8/19/2019 Problem Set on N and Lime

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ChE 140 WCD/FRU & SDE/SWX

Problem Set on Nitrogen Compounds and LimeDeadline: 28 March 2016 (Monday)

Show your complete solution to the following problems.

1. In a Haber plant the gas leaving the CuCl tower contains 75.16% H 2, 24.57% N 2, and 0.27%inerts. The gas entering the first bank of converters contains 79.52% H 2, while the gasleaving the absorber, which follows the first bank, contains 80.01% H 2. Absorption of NH 3is substantially complete, and the design of the absorber is such that the amount of

permanent gases removed from the system in the absorbing medium is negligible. What isthe efficiency of utilization of H 2 in the first bank? What is the percent conversion of H 2 per

pass, i.e., the mols of H 2 reacting to form NH 3 per 100 mols of H 2 entering the converters?2. A synthetic-ammonia unit with a single converter is converting a fresh feed gas containing

75.8% H 2, 23.7% N 2, and 0.5% inerts. The gas leaves the converter containing 18.6% NH 3and 70.0% H 2. This converted gas is fed to a cooler under conditions of temperature and

pressure such that most of the ammonia leaving the converter is condensed to a liquid andremoved. On reduction of pressure all the dissolved gases are evolved from this liquidammonia. These are compressed and recycled to the inlet of the converter, except for a purge

provided in the recycle line. The uncondesed ammonia leaving the cooler in these gases isfound to be 8% of that leaving the converter. Calculate the amount and composition of the

purged gases per 100 mols of feed gas, and determine the net mols of residual gas recycledto the converter inlet per 100 mols of feed gas.

3. A plant consisting of five identical vertical lime kilns was tested over a 12-hr period undernormal operating conditions to determine its performance. Each kiln was 63 ft high and hadan outside diameter of 10 ft. The kilns were housed in a building 40 ft high. Below the roof,the average temperature was 120°F. The average gas analysis of the charge was 97.5%CaCO 3. The total production of lime from all five kilns during the 12-hr period was 139,500lb, and the average analysis 93% CaO, 3.8% core, and 3.2% inerts. The average temperatureof the lime at the fire boxed was 1920°F and at the discharge table 569°F. The fuel was

producer gas, which entered the kilns at an average temperature of 787°F. The producer gascontained 7.9% CO 2, 1.0% O 2, 18.4% CO, 3.7% CH 4, 12.1% H 2, and 56.9% N 2; and its dew

point was 112°F. The average composition of the top gas was 22.4% CO 2, 5.6% O 2, 0.3%CO, and 71.7% N 2; and its temperature averaged 626°F. The air entered the bottom of thekiln at an average temperature of 626°F. The air entered the bottom of the kiln at an average

temperature of 60°F, carrying 0.0046 lb H 2O per pound dry air. Calculate the followingquantities:a. Mols of dry producer gas per ton lime

b. Mols of dry air per ton limec. Mols of dry top gas per ton limed. Mols of H 2O in the top gas per 100 mols dry gase. Percent excess airf. Btu lost to the surroundings through the walls of the kiln per ton of stone