Critical Process Measurement for CCS: Part One

An Introduction to Carbon Capture Processes

Every ton of carbon dioxide (CO₂) captured and stored from industrial processes is a step towards mitigating the effects of climate change. A critical aspect of drying, transport and sequestration projects is the accurate and continuous measurement of process variables such as purity, oxygen (O₂) content, and moisture levels. Advanced online analytical instruments like gas chromatographs (GCs), oxygen analyzers, and moisture analyzers are used to achieve this. These tools offer numerous process, safety, and economic benefits that enhance the efficiency and reliability of CO₂ sequestration projects. (See Part Two of this series to find out more about these instruments.)

Worldwide government initiatives on processes like Carbon Capture and Storage (CCS), Carbon Capture, Utilization, and Storage (CCUS) and Bioenergy coupled with Carbon Capture and Storage (BECCS) can play an important and diverse role in meeting global energy and climate goals. They are driving the need for the application of analytical tools to help maintain quality and safety for these projects.

Process Overview

CCUS refers to a range of processes that involves the capture of CO₂ from major industrial sources, such as petrochemical or power generation plants, utilizing either fossil fuels or biomass for fuel. The captured CO₂ is typically processed, compressed, and transported for downstream industrial usage or injected into existing geological formations, like depleted oil and gas reservoirs, which will hold the CO₂ in permanent storage.

BECCS is a series of processes typically employed by biorefineries to decarbonize their industrial biomass process and involves capturing and permanently storing CO₂ from the plants. A primary example of this process is the conversion of feedstock such as corn into high-efficiency ethanol. Crops like corn absorb CO₂ during their growth and this is, therefore, a direct method of removing it from the atmosphere.

CO₂ Drying

CO₂ can be captured from a variety of industrial processes, each of which will potentially introduce a range of contaminants that may affect the quality, safety, and efficiency of the downstream operations.  Contaminants can include:

hydrocarbons from petroleum refining

sulfur from flue gases

amines from gas stripping

moisture from process and transportation operations

Contaminants such as moisture can create a range of problems.  Water vapor can condense to a liquid, freeze to ice, and react with CO₂ and sulfur compounds to form aggressive acids.  The results will include corrosion of metal surfaces, pipeline blockages and damage to moving parts like high-speed compressor blades. 

In the US, the majority of bioethanol production involves a ‘dry mill’ process, where grain is ground and ‘slurried’ with water. This is followed by processes such as fermentation (including CO2 removal), distillation, and dehydration to produce high-purity ethanol.

In Europe, bioethanol is mainly produced from wheat, maize, and sugar beet feedstocks, using similar ‘wet’ fermentation processes. Meanwhile, in Brazil, bioethanol production predominantly relies on sugarcane as the primary feedstock, using a distinct method known as the sugarcane milling process. This involves crushing the cane to extract juice which is then fermented and distilled into ethanol. Brazil's reliance on sugarcane gives it a more efficient energy balance due to the use of bagasse (the fibrous residue) for energy in the distillation process.

In Mexico, bioethanol production is increasing, with maize and sugarcane being the key feedstocks, although the industry is still in development compared to Brazil and the US. In all regions, the CO2 removed during fermentation is typically saturated with moisture and must be dried as part of its processing for transportation or storage.

The European standard for CO₂ purity (ISO 27913) typically specifies moisture levels below 500 ppmV, but many CCS projects aim for far lower levels. The maximum allowable moisture content varies by project, with nominal process values of around 20 ppmV in normal operation, but typically high alarm points are in the 70…120 ppmV range.

The dehydration process removes moisture from CO2 to prevent damage to downstream equipment and mitigate pipeline corrosion and hydrate formation during transport. This is typically achieved using desiccants or refrigeration methods. This equipment is, however, energy intensive, so moisture dew-point measurement becomes an important technique both to ensure optimal energy efficiency and protection of equipment and pipelines from corrosion.

CO2 Transport & Storage

Once dried, CO₂ is transported through pipelines or via shipping to the sequestration site. Maintaining CO₂ in a supercritical state (high pressure and temperature) improves transport efficiency.

At the sequestration site, CO₂ is injected into geological formations such as depleted oil fields, saline aquifers, or basalt formations. Ensuring the purity of CO₂ and monitoring for pollutants is crucial to prevent environmental contamination and ensure long-term storage integrity.

Summary

The implementation of online gas chromatographs and oxygen and moisture analyzers in CO2 drying, transport, and sequestration projects offers significant process, safety, and economic benefits. These instruments provide real-time, continuous monitoring and control, ensuring that CO₂ remains within optimal purity and within O₂ and moisture content specifications. This not only enhances process efficiency and quality but also ensures the safety and longevity of infrastructure, reduces maintenance costs, and ensures regulatory compliance. By integrating these advanced analytical tools, CO2 sequestration projects can achieve higher levels of reliability, safety, and economic viability, contributing effectively to climate change mitigation efforts.

In Part Two we take a more detailed look at the analytical techniques used to verify the purity of captured CO₂, detect contaminants and prevent corrosive or hazardous activity.