Revamping a bitumen heating system
A redesigned oil based heating system for bitumen storage and sales saves energy and eliminates customer complaints.
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Tüpraş Batman refinery, located in the southeast of Turkey, is designed to process 1.4 million t/y of 15-21 API domestic crude oil. Bitumen is the main product with an approximately 60% yield. Since the refinery’s critical mission is to meet the bitumen and cutback needs of the surrounding region, storage and heating of bitumen stocks in the tank farm is a major operation in order for the refinery to meet customer needs.
Bitumen stocks at the refinery were heated by hot oil and steam. But the existing hot oil system was inadequate for heating the bitumen storage tanks. Since the main problems were rooted in the design of the hot oil system, in 2011 a revamp of the system was seen to provide the best solution to the problem.
Within the revamp project, the main purpose was to keep the temperature of the bitumen tanks and related lines at 140°C. The main problems relating to the existing system were detected. The first problem was to increase bitumen storage capacity. In the scope of the revamp project, construction of a new bitumen tank with 30000 tonnes of storage capacity was taken into account. Additionally, the hot oil system was designed in the event of any capacity increase in the future. The next problem was that the tanks far from the furnaces could not be heated easily by hot oil. Therefore, orifices for the hot oil pipelines were designed to set the oil pressure. The last requirement was the installation of ESD and DCS controls.
The new hot oil system started up with ESD and DCS control systems. After start-up of the new hot oil system, the efficiency of the system increased from 75% to 85%. Additionally, the equivalent of 10000 tonnes of CO2 emissions were avoided and a decrease of seven points in the refinery’s Energy Intensity Index was achieved. The new hot oil system also takes into account the construction of future bitumen tanks up to a total capacity of 60 000 tonnes.
Background to the refinery’s hot oil system
Before the revamp of the hot oil system, bitumen stocks in the refinery were heated by both steam and hot oil, although steam use was quite risky due to the foaming potential of the product in the event of any contact with steam. Since 2008, there had been a hot oil system for heating three bitumen storage tanks and related production and sales lines. However, due to a lack of design in the existing system, the temperature of stored bitumen could not be maintained at 140°C. Before the start-up of the revamped system, Batman refinery faced complaints from customers regarding the temperature of the bitumen sold to them.
At the end of 2011, when the previous hot oil system was constructed, it was realised that the current bitumen storage capacity of the refinery failed to meet demand in the region. In addition, customer complaints were increasing by the day in view of the hot oil system’s inability to meet the required sales temperature of the product. As a result, revamping of the existing hot oil system was decided to be the best solution. In 2011, a feasibility report including construction of a bitumen tank with a storage capacity of 30 000 tonnes and a revamp of the inefficient hot oil system was prepared. By means of basic and detailed engineering studies, the main deficiencies of the current system were identified stepwise.
Increase outlet temperature
In the hot oil process, fresh thermal oil is stored in oil drums then transferred to the expansion drum, where it is pressurised and preheated under a nitrogen blanket. Oil from the expansion drum is pumped to the furnaces. In the previous system, there were two furnaces, each having a lower heat load than the new ones. This means that the outlet oil temperature of the furnaces could not exceed 160°C and the efficiency of the system remained around 75%. Heat and hydraulic capacity calculations demonstrated that the design capacity of the furnaces and pumps was not enough to supply the required energy to the system. In the new system, two furnaces, each having a 20% higher heat load, were to be used so that the outlet oil temperature was able to reach 270°C. Unlike in the previous system, DCS and ESD control mechanisms were installed in the furnaces to contribute to process safety.
The system is optimised against high energy losses and, because of a bypass line placed between the hot oil supply and return lines, it has the capability to run in different modes:
• High temperature mode (270-230°C): When the two furnaces run parallel to each other, the system is capable of supplying maximum heat load. In this case, the system could supply the heat load required for heating three bitumen tanks, three sales lines, two production lines, two bitumen feed lines, and one suction heater in winter conditions
• Normal temperature mode (180-140°C): The system is capable of supplying the 2.2 Gcal/h heat load required for the whole system, apart from the suction heater
• The furnaces can be operated after circulation as long as there is a 40°C temperature difference between the furnace inlet and outlet temperatures.
Hot oil heated in the furnaces is conveyed to the collector and then goes to the system users which are tank coils, production and sales lines, and suction heaters.
Previously, at points distant from the furnace, lower oil flow resulted in lower product temperature in the storage tanks, which led to complaints from customers. As the distance between the pipelines and the furnaces increases, the temperature of hot oil flowing through the jacketed bitumen lines gradually decreases. As a result, at points distant from the furnace outlet, the existing system could not supply the required heat. To solve this problem, firstly the diameter of the pipelines was widened from 50mm to 100mm. Then, orifice designs with different diameters throughout the lines came into play. Descending orifice diameters lead to oil at a low flow rate but high pressure. In this way, and different from the previous system, even the most distant lines could be heated effectively. In addition to the orifice system, the isolation thickness of the widened pipelines was increased from 50mm to 100mm.
New storage tank construction
Within the scope of the revamp project, a new bitumen tank was to be constructed with a suction heater that could supply an almost 20°C differential temperature between the tank outlet and the truck loading arm. For the new tank, feasibility calculations showed that the insulation thickness for a new bitumen tank could be 150mm, compared with the previous designs allowing 100mm of isolation thickness. Construction of a new bitumen tank with a suction heater enabled the sale of product even if the product temperature was at 110°C.
Hot bypass line
One of the most important and notable points of the redesigned system is the bypass line placed between the furnace inlet and outlet.
In the previous system, although the outlet oil temperature of the furnace was almost 160°C, the oil temperature returning to the furnace was about 100-110°C. Since the furnace could not supply the required differential temperature, the efficiency of the furnace was almost 75%. In the new design, a bypass line has been installed from furnace outlet to furnace inlet which enables a 40°C temperature difference between inlet and outlet. This enabled oil to return to the furnaces with a temperature 40°C below the outlet temperature and the efficiency of the system rose to 85%.
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