Cequest: Sequestering Carbon for Large-Scale Impact
Written in Collaboration with Naila Moloo, Kristina Arezina, and Sophia Moloo
Abstract
The climate crisis is not fresh news. It’s been happening for years now, but is nearing the point of being irreversible. When examining the causes of a calamity like this it’s safe to say that there are more than one, but carbon dioxide emissions are certainly a large contributor, especially as they are caused by human activity. Carbon dioxide is a gas that we breathe out, but when fossil fuels like oil and coal are burned, and pursuits like deforestation occur, there results in an excess amount in the atmosphere. In 2019 CO2 made up 80% of US greenhouse gas emissions from human activity (source). Greenhouse gases trap heat in the atmosphere, and CO2 is contributing heavily to this effect, subsequently leading to respiratory disease in humans, disrupted food chains, wildfires, droughts, rising sea levels, ocean acidification, and more. This leads to hundreds of thousands of people and wildlife killed yearly. Because of climate change, over 1 million species of animals face extinction (source), and the rate of extinction is now over 1,000 times the natural rate (source). We need something — a radical solution — to play a role in putting an end to climate change. One way to do this is by removing that excess CO2 and putting it to a greater purpose. This is where Cequest comes in, a clean solution with the potential to sequester over 10 Gt of carbon dioxide per year by 2050. Cequest sequesters carbon to produce clean hydrogen fuel as well as a bicarbonate that can be released into the ocean to combat ocean acidification.
Outline of Paper
1. Background
1.1. Intro to Carbon Sequestration
1.2. Past Projects and Prototypes
2. How it Works
2.1. The Reaction Chamber
2.2. The Electrolysis Reaction and Bi-Products
3. Production of Hydrogen Fuel
3.1. Hydrogen Fuel Cells
3.2. The Chemical Reaction
3.3. Storing Hydrogen
3.4. Hydrogen as Electricity
4. Materials, Design, and Costs
4.1. Advances in Electrolysis Design
4.2. What Materials We Need for the Reaction
4.3. Scaling Materials
5. Becoming Profitable
5.1. Source of Revenue
5.2. Renewable Energy Source
6. Next Up
6.1. Our Impact
6.2. Positive Externalities
6.3. Scaling the Company
7. Conclusion
1. Background
1.1. Intro to Carbon Sequestration & Mineral Weathering
Carbon sequestration is the process of carbon dioxide being removed and stored to actively fight against climate change. This can occur naturally, for example, trees and plants store CO2, but when they die, that is released back into the air. Seeing as issues like deforestation are becoming rapidly more prominent, the increased CO2 from fossil fuels paired with fewer trees is only making matters worse. Where forest deforestation is a source of carbon emission, forest regrowth is a source of carbon sequestration. Now scientists are trying to use other techniques to speed up the process of carbon sequestration. CO2 is captured and separated from other gases contained in emissions. Then it is compressed and transported somewhere it can be permanently stored, or ‘sequestered’.
Mineral weathering is a process that occurs when rocks react with carbon dioxide to create mineral bicarbonates, which over time precipitate as carbonate minerals having been washed into the ocean. This is the reason behind why bicarbonate in seawater is such a huge carbon reservoir. Electro-geo-chemistry uses saline water electrolysis by connecting two electrodes to a renewable energy source (further discussed in section 2.1.) to create hydrogen fuel as well as a chemical sponge-like solution that absorbs carbon dioxide from the air and turns it into a mineral bicarbonate. This represents carbon storage on the scale of hundreds of millions of years and serves to combat ocean acidification when released into seawater (because bicarbonates are alkaline). Additionally, the hydrogen can be sold or converted to electricity.
It is important to note that existing carbon capture and sequestration solutions only deal with capturing CO2 from the air or the ocean, not both. Ocean acidification occurs because the atmosphere and hydrosphere are always seeking equilibrium with each other. By the same process, it follows that by simply removing CO2 from the air as most of the proposed or existing models do, half of the amount removed will equivalate back into the atmosphere. With Cequest, we will lower the pH of seawater via electrolysis so that CO2 is captured then combined with a dissolved mineral carbonate to form a mineral bicarbonate while also reacting a basic solution with the air, so concentrating dissolved CO2 in the ocean and removing CO2 from the atmosphere at the same time.
1.2. Past Projects and Prototypes
There has been extensive research performed on carbon sequestration in the past, however nothing has been done on a large scale. Stanford, for example, did an experiment in 2019 where they split seawater into hydrogen and oxygen in a lab. Stanford also did not produce a bicarbonate.
There was also an article by Y Combinator focusing on electro-geo chemistry. The idea behind this is accelerating mineral weathering: a natural process that occurs when rock reacts with CO2 to form a bicarbonate which captures carbon dioxide in the air. Through this geochemistry, approximately 1 billion metric tonnes of carbon dioxide is sequestered annually. This bicarbonate in the seawater explains why the ocean is the largest holder of carbon dioxide with 139,000 billion metric tonnes of CO2 being stored. Y Combinator compiled research and numbers from a variety of sources, going into depth about mineral weathering and its outstanding implications. The paper outlined different methods and business models that could potentially be used if such an experiment were to be carried out.
The Y Combinator paper proposed that factories running on ~500 MW of renewable energy would capture 7.9 million tonnes of CO2 from the atmosphere per year and sequester it in the ocean via bicarbonates. A renewable energy source would have to be built onsite or nearby to supply the plant with its energy needs and would cover ongoing costs. With 5078 plants across the world at this scale, they would be able to remove 40 Gt of carbon from the atmosphere each year, equivalent to humans’ emissions in the same period.
Another previous attempt at creating fuel using CO2 was with Google’s Project Foghorn, led by X, the moonshot factory. The purpose of Project Foghorn was to create clean fuel from seawater. It worked through electrolysis powered by renewable energy that extracted carbon dioxide and hydrogen from the seawater. The carbon dioxide and hydrogen produced were then placed in a catalytic reactor, where they reacted to form a fuel. The sea fuel could then be used to power cars. In theory, Project Foghorn was planned to cost between $5 and $10 per gasoline gallon equivalent (gge). This did not prove to be the case for two main reasons: pumping a significant amount of seawater turned out to be very expensive, and producing hydrogen was also costly. They looked into using solid oxide electrolysis to produce hydrogen. However, after careful consideration the Foghorn team decided to cancel the project because generating a reliable and cheap source of hydrogen would take more than “five years of research and significant capital investment”.
2. How it Works
2.1. The Reaction
At a high level, the reaction that will allow us to capture carbon and takes in sea water as an input. Then electrolysis is performed and NaOH is produced which then is bubbled to capture carbon dioxide. Furthermore, carbon dioxide is combined with crushed limestone to form alkalized water that is then returned to the ocean. The chemistry behind this process was inspired by the Development of an Electrolytic Cation Exchange Module for the Simultaneous Extraction of Carbon Dioxide and Hydrogen Gas from Natural Seawater research (source).
The reaction will occur in an electrolytic cation exchange module (E-CEM). The module includes a centre compartment and an outer electrode compartment on each side of the centre compartment that is capable of reversing polarities. Also, it has two cation-permeable membranes which separate the three compartments. The electrode compartments of the E-CEM configuration were designed with end plates constructed from polyvinyl chloride (PVC), and platinum-coated titanium mesh electrodes were used.
Both seawater and reverse osmosis water are used in E-CEM. The module we will build to replicate the paper will be incorporated into a portable skid along with reverse osmosis (RO) unit, power supply, pumps, a membrane contactor CO2 gas recovery system, hydrogen gas vacuum tower, and gas analyzer to form a carbon dioxide and hydrogen capture system. All of these materials will be operated by a software program capable of maintaining safe and continuous automatic operation.
Seawater will be supplied to the skid via a 12-Volt 0.12 HP 5.5 GPM water pressure diaphragm pump. The water will be filtered by two spin-down filters in series. After filtration, a portion of the seawater will be sent to a 1,100-gallon container made from high-density polyethylene. Before the seawater in the seawater feed tank is fed to the center compartment of the E-CEM, it will be pumped through a filter cartridge to remove any remaining impurities.
The other portion of the seawater supply is fed through a filter cartridge to the RO system for processing. The water is stored in a 1,100-gallon polyethylene container that is specified as the RO feed container. This water is the feedwater for the electrode compartments of the E-CEM. The flow is split within the E-CEM resulting in equal electrode compartment flow rates to each electrode compartment. The electrode compartments will have eight times less water flow than the center compartment.
A Mastech HY3030EX 0−30 A, 0−30 V, regulated DC power supply is used to supply the current to the E-CEM electrodes. The CO2 gas from the effluent acidified seawater is vacuum stripped using a commercial membrane contactor. Simultaneously, a standard purpose-built hydrogen gas vacuum tower processes the water from the cathode compartment of the module as it liberates H2 gas.
2.2. The Electrolysis Reaction and Bi-Products
There are several reactions that occur within our CO2 removal and H2 generation process.
Electrolysis
During the continuous flow of both sea and RO water in the reaction chamber outlined above, seawater is passed through the center compartment of the E-CEM, while RO water is passed through the anode and cathode compartments. The simplified version of the principle chemical reactions within the E-CEM are shown below:
When direct current is applied to the module H+ ions and O2 gas is generated at the anode by the oxidation of the RO water.
Then, O2 gas is flushed from the anode compartment with the flow of deionized water. Also, the H+ ions get moved to the center compartment moving through a cation-permeable membrane in the process of getting there. In the center compartment, the H+ ions replace the Na+ in the flowing seawater.
This process causes the seawater to be acidified without the need for any additional chemicals. This is the case as the measure of the hydrogen ion (H+) concentration in a solution is the definition of pH and an acid is a solution with a higher concentration of hydrogen ions than pure water. Meanwhile, a base is a solution with a lower concentration of hydrogen ions than pure water.
After the H+ ions get moved to the center compartment, the carbon dioxide(CO2) from the carbonic acid(H2CO2) in the seawater is removed via being vacuum stripped by a gas-permeable membrane contractor.
After that, the CO2 from the carbonic acid in the effluent acidified seawater is vacuum stripped by a gas-permeable membrane contactor resulting in water being formed.
The Na+ ions from the seawater in the center compartment are passed through the cation-permeable membrane closest to the cathode. The water is then decomposed at the cathode to H2 gas and OH. Then the Na+ reacts with the OH− to produce sodium hydroxide in the cathode compartment.
The overall reaction for the electrolysis showcases that a mole hydroxide(OH-) replaces each mole of bicarbonate(HCO3-) present in seawater. Furthermore, the amount of H+ generated in the chemical reaction follows Faraday’s law and is thus proportional to the applied electrical current.
Bi-products
From the electrolysis reaction, 49.86% of the water used is recycled to be used again in the RO process. The recycling of RO water is advantageous as less RO water needs to be created from seawater, reducing the total energy input of the system by 20%. This saves us time, energy, and money as it costs around $1,900 to $2,100 to perform reverse osmosis per acre-foot of seawater due to the energy expenditure of running an RO system.
From the cathode side, a vacuum pump extracts H2 which is reacted in a fuel cell to produce electricity for the membrane process or stored for future sale or use. The NaOH present at the cathode will react with carbon dioxide to form Sodium bicarbonate (NaHCO3). This solution will be bubbled for 0.5–1.5 hours.
Since the product imputed into the sea is a base, with an estimated pH of 8.3, due to the hydroxide present in it, it helps balance the acidity present in the ocean.
Equally, from the cathode reaction, seawater is transported to a hollow fiber membrane contactor. Here the seawater’s pH drops from 8 to below 6. Simultaneously, CaCO3 (crushed limestone) is added, then recombined with the CO2 to precipitate dissolved Ca(HCO3)2 which is long-term (hundreds of millions of years) carbon sequestration. The product of this reaction is then added back to the ocean, which helps balance the acidity of the ocean as well.
3. Production of Hydrogen Fuel
3.1. Hydrogen Fuel Cells
Using fuel cells, hydrogen can be converted into electricity without the negative effects of burning fossil fuels, with the only bi-product of the reaction being water. A fuel cell can be thought of as a battery, storing chemical energy and converting it to electrical energy. The chemical energy in this case is created through oxygen, from the ambient air and the hydrogen produced in the electrolysis reaction. The fuel cell where the hydrogen and oxygen produce electricity and water is essentially the opposite of the electrolysis.
3.2. The Chemical Reaction
The fuel cell is composed of two electrodes, a negatively charged electrode called the cathode and a positively charged electrode called the anode that surround an electrolyte. The H2 will be fed on the anode side of the cell where the positive electrode will ionize the H2 causing it to lose an electron resulting in H+ ions. These ions are then fed through the external circuit, creating a direct current that will be connected to an electric motor which will generate electricity. The H+ ions will then pass through the cathode side to react with the O2 that enters through the cathode side to produce H2O as the only bi- product.
The reactions on each electrode side can be depicted in the following:
The hydrogen will react in the anode side of the cell producing hydrogen ions and electrons.
The hydrogen ions and electrons will pass to the other side of the membrane, the cathode side, where it will react with the oxygen fed into the fuel cell to create water.
Overall, in the fuel cell a synthesis reaction will occur with the hydrogen fed through the anode side and the oxygen through the cathode side to form water.
3.3. Storing Hydrogen
Hydrogen is typically stored as a compressed gas in high-pressure tanks, as a liquid in dewars or tanks (stored at -253°C), or as a solid by either absorbing or reacting with metals or chemical compounds. Given that storage for Cequest is for the short term and in some cases to be sold to businesses, a compressed gas in high-pressure tanks is the most suitable option. The total cost for hydrogen storage as a compressed gas, specifically for above ground storage will be $0.60 per kilogram of hydrogen gas. To combat risk of combustion, inspections of all hydrogen systems, specifically to ensure that tank pressures are consistent, will be conducted on an annual basis at a minimum.
3.4. Hydrogen as Electricity
For the minimal viable product (our prototype at scale), Cequest will be using a polymer electrolyte membrane as a fuel cell. This was chosen because it has a system output of less than 250kW and operating temperature of 50–100 degrees celsius (122–212 degrees fahrenheit). The efficiency of the polymer electrolyte membrane fuel cell will be 50–60% for conversion from H2 to electricity.
The fuel cell Cequest will be using when fully scaled will be a solid oxide fuel cell. This was chosen because it has a system output of 5kW-3MW and operating temperature of 600–700 degrees celsius (1202–1832 degrees fahrenheit). The efficiency of the solid oxide fuel cell will be 60–85% conversion from H2 to electricity. 85% efficiency can be ensured through the thermal energy produced being converted to electricity. With the estimated 39–40 kwH produced from the electrolysis reaction, 33.15–34 kwH will be produced (source) with 85% efficiency per kilogram of hydrogen.
4. Materials, Design, and Costs
4.1. Advances in Electrolysis Design
When looking through papers and past projects performed within carbon sequestration, we found the most effective reaction chamber to be that of Stanford, where researchers used electrodes, saltwater, and solar power to create hydrogen fuel. They did not produce a bicarbonate, and they did this on a much smaller scale, only creating a prototype.
The anode sustained seawater splitting without corrosion for an estimated 5000 hours, primarily caused by chlorine in saltwater, and was fabricated from inexpensive and abundant materials. The proposed anode was highly active and allowed long-term stability provided by a unique bilayer structure. It was created by anodizing a NiFe alloy-coated NiFe foam, degreased via sonication in acetone and ethanol, in a bicarbonate solution. This was done at fairly high temperatures, from room temperature to approximately 80° C. and above. The catalyst was an in situ grown carbonate-intercalated nickel-iron hydroxide on a metallic substrate, such as nickel foam. This anode enabled direct electrolysis on seawater without expensive desalination, while being at densities and temperatures that are currently used in industrial water electrolysis. It maintained performance in the 1000 hour stability test, meaning, as opposed to other electrodes which last around 12 hours, this could last over 1000.
The anode must be paired with a cathode, also developed at Stanford’s Dai lab. This had incredible stability for a cathode, sustaining high activity for 80+ hours which was very impressive, and being able to last for around one week in seawater. What’s furthermore beneficial is that it used non-toxic solvents, and inexpensive earth-abundant materials. A nickel and chromium-based catalyst was used, and to make this catalyst, an electrodeposition process was carried out, a method that produces in situ metallic coatings through passing an electric current on a conductive material immersed in a salt-containing solution. The plated part becomes the cathode. This is a fast and simple technique for a highly active and low cost catalyst for water splitting. Compared to other methods where this is completed in 20 hours, electrodeposition can be completed in 3 hours. An alkaline electrolyzer was used to allow widespread hydrogen production from water, which increased the capacity for renewable energy storage.
Under 1.72V the anode and cathode could achieve an electrolysis current density of 400 mA/cm2 for stable water splitting without decay for over 1000 hours, which is record-breaking. We estimate that the electrode will be able to sustain this current density for over 5000 hours without decay. There is a long way to go, though. This can last for weeks, but to be truly scalable and long-term, it should ideally last for years.
This design did not incorporate water flow, so we will be building on this with titanium mesh electrodes, which are already used in chlor alkali processes. These will be resistant to oxidation and reduction, being both an anode and a cathode. Titanium mesh electrodes have shown incredible performance, demonstrated through being quickly picked up in the electrolysis industry. They have a very low power consumption (reduced by 10–20%) because of the low working voltage. They have even lower power consumption because the purity of chlorine gas allows heightened alkali concentration. That also saves money. Additionally a large benefit is that the anode has a working life of more than 6 years, resistant to chlorine and alkali in chlorine gas. A reverse osmosis water system will be considered until the continuous and stable utilization of titanium mesh electrodes for seawater electrolysis is verified.
4.2. What Materials We Need for the Reaction
In order for the reaction chamber to be assembled and for the chemical reaction to take place the following materials need to be acquired.
Firstly we need seawater. In order to obtain this for Cequest’s reaction, we will need to have a supply line of seawater which we will obtain via a seawater pump. Then a Mastech HY3030EX 0–30 A, 0–30 V, regulated DC power supply will provide the current to the E-CEM electrodes which is needed for the electrolysis reaction to take place.
To develop the electrodes we will need material for both the end plates and material to coat the cathode and anode in. The end plates of the module were combined with the electrode compartment and constructed from polyvinyl chloride. The electrodes will be made from titanium mesh electrodes and will be coated in platinum. Being light in weight, extremely corrosion resistant, and high in quality, titanium mesh electrodes will deliver many benefits. Platinum is used to enhance the titanium mesh as it is highly unreactive and resistant to oxidation. This is a great property to have when performing electrolysis as it will not take part in the Redox reactions occurring in electrochemical cells.
In order to separate the three components we will need two cation-permeable membranes. These membranes will need to be bought from Ionpure in order to use them for our reaction chamber.
We will also need a standard purpose-built hydrogen gas vacuum tower to process the water from the acting cathode compartment of the module. The tower will also spin down filters and a filter cartridge in order to filter the seawater. After filtration, a portion of the seawater is sent to a 1,100 gallon high density polyethylene container that functions as the seawater feed container. Lastly, we will need to acquire an RO system until Cequest is able to develop the technology to perform electrolysis effectively with seawater.
We will also need Vision 290 Unitronics hardware and software systems to control the system components (RO, pump water, E-CEM, well pump, vacuum towers, vacuum pumps, solenoid valves, and power supply) so they operate and function together as an integrated unit on a continual automated basis, with limited operator control required.
In order to get CO2 from the acidified seawater we will need a hollow commercial membrane contactor made out of polyethylene fiber. A Honeywell gas analyzer will need to be used to determine how much H2 gas and CO2 gas is produced in the reaction.
The total cost of the materials required to build the minimal viable product as a whole amounts to $5,835.31 plus assembly costs.
4.3. Scaling Materials
To scale up from the prototype mentioned above by a factor of 20 to achieve the milestone of 1 tonne of CO2 removed from the atmosphere per day, we will need to incorporate commercial materials on a large scale. The feed pipe for the seawater, for example, will need to be at least five to seven inches in diameter and be pumped by a 8 kW pump. Where it is most important that we use commercial processes is for the electrolysis reaction in order to become drastically more energy efficient.
Based on a exponential regression performed on five models of Nel electrolyzers (r2=1), ranging in output from 24.2g of hydrogen gas per hour to 22.13kg per hour, it was found that the energy required per mass of H2 gas produced fell by over 40% when scaling by a factor of 100. A similar increase in efficiency of between 15–28% was noted for every increase in hydrogen production by a magnitude of 10. Thus, when we scale from the paper to the prototype and again to the first large-scale plant (a magnitude of over 200), we can expect the efficiency of the electrolysis reaction to be in line with commercial electrolyzers, a decrease of around 60% from the paper’s energy use.
Logistics for both the storage and transportation of hydrogen gas (discussed in section 5.2) and the sourcing and transportation of limestone from the quarry to the plant site will need to be optimized for cost and quality. With regards to limestone, it is available crushed (to allow for a greater surface area to sequester CO2 faster) at $2 USD per metric tonne from many international vendors. Shipping costs are generally $0.007 per tonne per km and so the proximity of the plant to a port will also need to be considered (source).
Likewise, the reaction chamber where the water-containing CaCO3 (limestone) and CO2 will have to be substantially larger and — in terms of the gas that will be one part CO2 and nine parts ambient air, will have to be automatically monitored to keep the concentration of CO2 at that optimal proportion, adding in ambient air and allowing the non-sequestered CO2 to recirculate as necessary.
When it comes to scaling, nothing is perhaps more important than the proper disposal of both the NaHCO3 and Ca(HCO3)2 into the ocean. These sodium and calcium bicarbonates, respectively, will serve to make the ocean more alkaline, which will counter ocean acidification and may even increase phytoplankton growth where either of these minerals are the limiting factor. However, it is important to document the effects of such large-scale alkalinization in a localized area as that could very well have the opposite of the intended effect to increase fauna and flora in the region. Sites with strong nearby ocean currents to distribute this alkalinity over a larger area will mitigate said adverse effects while retaining the benefits that come with reversing ocean acidification. Alternatively, the CaCO3 can be disposed of on land or shipped to nearby areas to increase the alkalinity of the ocean there.
Finally, ongoing maintenance costs will represent 3% of the budgeted cost per tonne of CO2 removed and will ensure that the facility is running at optimal efficiency and to account for repairs and the replacing of parts (i.e., electrodes) that will have to occur every 5–10 years.
5. Becoming Profitable
5.1. Source of Revenue
Cequest has two primary sources of revenue and one secondary source. The two primary sources of revenue are from companies wishing to sequester a certain amount of CO2 to offset their carbon emissions to pay less in carbon tax and, from selling hydrogen gas to a worldwide market rapidly increasing and currently at 80 million tonnes per year.
In over 40 countries — most of which are primarily in Europe — carbon taxes have been enacted in order to try and reduce fossil fuel production and consumption for energy needs. When Cequest will be able to scale to the point where our price per tonne of CO2 sequestered is below that of the carbon tax of that country, companies will then be purely economically incentivized to offset their carbon emissions by way of paying us to sequester the corresponding number of tonnes. For other already environmentally conscious corporations, they will be able to fulfill their sustainability commitments for less.
Next is hydrogen gas. While ‘green’ hydrogen gas is priced between $2.50–6.80 per kg, hydrogen that comes from fossil fuel sources that release over 9 tonnes of CO2 per tonne of H2 produced are substantially cheaper, at around $1.20–1.80 / kg. In order to accelerate the transition away from fossil-fuel produced hydrogen, it has to be economically incentivized. In our calculations, we’ve priced our hydrogen at $1.50 per kg or $1500 per tonne. Thus, as we produce 1 tonne of hydrogen gas for every 66 tonnes of CO2 produced, we are able to recoup $22.73 per tonne of CO2 captured. One point to note is that in the state of California, hydrogen for use in fuel cells in cars sells at above $10 per kg, due to excessive demand and not enough renewable-derived hydrogen supply. If Cequest was to build a plant there, it would not only make hydrogen a much more viable alternative to gasoline cars but also enable us to become even more profitable, if we were to sell the hydrogen at, say, $3 per kg.
Finally, we derive a secondary source of revenue from selling electricity back to the grid during on-peak periods where electricity is between 2–2.5 times more expensive. Selling this electricity back to the grid at $0.10 per kWh would be equivalent to selling hydrogen at $3.20–3.50 and would increase our profitability. Equally, if we cover our own electricity needs during that period with energy produced onsite, costs will be reduced. While this secondary source of revenue is important in its own right, the exact financial details will depend on individual plant locations and other electricity demand factors and so was entirely left out of our calculations for the price per tonne of CO2 removed. Instead, an average electricity price was used.
5.2. Renewable Energy Source
Existing methods to produce hydrogen gas (H2) as an energy source — 90% of which are from fossil fuels — are very harmful to the environment. For every tonne of H2 produced, roughly 9 tonnes of CO2 are released into the atmosphere (source). Seeing as Cequest hopes to produce a negative-emissions fuel via H2, we are producing a cost-competitive H2 fuel using electrolysis of seawater, and using a renewable energy source to provide the necessary electricity for the electrolysis reaction to take place.
In the US, 1160kg (1.16 tonnes) of CO2 are released into the atmosphere per every 2 mW of electricity generated. Our reaction process — explained in more detail in the sections below — will sequester approximately one tonne of CO2 from the atmosphere and from carbonate in the water per 0.8 mW of electricity put into the system. As such, using electricity from the grid — which is still primarily fossil fuel-derived — nearly halves our net CO2 sequestration. On the other hand, supplanting this energy with renewable energy such as solar or wind (depending on the climate and various other factors), will enable us to achieve a much greater impact.
Additionally, there is the economic case to consider. Electricity rates vary by the hour, from off-peak prices mostly during the night to on-peak prices during the day when everyone is most active, at a rate more than 2x that of off-peak times. For example, in Ontario, off-peak electricity rates are $0.085 per kWh while they shoot up to $0.176 per kWh during on-peak periods. Across the world, most on-peak rates last 6 hours and so it would not make economic sense to have the plant sequestering CO2 during that time if we were to buy electricity entirely from the grid. By using solar or wind energy in specific coastal areas they are most reliable, our per kWh cost (after installation) would be $0.06 and $0.04, respectively.
To ensure that the plant is running at its maximum operational capacity, we will produce electricity from the hydrogen gas produced from the reaction via fuel cells for operation of the electrolysis reaction whenever our renewable energy source is not able to meet the plant’s energy demands. Moreover, if by using renewable energy we are able to nearly double our net CO2 removal amounts, then our net cost per tonne of CO2 removed from the atmosphere decreases proportionally.
Between wind and solar energy, the former is currently cheaper to purchase and install in North America and is more reliable. Our proof-of-concept at scale prototype will require approximately 1.1 mW of electricity. The cost to purchase and install 12 wind turbines (each rated at 100 kW) is $80,000 USD per turbine for a total of $960,000, while maintenance costs are factored into the per kWh price we will allocate for this electricity — which, at around $0.05 will be at least 40% cheaper than the off-peak rates (source).
6. Next Up
6.1. Our Impact
From our large-scale plant (more on that in section 6.3.), we will be able to sequester approximately 8.5 million tonnes of CO2 per year, equivalent to the amount sequestered by 380,000 trees over the same period. The cost per tonne at this stage will drop to around $32 per tonne of CO2 removed (assuming selling hydrogen gas below the cheapest rate on the market), making this technology half the cost of the theoretical cost of other carbon capture solutions such as BECCS that are not nearly as scalable (estimated max CO2 removal at 1.5 Gt by 2050). Furthermore, the company Carbon Engineering, headquartered in Canada, hopes to achieve a cost of $100 per tonne of CO2 captured. Our proposed solution will be 3x cheaper while also being carbon-negative — Carbon Engineering plans to turn the CO2 into jet fuel, meaning it will simply be released back into the atmosphere.
What’s more, building even one of these plants will create plenty of green-collar jobs in the surrounding region while helping sustain other industries such as eco-tourism and local small-scale fishing operations. The need for H2 fuel could drive sales of hydrogen-powered cars which are now selling poorly in many areas due to a lack of consistent supply of hydrogen. With over 366 tonnes of H2 being produced hourly, that is enough to supply more than 15000 cars running on hydrogen fuel cell technology.
6.2. Positive Externalities
Cequest’s carbon capture results in several second-order benefits which can be broken down into two categories: benefits from reducing the amount of CO2 in the atmosphere and benefits from adding calcium bicarbonate Ca(HCO3)2 to the ocean.
Excess carbon dioxide in the atmosphere contributes to climate change. Ultimately, removing this carbon from the atmosphere reverses and/or stops the detrimental side effects of climate change. This will economically benefit countries as in 2019, climate change contributed to extreme weather events causing at least $100 billion in damages. Furthermore, a 2017 survey of independent economists looking at the effects of climate change found that future damage estimates range “from 2% to 10% or more of global GDP per year.
Farmers will immensely benefit from carbon capture as it will save them time and money for farming as excess carbon dioxide found in the atmosphere causes increased weed growth due and an increased prevalence of pests and pathogens in livestock and crops.
When added to the ocean, bicarbonate can reduce sea-to-air CO2 emissions by neutralizing the effects of ongoing ocean acidification.
Making the ocean more alkaline will increase the amount of carbonate, which will help marine organisms, such as coral and some plankton, form their shells and skeletons. It is particularly important to keep coral reefs healthy as they protect coastlines from storms and erosion. Apart from being a key part of the coastline ecosystem they also provide jobs for local communities and offer recreation opportunities.
6.3. Scaling the Company
The plan to scale Cequest can be broken down into three steps: building a prototype, a facility to test out the idea at scale, and a final plant for mass-implementation worldwide.
Step #1: Building a working prototype
Based on the paper “Development of an Electrolytic Cation Exchange Module for the Simultaneous Extraction of Carbon Dioxide and Hydrogen Gas from Natural Seawater”, we will construct a prototype approximately ten times the size and with roughly 15x the CO2 sequestration capacity due to several optimizations made to the methods used in the paper. This working prototype will include all the necessary components — from a water pump to the devices for capturing and measuring CO2 and H2 gases. A reverse osmosis water system will also be considered until the continuous and stable utilization of titanium mesh electrodes for seawater electrolysis is verified.
Furthermore, we will have to streamline the process for sequestering CO2 via limestone as Ca(HCO3)2 — calcium bicarbonate — building off of the “CO2 Mitigation via Capture and Chemical Conversion in Seawater” paper. This prototype will allow us to interchange and test the effectiveness of various components within the system before we scale, ensuring that the cost per tonne of CO2 captured is as low as possible in terms of energy use. In short, to optimize and determine the feasibility of future models at scale, building a working prototype is necessary for rapid iteration.
Step #2: Scaling the prototype and building a small plant
Once the prototype is optimized after roughly 6–8 months of constant testing and iteration, it is then time to take those learnings and apply them to building a small plant where the cost per tonne of CO2 captured will be dramatically reduced and allow Cequest to be poised to achieve the greatest impact. This model plant will demonstrate the viability of our solution at scale and will be the bridge between our prototype and large-scale implementation.
This plant will be strategically located either in Canada, the USA, or the Scandanavian countries (Sweden, Norway, and Finland), depending on various factors including carbon tax in that country and possible grants that can be used. For example, Sweden has the highest carbon tax in the world at $126 USD per metric tonne as of 2020. Other nordic countries also have high carbon taxes with Canada’s set to reach $50 CAD in 2022 and increase up to $170 in 2030. Equally, the USA — under the leadership of President Joe Biden — has released a $2 trillion infrastructure plan, with billions earmarked for renewable energy, including carbon capture. It is important to consider these factors for plant location as this plant will still not be at the scale required to achieve the lowest price per tonne of CO2 removed. Rather, it is at the point where — if strategically located, will still be economically viable as an investment.
Additionally, this plant will be where renewable energy sources are integrated into the plant design to further reduce costs, as explained in section 5.2. Tariffs, such as those imposed on Chinese solar panels in Canada, are another factor to take into account when choosing the location of the plant, as well as the reliability of the energy source. The plant will require approximately 1.2 mW of electricity and be able to sequester roughly 24 tonnes of CO2 per day.
Step #3: A facility for implementation worldwide
With both the prototype as a proof-of-concept and the model plant as a proof-of-concept-at-scale, Cequest will now be able to create plants on the order of 500 mW to achieve the most impact. These plants will be located around the world, preferably where there is a carbon tax (to make the enterprise more profitable) though the fact that they are at such scale and supplied with on-site or nearby renewable energy whenever possible, means that — in addition to selling the produced hydrogen gas — these plants will be economically incentivized on the whole.
Standard procedures will be established for determining the location of new plants and all the necessary steps to get them up and running within the shortest time possible. While we will build plants wherever they make the most sense, Cequest will also be advertised to governments as a solution with both economic benefit and one that demonstrates their commitment to climate action. In order to achieve a target emissions reduction of 10 Gt per year by the year 2050, about 1100 plants operating at 500 mW will need to be constructed.
7. Conclusion
Our world is suffering because of climate change. Our vision is to create a place where, 20 years in the future, our children can walk outside and breathe in clean air, and where biodiversity is still thriving both on land and sea. This is an inexpensive and effective solution to the pressing problem of carbon capture, which has been looked at as sci-fi for far too long now — with Cequest, we want to bring the concept to a large-scale reality. Our combination of hydrogen fuel and bicarbonate to counter ocean acidification has the potential to make a substantial impact. Cequest has the capability to revolutionize our lives and change the world.
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