Power Generation/distribution Flashcards
What is a spinning reserve?
Capacity in the base load stations that can be accessed if necessary.
What is a peaking power plant?
A fast response unit that is operated when required
What are the disadvantages of electricity generation, transmission and distribution?
An ageing infrastructure means significant investment is needed in both the short and medium term
Transmission losses and cost
Stepping down causes conversion losses
Energy is effectively wasted due to stepping down and conversion losses.
Rural electrification causes large capital costs
Incumbent technologies are very inefficient causes waste heat that can not be utilised
Inefficiencies lead to more fossil fuel use which in turn leads to more environmental impact
There is a large number of people relying on a single plant. A failure will lead to power outages on a large scale. Even though a certain degree of redundancy is and connectivity is maintained to mitigate this risk.
Current methods of electricity generation, transmission and distribution?
Generation is Historically highly centralised to take advantage of economies of scale
The electricity is transmitted at high voltages from the source to the distributors who then step down the voltage of customer use
Fuel/energy source is primarily coal and natural gas and radioactive materials. But hydro power etc is being increasingly used.
Continuous operation supplies the bulk of in demand or load. To meet changes in demand a reserve is required. This is achieved through spinning reserve or peaking power plants.
What is distributed power?
Small scale power generation technologies located in close proximity to the load being served.
Connected in the distribution network directly rather than the transmission network.
Not centrally dispatched
Normally smaller than 50MW to 100MW
Ideal for diversification of energy sources (renewables)
A greater efficiency can be achieved because of fewer losses and thE use of cogeneration.
Methods of reducing of reducing fossil-fuel consumption in the transport sector.
Use of public transport
Battery electric vehicles
Fuel cell vehicles
Biodiesel powered cars
Outline the operating principles of a water-tube boiler
Water flows inside steel pipes and is heated by convection and thermal radiation for the combustion. Typically feed water is heated and dissed turning to steam which can be extracted from the drum
Outline the operating principles of shell (fire tube) boilers
Combustion takes place in a separate furnace. The hot exhaust gases pass through the smoke tubes immersed in a water bath. The water is heated to produce steam via heat exchange before leaving through a smokestack
Operating principles of vapour absorption refrigeration (VAR)
There are 4 components:
Evaporator and absorber (low pressure side)
Generator and a condenser (high pressure side)
Two working fluids, a refrigerant and an absorber, are employed.
The refrigerant flows from the condenser to the evaporator to the absorber to the generator and back to the condenser.
The absorbent flows from the absorber to the generator and back to the absorber.
Low temp and pressure vapour leaves the evaporator and enters the absorber where it comes in contact with the working fluid mixture, it is weak in refrigerant and this stage.
The solution then absorbs the refrigerant in an exoteric process. Heat Qa is rejected at sink temp T2 to the environment.
Solution then becomes rich in refrigerant and is pumped to the generator.
Heat Qg at Tg is supplied to the generator by a heat source generating vapour.
The refrigerant vapour at night temp and pressure goes to the condenser.
Heat Q2 is rejected to a high temp reservoir at T2 and it becomes a saturated liquid. It then passes through an expansion valve to the evaporator where it absorbs Q1 (refrigeration effect) at T1.
Solution in the generator becomes weak in refrigerant. An expansions device lowers the pressure.
What are the benefits of a VAR over VCC?
The energy required in the pumps in a var is much lower than the energy needed for he compressor in the VCC.
Low grade thermal energy is required that can come from waste heat making the vac much more efficient.
Define CHP
CHP technologies utilise the heat produced during a process to produce useful power or utilise the heat produced during power production.
How can CHP efficiency be measured?
The thermal efficiency (power output/total energy input).
The utilisation factor ( power output + heat output /total energy input).
Discuss in detail CHP
CHP makes use of waste heat generated during electricity production and is an effective use of energy resources. Power plants are large to take advantage of economies of scale and the efficiencies of combustion leads to large amounts of waste heat. CHP can be used for localised electricity generation with waste heat used to provide domestic heating. Aprox 2/3 of heat can be recovered in this way. This could dramatically reduce the use of fossil fuels.
It can be economical to generate power from steam before using it in the process or extracting steam from a turbine during expansion.
Provide examples of CHP systems
Steam-to-power
A boiler generates high pressure steam. This high pressure steam is fed into a turbine to generate shaft work. This drives an electrical generator and creates electrical power.
Power-to-thermal
A gas turbine, desist engine or fuel cell are used to generate electrical power. waste heat from the power generation is directed towards a boiler or heat exchanger which converts waste heat to useful heat for the plant.
Micro-CHP
Define as cogeneration installations with an electric capacity if
Disadvantages of CHP?
Expensive equipment
Not usually cost effective in plants that are small ie with small electrical and or thermal loads.
Equipment must be run for most of the year in order for it to pay for itself
Large cost for distribution of heat in pipelines and maintenance.
It could be cheaper to buy electricity/gas and generate the heat required.
