It is estimated that the cost of corrosion and deposits at petroleum and petrochemical refineries worldwide exceeds $15 billion annually. In cooling water systems, many measures can be taken to minimize this with the help of reliable smart measurement systems.

Large petrochemical refinery China Petroleum & Chemical Corporation (commonly known as Sinopec) is the world's second-largest chemical company by revenue. Saudi Basic Industries Corporation (Sabic) ranked fifth. In 2009, the two giants formed a joint venture to create the Sinopec SABIC Tianjin Petrochemical Plant, a world-class petrochemical facility near Tianjin, China. The massive facility cost $2.7 billion to build and its ethylene cracker and eight downstream units came online in 2010. The plant produces 3.2 million tons of chemical products annually, including ethylene, polypropylene, butadiene and phenol.

Controlling Circulating Water Quality A large amount of money is invested in the cooling water system of the plant. In order to maintain optimal condition, corrosion, scaling and fouling in the circulating water must be minimized. To achieve this, plant technicians must strictly control water quality through treatment with caustic alkalis, acids and biocides. Controlling the reagent dosage is achieved by pH and ORP measurements, with the goal of maintaining the pH of the circulating water in the range 6.5-7.5, with an ORP set point of 550 mV. No matter how good water quality conditions remain, total dissolved solids levels will gradually increase until blowdown is required. Identifying when to initiate blowdown is usually achieved through conductivity measurements. There are costs associated with blowing down too early (treating feed water more frequently) or too late (deposits in pipes), so the accuracy of conductivity sensors is critical.

High-Performance Sensors Are Critical There were issues with online pH, ORP and conductivity sensors installed during plant commissioning. Replacement parts were difficult to obtain, maintenance took too long, and laboratory analysis of samples showed that the sensors' measurements were often incorrect. The low cost of these systems quickly proved to be a false economy, and a search began for more reliable solutions. METTLER TOLEDO was asked to provide an online system that would provide measurement accuracy, long sensor life and low maintenance costs.

Combined pH/ORP sensor reduces the number of measuring points For pH measurement we propose that the InPro 3250i probe is the most suitable. The InPro 3250i is a pre-pressurized liquid electrolyte sensor that provides fast and accurate measurements. It has a secondary platinum electrode, which brings significant benefits to Sinopec SABIC. The sensor can also measure ORP.

ISM technology increases measurement uptime, simplifies sensor processing and reduces operating costs. These advantages are achieved by specially developed microchips embedded in the ISM sensors. For the InPro 3250i, this circuit allows the pH value to be calculated within the sensor itself. The pH value is then transmitted via a highly stable digital signal to the connected transmitter. The microprocessor also contains advanced diagnostic algorithms that provide continuous data on the "health" of the sensor so the operator knows when a sensor needs to be calibrated or replaced. The capabilities of the ISM also provide SINOCOM with significant advantages in conductivity measurements.

Typically, conductivity measurements of pure water, cooling system water and chemical processes require three different sensors due to the extremely different conductivities. To solve this problem, Thornton developed UniCond?, a digital conductivity sensor that can measure everything from pure water to wastewater to industrial process fluids. The UniCond has this excellent measuring range because, like the ISM pH sensor, the conductivity measurement and analog-to-digital conversion are performed within the sensor itself. This approach bypasses the problem of cable capacitance and resistance, which is why analog sensors have narrow measurement ranges. This limitation means that multiple analog conductivity sensor types are required throughout a petrochemical facility. With UniCond, only one sensor type is required for all these applications, reducing inventory and operator training.

For use with the InPro 3250i and UniCond sensors, Sinopec Sabic has chosen the multi-channel version of our M800 ISM transmitter series. It is a multi-parameter unit designed to provide maximum installation flexibility and is extremely easy to use thanks to its color touch screen. The M800’s iMonitor diagnostic utility predicts sensor maintenance and details corrective actions before process measurements are affected.