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Saturday, February 13, 2010

Zero Emission Coal Fired Power Plant Design Makes Carbon Capture Profitable, Produces H2 for 16-Cents per Kilo, Only Raw Materials Needed are Coal, Salt and Water

Carbon capture from a coal fired power plant could be made profitable and hydrogen could be produced for as low as 16-cents per kilogram. A kilogram of hydrogen in comparable to a gallon of gasoline in energy content.  The only raw material required is coal (or natural gas), sodium chloride (salt) and water.  The process locks carbon dioxide (CO2) and carbon monoxide (CO) into sodium bicarbonate and sodium carbonate.
 
The system of processes for sequestering carbon in coal-burning power plants and producing hydrogen gas that takes advantage of emission of CO and CO2 and heat from the plants has been developed by a professor of Mechanical and Materials Engineering at Florida International University (FIU) in Miami. The use of the process will lead to cheap hydrogen and hydride production and carbon sequestration and reduced global warming.

 FIU Center for the Study of Matter at Extreme Conditions Director Surendra Saxena  developed the system of reactions for a partial sequestration of carbon (CO2 and CO) from coal burning plants and zero emission production of hydrogen and hydrides. The only raw material to be used is salt (sodium chloride, NaCl), coal and water or a metal for the hydride. Sodium hydroxide (NaOH) generated from the chloride is used for locking carbon dioxide in sodium carbonate and bicarbonate, according to Saxena in U.S. Patent Application 20100028241

A process to sequester carbon from flue gas of a power plant, includes: reacting sodium hydroxide with carbon dioxide or carbon monoxide from the flue gas to form sodium carbonate.   The process further includes the step of adding natural gas and water to the carbon monoxide--sodium hydroxide reaction to produce sodium carbonate, or adding water to the carbon monoxide-sodium hydroxide reaction to produce sodium bicarbonate.  The process can be used for both natural gas and coal fired power plants.

Saxena process also generates hydrogen from the reaction.  The reaction takes place in a closed system to achieve zero emission of carbon gases while generating hydrogen from the reaction. The process of carbonation is not a direct conversion of NaOH to Na2CO3 but is a result of a reaction with other solids and gases usually producing hydrogen in important amounts. 

The process includes using any gas mixtures exhausting from the power plant; and adjusting the composition of the feed stock (sodium hydroxide) to react with components of gas selected from sulfur dioxide, nitric oxide, or both; and forming removable solids.

In the process it is possible to recover additional cost by selling reaction products selected from sodium carbonate, sodium bicarbonate, hydrogen, and chlorine at market prices to recover any additional costs that are incurred due to the use of sodium hydroxide.

The United States leads the world in per capita CO2-emissions. In 2004, the total carbon release in North America was 1.82 billion tons. World-wide industrial nations were responsible for 3790 million metric tons of CO2 (Kyoto-Related Fossil-fuel totals). There is little doubt that the world is choking with greenhouse gases, says Saxena.

No one can deny that there is an urgent need to develop innovative solutions to reduce the emissions from our automobiles and from our coal or gas burning power plants. Saxena’s invention may well provide an answer to the problem of greenhouse gas emissions and pave the way towards a clean energy future. The system addresses carbon sequestration in coal or gas burning plants used for power generation or for manufacturing (cement, steel etc.). The chemical process that sequesters carbon gases (thus preventing them from escaping to the atmosphere) also generates hydrogen as a byproduct.

Since the carbon gases are produced in industrial plants burning coal and thus are available at no cost. As these gases also can be obtained at relatively high temperature; the reaction of CO or CO2 and carbon with sodium hydroxide is exothermic and hence no additional heating may be required. The CO or carbon or natural gas and CO2 react to form sodium carbonate and thus carbon will be sequestered.

In Saxena's systems electric or thermal power may be produced from coal-burning plants with zero emission of greenhouse gases.  Hydrogen is produced economically with zero emission because of the low materials cost and low energy cost due to use of hot gases; use of hydrogen in transport will further reduce CO2-emission.

The figure (12) below shows a not-to-scale schematic diagram showing a possible industrial set up of a reactor to be linked to a coal-burning power plant and a sodium hydroxide production plant. The power plant provides hot CO or CO2 to the reactor. NaOH delivered to the reactor is advanced through the length of the reactor by a screw feeder over the required time period for reaction which could be usually 60 minutes. Since the reaction is highly exothermic, power must be adjusted by monitoring the temperature by use of a thermocouple. (Click images and tables to enlarge)

Maintaining the temperature at 400.degree. C. would ensure the result. It is permitted for CO pressure to be built up to some bars and for the newly formed hydrogen to exit through a membrane and be collected for use. The screw feeder delivers the finished product Na2CO3 and may be some unused CO and H2 mixture to a container. The gases from the container may be reused as necessary. This design will also apply to Process IV reactions where carbon is replaced by methane. Additional sequestration of CO2 is possible through the reaction of Na2CO3, water and CO2. The product sodium bicarbonate could then be sold or used in landfills.

The figure below (FIG. 13) shows a not-to-scale schematic diagram showing a possible industrial set up of a reactor to be linked to a coal-burning power plant and a sodium hydroxide production plant. The power plant provides electric power for the latter as well as hot CO2 to the reactor. NaOH is delivered to the reactor at the top and CO2 and if needed for reaction the natural gas from the bottom. This is a closed system reactor. The required time period for reaction could be usually 180 minutes. Since the reaction is highly exothermic, power must be adjusted by monitoring the temperature by use of a thermocouple.

Maintaining the temperature at 700.degree. C. would ensure the result. It is permitted for CO2 pressure to be built up to some bars. The newly formed hydrogen exits through a membrane and is collected for use. After the reaction is complete with no hydrogen flowing out, the reactor can be emptied into another container. The finished product would be Na2CO3 and some unused CO2. This design will also apply to Process IV reactions where carbon is replaced by methane. Additional sequestration of CO2 is possible through the reaction of Na2CO3, water and CO.sub.2. The product sodium bicarbonate could then be sold or used in landfills. 

FIG. 14 shows a not-to-scale illustration of a screw reactor sketched in FIG. 12. The reactor could be used for both CO and CO2 and if needed for reaction (5) the natural gas with different times and temperatures as required. 



FIG. 15 shows a schematic diagram for the flow of materials using a conveyor belt design. The sodium carbonate may further be used by using Process V to sequester additional CO2, which may be accomplished by passing the gas through series of tanks with water and the carbonate until all gas is adsorbed. 


FIG. 16 shows the cost calculations for carbon sequestration assuming that Na.sub.2CO.sub.3 sells for $100 per ton and production cost for NaOH varies from $100 per ton to $200 per ton. This calculation applies to the first several power-plants which use this technique. As the Na2CO3 supply continues to rise, the price structure would change. $2000/ton price of hydrogen is used for carbon sequestration calculation. (See Tables 2 and 3 for detailed calculation).


 The requirements are 80 kg of NaOH and 16 kg of CH4 which produces 106 kg of Na2CO3 and 8 kg of hydrogen; to the latter we can add the already produced 2 kg of H produced while manufacturing NaOH as discussed above. The cost of NaOH is (80.times.0.15=$12.0), the cost of CH4 based on ($0.04/kg) is ($0.16) selling price of Na2CO3 is $10.6 resulting in $1.86 for 10 kg of hydrogen produced for less than $0.16 per kg. To this we must add the energy costs. A hybrid process (a combination of reactions), which uses hot gases from the power plant, may be possible and energy efficient. Any one reaction or combination of reactions may be employed, adapted to local conditions as appropriate. The cost calculations for the reactions with natural gas are shown in Table 2 and are certainly quite exciting.

FIG. 16 shows plot of calculated costs for carbon sequestration. It is demonstrated that for a range of values for sodium hydroxide, the material costs remain negative i.e. money is actually saved by sequestering carbon gases and producing hydrogen. Note that none of the other costs of manufacturing, such as infra-structure development, energy and labor, are included in the calculations. 

Finally what if the price structure changes in such a way that we must totally discard sodium carbonate (possibly by burying it in an environmentally safe way)? The material costs would vary from $1.2 to $3.0 per kg of hydrogen. Table 2 shows that for practically every reaction considered, there is a profit if carbon is sequestered. Considering that the hydrogen is produced with zero emissions--and lets us burn coal to generate electric and thermal power, also with zero emissions--this process has enormous beneficial consequences for the world.  TABLE 3 calculates cost of the use of soda in sequestering additional CO2.



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