Results Published of Mini-Pilot Tests of Chilled Ammonia CO2 Capture Process
A recent EPRI report summarizes the results of the EPRI-sponsored large bench-scale pilot (mini-pilot) testing of a novel carbon dioxide (CO2) capture process known as the Chilled Ammonia Process (CAP). The testing, which was co-sponsored by Alstom and Statoil, was conducted from November 2006 through March 2007 and demonstrated the ability of the CAP to capture CO2.
The report is entitled Program on Technology Innovation: Operation and Testing of a 0.25 MW Mini-Pilot Plant to Evaluate Chilled Ammonia-Based CO2 Capture Process (Phase I) (1014325). Qualified funders may click on the link below to view or download a copy.
How to Apply the Results
Electric utilities face enormous cost and performance challenges in capturing CO2 emissions from fossil-fueled power plants presents. Installing current CO2 capture technologies (amine-based scrubbers) on power plants would increase the levelized cost of electricity (COE) by 50-80% and consume as much as 30% of the plant’s energy output.
CAP represents one promising post-combustion CO2 capture technology. However, before CAP or any other process can be installed with confidence on large, coal-fired power plants, they must be scaled up many-fold and tested. The mini-pilot is one step in this process, following earlier proof-of-concept tests and leading to a larger, 5-MW field pilot. Results of the mini-pilot offer utilities insight into the mechanisms of the CAP and the issues associated with its potential for success.
CAP Mini-Pilot
CAP is a solvent-based post-combustion CO2 capture process using ammonium carbonate as the solvent. Cold ammonium carbonate absorbs CO2 from flue gas and precipitates as ammonium bicarbonate, which can then be regenerated by heating to complete the cycle.
The EPRI-sponsored mini-pilot had a number of objectives, including determining the CO2 capture efficiency of CAP using various types of contactors, evaluating the CO2 absorption rates, and evaluating the conditions under which ammonium bicarbonate precipitation occurs.
For the mini-pilot, the project team designed, constructed, and operated a large bench-scale pilot of a CAP absorber system. The absorber system consisted of two columns in series that had the ability to: test different configurations of packing, spray tower, and sieve–trays; measure the pressure drop across the absorbers; and operate under ammonium bicarbonate precipitation conditions. The final column in the system was a cold water-wash designed to capture residual ammonia vapor from the absorbers followed by an external acid-wash scrubber to reduce ammonia emission to below 5-ppm level.
Between November 2006 and March 2007, the project team conducted an initial “scouting cycle” of 33 test runs to gain general experience in operating the system and determine the relative importance of the key process parameters.
Results
The findings of the 33 scouting tests were as follows:
· Parameters Controlling Capture Efficiency. The two major parameters that can be used to control CO2 capture efficiency are the R-value (defined as the molar ratio of total ammonia concentration ([NH3]aq) to total CO2 concentration ([CO2]aq) in the circulating solution and the gas flow rates. CO2 capture efficiency increases with the increase in solution R-value at a constant gas flow rate. At a constant R-value, CO2 capture efficiency increases and decreases proportionately with a change in gas flow rate due to changes in gas residence time in the absorber.
· Precipitation of Ammonium Bicarbonate. For solutions with ammonia concentrations greater than 6 M at temperatures below 20°C, precipitation of solid ammonium bicarbonate occurs. In addition, it was observed that the NH3-CO2-H2O system exhibited a significant level of supersaturation before precipitation of ammonium bicarbonate.
· pH Levels. The pH is an indicator of the solution composition and correlates well with R in low ionic strength solutions. Accurate pH measurement in the high ionic strength solutions is the subject of ongoing work.
· Ammonia Vapor Pressure. NH3 vapor pressure in the outlet gas of the absorbers correlates well with solution R-values and can be used as a control parameter for maintaining the composition of the circulating solution.
Next Steps
The results of this report have been used to commence the engineering of a larger field pilot to be constructed at WE Energy’s Pleasant Prairie Power Plant (“P4”) in Pleasant Prairie, Wisconsin. A batch regenerator has been designed and constructed, and future plans include the design and construction of a semi-continuous regenerator system to provide further information supporting scale-up of the process.
For more information contact Dick Rhudy, 650-855-2421,
View or download Program on Technology Innovation: Operation and Testing of a 0.25 MW Mini-Pilot Plant to Evaluate Chilled Ammonia-Based CO2 Capture Process (Phase I) (1014325).
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