The Situation

Power plants, paper and steel mills and other industries with rotating equipment often use recirculated water for the cooling of lubricating, hydraulic, turbine and transformer oil. If an oil cooler leaks, the loss of oil can cause significant damage to the pumps, compressors and motors. High oil & grease water discharge test results can be caused by oil contamination. In some cases, air quality issues can also occur. A UV fluorescence oil in water monitor from Turner Designs Hydrocarbon Instruments can prevent significant oil loss issues.

In many cases cooling towers are used to reduce cooling water temperature. These closed loop cooling systems feature large recirculated volumes of water which are treated with biocides, dispersants and corrosion inhibitors. The recirculated water can have high turbidity from solids, oils and other contaminants because the contaminants concentrate. Oil can be treated by adding chlorine to the water, but the cost can be high and toxins in the water might result. Some of the cooling water can be removed and replaced by clean water to reduce the contamination. This process is often referred to as blow down. The blow down water must be treated before it can be discharged or reduced.

Some power and industrial plants use once-through cooling water systems. The cooling water is taken from lakes, rivers, or the ocean and circulated through the plant to cool processes. Large volumes of water are used to keep the return water temperature low enough to prevent adverse effects on the environment. Any oil in the once-through cooling water will be directly discharged to the environment.

The Problem

Loss of lubricating oil can cause damage to the expensive pumps, turbines and compressors in a power plant. Operators can protect their equipment by noticing falling levels in lube oil tanks, which is a clear indication that oil is being lost. Visible oil drips on the ground can also indicate an oil leak. However, if the leak is in the cooling water due to the high water volumes and high turbidity it can be difficult to visibly detect a leak in the cooling water.

The most common method of detecting oil in cooling water is by manually collecting water samples for analysis. Sample analysis may not offer quick or sensitive enough measurement to protect a plant from oil leaks. Laboratory gravimetric analytical methods are not able to report oil in water concentrations less than 5 ppm and can take hours, to days, for a response to be generated. If the cooling water flow rate is 10,000 gpm, a leak that generates a 1 ppm oil concentration would lose 1 gallon of lube oil every 100 minutes. If daily water samples are analyzed for detection of leaks, a one-day-long leak at the 5 ppm minimum detection level would amount to 72 gallons each day (504 gallons per week).

Another challenge is that some leaks are intermittent as a process heats and cools, or as water or oil pressure changes. Occasional sample analysis of the cooling water may not catch the intermittent leaks or may not be frequent enough to prevent substantial oil loss.

Oil in makeup water from a raw water supply could be the source of oil detected in the cooling water. A laboratory analysis of discharge water that takes days for a result makes finding a leak source difficult because the original oil leak/sheen might have already passed by the intake before the results are returned.

An online oil in water monitor can quickly reveal small, intermittent leaks and indicate the potential for significant oil cooler tube failure before it occurs. Deep UV Fluorescence-based oil in water monitors from Turner Designs Hydrocarbon Instruments have been used extensively in power plants and industrial water processes for more than 20 years. These low maintenance fluorescence monitors have no significant measurement affect from water turbidity or naturally occurring organics in the water.

Most petroleum-based oils and fuels absorb UV light and spontaneously emit fluorescent light at longer wavelengths. UV fluorescence monitors are more sensitive to oil than UV absorption, turbidity, and light scatter monitors. TDHI’s online monitors can detect free, emulsified and water-soluble oils (WSOs), with no significant affect from water chemistry.

For once-through systems, oil in water monitors can help detect and prevent major oil spills that may cause significant environmental damage and regulatory compliance infractions. Additionally, an oil in water monitor can detect leaks before they damage critical equipment or require an extended shut down of the process for repair.

The Solution

The TD-120 detects most petroleum-based fuels and lubricating, hydraulic, transformer and turbine oils at less than 1 ppm. With multiple measurements per second, the response time of the TD-120 is fast for process control. The included, unique smart sensor is easily calibrated and incorporates a simple factory test to confirm your TD-120 is performing per factory specifications at any time. The TD-120 requires no sample preparation, reagents or instrument air supply. With a long-life LED and optical sensor(s), the TD-120 is expected to operate for more than 5 years with no significant maintenance or spare parts costs. These features make the TD-120 Oil in Water Monitor ideal for quick, reliable detection of oil in raw and treated cooling water.

TDHI offers a range of accessories to meet the most demanding cooling water applications.

  • Sample coolers
  • Sample pumps
  • Pressure regulators
  • Calibration standards
  • Heated and air-conditioned enclosures
  • Sea water corrosion resistant wetted parts

For hazardous area classifications, TDHI offers the TD-4100XDC Oil in Water Monitor, and for dirty water applications the TD-4100XD Oil in Water Monitor with a non-contact flow cell.


TD-120 lube oil Limit of Quantification examples

Oil Limit of Quantification (PPM) Linear Range (PPM)
Mobil DTE 25 0.12 5000
Mobil DTE 797 0.18 5500
Terresso 46 0.09 4500
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