Online cleaning: a mindshift for improving operational excellence
A patented method of chemical cleaning can reduce downtime arising from severe fouling in process units
MARCELLO FERRARA and JUSTIN WEATHERFORD
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Online cleaning of refinery and petrochemical production units has been positively proven in many severe applications such as the bottom section of visbreaker and vacuum columns with both trays and structured â€¨packing. In turnaround applications, visual inspection has confirmed the results. An entire unit can be cleaned online in as little as 24 hours. Furthermore, cleaning can be implemented during unit operations to recover unit performance, operate under clean conditions and improve operational performance.
In one recent case, ITW applied its Online Cleaning technology to the tar stripper section of an atmospheric vacuum distillation unit in a major US oil refinery. The crude unit was scheduled to operate at reduced rates for three to four days due to other maintenance activities. While at a reduced rate, the refinery performed online cleaning of the heavily fouled tar stripper section to improve operational performance and to validate the technology for strategic application in future turnarounds/slowdowns in lieu of mechanical equipment cleaning.
ITW’s asphaltene stabiliser was injected into a closed loop circulation that utilised 2-inch temporary piping to route liquids into the crude side of four preheat exchangers. Even withstanding the low circulation rate (normal circulation utilises 10-inch lines), the results achieved were impressive.
Due to the short duration of the unit slowdown, there was no time available to visually inspect the heat exchangers for cleanliness. However, the refinery isolated and visually checked one of the two tar stripper bottom coke pots as a first check of the results of cleaning.
The tar stripper coke pots suffer severe fouling of jack-hammer-type coke, and the coke screens are very difficult to remove after even very short operating times. According to the refinery’s maintenance superintendent, the previous time the tar stripper coke pots were dealt with, there was a need to chip the coke out and more than eight hours were required just to remove the basket.
After being cleaned online, the coke pot was clean. The coke basket was removed in approximately 10 seconds without any hindrance. Any remaining deposit was dry, soft and friable, and could be broken by hand. In addition, after the unit was returned to service, process data were compared to immediately prior to the cleaning. Heat exchanger duties were improved and the pressure drop across four heat exchangers in the loop decreased by approximately 15-17 psi, relieving the hydraulic limitation of the crude unit and allowing for an increase in throughput.
Safety and environmental factors
The hydrocarbon processing industry continues to try and limit airborne emissions through technical efforts and investments. For example, consider the investments and revamps required (valve substitutions, insulation of flanges, double seals on pumps and double seals on tanks, for instance) to limit volatile organic compounds (VOCs). Then imagine the effects of hydroblasting on these assets.
Until recently, hydroblasting was the only effective technology for cleaning heat exchangers and process equipment. However, by performing cleaning operations in a circulation loop, online cleaning eliminates the problems associated with hydroblasting. Moreover, sludge is converted to a fully reusable/reprocessable product and the washing fluids are compatible with the hydrocarbon processing industry (when reused as feed in a process unit) and combustion processes (when reused as a blending component in fuels). As a result, the equipment can be put on-stream immediately after cleaning.
Another problem encountered during turnaround is the duration of steam-out operations and their associated environmental problems, which directly impact equipment downtime.
Mechanical cleaning is currently performed only where there is a stringent need for it. This suggests that equipment is being allowed to degrade to the minimum acceptable performance before cleaning. This situation arises from a number of peculiarities in the hydrocarbon processing industry.
First, the industry sees cleaning as a troublesome, lengthy operation that leads to a loss in production, so it is avoided. Also, the mechanical cleaning process involves at least 20 operations, each of which has an associated hazard.
When the production/maintenance department faces a cleaning situation, it normally reacts in one of two ways:
• The situation is fairly typical and managed as a routine operation
• The situation is problematic and postponed until it can no longer be tolerated.
In the first case, the management team is unlikely to consider something that is not routine. Or, in the best-case scenario, it will be excited about trying something new. However, unless the management team is strongly committed to the necessary testing of the new technology, there is a tendency to procrastinate.
In the second case, the management team may not be inclined to look for a new technology. Instead, it addresses the problem in a manner that is inefficient and costly. In both cases, process unit economics and environmental performance can suffer significantly.
Advantages of online cleaning
An array of technologies is available for solving problems related to equipment cleaning, including ITW’s patented technology for cleaning heat exchangers and process equipment in a closed circulation loop.
Equipment can be cleaned online with this technology without having to extract the heat exchanger bundles. This is particularly beneficial in severe applications such as visbreakers and columns with structured packing internals. Crude distillation units and vacuum units have also been successfully cleaned online. An entire unit can be cleaned in as little as 24 hours. The advantages online cleaning have over hydroblasting include:
• Reduced downtime
• Closed loop operation, without the need for extracting the bundles
• Simultaneous cleaning of multiple process units
• No waste generation
• No emissions
• Improved safety.
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