Scrubbers have been operating in marine environment for almost 30 years, but the implementation of the IMO 2020 brought a modern era of emissions reduction. Supporting scrubber integration into the marine environment since their first application, ABS has gathered several lessons learned associated with the installation and operation of scrubbers.
In commissioning SOx Scrubber systems, there can be challenges associated with extensive test periods, usually the result of an owner/operator having limited test plans and/or pre-commissioning work. This may be relatively intuitive, but following an approved test plan and completing the pre-commissioning activities are the fastest way to avoid these problems.
Another recurrent problem we are seeing, specifically during the installation process, is when washwater is carried over with the exhaust gas. This is commonly the result of unsuitable or inefficient flowpaths for the exhaust gas and can be resolved by optimizing the flowpath and/or modifying the design of the demister, which removes liquid droplets from the vapor stream.
ABS provided some more symptoms that operators are experiencing, and potential solutions:
High exhaust back-pressure
This is likely due to either undersized scrubbers, sharp bends in exhaust piping, water-spray resistance, or a failure of the bypass-isolation valve interlock. Ultimately, the system’s design usually can be improved through simulations that identify the potential sources of back-pressure.
In the case of washwater supply, the problem can be caused by clogged filters in the supply piping. But when frequent operational interruptions become problematic, it is constructive to thoroughly examine your redundancy options. A failure mode and effect analysis can support this process.
Non-compliant performance (eg., washwater pH value, SO2/CO2 ratio)
These symptoms could be due to inadequacies in the washwater, low alkalinity in the water supply or simply an ineffective water-spray pattern. Improving the overall design, a process that can be verified through the use of computation fluid dynamics modeling, and verification of alkalinity levels in the water supply may resolve the issue.
Poor reliability of monitoring systems (including instrument malfunction)
These symptoms can be caused by many issues, including the simple fact that the monitoring system may not be designed for marine applications. Other possible causes include that it may not be calibrated or installed correctly. Start by ensuring that the monitoring system is approved for marine use, and then follow the manufacturer’s instructions for calibration and maintenance.
Possible causes include:
- The sampling tubing may have become clogged, preventing accurate readings of SO2/CO2 ratios in the exhaust gas
- The pressure transducers at the bottom of the pipe run may have become clogged with debris because the sensors were located in the wrong places
- The demister in the scrubber chamber may have malfunctioned due to a build-up of deposits
- Defective welds on piping system could have allowed washwater to leak
- Low-grade stainless steel (e.g. SS316 for fittings inside the scrubber chamber) may not have held up to the corrosive operating environment
- The metallic pipe section on the side shell used to discharge washwater also may be corroded
- The air pump that samples exhaust gases may not be working properly
- The scrubber’s uptake damper cannot be operated in manual mode
- The mechanical seals for the washwater feed pumps may have failed
- The automation controls for printed circuit boards may have failed.
See also: Scrubbers enquiries increase
Major incidents causing engine shutdown and damage
History has taught the industry that most costly asset failures are the result of human error.
The actions may be well-intentioned, but crews need to be fully trained to operate specific systems and to discourage any efforts to operate them in a mode that would disregard the control system, or manufacturer recommendations for upkeep.