Energy conservation in a crude unit
Online cleaning of a CDU/VDU heat exchanger network saved on time, energy and environmental impact.
YOSHINORI KANNO, JX Nippon Oil & Energy Corporation
GUIQING XU, Softard Industries
IAN BAXTER, Cat Tech International
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High energy costs and environmental regulatory demands mean that there is an ever increasing focus on energy efficiency in the oil refining industry. Crude oil distillation is an energy intensive process consuming around 20% of a refinery’s total energy consumption. The oil is first heated in a preheat exchanger network by recovering the heat from the product and reflux streams. It is then further heated in a furnace prior to entering the flash zone of the distillation column. In order to reduce fuel consumption in the furnace, the efficiency of the exchangers in the preheat train is crucial. Crude oil is complex in nature, containing many impurities, and the preheat exchangers are prone to severe fouling, which in turn reduces the thermal and hydraulic performance of the network. The immediate financial and environmental penalties associated with this are increased energy consumption at the furnace, higher CO2 emissions and eventually loss of capacity throughput. The total estimated cost of all heat exchanger fouling in the UK is in the order of $2.5 billion and $15 billion in America.1
JX Nippon Oil & Energy group (JX NOE) is a Japanese petroleum company that operates six refineries in Japan with a combined crude processing capacity in the region of 1.3 million b/d. JX NOE has a strong commitment to the environment, constantly striving to reduce environmental impacts and promote energy saving measures to reduce global warming. This commitment is demonstrated in an environmental plan with key objectives to cut CO2 emissions and take steps to reduce waste, water use and air pollution.2 In this regard, the opportunity to evaluate the Super Clean System (SCS) technology seemed pertinent. SCS is an online heat exchanger cleaning method for atmospheric and vacuum crude distillation units (CDU/VDU) that removes fouling in preheat trains, transforming it into a fully reusable product.
The CDU at JX NOE’s Sendai refinery has a processing capacity of 145000 b/d and historically required a two week timeline to clean the heat exchangers by a conventional hydroblasting method. This methodology involved the coordination of many process steps, created large amounts of wastewater and was time consuming. JX NOE was looking for other, more cost effective solutions to reduce the cleaning turnaround time and improve the reliability of its CDU turnaround. In 2000, the company elected to use SCS in a trial application on its CDU and, following validation, continued to apply the technology in subsequent years. In 2011, the refinery was shut down following the devastating Great East Japan earthquake and tsunami. Almost one year later, commercial production was restarted and JX NOE once again applied SCS from the 2012 turnaround of its repaired crude distillation unit.
History of Super Clean System
Softard Industries primarily developed the SCS technology to simplify and shorten the cleaning process for CDU/VDU units. The patented technology eliminates many of the processes and problems associated with cleaning by the hydroblasting method. Research and development started in Japan in 1996, with the first commercial application taking place in Korea in 1998. The cleaning process involves the application of an oil based detergent to the heat exchanger network whilst under oil recirculation. The oil detergent has the ability to penetrate fouling, effectively removing deposits from the internal surfaces of the tube and shell exchangers. After cooling the unit, the process crude oil is flushed out and replaced with cleaning oil such as light gas oil (LGO) or light cycle oil (LCO). Once the unit is flushed, it is put on oil recirculation, followed by application of the chemical. The cleaning solution is then circulated around all the exchangers in the circulation loop to remove fouling. This method is somewhat different to hydroblasting, which invariably involves many more processes, each with a time and cost implication and additional hazards that require control. SCS application costs are typically 30-50% those of hydroblasting, however this will depend on unit type, number of exchangers in loop, circulation loop volume and specification of cleaning oil type.
Since the first commercial application, the technology has undergone further development and optimisation, resulting in a high performance online cleaning technology. It has now been used to clean thousands of heat exchangers, with units typically being cleaned in less than 48 hours. SCS has been widely embraced throughout Japan, and Cat Tech International, a specialist catalyst handling and tower field services company, licenses the technology for application in Europe, South Africa, Asia (excluding Japan), the Americas and the Middle East.
For JX NOE, shortening the CDU maintenance turnaround time was a prime objective and key validation point of the technology. However the advantages of SCS extend beyond this and can be categorised as follows:
Time savings: unit shutdown time reduced
The ability to clean all exchangers in the network in less than 48 hours results in significant shortening of the turnaround schedule. As cleaning takes place online in a closed loop without the need to open exchangers, many of the processes associated with conventional hydroblasting such as isolations, steam purge, scaffold, bundle extraction, bundle transportation to wash area and hydroblasting are either eliminated or minimised. This has a direct impact on the time schedule but also on the costs and labour requirements associated with these processes. The simplified SCS procedure results in a reduced cleaning time line, reduced labour requirements, productivity improvements and improved reliability of the CDU turnaround.
In certain cases where there is a large number of exchangers in the preheat network, it becomes very difficult to effectively clean all exchangers by a hydroblasting method due to turnaround time constraints. Consequently, the desired heat recovery of the preheat network may not be realised as only those exchangers most badly fouled are prioritised for cleaning. In comparison, the simplicity and high cleaning effect of SCS with its ability to clean all exchangers in the loop in less than 48 hours becomes apparent. Application experiences in these cases indicate improved heat recovery of the preheat train, thus reducing fuel consumption at the furnace and lowering unit operating costs. Further energy savings come from the abolition of steam purge normally used to remove hydrocarbons when opening exchangers.
As well as for a major turnaround, the technology can also be used during a run to quickly recover heat transfer efficiency in order to manage energy consumption and unit capacity. The economics for each unit will differ and will also depend on market considerations.
Environmental impacts: waste, water pollution, air and noise pollution
Reducing the environmental impacts of refining operations is a major consideration for operators. It extends beyond legal compliance and social responsibility; it also makes financial sense:
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