Optimization of Operating Profit for the FEED of the PZAS Process for CO2 Capture on a 460 MW NGCC

• Published in: Industrial & engineering chemistry research Vol. 62; no. 35; pp. 13911 - 13921
• Main Authors: Babu, Athreya Suresh, Abreu, Miguel, Drewry, Benjamin, Chen, Yee Lee, Rochelle, Gary T.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 22.08.2023; American Chemical Society (ACS)
• Subjects: Absorption; ambient temperature; Atmospheric chemistry; carbon dioxide; chemistry; cold; electricity costs; Environmental pollution; equipment performance; heat; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; natural gas; piperazine; Power; profitability; Separations; Solvents; specific heat
• ISSN: 0888-5885; 1520-5045; 1520-5045
• DOI: 10.1021/acs.iecr.3c00874

A rating model of Piperazine with the Advanced Stripper (PZAS) for a 460 MW natural gas combined cycle was developed from vendor-provided equipment performance data. Surrogate rating models were built and used to optimize the variable profit of the system, subject to natural gas and electricity price, at a fixed value for CO2 of $80/tonne. Several process constraints were considered between ambient temperatures of 4.4 and 40.5 °C. Lower lean loading resulted in a lower reboiler heat duty of about 2.2 GJ/tonne. Lean loading at 0.2 mol/equiv. of N was sufficient at an ambient temperature of 4.4 °C to maximize variable profit. Solvent precipitation was avoided even at a low lean loading (0.18 mol/mol) in the absence of a trim cooler for the lean solvent between the absorber and the cold cross exchanger. Optimal CO2 removal was always higher than the design case removal of 90% and achieved a peak of 93.6% for a 4.4 °C ambient temperature. Lean solvent rate was a significant driver of profitability. The maximum capacity of the compressor was a significant constraint on profitability. Increasing compressor capacity by 20–30% could increase variable profit by about 21% in the case of 0.18 lean loading at 4.4 °C ambient temperature. This increase in profit was lower at a higher ambient temperature and higher lean loading. The breakeven gas price was $4.6/MMBtu at a high lean loading of 0.22 mol/mol. Below this value, profit was maximized by increasing the boiler heat rate. Above this value, profit could not be increased by burning additional natural gas, requiring a reduction in boiler heat rate and, consequently, specific heat duty. At lower lean loadings (0.2 and 0.18 mol/mol), this transition in heat duty was not observed due to the lower heat duty. As the ambient temperature increased, a similar trend in heat duty was observed at 0.22 lean loading, but the transition to a lower heat duty occurred earlier at $4/MMBtu. This was because of the lower CO2 production at higher ambient temperatures, making the process unprofitable at a gas price higher than $3/MMBtu unless the heat duty of the stripper and natural gas boiler is steeply decreased.