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Chapter 6: Natural Gas-Based Carbon Black Production Carbon black is an essential chemical raw material in industry, and it is an important pigment second only to titanium dioxide. It features stability, heat resistance, chemical resistance, and light resistance. At the same time, carbon black is also a modifying additive for plastic and rubber products. Section 1: Overview 1. Definition of carbon black: Amorphous carbon produced by the incomplete combustion or thermal cracking of gaseous or liquid hydrocarbons under conditions of insufficient oxygen; it is a loose, lightweight, and extremely fine black powder. 2. Development of carbon black: the black ash obtained from burning animal and plant oils serta pine branches in ancient China ； In 1872, the United States produced carbon black using the \"tank method\" for natural gas ； In 1912, S. C. Mott discovered the reinforcing effect of carbon black on rubber ； In the 1920s, gas furnace black and pyrolytic black made from natural gas ； Later, J. C. Creach developed the oil furnace process. Today, the oil furnace method is the most efficient and cost-effective way for producing carbon black, with oil furnace black accounting for 70–90% of the total carbon black production. 3. Raw materials for carbon black production: Gaseous raw materials: natural gas, mine gas, refinery off-gases, calcium carbide gas, etc ； Liquid raw materials: coal tar, distillates from petroleum refining, etc. Solid raw materials: naphthalene, anthracene, etc. 4. Classification of carbon black: classified by manufacturing method (1) Contact process carbon black: batch process carbon black, drum process carbon black, and disk process carbon black ； (2) Furnace black: gas furnace method, oil furnace method, lamp smoke method ； (3) Pyrolytic carbon black: Pyrolytic carbon black (natural gas), acetylene carbon black (acetylene); classified by application and usage characteristics. (1) Carbon black for rubber: Hard carbon black (reinforcement), soft carbon black (filling) ； (2) Carbon blacks not for rubber use (special carbon blacks): pigment carbon blacks, conductive carbon blacks, carbon blacks for plastics, and other specialized carbon blacks (carbon blacks for synthetic leather, carbon blacks for black agricultural films), etc ； 5. Properties of carbon black: (1) Surface area: It is one of the important properties for identifying, classifying, and naming carbon black, and it is determined by gas-phase or liquid-phase adsorption methods. Low-temperature nitrogen adsorption method (i.e., BET method), macromolecule adsorption method (such as CTAB), and iodine absorption method. (2) Structure: It depends on the aggregate size, shape, as well as the number of particles and average mass within each aggregate. The structure of carbon black is expressed by the oil absorption value of DBP (dibutylphthalate, dibutyl phthalate). (3) Coloring strength: It reflects the average volume and size distribution of the aggregates; carbon black with a high coloring strength has a high light absorption coefficient and a low reflectivity. (4) The chemical composition of carbon black varies; for example, the carbon content in oil furnace-produced carbon black used in the rubber industry is over 97% ； The carbon content of pyrolytic black and acetylene black is higher than 99%. The elemental analysis results of some carbon blacks are shown in the table below. Chemical composition of various types of carbon black: Types of carbon black – Carbon black for rubber use, thermally cracked carbon black, acetylene carbon black. Carbon/%: 97.3–99.3, 99.4, 99.8. Hydrogen/%: 0.20–0.80, 0.30–0.50, 0.05–0.10. Oxygen/%: 0.20–1.50, 0.00–0.12, 0.10–0.15. Sulfur/%: 0.20–1.20, 0.00–0.25, 0.02–0.05. Nitrogen/%: 0.05–0.30, NA, NA. Ash content/%: 0.10–1.00, 0.20–0.38, 0.00–0.40. Volatile matter/%: 0.60–1.50. Section 2: Production methods for carbon black from natural gas. 1. Mechanism of carbon black formation: The generally accepted process for the formation of carbon black includes the following stages: (1) Formation of gaseous precursors of carbon black at high temperatures; (2) Nucleus formation; (3) Growth and aggregation of particles; (4) Surface growth; (5) Agglomeration; (6) Vaporization of aggregates. Production equipment: A batch-type carbon black plant consists of dozens to hundreds of furnace chambers. Each furnace room contains a lamp trolley composed of gas pipes, distribution pipes, and burners, channel steel, pulleys, a carbon black collection hopper, and a screw conveyor connected to the hopper. In addition to the furnace room, the production equipment also includes slag removers, cyclone separators, granulators, bag filters, and more. The influence of process parameters on the performance and yield of carbon black produced by the tank method includes the type of burner, the gas consumption per burner, the distance between the burner and the channel steel, the spacing between burners, the amount of primary air introduced into the combustion chamber, the amount of secondary air, the hydrocarbon content in the feed gas, the height of the smoke plume, and the gas-phase conditions. (2) The ratio of the outer cross-sectional area to the inner cross-sectional area of the burner remains constant: it depends on the properties required for producing carbon black and the composition of the feed gas. The nozzle opening becomes narrow, resulting in a shorter and thinner flame; the width of the openings (holes) for the carbon black particles decreases, leading to a lower yield. (3) Nozzle spacing: A range of 114–140 mm is preferred; this spacing is the minimum required to protect the equipment inside the combustion chamber, and it also represents the upper limit for the airflow rate of the material fed to the nozzles. (4) Raw gas volume: As the gas volume increases, the temperature in the combustion chamber rises accordingly. As the flame intensity increases, the amount of carbon black produced rises, but the yield of carbon black decreases. Excessively large flames can eventually damage the channel steel as well. (5) Raw gas composition: The higher the average molecular weight of natural gas, that is, the higher the content of ethane, propane, butane, or other heavier hydrocarbons in it, the higher the yield of carbon black. Production process data (1) Nozzles: Nozzle spacing 70–140 mm ； The distance between the burner and the channel steel is 50–90 mm ； Air flow rate per burner: 1–2.9 m3/d ； Each burner produces 0.25–1.6 g/h of carbon black ； The nozzle groove width is 0.6～1.2 mm. (2) Raw gas pressure: 100～250 Pa at the burner inlet, 100～250 Pa at the burner outlet. (3) Gas consumption: 50–55 m3/kg of carbon black ； (4) Natural gas generation rate: 8–20 g/m3 ； (5) Temperature inside the furnace: 500～550 at the bottom surface of the channel steel℃ ； Temperature of exhaust gases: 340–360℃ ； The flame temperature is 1200–1400°C. (6) Composition of the exhaust gases from the furnace: O2 at 15–17% ； CO2 is 2–3% ； N2 is 80–81% ； CH4 is 0.1～0.2% ； CO is 0.1% ； H2 is 0.1%. Technical improvements: Fuel enrichment and oxygen-enriched production. Injecting anthracene oil or coal tar into the furnace can increase output and reduce costs. Oxygen-enriched production: oxygen-enriched air is used in place of regular air to produce carbon black. It can reduce the nitrogen content in exhaust gases, making the nitrogen-to-hydrogen ratio suitable as a feed gas for ammonia synthesis, thereby enabling the co-production of ammonia and carbon black using an oxygen-enriched gas furnace process. There are many factors that affect the properties and yield of carbon black produced by the gas furnace method, such as the composition of natural gas, furnace temperature and flue gas temperature, and the ratio of air to natural gas. Among these, controlling the ratio of air to natural gas is the most important process condition. Basic equipment for production facilities: reaction furnaces, which are usually cylindrical in shape; their outer shell is made of steel plates welded together, while the inner layer is constructed from clay bricks and lightweight bricks, or from refractory castables and insulating castables. Reactor furnaces come in three types: single burner, double burner, and multi-burner. Two burners form a group, with one common flue. Cooling tower: It is a hollow tower with an interlayer; circulating water is pumped into this interlayer, and high-pressure nozzles are installed around the tower to spray water mist into it ； Collection equipment: consists of a collection box, air-conveying pipes, and a shaking device. 32 to 40 glass fiber filter bags are installed on the box cover, with 30 to 36 filter boxes per production unit ； Furnace front blower: Forces air into the furnace for combustion ； Exhaust fan: Installed behind the cooling tower to force the remaining combustion gases into the filter bags ； (If the air pressure from the fan in front of the furnace is high, an exhaust fan may not be necessary.) Vibration device: This device uses the expansion and contraction action of the filter bag to shake off the carbon black on it. Production process data (1) Natural gas to air ratio: 1:4～4.5 ； (2) Residence time in the high-temperature zone: 4–6 s ； (3) Temperature: The temperature inside the furnace is 1250–1350℃ ； The temperature entering the cooling tower is 1050–1100℃ ； The temperature at the exit of the cooling tower is 350–380℃ ； The temperature entering the filter box is 200–250℃ ； (4) Pressure: The pressure in the burner box is 1000–3000 Pa ； The filter bag pressure is 900–1500 Pa ； (5) The filter bag load is 1.0～1.2 m3/m2·min ； (6) Filter bag area: 1500–2000 m3 per section ； (7) Natural gas generation rate is 140–150 g/Nm3 ； (8) Composition of flue gas (on a dry basis): CO2 is 3.5–4.0% ； CO is 9–10% ； O2 is 0.2～0.5% ； H2 is 19–20% ； CH4 is 0.5～1.0% ； N2 is 67–69% ； The moisture content on a wet basis is 35–40%. 4. Mechanical methods for processing carbon black: to remove hard carbon and impurities from carbon black as well as to granulate it. The processing steps for channel-processed carbon black and furnace-processed carbon black are basically the same, with all steps being carried out in a closed system. The refining fan first mixes carbon black with air and feeds the mixture into an impurity separator, where hard carbon and heavier ash are removed before it is sent to a cyclone separator. The separated carbon black enters the granulator through a rotary airtight valve at the bottom, where it is granulated ； The air discharged from the top of the cyclone separator contains a small amount of carbon black; it enters a recovery and filtration box where the carbon black is separated out, leaving clean air to be discharged. The granular carbon black flowing out of the granulator passes inspection; after being weighed and packaged, it becomes the finished product. Section 3: The Production Status and Prospects of Carbon Black in China. Driven by the automotive and tire manufacturing industries, China’s carbon black industry has achieved significant progress over the past 10 years, as evidenced by two main aspects: first, a continuous increase in production capacity and technical standards; second, notable improvements in the structure of its product portfolio. Although China’s carbon black production is growing rapidly, its carbon black enterprises are relatively scattered, generally small in scale, and the industrial structure is highly unreasonable. Therefore, it is necessary to rely on technological progress and innovation, adjust the product structure, improve management capabilities, and continuously elevate the level of China’s carbon black industry. Problems in China’s carbon black production: (1) Unreasonable industrial structure; (2) Shortage of raw oil resources; (3) Excess total production capacity for carbon black; (4) Persistent gaps in production technology; (5) Increasing environmental pollution. Prospects for the development of carbon black production in China: (1) Increased efforts to develop new varieties; (2) Full utilization of oil and gas resources; (3) Adoption of clean and safe production methods; (4) Improvement of production efficiency