New proportioning system ideal for refineries

4th September 2020 By: Darren Parker - Creamer Media Contributing Editor Online

New proportioning system ideal for refineries

A NEW GENERATION The Gen III foam proportioner can handle all types of foam agents, even highly viscous, alcohol-resistant and fluorine-free foam agents

Fire-suppression systems developer FireDos launched the third generation (Gen III) of its foam proportioner for fire extinguishing systems globally at the end of last year. The technology has since been made available in South Africa through local partner and distributor DoseTech.

The Gen III foam proportioner is aimed at reducing operating costs and enhancing the performance of fire-suppression systems. It represents the latest technology in hydraulically driven foam proportioner and is purported to be sturdier, safer and more functional than previous generations.

Fire-protection equipment supplier DoseTech MD Mike Feldon tells Engineering News that Gen III foam proportioner systems are essential for oil refinery applications, owing to the complex chemical composition of the highly viscous foams involved in successfully extinguishing flammable liquid fires.

Typical fields of application for the Gen III foam proportioner include oil and gas, industries such as logistics and chemicals, as well as the automotive, aviation and marine sectors. Highly viscous foam agents are also increasingly being used for firefighting in waste incineration and sorting plants.

The Gen III foam proportioner can handle all types of foam agents, even highly viscous, alcohol-resistant and fluorine-free foam agents. In addition, the proportioner allows for the cost-saving and environment-friendly testing of the proportioning rate, during which no foam is produced. This means that no foam agent is used in the testing and no premix has to be disposed of.

Feldon says advancements in foam chemistry over the past two decades have led to significant development in the proportioning systems that deliver the foam agent.

“Highly viscous foam agents have special requirements when it comes to proportioning systems. “As new foam technologies are developed, it has become more essential for proportioning systems to evolve in parallel.”

He says that, over the past decade, there has been a growing global trend in firefighting foams to steer away from fluorine-based chemistries in favour of chemistries that are less harmful to the environment.

Feldon notes that the adoption of these newer chemistries is still somewhat new for South Africa: “There is some resistance to change in the local petrochemicals industry because the risks involved are so large and the proper testing of new technology is complicated, given the large scale.”

However, he notes that there is significant pressure on the industry to adopt a more environment-friendly chemistry.

Aspects to Consider

When considering new foam chemistries, Feldon notes that successful firefighting depends, to a great extent, on the correct proportioning and handling of foam agents in fire extinguishing systems.

"The viscosity of foam agents is important to note because it has a major influence when selecting the proportioning system," FireDos sales manager Ingo Weiss explains.

The higher the viscosity, the less fluid the liquid. The viscosity of foam agents can be delineated as being classified as either Newtonian fluids or non-Newtonian fluids. Newtonian fluids include low-viscous extinguishing agents, such as aqueous film-forming foam (AFFF), Hi-Ex, Class A and multi-purpose foam agents, while non-Newtonian fluids include pseudoplastic foam agents such as alcohol-resistant AFFF and fluorine-free foam agents.

Weiss notes that the foam agent used depends on the intended use or the risk to be mitigated. For example, different foam agents are required for flammable solids and flammable fluids, as well as for polar fluids and non-polar fluids. The depth of the flammable fluid is also a critical factor when choosing the foam agent.

“The viscosity of foam agents has a major influence on the correctness of proportioning. “Highly viscous foam agents have a significantly higher pressure-loss while flowing than that of low-viscous foam agents.”

Weiss says the pressure loss for highly viscous foams means that many proportioning technologies that are based on pressure ratios have to be ruled out.

Many of these pressure-ratio-based proportioning technologies are suitable only when the highly viscous foam agent can be delivered by pumps. He explains that displacement pumps are the only type suitable for this application because air-trapping is a common problem when handling highly viscous foam agents.

“Off-the-shelf barrel pumps do not qualify, as too much air would be trapped during foam delivery. The high viscosity would prevent this air from escaping, making the foam agent useless,” Weiss says.

Moreover, the correct proportioning of a foam agent depends on the dimensioning of the foam agent suction line because the foam agent’s viscosity influences the pressure loss of a pump significantly while flowing through the suction line.

Other parameters, such as net positive suction head value, volumetric efficiency and flow velocity, must also be observed.

The vacuum-tight suction line should be constructed as short and as straight as possible. Nonsteady piping layouts and blind lines should be avoided.

Weiss notes that a common suction line for several tanks, as well as a common suction line for several foam pumps, should be avoided.

It should be ensured that the foam-agent tank connection and all fittings in the pipework are the same size as the suction line.

“Highly viscous foam agents can be applied efficiently only if the proper proportioning technology, such as the Gen III foam proportioner, is used,” Weiss concludes.