Evaluation of Carbon Dioxide Capture From Existing Coal Fired Plants by Hybrid Sorption Using Solid Sorbents

[摘要] A novel hybrid solid sorbent technology for CO??? capture and separation from coal combustion-derived flue gas was evaluated. The technology ??? Capture of CO??? by Hybrid Sorption (CACHYS???) ??? is a solid sorbent technology based on the following ideas: 1) reduction of energy for sorbent regeneration, 2) utilization of novel process chemistry, 3) contactor conditions that minimize sorbent-CO??? heat of reaction and promote fast CO??? capture, and 4) low-cost method of heat management. This report provides key information developed during the course of the project that includes sorbent performance, energy for sorbent regeneration, physical properties of the sorbent, the integration of process components, sizing of equipment, and overall capital and operational cost of the integrated CACHYS??? system. Seven sorbent formulations were prepared and evaluated at the lab-scale for energy requirements and CO??? capture performance. Sorbent heat of regeneration ranged from 30-80 kJ/mol CO??? and was found to be dependent on process conditions. Two sorbent formulations (designated HCK-4 & HCK-7) were down-selected for additional fixed-bed testing. Additional testing involved subjecting the sorbents to 100 continuous cycles in the fixed-bed reactor to determine performance as a function of time. The working capacity achieved for HCK-4 sorbent ranged from 5.5-8.0 g CO???/100 g sorbent, while the HCK-7 typically ranged from 8.0-10.0 g CO???/100 g sorbent. Overall, there was no deterioration in capacity with continuous cycling for either sorbent. The CACHYS??? bench-scale testing system designed and fabricated under this award consists of a dual circulating fluidized-bed adsorber and a moving-bed regenerator. The system takes a flue gas slipstream from the University of North Dakota???s coal-fired steam plant. Prior to being sent to the adsorber, the flue gas is scrubbed to remove SO??? and particulate. During parametric testing of the adsorber, CO??? capture achieved using the 2-bed configuration with recirculation in both beds was 65-70% with a high flue gas CO??? loading (~7%) and up to 85% with a low flue gas CO??? loading (~4%). A sorbent regenerator system consisting of a pre-heater, desorber, and cooler is used to heat the CO???-rich sorbent with direct and indirect steam producing a nearly 100% pure stream of CO???. Parametric testing of the regenerator system demonstrated the impact of process conditions on both desorption rate and the heat of regeneration. Clear evidence of the use of specific process conditions that lower the overall energy of desorption was identified. This observation validates measurements made at the laboratory-scale. Several longer-term continuous tests were conducted to evaluate the performance of the sorbent/process as a function of time. Using a 2-bed configuration, sustained capture efficiency of 40-60% with a high flue gas CO??? loading (~8%) and 70-80% with a low flue gas CO??? loading (~4%) were achieved. However, sorbent working capacity was found to be considerably lower than laboratory-scale measurements. The low working capacity is attributed to insufficient sorbent/gas contact time in the adsorber. Sorbent properties that had a significant impact on CO??? capture performance were identified. The results show that controlling these sorbent properties substantially improves CO??? capture performance, with preliminary estimates indicating that relative improvement of ~30% is possible. Testing culminated with an operationally trouble-free test of 15 hours with sustainable performance. Overall, several practical strategies to increase performance of the sorbent and process were identified. The initial technical and economic assessment of the CACHYS??? process estimated the cost of CO2 capture was $36.19/ton with a 48.6% increase in levelized cost of electricity (LCOE) for the 550 MWe net plant. Using additional data gathered over the course of the project, and with revised technical and economic assumptions, the estimated cost of CO??? capture with the CACHYS??? process is $39/ton (only includes the cost of the CO2 capture system) with an increase in LCOE of 55.9%. Overall, CACHYS??? represents a significant improvement over the benchmark MEA system, and has demonstrated progress towards achieving DOE???s goals for CO??? capture technologies.

[发布日期] 2014-12-31