Corrosion resistant resins, filament wound fiberglass composites and creative design engineering have been key to Ollearis’ work on several large petrochemical plant components for a subsidiary of SABIC. The components are shown here before shipping and installation.
Photo credit, all images: AOC
Composite materials are known for their durability in highly corrosive environments, but for optimum performance it is essential to select the right resin for each application. The Petrokemya petrochemical complex, a subsidiary of SABIC (Riyadh, Saudi Arabia), in Jubail, Saudi Arabia, produces a variety of basic chemicals such as ethylene, styrene, chlorine, industrial crude ethanol and more. For the production process, the complex required a combustion unit with several large components and pipes that must withstand hydrochloric acid without corroding.
The design and manufacture of the combustion unit quench tank, scrubber, exhaust tank and associated vessels and piping was entrusted to a team including corrosion-resistant equipment manufacturer Ollearis ( Martorelles, Spain), contractor China Tianchen Engineering Corp. (TCC, Tianjin, China) and the engineering company John Zink Hamworthy Combustion (Tulsa, Okla., USA). These components had to withstand contact with hydrochloric acid, overcome several design challenges, and be a cost effective solution.
Glass fiber reinforced composites were chosen as a material capable of withstanding highly corrosive chemicals, while providing a more cost effective solution than specialty metal alloys. All major components were made from Fiber Reinforced Plastic (FRP) with a few minor exceptions including the lifting and holding lugs (stainless steel), spray nozzles (thermoplastic or metallic) and gasket packing. purifier.
To provide the most economical solution while meeting performance requirements, Ollearis turned to three Atlac AOC resins (Collierville, Tenn., US). “We selected the resin types using the AOC chemical resistance guide as well as the expertise of the AOC technical service team, taking into account the fluids handled and the design temperatures detailed by the customer. . It was necessary to ensure that the proposed resins would perform well under [the required] conditions ”, explains Adriano Ureña, Technical Manager at Ollearis.
Quench tank and scrubber during testing and fit testing prior to installation.
Ollearis selected Novolac Atlac 590 epoxy resin for the quench tank, which is the first phase of the gas cleaning process. The reservoir is 11.8 meters high with an inner diameter (ID) of 3 meters. The challenge is that when operational, the exhaust gases from the combustion unit enter this quench tank at a temperature of around 300 ° C, and then are cooled very quickly by water sprayed by water. nozzles near the gas inlet. Atlac 590 was chosen to provide resistance to hydrochloric acid solution and high temperature resistance retention required.
For the 14.10 meter high scrubber, the 39.7 meter high exhaust stack from which the purified gas is released and the 1.45 meter long duct connecting the scrubber and the quench tank , the bisphenol A vinyl ester epoxy resin Atlac 430 was chosen. It is a versatile standard product that matches the comparatively less harsh temperature conditions for these components – design temperatures of the scrubber and exhaust stack reach up to 85 ° C. The scrubber is exposed to a hydrochloric acid solution from the quench tank as well as a sodium hydroxide solution present in the wash water which is used to neutralize the acid. The exhaust stack is also exposed to air containing a small amount of hydrochloric acid and wet chlorine.
For the piping system installed around the scrubber and quench pan, Atlac 383 unsaturated bisphenol A polyester was chosen for its chemical resistance against acidic and caustic fluids at a lower cost than standard vinyl ester resins.
The quench tank, scrubber, and cylindrical stack parts were fabricated through a hybrid manufacturing process, combining wet filament winding with an outer layer of bidirectional woven fabrics applied simultaneously. This combination produced parts with better mechanical properties both in the hoop direction (from the filament winding) and in the axial direction (from the fabrics, which align with the axis of the part. ). The addition of woven fabric also reduced the weight percentage of fiberglass per part, from 70% for a part fully wound in filament to 55%. This increases the amount of corrosion resistant resin per part. Other components were made by hand.
Solve design challenges
Ollearis faced several challenges when designing the equipment for this project. A challenge arose from the need to include a high resin corrosion barrier layer on the inner surface of the quench tank, which presented the potential for cracking – or cracking – due to thermal shock during operation. The team improved the component’s resistance to thermal shock by reinforcing the corrosion barrier with a carbon fiber surfacing veil.
The final system installed at the Petrokemya plant.
A second challenge was that Ollearis had to find a way to support the weight of the packaging inside the scrubber – the packaging is the material that removes gases from the air passing through the scrubber. To solve this problem, Ollearis installed a composite grating under the lining, supported by a composite ledge and two composite beams. The rim and beams have a hollow rectangular cross section, and the rim is filled with polyurethane foam. The flange was fabricated directly in the cylindrical filament wound scrubber in one piece; bonding after manufacture would present a risk of detachment due to the loads due to the weight of the packaging. The beams are supported by specially designed composite nozzles glued to the scrubber shell.
A third design challenge came from the fact that the quench tank and scrubber operate under vacuum but have flat bottoms – flat composite panels have low resistance to pressure and vacuum and generally need to be very thick to withstand heavy loads. such fillers, which makes them expensive to manufacture. To achieve the objectives of the project, Ollearis developed a less expensive solution using a sandwich construction comprising a resin-impregnated 3D fiberglass fabric core covered with composite skin layers, in order to reduce the cost and weight of a solid composite part.
For this project, the composite components were designed and delivered in 2016, and the final installation was completed in 2017.