The deep processing of coal tar includes tar distillation, washing and decomposition of fractions, production of industrial naphthalene, modified asphalt, and purification of crude phenol.

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The deep processing of coal tar includes tar distillation, washing and decomposition of fractions, production of industrial naphthalene, modified asphalt, and purification of crude phenol. There are various processes for tar distillation, and they can be classified into vacuum distillation, atmospheric distillation, and combined vacuum-atmospheric distillation processes based on the operating pressure of the distillation tower. Vacuum distillation: The distillation process consists of dehydration and fraction distillation. The process involves dehydration at atmospheric pressure, followed by vacuum distillation of the tar in a fractionation tower. This process has low coal gas consumption ； Waste heat is fully utilized ； The naphthalene fraction has a high concentration ； Operation under negative pressure results in less gas leakage, which is beneficial to environmental protection ； However, vacuum distillation equipment has strict requirements and high investment costs; moreover, the technology in China is not yet mature, so it is necessary to introduce foreign technology. Atmospheric and vacuum distillation: In this process, dehydration takes place at atmospheric pressure; the phenol fraction and naphthalene fraction with lower boiling points are distilled under atmospheric pressure, while those with higher boiling points are distilled under reduced pressure. This process features a high concentration of naphthalene fraction, exceeding 95% ； The separation effect is good; the naphthalene content in the naphthalene oil fraction can reach 90% ； High distillation efficiency and precise fractionation, reducing the need for repeated distillation in subsequent processing and saving energy consumption ； Since distillation is carried out under negative pressure, there is less gas leakage, which is beneficial to environmental protection. However, this process is complex and requires high investment; moreover, domestic technology is not yet mature, so it is necessary to introduce foreign technology. Atmospheric distillation: The process involves dehydrating the tar in a first-stage evaporator; thereafter, the mixed distillate obtained from the second-stage evaporator is sent to a distillation column where atmospheric distillation takes place to isolate the desired fractions. This process has advantages such as mature technology, reliability, simplicity, low investment, and high product quality; the exhaust gas is treated through centralized washing, resulting in good environmental protection effects. The process widely used in China at present. The tar distillation process can be divided into several procedures based on the cutting of fractions: narrow fraction cutting, two-stage mixing fraction cutting, and three-stage mixing fraction cutting. The one-tower process for separating three fractions through distillation is currently widely used in China. It offers advantages such as mature technology, reliability, and simplicity; it not only simplifies the washing process but also increases the concentration of naphthalene (to around 95%), raising its yield. Additionally, high-quality wash oil with low levels of naphthalene can be obtained. Washing and decomposition include tri-mix washing for phenol removal, decomposition of sodium phenolate, and inter-washing for phenol removal from phenol oil. In terms of operation method, three-phase washing has two process flows: batch and continuous. Intermittent washing is labor-intensive and involves a poor working environment; it is generally used only in factories with a small production scale. The continuous washing process has a simple flow and equipment, provides good washing results, low operating costs, and low labor intensity. It is controlled by DCS, offering a high level of automation. Therefore, this method is widely used domestically. Decomposition is generally carried out using the sulfuric acid method or the carbon dioxide method. The carbon dioxide method has a complex process flow, high investment costs, low decomposition efficiency, and an immature process technology. The sulfuric acid process features a simple flow scheme, good decomposition efficiency, low investment, small land requirement, and easy operation. Its drawback is the generation of some sodium sulfate wastewater during production; this method is currently the intermittent process widely used in China. For the production of industrial naphthalene, large and medium-sized tar distillation units typically employ a continuous distillation process using tubular furnaces. This continuous distillation process comes in several configurations, including two furnaces with two towers, one furnace with two towers, and one furnace with one tower. The double-furnace double-tower distillation process consists of two distillation towers and two tubular furnaces. That is, the phenol oil fraction is separated in the initial distillation tower, while the industrial naphthalene and washing oil fractions are separated in the distillation tower; both distillation towers are heated by two separate tubular furnaces. The single-furnace double-tower distillation process consists of two distillation towers and one tubular furnace. That is, the phenol oil fraction is separated in the initial distillation tower, while the industrial naphthalene and washing oil fractions are separated in the rectification tower; both distillation towers are heated by a tubular furnace. The single-furnace single-column distillation process consists of a distillation column and a tubular furnace. Industrial naphthalene is obtained from the side stream of the distillation tower. The distillation tower is heated by a tubular furnace. Modified asphalt: This unit employs the atmospheric pressure thermal polycondensation method.