A refinery’s journey to energy efficiency
Identifying a series of areas for improvement transformed the energy performance of a refinery with a 60-year history
ZAFER KARATAS and SENA TURKOGLU
Tüpraş Batman Refinery
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The city of Batman is at the centre of a region of Turkey where 72% of state crude production takes place. Located in the south east of Turkey, Batman refinery is one of four refineries of Turkish Petroleum Refineries (Tüpraş). It was commissioned in 1955 as the first refinery in Turkey, with a crude oil processing capacity of 330 000 t/y. Following growing demand in Turkey for crude oil and its refined products, another crude processing unit was commissioned in 1972, taking Batman refinery to its current processing capacity of 1.1 million t/y. Besides Batman city itself, the refinery also has the advantage of being located near to other domestic sources in the region, so it was designed to process 15-22 API local crude.
The refinery consists of the following processing units: two CDUs, a VDU, a naphtha splitter, a straight run naphtha stripper and utilities, including wastewater treatment, a power plant and a tank farm with an oil heating system. Since it does not have any upgrading units, its configuration is simple and its Nelson complexity index is 1.83. The refinery therefore runs as a bitumen and cut-back production plant. Intermediate products like straight run naphtha, kerosene, gasoil and heavy gasoil are sent to another Tüpraş refinery, Kirikkale, for further conversion and processing. Kirikkale’s final products of gasoil and gasoline are then returned to Batman to meet demand in the city and its surrounding region.
Although the refinery was originally situated far from any centres of population, it is now surrounded by urban development. In addition, since the refinery is 60 years old, energy efficiency was not considered an important target in its original design. For both of these reasons, the refinery needs be sensitive and ready to take precautions to support the environment, with due regard for emissions and human health. Revamping of old and inefficient equipment and systems is another important issue that requires the refinery’s attention with regard to economic performance and reliability.
After the handover of Tüpraş Batman refinery from the government to Koç Holding in 2006, several projects to improve energy efficiency and environmental performance, including many refinery revamp projects, were implemented.
Strategic planning and implementation
Since the scale and complexity of the refinery was known, it was not difficult to figure out the gap between actual energy consumption and target consumption based on a benchmark case. Additionally, preliminary calculations were made in order to see the potential for energy savings in the refinery. These calculations covered topics such as energy savings in the heat exchanger network by setting a delta T approach; existing process furnace efficiencies and their potential savings; comparison of steam production costs in different boilers at different grades; and a comparison of cogeneration, back pressure turbine and extractive condensing turbine efficiencies. After identification of areas for improvement (AFI) and their potential savings, a series of actions was taken and project implementations were set in motion.
AFI-1: Increase condensate recovery
Steam leaks were observed everywhere in the plant. Most of the traps were leaking and at many points in the steam network there were no traps. A condensate return system was not operated. Estimations based on some of the leaks gave a loss of >100 kg/h each. In order to enhance the overall efficiency of the refinery and increase steam and condensate recovery, a project team was established with the support of all refinery staff.
Within the scope of the project, 300 traps were replaced and many condensate collectors, 2000 metres of carbon steel pipe, 5000 metres of insulation material, a condensate flash drum and a condensate pump were installed. The main condensate collecting lines were divided into two components for clean and oily condensate. Oily condensate was routed to a newly installed condensate recovery and treatment system, including precoat filters and activated carbon filters, in order to remove oil and recover flash steam in the surface condenser. Moreover, instead of raw water, demineralised water was used in the system as a cooling utility. In this way, the temperature was increased from 20°C to 67°C before the existing dearator in the power plant, and steam consumption in the dearator decreased by 55% as a consequence.
With the increased condensate recovery ratio, the utilisation capacity of the demineralisation plant was reduced to 50% of its base capacity, resulting in 10 540 Gcal/y of energy saving.
AFI-2: Reduce steam leaks and consumption
As AFI-1 indicates, prevention of steam leaks caused by instrumentation tracing lines vents, direct open heating vents and steam traps blowing to atmosphere was carried out continuously between the years 2006-2011 across the site. In other words, instrumentation tracing line vents were collected in a separate flash drum and the produced flash steam was used in the dearator. Additionally, new steam tracing lines and steam traps were installed for heating the bitumen production lines. Some of the existing blowing traps were replaced and other leaking traps were repaired. In parallel with AFI-2, implementation of AFI-3 was carried out.
AFI-3: Review power and steam generating strategies
Specifications for the steam boilers and turbogenerators in the power plant are shown in Table 1. Since the boiler tubes underwent widespread retubing and plugging in the past, their efficiencies and reliability were low. Boiler H-504 did not have the capacity for required electricity production, therefore two of boilers H-501, H-502, H-503 were run together with H-504 in order to supply steam demand for the turbogenerator and so sustain operational reliability. The most efficient boiler, H-508, was run for process heating purposes at 13 barg and 250°C.
The situation for the turbogenerators was similar: their efficiencies were very low and their electricity unit production costs (depending on the load) were very high, in the region of 4-8 times that of the grid, except for back pressure production. However, the back pressure turbogenerator was designed by taking into consideration a thermo-catalytic cracking unit that was dismantled in 2007, hence its design capacity was too big and this resulted in a case of unbalance in steam-electricity production.
Since there were boiler tubes failures every 3-4 months, the first action for improvement made was to improve the quality of demineralised water in order to reduce failures, and to increase the reliability and efficiencies of the boilers. As a result, the number of online boilers was decreased subsequently from four to one and H-508 began to be employed for both turbogeneration and process heating by using the existing let-down station. With the combined effects of AFI-1/2/3 in place, the resulting process steam and energy consumption figures are shown in Table 2.
As a result, between 2006 and 2011, process steam consumption was reduced from 264 000 t/y to 182 000 t/y. This means that over a period of five years there was a 31% reduction in total process steam consumption, or a 45% saving in steam per tonne of crude processed, resulting in 75000 Gcal/y of energy saving based on total annual process steam consumption, and 130000 Gcal/year of energy saving based on tonnes of crude processed.
When it came to electricity production, import from the grid was maximised with minimal site production. Later, electricity production was stopped completely for reasons of economy. Additionally, the standby conditions of the existing diesel generator were increased and, by taking the peak electricity demand of the refinery into account, one more diesel generator was installed in case of emergency and to provide redundancy. The inefficient J-503/504 condensing turbogenerators, with just 17% operating efficiency (based on electricity produced per unit of fuel consumed in the boiler), were stood by as redundant items but received weekly maintenance, for instance lubrication of rotors and bearings. As a result, 53 000 Gcal/year of energy saving was accomplished.
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