Advanced Stripper Research Articles

Cost details from front-end engineering design of piperazine with the advanced stripper

This Front-End Engineering Design (FEED) was funded by the U.S. Department of Energy (DOE) to estimate the cost to capture and compress 90 % of the CO2 from an existing natural gas combined cycle (NGCC) in Denver City, Texas, USA. The FEED used the PZAS (Piperazine with the Advanced Stripper) 2 G amine scrubbing technology developed and modeled by The University of Texas at Austin. This FEED is unique in providing more public cost details than other FEEDs funded by DOE. The primary objective of the FEED was to provide a comprehensive estimate for the total installed cost of the capture plant. The estimated capital cost of NGCC at the Mustang Station is $727 million for a capacity of 460 MW and 1.6 million tonnes CO2/yr. This includes a contingency of $104.6 million and a contractor's profit of $60.1 million. The total direct field cost is $384.1 million. With an optimistic fuel value of $3/MMBtu, the estimated cost of capture varies from $85/t at 4 % IRR/85 % load to $170/t at 10 % IRR/52 % load. Air cooling is technically feasible but expensive. The air cooling systems for the water wash and pump-around intercooling account for 23.4 % of the direct cost. The gas-fired boilers represent only 4 % of the direct costs, but steam extraction would reduce energy cost, free up cooling water, and reduce the direct costs of processing additional flue gas and CO2 from the boilers. The absorbers represent 9.6 % of the direct cost in this FEED with no direct contact cooler and only 7.6 m of packing. The solvent cross exchangers are less expensive than expected (2.5 % of direct costs). Doubling the number of these exchangers could reduce the heat duty from 3.0 to 2.5 GJ/t CO2.

Lessons Learned: Comparing Two Detailed Capital Cost Estimates for Carbon Capture by Amine Scrubbing

Two front-end engineering designs (FEED) for commercial-scale carbon capture from natural gas combined-cycle (NGCC) power plants have been published in full, including detailed capital cost estimates. The two studies are the Piperazine with the Advanced Stripper (PZAS) FEED at Mustang Station in Denver City, TX, U.S.A. (“Mustang FEED”) and the FEED at Panda Sherman Power Station in Sherman, TX, U.S.A. (“Panda FEED”). The design capacities are 197 tonne/h of CO2 captured in the Mustang FEED and 129 tonne/h in the Panda FEED. This work compares both designs with the aim of gaining insight about the cost of carbon capture processes. Direct field costs for each process are adjusted to account for differences in the estimating methodology in each FEED. This adjustment results in estimated direct field costs of $574MM for Mustang and $411MM for Panda. The breakdowns of capital costs for each process area are compared, to highlight differences in costs due to the respective processes or particular requirements of each host power plant. A key finding is that site-specific factors not typically represented in less rigorous cost estimates are observed to have a significant impact on cost. To compare both estimates on a similar design basis, the Mustang unit was scaled to the Panda FEED design capacity, resulting in direct field costs of $489MM for Mustang and $411MM for Panda. Additionally, the cost estimates of the CO2 absorbers are analyzed in greater detail to directly compare three equivalent designs that include rectangular and cylindrical absorber columns. Adjusting the absorber estimates to the same scope and scaling to the same size results in estimated costs of $19.7MM, $18.2MM, and $14.9MM, with the rectangular absorber being approximately 10% to 30% more expensive than the cylindrical designs.

Heat Loss Characteristics and Energy Use of Piperazine with the Advanced Stripper (PZAS) at the UT-SRP Pilot Plant

Heat Loss Characteristics and Energy Use of Piperazine with the Advanced Stripper (PZAS) at the UT-SRP Pilot Plant

Pilot plant results with the piperazine advanced stripper at NGCC conditions

CO2 capture is necessary to decarbonize natural gas combined cycles (NGCC) that will be used to provide power when renewable power is unavailable. The PZAS™ (Piperazine (PZ) with the Advanced Stripper) second generation capture technology has been successfully tested with coal-fired flue gas. This paper reports reliable testing of PZAS at NGCC conditions for 2000 h in a 0.66 m ID absorber at the National Carbon Capture Center (NCCC). Coal-fired flue gas diluted with air entered the absorber at 77 °C. 5 m PZ was regenerated by the Advanced Stripper with 2.45 gJ steam/tonne CO2 at 6.2 bara. With 40 feet of packing and pump-around intercooling the absorber provided 90–95% CO2 removal with a rich loading of 0.40–0.41 mol CO2/mol N. The apparent rate of PZ oxidation was 0.3 kg/tonne CO2. The water wash reduced PZ emission to less than 1 ppm. In the last 400 h of testing, carbon treating clarified the solvent color, reduced ammonia production by as much as 40%, and improved both absorber and stripper performance. Testing with coupons showed that 304 SS had an acceptable corrosion rate even at the severe conditions of the stripper at 150 °C.

Energy use of piperazine with the advanced stripper from pilot plant testing

Piperazine with the Advanced Stripper (PZAS™) was tested at the National Carbon Capture Center (NCCC) at coal and NGCC conditions. Energy performance was measured with accounting for heat loss. The net heat duty was found to be identical at 2.45 GJ/tonne for both 4 and 12% CO2 at 90% CO2 removal. The average measured heat loss was 0.38 GJ/tonne and represented 30% of the gross heat rate. For PZAS, the warm rich piping before the control valve is the largest in surface area. Heat loss at this location increased heat duty by 80% of the heat loss value. Therefore, the total heat duty was decreased by 80% of the heat loss. The Independence™ model was validated using 112 steady-state pilot plant runs and predicted average net heat duty with an error of 9% and lean loading with an error of 10%.The model was used to simulate process impacts of heat loss for the PZAS and simple stripper configurations. For both strippers, heat loss was found to impact heat duty at locations other than just the steam heater. While heat loss in the steam heater was the most important for PZAS, heat loss in the column was the most important for the simple stripper due to a large top-side pinch and CO2 reabsorption at the same location. CO2 reabsorption in PZAS occurred only at high heat loss values (∼0.14 GJ/hr), compared to low heat loss values (∼ 0.03 GJ/hr) in the PZ-simple stripper. Excessive packing in the PZ-simple stripper caused a large top-side pinch at 0.23 mol/mol lean loading, making the column very sensitive to heat loss. Heat loss in the PZ-simple stripper increased heat duty by 120–150% at typical heat loss values and lean loading of 0.23 mol/mol. Heat loss in the MEA-simple stripper only increased heat duty by 1–13% in a typical lean loading range of 0.1–0.2 mol/mol. A large bottom side pinch at low lean loading for 7 m MEA made the effect of heat loss less pronounced.

Pilot Plant Results With the Piperazine Advanced Stripper at NGCC Conditions

CO2 capture is necessary to decarbonize natural gas combined cycles (NGCC) that will be used to provide power when renewable power is unavailable. The PZAS™ (Piperazine (PZ) with the Advanced Stripper) second generation capture technology has been successfully tested with coal-fired flue gas. This paper reports reliable testing of PZAS at NGCC conditions for 2000 hours in a 0.66 m ID absorber at the National Carbon Capture Center (NCCC). Coal-fired flue gas diluted with air entered the absorber at 77 oC. 5 m PZ was regenerated by the Advanced Stripper with 2.45 gJ steam/tonne CO2 at 6.2 bara. With 40 feet of packing and pump-around intercooling the absorber provided 90–95% CO¬2¬ removal with a rich loading of 0.40–0.41 mol CO2/mol N. The apparent rate of PZ oxidation was 0.3 kg/tonne CO2. The water wash reduced PZ emission to less than 1 ppm. In the last 400 hours of testing, carbon treating clarified the solvent color, reduced ammonia production by as much as 40%, and improved both absorber and stripper performance. Testing with coupons showed that 304 SS had an acceptable corrosion rate even at the severe conditions of the stripper at 150 oC.

Heat Loss and Energy Use in Pilot Plant Testing of Piperazine With the Advanced Stripper

Piperazine with the Advanced Stripper (PZAS™) was tested at the National Carbon Capture Center (NCCC) at coal and NGCC conditions and its energy performance and heat loss were measured. The net heat duty was found to be 2.45 GJ/tonne at 4% and 12% CO2 at 90% removal. The average measured heat loss was 0.38 GJ/tonne and represented 30% of the gross heat rate. Carbon treating increased the NTU of the cold and hot exchangers by 1.8% and 1.5%, respectively, by removing viscous solvent degradation products. The Independence™ model was validated using 112 steady-state pilot plant runs and predicted average net heat duty with an error of 9% and lean loading within 10% of the measurements. The model captured the effect of carbon treating on heat exchanger performance and predicted a reduction in heat duty of 1.2% but failed to predict the step decrease of 8% seen in measured heat duty data. In PZAS™, the warm rich pipe before the control valve is deemed the most important for heat loss due to its high surface area and its ability to increase flashing across the valve and decrease the total rich bypass temperature. Heat duty is corrected for 80% of the heat loss value, corresponding to the sensitivity of heat duty to heat loss at the same location. In the simple stripper, a large topside pinch makes heat duty most sensitive to heat loss in the column. Water condensation by heat loss increases the L/G and causes reabsorption at low heat loss values (~0.02 GJ/hr). Overdesigning strippers must therefore be avoided to mitigate this effect. Reabsorption in PZAS™ is not as sensitive to heat loss and occurs only at high values (~0.14 GJ/hr) due to the even temperature pinch in the column. 7 m MEA with the simple stripper has a lower measured heat duty than 5 m PZ due to the insignificant effect of heat loss in the column on with 7 m MEA. Unlike 5 m PZ, 7 m MEA has a bottom-side pinch that mitigates the effect of heat loss by water condensation.

Corrosion by Aqueous Piperazine at 40–150 °C in Pilot Testing of CO2 Capture

Corrosion data from two pilot plant activities of CO2 capture are presented. The pilot plant used 5 m (30 wt %) of aqueous piperazine (PZ) and the advanced stripper (PZAS). 316L stainless steel exp...

CO2 Absorption from Gas Turbine Flue Gas by Aqueous Piperazine with Intercooling

Amine scrubbing is the most mature technology for postcombustion carbon capture. Much bench- and pilot-scale work has been focused on CO2 capture from coal-fired flue gas. Because natural gas is inexpensive and readily available in the United States and other countries, the natural gas combined-cycle (NGCC) has been replacing coal for electricity generation. Carbon capture for NGCC is therefore an important technology for the modern power plants. The Piperazine (PZ) Advanced Stripper (PZAS) technology has been established as a benchmark system for second-generation amine scrubbing for CO2 capture from coal-fired flue gas. It has a fast absorption rate, good energy performance, and strong resistance to thermal degradation and oxidation. PZAS was operated with simulated NGCC flue gas (4.3 mol % (dry) CO2) at the National Carbon Capture Center (NCCC) in Wilsonville, Alabama in 2019. This paper presents the absorber performance and model validation for the campaign. The absorber was tested with in-and-out and with pump-around intercooling. The variable operating conditions included lean loading (0.19–0.25 m CO2/mol alkalinity), gas temperature (40, 78 °C), and intercooling temperature (35, 40 °C). Using 5 m PZ CO2 removal from 82% to 96% was achieved with intercooling and only 12 m of packing. A rigorous, rate-based absorber model accurately predicted the CO2 removal and temperature profile. The model shows that the delta loading of the solvent at NGCC conditions for 90% removal is greater than at coal conditions, but high CO2 removal (99%) is more difficult to achieve with NGCC gas than with coal-fired flue gas. The pump-around intercooling was effective, and the intercooling temperature had a large impact on the absorber performance. With pump-around, the delta loading penalty for hot gas feed into absorber without a direct contact cooler was less than 5%.