Operating Procedures for Distillate Washing Station

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1. Subject matter and scope of application 1.1 Subject matter: These regulations specify the responsibilities, operating standards, site hygiene and working environment, safety in production and labor protection, as well as record-keeping requirements for the positions involved in the distillate washing process. 1.2 Scope of application: Operation and inspection of the fraction washing, steam stripping, and phenolate decomposition units. 1.3 Terms: Washing: The process of carrying out a mixed reaction between one or more substances and a mixture under certain conditions, in order to remove one or more substances from that mixture. 2. Responsibilities 2.1 Responsible for the startup, shutdown, normal operation, special operations, and accident handling of the equipment under this position, ensuring that all operational parameters comply with technical specifications and maintaining safe production. 2.2 Be responsible for the cleaning and maintenance of the equipment assigned to this position, and cooperate with relevant departments in the inspection and acceptance of the equipment. 2.3 Responsible for carrying out defenolization on the unprocessed mixed mixture obtained from the tar distillation process; through steam stripping, pure phenoxide salts are obtained, which are then subjected to sulfuric acid decomposition to extract crude phenol and other compounds. 2.4 Responsible for dealing with defective products generated between different processing stages. 2.5 Be responsible for the use and management of the instruments associated with this position. 2.6 Be responsible for the use and maintenance of fire-fighting equipment in this position. 2.7, Assist laboratory technicians in sampling. 2.8 Be responsible for maintaining environmental hygiene in this position. 2.9 Fill in the operation records for this position carefully, and keep them complete and clean. 3. Process Flow 3.1 Continuous Washing Process The phenol, naphthalene, and washing fraction (the three mixed distillates) sent from tar distillation enter the unwashed tank. From the bottom of this tank, they are pumped out; at the same time, the alkaline phenolate from the alkaline phenolate storage tank is also pumped out. Both streams pass through sight glasses and are stirred by a primary continuous washing pump before entering the middle section of the primary continuous washing tower. The neutral phenolate discharged from the bottom of the tower flows automatically into the neutral phenolate tank, while the oil discharged from the upper part of the tower enters a primary dephenolization buffer tank. There, it mixes with 12–13% dilute alkali from the dilute alkali storage tank. After being stirred by a secondary continuous washing pump, this mixture is fed into the middle section of the secondary alkali washing tower. The oil with a phenol content of less than 0.5% discharged from the upper part of this tower flows into a static separation tower. The alkaline phenolate discharged from the bottom of the secondary alkali washing tower flows automatically into the sodium phenolate tank. The oil that enters the static separation tower undergoes further separation there. The alkaline phenolate discharged intermittently from the bottom of the tower flows automatically into the alkaline phenolate tank via sight glasses. The cleaned oil obtained from the top of the tower is then fed into the cleaned tank to serve as raw material for the industrial naphthalene distillation process. 3.2 In the steam stripping process, the neutral phenolate in the neutral phenolate tank is pumped by a steam stripping pump into the phenolate heat exchanger, where it exchanges heat with the steam and oil gas at the top of the steam stripping column. It then enters the steam stripping column of the phenolate steam stripping reactor; this reactor is heated by indirect steam, with direct steam also being introduced into it. The sodium phenolate free of water and oil, after being blown out, is cooled in a cooler before entering the sodium phenolate tank. Introducing compressed air into the sodium phenolate tank allows the sulfur-containing compounds in sodium phenolate to be fully oxidized and separated. The gas emerging from the top of the steam stripping column is exchanged heat with sodium phenolate in a heat exchanger, then cooled to 50°C using circulating water. It subsequently enters the steam stripping oil-water separator, where the water is sent to the phenol-water tank of the tar distillation unit, while the oil goes into the uncleaned tank. 3.3 Decomposition of sodium phenolate: Sodium phenolate is pumped into the decomposer, after which 93% concentrated sulfuric acid is slowly added to the decomposer from an acid storage tank. Mechanical stirring is carried out simultaneously, and indirect cooling water is used to remove the heat generated during the decomposition process. After the decomposition reaction is complete, stop stirring and let it stand for 8 hours. The lower-layer sodium sulfate wastewater is placed in the sodium sulfate tank and periodically pumped to the phenol-water tank in the oil depot. The upper layer of crude phenol is placed in a crude phenol tank, and then pumped to an oil storage facility or a phenol refining unit. 93% concentrated sulfuric acid is transferred from the finished product warehouse to the concentrated sulfuric acid tank, and then pumped to the sulfuric acid surge tank for decomposition purposes. 3.4 Exhaust Gas Cleaning: This unit is equipped with two sets of exhaust gas cleaning systems, each designed to treat the exhaust gases from the oil storage tanks and the phenol storage tanks respectively. The vent pipes of the oil storage tanks are connected together to an oil exhaust scrubber, with cleaning oil sprayed at the top of the tower. The washing oil is sent to the top of the tower via a washing oil circulation pump for spraying; it is reused, while the used washing oil is regularly transferred to the tar tank in the oil depot, with new washing oil being added on a regular basis. The phenol storage tanks, as well as the vent pipes of washers and decomposers, are all connected to the phenol exhaust cleaning tower, where they are cleaned by spraying with dilute alkali. The alkali solution is pumped by a dilute alkali circulation pump to the top of the tower for spraying; it is reused, and after circulating for a certain period of time, it is sent to the phenolate tank. 3.5 Process Control Parameters
Temperature of the primary and secondary washing towers and the static separation tower: 80–90°C
Operating temperature of the untreated tanks: 80–90°C
Temperature of the alkaline phenolate tank: 70–80°C
Temperature of the dilute alkali tank: 60–70°C
Temperature of the neutral phenolate tank: 80–90°C
Temperature at the top of the distillation column: 100–105°C
Temperature of the oil outlet from the cooler: less than 45°C
Direct steam pressure inside the distillation vessel: 0.01–0.05 MPa
Pressure at the bottom of the distillation vessel: less than 0.035 MPa
Temperature at the bottom of the distillation vessel: 105–110°C
Processing capacity of the material to be distilled: 1–2 t/h
Temperature of the refined sodium product at the outlet of the cooler: 50–60°C
Temperature of the raw material at the outlet after passing through the heat exchanger: 85–95°C
Temperature for the phenolate decomposition reaction: 90°C (maximum 100°C)
Stirring time during acid addition for decomposition: 1–1.5 hours
Stirring time after stopping acid addition: 0.5 hours
Time for standing after stopping stirring: 8 hours

5 Quality Parameters
5.1 Primary oil: Phenol content < 2.5%
5.2 Secondary oil: Phenol content < 0.5%
5.3 Alkaline phenolate: Phenol content 8–15%; free alkali content 6–8%
5.4 Neutral phenolate: Phenol content 18–22%; free alkali content < 1.5%
5.5 Pure phenolate: Phenol content 20–30%; neutral oil content < 0.3%
5.6 Dephenolated phenol oil: Phenol content 85%; initial boiling point > 170°C
5.7 Washed naphthalene oil: Specific gravity 1.01–1.04; water content %