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

Abstract

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.