Measures and effects of oil refining companies in optimizing energy use to reduce consumption

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The energy-saving and water-saving measures adopted by Dalian Petrochemical Company of China National Petroleum Corporation in its power and production systems have optimized the company’s overall energy consumption level, improved the efficiency of energy and water use, significantly reduced total energy consumption, and yielded notable economic benefits. 1 Main energy-saving and consumption-reduction measures 1.1 Production system (1) Optimizing the crude oil composition: Taking into account the characteristics of the facility, efforts should be made to select crude oil combinations that involve low processing costs, short processes, and a high degree of refinement. (2) Optimize the processing structure: To maximize the efficiency of the installed equipment and optimize energy usage, the structure of the equipment and the processing methods are adjusted in a timely manner based on market demands, thereby optimizing the production structure. By taking advantage of the favorable conditions for high-load operation in secondary processing, propylene production is increased to provide sufficient resources for chemical manufacturing. (3) Optimizing device operation: By addressing in a centralized manner the \"bottleneck\" issues that hinder the devices from increasing production volume, especially during the summer, targeted efforts were made to optimize their operation. This approach effectively alleviated the constraints imposed by these system bottlenecks on production, ensured that the devices could operate at full capacity, and reduced energy consumption across all devices while simultaneously cutting down system emissions. By adjusting the process and increasing the cooling area, the problems of diesel output from the 6.0 Mt/a distillation unit, atmospheric residue output, and high temperature at the top of the initial distillation tower were resolved ； By utilizing idle coolers, the issue of low cooling load for C6 in the continuous reforming unit was resolved ； By replacing the cooling tank and adjusting the operations, the problem of high temperature in the oil sent out from the bottom of the vacuum tower in the 4.5 Mt/a distillation unit was resolved. The resolution of the above issues ensures the operation of the continuous reforming unit under high load. The 300kt/a paraffin solvent dewaxing unit resolved the issues associated with the solvent recovery system, such as fluctuations in steam pressure that affected the heating temperature for recovery and thus limited the processing capacity, by optimizing the steam supply scheme for the steam pipeline network, thereby increasing the unit’s processing capacity. 1.2 Fuel Gas System: As the variety of crude oils imported for processing increases, and Daqing crude oil is blended with Russian crude oil, the sulfur content in the gas in the gas pipeline network rises. An increase in sulfur content causes severe corrosion in the convection chambers and rear heating surfaces of heating furnaces and power plant boilers. Especially in power plant boilers operating at low load levels during summer, corrosion and scaling lead to blockages in the economizers, forcing the shutdown of the boilers for cleaning every 2 to 3 months. These problems caused by low-temperature dew point corrosion have an adverse effect on heating furnaces and boilers in terms of reducing smoke emission losses and improving thermal efficiency. 1.2.1 Technological upgrades for desulfurization to improve the quality of fuel gas: To address the issue of increasing sulfur content in the gas in the pipeline network, a new sulfur recovery unit with a capacity of 7,000 t/year was constructed, utilizing a partial combustion method and a two-stage conversion Claus process for sulfur production ； The exhaust gas treatment employs a reduction-absorption process, achieving a sulfur recovery rate of 99.8% ； All acidic gases from the plant are incinerated to meet environmental emission standards, ensuring that such gases do not enter the gas pipeline network. Secondly, the dry gas desulfurization systems of the 3.5 Mt/a heavy oil catalytic cracking unit and the 500 kt/a steam cracker were upgraded, reducing the H2S concentration in most of the dry gas fed into the pipeline network to 20 mg/m3, thus meeting the specified requirements. The implementation of the above measures has improved the quality of the fuel gas, not only ensuring the reliability of the gas pipeline network but also significantly reducing corrosion and ash deposition in the heating furnaces. The exhaust temperature of these furnaces has decreased by an average of 10°C, thereby improving their thermal efficiency. 1.2.2 Balancing excess gas: On the one hand, the gas production is reduced by optimizing the process control parameters of heavy oil catalytic cracking, catalytic reforming, atmospheric and vacuum distillation, and gas separation units ； On the other hand, measures have been taken to increase the demand for fuel gas; the No. 2 and No. 3 boilers in the power plant, as well as the lubricating oil furfural refining units and atmospheric pressure/vacuum burners, have been modified to use gas as fuel. The boilers in the power plant burn gas to produce medium-pressure steam, which is used to drive turbines for electricity generation, thereby achieving combined heat and power production. After desulfurization, the gas is sold to the domestic gas distribution network, which not only solves the problem of excess gas but also generates economic benefits. 1.2.3 Improving the thermal efficiency of the heating furnace (1) Increasing the oil temperature entering the furnace reduces the load on the heating furnace, thereby improving its thermal efficiency. (2) Raise the temperature of the combustion air, improve heat transfer characteristics inside the furnace, and enhance the combustion efficiency. (3) Measures such as installing additional air preheaters, spraying ceramic fiber materials inside the furnace, replacing insulation materials, and sealing gaps are taken to reduce heat losses in the heating furnace and improve thermal efficiency. (4) Utilize the company’s existing production information platform to develop a dynamic management system for the entire plant’s heating furnaces. This involves transmitting parameters related to the heating furnaces from the DCS systems in various workshops, as well as laboratory analysis data on the exhaust gases from these furnaces, to the information platform via the company’s local area network, thereby establishing a real-time dynamic management system for parameters such as the excess air coefficient and thermal efficiency of the heating furnaces. (5) Take measures to improve the control instruments and other facilities of the heating furnaces throughout the plant, to ensure their stable operation. 1.2.4 Advanced processes are employed to reduce fuel gas consumption. In 2004, the 250 kt/a lubricant clay refining unit was upgraded by adopting advanced, energy-saving and environmentally friendly low-temperature nitrogen removal adsorption processes to cut fuel gas consumption. 1.3 Steam System The steam power system accounts for 1/3 of the total energy consumption, and its optimization plays a crucial role in saving energy across the entire plant. 1.3.1 Renovating steam piping networks to reduce heat loss; since 2003, ASPEN online monitoring for steam supply and demand systems has been in use ； Transform and optimize the system piping network, eliminate dead ends, establish a closed-loop operating system, and reduce steam drainage and venting ； Concentrate on repairing and improving the insulation materials throughout the entire pipeline network; add insulation to exposed valves and pipelines, repair leaking sections of pipes and valves, and install traps in a proper manner. 1.3.2 Utilizing steam resources at various stages to improve energy efficiency: To ensure the effective use of steam, its energy potential is exploited in a step-by-step and repeated manner. The steam used for process equipment is then employed for pipeline heating; the waste steam resulting from heating at 1.0 MPa (at 0.3 MPa) is used to heat pipelines containing heavy oil, paraffin, etc. The condensate water generated as a result of this heating is collected and sent back to the power plant, where it is processed to produce steam for the boilers, thereby enabling hierarchical utilization of the steam system. In applications where the heating requirements, such as tank heating or pipeline tracing, are not high, self-generated steam or waste steam is always used for heating. 1.3.3 Optimize the steam system to achieve co-generation of power and heat. Optimize the steam system to reduce heat losses in the temperature reduction and pressure reduction devices, thereby enabling co-generation of power and heat. By utilizing the flue gas heat from a 3.5 Mt/a heavy oil catalytic cracking unit, the waste heat in the flue gas is recovered through a waste heat boiler to generate medium-pressure steam at 3.5 MPa. Each year, catalytic cracking units generate 1,870 kt of medium-pressure steam, which is used in power plants to drive turbines for electricity generation, thereby recovering electrical energy ； At the same time, the low-pressure steam (1.0 MPa) generated is fed into the plant’s pipeline network to supply steam for the production units, thereby enabling an optimized combined heat and power operation mode for both the production units and the power plant. The implementation of this optimization technology enables a stable balance between steam supply and demand, as well as between power generated internally and that purchased from external sources, all within an optimized framework that ensures compatibility in terms of energy quality. This results in an energy system that makes comprehensive use of energy based on its different levels of efficiency. 1.3.4 Recover the waste heat from recovery units to replace fresh steam, thereby optimizing the operation of steam-generating units such as heavy oil catalytic cracking, continuous reforming, and ethylbenzene/styrene processes, improving steam quality, increasing steam production, and reducing the consumption of fresh steam. 1.3.5 Optimize system operation to avoid steam waste: By conducting a thorough inspection and calculation of the steam usage points and extraction points in the pipeline network, appropriate optimization measures are taken to prevent steam from being wasted. 1.4 Water Systems 1.4.1 Utilizing seawater desalination technology to develop new water sources – By employing seawater desalination technology to create new water sources, fresh water consumption can be reduced significantly. 1.4.2 Deeply develop recycled water resources to replace freshwater; implement recycled water treatment technologies to substitute for freshwater resources. Fresh water is produced by carrying out advanced treatment of wastewater using biochemical filtration and membrane separation technologies. The wastewater undergoes treatment via BSFFR submerged biochemical reaction, rapid mixing flocculation, and DAF/MMF air flotation filtration processes, followed by a UF+RO1+deaeration+RO2 process; as a result, the treated water meets the standards for makeup water for circulating water in oil refining plants (water used to replenish circulating water systems) as well as the standards for first-stage demineralized water (water used to generate steam in boilers). 1.4.3 Make full use of seawater as a cooling medium to reduce circulating water consumption. Seawater is primarily used for cooling oils in refining units, cooling condensers in power plants and facilities, as well as for fire suppression in facility areas and tank farms. 1.4.4 Reusing condensed water as boiler make-up water to save fresh water. 1.4.5 Reusing wastewater to increase the reuse rate of water resources; implementing wastewater reduction and reuse technologies to boost the reuse rate of water resources. The wastewater stripping technology is employed to purify the acidic water from the refining unit, which is then used to feed water into the electrodialysis cells of two distillation units ； By adopting a recycling approach, existing water storage facilities are used to promptly recover and reuse recycled water, rainwater, and steam condensate, such as the cooling water discharged from the liquefied gas tanks in the gas processing area. 1.4.6 Adopt comprehensive measures to reduce the make-up water rate for circulating water. Strengthen the monitoring of heat exchangers in the production system, install bypass filtration facilities to minimize leaks. Reduce the amount of make-up water used in the circulating water system, maintain stable water quality, lower the levels of bacteria and algae, and increase the concentration ratio of the circulating water. 1.5 Power System: With the commissioning of new equipment, the power consumption across the entire plant is on the rise. To reduce this consumption, it is necessary to adopt new technologies and optimize the operation of the refinery from a system perspective in order to save electricity. 1.5.1 Utilizing waste heat to replace electrical power – Lithium bromide refrigeration technology is an excellent method for making use of waste heat. The company recycles the low-temperature heat from the first and second distillation units, and utilizes hot-water lithium bromide absorption refrigeration technology to provide heating and cooling for the office building. This approach replaces 2.34×106 kW of electrical power, generating economic benefits of 1.17 million yuan. 1.5.2 Saving electricity through system optimization: Optimized control measures are employed in the plant’s air supply system to save electricity. 1.5.3 Apply frequency conversion technology to reduce power consumption. 1.5.4 Adopt efficient heat tracing measures; install automatic temperature-controlled electric heat tracing systems in oil pipelines carrying viscous fluids such as heavy oil and paraffin, in order to improve energy efficiency. 1.6 Utilizing the low-temperature waste heat from the equipment to achieve thermal integration between system units yields significant benefits. Through two years of energy-saving technological upgrades and optimized system operation, Dalian Petrochemical Company has achieved notable results in reducing energy consumption. It not only improved the overall technical level of the refining units and ensured stable operation of these units, but also significantly reduced processing costs. It has brought high economic benefits to the enterprise.