Apr-2008

Online cleaning of production units

Faster online cleaning avoids the production losses that occur when shutting down a unit for conventional cleaning. Other benefits, such as improved safety and longer run lengths, are also realised

Marcello Ferrara
ITW Technologies

Article Summary

Online cleaning of refinery and petrochemical production units as a preventive tool for refinery optimisation and improved operational excellence targets the loss of operating efficiency on a proactive basis. Online cleaning technology can optimise:
- Productivity
- Operability
- Safety, health and environment
- Reliability
- Product quality
- Energy efficiency
- CO2, SOX, NOX, VOC emissions
- Maintenance and repair
- Organisational requirements.

For example, by applying online cleaning to a topping unit on a proactive basis, a saving of about $37 000 for every ton per hour (tph) feed rate can be expected. Therefore, for the topping unit alone, an average 100 000 bpd refinery can gain savings (volume and yield increase, and direct cost avoidance) of about $20 500 000. This is also applicable to the majority of refinery units, which can be cleaned online simultaneously.

Case study
Reducing production loss
In reviewing a case involving a 100 000 bpd unit that is shut down for cleaning when required, comparisons are made between current practices (eg, shutdown for cleaning with a production loss of 25 days) and the application of online cleaning technology (eg, a production loss of one to one-and-a-half days without opening the equipment).

All the evaluations in this article are based upon assumptions that are accurate to the best of our knowledge. It is impossible to encompass the configura-tions of every refinery. Therefore, while the general meaning is still valid, these assumptions have to be modified to suit a specific refinery’s needs.

When considering ways to reduce production loss, why only undertake cleaning under end-of-run (EOR) conditions and accept a period of lower productivity? Online cleaning dramatically reduces downtime by increasing run lengths and avoiding shutdowns. It can clean a unit in just 24–30 hours, on an oil-to-oil basis, and multiple pieces of equipment (and different units) can be cleaned simultaneously, as there is no limit to the amount of equipment that can be included in the closed circulation loop. Table 1 analyses the difference between current procedures and online cleaning.

As can be seen in Table 2, the refinery gain of $11.75 million takes into account the production loss arising from turnaround operations only. A rigorous calculation should also take into account the production loss arising from sludge accumulation (TP increase, FIT decrease) as the unit is approaching EOR conditions. It is not unusual to run the unit at minimum capacity for the last two to four months of operation. ITW technology may allow an increased average feed rate due to cleaner run conditions.

Energy efficiency improvement
Due to the improvement in energy efficiency that results from online cleaning, the following energy bill will apply, thanks to a reduction in the furnace inlet temperature:

(556 T/h * 0.5 Kcal/Kg°C * 10°C *1000 Kg/T)/(9800 Kcal/kg * 250 $/T)/80% (furnace eff) = $809 000

Regular application will avoid this cost and the equipment will remain in a cleaner condition longer, resulting in optimised throughput.

In the refining industry, mechanical cleaning costs are normally allocated to maintenance costs. In this case study, we have to make the following observations when using ITW technology:
- Heat exchangers will not be mechanically cleaned
- Columns will not be mechanically cleaned
- Packings will not be replaced

We will ignore the costs for treating pyrophoric solids (eg, alkaline washing and washing fluids waste disposal costs or specific chemical treatment) to balance the eventual “column” without packings.
Based on some general assumptions, the costs and related refinery gain in using online cleaning technology can now be evaluated as shown in Table 3.

Yield improvement
During the application of online cleaning, packing and/or trays are also cleaned. Regular application of the technology will avoid packing and/or trays inefficiencies, thereby recovering on-product specifications and avoiding product giveaway.
By supposing only 1% of diesel is lost on the residue for the previously cited reasons, and diesel is 30% of the production, the following recovery will be achieved:

556 T/h * 30% * 1% * 325 $/T * 8760 h/year = $4 752 725

Of course, this figure is much higher if atmospheric residue conversion is taken into account. We will therefore assume unitary loss is $5 000 000.

Reliability improvement
When applying this technology, not only the relevant equipment, but also all the lines, pumps and valves are cleaned. Moreover, as equipment is not opened, there is no danger of equipment misalignment and leakage.