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Mining | Reacting | Sequestering | ZEC

ZEC-Zero Emission Coal Technology

 

What is ZEC?

 

Zero Emission Coal technology is technology for generating electricity from coal without emissions to the air.  It is being developed with the intent to use mineral carbonation for disposal of the carbon dioxide produced, although, technically, any form of sequestration would be possible for use.  

 

source

 

Who is Researching ZEC?

 

The research is being lead by the Los Alamos National Laboratory together with the Zero Emission Coal Alliance (ZECA) Corporation, although they are not the only ones in the field.

 

 

Why coal as opposed to natural gas or other fuel?

 

Coal has two big advantages over natural gas: 1) abundance on earth and 2) price.

"Coal cost at the mine mouth is about $0.50 to $1.00 per GJ. The cost for natural gas is $2 to $3 per GJ by comparison.  The low cost of coal is in part offset by larger handling coast and larger cleanup cost.  When it comes to carbon sequestration, the lower cost of coal allows one to budget a certain amount for CO2 disposal without losing the competitive edge.  For example, the price difference between nuclear and coal suggests a buffer of about $40 to $60 per ton of CO2.  Relative to renewable options like solar energy the margin is even higher.  Another comparison is relative to natural gas.  For every dollar difference in price between natural gas and coal, the cost of CO2 capture and disposal can go up by $22/ton of CO2.  This scenario assumes that the price difference between coal and gas is reduced because coal needs to pay an additional cost for removing that amount of CO­2 by which it exceeds the output from natural gas power plants [coal produces more CO2 than does natural gas]." [1]

 

 

How does ZEC work?

 

"[The ZECA process] combines a coal-based electric power plant with a process for safely and permanently disposing of the carbon dioxide generated.  The power plant is an ultra-efficient, coal-based power plant using an updated version of the CO2 acceptor process.  Hydrogen is produced from steam and coal, and electricity from hydrogen in solid oxide fuel cells.  Lime acts as the CO2 acceptor.  By removing CO2 from the reaction products, the carbonation of lime drives the water-gas-shift and steam reforming reactions forward.  Carbonation also provides the heat necessary to run the hydrogen production to completion.  To recycle the lime, we calcine the calcium carbonate with the waste heat from the solid oxide fuel cells while generating a concentrated stream of CO2 ready for disposal.  The coal gas is circulated through the plant without any gaseous emissions.  Pollutants from the coal, like nitrogen, sulfur, and heavy metal compounds or fine dust particles, leave the cycle either in liquid streams, or with solids.  The process includes CO2 disposal by a chemical reaction with readily available mineral rock to form inert mineral carbonates.  The reaction is exothermic and thermodynamically favored.  The resulting materials are inert and environmentally benign." [2]  

 

 

What are the advantages of ZEC? [3]

  • CO2 is captured as part of the process and no distinct separation step is required

  • Fuel energy is captured more efficiently from hydrogen than from the coal from which is it derived.

  • Because the process is essentially a closed loop, the removal of any residual contaminates from coal becomes much easier and all contaminates are completely contained within the system.

  • Air emission standards need not be considered since nothing is vented to the atmosphere and no extra effort is required to do so.

  • Impurities may cycle through the process numerous times before removal, allowing concentrations to increase and making the removal process easier and more efficient.

  • The technology is resistant to incomplete reactions due to the continuous cycling of the reactants.

  • Unreacted hydrogen from the fuel cells is recycled.

  • CO2 is continuously removed by reacting it with CaO.

source: Lackner 10/7/02 p.18

 

 

What are the disadvantages of ZEC?

  • If the hydrogen is used as a fuel for a hydrogen economy, a new infrastructure must be built for transport, storage, and utilization. [4]

  • Continuous requirements for coal mining which scars the earth's surface

 

How does ZEC relate to Mineral Carbonation?

 

The current zero emission coal process under development includes carbon dioxide removal by exothermically reacting the CO2 with mineral rock to form a thermodynamically stable, inert material.  The end results, magnesium carbonates, are stable, guaranteeing permanent disposal, and have no adverse effects on the environment.  The amount of mineral needed for ZEC technology is large in terms of volume, but the amount of deposits on earth greatly surpass the mankind's limit of producing carbon dioxide, and the areas invaded by the mining of the mineral are much smaller than those of coal mines needed to recover enough coal for the process to be feasible. [5]

 

source: Lackner 10/7/02 p.15

 

Schematic of the anaerobic hydrogen production and

fuel cell system. Material flows are idealized to the

predominant components. The major reactions are as follows:

Hydrogasifier: C + 2H2 ® CH4, H2O(liquid) ® H2O (gas)

CaO Reformer: CH4 + 2H2O ® CO2 + 4H2, CaO + CO2 ® CaCO3

Calciner: CaCO3 ® CaO + CO2

Fuel Cell: 2H2 + O2 ® 2H2O

references

[1] Yegulalp et al. p.59

[2] Lackner et al. p.58-59 (12/2001)

[3] Lackner et al. p.59-61 (12/2001)

[4] Spiro et al p.42

[5] Lackner et al. p.59 (12/2001)

 
Email: eglazer@princeton.edu or mokun@princeton.edu