CTE vs flat plate: The critical design choice for power plants

In today’s competitive power market, maximising operational efficiency and uptime is paramount. Plants with robust and effective water intake treatment systems have a clear advantage in reducing marine growth and optimising cooling efficiency. Here, Rob Jones, Sales Manager at Xylem, discusses the critical differences between two popular electrochlorination treatment technologies: concentric tube (CTE) and parallel plate (PPE), also known as flat plate systems.

Marine biofouling in water intake and cooling systems can be an underestimated issue for power plants. Not only does it cause blockages and reduce flow, but it also affects the efficiency of cooling systems. In some cases, microbial-induced corrosion (MIC) can also impact the service life of components, leading to unplanned downtime, increased maintenance costs, and lost revenue. The only proven and effective way to protect assets against biofilm and acid-producing bacteria is to treat seawater before use.

While electrochlorination is the go-to marine growth prevention system (MGPS) for many plants, the type of technology chosen during the initial design phase can have profound, long-term implications. It is necessary to understand and evaluate the sustainability, reliability, and whole lifecycle cost of potential systems. So, what is the most suitable, cost-effective, and dependable system available?

Electrochlorination in power generation

First, let’s discuss the core principles of electrochlorination. Electrochlorination is the generation of sodium hypochlorite, a biocide, from salt dissolved in seawater. The seawater is passed through electrolytic cells while a low-voltage direct current (DC) is applied before the resulting hypochlorite solution is injected into the water intake. 

This is an effective treatment to combat the settlement and growth of marine organisms while maintaining a continuous flow of cooling water to heat exchangers and condensers. The advantage of electrochlorination is that it avoids the safety, environmental and logistics risks associated with transporting, storing, and handling bulk chlorine gas or commercial hypochlorite solutions.

Concentric tube vs flat plate

Flat plate is the traditional solution used by the energy sector, where higher system capacities are often required. Unfortunately, many new builds continue to choose this technology despite superior alternatives such as Xylem’s Chloropac® high capacity CTE systems. 

Flat plate systems typically run at a lower flow rate than CTE cells, meaning potentially smaller pumps. But this allows deposits to build up on the cell plates, meaning they usually require regular acid washing, which requires a mandatory reduction or cessation of functionality. The knock on to this is increased system redundancy requirements to cover for this downtime and additional acid washing systems built into the design. The cells in flat plate systems can also be difficult to exchange, usually requiring several days down time and lifting operations using cranes or other equipment. Fortunately, a more modern and capable technology exists – concentric tube electrodes (CTE).

CTE uses bipolar cell technology that is far more compact (in footprint) for easier on-site integration. Xylem’s patented Chloropac system leverages these design advantages to offer a market-leading electrochlorination solution. Chloropac systems are self-cleaning due to high internal velocities, and their multi-cell modular design allows for simple in-situ replacement that is possible within hours. These factors massively reduce downtime and maintenance over other MGPS technologies.

N+1: A smarter approach

The conventional approach to redundancy in energy plants relies on oversized equipment or entire duplicate systems on standby, for example 2x100% or 3x50% specifications. This is a capital-intensive approach with a maintenance load to match and not only increases the cost of the electrolysers, but also ancillary components.

With Chloropac systems, Xylem utilizes an N+1 design philosophy, where ‘N’ is the number of cells required to meet maximum hypochlorite demand and ‘+1’ is a single additional electrolyser included within the system design. The additional electrolyser remains on standby and is automatically brought online should another cell go down. This system ensures 100% system availability and continuous protection without excessive costs or space. Lowering the number of anodes versus a 2x100% or 3x50% configuration also means reduced precious metal consumption and minimized environmental impact.

While the cost per anode may be higher in a Chloropac system, the overall lifecycle costs are significantly lower. This is because fewer anodes are required, maintenance is reduced, and plant uptime is maximized. 

Modern plants require modern intake treatment

If left unchecked, marine growth poses a significant risk to power plant cooling systems. Electrochlorination offers a capable and proven solution but selecting the right type of system during a plant’s design phase provides significant advantages. Working with a Xylem Chloropac CTE system provides intelligent N+1 redundancy, reduced maintenance requirements, and self-cleaning. Together, these benefits lead to a more sustainable and cost-effective solution with lower operational expenditure over the plant’s lifetime.