EES code for transient system

MEGN MEGN 598 (561) (561) Advanc Ad vanc ed Thermod ynamic yn amic s – Fall 2015 2015 Homework Set III-1

DUE: Wednesday 10/28

Instructions: Solve the problem below, providing (1) a neatly typed 1-page summary of your solution with approach, key equation(s), and final answers, and (2) formatted EES solution code  with commented sections and printout your: (a) formatted equations window, (b) solutions (or arrays) window with all variables assigned units, and (c) any written conclusions –which you can put directly into your EES code. Make sure your name and information is given at the top of your formatted code. Problem: Cogeneration for a Large University Campus

The buildings on a large university campus are heated with steam that is centrally produced. The steam is  produced at Ps = 600 psia, T s = 500°F in a ηb = 90% efficient coal-fired boiler (based on a heating value of  HV = 14,100 Btu/lb m for coal). The actual flow sheet of the campus heating system is quite complicated, but for the purpose of this problem, it can be represented as shown in Figure 1. The steam is throttled to Pout = 175 psia and then piped to the campus buildings. Condensate at T cond cond = 70°F, Pcond = 14.7 psia is returned to the plant, pumped to Ps using pump with efficiency η p = 0.42 and then sent back to the boiler to complete a cycle. The exergy of coal can be assumed to be 96% of its heating value.

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Figure 1. Schematic of (a) existing system and (b) proposed system

An alternative to the configuration shown in Figure 1 (a) is to utilize a steam turbine, rather than a throttle, to reduce the pressure of the steam from Ps to Pout , as shown in Figure 1(b). The turbine has an estimated isentropic efficiency of ηt = 0.70 and it drives a ηg = 90% efficient electric generator. Both systems provide Q = 2.3x1012 Btu of heat to campus buildings during an average heating season. Electricity is purchased to operate the pump. The purpose of this problem is to compare the two systems shown in Figure 1. Specifically, your solution should answer the following questions. a.) Determine the water-side state properties ( T, p, h, s, x f ) and steam mass required over the heating season

(in kg and lbm) at each of the 4 locations. Assume that the dead state is T 0 = 70°F and P0 = 1 atm. Print out the associated array table with units defined.

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MEGN 598 (561) Advanc ed Thermod ynamic s – Fall 2015  b.) How many tons of coal are used by the systems in Figures 1 (a) and (b) during the heating season? c.) How much electrical energy can be produced by the system in Figure 1 (b) during the heating season? d.) What are the major sources of exergy destruction for the systems in Figures 1(a) and (b)? e.) What are the 2 nd Law efficiencies of the boilers, and turbines in Figures 1(a) and (b)? f.) What are the 1 st and 2nd Law efficiencies of the two systems in Figure 1? g.) What is the annual cost to heat campus buildings with the system in Figure 1(a) if coal costs cc = $45/ton? Also determine the annual cost associated with the system in Figure 1(b) assuming that the electricity that is generated is valued at ec = $0.10/kWhr as charged by the local power company. h.) From a 2nd Law viewpoint, what should be the cost of electricity and process steam per kWh?

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