Bronswerk Heat Transfer explains how a serious design diet enabled dramatic cost reductions at an Iranian petrochemical plant
For obvious reasons, a large number of upstream and downstream projects have been put on hold in Iran over the last few years. One such project was the Bid Boland II Gas Processing Project, scheduled to be built in Khusestan Province in the country’s southwest. Although awarded to EIED (Energy Industries, Engineering & Design) in November 2007, Bid Boland had been postponed three times over the past few years. It was only in 2015 that a new owner – Persian Gulf Petrochemical Company – fully revived the project. This multi-billion euro development consists of a refinery with a processing capacity of 57 mcm per day of sour and sweet gases from four gas and NGL plants in the region. Additionally, it includes 600 km of feed and product pipelines, an export terminal in Mahshahr and a 600-unit residential camp, as well as industrial and non-industrial buildings and related facilities. Production capacity at the refinery would consist of 15 bcm per year of sweet gas, 1.48 million tonnes per year of ethane, 1.51 million tpy of LPG and 0.86 million tpy of NGL. This project is characterised by huge dimensions and big numbers, where any alternative solution in terms of plot space, energy consumption or weight reduction has the potential to translate into an enormous positive impact on the overall capital investment and also the operational costs of this project. The new owner has taken this opportunity to search for such alternative solutions with regards to the shell and tube heat exchangers of the Bid Boland gas treating plant.
Big numbers, big challenges It is clear that the project is characterised by its size. Specifically, that means a lot of engineering, plot space, transportation, construction, materials, energy consumption and maintenance. The plant consists of four trains, each train responsible for processing the sour and sweet gases into sweet gas, ethane, LPG and NGLs. Zooming in on the shell and tube heat exchangers, the original design consisted of four treated gas coolers, four inlet gas coolers and one gas heater per train. The three heat exchangers are needed for the treated gas cooler (cooling gas after treatment), the inlet gas cooler (cooling gas before it enters the next phase), and at a later stage, the gas heater (for heating the gas before entering the condensate drum). Altogether, these 36 heat exchangers had a combined weight of 1,704,400 kg. They also required a substantial amount of plot space, not to mention energy consumption, the cost of the materials needed to fabricate them, installation and spares for maintenance, the costs of transportation and the impact on the environment.
Design on a diet Because of the scope of this project, alternative solutions can have an enormous effect. Luckily, the new owner was very interested in alternative solutions and decided to grant Bronswerk (BHT) a chance to re-evaluate its plans for heat exchangers. BHT has a proven track record in the thermal and mechanical design and its engineers are trained to optimise the design, taking the overall process into consideration. That includes taking care of all client requirements regarding process design, thermal design, mechanical design, overall project execution steps, material handling and maintenance. For the treated gas coolers and the inlet gas coolers, the company’s engineers immediately saw ways to reduce the number of shells. Starting from scratch, they re-considered operating criteria such as the most convenient solution regarding pressure drop, the Logarithmic Mean Temperature Difference (LMTD) and an optimal heat transfer coefficient. They were thus able to optimise the design of the treated gas cooler and the inlet gas cooler significantly. The number of shells was reduced to just two exchangers per train – and 50% of these could also achieve a weight saving of more than 35%. It was also achieved with a vibration-free design which could be handled on site. The new design saw a total weight reduction of 600,000 kg, greatly reducing plant costs, operational costs and required plot space. Although the weight of each item in the process increased, the overall number of items decreased. The design also used less steel, meaning a 50% reduction in crane and handling cost, a 40% reduction in transportation, 50% fewer piping connections and all in all, considerably less capital investment. See image 1 for comparison between the conventional design (two heat exchangers) and the improved design (one heat exchanger). Table 1 and 2 indicate the differences between the conventional and improved designs for the treated gas coolers and inlet gas coolers.
Heat improvements For the gas heater design no significant savings in the thermal design could be achieved. However, it was possible to optimise the design by changing the nozzle locations. Instead of radial nozzles, axial nozzles were used, reducing the overall plot space and weight of the channels. In addition, all welding was eliminated by the use of a forged channel (see image 2). The benefits are less material and no welding – meaning no welding documentation was required and a minimal Non Destructive Examination (NDE) was needed. For Bronswerk, the lead-time was reduced significantly and risks during project execution minimised. Most importantly, this solution has resulted in significant client benefits like greater integrity (owing to the weld-less design, less plot space and reduced overall weight. These heat exchangers are all vibration free and have a complete thermal guarantee. Table 3 shows a comparison between the conventional and alternative designs.
Less is more With the Iranian market opened up again, many more projects are being revived. That creates a lot of opportunities for both plant owners and operation managers – who might now be able to afford another look at the cost of ownership of the plant, in terms of energy consumption and maintenance, and the capital investment for material and plot space. Bronswerk is keen to take up such challenges, and the above case study highlights the results that can be achieved. In this particular scenario, the number and – more importantly – the total weight and plot space have been reduced dramatically. Especially in the case of the inlet gas cooler and the treated gas cooler, these changes will have an impact on the total layout of the plant, reducing the necessary heat exchangers per train from four to just two, resulting in a reduction of installation and operational costs. Meanwhile, the gas heater also benefits from greater higher integrity as a result of the weldless design. Smarter design directly translates into advantages for both the plant owner and the plant manager. Having been granted the chance to alter the cost and efficiency of this project radically, Bronswerk engineers are keen to be given more opportunities to do similar work in the future.