Akermin post-combustion capture technology

I recently had the opportunity to pose some questions to Sean Black, VP of Business Development for Akermin, in regard to some very interesting carbon capture technology developments. I wanted to share with you some of the results of this excellent Q&A which highlight Akermin's novel and very promising approach to carbon capture.

Akermin is a technology development company located in St. Louis, Missouri, USA.  With a full-time staff of 23 people, including seven PhDs, Akermin is solely focused on developing a novel, low-cost, carbon separation and capture technology.

How does Akermin's technology work?

Akermin is developing an enzyme delivery system that uses a naturally occurring enzyme, called carbonic anhydrase, as a biological catalyst. Carbonic anhydrase belongs to a family of structurally and genetically diverse enzymes that catalyse the hydration of CO₂ and water to bicarbonate in all living organisms with remarkable efficiency.

Akermin's enzyme delivery system incorporates immobilisation and stabilisation techniques that deliver the enzyme, which is embedded in a thin polymer film, to the immediate vicinity of the gas-liquid interface in the absorber column. By concentrating the bio-catalyst at the critical point in the CO₂ absorption process, we are able to take full advantage of the enzyme’s power to accelerate the CO₂ capture process and prevent the enzyme’s exposure to high temperature in the desorber column.  This approach contributes to extending the enzyme’s lifetime and substantially reduces enzyme usage. The thin polymeric films that contain the enzyme can be cast on conventional contactor systems designed to maximise gas-liquid interface, as well as increase CO₂ absorption efficiency. This delivery system enables the enzyme to operate under extreme pH, temperatures, and shear forces and protects the enzyme against inactivation at gas-liquid interfaces. This extends the enzyme’s normal operating lifetime – from months to a year in conditions where it would otherwise inactivate within days.

Akermin incorporates a multi-discipline approach to efficiently integrate this bio-catalyst within our proprietary enzyme delivery system. This system works in a traditional, chemical absorption/desorption process to separate and capture CO₂ from different industrial applications.

What are the advantages of Akermin's enzyme delivery system to accelerate CO₂ capture?

Akermin's enzyme delivery system can greatly accelerate the kinetics of CO₂ absorption into any carbonate or tertiary amine solutions that operate on carbonate chemistry. This is opposed to carbamates that are typically formed when CO₂ reacts with primary and secondary amines. Our immobilisation approach not only increases the stability of enzymes at elevated temperatures but, more importantly, improves their operational performance. For example, immobilised CA operating in a counter-current flow column improves kinetics of CO₂ absorption in potassium carbonate at rates that significantly reduce the height of the CO₂ absorber column. A 10-fold rate improvement can reduce the height of a CO₂ absorber column, designed to capture 90 per cent of the CO₂ from a 550 MW coal-fired power plant, from 1,300 feet, without immobilised enzyme, to 130 feet using our enzyme delivery system. Akermin has conducted extensive tests in multiple, bench-scale reactors that demonstrate rate enhancement factors well beyond 10-fold. The key advantage is to drive significant capital cost reductions for CO₂ capture systems using energy-efficient and environmentally friendly carbonate chemistry. When, Akermin's enzyme delivery system is applied with conventional carbonate chemistry, it transforms the traditional chemical absorption process into a next-generation system for CO₂separation and capture.

How does this technology compare to other post-combustion technologies?

Specifically for post-combustion capture, Akermin is applying our enzyme delivery system with potassium carbonate chemistry. Our studies indicate that this process can be applied to large-scale, post-combustion CO₂ capture from coal-fired power plants at an avoided cost of capture that is up to 50 per cent lower than conventional amine systems, with the following benefits for the customer.

• Bio-catalyst enhanced, rate enhancement factors approaching MEA, translate into lower absorber column heights and investment cost (especially versus formulated or promoted amine solvents).
• Enzyme is resistant (not inhibited) by SOx and NOx. The Akermin system does not require upstream ‘polishing’ of these air emissions.
• Uses a non-volatile, low-cost commodity chemical (potassium carbonate) that is widely available and does not degrade in the presence of oxygen, SO₂ and other impurities. This eliminates the need for costly auxiliary equipment such as wash columns, solvent reformers and polishing FGD systems.
• 60 per cent lower heat of reaction versus MEA eliminates the capital and operating expense for absorber cooling.
• Replaces the need for expensive amine solvent formulations that require periodic monitoring and adjustment.
• Utilises a conventional absorber/desorber design which significantly reduces scale-up risk.
• More energy efficient process that results in a parasitic load (including CO₂ compression and purification to 2,250 psi) that is over 35 per cent lower than conventional amine processes.
• Operation at lower temperatures (40°C) and pH values results in low corrosion rates relative to conventional potassium carbonate and amine processes.
• Environmentally friendly process with no solvent emissions to the atmosphere and produces a benign, potentially re-usable, by-product with lower disposal costs and opportunities for profitable resale (e.g. for fertiliser).

Potassium carbonate chemistry is flexible in that CO₂ can be regenerated over a wider range of temperatures and pressures. Akermin's initial development and cost analysis has been directed towards low pressure regeneration at temperatures that are less than 85°C. This enables the utilisation of low pressure (LP) steam (or similar low-grade heat). This lower temperature regeneration also enables maximum integration with CO₂ compressor inter-stage cooling. This further reduces LP steam extraction and increases the net output from the power plant.

To explore the principle of LP steam integration using potassium carbonate chemistry, one can compare the reboiler heat duty for an unoptimised potassium carbonate system with that of higher energy solvents, like MEA. Since high heat of reaction solvents (such as MEA, ammonium carbonate, or piperazine) have a molar reaction enthalpy greater than the molar vaporisation enthalpy of water, their regeneration energy requirements are reduced with increasing temperature. In contrast, the molar heat requirement of low heat of reaction solvents (such as potassium carbonate and methyl-diethanolamine), is less than or equal to the heat of vaporisation of water. Therefore, all other things being equal, their regeneration energy requirement is reduced with decreasing temperatures¹.

When using potassium carbonate chemistry for a post-combustion application, operating the regeneration column at lower pressures and temperatures not only reduces total reboiler duty but also allows for the use of low pressure steam which increases the net output of the power plant (relative to a reference case using conventional MEA solvent). Simulation modelling conducted by Pacific Northwest National Laboratory (PNNL) for Akermin using AspenPlus^TM suggests that an increased power requirement for CO₂compression (due to the sub-ambient pressure in the desorber) is more than off-set by the increase in gross power generation.

We have applied the results of our simulation modelling to compare the performance of our technology to the DOE Case 12², where the carbon capture system is applied to a green field supercritical PC boiler that is sized to produce a net output of 550 MWe. The process employing Akermin's biocatalyst with potassium carbonate chemistry that was simulated by PNNL was ‘unoptimised’. Akermin has identified opportunities to improve the process and reduce energy requirements.  Under these more optimised conditions, the energy requirement for CO₂ capture is estimated at 0.268 kWh/kg of CO₂ captured, and is broken down into the following contributors.

Comments:

1. For Case 12, steam energy requirement for regeneration of 1,530 BTU/lb. is provided on page 313.
2. Estimated losses due to steam consumption for Case 12 are not provided but were estimated using AspenPlus^TM and the provided steam energy requirement of 1,530 BTU/lb. CO₂, (3.56 GJ/t-CO₂) provided on page 313 of study.
3. Estimated auxiliary load to compress CO₂ from regenerator outlet pressure to 2,215 psia.
4. Incremental auxiliary load for a larger boiler necessary to produce a net output of 550 MWe for a green field plant. For a retrofit case, there is an opportunity cost for lost power generation that must be assessed.

Relative to conventional amine technologies for post-combustion capture, the auxiliary load for CO₂ compression is marginally higher and the other auxiliary load is roughly the same. The key difference lies in the efficiency loss contributed by steam energy for regeneration, which is roughly 70 per cent lower than for conventional amine solvents. This is due not only to lower regeneration energy per metric ton of CO₂ captured, but also to the use of low pressure steam. This significantly reduces the impact on the power plant steam cycle.

It should be noted that potassium bicarbonate can also be regenerated at higher pressures and temperatures than amine solvents. For reasons discussed earlier, this is not expected to yield the most competitive performance for an ‘unoptimised’ process. However, Akermin and others are investigating novel approaches to concentrate potassium bicarbonate salts in the rich solution that is sent to the regenerator. Under these conditions, the water content in the rich solution is reduced.  This greatly reduces the large sensible and latent heating requirements and could result in a process flow scheme where CO₂ is regenerated at higher pressures, but at a reduced parasitic load, relative to the case discussed above. Akermin's development efforts are focused on developing a bio-catalyst driven system that leverages the advantages of our core technology and ultimately results in the most cost-effective CO₂ capture process.

In summary, Akermin's bio-catalyst enables the economic application of potassium carbonate chemistry, resulting in a simple, elegant and environmentally-friendly chemical absorption process for post-combustion capture that is lower in capital cost and operates with a lower parasitic load versus conventional and advanced amine technologies.

What markets is Akermin targeting?

Akermin's proprietary enzyme delivery system can be applied to work with different carbonate chemistries to provide a low-cost solution to separate and capture CO₂ for a range of industries such as those noted in the figure below.

Some of these applications are dependent on changes in regulations before owners and operators will aggressively install systems to capture CO₂. In contrast, other markets have purchased commercial solutions for CO₂ separation for many decades. The global market to process gas streams, including CO₂ separation, exceeds US$10 billion a year and is growing as technology is applied to an increasing number of industrial applications.

• Commercial markets for CO₂ separation
  • Natural Gas Processing: With annual expenditure of around US$7 billion for gas treating, changing market dynamics (shale gas, higher CO₂ content, increased demand, etc.) are creating technical challenges for processors and opportunities for new entrants.
  • Fertiliser: CO₂ is separated from syngas for ammonia and reused in the production of urea. This mature, cost-driven industry will benefit from a more cost-effective technology.
• Markets where CO₂ revenues drive new commercial opportunities
  • Industrial Hydrogen: A US$50 billion market with sustained high growth rates driven by the need to process heavier crude oil to lower sulfur diesel and upgrade bitumen from the oil sands. A concentrated CO₂ stream can be captured and sold for EOR, as well as improve hydrogen recovery and a lower-cost capture technology increases the ROI and, thus, drives additional projects.
  • Oil Sands: Operators in the Alberta Province are considering injecting CO₂ with steam from the ‘in-situ’ or Steam Assisted Gravity Drainage (‘SAGD’) processes to improve Bitumen recovery, or sell the CO₂ for EOR use.
  • Gasification: Countries in Asia are increasingly using existing fossil resources (e.g. coal and petroleum coke) to produce synfuels and other high-value products.
• Regulation driven markets (including CO₂ capture from coal-fired boilers and NGCC power plants)
  • Global regulations will eventually create a US$200 billion global market for CCS.
  • Strong focus on next generation technologies and novel, cost-effective solutions for CO₂ capture and re-utilisation.

Akermin's enzyme delivery system is a cost-effective solution for green field projects, as well as to retrofit existing units in service. Additionally we have confirmed not only our ability to handle gas streams with high CO₂ content, but CO₂ from air (ppm). Akermin can be the low-cost source for CO₂ feedstock or as part of an integrated solution for upgrading or converting to high value chemicals, fuels, or building materials. We have projects in various stages of development for such approaches.

What is Akermin's timing/roadmap for development?

Akermin is currently transitioning from lab research to field demonstration across various market applications. Under a US$3.5 million grant from the US Department of Energy, Akermin is constructing a field pilot plant that will commence testing in October 2012. This pilot will operate for approximately six months capturing 0.2 metric tons per day of CO₂ from the flue gas of a coal-fired power plant at the National Carbon Capture Center (NCCC) in Wilsonville, AL. We expect initial results will be available during the 2nd quarter of 2013.

In parallel, we are initiating several different projects that include third-party testing and feasibility studies covering other target markets (e.g. natural gas treating and gasification) with commercial partners and customers to confirm our techno-economic positioning. We expect the results of these studies to stimulate financial and commercial support to develop demonstration pilots. Successful completion of these milestones will position the company for commercial market entry in 2014. Specifically for post-combustion capture, we are working to develop a next stage field pilot plant that would scale up the technology by at least 25 times. Successful operation of this next scale pilot plant will provide the technical validation necessary to support a commercial-scale demonstration plant. Assuming the development of regulatory drivers or incentives that create market demand, operation of this demonstration plant will position Akermin to secure initial commercial orders.

For each target market, Akermin's business model is to develop strategic partnerships with commercialisation partners using a license and consumables business model. This approach will allow us to reduce our capital intensity, leverage the existing market infrastructure to accelerate adaptation and penetrate target markets and focus on maintaining a leadership position around the core technology and delivery system.

What do you see as the key challenges for commercial scale-up of the technology for post-combustion capture?

Akermin is applying our enzyme delivery system to a conventional absorber/desorber system which will help to mitigate scale-up risks. Chemical absorption systems using potassium carbonate chemistry have been operated commercially for several decades, separating CO₂ from high pressure gas streams. Our enzyme delivery system will be designed to work with conventional mass transfer devices and Akermin is working with established suppliers to mitigate the scale-up risk around the absorber design. The key challenges concerning scale-up of the proposed technology is to successfully demonstrate the enzyme delivery system at a progressively larger scale. Akermin must demonstrate that the rate enhancement that has been achieved in the laboratory can be maintained in larger field pilots and demonstration units. A second key challenge is to refine the design of the enzyme delivery system to facilitate minimal or no system downtime to replace the biocatalyst so that we minimise operating costs. Akermin is evaluating novel approaches to accomplish this objective.

The developmental enzymes that Akermin uses are manufactured using conventional fermentation processes. The supply of enzymes is a multi-billion dollar industry, with the market leaders already manufacturing other enzymes using the same approach in volumes that are similar to what is needed to support large-scale, post-combustion capture. The raw materials used to manufacture the polymer film are also widely available in sufficient quantities.

Does the technology allow capture of other compounds in the flue gas that normally are captured?

Potassium carbonate will absorb SO₂ and NO₂ and the resulting heat stable salts that accumulate within the process will have to be bled from the system for reuse or disposal. It is unclear whether other compounds like mercury and other heavy metals will be absorbed. If so, these concentrations will also be managed using a bleed stream. Laboratory experiments have determined that the enzyme is tolerant to levels of SO_X, NO_X and heavy metals that are higher than typical emissions downstream of conventional air quality control systems (e.g. ESPs or fabric filters for control of solid particulate matter and Flue Gas Desulfurisation (FGD) for control of SO₂ emissions). Field pilot testing will provide further validation of our enzyme delivery systems’ tolerance to impurities and the level of residual emissions capture.  Our system will be sufficiently tolerant that it can be retrofitted downstream of conventional FGD systems so that additional SO₂ removal will not be required. And, it may be possible to retrofit to plants that combust low sulphur coals, without an upstream FGD system installed to control SO₂ emissions. Field pilot testing will allow Akermin to define the practical operating envelope of the system.

References

1. J. Oexmann and A. (2010) International Journal of Greenhouse Gas Control, 4, pp. 36-43.
2. Cost and Performance Baseline for Fossil Energy Plants, DOE/NETL-2007/1281, Revision 1, August 2007, p. 403.