Anonymity Code: ___________________________________ 1
Process Design – Energy Carrier Production
7,5
ECTS
Ladok code:A500TA
The exam is given to: KMREC
Date of exam: May 31, 2018 Time: 09.00-13.00
Means of assistance: Calculator, Steam table, Dictionary
Total amount of points on exam: 50 points Requirements for grading:
Grade F: Less than 17 points Grade FX: Minimum 17 points Grade E: Minimum 20 points Grade D: Minimum 25 points Grade C: Minimum 30 points Grade B: Minimum 35 points Grade A: Minimum 40 points Additional information:
Next re-exam date:
The marking period is, for the most part, 15 working days, plus up to 5 working days for administration: Otherwise it´s the following date:
Important! Do not forget to write the Anonymity Code on each paper you hand in! Good Luck!
Examiner: Phone number:
Anonymity Code: ___________________________________ 2 1. When designing a heat exchanger network, one common strategy is to use Pinch technology. In this case you have 4 streams (2 hot and 2 cold) with the following stream data:
Tin (°C) Tout(°C) Heat capcity,
mcp ( kW/K) Hot stream 1 270 80 15 Hot stream 2 220 60 10 Cold stream 1 50 220 20 Cold stream 2 160 210 20 a. Draw the GCC curve (2p) b. What is the Pinch temperature? (2p) c. Determine the minimum energy requirement of hot and cold utility (2p) d. Design a minimum energy requirement heat exchanger network (5p) e. What will happen with the Pinch Point and the heating and cooling demand if the mass flow of Cold stream 2 is doubled? (2p) 2. A company is investing in a new process and has two different alternatives; project A and project B. The minimum company discount rate is 10%. Initial investment $million After tax cash flow (year 1) $million After tax cash flow (year 2‐9) $million Project A 60 11 13 Project B 100 15 21 Discount factors: P to F: 1 F to P: 1 A to P: a. Draw the non‐discounted cash flow diagram for both projects (2p) b. Find the NPV for each project (2p) c. What discount rate would give NPV=0? (2p) d. Which of the projects is recommended? Justify your answer! (2p)
Anonymity Code: ____________________________________________ 3. A common way to produce electricity from a solid fuel is first to combust the fuel and use the released heat in a Rankine cycle a. Describe how a Rankine cycle works and the main parts (2p) b. One way to increase the efficiency of a Rankine cycle is to introduce a feed water heater. Why will the efficiency increase if a feed water heater is added and what measures are necessary in the process in order to introduce the feed water heater? (3p) c. There are two types of feed water heaters; explain how they work and what the benefits and drawbacks are with each of them. (4p) d. Describe at least two other options to increase the electrical efficiency in a power boiler (2p) e. Why has it become easier to justify waste combustion in Sweden compared to other countries like Spain? (2p) 4. Within a power boiler, the heat exchanging to the steam occurs through a number of different heat exchanger sections. a. What sections are present in a typical boiler? (2p) b. What is the sequence with respect to flue gas and water respectively? (2p) 5. Waste with the net calorific value 11 MJ/kg is burned in a Clausius‐Rankine process producing electric power, see the figure below. The steam generated in the boiler has the temperature t=400 °C and the pressure p=40 bar. After some time, the fuel is changed to biomass, with the net calorific value 10 MJ/kg. The superheaters are modified in this case in order to produce a steam with the temperature t=540 °C and the pressure p=140 bar, which increases the efficiency of the process. One feedwater heater using an extracted steam at 3.5 bar is used and the condenser is cooled by river water and could thus maintain a pressure of 0.08 bar. The steam flow and the feed water temperature before the economiser are the same in both cases. The generator efficiency is 96% and the turbine internal thermodynamic efficiency is 85%. a. Calculate the electric power (MW) produced in both cases. (8p) b. Research work has made it possible to increase the steam temperature in waste combustion to 450 °C and in biomass combustion to 600 °C. How much extra income is made with the increased steam data, given that the electricity is worth 0.5 SEK/kWh? The yearly operating time is 6000 hours. (4p)
