Li Yizhong: Scientifically grasp and rationally select the hydrogen production process path

1. Several ways to obtain hydrogen sources today. There are no mineral deposits of hydrogen in nature. Hydrogen is a secondary energy source and needs to be prepared artificially. Hydrogen production is an old topic but also a new topic. It is said to be "old" because there are already mature hydrogen-carbon balance process technologies for producing hydrogen from fossil energy to produce water gas, synthetic ammonia, urea, methanol and other chemical products. ； It is said to be "new" because hydrogen is converted into electricity through fuel cells, which opens up new uses, creates new demands, and creates new problems. Therefore, it needs to be studied carefully and grasped scientifically. Generally speaking, there are several ways to prepare hydrogen: First, hydrogen production from fossil energy. Hydrogen production from coal, natural gas, and petroleum (including light hydrocarbons, naphtha, and heavy oil) generally does not use hydrogen as the final product, but rather for further production of chemical products or for deep processing to improve quality and yield. Coal contains very little hydrogen, only 2% to 5% depending on the type of coal. Hydrogen is mainly produced by producing water gas, which is accompanied by a large amount of CO and carbon dioxide. Further synthesis fixes the carbon in the target product, avoiding or reducing a large amount of carbon dioxide emissions. Natural gas and petroleum components contain relatively high hydrogen content, about 15% or more. Taking methane as an example, it reacts with water to generate hydrogen and carbon dioxide. The yield of hydrogen is high, and it is also further synthesized into related petrochemical products. If hydrogen is produced from fossil energy as the target product, the insurmountable problem is the outlet for carbon dioxide. The weight of carbon dioxide associated with the production of 1kg of hydrogen is about 11 when producing hydrogen from coal, about 5.5 when producing hydrogen from natural gas, and about 7 when producing hydrogen from light oil. Carbon dioxide, a greenhouse gas, must not be emitted in large quantities. Climate warming is a threat to mankind, and small emissions will impose high carbon taxes. The so-called carbon dioxide capture, utilization and storage technology (CCUS or CCS) is still under trial and has not been industrialized, and it is in urgent need of scientific and technological research. Therefore, it can be said that under the current technical conditions, although the fossil energy hydrogen production technology is mature, this path is not advisable and it is not suitable to build a new one. As for the use of methanol cracking to produce hydrogen, it is also associated with about 7 times the carbon dioxide, and it cannot be emitted in large quantities. Moreover, methanol is made from coal. Recently, the "World Energy Council" calls this kind of hydrogen accompanied by large amounts of carbon dioxide emissions "gray hydrogen", and the hydrogen that avoids the emission of carbon dioxide through CCS or CCUS is called "blue hydrogen". Obviously "grey hydrogen" is not advisable, only when it turns gray into blue can it be used. Second, the recovery, purification and utilization of industrial by-product hydrogen. Refining tail gas, ethylene tail gas, and chlorine tail gas contain different proportions of hydrogen. Hydrogen is a valuable resource in the petrochemical industry. Product quality and yield can be improved through processes such as hydrogenation and hydrocracking. Now we can generally collect and use everything we can. Even a small amount that cannot be recovered is mixed with gas as fuel. The hydrogen recovered from petrochemical exhaust gas is first of all for self-use. Whether there can be a larger amount for external supply needs to be studied and coordinated. As for coke oven gas, coal is heated and carbonized in isolation from air to produce coke as the main product, coke oven gas and coal tar as by-products. Coke oven gas contains about 50% to 60% hydrogen (V), and the rest is methane, etc. The weight yield of hydrogen is less than 2%. Coke oven gas is a suitable chemical raw material and can also be used as fuel gas. Regardless of safety, environmental protection or resource conservation, it is impossible to vent a large amount of gas. Methane is also a "powerful" greenhouse gas. From coke oven gas and other industrial hydrogen-containing exhaust gases, it must be purified to 99.99% hydrogen purity through desulfurization, CO shift, methanation, pressure swing adsorption (PSA) and other processes, and remove harmful impurities such as CO, sulfides, and halides. It is feasible to supply hydrogen externally. As far as coal coking is concerned, its main product, coke, is mainly used for ironmaking. One ton of iron requires about 0.4 tons of coke. If coke oven gas is used as the main product and the coking capacity is expanded, it will cause a serious excess of coke, which is putting the cart before the horse. Moreover, coking itself is high energy consumption and high pollution, and overcapacity must be prevented. Third, electrolyze water to produce hydrogen. It is a clean hydrogen production technology. Among them, hydrogen produced by electrolysis of water using renewable energy is called "green hydrogen" by the "World Energy Council" and is the development direction of hydrogen production in the future. One thing that needs to be studied is the use of clean power generated by non-fossil energy. It would be meaningless to use thermal power. This requires the establishment of a dedicated distributed power grid for clean power. Second, if the power consumption is too high, we must vigorously reduce power consumption and improve the energy efficiency of hydrogen production. Third, it is possible to use the "three abandoned" electricity amounts of abandoned water, abandoned wind, and abandoned light. Data shows that after hard work, my country's "abandoned water, abandoned wind, and abandoned light" rates in 2018 were 5.8%, 7%, and 3.1% respectively. The international advanced level is 3%, and there is still certain potential. Reducing the "three wastes" can dilute the total power generation cost. It would be better if power companies could supply water and use electricity at a preferential price. Nowadays, pilot projects are being carried out in Zhangjiakou, Inner Mongolia, Xinjiang and other places with rich wind power resources. If hydrogen energy is used nearby, it is more reasonable to avoid long-distance transportation. To sum up, it is hoped that while the industry is committed to fuel cell research, it will also pay attention to the source of hydrogen and seek environmentally friendly, economical and reliable hydrogen preparation paths. As for other methods of hydrogen production, such as nuclear hydrogen production, solar hydrogen production, biological hydrogen production, etc., they are still under research and development, and it is hoped that research can be accelerated. The preparation of hydrogen must be developed in coordination with storage, transportation, filling, and application. Only by implementing hydrogen sources can the entire industrial chain become a source of water and a tree.

2. The selection of hydrogen production path must grasp the environmental protection, economy, safety and energy efficiency. The hydrogen production path must scientifically grasp its special requirements on the basis of mature and reliable process technology. As for environmental protection, as briefly mentioned before, the hydrogen production process cannot produce large amounts of greenhouse gas carbon dioxide emissions. Obviously, this is primary and necessary. “"Gray hydrogen" is not advisable, "blue hydrogen" can be used, "waste hydrogen" can be recycled, and "green hydrogen" is the direction. The economic evaluation, safety assessment, and energy efficiency assessment of hydrogen production should also be highly concerned. The economic evaluation includes many aspects such as car purchase, energy consumption, maintenance and repair. From the perspective of hydrogen production evaluation alone, there are different versions and data on the costs of various existing hydrogen production process technologies. The discrepancies are large, but overall they are on the small side. Generally speaking, under the premise of reasonable raw material prices and electricity prices, the production cost of hydrogen per kilogram is 10 yuan for hydrogen production from coal, about 17 yuan for hydrogen production from natural gas, naphtha, heavy oil, and methanol, 21 yuan for recovery and purification of industrial by-product hydrogen, and 30 yuan for hydrogen production by electrolysis of water. On the basis of this cost price, firstly, the complete production cost of hydrogen should be calculated, which should include depreciation, taxes, labor and various expenses and the reasonable profit of the hydrogen production plant, to form the ex-factory price of hydrogen. The second is to calculate the costs, taxes, and profits of hydrogen storage, transportation, and refueling to form the retail price of hydrogen for fuel cell vehicles. It is fair and reasonable to compare this complete market price with the market retail price of gasoline and the commercial electricity price plus charging station fees, and corresponding policy support requirements can be put forward based on this. As hydrogen production process equipment improves and improves, there will be greater room for hydrogen price reduction to demonstrate its competitive economics. The use of small electrolyzed water hydrogen production and filling equipment can reduce storage, transportation and filling costs. The safety of hydrogen use cannot but be one of the hot topics of social concern. There is no doubt that the use of safe and reliable technology and equipment can provide security for the entire industry chain of hydrogen production, storage, transportation, refueling and use. But this does not mean that the natural properties of hydrogen can be changed. Hydrogen is colorless and odorless, has low gravity, high calorific value, and is volatile. Its explosion limit is very wide, ranging from 4% to 75.6% (V). It is flammable and explosive and is a dangerous product. Just as gasoline is safe to use in cars, gasoline is still flammable and explosive. The hydrocracking workshop of Daqing Refinery in my country on September 9, 1967, and the hydrogenation workshop of Fushun Petroleum No. 3 Plant on July 24, 1975, both experienced extremely serious and major explosions and personal accidents due to hydrogen leakage. ； On October 18, 2015, a hydrogen explosion occurred in a laboratory of a university's chemistry department and a personal accident occurred. It was recently reported that a hydrogen refueling station in Norway exploded. There have been many reports of explosions and burn injuries from hydrogen balloon toys. What I say is not to be sensational or unfounded, but the lessons of history are worth remembering. In the entire hydrogen industry chain, safety must be given top priority. As for the energy efficiency of hydrogen, there are issues that need to be studied. First, the hydrogen production efficiency, that is, the unit calorific value of the hydrogen produced/the unit energy consumption in the hydrogen production process, is currently only 60%. Second, when hydrogen is used in passenger cars, it consumes 1kg per 100 kilometers. Producing 1kg of hydrogen by electrolyzing water consumes about 56KWh, while electric passenger cars consume 15~20KWh per 100 kilometers. It is expected that the performance of fuel cell passenger vehicles will be further improved, so that hydrogen consumption per 100 kilometers will be greatly reduced, and at the same time, the power consumption of electrolyzed water will be greatly reduced to show its better energy efficiency.

Actively developing energy-saving and new energy vehicles is an inevitable trend. Since 2012, my country has determined that new energy vehicles include pure electric vehicles, plug-in hybrid vehicles and fuel cell vehicles. Today, the production and ownership of electric vehicles account for half of the world's total. Batteries, motors, and electronic controls are close to or reaching international levels. The construction of charging piles has also been accelerated accordingly, and they have entered the growth stage from the cultivation stage. However, it is still necessary to increase investment, accelerate technological innovation, and make unremitting efforts to promote the replacement of fuel vehicles. The research and development of fuel cell vehicles has also made progress. It has the advantages of high power, long battery life, fast refueling, and good low-temperature performance. It is suitable for commercial vehicles such as passenger cars and trucks. It has specific application scenarios that highlight its advantages. It can become an important member of the new energy vehicle family. It has good development prospects and will take longer. Therefore, it is necessary to consider comprehensively, plan carefully, overcome difficulties, and develop in an orderly manner.