my country's construction and sanitary ceramics industry contributes 1% of the country's GDP and consumes 1.7% of the country's energy, including 30% of the country's natural gas resources. Natural gas is a scarce resource, and more than 50% of the country's natural gas needs to be imported. . The huge gap in production ratio has made the energy efficiency of the building and sanitary ceramics industry criticized.
As my country has made a commitment to the world to "achieve carbon peaking and carbon neutrality in 2030 and 2060," how to further save energy and reduce emissions has become a key task for all walks of life.
In this regard, the China Building and Sanitary Ceramics Association pointed out that the proportion of industrial gas will not increase after 2025, and the proportion will decrease after 2030. Natural gas is a carbon-neutral transitional energy, and electricity will become the "main force of energy" in the future. Electric fired kilns (hereinafter referred to as "electric kilns") will be a new direction for the development of energy technology in the construction and sanitary ceramics industry.
So, is it reliable to use an electric kiln to produce ceramic tiles?
In the field of ceramic tile production, kilns are an indispensable and important component. Ceramic people have witnessed kilns that burn coal, heavy oil, diesel, coal gas, natural gas and other carbon-based fuels, but rarely see those that burn electricity. kiln.
Pan Jianhuan, director of Foshan Keda Mechanical and Electrical Technology Center, said that he had been exposed to electric kilns for producing daily porcelain in the 1990s; in recent years, Keda has practical application cases of electric kilns at home and abroad. For example, there are cases of electric kilns producing crystallized glass in France, and cases of electric kilns producing lithium batteries in China.
It can be seen that electric kilns are actually not new. In the eyes of professionals engaged in kiln R&D and innovation, electric kilns are part of their work. Cheng Zhaohua, general manager of Foshan Jiayao, pointed out that electric kilns have a wide range of applications and the technology is very mature. They are rarely used in ceramic tile production, but are widely used in magnetic ceramics, special ceramics, lithium batteries, glass mosaics, and third-degree firing. K gold bricks, wrapped color materials and other fields.
Anyone with a discerning eye will already understand at a glance that the above-mentioned fields are high-precision, high-value-added products, and have very strict requirements on the products’ firing atmosphere, physical and chemical properties, etc., so electric kilns can better control .
So, do electric kilns have no practical application cases in the field of ceramic tiles? It is understood that the kiln used in Laminam's Russian branch to produce slate slabs uses a mixed firing method of electricity and natural gas.
Pan Jianhuan also revealed that in 2015, Keda already had an electric kiln case in Russia for producing three-stage burnt flower slices. It first fired the blank at 1170°C and then grilled the flowers.
▲Keda’s case of three-stage fired electric kiln in Russia.
Since the technology is very mature and there are actual cases before it, why is there not a ceramic tile production line using electric kiln in China?
Cheng Zhaohua said that the characteristics of electric kilns are slow firing speed and long cycle, which means that their unit output is small (the output value is often not small). At present, it is not suitable for large-scale mass-produced products such as ceramic tiles. need.
What is the reason for the slow firing speed and long cycle? Cheng Zhaohua further explained that natural gas burning is mainly based on convection heat exchange, with radiation heat exchange as a secondary, and conduction heat transfer as a supplement; while electric kilns mainly use radiation heat exchange, conduction heat exchange as a secondary, and convection heat transfer as a supplement. The most efficient means of heat exchange is convection heat transfer. Just like adding a small fan to an air-conditioned room, this small fan will make people feel very cool. Therefore, convection heat transfer is more suitable for mass-produced products such as ceramic tiles.
If electric kilns really want to be promoted to the ceramic tile production field in large quantities, the first technical gap that needs to be overcome is to solve the installation problem.
Jing Haishan, deputy general manager of Foshan Delitai, pointed out that since electric power is mainly radiant heat transfer, electric power is more suitable to be installed in high-temperature zones, and high-temperature zones must be made of silicon carbide rods. The heating temperature is safe and durable. However, silicon carbide rods can currently only be about 3 meters in length. Now that the internal width of ceramic tile wide-body kilns reaches more than 3 meters, silicon carbide rods will face structural installation difficulties.
In addition, Jing Haishan also said that technical breakthroughs are needed in terms of temperature difference control of the internal cross-section of the electric kiln, as well as the life, replacement, maintenance, and safety of the silicon carbide rods on the high-temperature rollers.
▲Delita atmosphere push plate electric kiln.
Cheng Zhaohua also said that horizontal temperature differences will become a technical difficulty for electric kilns to produce ceramic tiles. This is because mass-produced kilns have a wide span and are prone to inconsistent firing temperatures between the middle and both sides of the kiln. In this case, the natural gas-fired kiln can be solved by adding a special burner (commonly known as a "spray gun"), but the electric kiln uses silicon carbon rods, silicon molybdenum rods or heating wires for radiant heat transfer, so the level of solution Temperature differences are more difficult.
However, Cheng Zhaohua believes that once electric kilns are used in large quantities and the industry joins forces to overcome the horizontal temperature difference, a phased breakthrough will definitely be achieved soon, such as adding a special structure like a maintenance channel for car repairs under the electric kiln. and heating devices, there must be many solutions.
As for the above-mentioned structural difficulties of electric kilns, Pan Jianhuan said that the industry has been exploring solutions. For example, adding a ceramic tile wide-body kiln in the middleThe hook hangs the silicon carbide rod to solve the installation difficulty of the silicon carbide rod being insufficient in length. In addition, Pan Jianhuan specifically mentioned the harmonics that can damage the power grid. Once the power consumption is large, and the ceramic tiles are fired, the voltage needs to be adjusted frequently to control the temperature. This requires the installation of filter capacitors similar to transformers to prevent the power grid from overheating and causing fires and short circuits. risk.
Compared with structural difficulties, the high cost of burning electricity is the biggest obstacle to the promotion of electric kilns.
As for the ceramic tile products themselves, Cheng Zhaohua pointed out the chronic problem of low thermal energy utilization efficiency of electric kilns. If converted into the thermal energy generated by natural gas consumed by existing kilns, the electricity consumed by electric kilns will be very huge. First, the installed capacity of ceramic factories will be very high.
Therefore, from a cost perspective, he believes that within the next five years, the probability of mass-produced ceramic tiles using electric kilns will be relatively small.
Jing Haishan revealed his calculation results. A kiln with a daily output of 20,000 square meters of ceramic tiles would have an installed capacity of more than 10,000 kilowatts if it only uses an electric kiln in a high-temperature zone. Such a huge installed capacity will be very difficult to meet.
As for the cost comparison between electricity and natural gas, Jinghaishan conducted a detailed comparison and conversion. Regardless of the conversion efficiency of the heating equipment, burning 1 kilowatt hour of electricity can theoretically produce 860Kcal of heat, while burning 1Nm³ of natural gas has a low heating value of 8300Kcal, which means that 1Nm³ of natural gas corresponds to 9.65 kilowatts of electricity.
The current average electricity price per kilowatt hour is 0.7 yuan, and the electricity price for 9.65 kilowatt hours is 6.76 yuan. The price of natural gas is usually only about 2.6 yuan/Nm³, and now the most expensive is about 4.3 yuan/Nm³. In this way, the price of natural gas for 1Nm³ It is 2.46 yuan lower than 9.65 kilowatt-hour electricity. The energy cost is very unequal, which is the biggest difficulty in promoting electric kilns.
▲Delitai natural gas rock slab wide-body roller kiln.
Don’t underestimate the energy cost difference of 2.46 yuan. Jing Haishan pointed out that for the current 800×800×11mm glazed tiles, the natural gas consumed by the tile kiln per square meter is about 1.6Nm³. A kiln with a daily output of 20,000m³ of ceramic tiles consumes 32,000Nm³ of natural gas per day (gas cost is 137,600 yuan). Converted into total electricity consumption, it is 308,800 kWh (electricity bill 216,160 yuan).
It can be seen that using natural gas can save 78,560 yuan per day compared with electricity, and 2,356 yuan can be saved based on 300 days per year.80,000 yuan. "With such a huge difference in fuel money, who can afford it?"
Moreover, even if the cost is not taken into account, considering the frequent power cuts in major ceramic factories across the country this year, the Guangxi production area even has power cuts for 28 days. If the ceramic tiles are switched to electric kilns, the substantial increase in electricity consumption will inevitably lead to Greater contradiction between power supply and demand.
It is well known that my country’s energy situation is “rich in coal, poor in oil, and short of gas”. The "China Electric Power Industry Annual Development Report 2021" released by the China Electricity Council on July 8 pointed out that my country's full-scale power generation in 2020 was 7,626.4 billion kilowatt hours, of which thermal power was 5,177 billion kilowatt hours, accounting for 67.88% of the country, while thermal power Among them, coal power accounted for 4,629.6 billion kWh, accounting for 60.70% of the country. In addition, hydropower accounted for 17.77% of the country, grid-connected wind power accounted for 6.12% of the country, nuclear power accounted for 4.80% of the country, and grid-connected solar power accounted for 3.42% of the country.
It can be seen that coal power is still the main energy source of my country’s power supply. If ceramic tiles are fully converted to electric kilns, they will inevitably rely on coal power in the next few years. As long as coal is burned, carbon emissions will be produced, but these carbon emissions will be concentrated in the upstream thermal power plants.
▲"Green electricity" can allow electric kilns to truly reduce carbon emissions.
Jing Haishan pointed out that the power generation capacity of 1 kilogram of standard coal is 3.3 degrees, but the combustion of 1 kilogram of standard coal will produce about 2.7 kilograms of carbon emissions. From the perspective of carbon peaking and carbon neutrality, electric kilns are definitely is a trend, but ultimately we have to consider whether it is "green electricity". If "green electricity" such as wind power, hydropower, photovoltaic solar power generation, etc. can satisfy industrial production in the future, then considering electricity consumption will be in line with the actual development situation. And the current The current situation is that industrial power consumption is insufficient, and many places are implementing power restriction measures such as "four on and three off".
Cheng Zhaohua said that thermal power plants are also under pressure to reduce carbon emissions, so they must also carry out upgrading and energy-saving transformation of power generation equipment. "Ceramic Information" learned from information released by the official website of the China Electricity Council that the national carbon dioxide emissions per unit of thermal power generation in 2020 were approximately 832 grams/kWh, a decrease of 6 grams/kWh from 2019 and a decrease of 20.6% from 2005. .
From a macro perspective, carbon peaking and carbon neutrality are answers that our country must submit to the world. But specifically in the field of ceramic tile production, considering the contradictions such as power restrictions,Shield, the top priority for energy conservation and emission reduction is not to switch fuels, but to improve the unit thermal efficiency of existing carbon-based fuels. We can also explore the path of mixed combustion of hydrogen and natural gas.
In fact, compared with the past, the natural gas consumed per square meter of ceramic tiles has been significantly reduced in recent years. According to Cheng Zhaohua, by continuously improving the kiln structure and increasing the efficiency of waste heat utilization, today, the consumption of natural gas per square meter of ceramic tiles has dropped from 3m³ to 1.6m³→1.5m³→1.2m³. Jiayao Company where Cheng Zhaohua works , only through technical transformation, it helped a ceramic company achieve 1.16m³/㎡, which is energy saving and consumption reduction achieved from a cost perspective.
▲The top priority for energy conservation and emission reduction is not to switch fuels.
Other kiln companies are also continuing to explore energy conservation. In early May this year, the Xinruncheng 600×600×9mm double-zero water absorption permeable tile production line constructed by Keda Manufacturing set a record of the lowest natural gas energy consumption of 1.13m³/㎡ after operating stably for more than a month. At the same time, the power consumption also increased. 20% less than the old kiln.
Under the guidance of the dual-carbon strategy, each ceramic factory is facing strict energy evaluation indicators. If it wants to increase production capacity, it can only improve energy utilization and reduce unit energy consumption.
Cheng Zhaohua believes that this is a top priority for the ceramic industry and is also a topic that must be overcome in the next five years. If the entire industry can further reduce the natural gas consumption by 1.2m³ or even 1m³ per square meter of ceramic tiles by 20%, then the pair will The contribution of the carbon strategy is self-evident.
The exploration of hydrogen energy is also on the way. On September 29, 2020, six departments including the Guangdong Provincial Development and Reform Commission issued the "Guangdong Province Action Plan for Cultivating New Energy Strategic Emerging Industry Clusters (2021-2025)", which pointed out that it is necessary to "promote the Foshan (Yunfu) Industrial Transfer Park, Guangzhou The construction of hydrogen fuel cell industrial parks in the Development Zone, Foshan Nanhai and Gaoming District, the establishment of Guangzhou-Shenzhen high-temperature fuel cell and system R&D and manufacturing bases, the establishment of hydrogen energy high-end equipment industry clusters in Guangzhou, Foshan, Dongguan, Yunfu and Huizhou, Maoming, Dongguan, Zhanjiang Hydrogen Energy Production, Storage and Transportation Industry Cluster".
According to Jinghaishan, Delitai is exploring hydrogen and natural gas mixed-firing kilns, and is currently deploying a project in China. Hydrogen accounts for more than 50% of the project, which can reduce carbon emissions by more than 50%. This is Because 1Nm³ of natural gas is close to 1Nm³ of methane, 1Nm³ of methane will produce 2 kilograms of carbon dioxide after combustion. IfMixing 50% hydrogen with natural gas is equivalent to reducing carbon emissions by 1 kilogram, and this reduced carbon is worth real money in the carbon trading market.
Pan Jianhuan pointed out that research on hydrogen in the industry has accelerated significantly this year, and Keda is also actively exploring how to utilize hydrogen energy.
In addition, for carbon reduction, Pan Jianhuan believes that in addition to improving energy thermal efficiency, another way is to recycle carbon dioxide in flue gas, because carbon dioxide has many uses, it can be made into dry ice, beer soda is also needed, and Used as plant fertilizer, carbon dioxide is also needed in various fields such as petroleum mining, machine casting, metal refining, biopharmaceuticals, and firefighting.
Currently, the overall carbon emissions of the building and sanitary ceramics industry are under investigation. According to data released by the China Building and Sanitary Ceramics Association, it is approximately 140-200 million tons per year, of which building ceramics account for 96%. In this regard, Jing Haishan believes that three trends in the building and sanitary ceramics industry, including production capacity decline, product upgrading, and energy structure adjustment, will help the building and sanitary ceramics industry achieve the goal of carbon neutrality by 2060.
(Article reproduced from Ceramic Information)
