The results are posted no longer than three weeks after the exam

Transcription

1 Energy Recovery 7.5 ECTS Ladok code: The exam is given to: TK691C Resource Recovery- Sustainable Engineering Name: Personal number: Date of exam: Time: Means of assistance: English Dictionary, Calculator, Steam tables Total amount of point on exam: 50 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: The results are posted no longer than three weeks after the exam Important! Do not forget to write your name on each paper you hand in. Good luck! Contact: Anita Pettersson Phone number:

2 Part I Combustion (16) 1. Mention three common combustion devices for solid fuel and describe them briefly. (3p) 2. High steam temperature and pressure enable a high electric efficiency of boilers. What are the traditional values of the steam temperature and pressure to the turbine in Energy-from-Waste boiler plants? What is the phenomenon that limits the increase of the steam parameters? (3p) 3. During combustion the flue gas generated contains moisture. Explain the source(s) of this moisture. (3p) 4. The net calorific value on combustibles (H ic ) is 20 MJ/kg for a certain fuel. It has the moisture content 20 % and the net calorific value (H i ) 15 MJ/kg. Calculate the ash content. (5p) 5. Compare a fluidised bed boiler plant located in India burning waste and producing electric power for air condition with the waste fired boiler plant at Borås Energy. What is (are) the main difference(s) of these applications? Compare the thermal efficiency of these two processes. Are they similar? If not, then explain the major difference(s). Part II Inorganic reactions (9 p) 6. Ash forming compounds often causes trouble in the boiler system during waste combustion. a. Especially in what/whish aggregation form? (1p) b. What 4 types of problem do they contribute to? 7. Different bio- and waste fuels have very different element compositions whish also gives large differences in the amount of ash. List the fuel groups after the their amount of ash starting with the fuel having the smallest ash fraction: Wood; Solid Waste; Straw; Oil; Sewage Sludge 8. When deposits are formed on super heater tubes and walls in boilers four mechanisms are identified. a. Describe how thermophoresis works. b. What is characteristic with the deposits formed by thermophoresis. (1p) 9. Waste derived ashes have both good and bad properties. Some of the bad are that they hold dioxin and heavy metals. Give four examples on good properties that these ashes often have. (1p) 1

3 Part III Gasification and thermal treatment (15 p) 10. Using Le Chatelier s principle, how would the partial pressures at equilibrium change as a consequence of a rise in i) total pressure and ii) temperature, respectively, in the following rections. The heats of formation for CO is kj/mol, for H 2 O -241,8 kj/mol, for CO 2-393,5 kj/mol and for CH 4-74,87 kj/mol. a. CO + H 2 O H 2 + CO 2 (3p) b. CH 4 + H 2 O CO + 3 H 2 (3p) 11. Compared with combustion, what are the main features, advantages and disadvantages of gasification. (4p) 12. Consider a rate equation for a chemical reaction of the type, where m, t and k are mass, time and rate coefficient, respectively. According to the Arrhenius equation. a) How shall the frequency factor, A, and the activation energy, E, be interpreted? b) Assuming that A and E be s -1 and 180 kj/mol, respectively, what is the mass loss rate for a piece of wood of 1 g at 350 C? c) How much would the temperature have to be risen to increase the mass loss tenfold? (1p) Part IV Materials, erosion and corrosion (10p) 13. Stress-Strain diagrams are used to determine some properties of different materials as metals. a. Describe how a stress-strain analysis is performed (1p) b. What properties can be determined and how? 14. A piece of Copper, originally 450 mm long is pulled in tension with a stress of 500 MPa. a) If the deformation is entirely elastic, what will be the resulting elongation? (1p) b) What is then the Strain? 2

4 15. Most metals form oxides on the surface and the properties of the formed oxide strongly depends on the environment the metal is exposed to. a. Give 4 properties a oxide need to have to be protective. b. Describe why the oxide formation of Fe and Cr are so different, se picture below. Good luck! 3

5 Stress, σ= Eε σ= F/Ao Strain, ε = (L-Lo)/Lo = L/Lo %EL = (Lf-Lo)/Lo)*100 Lf = Lo+ ε f Lo (1 N/mm 2 = 10 6 N/m 2 = 1 MPa) Oxidation kinetiks: Linear oxidation x k t + D = 1 Parabolic oxidation dx k p = x = 2 k dt x Logarithmic oxidation x = kl log t + A p t + C 4

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