Water treatment within the petrochemical industry

NALCO’s Arthur de Jong looks at environmental sustainability through the use of new technology for cooling water systems.

Refinery and petrochemical sites represent the most challenging water treatment environments. High heat fluxes, difficult water conditions and intense pressures on capital and consumable budgets require water treatment programs to operate under maximum stress. The goal: minimise operating costs and maximise energy efficiency, whilst preventing operational problems and maintaining production rates.

Poor operational control and high heat fluxes in a process heat exchanger in one petrochemical plant presented serious operational challenges. The temperature difference across the exchanger was routinely 4-10˚C. Loss of exchanger efficiency due to calcium phosphate (CaPO4) deposition was persistent and chemical cleaning routine. The critical exchanger could not be removed from service for cleaning without slowing production. Again this impacted significantly the energy efficiency of the entire production process. The unit was required to purchase hydrogen it would ordinarily have made itself at a cost of US$2200/day during exchanger cleaning.

A thorough review of the system identified three areas for improvement:

• Mechanical: The exchanger was undersized for the application and no redundancy was built in to allow for the stresses it encountered. High temperatures were therefore a source of system stress.
• Operational: For the demand placed upon it, control of the water chemistry was inadequate. Operators made manual adjustments to treatment control based upon routine testing. Response to upsets was therefore slow and imprecise. Without better control, operational problems were unavoidable.
• Chemical: The make up water chemistry varied between various city water, well water and reverse osmosis (RO) reject water. These changes varied the stress on the system continuously, but there was no mechanism to detect the changes and respond to them.

The root cause of the loss of energy efficiency was varying system stress and an inability to detect and respond to changes. Nalco recommended the 3DTrasar programme as a potential solution.

The inability to detect and respond to changes in cycles of concentration, pH, phosphate concentration, variations in water quality and high temperatures typically result in exchanger fouling and loss of efficiency. The plant used a measure of system fouling to track exchanger performance; degradation in heat transfer calculated as the plants fouling factor indicated a loss of performance.

3DTrasar measures the key parameters that result in fouling, detects upset conditions, takes appropriate corrective action and communicates with operators. By managing the system based on the stresses placed upon it, 3DTrasar improved system control. Indeed, constant measurement of system stress defines what 3DTrasar does. In this case, the amount of dispersant polymer needed to maintain the calcium phosphate deposition under control varied constantly with every change in temperature, pH, turbidity and phosphate concentration. 3DTrasar detected these changes in stress and applied exactly the correct polymer concentration to address it.

The petrochemical plant recognised a sustainable return on its investment in 3DTrasar by maintaining the efficiency of its operation. Production rates were maintained, cleaning expenditure and chemistries were not required and external production of hydrogen was no longer required.

In focus
NALCO’s 3DTrasar for Open Evaporative Cooling systems addresses the common problems associated with industrial water use. The technology continuously measures key parameters related to system stress (e.g. pH variability, process contamination and changes to make up water source and quality), process changes and heat load. It detects upset conditions, and takes automatic corrective actions. It controls scale, corrosion and microbiological fouling through precise system monitoring and control. This maximises heat-exchange efficiency, minimises the demand for freshwater, and reduces wastewater flow and the additives contained within.

3DTrasar addresses key objectives of the Integrated Pollution Prevention and Control (IPPC) Directive. The objective of the latter is to foster a high level of protection of the environment as a whole throughout Europe so as to protect both the population and the natural environment from any detrimental impact of industrial production. The IPPC Directive identifies the best available techniques (BAT) for different types of industrial installations, and therefore other industrial customers outside of the EU will also benefit from the most recent developed technologies such as 3DT.