Apr 23, 2018

Petrol Payback

How a change in cooling tower chemistries minimized scaling & improved operations

Graham Wells writes on scaling and improving operations by changing cooling tower chemistry

The Grangemouth facility, located on the Firth of Forth in Scotland, is a petrochemical and crude oil refining plant that produces more than 1 million metric tons of product per year in addition to the bulk of fuels used in Scotland. Owned by INEOS, a global manufacturer of petrochemicals, specialty chemicals and oil products, the plant is one of the company’s largest manufacturing sites by volume of product. It produces synthetic ethanol, ethylene, propylene and polymers that are used as the building blocks in the manufacturing of household items. 

At the Grangemouth facility’s ethylene plant (KG), local municipal water supply is used as the makeup water supply for a large evaporative recirculating cooling tower. In industrial operations, cooling towers typically require tremendous volumes of water. However, opportunity often is available to incorporate water-saving technologies with these systems to reduce water usage and associated costs. 

Historically, the cooling water system serving the KG plant was water-intensive, with makeup water requirements reaching approximately 9,600 cu meters per day of municipal supply. Improving the water efficiency of the cooling tower system—and thus reducing usage and freshwater withdrawals—would not only enable INEOS Grangemouth to cut its raw water costs, but also allow the facility to improve its environmental performance and contribute to achieving corporate sustainability goals by conserving water resources. 

Scaling Limits Water Cooling System Cycles 

Previously, the KG plant’s cooling tower was limited to four water cycles due to increased scaling risks in the system’s heat exchangers at higher cycles. The makeup municipal water supply is characterized by low hardness and low levels of phosphate, which is added by the municipal supplier to reduce lead levels in the water network.  Under the former dosing program, calcium phosphate and calcium carbonate scaling could be controlled by operating at four cycles. However, a change in phosphate concentrations to the makeup water could still increase scaling risks to the system. 

If, however, calcium phosphate and calcium carbonate scaling were better controlled, thus minimizing the risk, cooling water cycles could then be increased, thereby reducing the volume of makeup water needed to feed the cooling tower system. 

night_city_skyscraper_cityscape_downtown_reflection_267909_pxhere_com_copy

A change in cooling water chemistry enhanced protection against calcium phosphate scaling.

Upgrades Control Scaling & Optimize Treatment 

The KG plant team collaborated with Suez Water Technologies & Solutions to develop a solution to more effectively manage and monitor calcium phosphate and calcium carbonate scaling in the cooling water system. 

Suez conducted a pilot plant study comparing the performance of the existing cooling water treatment chemistry used to control scaling against its GenGard corrosion treatment chemistry. Using water from the cooling tower system, Suez tested both treatment chemistries under stressed conditions that included low flow and high temperature. Results from the study demonstrated that the GenGard technology provided enhanced protection against calcium phosphate scaling and deposition compared to the existing program. Dosing of sulfuric acid also brought the pH to neutral, thus decreasing issues associated with calcium carbonate scaling. 

To formulate the most effective solution, sulfuric acid dosing in combination with GenGard technology was used to decrease scaling in the cooling tower and provide improved protection under stressed conditions. The designed solution also included Suez’s InSight asset performance management (APM) system, which combines advanced data and analytics for continuous monitoring of water parameters between service visits. It ensures any issue that could intensify scaling due to increased cycles would be addressed quickly and efficiently. 

By applying data analytics to online information from the plant’s cooling system, the APM system provides Suez with the ability to optimize the chemical treatment solution. Utilizing its industrial internet, several different cooling tower parameters are monitored including recirculating pH, conductivity and chemical levels in the dosing tanks. This allows Suez to detect and identify actions on issues that otherwise would not have been spotted until the next service visit—such as an increase in the cooling water pH, which could be caused by an issue with the acid dosing pumps. Monitoring the tank volumes also enables Suez to ensure that the chemistry is dosing properly. 

Greater Cycles, Multiple Paybacks 

Following implementation of the technologies, scaling in the cooling water system has been effectively suppressed, allowing the water cycles to be doubled—from four to eight—and reducing the amount of makeup water that needs to be added to the system. By significantly decreasing water usage, the KG plant will conserve approximately 100 million gal of water per year. 

The resulting economic benefit includes annual cost savings of £278,000 ($386,700) from reduced water usage, and £58,000 ($80,600) from decreased chemical use. In addition to these direct cost savings, Suez’s solution provides INEOS Grangemouth with indirect benefits. For example, by lowering the amount of chemical use, fewer chemical deliveries and transfers to the facility are required.

About the author

Graham Wells is account manager for Suez Water Technologies & Solutions. Wells can be reached at [email protected]

expand_less