From renewable diesel to sustainable aviation fuel, biofuels are at the centre of the global shift towards more sustainable transport. And with the demand growing all the time, refiners are racing to ensure their facilities and infrastructure are able to serve this burgeoning sector.
One area in need of attention is fuel tank linings. For decades, organisations have used specialised coatings to protect the interior of crude storage tanks from corrosion.
Yet unlike conventional fossil fuels, biofuel feedstocks contain aggressive new compounds. Traditional long-term testing methods have identified that these compounds pose significant challenges to traditional tank linings, however, these tests fail to reflect the real-world reality of the biofuels business model.
Here, Joao Azevedo and Michael Harrison from Sherwin-Williams explain how biofuel adoption is driving changes in tank storage and refining practices, and how updated testing methods reflect real-world storage conditions.
Corrosion protection considerations
With the global shift towards more sustainable transport taking hold, biofuel demand is set to expand by 38 billion litres in the period 2023 to 2028. That’s a near 30% increase from the last two five-year periods.1
This growing market is in the process of building the protocols and practices it needs to operate safely, effectively, and profitably. One important area is biofuel storage, and the appropriate methods needed to protect expensive infrastructure from corrosion.
For years, the fossil fuel production sector has used specialised coatings to perform this function, and the expectation is that biofuel operators will follow suit.
However, there are a number of sector-specific considerations. While finished biofuels are chemically identical to traditional fuels, bio-feedstocks, such as recycled cooking oil, are more aggressive in nature, presenting a risk of degradation.
These lipid-based bio-feedstocks are “living substances” that decompose into aggressive fatty acids during storage, particularly at high temperatures. With prolonged storage these fatty acids will increase in the bulk liquid, further compounding the corrosion risk and damage to internal linings.
In addition, operators face challenges during the vapour stage. Because exposing bio-feedstocks to air at high temperatures can lead to rancidification, or the formation of corrosive organic acids (including acetic and formic acid) and aldehydes.
Evolution of testing methods
Biofuel adoption, then, is driving a change in how refiners think about and assess, storage tank lining.
Traditional long-term testing methods for fossil fuel, for example, evaluate tank corrosion after six months of exposure. When this approach was utilised in the biofuel arena, it revealed significant damage to traditional tank linings.
But the method was not reflective of the real-world conditions of this emerging industry. Biofuel tanks are regularly replenished, with the turnaround of feedstocks in storage typically being less than three weeks.
A new method of cyclic testing, developed by Sherwin-Williams, incorporates regular inspections and the partial replacement of feedstocks on a monthly basis. Compared to traditional long-term storage tests, this provides a much better simulation of realistic storage and replenishment cycles and, therefore, more accurate and reliable data on coating durability and performance
This new method is currently being tested in a comparative study, with the first six monthly results demonstrating that uncoated panels show pitting corrosion during the vapour phase and at the bottom.
Such updated testing methods have enhanced accuracy in predicting real-world outcomes, which means refiners can now consider a broader range of lining materials. And test results are driving the development of next generation, high performance bio-feedstock tank linings.
The potential economic benefits are clear. By investing in infrastructure protection, facility owners can maximise the use of existing tanks, and embrace this new, rapidly expanding market. It all adds up to greater reliability and confidence for refiners and storage operators alike.
The view ahead
Biofuel adoption is gaining fast momentum, but their distinct chemical behaviour is challenging the traditional approach to tank lining corrosion protection.
Early assumptions about long-term degradation ignored the way biofuel feedstock tanks are used in practice, and ended up overstating the risks.
With cyclic testing, which mirrors real-world feedstock storage conditions, the industry can now better evaluate tank lining performance, confidently protect their biofuels infrastructure, and help support the wider adoption of biofuels as a sustainable energy source.
