Gulf Construction Online - Dow HTF optimises use of solar power

Power Generation

Noor One solar thermal plant ... a project by engineering and technology group Sener.

Dow HTF optimises use of solar power

01 September 2016

MARTA GOMEZ, renewable energy market segment manager – industrial solutions at Dow Chemical, describes how Dowtherm A can efficiently convert solar energy into power offering a reliable renewable energy source.

Concentrated solar power (CSP) is a technology that uses parabolic mirrors to concentrate sunlight into a specific point (closed circulation loop) where a heat transfer fluid is heated. The fluid transfers the heat to water, forms steam, and powers a turbine. The heat is typically generated in excess during the day and stored to keep on operating the turbine after sunset.

Solar power technology like CSP offers many advantages in regions (such as the GCC) that require reliable new sources of energy, and has the capability to generate on a 24/7 basis. The technology helps diversify energy supply, is capable of producing power during periods of peak demand, and reduces dependence on fossil fuels. When replacing fossil fuel generation plants, CSP facilities offer improved air quality and can help many nations to address off-set goals for carbon emission produced by existing fossil fuel power plants.

Unlike photovoltaic solar power and wind energy technologies, the main advantage of CSP plants is that it can operate in conjunction with cost-effective thermal storage technology to deliver energy on demand, making CSP a highly flexible source of renewable energy.

There are many different technologies within the CSP segment, parabolic trough mirrors being the one that is highly deployed and proven bankable. The main advantage of parabolic trough is the modularity which allows for an unlimited size of the plants. The solar field can be designed to feed the largest turbine in the market with no impact on the efficiency.

These CSPs rely on high-performance heat transfer fluids (HTFs), which are essential for energy creation at the plants. Most often, a synthetic organic HTF consisting of 73.5 per cent diphenyl oxide (DPO) and 26.5 per cent Biphenyl is used.

Dowtherm A from Dow is the most widely used HTF for CSPs and has 99.9 per cent purity. Dow research indicates that using high-quality HTFs like Dowtherm A is key to increasing fluid lifetime and minimising maintenance and operating costs in CSP plants.

Dowtherm A is crucial for a CSP plant, where half a degree of operating temperature makes a big difference at the end of the year. The fluid purity, when well maintained and controlled, allows the plant operators to come very close to the recommended operating temperature limit without significant degradation.

Dowtherm A is capable of accommodating temperatures up to 400 deg C and is used in almost 40 of the largest CSP projects around the world. Solar plants filled with Dowtherm A provide enough electrical generation capacity to meet the needs of more than one million homes, helping save more than 4 million tons of carbon dioxide emissions per year.

Compromising on fluid purity leads to major disadvantages over a CSP plant’s lifetime. Most notably, 99.5 per cent of purity fluids degrade almost 2.5 times more than higher purity fluids like Dowtherm A. With lower-purity fluids, more frequent degradation separation operations are needed, which ultimately means extra operating cost. In addition, refill cost for lower-purity fluids needed over 25 years of operation is $2 per kg higher.

Gomez ... tapping alternative sources.

The difference in fluid purity comes from Dow’s high-purity DPO. Lower-purity DPO contains low thermally stable organic compounds, the cause of increased degradation. In addition, most low purity grades contain chloride that will cause pitting in steel under the right conditions, like under deposits, gaskets or in small crevices in a metal surface. Over time, this can lead to failure of piping and relief components at the high points. Another type of corrosion from chloride is chloride stress cracking, which can lead to leaks at joints and ultimately weld failures all over the plant.

Dowtherm A contributes to the extended lifetime of a CSP plant at a lower operating cost, making it the most reliable heat transfer fluid on the market. And because the fluid’s viscosity is low throughout its operating temperature range, system efficiency and pumpability are excellent.

For more than 80 years, Dowtherm A fluid has proven to be the most thermally stable synthetic organic fluid under the sun. The fluid is used in systems employing either liquid phase or vapour phase heating. Suitable applications include indirect heat transfer.

As a result, Dow has been the supplier of choice for a number of large-scale CSP projects in the Middle East and Africa including the Noor One 160-MW CSP plant in Morocco, the Bokpoort 50-MW CSP plant, and Kaxu Solar One in South Africa.

The contributions of Dowtherm A to renewable applications like solar power technology help regions around the world reduce dependence on fossil fuels, meet goals for carbon emissions and improve overall air quality.

Dow is a key player in promoting technology innovation for renewable energy applications and has collaborated with global partners over the years to help develop next-generation solutions. For example, last year Dow announced its collaboration with Norwegian firm NEST (New Energy Storage Technology) on a thermal energy storage (TES) pilot project in Abu Dhabi, UAE, in association with Masdar Institute of Science and Technology.

The project, undertaken at Masdar’s ‘Beam-Down’ CSP installation in Masdar City, sought to study the feasibility and benefits of a novel TES system developed by NEST. Dow’s contribution to this project was to supply Dowtherm A as well as provide associated technical support throughout the project. Masdar’s Beam-Down facility, a 100-kW CSP pilot plant, is specifically designed to allow researchers to look into alternatives of employing solar energy in a more accessible way. Through these efforts, Dow, NEST and Masdar Institute aim to develop flexible, scalable and ultimately cost-effective solutions for the global CSP market.

Dow is very much aware of the industry’s most pressing challenges: the need to reduce cost, improve thermal energy storage effectiveness, and ensure safe operation of the plants in very sensitive environments.

It is always open to collaborating with customers and industry players to find solutions to the region’s unfulfilled renewable energy needs.

Dow offers to its customers a powerful combination of the world’s leading high temperature heat transfer fluid technology with global-scale production capacity and the industry’s foremost supply chain capabilities, to deliver the high volumes of fluid required for major CSP installations, within tight timeframes and to the most remote locations.

In addition to providing HTF for CSP plants, Dow provides technical support in the CSP plant design phase and can be a great support when it comes to simulating operating conditions. Dow is supporting and will continue to support CSP and renewable energies on three different dimensions:

• By continuously looking for partnerships to support technology development while continuing to feed its innovation pipeline;

• By advocating the use of CSP, a relatively lesser known technology in the renewable energy space (because of its strong presence in the Middle East with operating facilities, Dow’s voice is heard by policy makers); and

• Proactively delivering on every opportunity to supply its production sites with competitive renewable energy, thus helping it reduce its carbon footprint and contribute to solving global energy challenges.