Lecture 8 - CCS and CCU

Question 1

What percentage of global energy use comes from fossil fuels?

Answer 1

About 80%

Question 2

How much CO₂ is emitted annually due to fossil fuel combustion?

Answer 2

3 to 4·10¹³ kilograms of CO₂ per year

Question 3

What are the three main strategies for carbon capture?

Answer 3

1. Post-combustion capture
2. Pre-combustion capture
3. Oxyfuel combustion.

Question 4

Which part of the CCS process is the most expensive?

Answer 4

CO₂ capture is the most expensive part of the process, as it involves separating CO₂ from flue gases or fuel streams. This stage requires significant energy and specialized equipment, which increases operational costs

Question 5

What is the parasitic load in the CCS capture process?

Answer 5

Around 30% of the power generated by the plant is consumed by the CO₂ capture process. This reduces the overall efficiency of the power plant, as a substantial amount of energy is diverted to the capture technology.

Question 6

What is post-combustion capture?

Answer 6

Capturing CO₂ after the combustion process, separating it from other gases like nitrogen. It uses chemical solvents like amines to selectively absorb CO₂, and is widely considered because it can be retrofitted to existing power plants.

Question 7

What is pre-combustion capture?

Answer 7

Capturing CO₂ before combustion by converting fuel into a mixture of CO₂ and hydrogen. The hydrogen is used for power, while the CO₂ is separated and stored; this method is more efficient but requires significant plant modifications

Question 8

What is oxyfuel combustion?

Answer 8

A process where fuel is burned in pure oxygen instead of air, creating a flue gas mostly composed of CO₂ and water vapor. The water is condensed, leaving nearly pure CO₂ ready for capture, making it easier to capture CO₂ at a higher concentration.

Question 9

What is terrestrial sequestration?

Answer 9

Incorporating CO₂ into biomass for short-term storage, where plants absorb CO₂ during photosynthesis. This is not permanent, as the CO₂ can be released back into the atmosphere when plants decay or are burned.

Question 10

What is oceanic sequestration?

Answer 10

Storing CO₂ in the ocean, where it dissolves and disperses over hundreds to thousands of years. While this offers large storage potential, it risks altering the ocean’s pH, leading to acidification and potential ecological damage.

Question 11

What is geological sequestration?

Answer 11

Injecting CO₂ into deep underground formations, where it remains trapped for thousands to millions of years. This method uses depleted oil and gas reservoirs or saline aquifers, offering long-term, stable storage with minimal risk of CO₂ re-release.

Question 12

What is Direct Air Capture (DAC)?

Answer 12

DAC captures CO₂ directly from the ambient air using chemical processes. It can be deployed anywhere but is energy-intensive and currently expensive, making it a promising but challenging solution for large-scale CO₂ removal.

Question 13

What is the potential CO₂ capture capacity of DAC plants by 2050?

Answer 13

DAC plants could capture 0.5 to 5 gigatonnes of CO₂ per year by 2050. This technology, though still in early stages, could play a significant role in global carbon reduction strategies if it becomes economically viable.

Question 14

What is Bio-Energy with Carbon Capture and Storage (BECCS)?

Answer 14

BECCS involves burning biomass (like wood or waste) for energy, capturing the emitted CO₂, and storing it underground. This technology is carbon-negative because plants absorb CO₂ as they grow, offsetting the emissions during combustion.

Question 15

Where is BECCS considered to have significant potential?

Answer 15

BECCS is particularly promising in Sweden, where large pulp mills near the coast could combine biomass energy with CCS, storing CO₂ under the North Sea. This could help Sweden achieve its carbon-neutral goals.

Question 16

What is the main challenge associated with Direct Air Capture (DAC)?

Answer 16

The primary challenge is its high energy consumption and cost, making it difficult to scale up for significant global impact without cheaper and more efficient energy sources.

Question 17

What is Carbon Capture and Utilization (CCU)?

Answer 17

CCU involves using captured CO₂ as a raw material for producing fuels, chemicals, and building materials. Although it has better public perception than CCS, CCU is limited by the scale at which CO₂ can be economically utilized.

Question 18

Name 3 niche application of CCU.

Answer 18

Precipitated Calcium Carbonate (PCC): CO₂ can be used to produce PCC, which is widely used in paper manufacturing and other products like latex gloves.

Carbonation of Beverages: CO₂ captured through CCU can be used to carbonate beverages, replacing CO₂ that is traditionally mined from underground sources.

Fire Extinguishers: Captured CO₂ can be used in fire extinguishers, providing an alternative to sourcing CO₂ from natural reserves.

Question 19

What is the public perception of CCU compared to CCS?

Answer 19

CCU is generally viewed more favorably by the public because it turns CO₂ into useful products, whereas CCS is seen as “burying” the problem. However, CCU’s contribution to climate goals is limited due to scalability issues.

Question 20

What is one potential use of CO₂ in industrial applications without changing its oxidation state?

Answer 20

CO₂ can be converted into bicarbonates or carbonates, which are useful in applications like building materials or in industrial processes where CO₂ is required without changing its chemical properties.

Question 21

What is C1 chemistry in the context of CO₂?

Answer 21

C1 chemistry involves reducing CO₂, changing its oxidation state, and converting it into fuels like methanol. This process is energy-intensive but opens up many possibilities for CO₂ utilization.

Question 22

What is the challenge associated with reducing CO₂ to C1 products?

Answer 22

The main challenge is the large energy input required to change the oxidation state of carbon in CO₂. This makes the process expensive unless low-cost renewable energy is available.

Question 23

What is electrochemical reduction of CO₂?

Answer 23

Electrochemical reduction uses electricity to reduce CO₂ into useful chemicals, bypassing some thermodynamic limitations. This process is being researched for large-scale application, using catalysts to improve efficiency.

Question 24

What is photoelectrochemistry?

Answer 24

Photoelectrochemistry combines light and electrochemical processes to reduce CO₂ into fuels or chemicals. This method is still experimental, with challenges related to the efficiency and durability of catalysts under light conditions.

Question 25

What enzyme is involved in natural CO₂ capture in most plants?

Answer 25

The enzyme Ribulose-1,5-bisphosphate carboxylase-oxygenase (RUBISCO) captures CO₂ during photosynthesis. It is a key component of the Calvin cycle, which converts CO₂ into organic compounds.

Question 26

What is the role of C4 plants in CO₂ fixation?

Answer 26

C4 plants use a specialized mechanism to concentrate CO₂ around the RUBISCO enzyme, increasing the efficiency of photosynthesis. This adaptation allows them to thrive in environments with low CO₂ or high temperatures.

Question 27

What are the challenges with scaling up CCU?

Answer 27

Scaling up CCU is difficult due to the high energy demands for converting CO₂ into useful products and the relatively low market demand for CO₂-derived materials, making large-scale implementation economically challenging.

Question 28

What is one advantage of BECCS in Sweden?

Answer 28

BECCS in Sweden benefits from large pulp mills located near the coast, which makes it easier to capture and store CO₂ in nearby geological formations, potentially under the North Sea.

Question 29

Why is geological sequestration considered long-term?

Answer 29

Geological sequestration offers long-term storage because CO₂ is injected deep underground, where it remains trapped in porous rock formations, potentially for millions of years with minimal risk of escape.

Question 30

Why is public perception of CO₂ storage challenging for CCS implementation?

Answer 30

The public often perceives geological storage as risky due to the potential for leaks and environmental damage, despite decades of safe storage in industries like natural gas and oil extraction.