Exploration of energy-saving renovations for steam condensate recovery

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Discussion on Energy-Saving Renovation of Steam Condensate Recovery Yang Xuyao, Lu Mingfang (Lanzhou Petrochemical Engineering Company, Lanzhou 730060, Gansu) Abstract: As the processing scale of petrochemical enterprises expands, the rational allocation and use of energy resources, along with proper design and renovation of steam condensate systems, play a crucial role in helping these enterprises save energy and reduce consumption. Taking the renovation of the steam condensate system in a tank farm as an example, it discusses the existing problems in the current condensate system and the corresponding solutions, and analyzes the economic benefits after the renovation. Keywords: condensate water; recovery; energy-saving renovation Chinese Library Classification Number: TQ522.64 1 Overview The Storage and Transportation Plant of Lanzhou Petrochemical Company is responsible for the storage, transfer, loading and unloading, and blending of crude oil, refined oils (gasoline, kerosene, diesel, etc.), as well as certain intermediate products in the refinery. As the refinery’s processing capacity evolved from 1 million tons per year at its inception to 10 million tons per year today, the storage and transportation facility also went through a process of gradual development, expansion, and improvement. The capacity of the crude oil storage tanks has now reached 51x104 m3, while the capacity of the diesel storage tanks is 13.2x104 m3. Due to the inherent properties of the storage media, in order to ensure the normal operation of production, a large amount of steam is required for heating and insulation during the storage and transfer of oils such as crude oil, diesel, and residue. Given the large volumes of crude oil and diesel stored, the crude oil tanks and diesel tanks become the major energy consumers in the storage and transportation facility (Table 1). Due to various objective factors such as multiple renovations and expansions, there are significant issues with the heating systems, heat supply systems, return water systems, as well as the heating systems in the pump houses of the storage and transportation plant’s tank areas. These problems arise in aspects such as design, on-site management, and the rational allocation and use of energy. As a result, a large amount of condensate water cannot be fully recovered, and energy is not utilized efficiently, leading to serious waste. Given the above circumstances, and in order to save costs and improve efficiency, Lanzhou Petrochemical Company carried out energy-saving renovations on the tank areas and pump houses in its storage and transportation plant in 2005. By adopting advanced and reliable process technologies and equipment, organizing the process flows reasonably, and establishing an efficient and effective wastewater recycling system, the quality of the recovered energy was improved. The condensate water was fully collected at the central condensate station, which not only prevented energy waste but also enhanced the economic efficiency of the storage and transportation plant through the rational allocation and use of energy at different levels. 2 　Problems existing in the condensate water recovery system ⑴ The return water system is unreasonable. In the existing condensate recovery process, the condensate flows by gravity into the 140 Condensate Recovery Main Station. For most tank areas, the return pipelines are quite long, with the longest distances reaching 1200 meters. This leads to two problems: firstly, the system backpressure is high, at around 0.3 MPa, which prevents the condensate from the heating coils or heat tracing lines in some tank areas from being discharged into the system; secondly, the large pressure difference results in severe secondary evaporation within the condensate system pipelines. As a result of this secondary evaporation, the gas passes through the condensate tanks and is directly released into the atmosphere, causing waste. Table 1 Steam Consumption Table for the Year 2003 Month: Steam consumption in crude oil and diesel storage areas (t), Steam consumption in storage and transportation facilities (t), Total 1 12786/ 10792 27522 2 10762/ 22319 42827 3 11272/ 14414 24613 4 3970/ 9378 14830 5 1654/ 5757 9010 6 8543/ 4147 5887 7 330/ 4006 6414 8 8218/ 3752 7642 9 731 10 6200/ 7006 14628 11 14709/ 10792 27522 12 16310 Total: 95485 (2) Energy of different levels is not utilized in a proper manner. Due to the lack of a comprehensive approach to the utilization of heat from different energy levels, most of the facilities in the storage and transportation plant, such as control rooms, pump houses, and rest areas, are heated using main steam (the consumption amount is shown in Table 2). Steam is also used for flushing the oil unloading platforms, which results in energy waste and increased production costs. ⑶The return water system within the tank area is chaotic. The return water from the heating of oil tanks within the tank area and the return water from pipeline heating converge into a single pipeline. Due to uneven pressure of this return water, water hammer can easily occur, affecting the proper operation of the steam trap equipment. Prolonged operation can lead to the \"failure\" of these steam trap devices, allowing steam to enter the pipeline network directly and be discharged in the condensate storage tank, resulting in energy waste. ⑷The pipeline network of the return water system lacks a unified design. Due to the lack of a unified design for the return water system pipelines within the tank area, the flow direction of the condensate water in these pipelines is chaotic, resulting in unstable pressure. In some storage tanks, the condensate water in the heating coils cannot be drained; when heating is required for production purposes, water hammer occurs within these coils. There have been incidents where water hammer caused the heating coils to break, leading to contamination of the system and the oil products. Moreover, some storage tanks lack a return water system network, so the condensate is discharged directly, resulting in energy waste. Table 2 Heating Steam Consumption Table Unit Number Name Heating Area Heat Load Steam Consumption m2 kW Kg/h 42/6 Pump Room 9 6 7.66 12.74 Control Room 12 1.2 1.91 42/8 Pump Room 40 3.19 5.31 Control Room 40 4 6.65 63 Pump Room 164 13.09 21.77 Control Room 5 4 5.4 8.98 64 Pump Room 200 15.96 26.55 Control Room 60 6 9.98 65 Pump Room 54 4.31 7.17 Control Room 180 18 29.94 72 Pump Room 27 2.15 3.58 Control Room 18 1.8 3 160 Control Room 16 1.6 2.67 160/1 Control Room 12 1.2 1.98 161 Control Room 40 4 6.65 163 Control Room 20 2 3.33 164 Control Room 200 20 33.28 Control Room at Southwest Entrance 40 4 6.65 Total 1273 115.68 193 (5) Strainers are malfunctioning. The selected traps have poor performance; they may be damaged or installed incorrectly (for example, due to the large volume of the storage tank, heaters usually have two inlets, but each set of heating coils in the oil tank shares one trap, resulting in uneven water removal). In most cases, these traps fail to perform their function of preventing steam from escaping, leading to significant steam leaks. 3 Reform Plan 3.1 Use new-type automatic condensate pumps instead of the option of adding a separate condensate collection station. The distance from the condensate return pipelines to the main condensate station is long; in some cases it reaches 1200 meters. To overcome the significant pressure losses along this distance, the initial plan was to establish an additional condensate collection station, from which the liquid would be pumped to the main condensate station. However, this solution has significant drawbacks. Firstly, after years of development, land within the factory complex is scarce, making it difficult to build new condensate stations. Additionally, the condensate return pipelines are spread out over a large area, so implementing this solution requires the construction of new condensate stations in multiple locations. Condensate stations require a large amount of space, contain many pieces of equipment, and entail high investment costs. Later, through investigation, it was determined that automatic condensate pumps could effectively solve the aforementioned problems. The Nixon condensate automatic pump is a type of pressure-controlled pump. Its driving force comes from steam; as it lacks rotating sealing mechanisms, electric motors, and pump impellers, it not only has a long service life and low maintenance costs, but is also highly suitable for installation in explosion-proof areas such as crude oil storage tanks and diesel storage tanks. The automatic condensate pump is reasonable and **solves the problem of pressurized transportation of condensate. Based on the actual conditions on site, 8 condensate pumps are selected for this renovation. Depending on the volume of condensate produced, 4 PCH - SP3x2 single-pump units, 3 PCH - DP3x2 double-pump units, and 1 PCH - TP3x2 triple-pump unit are used; these pumps are installed in the respective crude oil tanks and diesel tanks. According to calculations, with a recovery rate of 22.5 tons per hour, 18 x 10^4 tons of condensate can be recovered throughout the year. 3.2 Adjust the process flow: Separate and organize the various heating systems within the tank area (main steam, waste steam) as well as the return water systems (heating return water system, heat-traced return water system). The heating return water and the return water from pipelines with heat tracing should be fed into the automatic condensate pumps located within the tank area; after being pressurized by these pumps, they are sent to the 140 Condensate Collection Station via the condensate recovery network. 3.3 Rational use of energy at different levels: To save energy and reduce operating costs, this project involves modifying the existing heating system by adopting low-temperature hot water as the heating medium; the heating water at 80/60 ℃ is supplied by the condensate water station No. 140. The original design capacity of unit 140# was to supply heat to an area of 25,000 m2; currently, it supplies heat to an area of 21,500 m2. Thus, there is still a remaining capacity of 3,500 m2 for providing heat, which is sufficient to meet the increased heating demands after the renovation. For this renovation, one heating hot water pipeline and one heating return water pipeline are installed. The total length is approximately 6,000 meters, with a total weight of around 28 tons. The pipelines are insulated over an area of 100 m3, and as a result of this installation, 625 tons of steam can be saved annually in the heating system. Additionally, the recovered condensed water is sent to platforms 164# and 159# to replace the steam currently used for flushing the platforms. According to calculations, Platform 164 can save 734 tons of steam per year, while Platform 159 can save 1,803 tons of steam per year; in total, 2,537 tons of steam are saved. 3.4 Reform of the heating and return water system pipelines: Modify and improve the heating and return water system pipelines both inside and outside the tank areas. Transform the current steam heating system in tanks 42/7–9 into a main steam heating system, and convert the return water system into a heating return water system. New insulated return water systems and waste steam heating systems will be established, as well as new condensate pipelines for tanks 42/1, 44/2, 44/3, and 44/4. This will enable the condensate recovery system to function as a complete and closed system, eliminating the chaos, deficiencies, interconnections between different systems, and even the direct discharge of condensate that existed in the previous system. During this renovation, approximately 7,500 meters of pipelines were laid, with a total weight of around 55 tons; the insulation for these pipelines covered an area of 170 cubic meters. 3.5 Replace the steam traps: All the steam traps in the tank area that are not performing well or are damaged should be replaced with thermostatic steam traps that offer reliable performance and high efficiency. A total of 356 steam traps were installed in this renovation. 4 Benefit Analysis ⑴ Project Investment: For this project, 8 new condensate pumps and 356 steam traps will be installed. A total of approximately 13,500 meters of piping will be laid, with a total weight of around 83 tons. Insulation work will cover an area of 270 cubic meters. The total cost of the project is 2.3657 million yuan, of which 2.116 million yuan is allocated to equipment and main materials, while 249,700 yuan covers installation costs. For specific calculations, see the table below (project investment costs are shown in Table 3). Project Investment Costs Table: Serial Number, Name, Equipment/Primary Material Cost (10,000 yuan), Installation Cost (10,000 yuan), Total Project Cost (10,000 yuan). 1. Condensate pump: 57.26, 0.88, 58.14; 2. Drainage equipment: 57.80, 6.40, 64.20; 3. System pipelines: 96.54, 17.69, 114.23; 4. Total: 211.60, 24.97, 236.57. ⑵ Benefit Analysis: ① Fuel and power prices provided by Lanzhou Petrochemical Company’s refinery (including taxes). Power Price Table: Item, Steam, High-temperature Condensate Water; Price (yuan/ton): 71.22, 3. ② Additional benefits resulting from the implementation of this project: At the No. 164 unloading platform, steam usage is reduced by an average of 2.2 tons per day during winter, with 150 days considered in winter, resulting in a savings of 330 tons of steam per year. During summer and the transitional periods, steam usage is reduced by 1.88 tons per day, with 215 days considered in these periods, resulting in a savings of 404 tons of steam per year. In total, 734 tons of steam are saved throughout the year. 159 # The oil unloading platform consumes an average of 5.4 tons of steam per day in winter; assuming 150 days in winter, this results in a savings of 810 tons of steam per year. In summer and during the transitional periods, the steam consumption is 4.62 tons per day, and with 215 days in such periods, the savings amount to 993 tons of steam per year. In total, the annual savings amount to 1803 tons of steam. The use of low-temperature hot water instead of steam for heating can save 193 kilograms of steam per hour; assuming a heating period of 135 days, this results in a yearly savings of 625 tons of steam. The steam trap prevents steam leakage: —— The leakage rate in the case of no steam trap or a malfunctioning steam trap is estimated to be around 10% of the total steam consumption. —— It is assumed that there are 333 days of production time per year, totaling 8,000 hours. —— The average steam consumption is calculated at 22.5 tons per hour; the consumption in summer is half that of winter, with a combined coefficient for summer and winter usage of 0.75. Based on these calculations, 18,000 tons of steam can be saved throughout the year as a result of preventing leaks. Steam condensate recovery: —— The storage and transportation plant’s tank area consumes 180,000 tons of steam per year, with 180,000 tons of condensate being recovered. Taking all of the above into account, the implementation of this project will result in a savings of 21,162 tons of steam per year, as well as cost savings of 1.5072 million yuan. 180,000 tons of condensate water were recovered, saving 540,000 yuan in costs. The two measures together resulted in cost savings of 2.0472 million yuan. ③Additional costs resulting from the implementation of this project: The driving force for the new automatic condensate pumps is steam, with the steam consumption amounting to 0.3% of the amount recovered. In this project, 180,000 tons of condensate are recovered per year; thus, the additional steam consumption is 540 tons, resulting in an extra cost of 39,000 yuan. Heating is provided using low-temperature hot water, and the heating cost is calculated at 2.5 yuan per m2 per month. According to Table 2, the heating area is 1,273 m2, the heating period is 5 months, resulting in an additional cost of 16,000 yuan per year. Condensate water is used for flushing the oil unloading platform; 87,000 tons of condensate water are required throughout the year, resulting in an additional cost of 261,000 yuan. Taking all of the above into account, this project results in an additional cost of 316,000 yuan. ④Net project benefit: After the implementation of this energy-saving renovation project, costs can be saved by 1.7312 million yuan. It offers significant energy-saving effects. ⑶Static payback period: Calculations show that the static payback period for this project is approximately 1.4 years, which is lower than the industry standard of 12 years. The project is feasible. The specific calculations are shown in Table 5. Table 5 Calculation Table for Static Payback Period: Investment cost: 2.3657 million yuan; Estimated benefits: 1.7312 million yuan; Payback period: 1.367 years (16.4 months). 5 Conclusion: The investment required for this project is 2.3657 million yuan. This renovation project effectively reduced the energy consumption in the oil storage tank area of the storage and transportation facility by selecting advanced and reliable process technologies and equipment, arranging the process flows reasonably, and making full use of energies at different levels. This led to cost savings and an improvement in the company’s economic efficiency.