Tarong post combustion pilot plant

Sep 29 2013


Australian power company Stanwell Corporation Limited and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) have developed an amine based carbon dioxide capture facility. By Sanger Huang, Ashleigh Cousins, Aaron Cottrell, Paul HM Feron, CSIRO.

The Tarong project is supported by the Asia-Pacific Partnership on Clean development and Climate (APP). Initial operation of the facility was completed with 30wt% monoethanolamine (MEA). This was followed by evaluation of concentrated piperazine (8 molal) sponsored by the Australian National Low Emissions Coal Research and Development program.
 
Description of Tarong PCC pilot plant
The pilot plant, located in Queensland Australia, was officially opened in December 2010.
It was the third PCC pilot plant from CSIRO evaluating new and existing amine based technologies for CO2 capture from coal combustion flue gases. Australian power stations do not employ de-NOx and de-SOx technologies due to the low sulphur content of coal. A typical flue gas composition entering the Tarong pilot plant is given in table 1:
 
Pilot Plant Details
The Tarong PCC pilot plant is designed to capture CO2 using amine-type solvents at a rate of ~100kg CO2/hr (roughly 1000tpa). A slip stream of flue gas is taken from the power station flue gas duct downstream of the electrostatic precipitators and induced draft fan. 
The process consists of three main steps: Pre-treatment / Absorption / Stripping. The flue gas first undergoes a basic caustic scrubbing where the hot gas (~100-110°C and 1 atm) is washed with a dilute caustic solution (pH ~9). This gas cleaning cools the flue gas to 45°C and removes some of the acid components and particulates. The cleaned flue gas then passes through a blower before entering the absorber column. 
In the absorber, the solvent flows counter-currently with the flue gas to capture CO2. The Sulzer Mellapak M250X structured packing in the absorber column is divided into 4 sections. This allows gas and liquid sampling between each packed section and further provides tie-in points for various process modifications such as inter-stage cooling. The CO2 lean flue gas goes through a water wash section at the top of the absorber to remove potential solvent carry over. The CO2 rich solvent flows through a lean/rich heat exchanger where sensible heat is recovered from the lean solvent. 
The heated CO2 rich solvent then enters the stripping column and flows through two Sulzer Mellapak M350X packed sections. The CO2 and water vapour generated from the reboiler rises up the column and flows to the condenser. The CO2 and condensate are separated in the knock out drum with condensate returning to the stripping column as reflux. The regenerated solvent is pumped back to the absorber to start the cycle again. 
A number of gas and liquid samples can be collected from various locations around the pilot plant as indicated in Figure 2. The gas analysis employs a Fourier Transform Infra-Red Spectroscopy (FT-IR) system with an accuracy of 2% of the measurement range for each analysed component. 24 gas species are analysed, including CO2, H2O, NOx, SOx, NH3, solvent and solvent degradation products.  Solvent concentration and CO2 loading are determined offline by acid-base titration. 
 
Special features 
The Tarong pilot plant operates 24 h per day, 5 days per week. It is typically manned by two engineers during the day. After hours the control system is able to shut the plant down automatically and alert staff via SMS if required. Round the clock operation allows for extended evaluation of the solvents on real flue gases. This is necessary for the determination of solvent degradation and the effect on plant operation. Over 500 h was achieved during the initial operation with 30 wt% MEA. This was followed by 1700 h of operation when evaluating concentrated piperazine.  
The flexibility built into the design of the Tarong plant allows for gas and liquid sampling at various packed heights in the absorber column. This provides CO2 concentration profiles vs. packed height in the absorber, which have provided a useful comparison with both the commercial and in-house process modelling packages used at CSIRO. 
 The unique design of the Tarong pilot plant allows for the evaluation of various process modifications. Process modifications such as inter-stage cooling (Figure 3) and rich split (Figure 5) have been evaluated with the plant. Inter-stage cooling typically removes heat from the solvent mid-absorber, shifting the equilibrium potentially increasing the solvent CO2 carrying capacity and efficiency of the process. The effect of inter-stage cooling on the temperature profile through the absorber column can easily be seen in Figure 4. 
The rich split (cold rich bypass) is another method which could potentially reduce the energy requirement of the CO2 capture process. The rich solvent leaving the absorber is split into two streams. The first stream enters the lean-rich exchanger as per normal operation while the second rich solvent stream enters the top of the stripping column cold. Vapour generated by the first stream passing through the lean/rich heat exchanger will preheat the second cold solvent stream potentially reducing the energy requirement from the reboiler. 
Another noteworthy feature of the pilot plant is that it is equipped with a broad range of connection points within the system for installing corrosion coupons. A total of 128 corrosion coupons were installed at 8 different locations (5 in/around the absorber, 3 in/around the stripping column) during the campaign with MEA. Coupons were installed below packed sections in regions of gas/liquid two-phase flow as well as in the solvent storage tanks. The comprehensive location coverage of the coupons provides valuable information for material selection relevant to CO2 capture conditions
 
Operation with MEA and Piperazine
 MEA has been used in the gas processing industry for many years, and is a well characterised solvent. It was used in the initial operation of the pilot plant to identify the operating range and also to provide a comparison to literature data. It further provides a baseline for comparing any new solvent evaluated on the plant in the future.
Concentrated piperazine is secondary di-amine that is being developed by the University of Texas in Austin as an alternative solvent for PCC processes. CSIRO has collaborated with Prof. Rochelle’s research group at the University of Texas in testing the piperazine solution at the Tarong PCC pilot plant. Piperazine is the simplest cyclic member of the ethyleneamine family, and has the following formula:
 
 HN(CH2CH2)2NH
 
Compared to the standard 30 wt% MEA, piperazine promises double the absorption capacity, fast reaction kinetics and potentially low regeneration energy requirement. Its thermal and chemical stability with low degradation characteristics offers the potential for significant capital and operating cost saving which in turn makes it a promising solvent for CO2 capture. 
Operation with MEA was completed in 2011. Results from the campaign showed MEA to be effective at capturing CO2 from the flue gas at Tarong power station with calculated energy requirements in line with literature data. Plant data (including absorber CO2 concentration profiles) showed good agreement with process modelling results. Two process modifications were also successfully evaluated during this campaign.  
The recent work with piperazine was completed in April 2013 and included parametric operation and duration experiments. The parametric runs evaluated the solvent under different operating conditions and provided a feasible operating range for the solvent at the Tarong pilot plant. Duration experiments were then completed in which a constant operating condition was held for an extended period (roughly two months). This allowed the stability of the solvent and the formation of degradation products to be assessed. The evaluation of concentrated piperazine was successful and it shows promise as an alternative CO2 capture solvent. 
 
Conclusion
CSIRO, in collaboration with Stanwell Corporation Ltd have designed, built, commissioned and operated an amine solvent based carbon capture pilot plant to produce 100 kg/hr of CO2 at Tarong Power Station, Nanango, Queensland. The plant is capable of performing 24 h of continuous operation on real flue gas. 
Two promising process modifications 1) Inter-stage cooling and 2) Rich split show potential in reducing the solvent regeneration energy requirement. Data from the corrosion study has provided valuable information for material selection relevant to CO2 capture processes. The trial with MEA has provided a useful baseline for any solvent evaluated on the plant in the future. Operation with concentrated piperazine was completed in April 2013. The duration experiments have provided useful information into the long term stability of the concentrated piperazine solution.  The experimental campaigns undertaken at the Tarong PCC pilot plant have provided valuable information on the CO2 capture process for flue gas conditions relevant to Australia.  
 
Acknowledgement
The initial pilot plant project was supported by CSIRO’s Advanced Coal Technology Portfolio and received funding from the Australian Government as part of the Asia-Pacific Partnership on Clean Development and Climate. The views expressed herein are not necessarily the views of the Commonwealth, and the Commonwealth does not accept responsibility for any information or advice contained herein.
The authors also wish to acknowledge financial assistance provided through Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is supported by Australian Coal Association Low Emissions Technology Limited and the Australian Government through the Clean Energy Initiative.

CSIRO
Stanwell


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