The growth in the number and scale of data centres in recent years has been mirrored by increasing concerns about the power they consume. As we reported in a recent blog, one possibility to reduce the strain on mains power grids is to use hydrogen fuel cells, ideally combined with renewable sources of energy, to generate power on-site.
This is not, however, always an option for many data centre operators, due to cost, geographic location or concerns over factors such as safety or scalability. Instead, they continue to rely on mains power, often with diesel generating sets as a means of providing a stand-by supply or to provide additional capacity at times of high demand. This approach is neither cost-effective nor sustainable, as diesel generators are increasingly expensive to run and come with significant environmental implications.
An increasingly attractive option is to use one of a new generation of gas turbine systems. These are typically single cycle gas turbines (SCGT), with a turbine and boiler, or combined cycle gas turbines (CCGT) where the waste heat from a gas turbine is used to produce steam in a heat recovery steam generator, which in turn powers a separate steam turbine; a further option is to introduce an absorption chiller for cooling data centre systems.
The importance of water treatment in data centre gas generation
Regardless of the type of turbine, it will require water for cooling, make-up water for high-pressure boilers and, in the case of CCGT systems, steam generation.
Water for use in the gas generation systems in data centres can be drawn from a mains supply, a local borehole or a surface source, either fresh- or salt-water. In each case, the raw water feed will include a range of contaminants, including particulates, minerals, salts, dissolved gasses, microorganisms and, in the case of most mains supplies, chlorine. All of these must be removed or reduced to a safe level to ensure that the cooling and, if used, steam generation systems are to function reliably.
If these contaminants are left untreated, they will lead to a number of problems that will affect the operation, efficiency and reliability of power generation system. For example, if dissolved minerals such as silica are allowed to carry-over to boiler components they will precipitate, causing scale deposits to form on boiler tubes, resulting in pressure loss and overheating. Similarly, fouling of heat exchanger surfaces or condenser tubes by scale, corrosion deposits or organic matter will reduce heat transfer and condensing efficiency and lead to a loss of pressure.
Corrosion is often an additional problem. This is generally caused by dissolved gasses, most notably oxygen, but also by the presence of chlorides and sulphates, in cooling water. These gasses and salts create electrochemical reactions on the surface of exposed metal surfaces, which subsequently degrade. The process can be exacerbated if the pH is too high or too low, or if microorganisms are present; these produce corrosive by-products and create biofilms that protect corrosive environments, which accelerate corrosion rates still further.
Water purity matters: integrating RO membranes in gas turbine systems
Introducing water purification technology is therefore a crucial part of gas turbine system design. Typically, such a system will include pre-treatment that reduces particulate matter and removes chlorine, to protect the downstream reverse osmosis (RO) membranes. These RO membranes form the heart of the system and are constructed from multiple layers of semi-permeable, spiral wound polymers, wrapped around a central tube.
This construction allows water to pass through but rejects up to 99% of dissolved salts, minerals and microorganisms. RO membranes are modular in design, enabling multiple units to be combined to match the exact water throughput requirements of each application.
Each water purification system is generally completed with an ion exchange or continuous electro-deionisation (CEDI) unit for final polishing, plus appropriate control and communications units to provide the option of remote monitoring. This configuration is extremely efficient and easy to maintain and upgrade.
Taking a holistic approach to water purification
Just as no two data centres are alike, so too will each power generation and water purification system have a unique set of requirements. That’s why at Purite we take a holistic view of system design and development, bringing together our many years of expertise in data centre water purification treatments and operations to help each customer optimise both PUE (power usage effectiveness) and WUE (water usage effectiveness).
For example, our technologies enable us to deliver higher cycles of concentration in cooling systems and the ability to recycle cooling system brine, thereby reducing makeup water demand and liquid discharge; in some instances, we are also helping data centres eliminate discharge altogether.