Calculation process for specialized knowledge in chemical engineering, 2011
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34. A factory originally had two quick-install boilers; when operating simultaneously, each boiler generated 11.5 Nm3 of flue gas per second, with an exit temperature of 150°C and a pressure of 110 kPa (A). To increase production now, another identical boiler is needed. In accordance with environmental regulations, the existing low and old chimney must be removed, and a new tall chimney must be built. If the velocity of the exhaust gas flow at the outlet is allowed to be 25 m/s, which of the following values should be chosen for the inner diameter of the outlet of the new chimney (in mm)? Tip: Flue gas can be considered an ideal gas. A、1000 B、1300 C、1400 D、160035、It is necessary to use a dust removal chamber to purify hot air with a temperature of 180°C and a flow rate of 2500 m3/h. The viscosity of hot air is 2.49×10-5 Pa·s, and its density is 800 g/m3. The purified hot air is required to contain no dust particles larger than 15 μm, with the density of such dust particles being 2100 kg/m3. Assuming that 15μm dust particles in hot air settle within the laminar region governed by Stokes’ law, what is the minimum settling area (in m2) required for the dust removal chamber? A、109 B、6.7 C、67 D、10.939. Air at room temperature is fed into the bottom of the packed tower; after coming into contact in reverse flow with the large amount of hot water sprayed from the top of the tower, it is discharged from the top. The air exiting the tower contains a large amount of water vapor, and it is required that the saturation degree be 80%. If the molar ratio of water vapor to air in the gas exiting the tower is 1:2.024, and the pressure inside the tower is 101.3 kPa (A), what is the temperature of the gas exiting from the top of the tower? Saturated vapor pressure of water at different temperaturest, °C | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72
pH2O0, kPa | 25.00 | 26.15 | 27.33 | 28.56 | 29.83 | 37.16 | 32.66 | 33.96
t, °C | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80
pH2O0, kPa | 35.48 | 36.95 | 38.54 | 40.18 | 41.88 | 43.63 | 45.46 | 47.34
t, °C | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88
pH2O0, kPa | 49.29 | 51.32 | 53.41 | 55.57 | 57.81 | 60.11 | 62.48 | 64.94
t, °C | 89 | 90 | 91 | 92 | 93
pH2O0, kPa | 67.48 | 70.10 | 72.31 | 75.60 | 78.48
A. 93 B. 87 C. 77 D. 66
I have no idea how to approach question 34 at all. Where can I find the relevant formula? I have no idea how to solve the other 2 questions either; please help!
For the first question, the flow rate under standard conditions must be converted to the flow rate under operating conditions, and then Q can be calculated using Au； The second question is related to the floor area of the dust removal chamber; Q=Au can be used to calculate it ； The third question is about calculating saturated steam – you just need to look it up in a table; it’s very simple
Agree with the person above. The landlord should read the textbook carefully. For the first question, it’s three times 11.5 NM3; once the temperature and pressure under operating conditions are known, they are used in the calculations, and then dividing by the maximum speed gives the area of the chimney. Question 2 asks for the settlement velocity ut, examining what parameters are related to the processing capacity of the sedimentation chamber. Question 3 tests the understanding of concepts: once the actual absolute humidity at a given pressure is known, the saturated humidity at the same pressure can be determined by reverse calculation; the temperature can then be found by referring to the table provided in the question.