CH 3070 - Model Questions - S5 - 2013

Model Questions CH 3070 – Energy Efficiency & Conservation

June 26 th 2016

Please note that these are model questions only. There is NO guarantee that similar questions would be given in the examination. Model questions are provided as a brief guidance on the depth of subject matter which will be assessed during the exam. Exam questions could be lengthier or concise than the model questions. There may be certain sections which are not covered in the model questions.

Q1. As a part of the exercise to find the heat loss with steam condensate streams it was first decided to measure flow rates of steam condensate at an average temperature of 75oC. Since there are no flow recorders in the condensate lines they decided to install orifice flow meters in all the condensate lines which are of considerable diameter. a. Since this method involves cutting of lines and inserting orifices can you suggest any other solution to get the measurements without cutting lines? b. In one of the pipes where cross section area is 900 mm 2 it gave a p of 500 Pascal Gauge. If they have used an orifice meter with an area ratio ‘R’ of 4. Calculate condensate flow through this pipe using equation

∆    ∙  ∙      . If any parameters are not available

assume suitable values and state clearly your assumptions. c.

During this exercise they have noticed that steam is also escaping through condensate lines. What could be the reasons for this? d. Suggest using a line flow a diagram where this condensate condensate can be used to conserve energy energy e. What is the effect of temperature variation of the flowing fluid to the measured flow value?

Q2. An industrial facility whose loads are mainly consisting of induction motors found out recently that their electricity bill is the major portion of their operating costs. a. Two of their bigger pumps which operate continuously, generates a pressure difference of 40 psi as per their readings and a flow of around 240 m 3/day. Calculate their contribution to monthly energy consumption. State clearly any assumptions you make. b. Explain Load current and Torque variations of a motor with its speed using graphs c. As a cost reduction measure the energy department of the facility thought of installing capacitors to the existing plant. If Market values for capacitors are 150 Rs/kVAr and Cost of supply is 260 Rs/ kVA derive an equation to get maximum savings for power factor variation and calculate the optimum of the power factor using given figures.

Q3. Boilers are used to generate steam at various various pressures and temperatures and they are heavy consumers of fuel. Safe and Efficient operation of a steam plant require superior engineering and technical skills. a. Explain the difference between saturated steam and superheated steam b. Gaseous Propane is fired to produce saturated steam in a boiler burner with an Air/Fuel ratio (volumetric) of 25. Find the Volumetric analysis of products and composition of dry flue gas

1| 5

c.

To verify the theoretical values derived in previous part (b), what analytical instruments can be used? d. If the producer wants to generate power using this steam plant what modifications should he be performing? Use sketches or line diagrams to clarify your answer if required e. While trying to extract as much as possible heat from flue gasses engineers got restricted by a certain scientific phenomenon. Explain the cause and effects of this phenomenon.

Q4. Psychrometry is a term used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas‐vapor mixtures. a. Explain the following terms with respect atmospheric air: Relative Humidity, Humidity Ratio and Psychrometer. b. Describe the process of dehumidification using a sketch of the Psychrometric chart. c. Space cooling in human activity areas is an essential aspect for efficient work output. Write a heat balance equation for a single human considering possible heat inflow and outflow streams. d. A workshop is 30 m x 15 m x 4 m and has to be maintained at 20 oC [  =1.1096, = 1.0048] with six (6) air changes per hour with a supply air temperature of 14 oC. Determine the Maximum Cooling load that can be achieved using this cooling medium.





Q5. Vapor cycles can be used to generate power while Carnot Cycle and Rankine cycles are two such cycles. a. Discuss the above statement critically highlighting difference in efficiency, practicality in real world use with reasons. b. In a steam turbine, steam at 20 bar, 360°C is expanded to 0.08 bar. It then enters a condenser, where it is condensed to saturated liquid water. The pump feeds back the water into the boiler. Assuming that this process follows ideal Rankine cycle, find Cycle efficiency. You may use the equations:

 efficiency η=   =  + (dryness fraction of steam) · (    ‐ )     =     Rankine cycle

c.

  Work done

Heat supplied

Suggest a mechanism to improve thermal efficiency of the above process

Q6. Gas turbines are a convenient way of generating power. When used with a cleaner source of fuel gas turbines provide more environmental friendly operation. a. What are Open Gas Cycles and Closed Cycles? b. Explain the operational stages of Gas a Turbine used in electric power generation? c. Find the efficiency of a Gas turbine using conditions given in Figure 6‐1. You may use following equations appropriately:

    :     ,    

2| 5

     :      ,      

′ 

Combustion Efficiency = 0.99 Cp=1.15 kJ/kg K ΔP = 0.2 bar

For Air Cp=1.005 kJ/ kg K,     

Air

Fuel

1

1100 K 2

G

Compressor

Combustio n Chamber

4

3

Gas Turbine

15 MW

Pressure Ratio = 10 Isentropic Efficiency = 0.82

Isentropic Efficiency = 0.88 For Gasses Cp=1.15 kJ/kg K,   

Gas Turbine Combined Mechanical and Electrical Transmission Efficiency = 0.97

Figure 6‐1

Q7. Compressed Air Systems are serious consumers of energy in any process plant facility. Careful selection of equipment and designing of systems can save considerable amounts of energy. a. What factors one should consider for selection of compressors for energy efficient operation of a compressed air system? b. What are the sources of losses that can occur in a compressed air System c. Explain the term Pressure Dew Point and its effect in air compression systems d. Why air receiver tanks require regular draining and if this is not performed what could be the results. e. Discuss the energy merits of staged compression with the use of pressure – volume characteristics of air compression. Use sketches wherever applicable f. What types of compressors are best suited for staged compression? g. Intercooling between stages is normally done in order to improve the efficiency of compression. Explain how efficiency improvements are realized by intercooling. h.

3| 5

Q8. Cogeneration is the sequential production of thermal and electric energy from a single fuel source. It is hence also called combined heat and power generation (CHP Generation). a. What user characteristics are essential for better effectiveness of using cogeneration systems b. Compare the merits of CHP using the following figure 8‐1 showing options to cater certain load requirements. Support the your argument with appropriate calculations

Figure 8‐1 c.

If one selects cogeneration as the main source to cater their heat and power loads what considerations that he should give in selecting the prime mover d. How a cogeneration plant should be prepared for unexpected requirements of heat and power demands?

Q9. An organization is about to start it’s planning for a power plant of 2000 tons/year HCl Manufacturing Plant. a. What principles that the planners should adopt when generating energy demand forecasts? b. What factors influence the forecast? c. Explain the terms ‘Peak Demand’ and ‘Load Factor’ and their significance in energy planning d. The planners have generated revenue and cost forecasts for next five years and it was then decided to evaluate all these figures into present day values. Explain why it is necessary.

4| 5

e. The two options Project A ad Project B that they have come up with are given in the figure 9‐1 below:

Figure 9‐1 Find out which project is more beneficial considering economic advantage using a suitable calculation. Make assumptions as required. Discuss the result with variations of the assumptions. For converting a future sum ‘F’ in year ‘N’ to a present value ‘P’ formula:   

 can be used with ‘I’ as discount rate.

N  

Q10. A thermal power plant is asked by the authorities to cut down their carbon emissions in order to support the government initiatives on climate change. a. What forms of carbon are emitted from the activities of thermal power plants and what are their local regional and global effects? b. What other atmospheric emissions could be expected from a thermal power plant which is using low Sulphur diesel oil in its combined cycle operations? Discuss briefly if there are any adverse effects of the mentioned emissions. c. Other than direct emissions what other Impacts that thermal power plants will have on the Environment? What are the mechanisms available to identify and assess Environmental impacts from such a complex operation? d. Suggest Technologies & mechanisms to cut down carbon associated emissions from thermal power plants.

5| 5