Economic analysis of electric heating and steam heating

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Overview 　　Heating as an effective method for pipeline insulation and anti-freezing has been widely used in thermal power plants. Its working principle is to release a certain amount of heat through the heating medium, and to compensate for the heat loss of the pipeline being heated through direct or indirect heat exchange, thereby meeting the requirements for temperature elevation, heat retention, or anti-freezing to ensure normal operation. For a long time in the past, steam tracing has always been a primary method of insulation in the vast majority of thermal power plants. Its working principle is to dissipate heat through steam tracing pipes to compensate for the heat loss of the insulated pipes. Since the heat dissipation of steam is difficult to control, its insulation efficiency remains at a relatively low level. Moreover, since the pipes that require heating in power plants are generally instrument pipelines, process pipelines, and chemical pipelines, which are quite complex, it is very inconvenient to lay steam heating pipelines. Furthermore, during winter operation, steam tracing pipes often experience problems such as leaks, spills, drips, and seepages. Every winter, the plant’s maintenance department has to invest a great deal of time and resources in insulating these pipelines to ensure the safe operation of the plant during those months. 　　In the 1970s, the U.S. energy industry proposed the use of electric heating as a replacement for steam heating. In the late 1970s and early 1980s, electric heating technology was widely adopted in many industrial sectors, including the energy industry, to fully replace steam heating. Over the course of its development, electric heating technology has evolved from traditional constant-power heating systems to self-temperature-controlled electric heating systems that utilize conductive plastics as their core component. 　　1 Principle and Application of Self-temperature-Controlled Electric Heat Tracing The self-temperature-controlled electric heat tracing solution is primarily implemented through self-temperature-controlled electric heat tracing wires. The self-temperature-controlled electric heat tracing wire is composed of conductive plastic, 2 parallel busbars with insulating layers, a metal shielding mesh, and an anti-corrosion coating. Among them, the conductive plastic, which is made by processing plastic with conductive carbon particles, serves as the heating core. When the temperature around the heat trace is low, the conductive plastic undergoes micro-molecular contraction; the carbon particles connect to form a circuit that allows current to flow, and thus the heat trace begins to generate heat ； At higher temperatures, the conductive plastic undergoes micro-molecular expansion, causing the carbon particles to separate gradually, which leads to a disruption in the circuit and an increase in resistance. As a result, the heating element automatically reduces its power output, and thus the amount of heat generated decreases. When the surrounding temperature drops, the plastic returns to its state of micromolecular contraction, and the carbon particles connect together to form a circuit, causing the heating power of the heat trace to increase automatically. Since the entire temperature control process is automatically adjusted by the material itself, the controlled temperature remains neither too high nor too low. Therefore, the excellent properties of electric heating make it incomparable to other heating systems. Self-temperature-controlled electric heat tracing systems are used for the insulation and anti-freezing of industrial pipelines. Meeting the specific technical requirements for heat tracing in power plants, these systems can effectively and conveniently provide insulation and protection against freezing, thus ensuring the proper operation of power plants during winter. Due to the obvious advantages of electric tracing over traditional steam tracing, it is widely used in the United States and Europe. Nowadays, it is difficult to find pipes with steam tracing in power plants in developed countries. The electric heating solution first entered the Chinese power market in 1986; power plants funded by World Bank or Asian Development Bank loans, such as the Shandong Shiheng Power Plant, adopted the self-temperature-controlled heating technology from the American company RAYCHEM at an early stage. At present, some more modern power plants, such as the Sanhe Power Plant in Hebei, the Huaneng Power Plant in Dalian, as well as the Yangcheng Power Plant in Shanxi and the Panshan Power Plant in Tianjin that are under construction, along with the power plants in Heze and Liaocheng in Shandong, have all adopted self-temperature-controlled electric heat tracing systems. 　　2 Comparison between steam tracing and electric tracing solutions Electric tracing technology is used for insulation and anti-freezing purposes in thermal power plants. It boasts advantages such as high heating efficiency, easy installation, reliable quality, and a long service life (usually 20 years). However, the initial investment required for self-temperature-controlled electric heating technology is higher than that of steam heating solutions, which is one of the main obstacles preventing the widespread adoption of electric heating technology in power plants in China at present. This paper focuses on comparing, from the perspectives of economic and social benefits, the steam heating and electric heating solutions for anti-freezing heating of 1,000-meter-long instrument pipelines in thermal power plants (to maintain a temperature of 5–10 degrees Celsius), using such installations as examples. 2.1 Investment Comparison 　　2.1.1 Steam Tracing Solution 　　(1) Tracing pipeline: One DN20 tracing steel pipe is selected in accordance with the process requirements. The total length of the pipeline is 1,000 m, with a total weight of 2.27 tons (DN20, 2.27 KG/m). The unit price is 5,000 yuan per ton; therefore, the material cost is 5,000 × 2.27 = 11,350 yuan ； The installation cost (including installation materials and labor) is 7,850 yuan. 　　(2) Steam supply pipeline: DN100 steam supply pipes are used, with a total length of 1000 M. Thus, the material cost is 102,180 yuan, and the installation cost (including installation materials and labor wages) is 40,423 yuan. 　　(3) Insulation for steam supply pipes: 50 mm thick rock wool is used, with a galvanized iron sheet as the outer protective layer; the total length is 1,000 m. It is estimated that the material cost is 20,250 yuan, and the installation cost is 44,200 yuan. 　　(4) Water supply and drain systems: including costs for steam supply valves, heat tracing pipe steam supply valves, trap isolation valves, traps, and trap inspection valves, amounting to 2,550 yuan. 　　2.1.2 Electric heating solution (1) Electric heating wire: Self-temperature-controlled electric heating wire, with a voltage of 220V; the heating temperature is 5 degrees Celsius, and the price is 133 RMB per meter. With a total length of 1000 meters, the material cost is 1000×133＝133,000 yuan ； The installation cost (mainly labor costs) is calculated at 3 yuan per cubic meter; thus, it amounts to 1000×3 = 3,000 yuan. (2) The power supply and distribution system: including materials such as the distribution room and transmission lines, the cost is 157,000 yuan. The installation cost is 6,810 yuan. Based on the above data, an investment estimate table is obtained (see Table 1). Table 1: Investment Estimate. Unit: yuan. Cost items: Main material cost, Installation cost, Total. Steam tracing scheme: (1) Tracing pipes: 11,350, 7,850, 19,200; (2) Steam supply pipes: 102,180, 40,423, 142,603; (3) Insulation for steam supply pipes: 20,250, 44,200, 64,450; (4) Steam supply and drain systems: 2,550, 2,550. Total: 228,803 yuan. Electric tracing scheme: (1) Electric tracing wires: 133,000, 3,000, 136,000; (2) Power supply and distribution system: 157,000, 6,810, 163,810. Total: 299,810 yuan. The ratio of total investments for the two schemes is: Steam tracing : Electric tracing = 1 : 1.31. 2.2 Comparison of operating costs. 2.2.1 Steam tracing scheme: (1) Steam consumption for pipe tracing: The heat consumption for tracing instrument pipes and the self-consumption of steam in the steam supply pipes is 0.30 tons/hour. At a cost of 50 yuan per ton of steam, and assuming 100 operating days per year, the annual steam consumption cost is 0.3 × 100 × 24 × 50 = 36,000 yuan. (2) The maintenance costs for tracing pipes include inspections, repairs, replacements, and various other maintenance activities, amounting to approximately 42,000 yuan per year. 2.2.2 Electric tracing scheme: (1) Electricity consumption: The most commonly used type of electric tracing wire consumes 33 W of electricity per meter. The total length of the pipeline is 1000 m, and the power consumption per hour is 1000×33/1000=33 kW.h. When the pipe temperature reaches the upper limit of the maintenance temperature, the heat generation of the electric heating element gradually decreases, and its output power also drops; as a result, the power consumption of the electric heating element is typically 60% of its rated power ； The cost of electricity for factory use is calculated at 0.20 yuan/kW·h. Assuming 100 operating days (2400 hours), the annual cost of electricity consumption is: (33×2400) × 0.20×60% = 9504 yuan. (2) Maintenance costs: Automatic temperature-controlled electric heating systems require almost no maintenance; according to regulations, it is only necessary to check the insulation level using a megohmmeter once a year. Here, the maintenance cost is estimated at 10,000 yuan per year. Based on the above itemized estimates, the estimated operating costs for the two options are shown in Table 2. Table 2: Estimates of Operating Costs, Unit: Yuan. Cost Item: Steam heating scheme; Electric heating scheme. Heating energy consumption: 36,000; 9,504. Maintenance costs: 42,000; 10,000. Total cost: 78,000; 19,504. Ratio of the two options: 4:1. 2.3 Economic benefit analysis: As can be seen from Tables 1 and 2, the investment required for the steam heating scheme is 80% of that for the electric heating scheme, but its operating costs are 4 times higher than those of the electric heating scheme. The output results of the two options are identical; both can meet the requirements for insulating and preventing freezing of instrument pipelines. Therefore, an analysis can be conducted by comparing their annual costs (assuming an economic lifespan of 10 years for steam heating and 12 years for electric heating). According to the calculations:
The annual cost for the steam heating option is:
Annual depreciation cost + annual operating cost = 228,803/10 + 78,000 = 10,088.3 yuan
The annual cost for the electric heating option is:
Annual depreciation cost + annual operating cost = 299,810/12 + 19,504 = 44,488.2 yuan
Based on the criterion of minimizing annual costs, it can be seen that the annual cost of the electric heating option is approximately 2/5 of that of the steam heating option, making it clearly superior to the former. 　　It can also be compared from the perspective of the dynamic payback period for additional investments. The one-time investment cost for the electric heating solution is high, but its annual operating costs are much lower than those of the steam heating solution. The time required to recover the additional investment through the cost savings provided by the electric heating solution is known as the payback period for that additional investment. According to the relevant formulas, it takes 1.4 years to recover the difference in investment costs between the two options. 　　2.4 Social Benefit Analysis 　　Self-regulating electric heat tracing adjusts its heating power based on the temperature of the tube wall (the medium), making it an energy-saving measure. Steam tracing can only utilize a portion of the thermal energy; a large amount of heat energy is reduced from a higher grade to a lower grade and becomes unusable, thus being wasted. According to calculations by foreign companies specializing in tracing systems, the energy consumption ratio between electric tracing and steam tracing is 1:5.8. Furthermore, since automatically controlled electric heat tracing can effectively prevent leaks and other such issues, it can also improve the manufacturing environment of enterprises. 　　3. Conclusion 　　From the above technical and economic analysis, it can be seen that although the initial investment for using self-temperature-controlled electric heating is high, the operating costs are significantly reduced, resulting in very substantial economic benefits. Furthermore, based on the operational performance of thermal power plants in China that have already adopted electric heating systems, it can be seen that these systems have achieved the expected results. It is foreseeable that in the insulation applications of the power industry, electric heating will inevitably replace steam heating as the preferred option. The electric heating products available in the current market can mainly be divided into two types: domestic and imported. Domestic electric heat tracing cables offer a relative price advantage, with lower initial investment costs. However, a significant portion of these domestic cables still use outdated constant-power heating technology, which results in substantial energy waste during use ； Furthermore, its efficiency, safety, and service life (the lifespan of some products is only 1–2 years) still need improvement. Imported temperature-controlled electric heat tracing wires offer technical advantages such as rapid startup, uniform temperature distribution, easy installation, and a long service life. Among imported electric heating products, the most widely used in China are the self-temperature-controlled electric heating wires produced by the American company RAYCHEM. Currently, the heat tracing systems for most foreign-owned power plants are designed and supplied by Raychem.