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DNV GL: Challenges in the installation and operation of desulfurization towers

At present, with global sulphur restrictions coming into effect, many shipowners have chosen the exhaust gas cleaning system (desulfurization towers) to ensure compliance. DNV GL conducted a survey to learn about the owners' experience in installing and operating desulphurization towers, which can help the shipping industry to avoid risks. For this reason, Great China Marketing Department of DNV GL interviewed Dr. Ke Feibin who was in charge of this research project.

Before joining DNV GL in 2009, Dr. Ke Feibin studied mechanical engineering in Hamburg, Sydney and Chennai, then entering the field of marine engineering development. He currently serves as the Director of Environmental Certification of DNV GL, and his department is in charge of environmental certification of marine diesel engines, marine exhaust gas aftertreatment systems such as SCR catalytic and desulfurization towers, and marine energy efficiency certification. Dr. Ke Feibin has been working in China for four years, and I believe everyone has seen him on many occasions.

DNV GL: What is the current status of the desulfurization tower market? Can all desulfurization towers be installed in time to ensure compliance with the IMO sulfur restriction order?

Dr. Ke Feibin: As far as we know, there has been a backlog of ships that should have been rebuilt at the end of last year, with the time being delayed for several months. As the number of ships to be improved is still accumulating, the epidemic in China has led to a serious shortage of supporting factories and shipyards. At the same time, the ships previously installed with open system may be converted into hybrid type later, so 2020 will still be the installation year of desulfurization towers

DNV GL: What caused the backlog?

Dr. Ke Feibin: There are many reasons, of which material shortages and limited shipyard capacity are the biggest problems. For example, China has the largest number of desulfurization towers installed, but the number of GRE manufacturers in China is very limited. Designers and shipyards are facing a huge amount of reconstruction and installation work. Due to lack of manpower, the average installation time at the shipyard has been extended from 40 to 80 days. At the same time, Classification Society has to cope with the need to inspect more ships during peak hours.

In addition, the recent coronavirus outbreak has complicated the situation. In some Chinese ship repair yards, workers are unable to resume work, and a large number of ships are waiting for the installation of desulphurization towers. The epidemic has also affected navigating sea lanes, with some jurisdictions being imposing the jurisdiction of bans. In order to alleviate some delays caused by this situation, DNV GL is providing remote inspections of exhaust gas purification systems for specific ships.

DNV GL: What do the shipowners need to know if the installation is delayed?

Dr. Ke Feibin: From January 1, 2020, ships must use ultra-low sulfur fuel oil (VLSFO) or desulfurization towers. If the desulfurization tower is not installed in time, the operators must switch to VLSFO before the desulfurization tower is installed and approved. The more difficult  deadline is March 1, 2020: From this day, ships without desulfurization towers are prohibited from carrying high-sulfur fuel oil (HSFO). This means that ship operators without desulfurization towers must remove all high-sulfur fuel oil on board and clean their tanks. Only after installing the desulfurization tower system, the high-sulfur fuel can be transported and used again.

DNV GL: What things need to be considered before installing the desulfurization tower?

Dr. Ke Feibin: Planning is an important factor because it takes a long time. For new shipbuilding projects, fuel price is a key factor in deciding whether to choose a desulfurization tower or VLSFO. If the difference of fuel price is about US$200/ton, the desulfurization tower solution is more attractive. But it is very difficult to accurately predict long-term price trends. In addition, it is essential to choose suitable materials and coatings to avoid corrosion of the piping system. GRE pipes up to 1 meter in diameter need to be supported to avoid damage caused by the gravity of a large amount of water washing.

DNV GL: According to the recently released operating experience research report, what are the main challenges faced by desulfurization towers in operation?

Dr. Ke Feibin: There are currently reports of leakage and corrosion in the outboard pipes of the desulfurization towers. In order to deal with this risk, DNV GL has updated its specifications, requiring annual thickness measurements for various outboard and short pipe designs. Sensor failure is also a major problem, and most importantly, planned maintenance interval should be ensured. When the sensor fails, the control system may get wrong data and respond with incorrect or unnecessary operations. Misleading sensor data may also falsely indicate that emissions are within limits, and the truth will only be found out when the responsible authority inspects the emissions. As a result, operators may face penalties in the form of high fines; In some ports, senior crewmembers responsible for this may even be detained. Some ports in European Union and China have installed sensors on the dock side, and in some cases, port state control officials will board the ship to check emissions with their sensors. Some areas also use drones to measure ship emissions.

DNV GL: How can ship operators avoid or overcome these challenges?

Dr. Ke Feibin: Following the planned maintenance cycle and signing a service agreement with the sensor manufacturer will be of great help. Ensuring that spare parts are kept on board is also critical to avoid long-term shutdowns of the desulfurization towers. In addition, initial testing of the control system is helpful to avoid failures in operation and costly repairs or reinstallation. DNV GL provides hardware-in-the-loop tests for the control systems in the workshop to check their performance under different conditions and extreme conditions. For example, the tests can simulate extremely low or high temperature environments.