Carbon capture and storage |


It is essential to effectively clean the EGR flue gases before reintroducing them into the gas turbine inlet, to remove NOX


, SOx , and


particulate matter. The EGR cooling loop with an enhanced direct contact cooler is intended to provide high levels of EGR flow scrubbing and cooling to ensure continuing gas turbine operation. The EGR DCC cooler is designed as a packed column, with cooling water recirculated to the top and sprayed in a counter-current


capture equipment is divided into four primary categories: pre-scrubber or DCC;


way. The EGR gas flow is cooled down as it encounters the spraying water. The EGR cooling temperature is determined by evaluating gas turbine performance and the cost of the EGR cooler. Depending on the site location and water availability, the EGR cooling loop can be equipped with a water, air, or hybrid cooling system. The CO2


Gas


turbine inlet


HRSG


NGCC cooling tower


CCS & EGR cooling tower


CCS absorber CCS stripper


absorption system; stripper system; and CO2 compression train. Flue gas cleaning and


capturing systems, including absorption and pre-scrubber systems, account for roughly 60% of overall capture plant equipment costs. The stripper system contributes around 24%


of the entire capture plant cost, while the CO2 compression train accounts for roughly 19%, see Figure 4.


It is important to keep in mind that this cost breakdown may vary depending on the specific configuration of the capture plant, but the absorption system consistently remains the most significant equipment cost in the capture plant.


Gas turbine EGR ductwork


EGR direct contact cooler


NGCC to CCS ductwork


CCS direct contact cooler


This emphasises the significance of cost reduction in the absorption system in order to reduce the total capture plant capex. Absorbers are typically dimensioned according to the volumetric flow of flue gases, with the absorber diameter selected to ensure a safe flooding velocity. EGR reduces the quantity of flue gas that is directed to the absorber by recirculating a portion of it back to the


gas turbine inlet and increasing the CO2 concentration in the flue gas directed to the CO2


capture plant. When 30% of the exhaust gas is


Figure 7. 3D renderings of carbon capture system integrated with James M. Barry natural gas fuelled combined cycle plant. The 3D model was collaboratively created by GE Vernova, Linde, Southern Company, and Kiewit. Existing equipment is in blue and new equipment is in green


capture plant, which includes the absorption system, regeneration system, and CO2


compression train, might be reduced by about 15% when compared to the non-EGR scenario. The total cost savings for a natural gas fuelled combined cycle power plant with CO2


recirculated, the cost of the pre-scrubber and absorption system equipment drops by 20- 25% due to the smaller column diameter. The cost savings vary depending on the column configuration, the number of columns, and number of capture plant trains. The total cost of the CO2


capture system including EGR equipment and required modifications, range between 5 and 8%, see Figure 5.


Figure 6 shows the decrease in capex for the capture plant when steam integration and a 30% EGR are implemented, in comparison to a bolt-on solution. Steam integration reduces the capture plant capex by up to 30%, with an additional 7% reduction achieved by implementing a 30% EGR. These estimates will vary depending on the actual plant specification parameters, the type of capture solvent, and site-specific constraints.


Gas turbine upgrade and advanced control systems The operation of a carbon capture plant requires a constant supply of steam for the regeneration of CO2


and provision of


electrical power for the operation of the CO2 compression train and the balance of plant


in the carbon capture process. Typically, a natural gas fuelled combined cycle power plant would experience a decrease in both net electricity export and efficiency because of the extraction of steam and supply of electrical power. A gas turbine, steam turbine, HRSG and plant upgrade is an efficient and cost-effective method for recovering a significant portion,


16 | November/December 2024| www.modernpowersystems.com


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