# Monetary Value - Environmental Engineering - Old Exam Paper, Past Exams for Environmental Science

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Main points of this past exam are: Monetary Value, Energy from Coal, Greenhouse Gas Savings, Modified Dulong Formula, Lack of Waste Infrastructure, Landfill Directive, Modern Landfill Site, Chemical Composition, Toxicity...
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CORK INSTITUTE OF TECHNOLOGY

INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ

Semester 2 Examinations 2011/12

Module Title: Environmental and Energy Engineering

Module Code: CIVL8008

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_Y4

ESENT_8_Y4

EENEN_8_Y1

External Examiner(s): Dr M. Richardson, Mr J. O’Mahony

Mr P. Kenny, Mr C. Buckley

Internal Examiner(s): Dr N. Power

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.

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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 ktCO2. (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 CO2 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 (H2 – 0.125O2) + 93 S + 23.26N where,

Cis the percentage of carbon, H2 is the percentage hydrogen,

O2 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

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89% methane (CH4), 6.7% Ethane (C2H6), 2.6% Propane (C3H8), 1.2% Butane (C4H10),

0.5% Pentane (C5H12) Combustion equations:

89.0% methane CH4 + 2O2 → CO2 + 2H2O

6.7% Ethane C2H6 + 3.5O2 → 2CO2 + 3H2O

2.6% Propane C3H8 + 5O2 → 3CO2 + 4H2O

1.2% Butane C4H10 + 5.5O2 → 4CO2 + 5H2O

0.5% Pentane C5H12 + 8O2 → 5CO2 + 6H2O

Combustion equation

C + O2 = CO2

Molecular weights:

C = 12, O = 16 H = 1

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Q2. Solid waste management

(a) Discuss Ireland’s lack of waste infrastructure and give a suggestion on the type of

infrastructure that is required. (5 marks)

(b) Explain the Landfill Directive with special emphasis on the targets for Ireland.

(5 marks)

(c) Sketch a modern landfill site and explain how landfill gas and leachate are collected.

(6 marks)

(d) Discuss dioxins and furans, including their chemical composition, toxicity level and

their effects on humans. (5 marks)

(e) Discuss waste generation from the construction and demolition sector, and describe

how the waste hierarchy could be used effectively to reduce waste from this sector.

(4 marks)

Q3. Biofuels

(a)Discuss the Renewable Energy Source Directive and explain how the targets set out

in this Directive could help Ireland reduce its reliance on imported fossil fuels. Please

state Ireland’s specific targets under this directive. (8 marks)

(b) Discuss the advantages and disadvantages of the biofuel obligation scheme in

introducing biofuels to the Irish transport fuel market (5 marks)

(c) Describe the DDGS production process (4 marks)

(d) Discuss briefly the four main ways in which biogas can be used (4 marks)

(e)Emissions from the transport sector have increased dramatically over the last number

of years. Discuss two reasons for the increase in emissions (4 marks)

Q4 Transport, Agri-waste and Biofuels

It is proposed to convert a city bus fleet to biomethane. In the vicinity of the city there is an

abattoir, which slaughters 200,000 cattle per annum, and an intensive pig farm, which houses

45,000 pigs (typically 1 pig generates 4kg of slurry per day). The pig slurry and the slaughter

waste will be pasteurised and then digested. Biogas will be produced in the digestion process

and cleaned to 97% methane. Biomethane is compressed and used as a transport fuel.

a) Estimate the quantity of biogas that may be produced from the slaughter waste and

pig slurry (m 3 pa). (5 marks)

b) How much biogas is required to heat the digester (m 3 pa) & how much electricity must

be imported from the grid per annum (kWhpa) (10 marks)

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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 528kgCO2/MWh? (assume biomethane is CO2-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 + O2 = CO2

Molecular weights

C = 12 O=16 H = 1

Modified Dulong formula

Energy content of fuel MJ/t = 337C + 1419 (H2 – 0.125O2) + 93 S + 23.26N where,

Cis the percentage of carbon, H2 is the percentage hydrogen,

O2 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 10 o C – 65

o C; the specific heat capacity of water is 4.184kJ/kg/

o C

Biogas and energy

1kgVSdestroyed = 1m 3 biogas at 53% CH4. CH4 has an energy value 37.78MJ/m

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Biogas is scrubbed to 97% CH4 and compressed to 200bar