Oil Gas Fuels & Electricity Generations (1-3) Flashcards
What is energy?
Energy is the capacity to do work, the chemical energy contained in fuel or electrochemical energy in batteries
What is power?
Power is the rate at which energy is transformed
e.g. determined by the size of the engine
What is primary energy?
Primary energy is the energy that is
embodied in resources as they exist in nature i.e. without
human transformation
What is secondary energy?
Energy carriers = energy vectors are
primary energy that has been subject to a human
transformation e.g. the refining of crude oil (primary
energy) to petrol or diesel (energy carrier)
What conversion of fuel to electricity in thermal power station in percent?
38%
What is final energy?
Final energy is the amount of energy that is delivered and/or
indeed sold to end-users
True or false? GridCarbon presents a summary of the generation mix data broken down into major categories of fuel type and various interconnectors.
True
What percent electricity generated from natural gas?
40% of electricity is generated
from natural gas
Why use gaseous fuels?
- the absence of mineral impurities;
- the consistency in quality;
- the convenience and efficiency in use;
- gas handling system is cheapest of all fuels;
- transported in long distance using network of piping system;
- ideal fuel in a region where there is a concentration of population.
What is Gross and Net Calorific Value (CV)?
The calorific value of a fuel is the chemical energy
released during combustion reactions, and is expressed
as, kJ (or MJ) per m3 for gaseous fuels or, kJ (or MJ) per kg for all fuels. Gross includes the latent heat of condensation of the water produced
The basic characteristics, which affect the combustion of gaseous fuels and their interchangeability are…
- Wobbe Number
- Weaver Flame Speed Factor
- Gas Modulus
Wobbe number equation?
Gross CV / Sqrt (specific gravity)
What is Weaver flame speed factor?
This is the flame speed of the gas relative to hydrogen, which is given an arbitrary flame speed factor of 100.
Definition Gas Modulus (M)
In order to maintain a given degree of pre‐aeration of the gas fed to an aerated burner, the Gas Modulus, M, must remain constant.
(M) Gas Modulus equation?
Sqrt (gas supply pressure) / Wobbe Number
Describe lower and upper flammability
The lower flammability limit, the mixture is too “lean” to support combustion (4%) , while above the upper flammability limit, it is too “rich” to propagate flames (75%).
Reactivity properties of gaseous fuel?
- Flame speed
- Flammability Limits of Gases and Vapours
- Ignition energy
- Ignition temperature
What is the cloud point?
The cloud point is the temperature at which a haze appears when an oil is cooled, and it indicates the onset of formation of wax crystals which can block filters.
What is the pour point?
The pour point is several degrees lower than the cloud point and is
defined as the temperature which is 2.8 K (or 5F) above the temperature at which the oil just fails to flow when cooled. In general, this is also due to the separation of wax from the oil.
Spray combustion accounts for __ % of the total world energy requirement.
Spray combustion accounts for 25 % of the total world energy requirement.
The spray can be divided into three regions
- the spray formation region,
- the vaporization region, and
- the combustion region.
At the end of the spray formation region, one would like to
know…
- the droplet size, velocity,
- The number distributions,
- the air velocity and temperature,
- the droplet temperature.
There are three different types of spray nozzles:
- Simple pressure nozzles
- Air or steam atomization nozzles
- Swirl nozzles
In spray nozzles, the breakup mechanism may be characterized by a set of six
steps:
- Stretching of fuel into sheets or stream
- Appearance of ripples and protuberances
- Formation of ligaments or holes in sheets
- Collapse of ligaments or holes in sheets
- Further break‐up due to vibration of droplets
- Agglomeration or shedding from large drops.
What are some sources of manufactured gas
Main: Wood, peat, coal, petroleum from cracking
others: carbides, electrolysis, fermentation, hydraulic fracking
XS air is calculated by:
(Nair-Nairstoic)/Nairstoic
Equivalence ratio
The equivalence ratio F is
defined as the actual fuel/air mass ratio f divided by the
stoichiometric fuel/air mass ratio f
%XS air= 100(1-F)/F
Adiabatic flame temp
highest gas temperature
achievable in combustion.
Has the following assumptions:
* no heat loss from the flame
* the heat is liberated instantaneously
* no dissociation of any gas occurs.
When do dissociation reactions occur
Above 1600C
Burning velocity
defined as the velocity with which a plane of flame front moves normal to its surface through the adjacent un‐burnt gas.
Factors Affecting burning velocity
Pressure
Temperature
Oxygen level
Reactivity of fuels
Composition: peak at stoic
Container surface slows down the propagation of the flame
What is fuel oil used for
burned in a furnace or boiler for
the generation of heat or used in an engine for the generation of
power. Long HC chains
Sources of fuel oils
- Crude petroleum (main source)
- Oil shades and oil sands (tar sands)
- Coal (by solvent extraction)
- Biomass (plants)
Heating oil has which effects
decrease in viscosity, decreased density means less weight of fuel delivered to the burner
How is heat of combustion determined
Bomb calorimetry
What is the ramsbottom carbon residue test
A known weight of oil is heated for at 550C for 20 minutes and
residue given as wt%
Flashpoint definition
the temperature at which the
vapour pressure of the substance gives a vapour pressure equal to the lower flammability limit. When the vapour ignites with just a spark then goes out
Firepoint definition
When it gives enough vapour to continue to burn if ignited
Gasoline boiling point
25-225C
Diesel fuels
Straight run products from crude oil distillation- higher bpt than gasoline
What is added to gasoline fuel to reduce knocking effect & increase the octane number
Tetra-ethyl lead
How to improve cetane number
alkyl nitrates, peroxides and metal‐organic
compounds.
