Thousands of miles of pipeline are dedicated to the transport of the carbon dioxide that is captured at industrial facilities that generate energy, process natural gas, refine oil, or manufacture materials and products used by other industries or consumers. To prevent corrosion in these pipelines, it is essential to minimize the water content within them.
Carbon capture and storage (CCS) involves the sequestration of large amounts of carbon dioxide emitted from the industrial burning of fossil fuels. Carbon capture technologies can remove 80 to 95% of the carbon dioxide emitted from a power plant or other industrial source. Power plants are the most likely initial candidates for CCS because they are large carbon dioxide generators.
There are many technological approaches to CCS. One common requirement for nearly all large-scale CCS schemes is a system for transporting carbon dioxide from capture sites (e.g. power plants) to storage sites (e.g. underground reservoirs). Pipelines are the most common method for transporting large quantities of carbon dioxide over long distances.
Carbon dioxide pipelines are operated at ambient temperature and high pressure, with primary compressor stations located where the carbon dioxide is injected, and booster compressors located as needed along the length of the pipeline. In overall construction, carbon dioxide pipelines are like natural gas pipelines, requiring the same attention to design, monitoring for leaks, and protection against overpressure. Carbon dioxide pipeline technology is mature because of its extensive use for enhanced oil recovery (EOR).
Maintaining a very low level of water in the transported carbon dioxide is very important. If water is present, it will react with the carbon dioxide to form carbonic acid. While carbonic acid is a relatively weak acid, its presence will result in corrosion of the pipeline over time.
Due to the vulnerability of pipelines to the presence of carbonic acid, one of the most critical factors to control is the water content of the carbon dioxide entering the pipeline. Carbonic acid can lead to corrosion depths up to 1 to 2 mm within a two-week period. A defective dehydration unit within a carbon dioxide capture facility, could lead to free water either flowing into the pipeline or condensing at some point along the pipeline. If this water collects at low points, corrosion could be an immediate issue. In contrast to atmospheric pressure gas phase carbon dioxide, dense phase carbon dioxide can store several hundred parts per million (ppm) of water, depending on the temperature. However, if the pressure falls or the temperature drops below the dew point, water will precipitate out and create carbonic acid.
Historically, electrochemical detectors have been used to monitor the water level in carbon dioxide gas streams, but this type of sensor degrades over time as it is exposed to low-level organic components in the stream. Electrochemical sensors require periodic replacement, calibration and can drift if exposed to interfering contaminants.
An alternative to an electrochemical sensor is tunable diode laser absorption spectroscopy (TDLAS) technology. Using this type of sensor, the detector element does not come into contact with the pipeline gas. Therefore, there is no change in system response relative to sensor contamination issues.
To learn more about this application, and the related AMETEK Process Instruments solution, refer to our Application Note on this topic.