Challenges & Solutions
Challenges for the PFBC Component
Challenge 1: Gas turbine durability: The PFBC system's gas turbine must withstand a harsh environment of high-pressure flue gases and fine dust particles. While ruggedized turbines have been developed and proven for older PFBC systems, integrating them with an advanced supercritical steam cycle requires further optimization.
- Solution: Because of the scrubbing required for the Benfield CO2 capture system, all dust particles are removed prior to the exhaust gas turbine.
Challenge 2: Particle separation: The flue gases must be meticulously filtered to prevent fouling and erosion of the gas turbine blades. Ensuring a reliable and effective particle separation system at high pressures is a critical, high-risk technical challenge.
- Solution: Because of the scrubbing required for the Benfield CO2 capture system, all dust particles are removed prior to the exhaust gas turbine.
Challenge 3: Operational stability: Issues such as bed agglomeration (clumping of bed particles), fouling, and maintaining a stable bed temperature are risks that can defluidize the system and harm components.
- Solution: These operational issues were solved in the demonstration project at Vartan, Sweden, which operated for well over 20 years. The changes made at Vartan, Sweden were incorporated in PFBC Cottbus power plants with a new P200 design which is the design PFBC-EET is still utilizing.
Challenge 4: Scaling and integration: Scaling up PFBC to a commercial utility size, especially when integrating multiple modular units with a supercritical steam cycle, requires careful optimization of the heat integration and control systems.
- Solution: These operational issues were solved in the demonstration project at Vartan, Sweden, which operated for well over 20 years. The changes made at Vartan, Sweden were incorporated in PFBC Cottbus power plants with a new P200 design which is the design PFBC-EET is still utilizing.
Challenges for the Benfield Carbon Capture Component
Challenge 1: Capture efficiency: Conventional amine-based (and other carbonate-based) capture systems, which the Benfield process uses, have limitations in capturing 100% of CO2 emissions. While capture rates of 90-99% are targeted, achieving these levels at scale is challenging.
- Solution: Our capture system is the UOP Benfield hot potassium carbonate system, tested in our PFBC test unit with capture results consistently above 97% capture.
Challenge 2: Energy penalty: A major drawback of many chemical absorption systems is the high energy input required to regenerate the solvent (separating the captured CO2 from the liquid). This "parasitic load" significantly reduces the plant's overall efficiency.
- Solution: There is always an energy penalty when adding CO2 capture, and as a repower, you are utilizing about 60% of the existing assets. Whatever the efficiently was before a PFBC repower, you can expect an overall efficiency drop of approximately 15 - 20%. However, since we can burn as low as 1500 BTU's, the addition of waste coal in the fuel mix will more than make up for the loss of efficiency on a PFBC repower and possibly qualify for accelerated depreciation.
Challenge 3: Solvent degradation: Amine solvents can degrade over time due to thermal and oxidative processes, which leads to increased corrosion, fouling, and foaming within the system.
- Solution: True for amine solvents. But, we use potassium carbonate which does not degrade and is circulated and reused with only minimal losses in the pressurized PFBC/CO2 UOP Benfield system, allowing for the lowest operating cost of CO2 capture from any coal fired power plant at approximately $20/ton of CO2 captured.
Challenge 4: (Corrosion and materials: The presence of CO2 and moisture can lead to corrosion of the metal equipment used in the capture process. Special materials or protective measures are needed to prevent leaks and costly repairs.
- Solution: In the UOP Benfield CO2 carbon capture system, all contact surfaces are stainless steel and, therefore, corrosion and leaks are not a problem.
Challenges for System Integration
Challenge 1: Total system energy balance: Successfully integrating the energy-intensive carbon capture process with the power cycle is a complex task. Optimizing waste heat recovery from the PFBC to offset the capture system's energy penalty is key to achieving high overall plant efficiency.
- Solution: When you are focusing on CO2 capture needed for Enhanced Oil Recovery and the cleanup of waste coal in America, overall plant efficiency is not the priority. However, with PFBC there is only a small efficiency drop because the boiler is pressurized. Also, the new boiler is much more efficient than the existing boiler being replaced.
Challenge 2: Process control: Managing the complex interactions between the combustion process, turbine operation, and capture system requires advanced digital control technologies to ensure flexibility and efficiency, particularly during load changes.
- Solution: The PFBC system has a special design feature for hot bed ash storage and reinjection, so load changes can occur very quickly, making a perfect partner for wind or solar power generation.
Challenge 3: Operational complexity: Retrofitting existing plants or building new facilities with both PFBC and carbon capture adds significant operational complexity. This includes managing multiple processes, equipment, and potential downtime for maintenance.
- Solution: The PFBC/CO2 system is very small and compact, so it's only about 1/5 the size of a standard boiler. Therefore, the design, in most cases, fits in the space of the existing boiler with minimal other changes required.
Challenges in Broader, non-technical areas
Challenge 1: High capital cost: The high upfront investment required for capture units, compression, transport infrastructure, and the plant modifications is a major barrier.
- Solution: The technology is best suited for a repower utilizing approximately 60% of existing assets. The capital cost with CO2 capture would be very competitive with any other fossil fuel power plant that also has carbon capture capabilities. Additionally, the operational cost to capture the CO2 is only around $20/ton, which is far less than other CO2 capture systems on the market today.
Challenge 2: Economic viability: Demonstrating that the system is economically sustainable without substantial subsidies or carbon pricing is difficult due to the high operational costs.
- Solution: The utilization of waste coal along with CO2 capture cost makes a PFBC/CO2 repower plant competitive, when the CO2 is sold for Enhanced Oil Recovery in the US markets without any subsidies or carbon pricing.
Challenge 3: Scaling and project risk: Historically, large carbon capture projects have faced a high risk of failure or being put on hold, suggesting that successful deployment on a large scale is difficult.
- Solution: A boiler change out with the PFBC/UOP Benfield is not a large project. We have 100 MW systems that can be used in multiple arrangements to produce and capture as much CO2 as needed for Enhanced Oil Recovery while cleaning up coal mining waste and producing much needed power for America.
Challenge 4: Long-term CO2 storage: If the captured CO2 is geologically stored, ensuring the long- term integrity of the storage site and managing liability associated with potential leakage are significant concerns.
- Solution: Our PFBC/UOP Benfield system is designed with the ability to clean up coal mining waste and the captured CO2 can be used for Enhanced Oil Recovery making it a necessary commodity that is in short supply in the United States today.