This invention relates to a process and apparatus for measuring the gaseous content of industrial process gas streams, in which a portion of a process gas stream is extracted, conditioned for analysis, and transported to a gas analysis system.
Many industrial processes can benefit from the continuous measurement of process gas streams before and after the process stream gas and/or particulate scrubbing systems. Due to the extreme environment of the process gas stream, before and after many process scrubbers, no gas analysis system to date has demonstrated reliable continuous operation in both of these environments.
Many gas analysis systems are not specific to one gas. Gases other than the gas or gases of interest may cause an erroneous response in the analysis system. Dilution of the process gas stream with air to achieve lower concentrations of the interfering gases has been demonstrated as a reliable way to eliminate many interference problems. In process streams with constant and known composition, dilution of the process stream with conventional flow controllers, such as needle valves, fixed orifice, or automatic compensation needle valves, has given reliable and accurate gas dilutions. However, in process streams with widely varying compositions, all conventional flow controllers demonstrate inaccuracies in flow due to the changing viscosity of the gases in the process gas stream. A method was needed to allow accurate and interference free measurement of process gas streams with widely varying gas compositions.
Filtering the process gas stream for particulate matter, water, acids, and other compounds that interfere with gas analysis has always been a serious problem for industry. To achieve the analytical response time required for process control and EPA mandated response time requirements, relatively high flow rates (1 to 80 liters per minute) were extracted from the process. The higher the flow rate extracted from the process, the larger the problem becomes for sample gas conditioning. A method was needed that extracts a very low volume of gas from the process, yet still allows the higher flow rates required for fast response time.
Due to trends in the EPA regulations to apply to smaller industries, and the needs of these smaller industries to achieve tighter process controls, a lower cost method of monitoring these processes needed to be developed. Current state-of-the-art continuous process gas analytical systems are very complex and require extensive training of maintenance and operation personnel to adequately maintain these systems. A gas sampling and analysis system was needed of greatly reduced complexity, while maintaining a higher level of reliability and accuracy.