How to choose between atmospheric and vacuum distillation in coal tar processing?

I believe that vacuum distillation is a good option for the following reasons: The process flow for continuous vacuum distillation of coal tar is as follows: Coal tar is heated to 120–130°C using a tar preheater (used only during startup) and Heat Exchanger No. 1 for soft asphalt, and then it enters the pre-dehydration tower, where most of the water along with a small amount of light oil are removed through flashing. The tar at the bottom of the pre-dehydration tower flows automatically into the dehydration tower, while steam and light oil gases escape from the top of the tower; ammonia water and light oil fractions are obtained through a light oil condenser and a light oil separator. Light oil reflux is fed into the top of the dehydration tower, while the anhydrous tar at the bottom of the tower is heated cyclically in a reboiler to provide the heat required by the dehydration tower. A portion of this anhydrous tar is heated to 335°C using Heat Exchanger No. 2 and a tubular furnace before being fed into the main tower. The phenol oil fraction vapor escaping from the top of the main tower is converted into phenol oil fraction through a phenol oil condenser and a cooler; a portion of this fraction is sent back as reflux to the top of the main tower. Naphthalene oil fraction, washing oil fraction, and anthracene oil fraction were separately extracted from the side streams of the tower. Inside the steam generator, steam at 0.3 Mpa is generated using the heat from the washing oil fraction and the anthracene oil fraction, for use in heating the equipment. Each fraction is sent out after cooling. The soft asphalt at the base of the main tower is sent out after heat is released by Exchangers No. 1 and No. 2. The phenol oil cooler is connected to the vacuum system to create a negative pressure in the system. The main operational parameters for vacuum continuous distillation are as follows: Temperature at the tar outlet of the No. 1 soft asphalt heat exchanger/°C: 130–150; Temperature at the top of the pre-dehydration tower/°C: 110–120; Temperature at the top of the dehydration tower/°C: 100; Temperature at the bottom of the dehydration tower/°C: 205; Temperature at the tar outlet of the tubular furnace/°C: 330–335; Temperature at the top of the main tower/°C: 118–120; Temperature of the naphthalene fraction side stream/°C: 152; Temperature of the washing oil fraction side stream/°C: 215; Temperature of the anthracene fraction side stream: 360–370; Temperature at the bottom of the main tower/°C: 25–330; Pressure at the top of the main tower/KPa: 13.3; Pressure at the bottom of the main tower/KPa: 33–41. The yields of various fractions obtained through vacuum continuous distillation (as a percentage of anhydrous tar) are as follows: Light oil fraction: 0.5%; Phenol oil fraction: 1.8%; Naphthalene fraction: 13.2%; Washing oil fraction: 6.4%; Anthracene fraction: 16.9%; Soft asphalt: 61%. The softening point of this soft asphalt (according to the Global method) is 60–65°C. This process is suitable for coal tar processing plants with an annual processing capacity of 100,000 tons. This process is widely used in countries such as Germany, Japan, Italy, Australia, and Belgium

Reducing pressure allows for the recovery of more light components, but there are more heavy components as well; this is not yet the best outcome. Please engage in more discussions among yourselves.