Capturing CO2 from combustion

 

Capturing CO2 from combustion

As the famous recipe for rabbit stew starts off: "First catch your rabbit."

On this page we'll look at the technologies for capturing CO2

  •      before combustion
  •      after combustion, from the flue gas
  •      from the atmosphere - Next page.

 

 

Pre‐Combustion Capture 

Coal, oil, gas, can be converted to H2 and CO2.

Coal + O2  ---> CO + H2             (Syn gas or or Synthesis gas)

CO + H2O  ---> CO2 + H2           (Water gas shift reaction)

 

The CO2 is captured, and the H2 is burnt to produce only water.

The ZeroGen2  project in Australia is an example of this technology. 

Ref

Gasifica​tion of coal

Post‐Combustion Capture 

Flue gas concentrations range from 3% to 5% CO2, for natural gas fired power plants, to 10–15% for coal fired power plants. They are a hundred to three hundred times higher than CO2 in air.

The most advanced post-combustion capture process uses a chemically reactive solvent (amines, ammonia, etc) to capture CO2 from power station flue gases. The CO2 is subsequently removed from the absorbing solution at higher temperatures using steam, allowing the absorbing solution to be used again for capture.

The entire process is energy intensive, especially regenerating the solvent by heating it to between 100 and 140 degrees Celsius in the stripping unit. Capturing the CO2 from a typical coal-fired power plant would use 25 per cent of the total electrical output from the plant.

"For a modern (high-efficiency) coal-burning power plant, CO2 capture using an amine-based scrubber increases the cost of electricity generation by approximately 40-70 per cent while reducing emissions per kilowatt-hour by about 85 per cent," (the Intergovernmental Panel on Climate Change.)

USA and Canada are both spending $5 billion dollars, and the Australian govt is spending $1.7 billion on CCS. The coal industry is only investing 0.1 per cent of its own revenues. 

 

 

 

 

Calcium Oxide - quicklime

CaO will react with COand remove it from an air stream. The CaCO3 is then heated to recover the CaO.

 

Aluminum nitra​te absorber

Reuters.
Researchers have created a new absorber, dubbed NOTT-300,  aluminum nitrate salt, cheap organic materials and water, is non-toxic and requires less energy to strip out the carbon when it becomes saturated 

"When the material is saturated, the exhaust gases are diverted to the second container where the process continues," he said."The full container is disconnected from the system and the CO2 is removed using a vacuum and collected. The regenerated container can then be reconnected and used repeatedly."
The team, which also included scientists from the University of Oxford and Peking University in China, say the new material captured close to 100 percent of the carbon dioxide in experiments using a cocktail of gases.

Ref

 

Solar gas

Another idea being developed by CSIRO  passes methane though a solar thermal heat source. Under the right conditions the methane is converted to Hydrogen and CO2. The separation of  CO2 and H2 is relatively simple as the molecules re so different in size..

They call it solar gas. The hydrogen has more energy than the original methane and is a good way of storing solar thermal energy, and capturing the CO2.

Solar gas

Gasification

The coal can be gasified into hydrogen and carbon monoxide, and then burnt in a combined cycle gas and steam turbine. The concentrated stream of CO2, which is easier to treat.

A plant is being built at Kemper in Mississippi, but is going wildly over budget: $1.8 billion to $5.5 billion.

 

Burning in oxygen - Oxyfuel combustion

If the fuel is burnt in pure oxygen, then there is no need to separate the nitrogen. The separation is cheaper, but the cost of pure oxygen is usually  more expensive.

Vattenfall, the Swedish energy giant that has built a pioneering carbon-capture power station in Schwarze Pumpe, Germany. This pilot-scale plant uses the so-called oxyfuel approach to capturing carbon. Nitrogen is removed from the air, enabling the fuel to burn in pure oxygen. This results in a waste stream of virtually pure CO2, ready for capture and storage. 

White rose project Yorkshire UK

The standalone power plant will be located at the existing Drax Power Station site near Selby, North Yorkshire, generating electricity for export to the Electricity Transmission Network as well as capturing approximately 2 million tonnes of CO2 per year, some 90% of all CO2 emissions produced by the plant. The CO2 will be transported through National Grid’s proposed pipeline for permanent undersea storage in the North Sea.

The power plant technology, known as oxyfuel combustion, burns fuel in a modified combustion environment with the resulting combustion gases being high in CO2 concentration. This allows the CO2 produced to be captured without the need for additional chemical separation, before being piped for storage.

http://www.whiteroseccs.co.uk/about-white-rose

Recycling solvent with solar thermal

One way of saving on steam for heating the charged solvent is to heat it with solar thermal. 

​The idea is that storing the liquid used for CO2 capture may be more economic than storing hot salt.

 

Where Australia stands on CCS

The Conversation

Coal remains an important energy resource for Australia providing around 75 per cent of our electricity and some 20 per cent of export income. However it is also responsible for approximately 40 per cent of greenhouse gas emissions.

Over the last decade, carbon dioxide capture and storage (CCS) technology has emerged as an essential pathway for countries dependent on coal for their energy supply but committed to reaching the targets for a carbon constrained global environment.

Post-combustion capture (PCC) is the first stage in the CCS chain. Amine-based liquid absorbents, including ammonia, capture CO₂ from the flue gases before it is emitted to the atmosphere. The captured CO₂ product is pure enough that it is ready for compression, transport and storage.

PCC pilot plants have been set up in other parts of the world, but Australia is a unique place to study this method. We have low-cost coal resources, a highly competitive electricity market, restricted water resources and limited emission controls at power stations.

CSIRO has been working with industrial partners Delta Electricity and Stanwell Corporation, constructing and operating PCC pilot plants at Munmorah (New South Wales) and Tarong (Queensland) power stations to demonstrate carbon capture on actual flue gases during power production. (One of the advantages of PCC is that it can be retrofitted to existing power stations.)

At the PCC pilot plant in Queensland, we used amines as the absorbent and focused on examining different process designs and flow configurations to identify the most effective use of the technology.

The NSW pilot plant demonstrated the use of aqueous ammonia as an absorbent. This is considered by some researchers as the most promising agent for CO₂ capture.

In both plants more than 85 per cent of the carbon dioxide present in the flue gas was captured as a result of the chemical reaction between carbon dioxide and the absorbent. The carbon dioxide was released from the liquid absorbent by heating up the liquid absorbent to the point were the chemical reaction is reversed.

So heat is needed to run the capture process. We looked into using solar thermal energy as a heating source and found that renewables are able to reduce the additional electricity burden on the power station.

In parallel with the pilot plant program, laboratory studies examined more than 100 different commercially available amine based liquid absorbents. The team also explored the synthesis of “designer amines”. These are specifically designed and optimised for use as liquid absorbents for PCC.

Ionic liquids

As an alternative to amines, ionic liquids showed considerable promise. They are chemically robust, also at the higher temperatures needed for the release of the captured carbon dioxide. The absorbent robustness is particularly important in the challenging conditions of Australian power plants where there are limited emission controls. The ionic liquids we produced during this study improved CO₂ absorption capacity and reduced energy consumption by 70 per cent compared to the standard amine based process.

One of the important aspects of the program was that the power companies taking part now fully understand how PCC technology can reduce greenhouse gas emissions.

Energy required

There are still challenges before PCC can be commercially implemented. The capital cost of the PCC plant will have to come down. So will the “efficiency penalty” – currently the capture of 90 per cent carbon dioxide results in a 30 per cent loss in electricity output at the power station. PCC will also have to be demonstrated on a large and integrated plant as part of an overall carbon capture and storage chain.

CSIRO is working on improving the capture process and reducing efficiency penalties. This should substantially reduce the costs of installing and operating a PCC system.

While Australia continues to rely heavily on its low-cost and easy-to-mine coal reserves, technology can be retrofitted to the power sector to reduce its contribution to Australia’s CO₂ emissions.

Paul Feron is Research Program Leader at CSIRO.

​Reprinted from The Conversation

 

 

Research in Australia

http://www.co2crc.com.au/research/capture_research.htmlCO2CRC