The Furnace Black Process

Furnace Black One of the three principal processes used for making carbon black the others being the Thermal Black and the Channel Black processes. In the Furnace Black process, aromatic fuel oils and residues are injected into a high velocity stream of combustion gases from the complete burning of an auxiliary fuel with an excess of air. Some of the feedstock is burned, but most of it is cracked to yield carbon black and hydrogen. The products are quenched with water. 

The increasing demand led to new production processes. The most important process today is the furnace black process. It was developed in the United States in the 1930s and substantially improved after World War II. It is a continuous process, which allows the production of a variety of carbon black types under carefully controlled conditions. Nearly all rubber grades and a significant part of pigment-grade carbon blacks are now manufactured by the furnace black process. Nevertheless, other production processes, such as gas black, lamp black, thermal black, and acetylene black processes, are still used for the production of specialties. 

Natural gas, which was previously the predominant feedstock for the production of channel blacks and furnace blacks in the United States, has lost its importance for economic reasons. Currently, only thermal blacks are produced with natural gas. However, natural gas is still the most important fuel in the furnace black process, even though the use of other gases and oils is also possible. In several patents recycled tail gas in combination with oxygen or oxygen-enriched air, has also been proposed as a fuel, but has not reached any commercial importance. 

The furnace black process is currently the most important production process. It accounts for more than 95 % of the total worldwide production. The advantages of the furnace black process are its great flexibility in manufacturing various grades of carbon black and its better economy compared to elder processes. The following comparison makes this apparent for similar grades of carbon black, the production rate of one flame is ca. 0.002 kg/h for channel black, ca. 0.2 kg/h for gas black, and ca. 2000 kg/h for a modern furnace black reactor. However, in spite of the more advantageous furnace black process, the production processes listed in Table 27 (except for the channel black process) are still in use for the production of special carbon blacks which cannot be obtained via the furnace black process. 

In the past decades the rapidly expanding automobile industry required increasing numbers of tires with various characteristics. This led not only to the development of new rubber grades, but also to the development of new carbon blacks required by the increasingly refined application processes and to the development of a new and better manufacturing process, the furnace black process. Unlike the old channel black process, this process allows the production of nearly all types of carbon black required by the rubber industry. It also meets the high economic and ecological requirements of our times. 

In the gas black process (Fig. 55), the feed stock is partially vaporized. The residual oil is continuously withdrawn. The oil vapor is transported to the production apparatus by a combustible carrier gas (e.g., hydrogen, coke oven gas, or methane). Air may be added to the oil-gas mixture for the manufacture of very small particle size carbon black. Although this process is not as flexible as the furnace black process, various types of gas black can be made by varying the relative amounts of carrier gas, oil, and air. The carbon black properties are also dependent on the type of burners used. 

Most of the carbon black used in the plastics industry is produced by the furnace black process (see Section 4.4.1). Fine furnace blacks often appear more bluish than coarse ones in incident light (full-tone tinting) but more brownish in transmitted light (transparent tinting) and in gray tints. By controlling the conditions of black manufacture, however, substantial shifts in hue can be achieved. Bluish carbon blacks are commonly preferred because of the impression of greater color depth. 

The furnace black process is capable of producing a chemically pure, fine-particle carbon black with low volatile content, 1-2%, and pH ranging from 6 to 10, which is suitable for most plastics end uses. This process allows precise control of a carbon black s particle size and shape (or morphology), which ensures uniform color and physical properties in plastics applications (Fig. 11.1). 

Carbon black is produced by the partial combustion or thermal decomposition of hydrocarbons. Several methods are used, including the furnace black, thermal black, lamp black and acetylene black processes. The furnace black process is the most common. In this process, natural gas (or another fuel) is burned to form a hot gas stream that is directed into a timnel. An aromatic oil is sprayed in and the black forms as the gas moves down the tunnel. The reaction is quenched with the addition of water, and the product is collected as a low density powder (fluffy black) or is further processed into millimeter sized peUets. 

Plants operating the furnace black process can produce up to 16 10- t/a in a single reactor. The reactor lifetime is almost two years despite the high thermal and mechanical stress. 

The furnace black process was developed in the US in the 1920s and, since that time, has been greatly refined. It is a continuous process, carried out in closed reactors, which produces a flame carbon. Using petrochemical and coal tar oils as feedstocks, this... 

The two major commercial processes for manufacturing carbon black are the thermal black process which uses natural gas as the hydrocarbon feed stock, and the furnace black process which petroleum oil as the feedstock. The thermal process produces the largest particle size (0.1 to 0.5 xm) and lowest structure blacks. The furnace process accounts for over 95% of the total carbon black produced and can be controlled to produce both small and large particle size grades in the range of 0.01 to 0.10pm. 

This is a more advanced partial combustion process. The feed is first preheated and then combusted in the reactor with a limited amount of air. The hot gases containing carbon particles from the reactor are quenched with a water spray and then further cooled by heat exchange with the air used for the partial combustion. The type of black produced depends on the feed type and the furnace temperature. The average particle diameter of the blacks from the oil furnace process ranges between 200-500 A, while it ranges between 400-700 A from the gas furnace process. Figure 4-4 shows the oil furnace black process. 

Carbon blacks are manufactured from hydrocarbon feedstocks by partial combustion or thermal decomposition in the gas phase at high temperatures. World production is today dominated by a continuous furnace black process, which involves the treatment of viscous residual oil hydrocarbons that contain a high proportion of aromatics with a restricted amount of air at temperatures of 1400-1600 °C. 

A flow diagram summarizing the complete furnace black process is shown in Figure 54. 

In the thermal black process, natural gas is cracked to carbon black and hydrogen at 1100 to 1650°C in a refractory-lined furnace in a two-cycle (heating and making, or decomposition) operation. The reaction is... 

The gas furnace process, is similar to the oil furnace process but, like the thermal black process, uses natural gas as feedstock. 

Globular particles of relatively large size ( 200 nm) and low specific surface ( 10 m2 g"1) can be produced by the thermal process, which involves the the cracking of natural gas. The thermal blacks (e.g. Sterling FT) have lower ash co than the furnace blacks for this reason, and because of the discrete nature of primary particles, they are favoured for adsorption studies. 

In order to separate the soUds, process gases containing carbon black are passed through a filter after the cooling stage. Onward processing is similar to that of the furnace black manufacture. 

S.7.6.2.2 Pyrolysis Processes in the Presence of Oxygen Furnace Black Process... 

Furnace black processes currently account for more than 95% of the carbon black manufactured. A great advantage of such processes is their flexibility in producing different carbon black types, types with primary particle sizes between 10 and 80 nm being producible. 

The lamp black process produces particularly coarse particulate carbon black with a high density ( heavy black ). Due to the broad particle size distribution of 60 to 200 nm, it has not been possible to replace lamp black with furnace black in some applications. 

The thermal black process operates discontinuously and generally utilizes natural gas as a feedstock. A production unit consists of two cylindrical furnaces connected to one another, in which refractory bricks are piled one on top of another for heat storage with a large cavity in between. The two furnaces are operated alternately while the first furnace is being heated to the reaction temperature (ca. 1300 to 1500°C) with a stoichiometric mixture of air and combustible gas (mainly natural gas), natural gas is fed into the second already heated furnace and is thermally pyrolyzed. Since the reaction is endothermic, the furnace cools and the gas flows are switched when a critical minimum temperature is reached and the first furnace utilized, while the second is heated up again. The cycle time is about 5 minutes. 

The reaction products are quenched by water sprays in a cooling zone and the carbon black separated in filter units. The yield is ca. 35% of the carbon content of the feedstock and combusted gas. The residual gas consists almost entirely of hydrogen and can be mixed with natural gas for heating the furnace or for diluting the gas to be pyrolyzed. Coarser carbon black is produced than in the lamp black process, with primary particle sizes of 120 to 200 nm or 300 to 500 nm being attained depending upon whether the natural gas is diluted with inert gas or not. 

An application-oriented classification of pigment blacks distinguishes between High Color (HC), Medium Color (MC), Regular Color (RC) and Low Color (LC) pigment blacks. A third capital letter relates to the manufacturing process furnace black process (F) or gas black process (C, from the historically similar channel black process). 

Of processes using incomplete combustion, the most important is the so-called oil furnace black process, in which aromatic residuum petroleum oils are preheated and then injected (atomized) into a furnace at around 1400°C. Combustion is halted by the injection of a water spray, and the carbon black is formed. The degree of aggregation of the carbon black spheres increases with increasing aromaticity of the feedstock properties and yield can be changed by varying processing variables. Other carbon blacks prepared by incomplete combustion are lampblack and channel black. 

Better yields of carbon black are obtained by improved separation of the combustion function from the carbon-forming function, as is accomplished in the newer furnace black processes. This approach enables gas oil (high boiling point liquid petroleum fractions) or natural gas to be used to produce carbon black. The cooling function from 1,400°C to about 200°C is accomplished by direct water sprays. The product is removed from the gas stream via a combination of cyclone collectors and glass or Teflon fiber bag filters. One tonne of furnace black is obtained from 5,300 to 7, OOOm (1 atm 15.6°C) of natural gas, or 1,400-2,800 L of gas oil corresponding to 50-70% yields. Oil-based furnace black now supplies about 90% of the current carbon black market, although the special features of the product from small-scale processors still contribute some product [4]. 

Carbon black is the most important and powerful filler for rubbers. Each of the above characteristics of the carbon black has its effect on the properties of rubber in which carbon black is incorporated and careful selection of grade is necessary to ensure a correct balance of processing and vulcanising properties. The furnace black type, which has fine particle size, is used in lining, where high strength and resistance to abrasion are required. 

For the process scenario discussed, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent C02/kg H2 produced as compared to conventional steam-methane reforming and furnace black processing. 

The properties of the carbon black are particularly dependent on the reaction conditions of the pyrolysis. The distribution of particle sizes from furnace carbon black extends from around 10 nm to 100 nm. (Smaller particles can be produced by the gas black method, larger particles by the thermal black process.) Small carbon black particles are obtained with high reaction temperatures and reaction times of around 10 sec., whereas the manufacture of carbon black with a particle diameter of 35 to 65 nm requires lower temperatures and reaction limes of 1 to 2 sec. 

Impingement (Channel, Roller) Black Process. From World War I to World War II the channel black process made most of the carbon black used worldwide for mbber and pigment applications. The last channel black plant in the United States was closed in 1976. Operations still exist and are even being expanded in Europe. The demise of channel black was caused by environmental problems, cost, smoke pollution, and the rapid development of oil-furnace process grades that were equal or superior to channel black products particularly for use in synthetic rubber tires. 

In the channel black process, diffusion flames burning natural-gas impinge on reciprocating metal channels where carbon is deposited. Rotating drums may also be used. The carbon is scraped off, collected, micro-pulverised and then usually pelletised. These blacks have a much higher combined oxygen content than furnace blacks. This process is little nsed now largely dne to unfavourable economics and environmental problems. 

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