13. Chilled Ammonia Process at Technology Center Mongstad – First Results (2013)

Gerard Lombardo^a, Ritesh Agarwal^b, Jalal Askander^b,*

^aTCMDA Mongstad Norway ^bALSTOM Power Inc. Knoxville TN USA ^*Corresponding author

1876-6102 © 2013 Alstom Technology Limited. Published by Elsevier Limited. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of SINTEF Energi AS
doi: 10.1016/j.egypro.2014.07.004

Abstract

According to the latest IEA report, Carbon Capture and Storage (CCS) from fossil fuel fired power plants is a key option to mitigate CO₂ emissions in the 450 scenario. In addition it is the only technology capable of large CO₂ emission reduction from industrial applications and in combination with biomass firing the only currently available technology for reducing CO₂ concentration in the atmosphere by means of negative emission performance. Alstom develops CCS technologies for post- combustion and oxy-combustion, and have shown that these technologies can compete with renewable power generation on the basis of Levelized Cost of Electricity (LCoE). It is now essential that governments give the same priority to CCS as to renewables in order for large demonstration plants to be built, a necessary step in the development of the technology.

The Norwegian Government, through its special purpose company Gassnova, is at the forefront of making this happen by construction of the world’s largest test site for Carbon Capture. The Technology Center Mongstad (TCM) is owned by Gassnova, Statoil, Shell and Sasol. The unique location of TCM, next to the Mongstad refinery, provides interesting opportunities in terms of gases to be treated. The plant at TCM is designed to treat both refinery off-gas from a cracker operation as well as the exhaust from a gas turbine based combined heat and power plant. In addition, the captured CO₂ can be recycled to achieve any CO₂ concentration between 4 and 13% by volume. The Alstom Chilled Ammonia Process (CAP) is post-combustion technology that captures CO₂ emitted from power plants or industrial sources. Deployment of this technology requires operating data and validated simulation tool for design that can evaluate various CAP configurations to achieve the lowest possible capital cost, energy demand and operating cost. A special focus will be directed to the CAP Installation at TCM, which was commissioned in 2012. The plant is designed to treat both refinery off-gas from a cracker operation as well as the exhaust from a gas turbine based combined heat and power plant.

This paper will report on the first results of Chilled Ammonia Process (CAP) as part of Alstom’s development program of commercial solution for carbon capture, at Technology Center Mongstad in 2012.

© ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

1. Introduction

Power generation is one of the biggest sources of man-made carbon dioxide (CO₂) emissions, the main anthropogenic greenhouse gas. Innovative carbon neutral technologies will be required to enable the power sector to meet the global demand for electricity, while controlling CO₂ emissions and thus reducing the impact on global warming. To achieve meaningful reductions, it will be necessary to develop technologies that can be applied to both Greenfield projects and to the existing fleet through cost effective retrofits.

Alstom is currently developing two main technologies for carbon capture; post combustion capture and oxy combustion. Among these technologies, post-combustion carbon capture and storage (CCS) using the Chilled Ammonia Process (CAP) is one of the more promising solutions.

The Chilled Ammonia Process uses an ammoniated aqueous carbonate solution to absorb CO₂ from the flue gases at ambient pressure and low temperature. Unlike other technologies, the ammonium solution stability is not affected by oxygen or acidic trace components present in the incoming flue gas. The CAP process consumes a comparatively low parasitic load, which offers savings in OPEX over the life of the plant. Operation at low process temperatures allows the use of waste energy that is not available to other post-combustion CO₂ capture technologies. Since gaseous emission and liquid waste streams are non-toxic, no additional treatment facilities are required.

From the standpoint of plant operations, the Chilled Ammonia Process has demonstrated stable operation at turndown conditions. The CAP process offers the flexibility and ability to follow daily and weekly changes in plant load requirements in the typical range of 25-100% without impact on the process.

As ammonia is a common and widely used chemical, the ammonia reagent in the CAP plant also lends itself to established permitting requirements, including any waste disposal issues that may arise. The by-product from the CAP facility is a liquid ammonium sulfate stream with commercial value as a fertilizer. Optionally the ammonia is recovered in a dedicated Ammonia Recovery Unit, and in this case the final by-product is gypsum, which is a well- known by-product for Power Plant Operators.

The power consumption for CO₂ compression represents a substantial part of the total power consumption for the different CO₂ technologies. The CAP concept involves the production of higher pressure CO₂, resulting in significantly lower power consumption of CO₂ compression equipment.

This paper will give an introduction to the CAP plant at TCM as well as a summary of the data collected from the operations in 2012 in comparison with simulation results. The unique location of TCM, next to the Mongstad refinery, gives interesting opportunities in terms of gases to be treated. The plant at TCM is designed to treat both refinery off-gas from a cracker operation as well as the exhaust from a gas turbine based combined heat and power plant.

2. Description of the chilled ammonia process

The Chilled Ammonia Process (Figure 1) is based on the chemistry of the NH₃-CO₂-H₂O system and the ability of the ammoniated solution to absorb CO₂ at low temperature and to release the CO₂ at moderately elevated temperature.

Figure 1 Chilled Ammonia CO₂ Capture and storage (Alstom).

The primary CAP chemical reactions for CO₂ capture are presented in Equations 1–4. During absorption, CO₂, ammonia, and water combine to form ammonium carbonate, ammonium bicarbonate and ammonium carbamate mainly in ionic forms.

CO₂ (g) ļ CO₂ (aq) (1)

2NH₃ (aq) + H₂O (l) + CO₂ (aq) ļ (NH₄)₂CO₃ (aq) (2)

(NH₄)₂CO₃ (aq) + CO₂ (aq) + H₂O (l) ļ 2(NH₄) HCO₃ (aq) (3)

(NH₄)₂CO₃ (aq) ļ NH₂CO₂ NH₄ (aq) + H₂O (l) (4)

The reactions in the process are all reversible and their direction depends on pressure, temperature and concentration in the system. Equations 1-4 are exothermic reactions in the left to right direction requiring removal of heat from the process in order to maintain the desired CO₂ absorption temperature. Equations 1-4 are endothermic reactions in the right to left direction that require energy to produce the desired products.

A distinguishing feature of the Chilled Ammonia Process, relative to a host of amine-based technologies is solvent stability. Ammonia does not undergo the types of oxidative and thermal degradation reactions that are encountered with amines. The latter characteristic allows for higher temperature regeneration to produce a higher pressure CO₂ product. The Chilled Ammonia Process (CAP) consists of the following unit operations:

Flue gas conditioning
CO₂ Absorption
Water wash for NH₃ capture
Regeneration for CO₂ release
Stripper for ammonia recovery and wash water conditioning
CO₂ dehydration and compression
Refrigeration system

A flow diagram of the process is shown in Figure 2.

Figure 2 Chilled Ammonia Process flow diagram (Alstom).

3.Field pilots and validation facilities

3.1 CAP Field Pilot Facilities

Alstom has over 18000 hours of operating experience with CAP, through partnerships with SRI international (Menlo Park, CA) the electric Power Research Institute (EPRI –Palo Alto CA), WE energies (Pleasant Prairie, WI) E.ON (Karlshamm, Sweden) and Electric Power (AEP- Columbus OH).For description of early field pilots, please see article “CCS with the Alstom Chilled Ammonia Process Development Program -Field Pilot Results” from GHGT-10[1, 2].

3.2 Mountaineer Product Validation Facility

The Product Validation Facility is extensively described in [1]; however a short description is repeated here for better understanding of the final achievements listed below.

The CCS plant treated a slipstream of power plant flue gas using Chilled Ammonia Process (Figure 3). The flue gas was taken from a location downstream of an existing Wet Flue Gas Desulphurization system. The unit was designed to capture and store approximately 100,000 metric tons of CO₂ annually and treat approximately 80,000 Nm3/hr of flue gas, or 1.5% of the total plant flue gas flow.

All the achievements were confirmed during steady-state operation of the CCS validation plant. The formal testing program for the validation project was successfully completed end of May 2011 after a 21 month period. Analysis of the operating results has been used to validate the predictions of Alstom’s process simulation models.

Figure 3 : Mountaineer Product Validation Facility (AEP – Alstom).

4. TCM Installation

4.1 Technology Centre Mongstad (TCM)

TCM, which is owned by Gassnova, Statoil, Shell and Sasol, is the world’s largest facility for testing of Carbon Capture technologies. The centre is located next to the Mongstad Refinery on the west coast of Norway. The CAP installation at TCM is a natural step to follow after the successful application of CAP at American Electric Power’s Mountaineer Plant, where Alstom successfully showed the robustness and competitiveness of the CAP Technology applied to coal power plant flue gas. Figure 4 shows the CAP installation at Mongstad.

The unique location of TCM, next to the refinery, provides interesting opportunities in terms of gases to be treated. The plant at TCM is designed to treat both refinery off-gas from an oil residue cracker unit as well as the exhaust from a gas turbine based combined heat and power plant.

Figure 4 : CAP Installation at Mongstad (TCM DA).

4.2 CAP design at Mongstad

The design conditions for the Mongstad plant is shown in Table 1.

Table 1 CAP TCM design parameters†.
† The capture efficiency is the targeted efficiency for each stream. Higher capture efficiency can also be achieved.

The plant, which initially was designed in 2008, is of a very compact design. The footprint is only 1300 m², and the height of the absorber tower is limited to 29 meters. Figure 5 shows a cut-out of the absorber tower, which in addition to 3 separate absorption sections (ABS 1, ABS 2 & ABS 3) also houses the Direct Contact Cooler (DCC), the Water Wash (WW) and the Direct Contact Heater (DCH), all of which also are of a packed bed design. All-in- all the 29 meter high structure houses almost 50 meter of packed bed height, 24 meter of sump hold-up and 15 meter of gas space!

Figure 5 : TCM Concrete Structure showing the 6 packed beds (TCM DA) The flow path of the flue gas in the tower is: DCC –>ABS 1–>ABS 2 –>ABS 3 –>WW –>DCH , and the function of the beds are in consecutive order: cooling, CO₂ absorption (ABS1 & ABS 2), NH3 recovery, NH3 polishing and re-hating.

Also the regeneration section of the CAP plant is of a compact design, since the elevated pressure (approx. 20- bar) allows for a relatively small vessel. In addition to the regenerator, which is used to release the CO₂ from the ammoniated solvent, the plant is also equipped with an ammonia stripper to recover NH₃ and CO₂ from the water wash liquid, and an appendix stripper to control the water balance and impurity build up. Figure 6 shows the regenerator to the left and the ammonia stripper to the right.

4.3 Operation Modes

As described above, the Mongstad installation is able to run either on Refinery Off-gas from the Residue Fluid Catalytic Cracker (RFCC), or on flue gas from the gas turbine powered Combined Heat and Power (CHP) plant.

The two gases differ not only in CO₂ concentration as described in Table 1, but there are also differences in terms of SO_x, NO_x and particulate loadings. In order to provide flexibility in terms of testing, the RFCC gas supply system has been equipped with a dilution system that allows in bleed of air to lower the incoming gas CO₂ concentration.

Figure 6 : CAP Regenerator and Ammonia Stripper (TCM DA).

Initial operation at TCM had been focused on achieving steady state operation as outlined in the Technology Qualification Program (TQP) for the CO₂ Capture Mongstad (CCM) full scale capture project. The modifications of the plant which has been completed in April 2013 are based on development of the CAP technology since the initial design of the TCM Mongstad installation in 2008. Among other things, an additional heat exchanger will be installed to improve the heat integration concept and solvent lines will be added to increase flexibility in terms of lean solution feed to the absorption beds.

4.4 Validation Objectives

In parallel to the qualification for CCM, the TCM installation is serving as a validation facility for several improvements which have been engineered following the Mountaineer PVF experience as well as testing in the in- house pilot located in Alstom’s research facility in Växjö. These validation objectives include, but are not limited to:

Absorption performance
Improved two stage water wash design
Advanced control system
Concrete design of flue gas contactors
Low pressure stripper design
Trace component balance and impact
Predictive capability of modelling software
Energy consumption with optimized heat integration
No degradation of solvent

5. TCM operation tuning first results

During start-up and tuning operation, there were at least 18 stable periods that were considered for data analysis. Data analysed for the full range of operations during start-up, including refinery cat-cracker gas diluted with air. Observations during this provided confidence that the unit will meet performance targets when all units are operating at design conditions as the followings:

Start-up focused on achieving the target solvent molarity and performance of each unit operation.
NH3 Emissions (from DCH and CO₂ product) – The CAP process demonstrated l NH₃ emission in both the flue gas outlet through the DCH, and the CO₂ product at the CO₂ wash outlet. Solvent degradation is not an issue for ammonia; however, the control of ammonia emission was acceptable even before any major tuning
CO₂ Capture – rates varied between 75 and 85%, as expected while building solvent molarity and tuning the operations.
The CAP Performance at TCM was very much in line with what we have experienced at the AEP Mountaineer plant like quick start up, low ammonia emissions and satisfactory of individual unite operation performance.

Summary and conclusion

Alstom CCS development road map involves commercialization of CAP by 2020 and includes Bench scale research and testing, pilot plant, validation facilities, large scale demonstration plant. A delayed large scale demonstration plant has extended the CAP Commercialization date.

TCM is the largest CO₂ capture test facility in the world .The Mongstad installation is the stepping stone towards a fully validated product offering which is needed to combat climate change. Alstom is fortunate to be part of the unique facility for testing CCS installations at TCM Mongstad and intends to make best use of the involvement by showing that CAP is a viable option not only for coal plants but also for gas and industrial applications

The Alstom CAP technology offers major advantages like Low cost, commodity chemical solvent, No thermal or chemical degradation, No harmful emissions or liquid waste streams, Saleable Ammonium Sulphate as by-product, and High purity and high pressure CO₂ product.

CAP operation at TCM tuning first results is: CO₂ capture rates from 80% to as high as 87%, CO₂ purity of greater than 99.9%, Low NH3 emissions

The Process improvements that have been derived from operating experience and tests conducted at the TCM facility offered an opportunity to design and construct large CAP facility in Norway

References

V. Telikapalli F. Kozak et al (2011) “CCS with the Alstom Chilled Ammonia Process Development Program – Field Pilot Results”, Energy Procedia, Volume 4, 2011, Pages 273–281.
S. Jönsson, V. Telikapalli (2013)” Chilled Ammonia Process installed at the Technology Centre Mongstad” GHGT-11 (11th International Conference on Greenhouse Gas Control Technologies), Kyoto, 18-22 November 2012,