Chemical cleaning and fouling removal technologies
Chemical cleaning technologies for the removal of hazardous gases and problematic fouling deposits are explained
Berthold Otzisk and Luis Del Castillo Kurita
A refinery or petrochemical plant shutdown can last several weeks if storage tanks, vessels, distillation equipment, and pipework have to be cleaned exten - sively. The reduction of cleaning and shutdown times helps minimise cleaning and maintenance costs. The safety of the employees who have to enter the columns, vessels, and tanks is always the top priority. Under no circumstances should they come into contact with hazardous gases or other dangerous substances. The use of chemical clean - ing programmes is part of very well-developed safety concepts. Chemical cleaning and degassing concepts have proven very successful in recent years. Cleaning and decontamination A shutdown is a very labour-intensive time and requires perfect organisation and scheduling. Often hundreds of workers are on site for mechanical cleaning, repair, or replacement of equipment, where every delay means high production losses. Persons in charge try to minimise expo - sure of workers to any situations where health risks or pyrophorically induced fires could be initiated. The forma - tion of iron sulphide (FeS) is very common in oil refineries and ethylene production plants. Iron sulphide deposits accumulate in distillation col - umns, pipes, trays, structured packings, vessels, and heat exchangers. During shutdowns, there is a high potential for spontaneous ignition in the presence of oxygen due
to the pyrophoric iron sulphide nature. Keeping such deposits wet to avoid unwanted fire hazards is not a good option. Pyrophoric materials must be eliminated and removed safely. Meanwhile, very efficient cleaning and degassing pro - grammes have been established where chemical additives can be used to clean the equipment quickly in a proper way. Pyrophoric iron sulphide species are neutralised and elimi - nated, reducing the risk of unwanted ignition in contact with the ambient air. Distillation columns and heat exchangers no longer need to be mechanically cleaned, and packings can often remain in the columns during shutdowns if they are clean and no longer contain pyrophoric iron sulphides. Dangerous emissions, including benzene, H 2 S, NOx, CO 2 , SO x , and VOCs, can be reduced to a minimum. This is becom - ing increasingly important in today’s world. The high partial pressure of light hydrocarbons makes it more difficult to separate them from other volatile gases in the vapour phase. To trap (scavenge) light hydrocarbons into the wash water, the gas molecules need to be polarised. This polarisation can be achieved by electric induction or by using chemical clean - ing programmes. Downtimes can be shortened, resulting in higher productivity, reliability, and operability. Chemical cleaning methods After distillation columns, vessels, heat exchangers, and piping have been drained for cleaning, it is common to
Recirculation method
Steaming method
To are
To are
Sewer
Steam
Figure 1 Chemical cleaning methods
27
Revamps 2022
www.digitalrefining.com
Powered by FlippingBook