Methanol Butterworthing: a revolution in tank cleaning

Methanol Butterworthing has emerged as a promising alternative to traditional tank cleaning methods for chemical and product tankers. L&I director, Guy Johnson, presented* this innovative approach showcasing the significant environmental benefits, particularly in reducing greenhouse gas (GHG) emissions.

Tank cleaning is a critical operation in the chemical carrier and product tanker sectors, essential for maintaining cargo quality and safety. However, it is also a significant contributor to GHG emissions. Mr Johnson highlighted the role of tank linings in this process, noting: "Stainless steel and premium organic-coated vessels provide the greatest opportunity for optimisation of tank cleaning operations" due to their superior absorption, desorption, and retention characteristics. Despite this, commercial pressures often lead to over-cleaning, irrespective of the tank lining, driven by the need to meet stringent cargo quality standards.

Traditional tank cleaning methods, such as hot water washing and steaming, are energy-intensive and produce substantial emissions. Mr Johnson provided alarming statistics: each hour of hot water washing at 65 to 70 degrees Celsius consumes approximately 0.6 tonnes of fuel, producing just under two tonnes of CO2. Steaming, which uses even more fuel, results in roughly three tonnes of CO2 per hour. For an average chemical tanker with eight pairs of cargo tanks, cleaning can consume around 33 tonnes of fuel and generate over 100 tonnes of CO2. If repeated to meet inspection standards, fuel consumption can increase to 52 tonnes, equating to approximately 48 hours of sailing time in emissions.

Methanol Butterworthing offers a viable alternative to these traditional methods. This process involves cleaning tanks with methanol, a solvent that dissolves cargo residues more efficiently than water, eliminating the need for heating. Consequently, it reduces both cleaning time and fuel consumption, significantly lowering GHG emissions. Mr Johnson emphasised that "methanol Butterworthing is no more risky than crude oil washing," a widely accepted practice in the industry, provided it is conducted with proper risk assessments and under the guidance of classification societies.

Real-world applications of methanol Butterworthing have demonstrated its effectiveness. For instance, a case study involving the cleaning of zinc-coated tanks from gas oil to methanol showed that the process required only one round of cleaning, compared to multiple rounds with traditional methods. This resulted in substantial fuel savings and reduced emissions. "The potential is extraordinary," Mr Johnson noted, "not only in terms of reducing GHG emissions but also in operational efficiency."

Feedback from cargo owners has been positive, and Mr Johnson highlighted the success of companies like Dow Chemical, which has adopted methanol Butterworthing, allowing its ships to load one or two extra voyages per year due to the time savings. This demonstrates the commercial benefits alongside the environmental gains, but as Mr Johnson aptly put it: "It is possible to significantly reduce GHG emissions related to tank cleaning, but this is not going to happen unless we are allowed to change."

*The discussion took place at the International Chemical & Product Tanker Conference in April 2024, which was sponsored by Bureau Veritas, DNV, The Marshall Islands Registry/IRI, Jotun, Lloyd’s Register and MarFlex.

Further insights into tanker operations will be available at the Crude Tankers & Terminals Conference, Awards & Exhibition 2024 being held in London 22 - 23 October 2024. Register your interest here and be sure to nominate contenders for the Awards.