Gases & Instrumentation - March/April 2008

TDL Technology Promises

Improved Process Control in Gas Plants

SAM MILLER

Ultra-fast and highly accurate, a new Tunable Diode Laser analyzer technology is replacing conventional sensors at refineries and gas processors, saving on maintenance while providing enhanced control over process integrity.

Confronted with increasing costs and product integrity issues, the hydrocarbon processing industry has become increasingly dependent on sensors for detection and measurement of impurities in gas streams. For some sensing technologies this can be a hit and miss situation that can compromise process control and result in costly actions including high maintenance costs, unplanned shutdowns and unanticipated shut-ins where the buyer can block the seller from shipping gas.

Gas processing plants require fast and accurate measurements of moisture (H₂O), hydrogen sulfide (H₂S), and carbon dioxide (CO₂) because these contaminants damage expensive equipment such as turbo-machinery and pipelines, shorten desiccant, contactor, or mole sieve lifetimes, and threaten the operator’s ability to maintain tight process control and product quality. In some cases, the gas processor’s downstream customer can shut in their supplier which costs hundreds of thousands of dollars.

Tunable Diode Laser ( TDL) based analyzers are increas-

ingly being used in these “pain-point” analytical applications to measure contaminants reliably while reducing maintenance and operating costs. TDL absorption spectroscopy employs a laser mounted behind a window that protects it from the wear and tear of caustic gas contents, while enabling the analyzer to accurately and quickly read varying gas concentrations. The laser does not come into contact with the gas and calibration does not change or drift over time. (Figure 1 and 2)