on the mass concentrations of colloidal and particulate matter, it was concluded that only a small portion of the colloidal " Th actively participates in Arctic Th cycling (Baskaran et al. 2003). 

Americium released to the atmosphere will be associated with particulate matter and will be deposited on land or surface water by dry deposition or wet deposition (Essien et al. 1985). Dry deposition results from gravitational settling and impaction on surfaces, and wet deposition returns americium to earth in precipitation. Radionuclides resulting from atmospheric weapons tests are often injected into the lower stratosphere, while other atmospheric releases are into the troposphere. The residence time of particles in the atmosphere will depend on the altitude, latitude, season, and hemisphere because of atmospheric... 

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