Energy storage 2

what industries are hard to decarbonise

• cement

• iron, steel

how is carbon captured in industry

• waste gas w/ CO2 is passed through separattor tower

• tower has amines

• CO2 dissolves into amines

• CO2 is taken to storage site for injection

what depth is CO2 injected to and why

1.5-2.5km, density increases as P increases so more CO2 can be stored, also becomes supercitical so it acts like a liquid

what is structural trapping

when buoyant CO2 accumulates in a confined aquifer below a seal rock layer (i.e. in an anticline) so it cannot move

speed of CO2 plume for structural trapping

U = (k*∆ro*g)/µ, ∆ro = density difference between CO2 and water

volume flux of CO2 plume into anticline (SS)

Q = uLh

if porosity is f, what is the actual speed through rock

u / f

capillary trapping

CO2 is trapped within pore spaces, surrounded by water, limiting movement and resulting in small CO2 bubbles

how can a CO2 bubble move in capillary trapping

the water-CO2 interface needs to deform to make the CO2 fit through

how does capillary pressure scale

y/r, y = interfacial tension, r = radius of pore throat

viscous stress to drive CO2 bubble forward

µu/r

when does capillary trapping occur (eqn)

Ca = µu/y < < 1 (Ca = viscous stress / capillary pressure)

how does the size of a plume migrating upwards change

decreases as more CO2 is trapped

at what length is all the CO2 capillary trapped

L = d0 / S

what is dissolution trapping

when CO2 dissolves into water at the anticline

what is the depth of CO2 dissolved, d (mass balance)

ro_c*d = ro_w*C_sat*H
- Csat is CO2 solubility
- H is depth of water layer

how can the CO2 move into the water

molecular diffusion or convection

why would the CO2 move into water by convection

density of water increases with conc. of CO2

convection speed for dissolution trapping

U = kg ∆ro/µ

time to diffuse over distance d scales as..

d²/D
- D = diffusivity of CO2 in water

condition for convection

Ra = Hkg ∆ro/µD

rate of dissolution of CO2

dM/dt = ro_w*Q(C_sat-C₀)

what proportion of energy does heat usage make up in buildings

1/3

dominant source of energy for domestic heating

natural gas

what opportunites are available when switching energy supply for heating

1. improved control of heat supply

2. improved insulation

3. change of system from gas boiler to heat pumps

relationship controlling heat transfer from a building to the exterior

CM dT/dt = Q_heating + Q_people - U(T-T_ext) - Ventilation

left: heat content

right: sum of sources and sinks

what does the heating system respond to

tempertaure, time

what does heat loss depend on

insulation quality

what does ventilation heat flow depend on

volume flow of ventilation, temperature contrast w/ outside

what is thermal mass

mass of fabric in the building in good thermal contact with the air

how can heating be decarbonised

replacement of gas boilers with heat pumps

phases of heat pump operation

1. compression phase which raises temperature of working fluid from cold side to hot side

2. compression phase a constant high T where heat is transferred from the heat pump

3. adiabatic expansion phase where working fluid cools down as it moves back to the cold side

4. expansion phase at constant cold T where heat is supplied to heat pump from heat source

why must the fluid be colder than the cold source and hotter than the heat sink

so heat is transferred from the cold source to the fluid, and from the fluid to the heat sink

heat sources for heat pump

• air

• ground

• water

how do air pumps work + Q_in

extracting heat from the outside air, even in cold weather, and using it to heat, Q_in = ro*CQ∆T

how do ground source heat pumps work

they draw in heat from the ground around a vertical loop

how do water source heat pumps work

draw heat from a lake or river

how much CO2 does an electric vehicle emit compared to a petrol car

1/5 to 1/6

what do a lot of renewable technologies demand

large masses of critical minerals (i.e. Cu, Mn, Ni, Li, Co)

where is one important deposit of critical minerals

deep sea

what is a concern regarding extraction of metals from the deep sea

sediment suspension disrupting seabed ecosystems