In recent years, the field of new energy has become a key field for the development of countries around the world. In several major energy-consuming countries, solar energy, wind energy and other various new energy sources are developing rapidly. However, it is also a new energy source. Various methods for power generation have developed rapidly. Several major technical routes have shown environmental benefits over fossil energy. Their contribution to the power grid is getting higher and higher. In the field, the situation is much more complicated.
Oil currently provides more than 90% of the energy used for human transportation. There are many reasons why people choose oil as the main form of energy for transportation. The reserves of oil are huge. People have already extracted hundreds of billions of tons of oil. The current known reserves can still be maintained for several decades at the current rate of extraction of about 4 billion tons per year. This amount is currently unmatched by other non-fossil energy sources. Petroleum belongs to material energy, that is, energy exists in the form of matter. In this way, compared with electricity, energy storage and transportation are very convenient. It can be easily transported across the ocean or to remote areas. Locally, it does not completely rely on a fixed transportation network, and can be easily carried by airplanes, ships, and vehicles. The energy density of petroleum is also very high. For transportation equipment with limited volume and limited load, this feature is very important, and it is currently unmatched by other forms of energy.
Although petroleum is much cleaner than coal, which is also fossil energy, it still has many environmental impacts during its mining, transportation, processing, and use. Especially after the accident, the impact may be very large. For example, the oil spill in the US Gulf of Mexico in 2010 had a large impact on the Gulf of Mexico and the surrounding land areas. In some underdeveloped oil-producing countries, the losses caused by poor supervision and poor governance have been ignored by people for a long time. The problem of temperature gas emissions caused by the use of petroleum is also very serious. Fossil energy is a carbon-based resource, and carbon dioxide needs to be emitted after use, and oil is no exception. The problem of climate change caused by the huge amount of greenhouse gas emissions is a problem that the entire international community is striving to solve. Looking for a clean alternative to oil is an important part of the fight against climate change.
Even without considering environmental issues, people need to start looking for oil substitutes because oil is not enough. In recent years, the price of oil has been at a high level. Even the worldwide economic depression has not caused oil prices to drop much. An important reason is that cheap and easy-to-exploit oil has been unable to meet human demand for oil, and more and more unconventional oil Resources are mined. These unconventional oil resources use complex technologies, high energy consumption, and large investment, all of which increase the cost of oil extraction and push up the price of oil. From this perspective, people also need to find alternative fuel products that can suppress the rise in oil prices. Of course, the high price of oil also makes it possible for some alternative routes that were originally considered economically uneconomical to be promoted economically.
Compared with the diversity of energy sources for power generation, oil substitution options are limited. To replace oil, it is necessary to find resources with a huge amount, easy storage and transportation, and high energy density, and at the same time, there are few resources and technical approaches that meet these points. An important candidate, also relatively mature in technology, is coal liquefaction technology. The reserves of coal are much higher than that of petroleum. After being converted into fuel oil, it can have all the advantages of petroleum fuel. Technically, coal liquefaction technology has a history of nearly ninety years. It was industrialized in Germany during World War II. Now this technical route provides nearly one quarter of the fuel supply for South Africa. However, coal itself is also fossil energy. Although its total reserves are much richer than oil, it is still limited. Even if it becomes the main force to replace oil in some places, it is not a long-term solution. At the same time, the current coal liquefaction technology is significantly more harmful to the environment than traditional oil routes. To overcome these environmental hazards, people need to pay a huge capital cost, and some technologies are not yet mature. There are similar problems when using natural gas liquefaction processes to produce oil products. Using one kind of fossil energy to replace another kind of fossil energy is definitely not a long-term solution to the problem. To find a long-term oil substitute solution, you need to rely on renewable energy.
The material energy characteristics of petroleum that are easy to preserve and transport make few alternative energy sources that can replace petroleum. In fact, among the renewable energy, only biomass energy is material energy, and other renewable energy is difficult to be transformed into material form. From this perspective, the application of biomass should consider the direction of alternative oil as much as possible, and give full play to the benefits of biomass energy. Simple power generation applications cannot take advantage of this feature of biomass energy. However, it is actually more difficult to implement. At present, there are not many mature technologies for converting biomass into biofuels. The most mature technology is biodiesel with sugar, starch ethanol and vegetable oil as raw materials. The two most widely promoted are these two biofuels. Almost 3% of the world’s fuel supply. Among them, ethanol is mainly composed of corn ethanol in the United States and sugarcane ethanol in Brazil, which together account for 90% of the world’s fuel ethanol supply; biodiesel is mainly in the European Union, which produces half of the world’s biodiesel production. However, these two types of biofuels use starch, sugar, and oil crops directly related to human food, occupying a lot of agricultural resources. At the beginning of expanding cultivation, they assumed the reputation of competing with people for food and land. The promotion in other parts of the world is obviously hindered. For many countries in the world where food security cannot be guaranteed, these two types of biofuels have no promotion conditions. Even in Europe and the United States, these two oil alternative routes have been criticized. Obviously, to achieve biofuels accounting for a quarter of the world’s fuel supply by 2050, it is impossible to rely on these two technical routes.
In fact, from the perspective of greenhouse gas emission reduction throughout the entire life cycle, the performance of these two routes is not good. Life cycle assessment is a comprehensive evaluation method, which examines the consumption of materials and environmental impacts of each link of a process route, including the collection and transportation of raw materials and important auxiliary materials, various processing links, and the delivery of finished products , The disposal of waste, etc., consider the material consumption and environmental impact of a product from raw materials to finished products to waste throughout the entire stage. Through such a detailed investigation, you can understand the advantages and disadvantages of different process routes. When you screen different technical routes, you can learn the actual resource consumption and actual environmental impact of each different technical route. The choice of technical route provides an important reference. For the same technical route, such analysis can also be used to understand what steps affect the overall effect and provide direction for process improvement. When considering the many candidates for petroleum substitutes, such an analysis can reveal whether the alternative methods chosen have many of the expected benefits.
For example, to evaluate the advantages of a biofuel route over petroleum, you need to start from the crop planting stage to investigate the energy and material consumption of each planting, sowing, and harvesting stage. The environmental impact includes not only the direct consumption in the field, but also Including the consumption of raw materials and environmental impacts during the production and transportation of chemical fertilizers and pesticides used. After the crop is harvested, it is necessary to examine the various preliminary processing steps and product transportation. After entering the fuel production line, we also need to investigate the consumption and impact of the entire process and the various raw materials and auxiliary materials used. After obtaining the product, you also need to consider the product distribution trial process. If there are by-products or emissions that need to be treated, then these by-products and emissions need to be taken into account. Because the investigation is a very tedious and detailed process, such an investigation has very strong regional characteristics. Even if it is the same process route, the results obtained in different regions will be different. You need to be very careful when looking at these inspection results. .
In 2007, the European Union published a life cycle assessment of automotive fuel alternatives based on the European Union. In this report, the EU’s own ethanol production raw materials are sugar beet and wheat. The conclusion is that such a route can reduce fossil energy consumption by 27% compared to the life cycle of traditional gasoline, while reducing greenhouse gas emissions by 30 %. When using rape to produce biodiesel, fossil energy consumption should be reduced by 64% compared to traditional diesel, and greenhouse gas emissions should be reduced by 53%. From this report alone, it can be seen that in the EU environment, the ethanol and biodiesel routes are valuable for reducing fossil energy consumption and reducing greenhouse gas emissions.
But the situation in China is very different. In 2008, a doctoral thesis from Tsinghua University examined the actual life cycle of ethanol production in China. The conclusion is that fossils consumed in the life cycle of ethanol fuel are produced using corn, cassava, sweet potato, sweet sorghum, sugarcane, etc. as raw materials. Energy is much higher than the fossil energy consumed in the production of gasoline, and the greenhouse gas emissions of these routes are also higher than the gasoline route. According to this calculation, it can be said that the ethanol fuel project promoted by China at this stage has neither played a role in energy saving nor reduced greenhouse gas emissions, and has no positive environmental significance. Although it still has a positive meaning in terms of providing oil substitutes, it is somewhat unreasonable to continue to enjoy state subsidies for such high energy consumption and high emission alternatives.
In a similar international study, the number of ethanol routes in China is the worst, but it is not incomprehensible. There are mainly one reason for this result. The first is that China’s current agricultural production management is extensive, and the abuse of chemical fertilizers and pesticides is serious. The production and transportation of chemical fertilizers and pesticides all require energy consumption and cause greenhouse gas emissions. Especially when nitrogen fertilizer is not used properly, it will also increase the emission of nitrogen oxides in the land. Nitrogen oxides are nearly three hundred times more serious than the greenhouse effect of carbon dioxide. A small amount of emissions is enough to offset the carbon dioxide absorbed by plant growth. Then there is the issue of the fuel ethanol production process currently used in China. Fuel ethanol has high requirements on the purity of ethanol, so it needs to be purified by a certain process. The most common method is ethanol rectification. Ethanol rectification is a very energy-intensive process. Most of these domestic production lines use small self-provided cogeneration units to meet the energy required for production. These units often use raw coal that has not been washed, resulting in problems such as low unit efficiency. This also increases energy consumption and greenhouse gas emissions during fuel production. In other words, it does not mean that China’s fuel ethanol production will definitely have no environmental benefits. After addressing these two major problems in a targeted manner, China’s fuel ethanol industry can also achieve real energy saving and emission reduction like other counterparts in the world. This targeted technological improvement should be the direction of government policy encouragement.
Domestic biodiesel production has similar problems. The investigation results of the doctoral thesis mentioned above are the fossil energy consumed during the life cycle of biodiesel produced by using soybean, rapeseed, cottonseed, jatropha, pistacia, light bark and even catering waste oil under domestic actual conditions. Are higher than the fossil energy consumed in the production of diesel; in terms of greenhouse gas emission reduction, only the route of using imported soybeans and containing forest trees as raw materials can achieve greenhouse gas emission reduction compared with diesel, and the use of other raw materials does not To the effect of reducing carbon emissions. The reason why this number is not very attractive, also in the two stages of planting and product processing, is similar to the situation of ethanol.
There are no obvious environmental benefits, and it also threatens food security. This may be one of the reasons for the recent slowdown in the domestic biofuel field. However, this does not mean that biofuels have no prospects in China. In fact, the problems encountered by China are not unique to China. Grain ethanol and biodiesel that use grain and oil as raw materials are internationally called first-generation biofuels. At present, the international research interest in biofuels has been concentrated on second-generation biofuels. The difference between the second generation and the first generation is that the second generation biofuel can use various biological wastes, or all or most of the crops, instead of the first generation biofuel, it can only be used as the most valuable thing. part. In this way, the energy consumed during the planting stage can be recovered more effectively. In addition, after most of the plants can be used as energy raw materials, the potential supply of biofuels has also greatly increased.
Because the research and development of related technologies started late, the second-generation biofuel has not yet entered the stage of industrialization, but the raw material range of the second-generation biofuel is very wide, and the fuel itself has many options. In the aforementioned EU report, several possible routes were examined for biogas, non-food ethanol, hydrogen, dimethyl ether, and synthetic diesel. Because the second-generation biofuels can use bio-waste as raw materials, and the energy consumption during the crop planting process will not be spread to the waste, so the life cycle energy consumption and greenhouse gas emissions of these paths have advantages. In the EU report, the biogas route is not outstanding in terms of saving fossil energy. It still consumes more fossil energy than the gasoline route, but it has achieved remarkable results in reducing greenhouse gas emissions. In the ethanol route, the use of lignin to produce ethanol is superior to the grain ethanol route in both respects. The route of using biomass gasification to produce dimethyl ether and synthetic diesel and the route of hydrogen production do not perform well in terms of energy consumption, but they have made outstanding achievements in reducing greenhouse gas emissions, which can reduce greenhouse gas emissions by more than 90%. . Synthetic diesel and traditional diesel are mixed in any ratio, without any changes to the distribution system and engine, which is an important advantage for the promotion of fuel.
The situation in China is similar to the EU in terms of second-generation biofuels. The research results of Tsinghua University cited above pointed out that from the perspective of life-cycle greenhouse gas emissions, the carbon dioxide emission reduction effect of the dimethyl ether, synthetic diesel, and hydrogen routes is significant, and the routes such as biomethanol and bioethanol are different because of the different engines used. The carbon emission reduction is slightly worse, but it is still better than the gasoline route, and can all play a role in reducing emissions. The study also pointed out that the actual emission reduction and energy-saving effects of biofuels with different raw materials and routes vary greatly, and this difference has obvious regional characteristics. Different regions may have solutions that suit their specific circumstances. The diverse choices of second-generation biofuels also give people plenty of choice, and they can find suitable development methods in the region according to local conditions.
After all, the second-generation biofuel has not yet entered the commercial promotion stage. These calculations are often based on theoretical models and calculations. The accuracy of the conclusions is certainly not as good as the data measured from actual production. With more and more industrial attempts in this field, people will have more and more understanding of these technical routes, and the evaluation indicators will more and more truly reflect the actual situation. However, these investigations have shown that the second-generation biofuel is indeed the direction of biofuel development. It can be said that since the raw materials of the second-generation biofuels are more extensive than the first-generation biofuels, the total amount of energy they can provide is also greater, which should play a great role in the replacement of oil.
For biofuels to play an important role in the field of replacing oil, it is not enough to rely solely on agricultural and forestry wastes, and special energy crops need to be cultivated. In order to avoid competing with people for food and land, these energy crops need to occupy as little land as possible and use places that are not suitable for commercial agricultural development. This puts forward higher requirements for the planted energy crop varieties. However, some energy crops in the current study can still meet these requirements. In addition to herbaceous woody energy crops, artificially grown algae is also a very promising biomass material. Algae are highly efficient for photosynthesis. Under appropriate external conditions, the growth rate of algae is generally higher than that of herbaceous and woody crops. This feature makes algae the best candidate for energy crops. There are also many options for the use of algae. Both special varieties can be screened to increase the oil content in the algae to eventually produce biodiesel, or biomass can be used for the purpose of providing carbon and energy for downstream fuel production. Some people in the world have listed algae-based fuel production as the third-generation biofuel, and they have seen this good prospect.
However, the current level of algae energy utilization is still far from practical application. Not only does the current cultivation and harvest of algae depend on a lot of machinery and consumes a lot of energy, the quality balance of algae growth determines that the current level of algae cannot be a reliable rely on energy issues. The growth of algae requires not only sunlight to drink carbon dioxide but also various other elements, especially nitrogen. At present, the supply of nitrogen is mainly provided in the form of chemical fertilizers. In fact, given sufficient sunlight and carbon dioxide, the growth rate of algae depends on the supply of nitrogen fertilizer. At present, the production of nitrogen fertilizer depends on fossil energy, which increases the fossil energy consumption of the algae route and increases the carbon dioxide emissions in the life cycle. In addition, the use of nitrogen fertilizer will also cause problems of nitrogen oxide emissions in the growing area. To achieve large-scale energy utilization of algae, it is necessary to develop biological direct nitrogen fixation technology. In this regard, it may depend on very advanced bioengineering technology. The same is true for other energy crops. If the clean supply of nitrogen fertilizers can be solved, the output of biofuels may increase significantly, and oil can be replaced in a larger proportion.
While studying biofuels, people are also trying to use alternative ways to replace oil, which is to change the current transportation industry that relies heavily on internal engines to use electrical energy for transportation. Electricity has played a role in the transportation industry. In the railway system, electric traction locomotives have become very popular. In the field of civilian vehicles, electric vehicles have also become popular as new energy vehicles in recent years. The advantage of electric vehicles is that they can use electricity, and the sources of electricity are very wide, which can be traditional thermal power generation or various new energy sources. In this way, the promotion of electric vehicles can get rid of dependence on oil. For oil importing countries, this is sometimes very important. In addition, there is no pollution on the user side of electric vehicles, which can eliminate car pollution on the user side. For large cities with high population density and crowded vehicles, improving the ownership rate of electric vehicles is also very important for clean city air. In fact, in terms of terminal environmental impact, electric vehicles have a great advantage over bio-carbon-based fuels, and only bio-hydrogen can be compared.
However, there is still a long way to go before electric cars can truly replace current internal combustion engine cars. The key problem is that the vehicle carries too little power. The storage of electricity has always been a hassle. Although battery technology is developing rapidly, the energy density that the battery can carry is still orders of magnitude worse than that of liquid fuel. Although the energy conversion efficiency of electric vehicles is much higher than that of internal combustion engines, the single-charge mileage of electric vehicles of the current technology still cannot meet people’s use requirements. In this regard, we still need to wait for technological progress. Plug-in hybrid vehicles that use electric power but still carry liquid fuel to meet long-distance needs provide new ideas for solving this problem, but related technologies are still being developed, and when to enter the market is still a problem.
In addition, the popularization of electric vehicles at this stage is also suspected of transferring pollution. Since the current main source of electricity is thermal power, thermal power itself has a great environmental impact. Life cycle studies have shown that in the United States and China, where coal accounts for a relatively high proportion of energy, the use of electric vehicles at this stage refers to cars with internal combustion engines, which have no significant effect on carbon dioxide emissions reduction, but in terms of sulfur dioxide and nitrogen dioxide emissions, in fact Increased pollution. Of course, it is not possible to deny the development direction of electric vehicles, but when promoting electric vehicles and promoting them, we should indeed consider the impact in this regard.
In short, there is really no good way for people to replace oil. At least for the expected 20 to 30 years, oil will still be the main energy used by the transportation industry, but it should also be seen that with the replacement technology Development, the proportion of oil in the transportation industry will become lower and lower.
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