Oil in Water Monitoring: The Continuous On-line Advantage

Dec. 28, 2000
High-Tech Products

Virtually every industry is challenged with developing and implementing monitoring programs that detect oil and refined petroleum products like fuels and lubricants in water. Primarily, monitoring programs focus on leak detection, treatment verification, pollution prevention and environmental discharge compliance. Although monitoring programs are required for environmental discharge compliance, industries can realize significant economic advantages for implementing non-regulatory monitoring programs.

For instance, rapid leak detection of petroleum hydrocarbons (like heat transfer fluids) in water from heat exchanger failures can prevent fouling of boilers or heat exchanger tubes, thereby saving thousands of dollars in operational and maintenance costs associated with heat exchanger retrofits and cleaning.

Traditionally, discrete grab or batch sample collection followed by laboratory analysis is used to monitor water for the presence of oil and refined petroleum products. Grab sample analysis provides only a brief, albeit temporary snapshot of a treatment systemís performance, heat exchangerís integrity or discharged water quality. This problem is normally exacerbated by delays in completing laboratory grab sample analysis whose results are reported beyond a few days to several weeks. Under these circumstances, the effectiveness of monitoring dilutes operational and maintenance tactics to prevent pollution, avoid discharge fines and eliminate leaks that lead to costly repairs.

Solving the Problem

On-line monitoring of petroleum hydrocarbons in water can easily and continuously identify water contaminated with oil and refined petroleum products. Yet, historically, continuous on-line measurement and detection of petroleum hydrocarbons in water has been difficult. The primary difficulty is finding a monitor that simply does not get dirty (non-fouling) from continuous operation. The secondary concern is finding a monitor that is easy to operate with limited to no maintenance and is sensitive and selective in its measurement of targeted petroleum hydrocarbons in water.

Recent advances in the development of a continuous on-line monitor, based on an optical instrument called a fluorometer, can detect dissolved petroleum hydrocarbons in water. This monitor utilizes a

non-contact falling stream flow cell to prevent fouling of the sample detection system. The on-line monitor takes advantage of fluorescence technology to gain very sensitive, highly selective and specific detection of dissolved, dispersed and emulsified petroleum products in water ranging from low ppb to high ppm concentrations.

With this choice, a power plant can implement uninterrupted heat exchanger leak detection to protect fouling of exchanger tubes or unwanted oil discharges in non-contact cooling water. The continuous on-line monitor designed for the fluorescence detection of oil and petroleum products in water is the TD-4100.

Designed to overcome problems that are commonly encountered in continuous on-line monitoring applications, the TD-4100 is manufactured by Turner Designs in Sunnyvale, Calif. There are several key design elements of this monitor.

  • A non-contact, non-fouling detection system (falling stream flow cell) virtually eliminates the need for routine cleaning or maintenance to sustain instrument performance. The non-contact non-fouling detection system provides instantaneous recovery from upset or high oil concentrations that may be detected in water from monitoring programs.
  • Direct fluorescence measurement of oil and petroleum products in water does not require sample pre-treatment or extraction prior to sample detection.
  • Continuous monitoring allows the instrument to take uninterrupted, real time, measurements of targeted hydrocarbons in contaminated water.
  • On-line process control allows real time data generated by the monitor to activate alarms, emergency telecommunications or automatically modify pollution control or water treatment systems.

The TD-4100 works by detecting fluorescent hydrocarbons in oil and petroleum products to monitor their presence in water.

Commonly known petroleum hydrocarbons that are detected include gasoline, diesel oil, jet fuel, crude oil, lubricating oil, tall oil, hydraulic oil, heat transfer fluids, aromatic solvents and BTEX.

What is Fluorescence?

The process which allows the detection of fluorescent hydrocarbons in water is simple. Fluore-scence is a process that occurs when a compound, like benzene, absorbs light at one wavelength or energy and spontaneously emits light at a different wavelength or energy. The fluorescence process produces an excitation - emission fingerprint that is unique to aromatic hydrocarbons, much like humans are uniquely identified by their own fingerprints in a population of people.

Continuous on-line monitoring provides industry with an immediate feedback loop that supports rapid and effective process control programs which manage leaking heat exchangers, verify water treatment systems, prevent pollution and environmental discharge compliance.

Major improvements in on-line monitoring, such as the Turner Designs TD-4100, eliminate the historic problems of flow cell fouling and poor detection limits. On-line monitoring will reduce costs by allowing industry to implement tactics to prevent pollution, avoid discharge fines, and provide early detection of leaks in systems, like heat exchangers, that lead to costly repairs.

Mark D. Uhrich is the director of sales and marketing for the Hydrocarbon Business Group at Turner Designs. For further information, contact Turner Designs - phone 408-749-0994, fax 408-749-0998, http://www.turnerdesigns.com.