Carbon capture is a concept that uses chemicals or any physical process to capture carbon from atmosphere and turn it into solid or liquid. Ideally the concept works if the amount of carbon dioxide (CO2) released tp atmosphere is equal to the amount of CO2 sequestered. For example, one of the important hydroxides is CaO which is produced by CaCO3 thermal decomposition where,
In this process, there are two sources of CO2 emission, CO2 released by the burning of coal and CO2 as a byproduct of the decomposition reaction. We can capture carbon dioxide by reacting CaO with CO2 (atmosphere) but this cannot be considered carbon capture because a basic commodity material CaO is totally consumed with 1 mole of CO2 from coal burning is in excess. The same applies for other chemicals such as the alkyl amines and ammonia where CO2 is released at one stage in the production process. However, for some types of coal the burning process has one more byproduct which is the Alkaline Fly Ash (AFA). The AFA product contains various oxides such as Na2O, K2O, CaO, MgO, SrO, . . . which when mixed with water produce alkaline solution of 11<pH<12.5. In solution cations such as Na+, K+, Ca++, Mg++, . . . and the hydroxide ion OH− are present plus other impurities such as sulfates and carbonates. The burning process can be represented as,
C(s)+O2(g)→CO2(g)[to atmosphere]+AFA+HEAT
where AFA can be processed to produce an alkaline solution OH−, thus
OH−+CO2(g)[from atmosphere]→CO32− or HCO3−
Effectively, the above can be considered a carbon capture process because no energy penalties were paid in the production of basic chemicals for CO2 sequestration. Effectively, with the introduction of AFA we can refer to the net release of CO2 to the atmosphere where ideally,
CO2(net)=CO2(release by burning) CO2(sequestered by AFA).
In the real world attempts were made to sequester CO2 with Fly Ash by direct purging of the CO2 gas with Fly Ash Slurry [1,2,3,4] but no carbonate or bicarbonates can be collected and the efficiency is low. Our Ion Exchange/Reverse Osmosis patented setup would allow the production of carbonates with some energy penalty.
The invention uses alkaline fly ash (AFA) a waste product of power plants that operate on certain types of coal. It can also use alkaline red mud (ARM) a byproduct waste of aluminum industry or similar. The novelty in this invention is that no prior work used AFA or similar byproduct (i.e. ARM) as an input or feed chemical in an Ion Exchange/Reverse Osmosis patented setup to sequester CO2 a greenhouse gas released to the atmosphere.
The invention accommodates several stages,
The major advantage in the disclosed carbon capture process shows that no outside chemicals being used to sequester the emitted CO2 from the power plant. For example, the AFA, ARM, or similar process does not use pure chemicals such as ammonia or alkylamines in various forms, NaOH, Ca(OH)2, or CaO to remove CO2 from flue gas. Note, in reality the process might need make up CaO or Ca(OH)2 to achieve the required hydroxide content prior to IE/RO processing all depends on the type of alkaline Fly Ash or red mud used. The said process does not consume large energy as in CO2 underground storage or CO2 liquefaction. The patented process simply uses its own waste byproducts to sequester CO2 and lowers CO2 emission into the atmosphere.
The mechanism of sodium carbonate Na2CO3 production follows a similar scheme as in patent WIPO Patent App. No. PCT/IB2009/007713 where, The invention in the Enpro/ESL process uses alkaline fly ash (AFA) a waste product of industrial and coal fired power plants that operate on certain types of coal. It can also use alkaline red mud (ARM) a byproduct waste of aluminum industry. At this stage of operations ENGSL present the schematic in,
Although tens of millions of tons of fly ash goes to construction and road industries, there are also tens of millions of tons of useful AFA disposed off every year in landfills or mines. These can be obtained for free or even charged on the generator plant as fees for helping in its removal. Countries such India and China can be a good source of AFA however if waste AFA is available locally from power plants and other industries it can be used as well. The same applies for red mud which is dumped in millions of tons in landfills all around the world and can be a major hazardous waste.
The ENGSL AFA or ARM processing technology is expected to cut down on Ca(OH)2 usage to less than 10% depending on the quality of AFA or ARM used in its IE/RO process while at the same time consumes CO2 gas.
Alkaline byproduct processing Unit: The said unit is similar in design to a commercial quick-lime processing unit where the powder is subjected to mixing and filtering to collect the alkaline filtrate with pH>12,
Ion exchange system: Would receive the alkaline liquor (e.g. ˜0.9 g/L) to produce dilute caustic soda liquor at 1000 ppm concentration. The ion exchange battery is of dual purpose where,
R—SO3−Na++M2+→R—SO3−M2++Na+
R—(R2)N+Cl−+An−→R—(R2)N+An−+Cl−
Reactors design: Carbon dioxide gas is sparged through caustic soda NaOH in a reactor to form a dilute sodium carbonate liquor Na2CO3 (e.g. 700 ppm Na2CO3 to 300 ppm NaOH). The latter is then subjected to further filtration to remove impurity particulates then passed to reverse osmosis system. The low % liquor needs to be converted and concentrated to higher % sodium carbonate NaOH liquor (e.g. 2400 ppm Na2CO3 to 1000 ppm NaOH) by passing it to a reverse osmosis system.
Reverse osmosis (RO) unit contains RO cartridges cascaded with the CO2-NaOH reactors in between. The objective is to keep the NaOH concentration below 300 ppm as the concentration of Na2CO3 is increased. The concentration process should keep going until a 6% to 7% Na2CO3 solution,
Ion exchangers that are used in this process are regenerated from either the brine of desalinated seawater, any source of brine water, or prepared brine water. In the above schematic, if brine water salinity C is >8% then a desalination plant is not necessary. Otherwise, brine water concentration 6%<C<9% salinity can be obtained from the reject of an RO desalination plant to eliminate the calcium, magnesium, and any multivalent ions thus wash the regenerated ion exchange and convert it to the Na+ form. One important aspect about this process is the circulation of the RO permeate which saves on pure water production and chemicals supply. There are waste products such as calcium chloride and magnesium chloride that can be diluted with pure water produced from the complex membrane and heat exchanger system and returned back to the sea without harming the marine environment. The net production of potable water is difficult to estimate at this stage and depends on the government tolerance level of Ca++, Mg++salts after dilution.
Excessive release of carbon dioxide CO2 into the atmosphere is a major problem faced by human communities worldwide. The proposed invention attempts to bring this problem to a partial green solution while making a financial benefit. The green solution fulfilled by using alkaline fly ash (AFA) or alkaline red mud (ARM) instead of any pure industrial alkaline chemical at the input of an Ion Exchange/Reverse Osmosis patented process. The financial benefit comes from selling the soda ash chemical as byproduct of the combined processes. In a sense the production of soda ash by the said invention is a new process for the production of three commodity soda chemicals, NaHCO3, Na2CO3, and NaOH. The said patented process would consume less energy and purified start up chemicals than all exiting technologies for the production of these soda chemicals. Other issues such as safety problems in the chloro-alkali cell process tied up to chlorine production, poisonous gas storage, or poisonous gas handling such as ammonia in the Solvay process is eliminated. The soda ash production from alkaline fly ash (AFA) or alkaline red mud (ARM) process is most convenient for industries that emit brine water (i.e. salinity between 6 to 10%) with available waste heat and CO2 emission sources. Examples, include industrial plants, coal fired power plants, and solid waste incineration plants. There are industrial processes that require one of the soda chemicals at one stage of the production process thus the patented processes can be harnessed in CO2 sequestration and the provision of caustic soda, baking soda, and soda ash. Moreover, the demand for AFA or ARM increases worldwide causing a global distribution of the material thus decreasing its local impact on one dumpsite or landfill.
A copy of Excel worksheet gives detailed mass balance analysis of the entire process starting with the masses of hydroxides involved and required water and ends with the production of 18 kg of soda ash from 75 kg of fly ash.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB10/03162 | 12/8/2010 | WO | 00 | 8/20/2013 |