The stripper off-gas in Problem 13.29 is typically sent to a Claus unit for sulfur recovery. For maintaining the minimum flame temperature in the Claus furnace, it is necessary to maintain the H S concentration in excess of about 25 mol%. Implement a design block that manipulates the bottoms/feed ratio in T-2002 to maintain the H S concentration in the stripper off-gas at 40 mol%. Did you face any convergence problems? How did you solve them? (Make a considerable change in the bottoms/feed ratio in the absence of the design block. Did it converge? What should you have done to aid in the convergence for a large change in any of the operating variables?) 

Problem 13.29

Consider Problem 13.28. The solvent MDEA becomes rich in acid gases. To recycle this solvent, it is first heated to 90°C in exchanger E-2001 and then sent to the top stage of the stripper T-2002 as shown in Figure P13.29. Develop a nonequilibrium-stage model of the stripper with 20 theoretical stages, a partial-vapor condenser, and a kettletype reboiler. Reflux ratio (mole basis) = 0.7 and bottoms/feed ratio (mole basis) = 0.97. The pressure in the condenser is 1.4 atm, and the pressure drop through the entire column should be calculated. Consider the ionic reactions in all the stages, including the condenser and reboiler. It can be assumed that all ionic reactions reach equilibrium in the condenser and reboiler because of the longer residence times. Assume that the tray hardware is similar to the absorber. The mass transfer and the ionic reactions in the liquid and vapor films can be modeled similarly to Problem 13.28. For this problem determine the following:

1. What are the duties of the stripper and reboiler?

2. What are the compositions of Streams 6 and 7?

3. What operating condition(s) of the stripper would you change if you wanted to increase the purity of Stream 7?

Transcribed Image Text:

Solvent Acid Gas 2 1 3 T-2001 4 Sweet Gas E-2001 5 T-2002 6 7 Stripper Off-Gas Rich Solvent Figure P13.29 Schematic of the Absorber and Stripper of an AGR Plant Using MDEA as the Solvent Lean Solvent