Technologies Flashcards
Pulverised coal combustion process?
Standard way of producing of electricity from coal worldwide since the middle of the twentieth century.
Essentially mix of pulverized fuel => into combustion chamber => fuel is burnt => heat is transferred to steam => passed into turbine that generates electricity => steam is cooled => closed loop system.
Sub-cricial – conventional pulverized coal combustion. Steam below critical pressure of water. 30% efficiency = 70-75% of operating plants; over 50% of fleet > 25 yrs. Mainly China – you can’t upgrade one plant to another – easier to build new.
So complex to transfer an energy system that is already functioning onto a new one. Dynamic of relative costs of new technologies.
- China aware dirty but also of demand for electricity - immediate and this is how demand is being met.
What impacts efficiency of a coal fired power plant?
- Quality of coal, size of plant (economies of scale), temp and pressure of operations (main one) => higher pressure and temperature, the more energy out & higher efficiency. We have to build power plants that overcome temperature limitations with higher alloys and metals
What does more efficient coal-fired generation look like?
Called HELE techs (High efficiency, low emission)
After sub-critical:
- (SC) Supercritical – steam above critical point of water
- (USC) Ultrasupercritical – similar to SC but higher temp & pressure (600)
Still being developed:
- (AUSC) Advanced ultra supercritical – Higher temp still. (700)
- (IGCC) Integrated gasification combined cycle – gasification of coal to produce syngas = then combusted and hot gas also used to run a turbine generator.
Efficiency and CO2 interlined – increases by about 5% efficiency per tech. & reduces by about 100g CO2/kwh.
- Including CCS tech at finish loses 7-12 efficiency points (only capture 90%)
Natural Gas in electricity generation key technologies & advantages?
= 22% of electricity supplied.
OCGT = open-cycle gas turbine CCGT = Combined cycle gas turbine – similar to integrated gas cycle; but dual generation (two generators) + hot gases from combustion are also used to drive turbine.
Advantages of gas over coal:
- Cheaper & quicker to build; higher efficiency; less pollutants & lower CO2 intensity
- Can be operated more flexibly + gain between techs is in economies of scale.
- CARBON: CCGT much more efficient, not OCGT
What is CCS & techs?
The process of preventing CO2 from entering the atmosphere by capturing (i.e. collecting) it from large point emissions sources (e.g. fossil fuel power stations), compressing and transporting it to a storage site and the depositing (i.e. storing) it ‘permanently’.
Allows for more captured than avoided
Cost of CO2 avoided would be greater than cost of captured.
Different capture techs:
- Post + pre combustion, oxyfuel combustion, advanced capture processes (chemical looping combustion)
Post-combustion capture?
End of pipe separation using solvent (10% penalty)
1) CO2 in flue gas is passed through absorber counter-current to absorbent; 2) CO2 is absorbed onto the absorbent; 3) Spent absorbent is passed into stripper where is it heated to release the CO2; 4) Regenerated absorbent is then reused
Advantages: Easily retrofitted; Allows for continued use of existing capital + closest to commercialisation
Disadvantages: might not be very flexible, relatively high efficiency penalty, sorbent degeneration in presence of SOx and NOx.
Pre-combustion Capture?
Removal of carbon (in the form of CO2) occurs prior to combustion. (7% penalty)
1) Fuel is ‘gasified’ to produce syngas 2) Shift reaction increases CO2 content; 3) CO2 is removed. 4) H2 rich fuel is burnt in air.
Advantages: Shift reaction and CO2 removal is a commercial practise; Higher CO2 concentrations allow for easier separation of CO2; Lower energy penalty
Disadvantages: Not easy to retrofit; High capital cost of gasifier limits flexibility; Hydrogen fired turbines yet to be demonstrated commercially
Oxyfuel Capture?
Fuel is burnt in pure oxygen (+ recycled CO2) instead of air. (10% penalty)
1) Oxygen is separated from nitrogen in an air separation unit. 2) Fuel is burnt in oxygen. 3) Flue gas consists of CO2 and H2O. 4) H2O is condensed. 5) CO2 is compressed ready for transport and storage
Previous try to address burning in air – this tries to separate oxygen from air (removing nitrogen)
Advantages: easily retrofitted
Disadvantages: Air separation unit (ASU) is expensive; might not be very flexible due to operation of ASU
Advanced CCS: Chemical looping combustion?
Fuel is oxidised or ‘burnt’ using a metal oxide rather than air (new option nowhere near commercial)
1) Metal oxide reacts with fuel in presence of steam in fuel reactor. 2) Producing CO2 and steam. 3) ‘Reduced’ metal oxide is regenerated with air in air reactor
Advantages: doesn’t require separate CCS unit; theoretically a lower energy penalty because separation and combustion occur together
Disadvantages: Still in very early research stages; requires a circulating fluidised bed reactor challenging to build at scale
Biomass co-combustion?
Cheapest method of reducing CO2 from a large boiler, assuming the additional fuels (biomass/wastes) are considered CO2 neutral
Possibly the least complicated way of using biomass and wastes for replacement of fossil fuels for energy conversion/ relatively uncomplicated but on ground challenges = 2% electricity production.
Types of Solar Technologies?
Solar PV, Printable Photovoltaics, Concentrated Solar Power (CSP), Solar thermal panels
How Solar Photovoltonic Panel works & trends?
Solar PV panels most famous = converts photonic energy from sunlight directly into electrical energy. Consists of small solar “cells” connected in series to form module.
Rapid scaling, consistent cost reduction (costs down 40-60% in 4 years), strong policy support, year on year 40% growth & reaching grid parity.
Cost reduction & policy driving Solar PV?
Costs: Cheaper solar grade silicone + less wastage/thinner wafers + more efficient cells + tougher + overall manufacturing process & automation
Policy: R&D support until 80’s; then demonstrated support; now deployment = tax credits, subsidies.
Advantages of Solar PV? (4)
- Low GHG per unit electricity produced;
- Able to operate economically at a range of scales;
- Cost per unit electricity are falling rapidly, and reaching parity with the grid in many regions.
- Low operating and maintenance costs, no moving parts, silent and no direct emissions associated with operation.
Disadvantages of Solar PV? (3)
1.Intermittent, 2. Requires inverter DC to AC, 3. Upfront capital remains high relative to conventional
What are Printable Photovoltaics?
Emerging tech. potential for low cost, low embedded energy (important for rapid mitigation) & flexibility – doesn’t take much to make.
- Research cell efficiency approach conventional PV.
Challenges remain around long term stability and further raising efficiency.
How does concentrated solar power (CSP) work?
CSP uses mirrors/lenses to concentrate sunlight into small area => converted into heat => drives engine => generates electricity. Heat often stored in molten salt => allows generation after sunset.
Advantages of CSP?
Low GHG/unit elec. + time may be controlled by storage in molten salt => changes on supply to meet demand; no direct emissions.
Disadvantages of CSP?
Typically large project, high upfront, long construction & only suitable with much direct sunlight close to large demand centers; relatively expensive compared to other forms of generation
How do Solar thermal panels work?
Convert photonic energy from sunlight into heat to provide hot water! Cost effective in many regions for over 30 years. Projected cost decline of 43% in Europe & deployment increase from 23GW to 102GW from 2010 to 2020.
Advancements: better integration into buildings, better interface with backup heating, RD&R into cost-efficient heat storage
