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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2011/
Module Title: Environmental and Energy Engineering
Module Code: CIVL
School: Building & Civil Engineering
Programme Title: Bachelor of Engineering (Hons) in Structural Engineering Bachelor of Engineering (Hons) in Sustainable Energy Certificate in Environmental & Energy Engineering
Programme Code: CSTRU_8_Y ESENT_8_Y EENEN_8_Y
External Examiner(s): Dr M. Richardson, Mr J. O’Mahony Mr P. Kenny, Mr C. Buckley Internal Examiner(s): Dr N. Power
Instructions: Answer all questions.
Duration: 2 Hours
Sitting: Summer 2012
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1. Energy from Coal A coal burning plant produces 850MWe at maximum efficiency. An efficiency of 35% is obtained. The plant operates on average 92% of the time. It is proposed to convert the plant to an oil burning plant which operates at 40% efficiency or natural gas plant operating with an electrical efficiency of 46%. Again the plants operate on average 92% of the time. (a) Determine the quantity of coal, oil and gas that is required to fuel the power plant (in units of tpa and m^3 pa). (10 marks) (b) Calculate the greenhouse gas savings in units of ktCO 2. (10 marks) (c) Estimate a monetary value of this saving based on a carbon tax of €120/t carbon. (2 marks) (d) A wind turbine operates at maximum efficiency 42% of the time; electricity from wind may be considered CO 2 neutral. What size of wind farm (MWe) is required to affect the same greenhouse gas savings? (3 marks) Modified Dulong formula Energy content of fuel MJ/t = 337C + 1419 (H 2 – 0.125O 2 ) + 93 S + 23.26N where, C is the percentage of carbon, H 2 is the percentage hydrogen, O 2 is the percentage oxygen, S is the percentage sulphur and N is the % nitrogen.
Properties of coal 67 % carbon, 7 .5% hydrogen, 5 .5% sulphur, 10% oxygen, 3 % nitrogen, 7 % ash Properties of oil 87% carbon, 11.7% hydrogen, 0.2% sulphur, 0.6% oxygen, 0.5% nitrogen Properties of natural gas Energy value of natural gas = 43.6MJ/m^3 Density of natural gas (kg/m^3 ): molecular weight divided by 22.412m^3 89 % methane (CH 4 ), 6. 7 % Ethane (C 2 H 6 ), 2. 6 % Propane (C 3 H 8 ), 1.2% Butane (C 4 H 10 ),
- 5 % Pentane (C 5 H12) Combustion equations: 89 .0% methane CH 4 + 2O 2 → CO 2 + 2H 2 O
- 7 % Ethane C 2 H 6 + 3.5O 2 → 2CO 2 + 3H 2 O
- 6 % Propane C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O 1.2% Butane C 4 H 10 + 5.5O 2 → 4CO 2 + 5H 2 O
- 5 % Pentane C 5 H 12 + 8O 2 → 5CO 2 + 6H 2 O
Combustion equation C + O 2 = CO 2 Molecular weights: C = 12, O = 16 H = 1
c) How much biomethane can be produced (m^3 pa) and estimate the quantity of diesel displaced (Lpa). How many buses can be served if a diesel bus uses 30,000Lpa. (6 marks) d) What is the potential greenhouse gas savings associated with this proposal, if electricity is produced at 528kgCO 2 /MWh? (assume biomethane is CO 2 -neutral) (4 marks) Analysis of diesel Ultimate analysis of diesel 85.4% carbon, 12.1% hydrogen, 0.7% sulphur, 0.2% oxygen Combustion equation C + O 2 = CO 2 Molecular weights C = 12 O=16 H = 1 Modified Dulong formula Energy content of fuel MJ/t = 337C + 1419 (H 2 – 0.125O 2 ) + 93 S + 23.26N where, C is the percentage of carbon, H 2 is the percentage hydrogen, O 2 is the percentage oxygen, S is the percentage sulphur and N is the % nitrogen. Density of diesel 810kg/m^3 Cattle Slaughter (kg/cattle) Weight wet (kg)
Total solids (kg)
Dry solids (%) Stomach, intestinal content 98 12 11 Low risk 123 43 34 Blood 25 5 16 Total Slaughter waste from cattle amenable to digestion Slaughter waste Pig slurry Dry solids content (%)? 7 Volatile solids (%) 82 82 Destruction of volatile solids (%) 84 53 Parasitic electric demand Electricity is imported for green sources Digester requires 11kWh/t substrate Scrubbing and cleaning require 0.72kWh/m^3 biomethane Parasitic thermal demand Biogas is burned in a boiler at 87% efficiency. The temperature of the waste/slurry is raised form 10oC – 65 oC; the specific heat capacity of water is 4.184kJ/kg/oC Biogas and energy 1kgVSdestroyed = 1m^3 biogas at 53% CH 4. CH 4 has an energy value 37.78MJ/m^3 Biogas is scrubbed to 97% CH 4 and compressed to 200bar
