The CASTOR project involves a CO2 absorption pilot plant operating alongside the Esbjerg
power station in Denmark. The pilot plant was commissioned in 2005 and in the period from 2006-2007 a total of 4000 hours experimental work were performed. The main focus of the pilot plant was to investigate the operation of such a CO2 absorption plant in conjunction with a
full scale power station. The CASTOR project made use of only a portion of the flue gas from the coal fired power station for CO2 absorption studies. The split stream was channelled to the
absorption plant and the captured CO2 was reintroduced into the flue gas stream after passing
through the pilot plant set-up (Knudsen et al., 2009).
2.6.1.1. PILOT PLANT SETUP
The pilot plant has a total maximum capacity of 1 ton of CO2 per hour to be absorbed from the
incoming flue gas stream. It consists of an absorber and a stripper column both with internal diameters of 1.1 meters. The absorber has a total of four sections, each 4.25 meters high,
25 packed with IMTP50 random packing. The stripper column is also packed with IMTP50 random packing and consists of 2 sections of 5 meters each. Both columns have wash sections installed above the packed beds. Structured- and random packing (IMTP50) are used respectively for the wash sections of the absorber and the stripper. The stripper makes use of a thermosyphon reboiler, driven by 2.5 bar(g) saturated steam. The columns are joined by a rich/lean plate heat exchanger with a delta T of about 10°C (Knudsen et al., 2009).
2.6.1.2. EXPERIMENTAL STUDIES PERFORMED AND OUTCOMES
CASTOR 1 and CASTOR 2 are new blends of amine solvents. These solvents were developed in the CASTOR project in order to find the solvent that would improve the energy efficiency of the CO2 capture process (Knudsen et al., 2009). This pilot plant was used to perform a comparative
study when using these new solvents. Other studies on this pilot plant also include validating simulated data with actual data gathered from the pilot plant (Dugas et al., 2009).
BACKGROUND
The CASTOR project was divided into four 1000 hour test campaigns in order to provide sufficient data for a comparative study. The campaigns are summarised in Table 5.
TABLE 5 SUMMARY OF THE CAMPAIGNS OF THE CASTOR PROJECT
Campaign No.
Solvent Used
Description of the Campaign Duration
[h]
1 30 wt%
MEA Operating with the reference solvent 1000
2 30 wt%
MEA
Operation with reference solvent (similar to
Campaign#1) 1000
3 CASTOR 1 Experiments and operation with a new solvent 1000
4 CASTOR 2 Experiments and operation with a new solvent 1000
PHASE ONE: PARAMETRIC STUDY
The first 500 hours of each campaign were used to perform a parametric study in order to optimize the operating conditions of the process with regards to energy efficiency. The second 500 hours of the campaign was then used to study continuous operation in conjunction with the coal fired power station (Knudsen et al., 2009).
The parametric study was performed optimising the liquid-to-gas (L/G) ratio in the absorber column. Knudsen et al.(2009) report an optimum L/G ratio of 2.5 kg/kg for MEA. This limits the
26 steam requirement to 3.6 GJ/ton CO2. CASTOR 1 showed a minimum steam requirement of 3.8
GJ/ton CO2 at L/G ratios of between 2.5 and 3 kg/kg. CASTOR 2 appeared to be the more
promising solvent of the two new ones with a minimum steam demand below 3.6 GJ/ton CO2 at
an L/G ratio of 2 kg/kg (Knudsen et al., 2009). This indicates that CASTOR 2 has a higher cyclic capacity for CO2, seeing that the solvent flow rate can be lower for the same gas flow rate when
compared to the other solvents.
The optimum L/G ratios for each solvent were used in order to investigate the effect of percentage CO2 removed on the reboiler steam requirement. It was found that there is a
considerable increase in the steam requirement when increasing the CO2 captured from 90 to
95%. The target for CO2 capture was thus set to be 90% (Knudsen et al., 2009). PHASE TWO: CONTINUOUS OPERATION
The second phase of each campaign had objectives of continuous operation for 500 hours at the optimized conditions, investigating the corrosive nature of each solvent, as well as gathering some valuable information on solvent degradation (Knudsen et al., 2009).
The results showed that initially the steam demand of CASTOR 2 was the lowest with an average values of 3.5 - 3.6 GJ/ton CO2. However, unexpected solvent losses from the process had a
negative effect on the overall results for all 500 hours. The average steam demand of MEA for the 500 hours was reported to be 3.7 GJ/ton CO2, while that of CASTOR 1 was slightly higher
(Knudsen et al., 2009).
The corrosion monitoring was performed by strategically installing weight loss coupons in the pilot plant. The corrosion coupons were samples of carbon steel, stainless steel 304 and 316. Kittel et al.(2009) report on the results of exposing these weight loss coupons for the solvents during the 500 hours of operating. It was found that the stainless steel is superior to the carbon steel, as expected. It was also clear that temperature greatly affects the rate of corrosion. This is apparent when considering that the coupons at the stripper inlet and outlet were subjected to considerable corrosion (Kittel et al., 2009).
In monitoring the degradation rates of the different solvents, the presence of heat stable salts were used as an indication of the extent of solvent degradation (Knudsen et al., 2009). The results from this study showed that the concentration of the heat stable salts increased considerably faster for MEA when compared to using CASTOR 2. According to Knudsen et al.(2009), this is an indication that the new solvent, CASTOR 2, is chemically more stable than MEA.
27
VALIDATING SIMULATED DATA
Dugas et al.(2009) made and attempt at comparing simulated data to actual data obtained from the CASTOR pilot plant. The main experiments were performed at different solvent flow rates, varying between 13 and 24 m3/m2.h as well as varying lean loading, between 0.16 and 0.28
mole CO2/mole MEA. Twelve different runs were performed while running the CASTOR pilot
plant project. The results obtained for the absorber gas temperatures and CO2 concentrations
were simulated using Aspen Plus®. The study showed that the simulation can be used to
reliably model the absorber for a MEA-CO2 capture system (Dugas et al., 2009). OUTCOMES
The CASTOR project showed that there is potential for developing new solvents which require less energy for regeneration. It also provided some useful information on the corrosion effect and degradation of the various solvents that were investigated. The CASTOR project also provided a basis for comparison for simulations performed in Aspen Plus®.