Application of superconducting heat pipe technology in asphalt heating

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Application of superconducting heat pipe technology in asphalt heating author: Hunan Provincial Highway Administration Xiong Shiling Zhang Amateur Song Tao Abstract: In view of the unsolved technical and economic problems of asphalt heating in Dengshiqiao asphalt oil field and various highway stations in Yiyang, the trial of the superconducting asphalt heating tank produced by Xiangtan Highway Machinery Factory and the study of related asphalt oil fields were combined. * During the investigation, this article introduces the main features of superconducting heat pipe technology and superconducting heated asphalt tanks, analyzes the necessity, urgency and feasibility of technical transformation of asphalt heating facilities, and puts forward the basic idea of ​​technological transformation of asphalt supply stations and highway station asphalt heating facilities and several issues that should be comprehensively considered. keywords: Comprehensive considerations for the application of new technologies in asphalt heating superconducting heat pipe technology. With the continuous advancement of science and technology, asphalt heating has gone through different stages of different forms such as open flames in wood stoves, heavy fuel oil, gas, solar energy, far-infrared radiation, medium-pressure water carriers, thermal oil carriers, etc. However, it has never been able to achieve perfect unity on issues such as energy consumption, asphalt quality, labor intensity, environmental protection requirements, and one-time investment and maintenance costs of equipment. Especially for asphalt heating at highway stations affiliated to county (city, district) highway bureaus, the method is basically to use brick-built oil pools and iron pots for direct external heating with open flames. Open iron buckets are used to receive oil for road construction. When the oil temperature is low, open flames are used to heat it up. This extremely primitive heating method has hardly changed in decades. As a highway technical worker, we should think deeply about this issue. 1 Face up to the technical and economic issues of asphalt heating Asphalt heating is an important link in asphalt pavement construction and maintenance. It not only restricts the quality of highway construction and maintenance, but also affects the cost of highway construction and maintenance. It is also closely related to the labor intensity of road maintenance workers, the construction environment and the surrounding ecological environment. For decades, highway science and technology workers and relevant experts and scholars have made unremitting efforts around this issue. Yiyang Municipal Highway Administration Bureau, relying on the strong support of the provincial bureau, has carried out multiple technical transformations of its Dengshiqiao asphalt oil field in stages, and each time has received considerable social and economic benefits to varying degrees. The several main stages experienced by the technical transformation of Dengshiqiao Oilfield and the main technical and economic problems that still need to be solved can be summarized as follows:: 1) In the 1960s, with the construction of asphalt pavements, Yiyang City established the Dengshiqiao Asphalt Oil Field in 1964. Affiliated highway management and maintenance units have also successively built asphalt oil fields of varying sizes. These oil fields all use brick oil pools and earthen stoves for external heating. The asphalt is basically transferred from the brick pool to the iron pot manually in half-section open iron drums. This method of heating asphalt consumes a lot of energy, losses, high labor intensity for workers, poor working conditions, high production costs, and serious environmental pollution, but the one-time investment in heating facilities is not large. Major highway repairs and new reconstructions require a large amount of asphalt every year. During high-temperature seasons, the asphalt oil fields billow thick smoke and smell unpleasant, harming people, livestock and crops. Neighboring residents complain and often get into disputes. This method of externally heating asphalt with an open flame continued until the 1980s; however, the heating of asphalt for minor highway repairs has not changed significantly due to many factors such as insufficient investment in highway infrastructure. 2) In June 1983, the "Dengshiqiao Asphalt Oilfield Renovation Research Group" was established and began to research and improve it. By August 1984, an oil refinery using solar energy and far infrared to comprehensively heat asphalt was completed. The oil field is equipped with 4 solar-powered stone oil pools, with a lighting area of ​​428.5 square meters and an asphalt reserve of more than 1,100 tons. ； There is an asphalt refining workshop equipped with 5 far-infrared heating oil pots with a capacity of 5 tons and a total installed power of 240 kilowatts. At the same time, an emulsified asphalt production line and an asphalt laboratory were built to provide basic equipment for asphalt storage, heating, testing, and oil discharging. From the solar oil pool to the heating oil pan and the finished oil out of the pan, a production line with a new technology is formed. It has changed the old process of high price, poor oil quality, dirty and bulky, and achieved the transformation goals of low consumption, high quality, clean and civilized. The main problem is: ①When the far-infrared electric heating tube is working, the surface temperature is above 350°C. During the heat transfer process to the asphalt, the surface of the high-temperature metal tube causes a serious loss of "asphaltene". After the asphalt is heated (especially repeated heating), its penetration increases by about 3%. ② The contact between high-temperature metal pipes and asphalt causes the asphalt to spontaneously ignite and catch fire during the refining process, posing serious risks to production safety. ③The power consumption is large, the thermal efficiency is low, the quality of the electric heating tube is difficult to pass, and maintenance and replacement are difficult. At the same time, maintenance fees and other expenses once increased to 12 yuan/ton, and heating energy consumption costs increased to 120 yuan/ton (in 1997). 3) In 1998, Yiyang Municipal Highway Administration Bureau invested more than 900,000 yuan to use medium-pressure water carrier heating technology to replace the far-infrared electric heating tube heating system of Dengshiqiao Oil Field. On the one hand, it ensures the quality of asphalt refining, and on the other hand, it reduces the refining cost, saving nearly 70 yuan per ton compared with before the transformation. A total of nearly 1 million yuan was saved in 6 years. The entire investment in technical transformation was recovered through savings. However, due to the increase in coal prices, the coal and electricity consumption for asphalt refining increased from 50 yuan/ton in 1998 to 66 yuan/ton in 2003, and reached about 80 yuan/ton in 2004. At the same time, the frequency of inspection and maintenance of medium-pressure water boilers and piping systems is high. If you are not careful, there will be a risk of boiler explosion, and there are still hidden dangers in production safety. There have been precedents for medium-pressure water boilers bursting, and some oil fields were forced to switch to thermal oil carrier heating after a year of trial use of medium-pressure water carrier heating. In addition, the stone solar oil pool at Dengshiqiao Oil Field has been in use for many years, and has serious oil leakage and water seepage, which increases the energy consumption and loss of asphalt refining. Moreover, the oil field can only produce hot asphalt, the emulsified asphalt equipment is also outdated, the asphalt laboratory is dilapidated, and the production of modified asphalt is blank. It is urgent to once again carry out technical transformation of the Dengshiqiao Oilfield, or to choose another location to build a modern asphalt supply station with functions such as processing, testing, and operation of various asphalt products. 4) With the above questions in mind, we went to the relevant municipal bureau asphalt oil field for a study in August 2004. * , inspection, the basic situation of the recent technical transformation of each asphalt oil field is as follows: Oil field name Oil field A oil field B oil field C oil field D Storage scale (tons) 8000260036003000/2000 Process type Thermal oil Thermal oil Super conductive heat pipe (Thermal oil preheating) Thermal oil/super conductive heat pipe Technology origin Jiangsu Changzhou Jiangsu Wuxi Shandong Heze Shandong Heze/Wuhan Changshi Recent investment scale (10,000 yuan) 2300280290800/110 Fund source Municipal bureau investment 1300160-110 Provincial bureau borrowing-90--Employee fund-raising-3 0290-Other groups invest in shares 1000--800 Normal annual output (tons) 5000200050006000 Product types hot asphalt, modified asphalt, emulsified asphalt, modified emulsified asphalt hot asphalt, emulsified asphalt hot asphalt , emulsified asphalt, hot asphalt, modified asphalt, emulsified asphalt loading and unloading mode, dedicated railway line, car transfer, car transfer, dedicated railway line, status of use, under construction, enabled, enabled, enabled, technical transformation, new construction, reconstruction, reconstruction, new construction, new construction, new construction, reconstruction, reconstruction, construction, new construction, new construction, reconstruction, reconstruction, reconstruction, construction, construction, construction, construction, construction, construction, construction: ①The application of new technologies, new materials and new processes in asphalt heating is fast and requires large investments. ； ②Intelligent asphalt heating, high level of civilized production ； ③Comprehensive consideration of asphalt unloading, refining and production of emulsified asphalt and modified asphalt has formed an integrated model ； ④ The railway connection leads to the oil field or nearby, long-term planning and full potential ； ⑤Asphalt field construction financing channels are diversified, operations are corporatized, and technological transformation is implemented simultaneously with the company's shareholding reform. ； ⑥The production of asphalt fields has transformed to an intensive type, with increased technological content and reduced labor intensity. The number of production workers has been reduced from dozens to less than ten. Take Oil Field A, for example, the new site is located in the Hi-Tech Industrial Park next to National Highway 207. More than 30 acres of land have been acquired. Asphalt trains go directly to the oil field. The street frontage is nearly 100 meters. It can carry out series processing and diversified comprehensive operations of a variety of asphalt products. The prospects are very promising. 5) At present, the most widely used methods of asphalt heating at home and abroad are thermal oil carrier and superconducting heat pipe carrier. Both can meet the quality requirements of asphalt refining, and their level of intelligent and civilized production is high. Their main difference is that: The thermal oil carrier of thermal oil requires an electric pump to pump it to the asphalt circulation to transfer heat. Superconducting heat pipes do not require external power and can transfer heat at high speed without thermal resistance. ； Thermal oil needs to be replaced regularly and is expensive, while superconducting heat pipes have a service life of about 10 to 15 years and are cheap. ； Thermal oil boilers and piping systems are large and complex, while superconducting heat pipe heating technology has a simple and compact structure. 2 The prospect of superconducting heat pipes for heating asphalt is very broad 2.1 Introduction to superconducting heat pipes Superconducting heat pipes, also known as dielectric heat pipes, are a new type of heat conduction element developed in recent years. The heating principle is to fill a sealed metal tube with a special medium that carries a large amount of heat. It will produce high-energy physical changes immediately after being heated and transfer heat quickly. The application of superconducting heat pipe technology breaks the traditional heat transfer method using water and oil as media. It can transfer a large amount of heat through a very small cross-sectional area to achieve rapid transmission over long distances without the need for external power, thus achieving the goals of high efficiency, energy saving, low consumption, and environmental protection. Tested by relevant experts, its heat transfer speed can reach 80-100 cm/second, which is thousands of times that of good conductors such as silver, copper, and aluminum. ； The transmission process is almost isothermal heat transfer, the heat loss is negligible, and the service life is tens of thousands of hours; the superconducting heat pipe uses ordinary metal pipes, the medium in the pipe is very cheap, and the production is very simple. In recent years, superconducting heat pipe technology has been widely used in many fields and developed very rapidly, such as intelligent superconducting heat pipes, asphalt heating tanks, etc. 2.2 Main features of the intelligent superconducting heat pipe asphalt heating tank. The superconducting heat pipe asphalt heating tank integrates asphalt storage, heating, dehydration, insulation and transportation. It can be designed and manufactured as a horizontal or vertical metal tank. The horizontal tank capacity can range from 1.5 to 100m3, and can be made into a self-propelled, towed or portable type. ； Each vertical tank can be made from 50 to several thousand m3. The heat source can be fuel, gas, coal, etc., and the heating method is superconducting heat pipe carrier heat transfer. The tank can be used both for fixed asphalt supply stations and for asphalt transportation ； It can be used for both mass production and sporadic supply of hot asphalt. It is very convenient to use and maintain. Its main features are: 1) Compact structure. It integrates asphalt storage, combustion heating, dehydration and heating, transportation, and piping preheating, and occupies a small area; 2) Save energy. Heating one ton of asphalt only requires about 10L of diesel or 15kg of coal; 3) The heating cost is low. Heating one ton of asphalt costs about more than 30 yuan in fuel. Mass production and the use of gas and coal are cheaper, and the one-time investment is not too large. According to market research, building a 50-100m3 portable horizontal tank only requires an investment of 160,000-220,000 yuan; building a 1,000m3 vertical tank only requires an investment of about 550,000 yuan, which is only about 60% of the thermal oil carrier heating equipment and about 20% less than the medium-pressure water carrier heating equipment. The investment can be recovered within 3-5 years; 4) Asphalt quality is guaranteed. There is a tank in the tank with local heating, which can heat and output high-temperature asphalt on demand without the need for repeated heating of the entire body. ； At the same time, the spiral pump is used for bidirectional circulation disturbance to avoid local aging of asphalt; 5) The pipeline is simple and can be completely built into the tank. The heat transfer surface has strong dirt resistance and long service life; 6) It saves time and labor. It only takes about two hours to use this tank to heat hot asphalt to 150--170℃ at normal temperature. The time required for continuous batch production is shorter each time, and the asphalt heating process only requires one person to observe the instrument and simple operation; 7) Intelligent control. The tank can dynamically regulate asphalt temperature, have automatic digital display, automatic alarm, and is equipped with a liquid level gauge; 8) It meets environmental protection requirements. Due to the use of advanced thermal conductive materials and process design, it has high thermal efficiency, low exhaust gas emissions, and no other pollution. The XTG/CTG-1.5 superconducting asphalt heating tank used by the asphalt pavement mechanical maintenance team of the Anhua Highway Administration Bureau can use hot asphalt in 90 minutes after startup, heating 1.5t of asphalt, consuming 10L of diesel, and costing 32 yuan, saving about 70 yuan in processing fees per ton. 3 Several issues that should be comprehensively considered and solved when applying superconducting heat pipe asphalt heating technology 3.1 The technical transformation of asphalt supply stations should be coordinated with the transformation of asphalt heating facilities at highway stations. The period for technical transformation of asphalt heating facilities at highway stations is also fully mature. This is not only a technical and economic requirement to achieve leap-forward development of highways, but also a realistic requirement to improve workers’ working conditions and reduce labor intensity. 1) Reform the maintenance operation mechanism and promote specialization and mechanization of highway maintenance, which provides opportunities for the technical transformation of asphalt heating facilities for minor highway repairs. According to the pattern of setting up a professional mechanical maintenance team for every 100km of asphalt pavement (basically a county-level management and maintenance unit), all asphalt soil ponds and earth stoves within the management and maintenance range can be dismantled. Choose an appropriate location and build a 50-100m3 superconducting heat pipe asphalt heating tank to be responsible for asphalt refining within the management range. Especially for remote production operations, it can be used in conjunction with a small superconducting heated asphalt tank (towable type). Some municipal bureaus have already started this and have achieved initial results. 2) The size of the portable asphalt tank of the asphalt pavement mechanical maintenance team is determined by its distance from the asphalt supply station. If it is within 50km from the supply station, only asphalt for minor highway repairs can be considered, and its reserve can be within 50m3; if it is more than 50km from the supply station, the heating of asphalt required for major and medium repairs and new reconstruction of some roads within the team's scope should be considered, and the asphalt tank storage should be about 100m3. 3) The size of the tank within the tank depends on the purpose and daily usage of asphalt. Small tanks that are only used for minor road repairs and have small daily usage should not be larger than 1m3: those that need to supply asphalt for large and medium-sized repairs can be made into about 6m3. Controlling the size of the small tank is mainly to avoid long-term insulation and repeated heating of asphalt and to prevent the aging of asphalt. 3.2 The selection of the location of the asphalt tank should fully consider the relevant natural factors. Whether it is a fixed vertical tank at an asphalt supply station or a portable horizontal tank for a professional maintenance team, the following factors should be considered: 1) Choose a mountainside with a height difference as much as possible to meet the requirements for self-fluidization from the crude oil transfer truck to the heating tank and the finished hot asphalt out of the tank (as shown in the figure). This arrangement can not only eliminate the electric pump oil device, but also make the structure simple and easy to maintain, and also reduces the consumption of oil pumps, electric energy and heat energy. If the height difference requirements cannot be met due to geographical constraints, we should consider the long-term technical and economic benefits. We would rather increase the one-time investment in man-made overpasses and approach roads, but also form a height difference for the artesian flow of asphalt. This point should be fully considered when planning and designing a new asphalt supply station. 2) When building a new asphalt supply station, railway connections should be considered as much as possible, and the location should be close to or directly accessible as a sand and gravel yard, so as to facilitate the unloading of asphalt and the production of asphalt mixture and reduce secondary transfer costs. When the two cannot be balanced, the pros and cons should be weighed and at least one of the requirements should be met. 3.3 When heating asphalt, multiple heat sources should be comprehensively utilized. When conditions permit, natural gas should be used as much as possible because it is more economical and less polluting than fuel. When using coal, we must fully consider the control of environmental pollution to ensure that it meets environmental protection requirements. For asphalt preheating in vertical tanks, solar heating devices can still be installed on the top of the tank and used in conjunction with superconducting heat pipes, but the top should be fully waterproofed. 3.4 Asphalt supply should be considered comprehensively with the processing and operation of various asphalt products. The asphalt supply station should not be limited to the single production of asphalt heating, but should become a comprehensive base for the production, processing, testing, and operation of heated asphalt, emulsified asphalt, modified asphalt, modified emulsified asphalt, asphalt cold mix, hot mix, joint filling materials, etc., and should consider developing its related industries. The size of its scale and the selection of business projects should be based on market demand and its own conditions. 3.5 The technical transformation of asphalt heating facilities should be implemented simultaneously with the update of business methods. 1) The financing of funds should be mainly self-raised. You can apply for support from superiors, and each unit should conserve and tap potential, mobilize employees to raise funds, and invest in shares to raise funds. ； It can also absorb idle funds from the society. When necessary, it can borrow money from banks and invite partners to invest in capital, space and facilities. 2) The operation of asphalt supply stations should be carried out joint-stock reform at the same time as technical transformation, and the legal person governance system should be implemented in accordance with the requirements of the Company Law. The asphalt boiling of the professional maintenance team should also carry out individual economic accounting and implement an operating accounting system and a cost assessment reward and penalty system or an individual contracting system. 3) The one-time investment in the technical transformation of asphalt heating facilities should be recovered through the collection of facility depreciation fees. Its operating gross profit will be returned year by year to enhance its development potential. References: 1. Wang Zhiyan, Jin Changzheng, Han Xiansuo, Lou Xiaozhen "Asphalt Heating Technology" 2. Yiyang Regional Highway General Section "Yiyang Regional Highway Chronicle"