Lessons learned from scrubber installation and operation
At the beginning of this year, the IMO’s global sulfur cap on marine fuels entered into force and shipowners who chose the SOx -scrubber pathway to compliance began the modern era of emissions reduction.
Scrubbers have been operating in marine environments for almost 30 years, so owners were not exactly entering a brave new world of technology. But any time a new technology is integra¬ted into an individ¬ual vessel’s operating system, lessons are learned; and these lessons create a knowledge base that operators with less experience with scrubbers can draw from.
Leading class societies have been supporting scrubber integration in the marine environment since their first application. ABS, for one, has gathered the depth of market intelligence required to help owners to improve the process of installing and operating most scrubber systems.
Lessons have been learned about everything from installation and commissioning to the most common hardware failures for operating systems, and the type of consumables that are typically needed.
In this post, we will discuss some of the key issues associated with the installation and operation of scrubbers. But for a comprehensive list, please download ABS’s guide, Practical Considerations for the Installation and Operation of Exhaust Gas Cleaning Systems.
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-commis¬sioning 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 wash¬water 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.
Below are 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.
(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.
When a SOx Scrubber system suffers a hardware failure there can be multiple causes. Below are some that industry-operating history suggests owner/operators may want to consider investigating when searching for solutions:
• 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
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.
In one recent event, a main engine stalled due to high backpressure after a scrubber by-pass damper failed to open when the scrubber uptake damper was closing. The programmable logic controller that was designed to control the interlock of the by-pass and uptake dampers had failed. Regular mainten¬ance and testing in accordance with manufacturer’s instructions could have identified the problem.
The incident made clear that safety features require regular maintenance and testing in accord¬ance with the manufacturer’s instructions, and that crews in charge of any system need to be familiar with basic starting procedures, such as checking damper positions and safety features.
In general, the industry has learned a lot about exhaust-gas scrubbers in the 30 years since they were first used in marine applications. The average owner may have become relatively familiar with the indivi¬dual systems they chose to use.
However, leading class societies such as ABS will have learned the lessons from many sys¬tems, and have the depth of knowledge to help owners with any challenges they may face.
Source: Hellenic Shipping News