Question bank for Energy Managers & Energy Auditors Chapter 1.4 Material and Energy Balance Part – I: Objective type questions and answers 1. The objective of material and energy balance is to assess the: a) input-output b) conversion efficiency c) losses d) all the above e) none of the above 2. In the material balance of a process or unit operation process, which component will not be considered on the input side? a) Chemicals b) Water/air c) Recycle d) By product3. In material balance of a process, recycle product is always considered as a) input to process b) output to process c) both (a) and (b) d) none of them 4. Losses in material and energy balance is considered as a) inputs b) outputs c) both (a) and (b) d) none of the above 5. Sankey diagram shows in graphics ___. a) energy input b) energy output c) energy balance d) all the above6. In a chemical process of two reactants A (200 kg) and B (200kg) is used as reactants. If conversion is 50% and A and B reacts in equal proportion then calculate the weight of the product formed. a) 150 kg b) 200 kg c) 250 kg d) 400 kg 7. In a furnace, the lower the exhaust temperature ____ is the furnace efficiency. a) lower b) moderate c) higher d) none of above 8. Which of the following is the predominant loss in a furnace oil fired boiler? a) dry flue gas losses b) heat loss due to moisture in air c) heat loss due to radiation and convection d) heat loss due to moisture in fuel 9. In a heat treatment furnace the material is heated up to 800 °C from ambient temperature of 30 ° C considering the specific heat of material as 0.13 kCal / kg °C. What is the energy content in one kg of material after heating? a) 150 kCal b) 250 kCal c) 350 kCal 4) 100 kCal10. If feed of 100 tonnes per hour at 5% concentration is fed to a crystallizer, the product obtained at 25% concentration is equal to ____ tonnes per hour. a) 20 b) 25 c) 35 d) 40 11. In an utility steam boiler, heat loss due to radiation normally is in the range of a) 10% b) 14% c) 1% d) 8% 1.4 Material and Energy Balance 23Question bank for Energy Managers & Energy Auditors 12. Energy supplied by combustion of fuel is equal to a) mass of fuel consumed x its calorific value b) mass of fuel consumed x its density c) mass of fuel consumed x its specific heat d) mass of fuel consumed x its heat capacity 13. In a coal fired boiler, hourly consumption of coal is 1000 kg. The ash content in the coal is 3%. Calculate the quantity of ash formed per day. Boiler operates 24 hrs/day. a) 50 kg b) 300 kg c) 33 kg d) 720 kg14. Sankey diagram represents an entire input and output energy flow. State True or False? 15. Material and energy balance will identify areas to concentrate for energy conservation. True or False 16. In a drying process moisture is reduced from 60% to 30%. Initial weight of the material is 200 kg. Calculate the final weight of the product. a) 100 b) 120 c) 130 d) 114.317. Energy supplied by electricity, Q in kCal is equal to _____ . a) kWh x 8.6 b) kWh x 86 c) kWh x 860 d) none 18. Which one is a secondary form of energy? a) Furnace oil b) natural gas c) electricity d) coal 19. In material and energy balance, cycle time play an important role. True or False 20. Sankey diagram is an useful tool to represent ____. a) financial strength of the company b) management philosophy c) input and output energy flow d) human resource strength of the company Part – II: Short type Questions and answers:1. The plant has four heat exchangers and cooling water is circulated through these exchangers. The details are given below. Heat exchanger Water flow, m3/h Temperature raise, °C 1 200 7 2 300 8 3 400 3 4 500 2 1.4 Material and Energy Balance 24Question bank for Energy Managers & Energy Auditors Evaluate heat rejection (kCal/h) of each heat exchanger and total heat rejected to cooling water. Heat exchanger Water flow, m3/h Temperature raise, °C Heat rejection, kCal/h 1 200 7 14,00,000 2 300 8 24,00,000 3 400 3 12,00,000 4 500 2 10,00,000 60,00,000 2. Define specific power consumption with an example. The specific energy consumption is defined as the energy required to produce a unit of output. e.g. : Compressors: A compressor generates 100 cfm of air at 7 kg/cm2 pressure. The power drawn by the motor is 18 kW. i.e. Specific energy consumption is = 18/100 = 0.18 kW/cfm @ 7kg/cm23. Why Sankey diagram is useful in energy balance calculations? The Sankey diagram is very useful tool to represent an entire input and output energy flow in any energy equipment or system such as boiler generation, fired heaters, furnaces after carrying out energy balance calculation. This diagram represents visually various outputs and losses so that energy managers can focus on finding improvements in a prioritized manner. 4. List any three guidelines for mass and energy balance. • For a complex production stream, it is better to first draft the overall material and energy balance. • While splitting up the total system, choose, simple discrete sub-systems. The process flow diagram could be useful here. • Choose the material and energy balance envelope such that, the number of streams entering and leaving, is the smallest possible. • Always choose recycle streams (material and energy) within the envelope. 1.4 Material and Energy Balance 25Question bank for Energy Managers & Energy Auditors 5. Draw a typical Sankey diagram of reheating furnace Ans. 6. How material and energy balance helps in energy conservation? In material and energy balance study by assessing the input, conversion efficiency, output and losses helps in establishing the basis for improvements and potential savings. It helps in finding improvements in a prioritised manner. 7. What way material and energy balance study is useful for a Top management? a. Material and energy balances are important, since they make it possible to identify and quantify previously unknown losses and emissions. b. These balances are useful for monitoring the improvements made in an ongoing project, and while evaluating cost benefits by the Top management. c. Inefficient use of raw materials and energy in production processes are reflected as wastes. This makes the top management to take quick remedial actions. 8. What is the purpose of material and energy balance?