Accurate emissions monitoring from industrial processes is critical for determining overall system combustion efficiency, environmental compliance and safety. However, there is no ‘one-size-fits-all’ approach, as each application encompasses different system considerations. The art of emissions monitoring and sampling requires:
1. An understanding of the application.
2. An assessment of the requirements to be met.
3. Once the criteria for monitoring have been identified, a monitoring strategy can be implemented that will meet the particular application goals.
Maintaining gas integrity is critical for ensuring an accurate emissions reading, but understanding proper sampling techniques for each application is necessary to achieve the goal. The mechanism for gas sampling, including a breakdown of the five critical component steps and application considerations, is as follows:
• Which gases need to be measured?
• What are the ranges for each gas?
• Is monitoring of water-soluble gases, such as NO2 and SO2 required?
• At what temperature is the application running?
• Are there significant amounts of dust/particulates/ash in the sampled stack gas?
Understanding the mechanisms for gas sampling
Maintaining gas integrity is critical for ensuring an accurate emissions reading, but understanding proper sampling techniques for each application is necessary for achieving that goal. The mechanism for gas sampling, including a breakdown of the five critical component steps and application considerations, follow.
The criteria for the optimal probe implementation for acquiring a representative gas sample include:
Correct sampling probe: Identifying the correct sampling probe will depend on each application’s needs. A high temperature system will require an inconel probe capable of withstanding the harsh conditions. High dust applications will require a sintered pre-filter with half-shield to protect from clogging.
Probe length and location: The testing location will ideally be at least eight stack diameters from the previous disturbance and at least two stack diameters from the exhaust vent, or as far as possible from any disturbances. The length of the probe should be chosen based on the diameter of the stack; the tip of the probe should be as close to the centre of the stack as possible, and away from the walls.
The testing port should be large enough to fit the probe and the sintered pre-filter if it is used. The area around the probe should be appropriately sealed to ensure that no gas escapes the stack in cases of positive pressure, which could pose a safety hazard to the operator. In cases of negative pressure, the seal will prevent air from entering the stack and diluting the stack gas sample.
Sample conditioning unit (SCU)
Moisture in a sample may affect the accuracy of a gas measurement depending on the range of soluble gases under measurement. Gases that are highly water soluble such as NO2 and SO2 could be absorbed in the medium, therefore reducing the readings. If these gases need to be measured at low ranges, an SCU is recommended to remove moisture directly at the probe handle so that gas integrity is maintained prior to reaching the monitoring unit. This is a critical step for accurate emissions monitoring of soluble gases, present in flue gas from industrial and commercial processes. An SCU ensures maximum gas sample integrity for those who must meet certain emissions requirements.
Standard or heated sampling hose
The standard sampling hose that transfers the gas from the probe to the analyser is constructed of material that will not react with components of the sample gas and is relatively hydrophobic. In cases where ultra-low NO2 and/or SO2 levels must be measured, or a longer sampling hose is required, a heated sampling line keeps the gas above dew point temperature. This prevents condensation from occurring in the hose.
Accurate emissions monitoring and sampling solutions:
E8500 Plus and E9000
E8500: The E8500 Plus portable emissions analyser can include up to nine gas sensors including O2, CO, NO, NO2, SO2, H2S, CO2 and CxHy hydrocarbons, as well as low NOx and low SO2 sensors. Other key features include a built-in thermoelectric chiller with automatic condensate drain, internal filter assembly, SCU, multiple probe lengths with various temperature ratings, sintered pre-filter, pitot tube for stack gas velocity analysis, real-time software package with wireless Bluetooth communications, and automatic data logging.
E9000: The E9000 transportable emissions analyser can also measure up to nine gas sensors with low NOx and low SO2 capabilities and a built-in thermoelectric chiller with automatic condensate drain. The E9000 is available with a heated probe head and heated sample hose for applications that require measurements of ultra-low NOx or SO2 levels.
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