At the end of the last century, China's household biogas made good progress, and played an important role in solving the problems of rural ecological protection, lack of fertilizers, and energy use for fuel and lighting at that time.
However, entering the 21st century, the rural production and living conditions have changed, and the household small biogas and farm biogas projects are gradually in an awkward situation while achieving faster development.
In 2015, China put forward the transformation and upgrading of biogas, learning from the European experience, shifting the focus of development to industrialized large-scale projects, focusing on the development of large-scale biogas and biogas projects (a single project with a daily production of biogas of more than 10,000).
In recent years, with the introduction of the "double carbon" goal, the whole society needs the biogas industry with negative carbon emission characteristics to make corresponding contributions. In the new era, under the background of "double carbon" goal, it is very necessary to summarize the history of biogas industry in China, to find a path of biogas development adapted to Chinese characteristics, and to let the biogas industry play an important role in its own right.
I. Main problems in the development of industrialized biogas industry
1 Technical process immaturity
1.1 The core fermentation technology is still in the exploratory stage
Currently, the core fermentation process of the domestic industrialized biogas project is the introduction of the European technology process.
The current core anaerobic fermentation process has three kinds of wet (fermentation concentration < 12%), semi-dry (12% ≤ fermentation concentration < 20%), dry (fermentation concentration ≥ 20%), wet process is widely used in livestock and poultry wastewater, the adaptability of the raw materials of the dry yellow straw is poor, and the raw material particle size is required to be less than 3 cm, and the quantity of impurities and soil content is strictly required. Wet process to flow field to achieve homogeneous mixing, dry yellow straw is difficult to homogenize, prone to scum crust phenomenon, and fermentation concentration is low, solid-liquid separation of methane concentration (5 ~ 8%) is high, methane reflux is very difficult, the actual volumetric gas production rate is low (0.8 ~ 1.2), high investment, large floor space, high energy consumption.
Compared with the wet process, semi-dry process is simple, less investment, strong adaptability of raw materials, low self-consumption, high volumetric gas production rate, low pressure on the discharge of biogas, and more thorough anaerobic digestion. The semi-dry process introduced in China also has the problem of raw material adaptation. For example, poor stability of feeding, mixing and homogenization difficulties, material stratification is serious, inlet and outlet system is often blocked, the existing imported solid-liquid separator is not applicable and a series of problems. But the semi-dry process on the material requirements of low (raw materials 5cm or so can be), the soil content of the requirements of a wide range of impurities, adaptable, convenient control, the actual operation of the volumetric gas production rate can be stabilized at more than 1.5, with the enhancement of localization of equipment, the construction of the investment to reduce the space is larger.
Dry process introduced into the country in recent years, because of the confidentiality of foreign technology, the need for a full set of technology and equipment imports, high cost, and is currently in our country basically in the experimental exploration stage.
1.2 Raw material crushing and pre-processing technology is immature
China's dry yellow straw collection and storage to the landing baling-based, raw materials containing soil with a high rate of impurity, more than 30% in severe cases; subject to the collection and storage constraints, the water content changes in 20 ~ 75%. Market mainstream crushing to small agricultural machinery, equipment level is low, poor reliability, no soil, impurities, iron function, the change of raw material characteristics and multiple types of raw materials basically have no adaptability, and at the same time need to manually unpacking, processing capacity is low (2~3 t/h). At present, there are no professional straw crusher manufacturers and complete sets of equipment to meet the needs of the industry.
Straw pretreatment can improve the efficiency of straw fermentation, to solve the floating residue crusting, fermentation difficulties, layering and other issues. Commonly used pretreatment methods are physical methods, including crushing, kneading, steam blasting, radiation, etc.; chemical methods, including acid treatment, alkali treatment, wet oxidation, etc.; biological methods, including yellow storage, fungal treatment, enzyme treatment, etc.. At present, China has not yet formed a mature and reliable straw pretreatment technology process that can be adapted to different types of domestic raw materials.
Different core fermentation and pretreatment technologies are still in the stage of engineering verification and application in China. After several years of unremitting efforts to achieve certain breakthroughs, there are already enterprises that have systematically mastered the technical process routes that can effectively solve the adaptability of domestic raw materials, and are in the process of demonstration and popularization.
2 Process, design, equipment manufacturing service unit capacity
Currently on the market, the relevant service units are generally growing in the rural household biogas era, the lack of industrialization concept and systematic thinking. There is no mature and professional industrialized biogas engineering process design unit in China. The key technology and core equipment are all introduced from European countries, and the selection of equipment is rigidly copied without combining with the characteristics of Chinese raw materials and then innovated. Professional equipment manufacturing enterprises are mainly small agricultural machinery manufacturers, low degree of standardization, equipment reliability, poor stability, low degree of automation, far from forming a series of equipment manufacturing. In addition, the general contracting unit generally hold "only construction regardless of the operation" inherent concepts, the general contracting project is difficult to do after the completion of steady production.
3 Industrial biogas project industry chain is long, the business model is immature
3.1 Raw material collection, storage and transportation system has not been established
At present, China's agricultural and rural organic waste collection, storage and transportation system is still in the primary stage, the lack of stable collection, storage and transportation organizations, raw material quality, quantity, price and reliable protection is more difficult; collection and storage standards and norms have not yet been established, the collection, storage and transportation team lack of professionalism, in addition to the basic quality is difficult to guarantee, even if it is difficult to guarantee the quality, the quality and price, the price of raw materials. In addition to the basic quality is difficult to ensure, and even the occurrence of raw materials rot or high-temperature spontaneous combustion. The market is relatively chaotic, the government did not refer to the urban garbage collection system, in-depth guidance to establish a sustainable agricultural and rural organic waste storage and transportation security system. Take straw as an example, raw materials belong to more than one season a year, the storage time of more than 8 months; the amount of large (daily output of 40,000 m? biogas project, the annual amount of straw more than 70,000 t), especially in the northeastern region of the corn stover, fall and winter storage of straw moisture content varies, there is a large number of snow bags of straw, which further increases the difficulty of the collection and storage.
3.2 Lack of high-value utilization of biogas
Biogas direct supply and heating need to build an independent pipeline network, biogas projects are located in townships and rural areas, and the economy is generally underdeveloped, the price affordability is poor, the degree of pipeline network coverage is low, and part of the project is subject to the restrictions of the franchise, the existence of the network is difficult, the price of the low and other issues. Although the state encourages non-electric utilization of biomass energy, it has not yet issued specific support policies for non-electric utilization, biogas power generation and direct biomass combustion competition, subsidies in arrears, poor project cash flow, and lack of sustainable profitability of energy-side products. Biogas direct supply and heating just started, few mature cases, low market acceptance.
3.3 High-value application of biogas residue and biogas liquid is in the primary stage
High-value application of biogas residue and biogas liquid is an important factor of project profit and loss, and the basis of normal and stable operation of the project. Industrialized biogas project digestate, biogas liquid volume (semi-dry process daily production of 40,000 square meters of biogas project, the annual production of 72,000 tons of digestate, biogas liquid 14,000 tons; wet process biogas liquid volume is even larger). Biogas residue and digestate are high-quality raw materials for the production of organic fertilizers, rice-planting substrates and liquid organic fertilizers, but the production and marketing of related products are in the initial stage, with a low degree of user acceptance, and large-scale popularization and application still need to be cultivated. Part of the regional environmental protection department on the digestate, digestate awareness, to take a "one-size-fits-all" policy, prohibit the digestate, digestate directly to the field use, subverted the common sense of agricultural development over the centuries.
4 Straw and mixture biogas carbon emission reduction methodology has not yet been developed
Carbon asset income is the social benefits of industrialized biogas project embodied in the project to increase revenue and increase the profitability of the fundamental. At present, the carbon emission reduction methodology for straw biogas and straw mixture biogas projects has not been formulated, and it is necessary for the relevant departments, enterprises, associations and organizations to collaborate on innovative research to clarify the baseline emissions, the principles and methods of calculating the project emissions, as well as the monitoring data and methodology, and to carry out the project filing, the annual emission reduction accounting, and the carbon market trading as soon as possible after the endorsement of the Ministry of Ecology and Environment.
5 Multi-departmental management, unclear lead department, difficult policy coordination
The country attaches great importance to the development of biogas, and the special characteristics of the biogas industry at this stage are also very much in need of policy support. However, the biogas industry chain is long, involving energy, development and reform, finance, agriculture and rural areas, ecological environment, housing and construction and other departments, multi-disciplinary management, nine dragons to rule the water, the lead department is not clear, for many years has not been able to form a concerted effort to promote the development. Politics out of many heads, principle supportive of the views of many, specific measures to implement the implementation of less, the policy to lead the development of the effect is difficult to highlight.
Two, continue to firmly believe that in the "dual-carbon" background, biogas industry has great potential
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1 Europe's advanced experience provides reference for the development of China's biogas industry
Europe is an advanced region for the development of the global biogas industry, with more than 40 years of experience in the development of industrialized biogas, and mature technology and business models. Biogas has become an important part of renewable energy in Europe, and is a key pillar for the sustainable development of Europe's modern agricultural circular economy and a major alternative to fossil natural gas in the future.
The number of biogas projects in Europe is large and spread all over the country, with more than 9,600 in Germany and more than 1,500 in Italy. European biogas raw materials are diversified, mainly energy crops, straw, livestock and poultry manure, domestic waste, etc.; the process is mature and technologically diversified, with wet, semi-dry, dry anaerobic fermentation and other processes, gas production efficiency, low self-consumption of energy, a high degree of automation; equipment manufacturing, design and construction, operation and management, and product services, etc., the formation of a complete industrialized, large-scale industrial system and mature business models. Germany In Germany and other countries with mature biogas industry, 25% of farmers' income comes from biogas. In addition to biogas power generation in the ascendant, in recent years, all countries are vigorously develop biogas purification system of biogas, by 2030, biogas in major countries will account for 10% of the gas consumption. Because of large-scale biogas residue and biogas liquid returned to the field, the use of chemical fertilizers and pesticides in Europe is at a lower level in the world, and the content of organic matter in the soil is maintained at a high level. The negative carbon emission characteristics of biogas make it the most popular emission reduction category in the carbon market in Europe, and the biogas industry has become an important support for the EU to achieve the carbon neutrality goal in 2050.
2 The development of industrialized biogas industry is the main force to achieve the dual-carbon target
The comprehensive utilization of anaerobic fermentation of straw can bring the CO2 absorbed by plants in the process of growth into the soil partly through the biogas residue and biogas liquid, and increase the soil carbon pool. Compared with the low carbon emission of wind energy and solar energy, the comprehensive utilization of biogas industry has typical negative carbon emission characteristics and can play a more significant role in carbon emission reduction.
According to the research, every 10,000m?of biogas can reduce 115 t of greenhouse gas emissions, and it is expected that China's biogas industry can reduce greenhouse gas emissions by 1 billion t in 2060. China's carbon emissions will be about 10.6 billion t in 2030 when carbon reaches its peak, and the biogas industry can contribute 9.4% of the emission reduction to carbon neutrality in 2060, which will surely play a key role in realizing China's dual-carbon goals. The biogas industry will certainly play a key role in realizing China's dual-carbon goal.
3 Developing industrialized biogas industry is an effective way to solve the surface source pollution and increase the supply of clean energy
Organic waste from agricultural planting and breeding is the most difficult surface pollution source to manage. 2020 China's production of crop straw will be about 860 million tons, and fecal waste will be 3.8 billion t. Referring to the experience of Europe, the biogas industry is mainly to deal with straw, and auxiliary to deal with fecal waste. Agricultural organic waste through anaerobic fermentation treatment, not only harmless solution to surface pollution, but also the production of clean gas, biogas residue, biogas production of high-quality organic fertilizer, to promote the green and sustainable development of agriculture. By 2060, such as only considering 40% of straw and farming manure through the system of biogas harmless treatment, the annual production of biogas 200 billion m?, such as purified biogas, can reach the current domestic conventional fossil natural gas annual extraction of 80%, can make the future of China's natural gas dependence on the outside world from 66.7% down to 41.7%.
4 The development of industrialized biogas industry can promote the rural energy revolution, and promote the construction of beautiful countryside
China's rural areas are widely dispersed, transportation and energy supply is relatively weak, the difficulty of environmental management, the majority of rural areas in the social energy supply system at the end of the countryside, facing the dispersion of energy, insufficient energy supply, poor quality, high cost and many other difficult problems, and many areas can not be detached from the straw, Many areas are unable to get rid of straw, firewood, coal as a source of energy for life, low efficiency and environmental pollution.
Biogas can be adapted to local conditions, gas is suitable for gas, electricity is suitable for electricity, gas, electricity, heat and integrated development, to achieve a certain degree of energy storage and convenient regulation of the function of stable and diversified clean energy supply, in reducing the cost of integrated energy, while improving the quality and reliability of rural energy supply.
The straw-based, synergistic treatment of livestock and poultry manure, organic waste biogas projects can reduce surface pollution, protect the ecological environment, and effectively solve the problem of new rural construction and environmental governance. Biogas, biogas alternative fertilizer, pesticide reduction, can establish a green cycle of agriculture industry model to improve the quality of agricultural products, increase farmers' income, to ensure food safety, in promoting the transformation and upgrading of the structure of the rural energy use, to achieve the rural energy revolution at the same time, to promote the construction of a beautiful countryside.
5 Biogas, biogas effective protection of arable land, to ensure the sustainable development of agriculture
Arable land capacity determines our food production capacity, is an important guarantee of food security. For a long time, excessive use of chemical fertilizers and pesticides, organic matter supplementation is small, resulting in serious overdraft of China's geotechnical capacity, soil sclerosis is serious.
Since the 1950s, large-scale reclamation of black soil in Northeast China, the black soil layer has been reduced by an average of 0.3~1.0 cm per year, and the thickness of part of the black soil layer has been reduced to 0.2~0.3 m. The biogas project produces biogas residue and biogas liquid, which is a high-quality organic raw material that can improve the soil, enhance the soil's ability to retain water and fertilizer and increase the number of beneficial microorganisms in the soil, effectively increase the efficiency of fertilizer utilization, and achieve long-term efficient reduction in the application of fertilizer and pesticides, and promote green agricultural production. Long-term efficient reduction of fertilizers and pesticides, promote the green and sustainable development of agriculture and land protection, the realization of the national "food in the ground" strategy has an irreplaceable role, and is conducive to ensuring food security and ecological security.