Chemical Process Design and Integration. Robin Smith. Chapter 23 Exercise 9

9. Complete the steam balance provided in Figure 23.57. a. Calculate extraction flows through T1 and 12 b. Calculate condensing flows of t1 and T2 from a power balance around each turbine, assuming the power generation is fixed and that the mechanical efficiency to be 97%. Assume steam turbines to be modeled by the Willans' Line Model with parameters from Table 23.1 and an intercept ratio of 0.05. Steam properties for the inlet to steam turbines can be taken to be those of the steam mains, which are given in Table 23.13. Isentropic enthalpy changes between the steam mains in Figure 23.57 are given in Table 23.14. Table 23.13 Steam properties for the steam mains in Figure 23.57. Pressure (bar) Superheat Enthalpy Saturation temperature (kJ kg) temperature (C) (C) VHP HP MP LP Condensation 100 40 15 4.5 0.12 500 400 300 200 3375 3216 3039 2858 2591 311 250 198 148 50 Table 23.14 Isentropic enthalpy changes in Figure 23.57. Inlet Outlet Isentropic enthalpy change (kJ-kg- HP MP 272 508 257 MP VHP VHP HP HP HP MP MP 507 LP Condensation LP Condensation 1049 268 824 c. Determine the steam production required from the utility boilers to meet the steam demand. d. Calculate the isentropic and overall efficiency for Turbine 14 (load = 3.75 MW), assuming the inlet conditions are given in Table 23.14 and the mechanical efficiency is 95%. c. Turbine T3 is to be shut down and the driver switched to an electric motor. It can be assumed that the inlet conditions to the turbines do not change as a result of any changes to the steam balance. The steam flows through Turbines 14 and 15 are to be maintained at their current values. However, the flows through Turbines T1 and T2 can be changed to rebalance the steam system. How much steam is needed from the utility boilers if this is done? What are the cost savings from the change? Assume that the conditions of the steam in each main are fixed to the values in Table 23.13. Boiler efficiency Fuel cost Power cost = 0.92 = 5.69 S-GJ-! = 55 S.MWh