Revamps 2022 Issue

was carried out over 38 hours, after 36 hours were fore- seen in the preliminary plans. For later cleanings, it is recommended to install appropri- ate manifolds and valves so two separate cleaning circuits with a pre-washer plus extractor and sand filter system plus accumulator drum can be operated simultaneously. Compared to previous treatments, cleaning times have been significantly reduced, and safe conditions for workers have been achieved. The refiner was very pleased with the results obtained. Previously, very strong odours had always been reported, and it had been fraught with danger to remove the Raschig rings, which were still dirty and highly contami- nated. With the achieved work done now, the Raschig rings were clean, no bad odours were noticeable, and further treatment by the customer was easy to perform. Case study 3: Amine unit cleaning After draining an alkanolamine system, clean water was recirculated to remove sludge and hydrocarbons. To ensure that all important equipment parts in the amine plant could be cleaned and decontaminated, two independently oper- ating circulation circuits were set using flexible hoses and mobile mixing tanks. In the first run, the flexible hoses were installed so a closed circuit could be connected between the absorber column, flash tank separator, two rich amine heat exchangers, and the four air-fin coolers up to the filter sys - tem. From there, the return flow was sent back. For better contact of the cleaning solution with the vapour phase in the flash tank separator, two valves were used to recirculate the cleaning solution into the vessel. Low-pressure steam was added to maintain 60-80°C of the cleaning solution. Excess gas was routed to a scrubber to scavenge the volatile gases. To improve the dissolution of the sludge in the bottom area of the flash tank separator, three perforated diffusers with a length of approximately 3-4 metres were inserted through the open bottom valves via packing gland systems at the bottom left, middle section, and bottom right. These quills were connected to the circuit and ensured a good agi- tation in the sludge phase. For the chemical cleaning, a 1 wt% chemical cleaning solution, based on about 20% total volume, was prepared and distributed for 12 hours. In the second circuit (see Figure 3 ), the amine regenerator with an overhead system including air-fin coolers and the overhead accumulator drum were connected via flexible

hoses to a mixing tank. Also, a 1 wt% cleaning solution with about 20% of the total volume was distributed by two pumps for 12 hours in the defined temperature range. The overhead accumulator drum was also equipped with three diffuser quills in the bottom area so the sludge could be loosened and better transported away. First, according to the usual cleaning procedures, the liq- uids in the absorber, regenerator, and flash tank separa - tor were drained, and clean water was circulated in both installed circuits. To help dissolve the fouling deposits in the columns and vessel, Turbodispin D80 was dosed into Distillation columns and heat exchangers no longer need to be mechanically cleaned, and packings can also remain in the columns during shutdowns the water and circulated for 10 hours. Subsequently, the very contaminated cleaning solution was drained, and both circulation systems were refilled with clean water. The flash tank separator was filled to 20%, and the absorber, regen - erator, and heat exchangers were filled with 30% wash water, based on the total volume. Then the appropriate amount of Kurita CD-5201 was added to use a 2% clean- ing solution. Both circuits were rinsed for 18 hours. After cleaning, the very dirty cleaning solutions of both circuits were sent to the wastewater plant. No pyrophoric iron sul- phide was detected and, as defined before, no VOCs or LEL concentrations were analysed. Conclusion Chemical cleaning has now been proven in practice at many refineries and petrochemical plants. Ensuring safe working conditions is a very important factor that must be considered during shutdown planning. Cleaning metal surfaces, remov- ing pyrophoric iron sulphide, and eliminating H₂S, benzene, and other harmful gases are very important measures. This can significantly reduce downtime and increase productivity, which helps to achieve the targets at the end of a fiscal year. References 1 Otzisk B, Chemical cleaning and degassing refinery equipment, PTQ Q1 2008. 2 Otzisk B, Urschey M, Chemical cleaning and decontamination of re - finery and petrochemical distillation equipment, International confer - ence on heat exchanger fouling and cleaning, June 2015, Ireland. 3 B Otzisk, L Uradnicek, Maximising heat exchanger cleaning, PTQ Q2 2018. Berthold Otzisk is Senior Product Manager for process chemicals with Kurita Europe, located in Germany. Email: berthold.otzisk@kurita-water.com Luis Del Castillo is Account Manager with Kurita Europe, located in Spain, focusing on refinery and petrochemical applications. Email: luis.delcastillo@kurita-water.com

OVHD accumulator

Regenerator

Reboiler

Steam

Mixing tank

Figure 3 Second cleaning circuit amine unit

Revamps 2022