Week 2- Energy and environmental pollution

Question 1

How many hours a day do geothermal power plants operate?

Answer 1

24

Question 2

What are most geothermal systems currently producing power called?

Answer 2

Hydrothermal systems

Question 3

What characteristics do geothermal reservoirs suitable for hydrothermal systems have ?

Answer 3

Presence of very hot water or steam

Question 4

Characteristics of shallow geothermal energy

Answer 4

-Shallow geothermal (0-500 m) is considered low-grade heat and mainly comes from solar radiation stored near the surface (up to 15 m).

• Heat is distributed via meteoric water, groundwater, or flood water (e.g., from old coal mines).
• Deep geothermal taps into heat from deeper subsurface layers.

Question 5

What is deep geothermal energy?

Answer 5

Deep geothermal energy refers to heat resources from depths greater than 500 m beneath the Earth’s surface, primarily derived from Earth’s internal processes and radioactive decay.

Question 6

Where does the heat in deep geothermal energy come from?

Answer 6

The heat comes from two sources:

• Residual heat from Earth’s formation (friction and gravitational pull).
• Radiogenic heat from the decay of isotopes like K-40, Th-232, and U isotopes (U-238, U-235).

Question 7

Which isotopes contribute to radiogenic heat in deep geothermal energy?

Answer 7

K-40 (half-life: 1.25 billion years)

Th-232 (half-life: 14 billion years)

U-238 (half-life: 4.468 billion years)

U-235 (half-life: 703.8 million years)

Question 8

What do deep pressurised hot water and dry steam sources contain?

Answer 8

Quantities of dissolved gases (CO2, H2S, Ammonia and CH4)

Question 8

What do dissolved gases released during depressurisation and cooling generate?

Answer 8

Oxidation products e.g. SO2 and NOx

Question 8

What are mineral-laden brines?

Answer 8

Salts in solution (e.g. Hg, B, As) which may precipitate in geothermal ponds forming pipe scale which ,must be disposed or released into atmosphere from cooling towers

Question 9

What happens in flash steam power plants?

Answer 9

Extremely hot water is rapidly depressurised or ‘flashed in steam and is then used to drive the turbine

Question 10

What happens in dry steam power plants?

Answer 10

They draw steam directly through a turbine where it then condenses and becomes water

Question 11

How do Binary plants operate?

Answer 11

In a closed-loop mode with direct return of fluids to depth

Question 12

What does a closed loop system mean in terms of geothermal energy?

Answer 12

The plants do not produce
either liquid or gaseous emissions

Question 13

Negatives of binary plants

Answer 13

Extraction and injection of fluid into the wells of geothermal plants causes stress underground, which causes seismic activity by transferring these stresses to the ground

Question 14

What can increasing fluid flow rates in binary plants lead to ?

Answer 14

Enhance the efficiency of the power plant but can lead to higher stresses and enhance risk of induced seismicity

Question 15

What is the geothermal gradient?

Answer 15

Refers to the rate at which temperature increases with depth. It’s typically measured in degrees Celsius per kilometer, ranging from 25 to 30°C per km, depending on the local geological conditions.

Question 16

What is the geothermal gradient in the UK?

Answer 16

In the UK, the geothermal gradient is approximately 27°C per km, meaning the temperature increases by 27°C for every kilometer of depth.

Question 17

How can geothermal energy be used in the UK despite low temperatures?

Answer 17

While UK geothermal temperatures (low enthalpy) are too low for conventional power generation (which requires >160°C), they are sufficient for direct-use heating and applications in industry (e.g., timber drying) and agriculture (e.g., milk pasteurization, aquaculture).

Question 18

How are high-temperature geothermal resources accessed?

Answer 18

High-temperature geothermal resources are accessed by drilling production wells, which bring steam or hot water to the surface for energy extraction.

Question 19

What happens to geothermal water in a power plant?

Answer 19

The steam or hot water from geothermal wells is used to power a steam turbine to generate electricity. Afterward, the cooled geothermal water is pumped back into the reservoir, and the cycle repeats.

Question 20

Why do geothermal power plants operate 24 hours a day?

Answer 20

Geothermal heat source is always available providing baseload electricity without interruption

Question 20

Why does water in a geothermal reservoir turn to steam?

Answer 20

As water ascends from deep geothermal reservoirs, the pressure drops, causing the hot liquid to flash to steam, expanding and driving a turbine —similar to how soda bubbles when a can is opened.

Question 20

How does flashing water generate electricity?

Answer 20

As water flashes to steam due to pressure release, it expands and drives a turbine to generate electricity, similar to the way soda bubbles when opened.

Question 20

What gases are commonly released from geothermal steam plants?

Answer 20

Dry and wet steam plants may emit CO₂, H₂S, NH₃, and CH₄. Upon depressurisation, H₂S → SO₂ and NH₃ → NOx, contributing to greenhouse gases, acid rain, and respiratory health impacts.

Question 21

What toxic elements can be found in geothermal fluids?

Answer 21

Hg (mercury), B (boron), and As (arsenic). These can be released to the atmosphere, bound to fine particulate matter posing environmental and health risks

Question 22

What is pipe scaling in geothermal plants?

Answer 22

When minerals precipitate from geothermal fluids inside the plant, potentially clogging systems and reducing efficiency.

Question 23

Do closed binary cycle geothermal plants emit gases or liquids?

Answer 23

No.Closed-loop binary systems reinject fluids underground, avoiding atmospheric emissions. However, some environmental concerns may still arise depending on site and maintenance.

Question 24

What method of geothermal energy production is better for the environment?

Answer 24

Closed loop binary systems

Question 25

What are the pros and cons of binary geothermal systems?

Answer 25

Pros: - Lower environmental impact - No emissions (fluids are re-injected) - Operate at lower temperatures (70–150°C) - Reduced scaling and corrosion risks Cons: - Lower thermal efficiency at high temperatures -More complex due to heat exchanger systems

Question 26

What are the pros and cons of flash steam geothermal systems?

Answer 26

Pros: - Higher efficiency at high reservoir temperatures (>180°C) - Simpler system design Cons: - Gas emissions (CO₂, H₂S, NH₃) - Potential release of toxic elements (e.g., Hg, As) - Higher risk of scaling and corrosion

Question 27

What can cause seismic activity resulting from geothermal energy?

Answer 27

Extraction and injection of fluid into the wells of the geothermal plants cause stress in the underground, which causes seismicity by transferring these stresses to the ground e.g. increasing fluid flow rates

Question 28

Seismic generation mechanisms

Answer 28

- increasing the pore pressure (decreasing effective normal stress and reduces frictional resistance of a fault) - decreasing temperature (thermal stresses create when injected a cool working fluid in the hot reservoir rock and increase the pore pressure) - changing the volume of the fluid - chemical alteration of fracture surfaces (when non-native fluids injects into reservoirs cause chemical alteration)

Question 29

What is the Caerau mine-water project and why is it significant?

Answer 29

The Caerau project in Bridgend, Wales, is the UK’s first large-scale mine-water heating scheme. - Uses warm water (20°C) from a disused coal mine (230m depth) - Heat pumps and pipe networks will provide heating to 150 homes, a school, and a church - Inspired by similar tech in Heerlen, Netherlands - Part of the UK’s low-carbon heating trials (alongside Manchester and Newcastle)

Question 30

What is a ground-source heat pump (GSHP) system?

Answer 30

A GSHP system extracts low-grade heat from the ground and uses a heat pump to raise it to useful temperatures (>40°C) for heating buildings. Viable in the UK

Question 31

What are the main types of GSHP systems?

Answer 31

Closed-loop: Circulates fluid through underground pipes Open-loop: Pumps groundwater from aquifers or mines Hybrid & mine-water systems: Combine elements or use flooded mine workings

Question 32

How do GSHP systems operate?

Answer 32

They use a heat exchanger to absorb heat from the ground, a heat pump to upgrade it, and return the cooled fluid or groundwater to the subsurface.

Question 33

What is the Glasgow Geoenergy Observatory designed to do?

Answer 33

It investigates the potential of mine water for heat energy and storage, focusing on subsurface conditions, environmental impacts, and long-term monitoring in Glasgow’s post-industrial landscape.

Question 34

How does the observatory study underground systems?

Answer 34

Builds geological models using borehole and rock data Monitors underground water temperature, flow, and chemistry Models hydrogeological systems and tracks seismic activity

Question 35

What environmental concerns must be considered when developing a mine water geothermal facility in Glasgow?

Answer 35

- Historical industrial activities (coal mining, chemical production) have affected the subsurface at Glasgow’s geoenergy sites. - Changes in subsurface fluid flow can impact near-surface flow and soil saturation, altering soil chemistry. - Soil geochemistry surveys are essential to monitor and prevent negative environmental impacts during and after development.

Question 36

How can decarbonisation be achieved by avoiding emissions?

Answer 36

-Use AI and robotics to reduce waste and create circular recycling systems. -Produce sustainable second-life feedstocks for industry. -Design products, like batteries, to be more circular, reducing future emissions.

Question 37

How can decarbonisation focus on reducing emissions?

Answer 37

- Enhance electrification with renewable sources for industry and transport. - Reduce energy needs through industrial process innovation (e.g., biotechnology). - Develop new information storage devices with lower energy consumption.

Question 38

How can we replace emissions in decarbonisation?

Answer 38

- Recover and reuse critical elements/materials from waste. - Scale up element/material recovery linked to recycling networks. - Develop biomethane pyrolysis for waste-heat supported hydrogen production.

Question 39

How can we remove CO2 from industrial processes? ## Footnote Carbon capture

Answer 39

-Integrate carbon capture and storage (CCS) technologies at scale. -Exploit geological storage conditions for long-term CO2 storage.

Question 40

What methods are used to recapture CO2?

Answer 40

-Deploy negative emissions technologies (e.g., biochar, direct air capture). -Enhance rock weathering processes to absorb CO2. -Develop carbon accounting methods to measure and optimise recapture.

Question 41

How can we offset emissions in the decarbonisation strategy?

Answer 41

Peatland restoration and afforestation to enhance natural CO2 absorption processes.

Question 42

What is the Elexol Process for CO2 capture?

Answer 42

Uses dimethyl ethers of polyethylene glycol as a chemically inert solvent. Captures H2S and CO2 through a dual-stage process. Has been used commercially for >30 years, but requires concentrated CO2 and high solvent viscosity.

Question 43

What is the role of amine absorption in CO2 capture?

Answer 43

Uses alkylamine solvents (e.g., MEA, DEA, TEA) for CO2 capture. Amine absorption is well-established but has high energy requirements for solvent regeneration and corrosion risks.

Question 44

What are the challenges of amine absorption for CO2 capture?

Answer 44

Low amine concentration limits CO2 capacity and creates hazardous by-products. High energy required for solvent regeneration and loss due to mist formation. SO2, NOx, and O2 in flue gases can damage the solvents.

Question 45

What developments are underway in amine absorption technology?

Answer 45

New amine-based solvents with higher loading capacities and faster reaction rates. Process improvements to reduce energy consumption and increase efficiency.

Question 46

What is the process of amine absorption for CO2 capture?

Answer 46

Flue gas is cooled and treated to remove impurities like SO2, NOx, and particulates. CO2 reacts with amine to form an adduct, driving more CO2 into the solution. CO2-rich solvent is heated to release high-purity CO2, which is compressed for storage. The amine solvent is recycled.

Question 47

What are the key requirements for a typical amine absorption plant?

Answer 47

CO2 is captured and separated, then compressed for geological storage. The process is energy-intensive, requiring heating to release CO2 and solvent regeneration. A high-purity CO2 stream is obtained at near-atmospheric pressure, requiring compression before storage.

Question 48

What is the process of deep ocean CO2 storage?

Answer 48

CO2 is injected into the deep ocean at depths >1000m, where it becomes denser than seawater. CO2 can be stored as liquid or hydrates on the ocean floor.

Question 49

What are the challenges of deep ocean CO2 storage?

Answer 49

Economic feasibility: Currently, CCS costs are $120/MWh, double without CCS. Operational downtime: The facility had initial issues but now operates 80% of the time. Long-term monitoring of the CO2 integrity is necessary.

Question 50

How does deep saline formation store CO2?

Answer 50

Supercritical CO2 is injected into deep saline reservoirs (>800m). Requires overlying seals to prevent leaks and capacity to avoid contaminating freshwater zones. Offshore areas are preferred to avoid groundwater contamination.

Question 51

How can empty oil and gas reservoirs be used for CO2 disposal?

Answer 51

CO2 is injected into old reservoirs (e.g., Statoil's Sleipner Project) after natural gas recovery. This helps reduce CO2 emissions and offsets some of the capture costs. Low permeability reservoirs are ideal to minimise leakage.

Question 52

What is the method of CO2 disposal in coal seams?

Answer 52

Similar to the Sleipner Project, CO2 is injected into coal seams. In-situ coal gasification may enhance natural gas recovery and increase coal's carbon storage capacity. The process can reduce capture costs by using the coal for fuel recovery.

Question 53

How does the effective half-life (Teff) differ from the physical half-life of an isotope in the body and why?

Answer 53

Always shorter - Biological Clearance: The body typically eliminates substances through urine, sweat, respiration, or other metabolic pathways. This biological elimination reduces the amount of the isotope present in the body, effectively speeding up the "apparent" decay process