Improving turnarounds and operations with online cleaning
Case histories illustrate the financial and operational gains achieved by replacing mechanical cleaning with online, closed-loop operations. The conventional perception of the cost of mechanical cleaning is that it amounts simply to the cost of cleaning or hydroblasting. In reality, the cost of mechanical cleaning is more than 30 times the cost paid to the mechanical cleaning company.
MARCELLO FERRARA and CRISTINA FERRARA
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Consider a preheat train to be cleaned in a major turnaround when it is usual to replace gaskets and bolts after bundles are extracted and cleaned. In a 40-exchanger preheat train, this alone can amount to more than $200000. This amount could be saved simply by not opening the bundles during cleaning.
However, not opening the bundles will mean a saving in downtime. A 100000 b/d refinery can make a profit of around $2 million/d, so a saving of seven days in downtime equals a preserved $14 million of profit.
We believe that a reduction in overall costs and an increase in margin can be achieved by a shift in refiners’ approach to operations. Recovery of losses will allow operators to meet and even reduce their budgets.
The online cleaning approach
ITW Online Cleaning is a patented technology for cleaning heat exchangers and process equipment in a closed loop, in the hydrocarbon phase. The technology includes a cleaning method and process steps, chemicals, and a monitoring system, all covered by patent. The technology cleans an entire production unit in as little as 24 hours on a feed-out/feed-in basis, thus reducing downtime during a turnaround.
The washing fluids arising from ITW Online Cleaning are fully reusable/reprocessable, which means no waste will be generated by the cleaning operations. By operating on a closed loop basis, the process generates no airborne emissions during cleaning.
The gains in value which can be achieved with online cleaning can be identified by measuring key performance indicators before and after the cleaning operation and loading into a spreadsheet all of the cost items which would have impacted the run by using conventional mechanical cleaning.
For instance, if a 1°C furnace inlet temperature (FIT) loss in a 100 000 b/d crude distillation unit costs, say, $1 million/y, the recovery of 10°C FIT will have a value of $10 million/y. If fouling is impacting the capacity of the unit (by increased delta P, for instance) then the gain in value is given by the recovery in production. And if the crude unit has reduced capacity by 5% and is making $8/bbl, the daily recovery in margin (over losses) will be $40 000.
This does not take into account the savings achieved through many other factors, including reduced pumping costs, reduced energy consumption, and avoiding the many costs of preparing and implementing a mechanical cleaning operation.
Online cleaning of refining plant
In the refining industry, most fouling is related to the precipitation of asphaltenes. This occurs because of destabilisation of the asphaltenic micelles, which can be driven by chemical or thermal factors.
Among the causes of chemical destabilisation, the most common is the incompatibility of different feedstocks. It is well known that when a paraffinic feed is blended with an asphaltenic feed, asphaltenes will precipitate out of the blend and will deposit in the equipment.
The current trend in the refining industry of processing opportunity crudes (which are normally heavy crudes) makes this problem even more evident in that refineries cannot have enough storage capacity to segregate the many crudes which are processed on a daily basis.
Another type of fouling occurs when processing tight oils, which are basically very light oils, mostly of a paraffinic nature. In this case, heavy paraffins may separate out and precipitate, together with the relatively small amount of asphaltenes which are present in the oil.
Online cleaning technology can effectively address both types of fouling. The following case histories will better illustrate the results achievable by ITW Online Cleaning.
Case history: avoiding unscheduled shutdown of a visbreaker
ITW Technology has been applied on the vacuum section of a visbreaker unit. The refinery layout features a CDU, VDU, VBU, the vacuum section of the VBU, storage for visbreaker residue, and an integrated gasification combined cycle unit.
The problem was related to an increase in vacuum section bottom train outlet temperature (tag TI1826). The refinery’s procedure was to clean the exchangers when the outlet temperature was approaching 280°C. During a run, the refinery normally mechanically cleaned two exchangers in order to reach the targeted run length.
Before the application of ITW Technology, mechanical cleaning did not help in recovering the temperature, so there was a steady increase of outlet temperature values, reaching the shutdown limit six months before the scheduled turnaround.
The visbreaker unit therefore required an unscheduled shutdown to clean all of the vacuum section bottom. To solve the problem, ITW Online Cleaning was applied in the vacuum section, and the visbreaker resumed production immediately afterwards.
Outlet temperature recovery was an average 45°C, which remained stable (see Figure 1). The unit could run easily for five more months without any issues up to the scheduled turnaround.
Case history: eliminating mechanical cleaning during a turnaround (1)
The atmospheric and vacuum distillation units of a refinery had scheduled a turnaround and the refiner wanted to validate ITW Online Cleaning and ITW Improved Degassing/Decontamination on the vacuum section. The units were under end-of-run conditions.
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