Guidance

Monitoring stack emissions: carbon capture plants with solvent-based abatement

Published 28 March 2025

Applies to England

This guidance is for operators of post combustion carbon capture plants.

This document provides guidance on monitoring approach, sample strategy and sample locations. It also specifies manual and automated monitoring methods that you must use to measure stack gas emissions.

The measurands listed in this document relate to the use of amine-based solvent technology. Other measurands will be added if other types of solvents are used.

1. Monitoring approach                                                   

The Industrial Emissions Directive (IED) states you must have suitable stack emissions monitoring requirements in place.

Where available and practical to do so, you should use methods that comply with European standards. Information on European standards is available in Monitoring stack emissions: techniques and standards for periodic monitoring.

You may use continuous emissions monitoring systems (CEMS) as an alternative to periodic measurements. Your CEMS must be certified at the appropriate range according to our monitoring certification scheme (MCERTS). They must also meet the quality assurance requirements of EN 14181. You can find information on EN 14181 in M20 quality assurance of continuous emission monitoring systems.

2. Sample strategy

Stack gas conditions in amine-based post combustion carbon plants are usually around 35°C to 100°C. This means the gas may be saturated because the hot combustion gas is cooled below the dew point. Additionally, there is the potential for solvent to be present in droplet form. This can lead to super saturated conditions with larger droplets of the amine-based solvent suspended in a matrix of saturated combustion gas.

The presence of liquid aerosol in the stack gas means that the distribution of soluble or reactive pollutant species within the stack are heterogenous. You must extract the gas isokinetically unless you can demonstrate that no mist or droplets are present at the monitoring location. The applicable standard for isokinetic sampling is EN 13284-1. For some of the measurands a surrogate may be used to establish if the stack gas is sufficiently homogeneous to allow sampling from a single representative point.

If you are not required to sample isokinetically and you wish to sample from a single representative point, you must do a stack gas homogeneity test according to the requirements of EN 15259 and the associated Method Implementation Document for 15259.

When sampling for breakdown products, you should consider the potential for thermal breakdown of the amine-based solvent. Thermal breakdown can occur from 120°C upwards. Stack emissions monitoring equipment (that is the sample probe, filter, heated sample lines) are typically operated above this temperature (that is 150°C to 180°C depending on the monitoring method) to prevent condensation and sample loss within the sample system.

When sampling for breakdown products, you must operate the heated elements of the sample system at no greater than 100°C.

When using CEMS, you must make sure that the system is capable of handling saturated gas streams containing droplets. In-situ cross stack and in-stack CEMS may not be suitable because of the presence of droplets.

3. Sample locations

Your sample location must comply with EN 15259. You can find more information in Monitoring stack emissions: measurement locations.

  4. Amines

The monitoring technique is isokinetic sampling and impingement into 0.1M hydrochloric acid and analysis by gas chromatography and thermal energy analysis.

The relevant monitoring standard follows the principles of EN ISO 21877.

You must use a sample duration of 4 to 6 hours. Your monitoring equipment must be operated at no greater than 100°C.

You must store samples below 6°C, including during transport to the analytical laboratory.

You should use an analysis method that has a typical expanded uncertainty at a 95% confidence interval of 30%.

You should use a method that has a typical sampling limit of detection (LOD) of 0.2μg/m3 or less.

5. Nitrosamines

Here are the methods for monitoring nitrosamines.

Manual monitoring technique

The relevant monitoring method is Determination of mass concentration of mass concentration of volatile nitrosamines from installations implementing carbon capture systems – absorber-based method.

This method specifies that you must not heat the heated elements of the sample equipment to greater than 80°C.

Automated monitoring techniques

The monitoring techniques are proton transfer reaction time of flight mass spectroscopy and selected ion flow mass spectroscopy. These types of analysers are emerging technologies in the field of stack emissions monitoring.

You must extract the gas isokinetically, unless you can show that no mist or droplets are present at the monitoring location.

6. Ammonia

Here are the methods for monitoring ammonia.

Manual monitoring technique

The relevant monitoring standard is EN ISO 21877.

Periodic automated monitoring technique

The relevant monitoring standard is CEN TS 17337.

You must extract the gas isokinetically, unless you can demonstrate that no mist or droplets are present at the monitoring location.

Continuous monitoring technique

Your CEMS must meet the quality assurance requirements of EN 14181.

Your CEMS must extract sample gas isokinetically from a representative point, unless you can demonstrate that no mist or droplets are present at the monitoring location.

7. Formaldehyde

Here are the methods for monitoring formaldehyde.

Manual monitoring technique

The relevant monitoring standard is EN TS 17638.

Periodic automated monitoring technique

The relevant monitoring standard is EN TS 17337.

You must extract sample gas isokinetically unless you can demonstrate that no mist or droplets are present at the monitoring location.

Continuous monitoring technique

The relevant monitoring standard is EN 14181.

Your CEMS must extract sample gas isokinetically from a representative point, unless you can demonstrate that no mist or droplets are present at the monitoring location.

8. Acetaldehyde

Here are the methods for monitoring acetaldehyde.

Manual monitoring technique

The relevant monitoring standard is EN TS 17638.

Periodic automated monitoring technique

The relevant monitoring standard is EN TS 17337.

You must extract the gas isokinetically unless you can demonstrate that no mist or droplets are present at the monitoring location.

Continuous monitoring technique

The relevant monitoring standard is EN 14181.

Your CEMS must extract the gas isokinetically from a representative point, unless you can demonstrate that no mist or droplets are present at the monitoring location.

9. Oxygen

Here are the methods for monitoring oxygen.

Periodic automated monitoring technique

The relevant monitoring standard is EN 14789.

 Continuous monitoring technique

The relevant monitoring standard is EN 14181.

10. Carbon dioxide

Here are the methods for monitoring carbon dioxide.

Periodic automated monitoring technique

The relevant monitoring standard is CEN TS 17405.

 Continuous monitoring technique

The relevant monitoring standard is EN 14181.

11. Reporting results

You must standardise your emissions monitoring results to a dry gas, at a standard temperature and pressure (273.15K and 101.3kPa).

Where you are carrying out compliance monitoring of the parent plant after the absorber you must also report your results corrected to a reference oxygen concentration based on the parent plant. The following reference oxygen concentrations are specified in our permits:

• 3% for liquid or gaseous fuels
• 6% for solid fuels
• 15% for engines and gas turbines
• 11% for waste incinerators