Question

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The context for the set of questions below is a gas-fired industrial boiler. Continuous emission monitoring requires that the flow of combustion gases be quantitated to allow for estimation of the total mass of each constituent emitted from the stack. Assume that the duct leading from the combustion chamber is exposed to outside air in a vertical run as it leaves the combustion chamber. Velocity of flow is to be measured within the outlet duct of the natural gas combustion chamber. The apparatus will employ a 1 mm diameter hot-wire anemometer. The wire is polished, AISI grade 316 stainless steel wire, connected within a Wheatstone bridge circuit to maintain a constant wire temperature. Flow velocity will be correlated with current draw necessary to maintain constant wire temperature. The inside diameter of the duct is 2 m and the wire is stretched across a diameter of the duct at a position 4 m downstream of the beginning of the duct, which has a rough-edged intersection with the combustion chamber. The composition of the combustion off-gas is 85% nitrogen and 15% carbon dioxide, on a molar basis. At the point of measurement, the temperature of the flowing gas will be 750 °K. The temperature of the wire is held constant at 800 °K and the temperature of the inside wall of the duct is nearly constant at 650 °K. A thermocouple employing a 2-mm junction bead, also constructed from polished AISI grade 316 stainless steel, is used to simultaneously measure the temperature of the gas. This pair of measurements (gas velocity and temperature) is used to determine the molar gas flow rate for the continuous emission monitoring system operated to quantitate emissions from this industrial boiler. The duct walls are configured as a layered system with the inner wall being ½” thick plain carbon steel and the outer wall being 3” of cement mortar. At the point of measurement, the exterior of the duct is open to the ambient atmosphere. The worst-case weather conditions for heat loss from the duct include a wind speed

Answer 1