Sulzer completed an overhaul of three General Electric steam turbines and five Clark compressors for a large ethylene plant in Colombia. Sulzer’s service centers in Texas and Bogotá worked together to inspect and repair the three turbines. Sulzer staff helped the customer with project planning, full commissioning, and testing within a very tight timeframe.
The city of Barrancabermeja is known as the “oil capital” of Colombia — a good location for an ethylene plant. The customer’s mill can produce 44 000 tons of ethylene and 8 800 tons of propylene per year — which equates to 144 tons per day. Such mills run continuously. It is of vital importance that regular, preventive maintenance is performed to keep the installations running reliably and at maximum efficiency. To minimize production losses, the time for maintenance breaks must be as short as possible. For its steam cracking process, the plant in Barrancabermeja employs steam-powered turbine compressor trains before the distillation phase of processing the gases. Ethylene — the world’s most-used organic compound Ethylene, also named ethene, is a colorless, flammable gas. Ethylene has the formula H2C=CH2 . It is widely used in the chemical industry. The global production of ethylene exceeds that of any other organic compound. More than half of the ethylene supply goes toward making polyethylene, which is the world’s most widely used plastic. Polyethylene is used to make films in packaging, carrier bags, and trash liners.
Ethylene is often produced in the petrochemical industry by steam cracking. This process converts large hydrocarbons into smaller ones and introduces unsaturation. In steam cracking, gaseous or light-liquid hydrocarbons are heated to 750 – 950 °C. This initiates numerous free-radical reactions. These reactions only take place briefly. Once the cracking begins, the gas is immediately quenched to stop these reactions. Ethylene is separated from the resulting complex mixture by repeated compression and distillation. Other methods produce ethylene by using naphtha or gas-oils.
Fig. 1 Ethylene is the base for many packaging products, such as PET bottles.
Planning started one year ahead
Carrying out maintenance during a planned outage on time and within budget requires considerable planning and careful management throughout. Since 1999, the Colombian mill relied on Sulzer’s expertise in the repair of turbomachinery equipment. The customer initially contracted Sulzer to perform all the planning activities for the compressor deck during the outage and to inspect and repair the spare set of rotors. Sulzer exchanged the running compressor rotors with the shop repaired spare units which were repaired in Houston before, to allow fast turnaround during the outage. Subsequently, the customer also asked Sulzer to carry out all the compressor deck activities during the outage. All of this work had to be completed within 30 days.
Those who have ever organized a wedding or similar event know how much time is required to plan a one-day event and how much discipline it takes to keep activities within a budget. Imagine how much time it takes to plan a 30-day overhaul with 12 service technicians. Sulzer deployed two project managers during the planning phase to provide a project execution plan and an overall schedule. The planning started over a year ahead of the actual work.
Excellent project management
One of these project managers was José Saldana, a talented young engineer who speaks fluent English and Spanish. “The project manager is responsible for the smooth workflow of the whole project. One important planning step is to break down the overhaul maintenance work into sequences of work. Then we list all requirements for this sequence, timeframe, and how many people are needed to manage the project on time.”
Uncertainties have to be considered in planning as well. Saldana explains, “Jesus Leotaud, the project manager from the Sulzer Bogotá office, always checked whether the equipment and spare parts we needed were on hand in the right quality at the customer’s warehouse. We also checked whether tools, lifting devices, or cranes were available. Such detailed planning has to consider budget aspects so that the team can complete projects safely, on time, and within budget.”
Furthermore, good communication is vital. Saldana continues, “When the overall schedule was set up, we also established a communication plan. People underestimate how important communication is for the success of a project. Downtimes are very often caused by a lack of communication or by uncertainty about the line of communication. It is important for project leaders to speak the local language.”
Compressor deck arrangement
With the working schedule established, Sulzer assigned a team of 12 field service technicians to complete the maintenance project. The ethylene plant uses several General Electric steam turbines to drive a series of Clark (today Siemens Dresser-Rand) compressors — all common equipment within the petrochemical industry and very familiar to the Sulzer engineers. The compressor deck arrangement in this project consists of two turbines each powering single compressors and a third turbine running a train of three compressors. Each arrangement has a unique setup and operating specifications, which are detailed by the original equipment manufacturers (OEMs). Each piece of equipment has a unique designation that ensures that all the information relating to its maintenance and setup is recorded correctly and that the right spare parts are stocked. The compressors are designed to take the cracked gas from an intake pressure of around 1.3 bar (19 psia) to a discharge pressure of around 35 bar (510 psia), having passed through 47 stages of compression (Fig. 2).
Fig. 2 Compressor trains for the rotor exchanges done by Sulzer.
Overhaul and testing in Houston
The spare rotors that were prepared and installed by the Sulzer Field Service team had been previously remanufactured at the Houston facility; each component had been brought back to engineering specification. “Houston is our flagship repair center.” José Saldana adds, “We have a systematic approach with checklists for each remanufacturing order. Starting with an initial inspection, and comprehensive measurements followed by grit cleaning and disassembly with further non-destructive testing (NDT). This allows us to determine exactly the repairs we will recommend to the client. Each inspection and test report provides details of the scope of work for any proposed repair, which may extend to remanufacturing of the rotor shaft or compressor disks. Extensive machining capabilities and state-of-the-art five-axis CNC mills enable the experienced engineers at Sulzer to create new components, including complex turbine blade designs.”
In cases where the rotor has suffered a shaft failure at one end, it may be necessary to replace the end section of the rotor shaft with a shaft stub. Fixing the stub interface to the shaft is extremely demanding. At Sulzer, a PhD-level materials engineer manages the material selection and welding process. In some cases where original components, such as impellers, are damaged, it is necessary to create new parts. If no original drawings exist, Sulzer engineers can still manufacture new components through reverse engineering.
Sulzer engineers use finite element analysis as part of the design process to ensure the mechanical integrity of the impeller design. After manufacturing, the new impeller passes harmonic impact testing to validate the design. Once the engineers have refurbished or remanufactured the components, they then progressively restack and balance the rotor at each stage. After the entire rotor assembly is complete, it is ready for a rigorous quality control inspection. One of the last steps is to carry out an at-speed balance test, the parameters of which are normally agreed on with the client prior to testing. For projects that involve large components, such as the steam turbines from the plant in Colombia, the balancing process requires a large and specialized balancing bunker. The Sulzer balance bunker in Houston is equipped with advanced electronics and diagnostics to provide state-of-the-art analysis capabilities (Fig. 3).
Parameters of the high-speed balancing bunker in Houston are:
- Rotor weight capacity: 25 tons
- Max operating speed: 40 000 rpm
- Max rotor length: 7.11 meters
- Max rotor diameter: 2.4 meters
Fig. 3 Balancing at the Sulzer shop in Houston, TX, USA.
Sulzer handed the complete compressor deck back to the satisfied customer on time. After the original project was completed, the plant engineers requested some additional assistance with the commissioning and startup of the compressor deck. Sulzer sent the field service team back to the plant. The experience and expertise of the team enabled the plant to complete the commissioning phase and get the plant back into normal production after the overhaul.