Microbiological control in cooling water systems can present unique water treatment challenges for refineries and petrochemical plants. With make-up water conditions varying, and process contamination originating from several sources, it is challenging to achieve efficient system operation while meeting tightening regulatory requirements.
Microbiological growth in a cooling system poses various risks:
- Biofilms promote the development of pathogens.
- Biofouling impedes heat transfer, often increasing energy spend or reducing production capacity.
- Under-deposit pitting corrosion reduces life expectancy of critical assets.
The key cooling system characteristics that influence microbial growth are:
- Make-up water quality, e.g. treated sewage effluent can add bacteria as well as nutrients (N, P) for growth.
- Contaminations from process (e.g. organics, ammonia).
- Chemical treatment strategy.
Traditional biofouling control through bleach or chlorine gas leads to more aggressive water conditions (high oxidation-reduction potential [ORP] and chlorides) that increase corrosion potential. Biofilm control is limited due to side reactions that produce chlorinated organics, some of which are regulated. With these challenges, having a holistic view of microbial control cooling water systems benefits plant operations and profitability.
Proactive risk management: monitoring and data management
To manage the operational risks that corrosion and biofouling pose, it is essential to understand the changing process conditions and their triggers; this allows operators to put mitigation plans in place. Key components of risk management include the following:
- System optimisation (flow distribution, mixing, chemical injection points, etc.).
- Online cooling water quality monitoring and control (pH, treatment dosed, etc.).
- Critical data point capture (e.g. HX-efficiency, bioactivity spot checks).
- Real-time and remote aggregated data and key performance indicator (KPI) visibility.
- Digital alarming with rapid response from service experts.
Biofouling treatment is typically managed by online ORP or oxidant-specific automation control with additional monitoring of microbiological populations. Bacteria grow exponentially, while dip slides take 48 hours or more to complete. Nalco Water’s new Rapid Bio Intelligence is a measuring technology that can provide immediate aerobic bacteria counts in as little as 15 minutes. This delivers agility to accelerate response time while documenting events in the online monitoring system for trending and preventative risk management planning.
Written by Livia Fallet and Renate Ruitenberg, Nalco Water, an Ecolab Company, USA.
This article was originally published in the December issue of Hydrocarbon Engineering magazine. To read the full article, click here. To register for a free trial subscription of Hydrocarbon Engineering magazine, click here.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/30122020/biofouling-mitigation/