Which of the following describes Extractive systems in CEMS?

The choice indicating that extractive systems in Continuous Emission Monitoring Systems (CEMS) draw gas samples and transport them to analyzers accurately describes how these systems function. In extractive CEMS, gas from the flue or stack is sampled and transported through a system of pipes to an analysis point, where various instruments measure the concentration of pollutants or other parameters of interest. This method is beneficial because it allows for detailed analysis of the gas composition without requiring direct measurement in the potentially harsh conditions of the stack.

This method is preferred in many situations due to its ability to provide a controlled environment for the analyzers, often leading to more accurate results. It also allows for the use of various types of analytical equipment that might not withstand the extreme conditions found directly in the stack, such as high temperatures and pressures or corrosive gases.

Understanding this operational principle is crucial for those in power engineering, as it highlights the importance of the sampling process and the reliability of the data collected via this method. Consequently, this is why the statement about drawing gas samples and transporting them to analyzers is considered correct in the context of extractive systems in CEMS.