PMC:4534144 / 4757-9306 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4534144","sourcedb":"PMC","sourceid":"4534144","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4534144","text":"Materials and methods\n\nIncinerator specification\nA rotational PCBs incinerator with one inlet and one outlet for pollutants was studied. The incinerator was designed for one of PCBs isomers called Arochlorine-1242 (a mixture of 1 % C12H9Cl, 13 % C12H8Cl2, 45 % C12H7Cl3, 31 % C12H6Cl4 and 10 % C12H5Cl5 with average Cl content of 42 %. Arochlorine-1242 is among the most commonly used types of PCBs, especially in power transformers in great plants. The specification of the incinerator was selected according to Theodore and Reynolds [23]. The Arochlorine-1242 incinerator was designed manually and with the help of software. The design principles in different parts of incinerator such as primary and secondary combustion chambers, furnaces, boilers, suppressor devices and air pollution control devices were similar to the incinerator modeled in [23]. Design calculations were performed according to Charles’s law and Dulong’s equation. Table 1 summarizes the specification calculated for the incinerator. The technical specifications presented in Table 1 were used as initial inputs to Fluent model for simulating the incinerator.\nTable 1 The technical specification of the incinerator\nValue Parameter\n2270 (kg/h) Maximum capacity\nC12H7Cl3 Input pollutant\n20,277 (KJ/Kg) Net thermal value\n50 % Excess air\n2.76 m Initial diameter\n11 m Initial height\n0.5 m Inlet and outlet diameter\n2.7 s Initial residence time\n\nThe equations governing the pollutant flow in the incinerator\nGiven the air flow velocity and the dimensions of the incinerator as well as the high temperatures, the flow regime is turbulent. Neglecting the net rotating flows, since all changes along the flow and in vertical direction are important, the k-ε turbulence model is a good model for analyzing this problem. The equations required to solve the isothermal gas flow in the incinerator include time-averaged mass and momentum conservation equations [24]:\nMass conservation ∂Ui∂Xi=0 (1)\nMomentum conservation2 ∂ρUi∂t+∂ρUiUj∂Xi=∂p∂Xi+ρ∂∂Xjv∂Ui∂Xi+∂Ui∂Xi−∂Ui′Ui′∂Xj+SMiWhere Ui is velocity along i, i = 1, 2, 3, Xi is x, y, z coordinates along i, Y mass fraction of gas emissions, ρ air density, υ kinematic viscosity, Ui turbulent velocity component along i’ and SMi is the momentum source along i’.As mentioned previously, since the Reynolds removal process and time-averaged equations will lead to unknown relationships for fluctuating velocity components, so a turbulent model is also needed. Thus, the k-ε model was used. This model requires the solution of two additional transport equations, one for turbulent kinetic energy, k and the other for its dissipation rate or ε [24]:3 ∂∂xiρuik=∂∂xiμ+μtδk∂k∂xi+P−ρε4 ∂∂xiρuiε=∂∂xiμ+μtδε∂ε∂xi+C1εkP−C2ρε2k\nEnthalpy conservation: ∂∂xiρuih=∂∂xiμ+μtδh∂h∂xi+Sh (5)\nChemical species conservation: ∂∂xiρuims=∂∂xiμ+μtδh∂ms∂xi+Ss (6)\nEquation of State: ρ=PRTσmj/Mj (7)\n\nIncinerator simulation\nTo simulate the studied incinerator, a Cartesian coordinate system with the dimensions of 20 × 20 × 20 mm containing 10,424 control volumes was used. The x, y and z axes represent the length, width and height, respectively [24]. In the regions where sharp gradients in the variables are expected, fine meshing is considered as possible. Structured meshes were used for meshing the model, because the number and distribution of meshes in different solution regions can be controlled. In addition, the boundary conditions can be well defined [24]. The boundary layer mesh generator was used in the regions where thermal analysis was important. Fig. 1a and b show the model, the meshed model and boundary conditions.\nFig. 1 a A view of the meshed model of the incinerator, (b) The geometrical charactersitics of the incinerator and boundary conditions\nWall boundary condition was considered on the studied incinerator, because the solid surface is in direct contact with the fluid [24]. Given that the size and profile of the inlet pressure to the studied incinerator are known, the pressure inflow and pressure outflow were selected for inlet and outlet boundary conditions, respectively. The walls were made of steel with a thermal conductivity of 202 W/M.K. For the flows with a velocity less than the speed of sound, a turbulence of less than 5 % can be considered as assumed in the present model. Other inputs are described in Table 2.\nTable 2 The inputs to the Fluent model\nValue Parameter\n3 % Turbulent Intensity\nStationary Wall Motion\nNo slip Shear Condition\n0.00004 (m) Roughness Height\n2.76 (m) Hydraulic Diameter\n0.5 Roughness Constant","divisions":[{"label":"title","span":{"begin":0,"end":21}},{"label":"sec","span":{"begin":23,"end":1413}},{"label":"title","span":{"begin":23,"end":48}},{"label":"p","span":{"begin":49,"end":1413}},{"label":"table-wrap","span":{"begin":1135,"end":1413}},{"label":"label","span":{"begin":1135,"end":1142}},{"label":"caption","span":{"begin":1143,"end":1189}},{"label":"p","span":{"begin":1143,"end":1189}},{"label":"table","span":{"begin":1190,"end":1413}},{"label":"tr","span":{"begin":1190,"end":1205}},{"label":"th","span":{"begin":1190,"end":1195}},{"label":"th","span":{"begin":1196,"end":1205}},{"label":"tr","span":{"begin":1206,"end":1234}},{"label":"td","span":{"begin":1206,"end":1217}},{"label":"td","span":{"begin":1218,"end":1234}},{"label":"tr","span":{"begin":1235,"end":1259}},{"label":"td","span":{"begin":1235,"end":1243}},{"label":"td","span":{"begin":1244,"end":1259}},{"label":"tr","span":{"begin":1260,"end":1292}},{"label":"td","span":{"begin":1260,"end":1274}},{"label":"td","span":{"begin":1275,"end":1292}},{"label":"tr","span":{"begin":1293,"end":1308}},{"label":"td","span":{"begin":1293,"end":1297}},{"label":"td","span":{"begin":1298,"end":1308}},{"label":"tr","span":{"begin":1309,"end":1332}},{"label":"td","span":{"begin":1309,"end":1315}},{"label":"td","span":{"begin":1316,"end":1332}},{"label":"tr","span":{"begin":1333,"end":1352}},{"label":"td","span":{"begin":1333,"end":1337}},{"label":"td","span":{"begin":1338,"end":1352}},{"label":"tr","span":{"begin":1353,"end":1384}},{"label":"td","span":{"begin":1353,"end":1358}},{"label":"td","span":{"begin":1359,"end":1384}},{"label":"tr","span":{"begin":1385,"end":1413}},{"label":"td","span":{"begin":1385,"end":1390}},{"label":"td","span":{"begin":1391,"end":1413}},{"label":"sec","span":{"begin":1415,"end":2880}},{"label":"title","span":{"begin":1415,"end":1476}},{"label":"p","span":{"begin":1477,"end":1928}},{"label":"p","span":{"begin":1929,"end":1959}},{"label":"p","span":{"begin":1960,"end":2725}},{"label":"label","span":{"begin":1981,"end":1982}},{"label":"label","span":{"begin":2655,"end":2656}},{"label":"label","span":{"begin":2686,"end":2687}},{"label":"p","span":{"begin":2726,"end":2780}},{"label":"p","span":{"begin":2781,"end":2845}},{"label":"p","span":{"begin":2846,"end":2880}},{"label":"title","span":{"begin":2882,"end":2904}},{"label":"p","span":{"begin":2905,"end":3754}},{"label":"figure","span":{"begin":3619,"end":3754}},{"label":"label","span":{"begin":3619,"end":3625}},{"label":"caption","span":{"begin":3626,"end":3754}},{"label":"p","span":{"begin":3626,"end":3754}},{"label":"label","span":{"begin":4344,"end":4351}},{"label":"caption","span":{"begin":4352,"end":4382}},{"label":"p","span":{"begin":4352,"end":4382}},{"label":"tr","span":{"begin":4383,"end":4398}},{"label":"th","span":{"begin":4383,"end":4388}},{"label":"th","span":{"begin":4389,"end":4398}},{"label":"tr","span":{"begin":4399,"end":4422}},{"label":"td","span":{"begin":4399,"end":4402}},{"label":"td","span":{"begin":4403,"end":4422}},{"label":"tr","span":{"begin":4423,"end":4445}},{"label":"td","span":{"begin":4423,"end":4433}},{"label":"td","span":{"begin":4434,"end":4445}},{"label":"tr","span":{"begin":4446,"end":4469}},{"label":"td","span":{"begin":4446,"end":4453}},{"label":"td","span":{"begin":4454,"end":4469}},{"label":"tr","span":{"begin":4470,"end":4498}},{"label":"td","span":{"begin":4470,"end":4481}},{"label":"td","span":{"begin":4482,"end":4498}},{"label":"tr","span":{"begin":4499,"end":4526}},{"label":"td","span":{"begin":4499,"end":4507}},{"label":"td","span":{"begin":4508,"end":4526}},{"label":"td","span":{"begin":4527,"end":4530}}],"tracks":[]}